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The impact of assimilating in situ temperature, moisture and wind observations from a WindBorne Systems balloon, with long duration and adjustable ballast, is evaluated using a case study from the 2022 THINICE field campaign. A case is selected wherein the WindBorne balloon directly sampled a jet streak associated with a tropopause polar vortex (TPV). The observed TPV merged with another TPV at the same time as a downstream Arctic cyclone (AC) redeveloped eastward. The case is used to better understand the role of the observed TPV in the evolution of the downstream AC. The assimilation of the WindBorne observations improves the forecast track and amplitude of the TPV during the ∼1 day forecast period that the TPV can be tracked as a distinct feature. The root mean square error of temperature at 350 hPa is improved by the WindBorne assimilation throughout the 2.5 day forecast period. The surface cyclone track forecast is improved by the WindBorne assimilation during the period of eastward redevelopment of the surface cyclone, and the sea level pressure RMSE in the surrounding region is reduced during the first ∼1.5 days of forecast lead time. Results demonstrate the capability of the long‐duration controllable WindBorne balloons to improve the analysis of the TPV associated with the jet streak, leading to improved forecast of both tropopause‐level and surface pressure features. Additionally, the importance of observing the upstream TPV amplitude for improving forecasts of the process of TPV merging and its impact on the evolution and longevity of the mature AC is confirmed. Plain Language Summary: During a recent field campaign, WindBorne Systems deployed novel weather balloons that remain in the atmosphere for weeks at a time, adjusting their altitude to follow winds towards features of interest. These balloons provide an opportunity to study the impact of the merging of two upper‐level disturbances on the performance of an Arctic cyclone (AC) forecast. WindBorne observations of one of the two merged disturbances allowed for an improved forecast of the eastward redevelopment of the AC. These experiments confirm the importance of observing such features for AC prediction and the importance of the merging process in the maintenance and evolution of long‐lived Arctic cyclones. Key Points: WindBorne balloons can improve in situ sampling of small scale features critical for Arctic predictabilityTropopause polar vortex (TPV)‐related jet streak is important for predictability of subsequent TPV merging and Arctic cyclone (AC) redevelopmentMerging of TPVs without associated surface cyclone should be included in conceptual models of AC longevity [ABSTRACT FROM AUTHOR]

Several damaging tropical cyclones (TCs) have occurred recently over the South Indian Ocean (SIO) region, causing enormous social and economic losses. Yet, while many studies have examined SIO TC characteristics using observations and reanalysis, only a few have assessed these characteristics specifically for this region in climate models, and fewer have investigated their projections under climate change. Here we do this for a historical (1980–2010) and future (2020–2050) period, using multimodel simulations from the High Resolution Model Intercomparison Project, as well as examine biases in the historical period relative to a reanalysis (ERA5). The models have horizontal resolutions of 25–50 km, which has enabled an improved ability to represent tropical cyclones globally in previous studies. TempestExtremes software is employed to detect tropical storm and cyclone tracks. In cases where TempestExtremes cannot be applied due to a lack of requisite variables in a dataset, we instead examine extreme wind speeds in that dataset. For the historical period, we find considerable variation in model biases compared to ERA5, which itself exhibits realistic spatial patterns of tracks and their monthly distribution. Models do at least agree on positive biases in track frequency east of Madagascar and somewhat in the Mozambique Channel. However, the models and ERA5 only produce Category 3 tropical cyclones at best. Wind speeds for 25 km resolution models have much larger positive biases than for 50 km ones, suggesting the former can simulate even higher‐category tropical cyclones. Considerable intermodel variation is also found in track changes between the future and historical periods. No systematic intercategory pattern of change exists, and low signal‐to‐noise may obscure any such patterns in the limited timespan of available data. Thus, no meaningful conclusions can be drawn regarding changes in track intensity. Nevertheless, track frequency broadly decreases across models for the region, as does accumulated cyclone energy. An east‐to‐west shift in track location from east of Madagascar toward the Mozambique Channel is also implied by track frequency and wind speed changes. Our findings provide information to potentially improve storm resiliency in this vulnerable region. [ABSTRACT FROM AUTHOR]

Climate change is associated with the modification of the polar jet stream, cyclone tracks and corresponding circulation patterns over midlatitudes. To apply these synoptic changes on regional climate, the changing sensitivity of a specific location to different pressure centre regions must be studied. An automated, objective circulation pattern detection method was developed to investigate the evolution of cyclonic and anticyclonic influence at any specific point within the European domain. The algorithm was used to assign each location to influencing low‐ or high‐pressure centres within the domain. Pressure centre displacements and the frequency redistribution among different centres were studied for each location. The 180‐year (January 1836–December 2015) mean sea level pressure dataset on the European domain with a 0.703° × 0.702° spatial and daily temporal resolution was obtained from NOAA 20th Century Reanalysis project. The presented method can apply the continental‐scale changes to specific locations. A significant increase of anticyclonic influence was found in southern and central Europe, in line with the northward displacement of Atlantic cyclones. Hundred and eighty year (180‐year) change of the number of days with anticyclonic versus cyclonic influence was found to be between +10% and 15% in the Mediterranean and +2% and 10% in most of Europe. The increasing anticyclonic influence in central Europe was strongest in the spring and the winter and was most attributable to the eastern European anticyclone. Results highlight the importance of research on the dynamical climate response of anticyclonic pressure systems. [ABSTRACT FROM AUTHOR]

The Great Lakes Region (GLR) of North America is at the intersection of multiple extratropical cyclone (ETC) tracks, and the region's cold‐season climate is heavily influenced by the large temperature gradients and intense precipitation associated with these cyclones. The goal of this study is to understand how ETCs are changing within a warming climate. Historical GLR cyclone characteristics from 1959 to 2021 are examined using a storm tracking algorithm and the ERA‐5 atmospheric reanalysis. Of the 886 cyclones identified, half are the large long‐track cyclones that are typically included in ETC studies, and half are smaller short‐track cyclones that, while not always considered in ETC studies, still have an important impact on the GLR with significant precipitation trends. While all cyclones exhibit strong interannual variability, storm trajectories appear to be migrating northward and, most notably, the cyclones are becoming warmer and wetter at a rate faster than the background climate. Plain Language Summary: Winter weather patterns in the Great Lakes Region of the United States are driven by large‐scale weather systems known as "extratropical cyclones." Even with a warming climate, the Great Lakes Region experiences highly variable winters, with cold‐air outbreaks, extreme snowfall, and mild temperatures all possible from year to year. This study uses historical analyzed atmospheric data to identify and track extratropical cyclones that pass through the Great Lakes Region in order to understand how the cyclones have changed along with our changing climate. We find that the airmasses within the cyclones have increased in moisture and warmed up faster than the overall climate. We also find that the cyclone tracks have shifted northward, implying that the frequency of warm temperatures and heavy rainfall in the wintertime is increasing for the lower portion of the Great Lakes. Key Points: Cold season extratropical cyclones that pass through the Great Lakes region are shifting to more northern tracksThe number and intensity of Great Lakes cyclones do not show an increasing trendGreat Lakes extratropical cyclones are warming and are increasing in moisture at a rate faster than the background climate [ABSTRACT FROM AUTHOR]

This study introduces new insights into the climatology of South Atlantic (SAt) cyclones by employing a novel cyclone life cycle detection method, the CycloPhaser. Utilizing the minimum relative vorticity series and its derivative at the cyclone centre, the program effectively identifies distinct phases in the cyclone life cycle. Cyclone tracks are obtained through the analysis of relative vorticity at 850 hPa, using the ERA5 dataset. The study identified six main cyclone life cycle patterns from the analysis of 28,458 systems. The predominant cyclone type, accounting for approximately 60% of the analysed systems, exhibited a four‐phase configuration: incipient, intensification, mature and decay. Detailed statistics for each developmental phase and the overall life cycle are presented, offering valuable comparisons and new insights while corroborating previous research findings. Key genesis regions in the SAt are identified, along with track density maps that reveal distinct preferences in cyclone developmental cycle. The main outcome of this study is the demonstration that the automated classification procedure enables the analysis of cyclones' life cycles to be conducted promptly and with low computing costs, facilitating the comprehensive study of cyclone behaviour with high efficiency. [ABSTRACT FROM AUTHOR]

The Great Arctic Cyclone 2012 (AC12) is used to understand the role of initial condition errors in the predictability at 2–3‐day forecast range of a high‐impact summer Arctic Cyclone (AC). Ensemble sensitivity analysis (ESA) is first performed to identify potentially sensitive regions of the cyclone evolution using an ensemble baseline forecast with conventional in situ observations assimilated. A pseudo‐observation method is then introduced to investigate impacts of hypothetical observations in these sensitive but unobserved regions. In the baseline experiments with in situ observations assimilated, the forecasted AC12 reaches its peak intensity 18 hr earlier than in the verifying Global Forecast System Analysis (GFS‐ANL) and the cyclone track is biased toward the southwest. Using ESA, the time of peak intensity and the cyclone track error are identified to be sensitive to the upstream trough, downstream ridge, and the tropopause polar vortex (TPV) to the northeast (NE TPV) of the AC12. These features were not observed by the in situ observation networks. To examine the impact of the observation gaps, pseudo‐observations drawn from GFS‐ANL are assimilated. Pseudo‐observations sample the three features separately to study the impact of the initial condition error on the predictability of AC12. The cyclone peak intensity timing error and track error are greatly reduced when the initial condition error is reduced near the NE TPV. A southward expansion of the NE TPV and the corresponding southward shifting low‐level front lead the forecasted AC12 to progress to the east, which better agrees with the verifying GFS‐ANL. Plain Language Summary: Accurate prediction of strong Arctic cyclones is critical to the scientific and economical activities in the Arctic. However, the sparse observation networks in the Arctic pose challenges to the data assimilation system to constrain the initial conditions in various features of the Arctic Cyclones. This paper used a case study approach to investigate the impact of initial condition errors in different features on the development of the 2012 Great Arctic Cyclone. Synoptic features that are sensitive to the track and timing of the cyclone were first identified using ensemble sensitivity analysis. Assimilating in situ conventional observations did not sufficiently constrain the initial conditions in the sensitive features. Hypothetical pseudo‐observations from an external analysis system were then designed and assimilated to study how each sensitive feature affects the prediction of the physical processes of cyclone development. The results showed that more observations inside the TPV to the northeast of the cyclone brought the most significant forecast improvements at a 2‐day forecast lead time. Key Points: Ensemble sensitivity analysis reveals track and deepening trend forecast biases of Arctic Cyclone 2012 are sensitive to unobserved synoptic scale featuresPseudo‐observation experiments show the northeast tropopause polar vortex (TPV) is the most impactful feature among sensitive featuresSouthward expansion of the northeast TPV impacts the cyclone evolution by shifting the low‐level front southward [ABSTRACT FROM AUTHOR]

