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Climatological monthly mean tropical cyclone (TC) genesis location in the western North Pacific exhibits a marked meridional shift from June to November and the physical cause of such a shift was investigated through the diagnosis of observational and reanalysis datasets. Two genesis potential indices were used to examine key environmental parameters affecting the meridional shift. The diagnosis results indicate that dynamic parameters such as vertical and meridional wind shears play a dominant role in promoting both the northward advance and southward retreat of the mean genesis latitude, while the effect of vertical velocity is negligible