Cyclones tracking northward across the Bay of Bengal represent a significant threat to life and safety when they make landfall. Surface moorings of the Ocean Moored Network for the Northern Indian Ocean in the Bay of Bengal have been deployed to provide real-time observations in support of improved alerts and predictions of cyclones. Engineering goals are both to develop robust surface moorings that survive and to field meteorological and oceanographic instruments that reliably provide data in real time. While the mooring design and reliability were previously reported, the focus here is on the motivations for installing the instrumentation, and on experience gained during the passage of cyclone Amphan in May 2020, examining the sensor as well as mooring performance. The paper presents reasons for fielding the chosen sensors, merits, and shortcomings during the effort to observe Amphan, and recommendations for how to better address the challenges of providing real-time observations of cyclones in the Bay of Bengal. [ABSTRACT FROM AUTHOR]

The risk posed by Arctic cyclones to ships has seldom been quantified due to the lack of publicly available historical Arctic ship track data. This study investigates Arctic ship tracks derived from automatic identification system (AIS) transponders from September 2009 to December 2016. These are analysed with historical synoptic-scale cyclone tracks derived from ERA-5 reanalysis data and reports of past Arctic shipping incidents. We determine the number of ship tracks that intersected with intense Arctic cyclones tracks and how many of these intersections resulted in a reported shipping incident. The number of ships operating in the Arctic has increased year-on-year from 2010 to 2016. The highest density of ships occurs year-round in the Barents Sea. Trans-Arctic shipping transits via the Northern Sea Route and the Northwest Passage are limited to summer and autumn months, when sea ice extent has retreated sufficiently from the coastlines. Ship track density along these trans-Arctic routes is far less than the thousands of ships travelling in the Barents Sea year-round. Between 2010 and 2016, 158 Arctic shipping incidents were reported, but only 6 % of these reported incidents occurred following the passage of an intense Arctic cyclone. Arctic cyclones with significant wave heights greater than 6 m are found to frequently intersect ships, but only 0.1 % of these intersections resulted in a reported shipping incident. Results from this study indicate that ships are frequently impacted by Arctic cyclones, but cyclones were not a dominant cause of reported Arctic shipping incidents between 2010 and 2016. This suggests that ships are resilient to the rough sea conditions that past Arctic cyclones have caused, therefore mitigating and reducing risk. [ABSTRACT FROM AUTHOR]

Ockhi was a devastating tropical cyclone that struck parts of Sri Lanka, India, and the Maldives in November 2017. The storm began as a low-pressure system over the Bay of Bengal and rapidly intensified into a very severe cyclonic storm, causing havoc along its path. Interestingly, Ockhi was a rare storm to have rapid intensification over the Arabian Sea basin during its cyclogenesis stage. In this analysis, we examine the factors that influenced Ockhi's genesis and rapid intensification. It is known that the warm core eddies have a potential role in the rapid intensification of tropical cyclones. However, in our study, it was observed that no warm core eddies were found along the track of tropical cyclone Ockhi during its rapid intensification. Thus, additional atmospheric and oceanic features that contribute to the development and intensification of tropical cyclones have been taken into account. A very high tropical cyclone heat potential of 60–90 kJ cm−2, an exceptionally high sea surface temperature anomaly of above 1–1.5 °C, and a high moist static energy of 340 × 103 J kg−1 or greater were observed to be persisting over the region where the intensification has taken place. The brightness temperature was < 200 K, indicating strong and very deep convective activity over the region of intensification. Along with favourable ocean and atmospheric features such as high tropical cyclone heat potential, sea surface temperature, and moist static energy, the presence of deep convection persisting for a prolonged time can eventually intensify the system. [ABSTRACT FROM AUTHOR]

In recent decades, there has been notable variability in the occurrence, frequency, and intensification of cyclones worldwide, and a significant trend has emerged in the northern Indian Ocean, notably the Arabian Sea. The recent cyclone, Biparjoy, occurred in June 2023 and stands out as a significant event among these occurrences. Through an extensive analysis utilizing available datasets (both in-situ and model-based) along the vertical trajectory of cyclone paths, it has been ascertained that the intensity of cyclones is influenced by the advection of warm saline (referred to as "Spicy") water originating north of the cyclone's track. This influx of high-saline waters occurs at various depths, inducing alterations in the vertical water column configuration. Notably, the diffusion of heat overtakes that of salt, resulting in the gradual dispersion of the saline water. These high salinity levels are prevalent at depths ranging from 0 to 300 m, with a pronounced concentration up to 100 m below the surface. The presence of these warm saline waters overlying the colder, fresher waters gives rise to a phenomenon known as "salt fingering" (45o < Tu < 90o), which establishes a stable surface layer predominantly controlled by temperature gradients. This stable surface layer, extending up to approximately 50 m in depth holding a substantial heat, fostering a positive feedback loop that amplifies cyclone intensity. As the spiciness of the Arabian Sea experiences an ascending trend in recent years, the continued extension of saline water advection bears intense implications for upper ocean heat content. This, in turn, creates a favorable environment for the formation and rapid intensification of cyclones. [ABSTRACT FROM AUTHOR]

We examined the seismic noise data collected from coastal and inland observatories in India, affected by the super cyclonic storm Amphan in the Indian Ocean, to understand the storm dynamics. Prominent disturbances in the 0.05–0.50 Hz frequency range were observed at the seismic stations, arising due to ocean‐continent interactions. The coastal stations displayed more pronounced ground motions contrary to the inland stations, with spindle‐shaped seismic wave envelopes intensifying as Amphan approached. The maximum ground displacements and energy occurred hours after the cyclone's eye, with maximum wind speed, moved away from the stations and not when it was close to the station. We observed significant variations in primary (0.05–0.10 Hz) and secondary microseism (0.10–0.50 Hz) energy during Amphan's directional changes. Secondary microseisms in short and long periods were found at 0.20–0.50 Hz and 0.10–0.20 Hz, respectively. Primary microseisms exhibited a simple pattern and were the weakest among the three energy bands. The CAL seismic station's seismic wave envelope showed an en‐echelon feature with increasing amplitude as Amphan approached, indicating the influence of ocean resonance and coastal wave reflection. This study demonstrates monitoring of the tropical cyclone paths based on seismic signatures obtained using microseisms recorded at seismic stations, a cost‐effective tool. Integrating these seismic signals with atmospheric observations in near real‐time would probably enable an effective monitoring of cyclones and timely issuance of their alerts. Key Points: Monitor the Super Cyclone Amphan in the Bay of Bengal using Coastal seismological ObservatoriesSecondary microseisms in the short and long periods were found at 0.20–0.50 Hz and 0.10–0.20 HzMicroseisms recorded at seismic stations can be potential source of information for cyclone tracking [ABSTRACT FROM AUTHOR]

In the Baltic Sea, sea level variations are often very pronounced. During the winter season, storm surges caused by strong extratropical cyclones (ETCs) can have major societal impacts on coastal cities. In this study, using reanalysis‐based cyclone tracks and in‐situ tide gauge records, we show that serial cyclone clustering (SCC) leads to higher sea levels in the Baltic Sea than situations where only one ETC passes the tide gauge. Consequently, almost half of extreme sea level events in the Baltic Sea are associated with cyclone clustering periods. For example, in Helsinki, 45% of the extreme sea level events coincided with SCC periods of three or more ETCs, while only 6% of the events coincided with a single ETC. Our study represents a significant advance in the understanding of the factors influencing sea level variations in the Baltic Sea. Plain Language Summary: Sea levels in the Baltic Sea can vary a lot. In winter, powerful storms can lead to storm surges that seriously affect coastal towns. Our research studied storm paths and sea level observations. We found that multiple consecutive storms within a week raise sea levels in the Baltic Sea more than when only one storm passes the same location. As a result, most of the high sea level events in the Baltic Sea are linked to periods when several storms pass the region. In Helsinki, for instance, almost half of all analyzed high sea level events co‐occurred with periods when at least three storms occurred, while only 6% of high sea level events occurred due to a single storm. Our analysis is a significant progression in understanding the reasons that impact the Baltic Sea water levels. Hence, these results could aid in preparing for possible coastal floods. Key Points: Serial cyclone clustering (SCC) commonly causes elevated sea levels in the Baltic SeaPeak storm surges during SCC are on average 2–2.7 times (25–48 cm) higher than during single cyclonesThe intensity of the cyclones within the SCC modulates the storm surge levels, with deeper cyclones more likely to induce higher surges [ABSTRACT FROM AUTHOR]

Madagascar has a harsh and stochastic climate because of regular natural disturbances. This history of regular cyclones has been hypothesised to have directed evolutionary changes to lemur behaviour and morphology that make them more resilient to sudden environmental change. These adaptations may include: small group sizes, high degrees of energy-conserving behaviours, generalist habitat use, small home ranges, small body size, and a limited number of frugivorous species. To date, however, no one has tested how variation in cyclone exposure across Madagascar is associated with variation in these resilience traits. In this study, we created a detailed cyclone impact map for Madagascar using Koppen-Geiger climate class, historical cyclone tracks, the Saffir Class of cyclone and hurricane intensity, and precipitation data. We also used existing literature to calculate a resilience score for 26 lemur species for which data existed on resilience traits. Our cyclone impact map was then overlaid on known geographic ranges of these species and compared to resilience score while controlling for phylogenetic non-independence and spatial autocorrelation. We found no association between cyclone impact in a lemur range and their resilience score. When assessing traits individually, however, we found that cyclone impact was positively associated with body size, suggesting that the more impacted a species is by cyclones the smaller they are. We also found cyclone impact to be negatively associated with frugivory, with species in higher impact zones eating more fruit. While unexpected, this could reflect an increased production in fruit in tree fall gaps following cyclones. While we did not find a pattern between cyclone impact and behavioural resilience in lemurs, we suggest a similar study at a global scale across all primates would allow for more taxonomic variation and reveal larger patterns key to understanding past and future vulnerability to natural disturbances in primates. [ABSTRACT FROM AUTHOR]

The role of large‐scale natural variability in influencing the distribution of midlatitude storm tracks and extratropical cyclones is well known. However, less understood is how compound natural variability—the concurrence of two modes of variability—influences the geospatial characteristics of extratropical cyclones. Here, we evaluate compound modes of Pacific‐North American variability—ENSO and PNA with the slow varying PDO—on extratropical cyclones over the North American region during 1950–2013, using an automated tracking algorithm applied to the Twentieth Century Reanalysis version 3 data. Seasonal analysis is conducted on spatial statistics including track, genesis and lysis density and some mean fields in varying compound phases. Spatial correlations of track density with seasonal mean of individual variability indices show that the PNA, ENSO and PDO enhance cyclone activity over Pacific storm track significantly while shifting the North American and Atlantic storm tracks in seasons, that is, equatorward in the positive phase. But the decadal variability of PDO moves the Atlantic storm track poleward, particularly in boreal winter. By comparing to the single Pacific variability impacts, compound Pacific variability results demonstrate the dominance of the higher‐frequency modes of ENSO and PNA on extratropical cyclone activity, while the slow varying PDO can modulate the ENSO‐ and PNA‐related cyclone variability. For example, during a negative PNA, cyclones over the North Atlantic become more (less) frequent during a positive (negative) PDO. The in‐phase modes of the PDO and ENSO influence Pacific storm track significantly, increasing (decreasing) cyclone frequency when both are positive (negative) in boreal winter. Results are linked to and used to explain the previous findings on how natural variability influences the occurrence of tornado outbreaks and high precipitation over the southeastern United States, Great Lakes, Ohio Valley and other US regions. Understanding compound variability modulations may be useful to predict extratropical cyclone frequency, development and decay regions seasonally and to study the physical mechanisms of extreme weather events. [ABSTRACT FROM AUTHOR]

In this study, we propose an easy and robust algorithm to identify and track extratropical cyclone events using 850 hPa relative vorticity data, gaussian filter and connected-component labeling technique, which recognize the cyclone as areas under a threshold. Before selecting the events, the algorithm can include essential characteristics that are good metrics of intensity, like minimum mean sea level pressure and maximum 10-m winds. We implemented the algorithm in the Southern Hemisphere, using a 41-year high resolution dataset. Sensitivity tests were performed to determine the best parameters for detection and tracking, such as degree of smoothing, thresholds of relative vorticity at 850 hPa and the minimum area within the threshold. Two case studies were used to assess the positive and negative points of the methodology. The results showed that it is efficient in obtaining the position of extratropical cyclones in their most intense stage, but it does not always perform well during cyclolysis. We compare the methodology using 1-h temporal resolution to that using a 6-hours temporal resolution, and their reproducibility regarding the literature. The extratropical cyclone climatology in the Southern Hemisphere is provided and discussed. The algorithm developed here can be applied to datasets with good spacial and temporal resolution, providing a better inventory of extratropical cyclones. [ABSTRACT FROM AUTHOR]

Large-scale meteorologic events (e.g. cyclones), referred to as synoptic events, strongly influence weather predictability but still cannot be fully characterised in the Arctic region because of the sparse coverage of measurements. Due to the fact that atmospheric dynamics in the lower stratosphere and troposphere influence the ozone field, an approach to analyse these events further is the use of space-borne measurements of ozone vertical distributions and total columns. In this study we investigate the link between cyclones and changes in stratospheric ozone by using a combination of unique measurements during the MOSAiC ship expedition, ozone profile and total column observations by satellite instruments (OMPS-LP, TROPOMI), and ERA5 reanalysis data. Three special cases during the MOSAiC expedition were selected and classified for the analysis. They consist of one 'normal' cyclone, where a low surface pressure coincides with a minimum in tropopause height, and two 'untypical' cyclones, where this is not observed. The influence of cyclone events on ozone in the upper-troposphere lower-stratosphere (UTLS) region was investigated, using the fact that both are correlated with tropopause height changes. The negative correlation between tropopause height from ERA5 and ozone columns was investigated in the Arctic region for the three-month period from June to August 2020. This was done using total ozone columns and subcolumns from TROPOMI, OMPS-LP and MOSAiC ozonesonde data. The greatest influence of tropopause height changes on ozone contour levels occurs at an altitude between 10 and 20 km. Moreover, the lowering of the 250 ppb ozonopause (about 11 km altitude) below 9 km was used to identify and track cyclones using OMPS-LP ozone observations. The potential of this approach was demonstrated in two case studies where the boundaries of cyclones could be determined using ozone observations. The results of this study can help improve our understanding of the relationship between cyclones, tropopause height, and ozone in the Arctic and demonstrate the usability of satellite ozone data for investigating cyclones in the Arctic. [ABSTRACT FROM AUTHOR]

This paper highlights the quality and impact of the COSMIC-2 bending angle through an Observation System Experiment, using a hybrid Gridpoint Statistical Interpolation – 4 Dimensional Ensemble Variational analysis scheme. The data quality is assessed by comparing it with the model's background field. Analysis and background field that fit to temperature, humidity and wind components from radiosondes are verified, and the impact over model forecasts is evaluated using various metrics. There is an overall improvement, especially over the tropical region, where consistent and statistically significant positive impact is observed over the troposphere extending up through the lower to the middle stratosphere. A case study of the Super Cyclonic Storm AMPHAN showed minor improvement in central pressure and maximum 10 m wind speed. Reduction in the direct positional error of the cyclone track showed improvement in the analysis. [ABSTRACT FROM AUTHOR]

Extratropical cyclones influence midlatitude surface weather directly via precipitation and wind and indirectly via upscale feedbacks on the large‐scale flow. Biases in cyclone frequency and characteristics in medium‐range to subseasonal numerical weather prediction might therefore hinder exploitation of potential predictability on these timescales. We thus, for the first time, identify and track extratropical cyclones in 20 years (2000–2020) of subseasonal ensemble reforecasts from the European Centre for Medium‐Range Weather Forecasts (ECMWF) in the Northern Hemisphere in all seasons. The reforecasts reproduce the climatology of cyclone frequency and life‐cycle characteristics qualitatively well up to six weeks ahead. However, there are significant regional biases in cyclone frequency, which can result from a complex combination of biases in cyclone genesis, size, location, lifetime, and propagation speed. Their magnitude is largest in summer, with the strongest regional deficit of cyclones of more than 30% in the North Atlantic, relatively large in spring, and smallest in winter and autumn. Moreover, the reforecast cyclones reach too‐high intensities during most seasons, although intensification rates are captured well. An overestimation of cyclone lifetime might partly but not exclusively explain this intensity bias. While the cyclone bias patterns often appear in lead‐time weeks 1 and 2, their magnitudes typically grow further at subseasonal lead times, in some cases up to weeks 5 and 6. Most of the dynamical sources of these biases thus likely appear in the early medium range, but sources on longer timescales probably contribute to the further increase of biases with lead time. Our study provides a useful basis to identify, better understand, and ultimately reduce biases in the large‐scale flow and in surface weather in subseasonal weather forecasts. Given the considerable biases during summer, when subseasonal predictions of precipitation and surface temperature will become increasingly important, this season deserves particular attention for future research. [ABSTRACT FROM AUTHOR]

Extratropical cyclones play an important role in shaping the weather and climate over vast regions across the globe. To effectively understand and manage the impact of these meteorological events, it is crucial to explore deeper into their structure and behaviour. Here, we have evaluated the characteristics and spatial distribution of extratropical cyclones that had their genesis in the Southern Ocean (SO) in the present climate, based on data from the HadGEM3‐GC3.1‐MM (HG3) global model and the ERA5 reanalysis. Both in winter and summer, cyclone tracks are spatially structured, forming a belt around the entire Antarctic continent, with greater concentration in the SO sector adjacent to the southern Pacific Ocean. The regions of the Somov, Amundsen and Bellingshausen seas exhibited a higher track density of moderate and strong cyclones, indicating a correlation with the strongest baroclinicity in these areas. In both datasets, the maximum occurrence of cyclogenesis was located over the regions of the Somov Sea and the Antarctic Peninsula, making these regions very important in the general configuration of cyclones along the SO. Despite underestimating the total number of cyclones along the SO, the HG3 model showed a good ability to represent the main patterns of cyclonic activity around the Antarctic continent, as well as its average behaviour. Knowing the characteristics and the behaviour of extratropical cyclones in such an important area for global climate is essential for understanding their role in weather and future climate resulting from climate change. [ABSTRACT FROM AUTHOR]

Baroclinic or extratropical cyclones (ETCs) transport heat and moisture to higher latitudes, making it fundamentally important to understand how their influence changes as Earth's climate evolves. A 2–8‐day Lanzcos bandpass filter is applied to European Center for Medium Range Weather Forecasting 5th Generation Reanalysis latent energy (LE) and kinetic energy (KE) data to assess how ETCs have changed from 1940 to 2020 relative to full‐scale changes in LE and KE. Full‐scale KE trends are more positive at high latitudes relative to mid‐latitudes, confirming several previous studies that ETCs have shifted poleward. LE increases have occurred globally, and trends in both full‐scale LE and KE are statistically significant in the southern high latitudes. The high relative fractional contribution of 2–8‐day LE wave power and trend clearly suggest that ETCs have an increasingly important role in poleward moisture transport but are not solely responsible for the observed statistically significant increases. Plain Language Summary: Understanding changes to mid‐ and high‐latitude storm locations is paramount to better predicting how Earth's climate has changed and may change going forward. This study extends several previous studies to focus on the role these storms have in transporting moisture poleward, and if changes in moisture transport over the last 80 years are significant. We find a significant increase in moisture across the southern midlatitudes, but this increase is not solely associated with significant increases in storm energy. No significant increases are found in the northern hemisphere. Key Points: Kinetic Energy trends from 1940 to 2020 confirm several existing studies showing a poleward shift in extratropical cyclone track locationsStatistically significant increases in kinetic and latent energy are found across southern hemisphere midlatitude cyclone track locationsCyclones at 2–8‐day time scales, however, are not solely responsible for these statistically significant increases [ABSTRACT FROM AUTHOR]

Extratropical cyclones (ETCs) are three-dimensional synoptic systems in the middle and high latitudes. Previous studies on ETC propagation have typically focused on cyclones identified at a single level. However, more recent studies have found that ETCs have diverse vertical structures and cyclones with different vertical extents always exhibit distinct characteristics and surface impacts. In this work, we study the movement of wintertime (December–February) extratropical cyclones by classifying North Pacific ETCs into deep cyclones, shallow low-level cyclones, and shallow upper-level cyclones, based on reanalysis data from 1979 to 2019. Applying a Lagrangian perspective, we track the cyclones at different vertical levels to investigate the different characteristics and mechanisms for the propagation of deep and shallow ETCs. A potential vorticity (PV) tendency analysis of cyclone-tracking composites reveals that, for deep cyclones, the diabatic heating at 850 hPa and the horizontal advection by the stationary flow at 500 hPa are the main contributors to the poleward movement. For shallow cyclones, the nonlinear advection terms play a dominant role in their meridional motion, advecting shallow low-level cyclones poleward but shallow upper-level cyclones equatorward. A piecewise PV inversion analysis suggests that the nonlinear advection by winds induced from upper-level PV anomalies is responsible for the different performance of nonlinear advection terms for shallow low-level and upper-level cyclones. These findings further our understanding of the mechanisms and variations of cyclone propagation. Significance Statement: Extratropical cyclones (ETCs) can be identified at different levels in the troposphere. These mobile low pressure cyclonic storms are the main sources of synoptic variability in the extratropics and often bring severe or even disastrous weather. Previous studies on ETC movement have typically been restricted to cyclones identified at a single level. Our study, by identifying ETCs at multiple levels, classifies cyclones into deep, shallow low-level, and shallow upper-level cyclones. For deep cyclones, their poleward movement is found to be a result of diabatic heating at lower levels and dominated by the stationary circulation at upper levels. For shallow cyclones, nonlinear advection determines whether they propagate poleward or equatorward. These findings further our understanding of the mechanisms of cyclone propagation and imply that the movement of deep and shallow cyclones may undergo different changes with different weather and climate impacts in the future, given the enhanced diabatic heating under global warming, which deserves further investigation. [ABSTRACT FROM AUTHOR]

In the current study, the decadal changes in Iran's precipitation regimes (PRs) were investigated by adopting Iran's precipitation dataset and using the precipitation index (PI). Our finding revealed that significant decadal variation occurred in the PI, which led to different spatial patterns during under investigation decades. From the 1st to last decades under study, the area decreased in the regions with equal monthly distribution of precipitation (ED). The regions with a relatively equal monthly concentration of precipitation (RED) presented a sharp decreasing trend in the first 3 decades and a slight increase in the last decade. The irregular distribution of precipitation (ID) in most of the decades covered an area above the long-term average. The highly irregular distribution of precipitation (HID) covered a small area of Iran's territory on the southern coasts. Nevertheless, its decadal variation, particularly in the first 3 decades, was relatively noticeable. The decadal variability of the number and tracks of cyclones affecting Iran showed that although the number of cyclones increased from the 1st to the last decade, the origins of cyclones in the 1st decade were mainly in the Mediterranean Sea and the Red Sea. In the following decades, the diversity of the origins of the cyclones was one of the decades' characteristics. In addition, from the 1st to 3rd decade, the cyclone centers (excluding the Red Sea-Sudanese cyclones) took a more northerly route. This decadal variation in cyclones' characteristics might lead to the decadal variation of PI in Iran. [ABSTRACT FROM AUTHOR]

The risk posed by Arctic cyclones to ships has seldom been quantified due to the lack of publicly available historical Arctic ship track data. This study investigates Automated Identification System (AIS) transponder derived Arctic ship tracks from September 2009 to December 2016. These are analysed with historical synoptic-scale cyclone tracks derived from ERA-5 and reports of past Arctic shipping incidents, to determine the number of ships intersected by the passage of intense Arctic cyclones, and how many resulted in shipping incidents. The number of ships operating in the Arctic has increased year-on-year from 2010 to 2016. The highest density of ships occurs year-round in the Barents Sea. Trans-Arctic shipping transits via the Northern Sea Route and the North-West Passage are limited to summer and autumn months, when sea ice extent has sufficiently retreated from the coastlines. But, ship traffic along these trans-Arctic routes is far less than the thousands of ships travelling in the Barents Sea year-round. Between 2010 and 2016, 248 Arctic shipping incidents were reported, but only 2 % of these occurred following the passage of an intense Arctic cyclone. So, shipping incidents do occur in the Arctic, but the vast majority appear unrelated to the passage of intense Arctic cyclones, despite ship tracks being frequently intersected by such hazards. Less than 0.0001 % of these intersections resulted in a reported shipping incident. This suggests that Arctic cyclones have not been hazardous to ships, and that ships are resilient to the rough sea conditions caused by intense Arctic cyclones. [ABSTRACT FROM AUTHOR]

Extreme precipitation events and associated flash floods caused by synoptic cyclonic systems profoundly impact society and the environment, particularly in arid regions. This study brings forward a satellite-reanalysis-based approach to quantify extreme precipitation characteristics over the Sinai Peninsula (SiP) in Egypt from a statistical–synoptic perspective for the period of 2001–2020. With a multi-statistical approach developed in this research, SiP's wet and dry periods are determined. Using satellite observations of precipitation and a set of derived precipitation indices, we characterize the spatiotemporal variations of extreme rainfall climatologies across the SiP. Then, using the reanalysis datasets, synoptic systems responsible for the occurrence of extreme precipitation events along with the major tracks of cyclones during the wet and dry periods are described. Our results indicate that trends and spatial patterns of the rainfall events across the region are inconsistent in time and space. The highest precipitation percentiles (∼20 mm per month), frequencies (∼15 d per month with rainfall ≥10 mm d -1), standard deviations (∼9 mm month per month), and monthly ratios (∼18 %) are estimated in the northern and northeastern parts of the region during the wet period, especially in early winter; also, a substantial below-average precipitation condition (drier trend) is clearly observed in most parts except for the south. Mediterranean cyclones accompanied by the Red Sea and Persian troughs are responsible for the majority of extreme rainfall events year-round. A remarkable spatial relationship is found between SiP's rainfall and the atmospheric variables of sea level pressure, wind direction, and vertical velocity. A cyclone-tracking analysis indicates that 125 cyclones (with rainfall ≥10 mm d -1) formed within, or transferred to, the Mediterranean basin and precipitated over the SiP during wet periods compared to 31 such cyclones during dry periods. It is estimated around 15 % of cyclones with sufficient rainfall >40 mm d -1 would be capable of leading to flash floods during the wet period. This study, therefore, sheds new light on the extreme precipitation characteristics over the SiP and its association with dominant synoptic-scale mechanisms over the eastern Mediterranean region. [ABSTRACT FROM AUTHOR]

This study evaluated the changes in cyclone track parameters, which include the maximum sustained wind speed (Vmax) and translation speed (Vt) during 2010–2019. It established the Vt and Vmax connection with the oceanic heat content for the upper 50-m, 100-m, and 150-m layers (UOHC50, UOHC100, and UOHC150) for cyclones that formed over the North Indian Ocean (NIO) basin. The study considered a total of 20 cyclone cases (10 each) for the Arabian Sea (AS) and Bay of Bengal (BoB) utilizing the India Meteorological Department (IMD) best-track data to establish a quantitative relationship connecting the UOHC with Vmax and Vt. The correlation of Vt is slightly positive with UOHC50 for NIO and moderately positive (+0.253) for the BoB; however, a proper correlation is lacking for AS region. Also, an inter-comparison was performed for UOHC50, UOHC100, and UOHC150 with Vmax. Maximum correlation of Vmax is obtained with UOHC100 for AS and UOHC50 for the BoB. Analysis was also performed with cyclone cases individually for the two periods 2010–2015 and 2016–2019. Results signify a phase reversal (positive to negative) for (Vmax-UOHC) correlation values from upper 50 to 100 m for BoB cyclones Phailin (2013) and Hudhud (2014). A similar negative (−0.182) to positive (+0.602) shift is observed for the recent BoB cyclone Fani (2019). The parameter Vmax for recent storms showed significant correlation with oceanic warming at 150 m depth for Titli (2018) (−0.869) and Fani (2019) (+0.735). Relationship between UOHC50 and Vt for AS cyclones is evident compared to BoB cyclones. Both the AS and BoB pre-monsoon cyclones viz; Sagar (2018), Vayu (2019), and Fani (2019) showed negative (Vt –UOHC50) correlation in spite of the overall positive correlation noticed for other cases. The above three pre-monsoon cyclones showed high (Vmax –UOHC) correlation values. Recent accelerated warming for the AS basin can further accelerate Vt over this region, with a higher probability of more rapidly intensifying storms. The proximal factors have collinearity in enhancing the coastal vulnerability over this region. [ABSTRACT FROM AUTHOR]

Large-scale meteorological pattern (LSMP)–based analysis is used in a novel way to understand meteorological conditions before and during short-duration dry spells over the northeastern United States. These LSMPs are useful to assess models and select better-performing models for future projections. Dry-spell events are identified from histograms of consecutive dry days below a daily precipitation threshold. Events lasting 12 days or longer, which correspond to ∼10% of dry-spell events, are examined. The 500-hPa streamfunction anomaly fields for the first 12 days of each event are time averaged, and k-means clustering is applied to isolate the dry-spell-related LSMPs. The first cluster has a strong low pressure anomaly over the Atlantic Ocean, southeast of the region, and is more common in winter and spring. The second cluster has strong high pressure over east-central North America and is most common during autumn. Over the region, both clusters have negative specific humidity anomalies, negative integrated vapor transport from the north, and subsidence associated with a midlatitude jet stream dipole structure that reinforces upper-level convergence. Subsidence is supported by cold-air advection in the first cluster and the location on the east side of the lower-level high pressure in the second cluster. Extratropical cyclone storm tracks are generally shifted southward of the region during the dry spells. Individual events lie on a continuum between two distinct clusters. These clusters have similar local, but different remote, properties. Although dry spells occur with greater frequency during drought months, most dry spells occur during nondrought months. Significance Statement: This study examines the large-scale weather patterns and meteorological conditions associated with dry-spell events lasting at least 2 weeks while affecting the northeastern United States. A statistical approach groups events together on the basis of similar atmospheric features. We find two distinct sets of patterns that we call large-scale meteorological patterns. These patterns reduce moisture, foster localized sinking, and shift the storm track southward along the Atlantic seaboard, all of which reduce precipitation. Besides greater understanding, knowing the meteorological patterns during short-term dryness in the region provides an important tool to assess how well atmospheric models reproduce these specific patterns. More dry spells occur in nondrought months than in drought months, which means that dry spells can occur without preexisting drought conditions. [ABSTRACT FROM AUTHOR]

This study examines extratropical cyclone tracks, central pressure, and maximum intensification rates from a widely used automated cyclone tracking scheme and compares them with the manual tracking of five well-known North Atlantic cyclones whose histories are available in the refereed literature. The automated tracking scheme is applied to sea level pressure data from four different reanalyses of varying levels of sophistication to test the sensitivity of the results to input data resolution and quality. Further, we test the tracking scheme using lower-tropospheric vorticity obtained from the most recent reanalysis (ERA5) for four of these cyclone events. Substantial discrepancies in cyclone position, intensity, and maximum intensification rates exist between the manual tracking and the automated tracking and are not eliminated by using higher-resolution reanalyses or by "turning off" the spatial smoothing feature of the automated tracking scheme (needed to reduce spurious cyclone detections). The results point to a particular problem in detecting weaker and earlier stage cyclones and confirm findings from studies that have examined a broad range of cyclone tracking schemes for a range of reanalyses. Notably, this early cyclone stage often involves a smaller-scale secondary cyclogenesis or cyclone wave, which are detected by the automated scheme only after subsequent growth in the ensuing 6–12 h. It is known that these early stages are critical for a comprehensive understanding of rapid intensification events. A discussion of possible future solutions to this problem is presented. Significance Statement: Because of the availability of large modern datasets portraying sea level pressure across the globe, meteorologists have turned to automated detection and tracking of midlatitude cyclones. Detection and tracking are of interest since these storm systems play an important role in weather and climate and potential changes in their location, frequency, and intensity are of considerable societal interest given climate change. This paper compares the results obtained from one commonly used automated tracking method with tracks obtained by human analysts. We find substantial discrepancies in cyclone position, intensity, and intensification rates and that these differences are not eliminated by using improved analyses. A discussion of possible future solutions is presented. [ABSTRACT FROM AUTHOR]

Climate change increases the frequency and intensity of extreme precipitation, which in combination with rising population enhances exposure to major floods. An improved understanding of the atmospheric processes that cause extreme precipitation events would help to advance predictions and projections of such events. To date, such analyses have typically been performed rather unsystematically and over limited areas (e.g., the U.S.) which has resulted in contradictory findings. Here we present the Multi‐Object Analysis of Atmospheric Phenomenon algorithm that uses a set of 12 common atmospheric variables to identify and track tropical and extra‐tropical cyclones, cut‐off lows, frontal zones, anticyclones, atmospheric rivers (ARs), jets, mesoscale convective systems (MCSs), and equatorial waves. We apply the algorithm to global historical data between 2001–2020 and associate phenomena with hourly and daily satellite‐derived extreme precipitation estimates in major climate regions. We find that MCSs produce the vast majority of extreme precipitation in the tropics and some mid‐latitude land regions, while extreme precipitation in mid and high‐latitude ocean and coastal regions are dominated by cyclones and ARs. Importantly, most extreme precipitation events are associated with phenomena interacting across scales that intensify precipitation. These interactions are a function of the intensity (i.e., rarity) of extreme events. The presented methodology and results could have wide‐ranging applications including training of machine learning methods, Lagrangian‐based evaluation of climate models, and process‐based understanding of extreme precipitation in a changing climate. Plain Language Summary: Increases in intense precipitation and faster onsets of droughts are just two of many precipitation‐related extreme events that worsen under progressive climate change. Surprisingly little is known about the weather systems that are driving these changes in many regions around the world. In order to better predict and prepare for these events, scientists need an improved understanding of the causes of the involved atmospheric processes and their interactions. A new algorithm called the Multi‐Object Analysis of Atmospheric Phenomenon has been developed to identify and track different types of weather systems, such as tropical and extra‐tropical cyclones, that can lead to extreme precipitation. The algorithm was applied to global weather data from 2001 to 2020. The results showed that certain types of weather systems, such as mesoscale convective systems, are frequently involved in causing the most extreme precipitation. Additionally, the study found that most extreme precipitation events are caused by a combination of different weather systems working together and that these interactions differ depending on event intensity. This research could be useful for improving climate models and understanding how extreme precipitation is likely to change in the future. Key Points: We track cyclones, anticyclones, jets, mesoscale convective systems (MCSs), atmospheric rivers, fronts, and equatorial wavesExtreme precipitation is typically associated with multiple atmospheric phenomena that interact across scalesMCSs are involved in most extreme precipitation events in the tropics and many sub‐tropical and mid‐latitude regions [ABSTRACT FROM AUTHOR]

This study investigated the structural and track change of cyclone Nepartak occurred over the western North Pacific in July 2021, a cyclone appeared at the surface level, using ERA5 data, focusing on the relationship with an upper‐tropospheric cutoff low (COL). The COL was shown to dominate the structural change of Nepartak which developed as a subtropical cyclone with a hybrid structure. As the surface cyclone approached the COL, it was overlapped by the COL and became a cyclone with a two‐storied structure, resulting in its abrupt track change. An analysis of the potential vorticity (PV) tendency showed that the movement of Nepartak toward the COL ceased because of the counter‐balance of the horizontal/vertical PV advection with the PV anomaly generated by diabatic heating, whereas the surface cyclone northward motion was primarily due to the horizontal PV advection associated with the COL. Nepartak is a case in which changes in the structure and track of a cyclone are controlled by a COL. [ABSTRACT FROM AUTHOR]

Tropical cyclones are one of the biggest threats to life and property. During cyclone period storm surge, flooding, extreme winds, tornadoes and lighting cause significant impacts on life and property and hence affects life of human being to a great extent. Nida was the third tropical cyclone requiring the issuance of tropical cyclone warning signals by the Hong Kong Observatory in 2016 and maximum hourly mean winds of 158 km/hr was recorded in Hong Kong. It affected many cities of China and about 500,000 people, more than 300 houses collapsed and made economic loss of about 500 million RMB. Investigation of lightning discharges around the cyclone track line revealed that the strong lightning activity is noticed during the cyclone period with a super lightning maxima on 30 July and 01 August. The effect of this typhoon on the ionosphere is studied using the TEC data from GPS measurements taken around the cyclone track and satellite based COSMIC measurements. Strong convective activity which is driver for the thunderstorm and gravity waves activity noticed from the negative cloud top temperature as low as −50°C observed from AIRS satellite during the cyclone period. Significant enhancement is atmospheric ozone is observed during the cyclone period which could be attributed to thunderstorm activity present during the cyclone period. The analysis found decrease in GPS‐TEC data at stations around Hong Kong region during the landfall of the cyclone. The magnitude of perturbation in TEC is found larger at stations lying toward right/eastward of the cyclone track as compared to those in the left/westward from the cyclone track. In addition, periodic signatures in ionospheric TEC data were also detected. Continuous wavelet transform to DTEC data has been made to estimate period and found the periodic structure in ionospheric TEC belongs to AGWs with period 9–20 min and frequency 1–2 mHz. Strong scintillation activity as high as S4‐index 1.35 from GPS measurements has been noticed at Sanya station during cyclone period on 02 August which is further confirmed by satellite based measurements from COSMIC. Both measurements show maximum scintillation activity during 1400–1600 UT. The strong scintillation activity as compared to normal days observed during the cyclone period is attributed to lightning induced electric filed as well as generation of AGWs due to deep convection which could act as seed perturbation for generation of ionospheric irregularities by Rayleigh‐Taylor instability mechanism. Key Points: Enhanced atmospheric ozone is observed during cyclone attributed to enhanced lightning activity which may be source of NOxMagnitude of ionospheric perturbation observed along left/right to cyclone track are significantly differStrong scintillation activity compared to normal days from ground and satellite based data are observed during the cyclone period [ABSTRACT FROM AUTHOR]

Cyclogenesis in the Mediterranean typically follows an archetypal scenario with the intrusion of a potential vorticity (PV) streamer over the Mediterranean, which results from a preceding Rossby Wave breaking (RWB) upstream over the North Atlantic. The RWB is amplified by the presence of warm conveyor belts (WCBs) in at least one North Atlantic cyclone about 4 days prior to Mediterranean cyclogenesis. This scenario has been found in several case studies of intense Mediterranean cyclones with a variety of different North Atlantic cyclone tracks and intensities, and different locations of PV streamers intruding the Mediterranean. While four main events (namely North Atlantic cyclone, WCBs, RWB and the resulting PV streamers) are suggested to be necessary for Mediterranean cyclogenesis, they rarely occur in a spatially consistent, fully repetitive pattern. To more systematically study this link between the upstream North Atlantic cyclone dynamics and the Mediterranean cyclogenesis, we perform a set of semi-idealized simulations over the Euro-Atlantic domain. For these simulations, we prescribe a constant climatological atmospheric state in the initial and boundary conditions. To trigger the downstream Mediterranean cyclogenesis scenario, we perturb the climatological polar jet through the inversion of a positive upper-level PV anomaly. The amplitude of this perturbation determines the intensity of the triggered North Atlantic cyclone. This cyclone provokes RWB, the intrusion of a PV streamer over the Mediterranean, and the formation of a Mediterranean cyclone. Therefore, our results show a direct causality between the presence of a North Atlantic cyclone and the downstream intrusion of a PV streamer into the Mediterranean, which causes cyclogenesis about 4 days after perturbing the polar jet, which we refer to as the upstream-downstream mechanism of cyclogenesis. To investigate the sensitivity of this mechanism, we vary the position and amplitude of the upper-level PV anomaly. In all simulations, cyclogenesis occurs in the Mediterranean. Nevertheless, the evolution, track and intensity of the Mediterranean cyclones are sensitive to the dynamical structure and intensity of the intruding PV streamer, which itself is sensitive to the interaction of the upstream cyclone and the RWB. By applying different seasonal climatological atmospheric states as initial conditions we show that the seasonal cycle of Mediterranean cyclogenesis indeed depends on the large-scale atmospheric circulation. In particular, we show that the Mediterranean cyclones in these semi-idealized simulations show characteristics that agree with the observed climatology of Mediterranean cyclones in the respective season. [ABSTRACT FROM AUTHOR]

In this work, we study long-term changes in the main directions of movement (storm tracks) of extratropical cyclones in the North Atlantic for the period 1873–2021, based on the data of the MSLP (Mean Sea Level Pressure) archives from the Climatic Research Unit and NCEP/DOE AMIP-II reanalysis. It was found that in the cold half of the year, the mean latitudes of storm tracks undergo oscillations with the periods ~80–100, ~40–45, and ~22 years, which indicates their possible association with solar cyclicity. Cyclone trajectories were found to shift northward at the minimum of the Gleissberg secular cycle (~1900–1930) and southward at its maximum (~1940–1960). The secular variations are the most pronounced in the western part of the North Atlantic, with the peak-to-peak amplitude reaching ~3–5°, and disappear at longitudes east of Greenwich. On the bidecadal timescale, cyclone tracks were found to shift noticeably to the north in even solar cycles and weakly to the south in odd ones. The most significant northward shifts (~1–2°) were detected during the descending phase and the minimum of the solar cycle (from the second to the sixth year after the solar maximum) in the eastern part of the North Atlantic (longitudes 30–10° W). The detected oscillations of cyclone trajectories may be caused by long-term changes in the intensity of the stratospheric polar vortex associated with galactic cosmic ray variations and geomagnetic activity. [ABSTRACT FROM AUTHOR]

Assessing the capacity of numerical models to produce viable tropical cyclones, as well as assessing the climatological behavior of simulated tropical cyclones, requires an objective tracking method. These make use of parameter thresholds to determine whether a detected feature, such as a vorticity maximum or a warm core, is strong enough to indicate a tropical cyclone. The choice of parameter thresholds is generally subjective. This study proposes and assesses the parallel use of many threshold parameter combinations, combining a number of weaker and stronger values. The tracking algorithm succeeds in tracking tropical cyclones within the model data, beginning at their aggregation stage or shortly thereafter and ending when they interact strongly with extratropical flow and transition into extratropical cyclones or when their warm core decays. The sensitivity of accumulated cyclone energy to tracking errors is assessed. Tracking errors include the faulty initial detection and termination of valid tropical cyclones and systems falsely identified as tropical cyclones. They are found to not significantly impact the accumulated cyclone energy. Thus, the tracking algorithm produces an adequate estimate of the accumulated cyclone energy within the underlying data. [ABSTRACT FROM AUTHOR]

An objective detection and tracking algorithm based on relative vorticity at 850 hPa using National Centers for Environmental Prediction--National Center for Atmospheric Research (NCEP--NCAR) Reanalysis-1 data was applied to track cyclones in the Southern Hemisphere during austral winters from 1948 to 2017. The climatological characteristics of extratropical cyclones, including track density, frequency, intensity, lifetime, and their related variabilities, are discussed. The frequency and average lifetime of cyclones have substantially decreased. The average maximum intensity of cyclones has shown an increasing trend over the 70-yr study period. The cyclone track density shows a decreasing trend in lower latitudes, consistent with the region where the upper-troposphere zonal wind weakens. Baroclinicity can explain the increase in cyclone intensity: when a cyclone moves to higher latitudes and enters the region with greater baroclinicity, it strengthens. As there is no discernible increase in cyclogenesis in the medium latitudes (45°-70°S), but significantly less cyclogenesis in lower and higher latitudes, it is hypothesized that there is no clear poleward cyclogenesis shift over the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Extratropical cyclones (ETCs) are responsible for the majority of cool‐season extreme events in the northeastern United States (NEUS), often leading to high‐impact weather conditions that can have wide‐ranging socioeconomic impacts. Evaluating the ability of climate models to adequately simulate ETC dynamics is essential for improving model performance and increasing confidence in future projections used by stakeholders and policymakers. ETCs are traditionally studied using techniques such as case studies and synoptic typing, however, these approaches can be time‐consuming, require subjective analysis, and do not necessarily identify the coincident large‐scale meteorological patterns (LSMPs). Here, we apply self‐organizing maps (SOMs) as an automated machine‐learning approach to characterize the LSMPs and associated frequency and intensity of discrete ETC events over NEUS. The dominant patterns of geopotential height variability are identified through SOM analysis of five reanalysis products during the last four decades. ETC events are tracked using TempestExtremes and are integrated with SOMs to classify the accumulated cyclone activity (ACA) associated with each pattern. We then evaluate the skill of CMIP6 historical experiments in simulating the LSMPs and ETC events identified in the SOM. Our results identify a robust bias toward more zonal patterns, with models struggling to reproduce the more amplified patterns typically associated with the highest cyclone activity. While model resolution has some impact on simulation credibility, model configuration appears to be more important in LSMP representation. The vast majority of CMIP6 models produce too few ETCs, although model errors are distributed around historical reanalyses when ACA is normalized by storm frequency. Plain Language Summary: Winter storms can have devastating socioeconomic impacts across the United States. Climate models are used to understand and predict these winter storms and how they might change in the future, therefore helping to inform climate policy and emergency services. It is essential that we evaluate these climate models so that their performance and accuracy can be optimized. One way of evaluating climate models is to assess their ability in reproducing the large‐scale atmospheric conditions which occur during extreme events. Here we apply a cyclone tracking algorithm and self‐organizing maps, a machine‐learning approach, to automate the process of identifying key patterns associated with historical winter storm activity. We then use this approach to assess if CMIP6 climate models are able to reproduce the same patterns including the winter storm frequency and intensity. Our results show that, regardless of resolution, most CMIP6 models struggle to simulate the more extreme patterns and tend to favor weaker patterns that are not as conducive to cyclone formation. As a result, most models simulate too few winter storms, however, the error in storm intensity is more varied, with some models producing stronger storms and others producing weaker storms on average. Key Points: Despite resolution, CMIP6 models struggle to reproduce amplified synoptic patterns over the US, with a robust bias toward zonal patternsMost CMIP6 models produce too few cyclones over the northeastern US, while model errors are more varied when considering cyclone intensityIncreased resolution increases the number and intensity of simulated extratropical cyclones but does not improve model representation of synoptic patterns [ABSTRACT FROM AUTHOR]

The formation of mid‐tropospheric cyclones (MTCs), responsible for a large portion of annual precipitation and extreme rainfall events over western India, is studied using an unsupervised machine learning algorithm and cyclone tracking. Both approaches reveal four dominant weather patterns that lead to the genesis of these synoptic systems. Specifically, re‐intensification of westward‐moving synoptic systems from the Bay of Bengal (type 1, 51%), in‐situ formation with a coexisting cyclonic system over the Bay of Bengal that precedes (type 2a, 31%) or follows (type 2b, 10%) genesis in the Arabian Sea, and finally in‐situ genesis within a northwestward‐propagating cyclonic anomaly from the south Bay of Bengal (type 2c, 8%). Thus, a large fraction of this region's rainy middle tropospheric synoptic systems form in association with cyclonic activity in the Bay of Bengal. The four variants identified also show a marked dependence on large‐scale environmental features. In particular, type 1 and type 2a MTC formation primarily occurs in phases 4 and 5, and type 2b and type 2c MTCs form mainly in phases 3 and 4 of the boreal summer intraseasonal oscillation. Further, though in‐situ formation with a Bay of Bengal cyclonic anomaly (types 2a and 2b) mostly occurs in June, downstream development is more likely in the core of the monsoon season. Out of all categories, type 2a is associated with the highest composite rain rate (60 mm·$$ \cdotp $$day −1$$ {}^{-1} $$) over western India and points towards the dynamic interaction between a low‐pressure system over the Bay of Bengal and the development of MTCs over western India and the northeast Arabian Sea. This classification, identification of precursors, connection with cyclonic activity over the Bay of Bengal, and dependence on a large‐scale environment provide an avenue for a better understanding of rain‐bearing MTCs over western India. [ABSTRACT FROM AUTHOR]

Tropical cyclones affect millions of lives in the Indian subcontinent which makes the region highly vulnerable to cyclones. Classifying the region's vulnerability greatly helps the stakeholders involved in the disaster management associated with tropical cyclones. This study is a comprehensive assessment of India's vulnerability to cyclones of different categories prepared at district level. It is based on recently updated cyclone track data, and considers both meteorological parameters such as surface-level winds, daily rainfall, storm surge height and socioeconomic parameters like population and household densities. Statistical tools like the cyclone return period as well as the landfall frequency count are also calculated for cyclones of varied intensities. A normalized cyclone vulnerability index is defined as a combination of above parameters that provides an overall vulnerability of each district to cyclonic, severe cyclonic and the total cyclonic storm categories. Results show that coastal districts of the northern most states of the east coast consisting of West Bengal and Odisha are most vulnerable to tropical cyclones followed by districts of Andhra Pradesh and Tamil Nadu on longer timescale. However, a southward shift in the cyclone activity as well as vulnerability is observed for the recent period. Along the West Coast, coastal districts of Gujarat show an increased vulnerability in the recent times than before. In terms of percentage of districts extremely vulnerable to cyclones, Andhra Pradesh dominates the list with 40–50% followed by Odisha (29–34%), West Bengal (13–14%) and Tamil Nadu (7–13%). [ABSTRACT FROM AUTHOR]

Mediterranean cyclones govern extreme weather events across the Euro-African basin, affecting the lives of hundreds of millions. Despite many studies addressing Mediterranean cyclones (MCs) in the last decades, their correct simulation and prediction remain a significant challenge to the present day, which may be attributed to the large variability among MCs. Past classifications of MCs are primarily based on geographical and/or seasonal separations, however, here we focus on cyclone genesis and deepening mechanisms. A variety of processes combine to govern MC genesis and evolution, including adiabatic and diabatic processes, topographic influences, land-sea contrasts, and local temperature anomalies. As each process bears a distinct signature on the potential vorticity (PV) field, a PV approach is used to distinguish among different "types" of MCs. Here, a combined cyclone tracking algorithm is used to detect 3190 Mediterranean cyclone tracks in ECMWF ERA5 from 1979–2020. Cyclone-centered, upper-level isentropic PV structures in the peak time of each cyclone track are classified using the Self Organizing Map (SOM). The SOM analysis reveals 9 classes of Mediterranean cyclones, with distinct Rossby wave-breaking patterns as discernible in corresponding PV structures. Though classified by upper-level PV structures, each class shows different contributions of lower-tropospheric PV and flow structures down to the surface. Unique cyclone life cycle characteristics, associated hazards (precipitation, winds, and temperature anomalies), and long-term trends, as well as synoptic, thermal, dynamical, seasonal, and geographical features of each cyclone class, indicate dominant processes in their evolution. Among others, the classification reveals the importance of topographically-induced Rossby wave breaking to the generation of the most extreme Mediterranean cyclones. These results enhance our understanding of MC predictability, by linking the large-scale Rossby wave formations and life cycles to coherent classes of under-predicted cyclone aspects. [ABSTRACT FROM AUTHOR]

East coast cyclones (ECCs) provide an essential reprieve from dry periods across eastern Australia. They also deliver flood‐producing rains with significant economic, social and environmental impacts. Assessing and comparing the influence of different types of cyclones is hindered by an incomplete understanding of ECC typology, given their widely variable spatial and temporal characteristics. This study employs a track‐clustering method (probabilistic, curve‐aligned regression model) to identify key cyclonic pathways for ECCs from 1950 to 2019. Six spatially independent clusters were successfully distinguished and further sub‐classified (coastal, continental and tropical) based on their genesis location. The seasonality and long‐term variability, intensity (maximum Laplacian value ± 2 days) and event‐based rainfall were then evaluated for each cluster to quantify the impact of these lows on Australia. The highest quantity of land‐based rainfall per event is associated with the tropical cluster (Cluster 6), whereas widespread rainfall was also found to occur in the two continental clusters (clusters 4 and 5). Cyclone tracks orientated close to the coast (clusters 1, 2 and 3) were determined to be the least impactful in terms of rainfall and intensity, despite being the most common cyclone type. In terms of interannual variability, sea surface temperature anomalies suggest an increased cyclone frequency for clusters 1 (austral winter) and 4 (austral spring) during a central Pacific El Niño. Furthermore, cyclone incidence during IOD‐negative conditions was more pronounced in winter for clusters 1, 2, 3— and clusters 4 and 5 in spring. All cyclones also predominantly occurred in SAM‐positive conditions. However, winter ECCs for clusters 1 and 3 had a higher frequency in SAM‐negative. This new typology of ECCs via spatial clustering provides crucial insights into the systems that produce extreme rainfall across eastern Australia and should be used to inform future hazard management of cyclone events. [ABSTRACT FROM AUTHOR]

It is not fully understood how near-inertial kinetic energy (NIKE) is spatially distributed near Tsushima oceanic front (TOF) as a typhoon travels across the region. Underneath TOF, a year-round mooring covering a major part of water column was implemented in 2019. During summer, three massive typhoons (Krosa, Tapah, and Mitag) consecutively traversed the frontal area and delivered a substantial amount of NIKE into surface mixed layer. According to a mixed-layer slab model, NIKE was widely distributed near the cyclone's track. The mooring observation exhibited the vertical distribution and pathways of surface-generated NIKE in response to the successive typhoon events. According to the modal decomposition, first three modes mostly explain the NIKE's elevations following the typhoon events. According to ray-tracing experiments based on the internal-wave theory, large-scale near-inertial waves (NIWs) rapidly descend to a depth greater than 1000 m, while mesoscale NIWs slowly descend and rarely reached beyond the main pycnocline. Following the passage of Tapah, a profound energy mass was found nearly stationary at shallow depths coincident with vertical shear of geostrophic current. We infer that the descending rate of NIWs fell and then they were amplified through the energy conservation when the waves came from the north side of TOF. [ABSTRACT FROM AUTHOR]

Since March 2020, the COVID‐19 pandemic has significantly reduced the availability of global aircraft‐based observations (ABOs), which has been restored later in 2021. This study focuses on the impact of ABOs on a regional reanalysis. Indian Monsoon Data Assimilation and Analysis (IMDAA) is a regional reanalysis for a period from 1979 to 2020 (originally up to 2018) over India and surrounding regions produced at the National Centre for Medium Range Weather Forecasting (NCMRWF), India, in collaboration with the UK Met Office. A comparison of the impact of ABOs on other conventional and satellite observations assimilated in the NCMRWF global model and IMDAA during 2019 and 2020 revealed the importance of ABOs, particularly in IMDAA, since it did not assimilate the latest satellite data as the IMDAA system was frozen in October 2016. A data denial experiment that removes all the ABOs from the IMDAA assimilation system for a period from March to November 2019 is designed. The results from the IMDAA reanalysis run, which assimilates ABOs during the same period, are compared with the data denial experiment. Assimilation of ABOs strengthened the upper tropospheric circulation, the Tropical Easterly Jet (TEJ), during the Indian summer monsoon compared to the data denial experiment. Analysis of the features of two cyclones that developed over the North Indian Ocean during the study period revealed that ABO assimilation played a key role in simulating the track and intensity of these cyclones when they were in the 'severe' category. Since the sample is small, more cyclone cases need to be analysed to consolidate the result. [ABSTRACT FROM AUTHOR]

An objective cyclone detection and tracking analysis is performed for the Mediterranean region with the use of 6-hourly (00, 06, 12, and 18 UTC) 1° × 1° mean sea-level pressure data obtained from the ERA5 database for the period 1950–2018. At first, the main cyclogenesis and high-density areas of cyclones are identified. Next, principal component analysis and cluster analysis are performed, classifying the detected cyclone trajectories into 12 clusters. In the following step, the application of the above methodology, this time on the intra-annual variations of the 12 cyclone clusters' frequencies leads to the objective definition of four seasons, which generally correspond to the conventional ones, but they present differences in their limits and duration. The results of this method are also compared with the ones of two other methods for defining the seasons, which are based (i) on the long-term mean intra-annual variations of various meteorological parameters and (ii) on the intra-annual variations of the frequencies of defined weather types, revealing larger winter and shorter spring seasons. Finally, a composition of all three aforementioned approaches is attempted, leading to the following seasons: "winter" (November 16–March 25) which lasts more than 4 months, "spring" (March 26–June 11) with a duration of approximately 2.5 months, "summer" (June 12–September 12) which lasts about 3 months, and "autumn" (September 13–November 15) with a duration of about 2 months. The long-term changes of the above seasons' characteristics are also examined. [ABSTRACT FROM AUTHOR]

Swells can cause coastal hazards. A unique example of such hazards is the Yorimawari‐Nami (YM‐wave) events that have been observed once every few years in Toyama Bay in the Japan Sea. Based on coastal in situ observations and hindcast simulations of ocean waves, the forcing mechanism for the record‐high 2008 YM‐wave event is investigated, focusing on the surface winds and the atmospheric disturbances that drove wind seas and swells in the Japan Sea. Detailed analysis of atmospheric mesoscale data along with cyclone tracking and wave spectral analysis revealed that the 2008 event was forced by an exceptionally persistent northerly wind off the Tohoku and Hokkaido regions associated with two successive extra‐tropical cyclones, passing across the Japan Sea and accompanying a well‐defined upper‐tropospheric cut‐off low. The first cyclone generated the initial northerly wind forcing toward the northwest of Hokkaido Island that was aligned with the direction of southward‐propagating wind seas toward Toyama Bay. This initial fetch caught up with the second cyclone, leading to an extension in the area of a large northerly wind component (>12 ms−1) that lasted longer than 24 hr and extended southward due to the southward extension of the cut‐off low with a propagation speed that matches the wave group velocity, reinforcing the initially generated swell. Plain Language Summary: Due to the frequent passage of storms to the north of Toyama Bay, the surrounding coastal region has been devastated by extreme ocean waves once every several years. Of these extreme waves, one that hit the bay in 2008 was the highest and most destructive. We investigated the factors that contributed to the 2008 wave event being so exceptional compared to previous moderate events associated with similar waves. Matching the wind and wave fields in the Japan Sea in conjunction with cyclone tracking revealed that two successive cyclones passing across the Japan Sea jointly contributed to the generation of the high waves. The first cyclone approaching northern Japan brought northerly winds in its wake that are favorable for generating a wind‐forced ocean wave. As the wave propagated toward Toyama Bay, the second cyclone from the west caught up with the region of initial wind forcing, further extending the area of a large northerly wind component that had continuously provided energy to the propagating wave, further amplifying the wave. While it has been reported that tropical cyclones or polar lows sometimes energize pre‐existing ocean waves, this study suggests that similar mechanisms in midlatitude migratory cyclones can trigger extreme ocean waves. Key Points: Detailed atmospheric forcing in the Japan Sea and the record high ocean wave that eventually hit Toyama Bay in 2008 is investigatedThe 2008 high wave was reinforced by a dynamical fetch‐like mechanism where the moving wind forcing matches the wave propagationA well‐defined cut‐off low in the mid‐troposphere made surface wind forcing persistent and expand southward [ABSTRACT FROM AUTHOR]

This study investigates the impact of future climate warming on tropical cyclones (TC) and extratropical cyclones (ETC) using the database for Policy Decision-Making for Future Climate Change (d4PDF) large ensemble simulations. Cyclone tracking was performed using the neighbor enclosed area tracking algorithm (NEAT), and TC and ETCs were identified over the western North Pacific Ocean (WNP). For cyclone frequency, it was revealed that, although a slight underestimation of the total number of TCs and ETCs in both the WNP and near Hokkaido, Japan, exists, the d4PDF reproduced the spatial distribution of both TC and ETC tracks well when compared with observations/reanalysis. The 4-K warming scenarios derived from six different sea surface temperature warming patterns showed robust decreases in TC frequency in the tropical WNP and a slight reduction in ETCs near Japan. Next, precipitation characteristics for TCs or ETCs in the vicinity of Hokkaido were examined using 5-km-mesh regional climate ensemble simulations. Four representative cyclone locations near Hokkaido are identified using K-means clustering and revealed distinct precipitation characteristics between clusters, with higher TC-associated precipitation than ETC-associated precipitation and the heaviest precipitation in the southern portion of the prefecture. The 4-K warming scenarios revealed increased precipitation for all cyclone placements for both TCs and ETCs. Last, average cyclone intensity, translation speed, and size were examined. It was shown that TCs in future climates are more intense, propagate more slowly, and are smaller in terms of enclosed vorticity area as they approach Hokkaido. For ETCs, mean intensity does not change much; they travel slightly faster, and become smaller. [ABSTRACT FROM AUTHOR]

This work analyses the extratropical cyclone-related extreme waves in the ocean surface and their trends in the North and South Atlantic Oceans. Atmospheric and ocean wave products are obtained from ERA5, from 1979 to 2020 with 1-hourly outputs, covering 42 years with the present climate changes evaluated by the difference between the two 21-years-time slices. The cyclones are tracked through the relative vorticity at 850 hPa and then associated with extreme wave events using an automated scheme that searches for an extreme wave region 1500 km from the centre of the cyclone, following criteria that exclude possible swell dominated events. The hot spot regions of cyclone-related waves occurrence found by the method agree with previous studies and relate to the cyclogenesis region, and storm track orientation. Most cyclones associated with extreme wave events are generated in the western boundary of the domains. The east-poleward side of the ocean basins presents the highest density of occurrences related to the higher density of cyclone track and the dominance of more mature stage cyclones while in the west side prevail systems on developing stages, with notable propagating fronts and consequently, lower wind persistence. The storm track variations alone cannot explain the observed changes in the wave occurrence during the period due to the lack of statistical confidence. However, the wave occurrence responds to changes in the cyclone intensity, modulated by cyclone displacement speed. Regions with an increase of extreme waves are related to the effect of more intense cyclones or cyclones with slower propagation, being the last associated with a longer interaction of winds with the ocean surface. [ABSTRACT FROM AUTHOR]

Generations of climate models exhibit biases in their representation of North Atlantic storm tracks, which tend to be too far near the equator and too zonal. Additionally, models have difficulties simulating explosive cyclone growth. These biases are one of the reasons for the uncertainties in projections of future climate over Europe, and the underlying causes have yet to be determined. All three biases are shown to be related, and diabatic processes are pointed to as a likely cause. To demonstrate this, two hemispherically symmetric storm tracks forming downstream of an idealized sea surface temperature (SST) front on an aquaplanet are examined using the seamless weather and climate prediction model ICOsahedral Non‐hydrostatic and its grid refinement capabilities. The analyzed perpetual boreal winter has a global grid spacing of 20 km, two bi‐directionally interacting grid nests over the Northern Hemisphere that refine the grid to 10‐km spacing over much of the stormtrack and further to 5‐km spacing near the SST front. In contrast, no grid refinement is performed for the Southern Hemisphere. Feature‐based cyclone tracking shows that the poleward propagation in the NH is enhanced, so the high‐resolution storm track is less equatorward and less zonal; explosive deepening rates are more frequent and precipitation rates are amplified. The implication is that resolving diabatic processes on the storm scale improves all three intersecting biases in the representation of storm tracks. While new challenges arise at cloud resolving scales, much improvement for the representation of storm tracks will be gained once climate models resolve the meso‐γ scale. Plain Language Summary: Most people in the mid‐latitudes will experience climate change through changes in their daily weather. Much of the daily weather variability is determined by the propagation of extratropical low pressure systems. The direction of propagation of these systems dictates regional precipitation patterns, and an accurate representation of the track is important to reduce uncertainties in future projections. However, climate models simulate tracks that are too zonal (i.e., east–west), too close to the equator and too weak. Using an idealized simulation, this study shows that individual tracks will propagate more poleward, intensification rates will increase and the tracks become less zonal at storm‐resolving model resolution, helping to reduce this well‐known circulation bias in climate models. Key Points: Generations of climate models simulate storm tracks too zonal, too equatorward and insufficiently represent explosive cyclone growthA 10‐year simulation with a local 5‐km grid nest suggests that all three biases are interrelated, because poleward storm propagation is inherently connected to intensificationEvidence is presented that diabatic processes are an important contributor to all three biases and convection‐resolving simulations have the potential to improve the storm track representation [ABSTRACT FROM AUTHOR]

Sea level response to extratropical cyclones, one of the most disastrous weather systems, varies depending on cyclone types and tracks. This study presents a systematic modeling assessment of storm surge induced by extratropical cyclones in the northern East China Sea using an ocean‐wave coupled model, based on the Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport (COAWST) model system. We identified the type of extratropical cyclone most likely to cause disasters and the areas likely to suffer the worst effects. We conducted sensitivity experiments to analyze the driving mechanisms (such as wind, air pressure, tide, and wave) and influencing mechanisms (such as local and remote meteorological effect and Ekman effect) of storm surge. During strong winds, positive and negative storm surges were consistent with the wind direction, and formed source of coastal trapped waves. When an abnormally high water level occurred in a semi‐enclosed sea area, it propagated mainly along the cyclone direction. The energy of coastal trapped waves was easy to dissipate in case of caps and other locations with large topographic changes. Tide‐surge‐wave interaction and propagation were also greatly affected by coastal trapped waves. Plain Language Summary: Different types of extratropical cyclones can cause different abnormal fluctuations in sea level. The northern East China Sea is a typical semi‐enclosed sea and prone to storm surge disasters. In this study, we used the numerical model to simulate the changes in a dynamic marine environment caused by extratropical cyclones of different types with different tracks. Through comparison, the most serious extratropical cyclone and the worst affected area were identified. The water level was decomposed according to the driving forces to quantitatively distinguish the primary and secondary influencing factors. Driving mechanisms of water level response were clarified. Other impact mechanisms of storm surge, such as spatial decomposition of meteorological force and Coriolis force were discussed. This study demonstrates that strong coastal trapped waves exist and propagate in an anticlockwise pattern along the coast of northern East China Sea under the influence of extratropical cyclones. Coastal trapped waves can help to explain the interaction among tides, storm surge, and waves. Key Points: The type of extratropical cyclone most likely to cause storm surge disaster is identified in the northern East China SeaThe main driving mechanisms and influencing mechanisms of sea level response to extratropical cyclone are clarifiedStrong coastal trapped waves exist, propagate counterclockwise and affect the tide‐surge‐wave interaction in the semi‐enclosed sea [ABSTRACT FROM AUTHOR]

Forests disturbance by tropical cyclones is mostly documented by field studies of exceptionally strong cyclones and satellite-based approaches attributing decreases in leaf area. By starting their analysis from the observed damage, these studies are biased and may, therefore, limit our understanding of the impact of cyclones in general. This study overcomes such biases by jointly analyzing the cyclone tracks, climate reanalysis, and changes in satellite-based leaf area following the passage of 140 ± 41 cyclones. Sixty days following their passage, 18 ± 8 % of the cyclones resulted in a decrease and 48 ± 18 % showed no change in leaf area compared to nearby forest outside the storm track. For a surprising 34 ± 7 % of the cyclones, an increase in leaf area was observed. Cyclones resulting in higher leaf area in their affected compared to their reference area coincided with an atmospheric pressure dipole steering the cyclone towards a region experiencing a dry spell caused by the same dipole. When the dipole was present, the destructive power of cyclones was offset by their abundant precipitation enabling forest canopies in the affected area to recover faster from the dry spell than canopies in the reference area. This study documents previously undocumented widespread antagonist interactions on forest leaf area between tropical cyclones and droughts. [ABSTRACT FROM AUTHOR]

A high-resolution ocean circulation model is customized over the region (80°E–95°E; 10°N–23°N) in the Bay of Bengal to study the changes in upper ocean properties as a result of super cyclone Phailin. The model when forced with high-resolution reanalysis winds, which are scaled on the observed along track wind data, gives realistic simulation of upper ocean (surface as well as sub-surface) variability during the cyclone. The cyclone causes significantly high decrease (increase) in sea surface temperature (salinity) to the right side of the cyclone track. A steep reduction in the sea surface height of the region is also noticed. The vertical stability analysis indicates the presence of high instability and turbulence during the cyclone. It is found that relatively higher (very low) energy is required for mixing during the cyclone (post-cyclone) period. The heat (salt) budget analysis suggests that strong temperature decrease (salinity increase) in the surface and sub-surface (i.e., at 50 m) occurs mainly due to the advection and diffusion (i.e., storm-induced mixing of colder and high-salinity waters from below) processes. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TCs) are the most distractive natural weather phenomena and cause extensive damage and socioeconomic loss over the North Indian Ocean (NIO) region. Convection and planetary boundary layer (PBL) system play a vital role in the origin and strengthening of the TCs. The various convective and PBL parameterization schemes are available in the statistical model, which integrates these processes. The efficient incorporation of these schemes is vital to enhance the performance of the numerical weather prediction (NWP) model. In the present study, twelve experiments have been designed to carry out the numerical simulations using Advance Research Weather Research and Forecasting (ARW) model. The behavior and performance of the schemes have been evaluated to verify the instantaneous forecast of the TCs. The simulated cyclone track, which is assessed with the Indian Meteorological Department (IMD) best track data, indicates that the vector displacement error and RMSE for the experiment MWBM and YWBM are < 100 km and < 10 km, respectively. The maximum sustained 10-m wind prediction shows MWKF for Luban and YWKF for Titli have the least RMSE value, accounting for 7.13 ms−1 and 9.75 ms−1. The equitable threat score (ETS) at 24-h accumulated rainfall is > 0.4 for MLBM and up to 60 mm in Luban. However, it is > 0.6 for YLBM and up to 40 mm for Titli. Based on the results and keeping the cyclone track, intensity, and rainfall, the BMJ convective scheme with the YSU and MYJ PBL has better predicting skills over the NIO region. The KF scheme has better skills in the prediction of TC intensity. [ABSTRACT FROM AUTHOR]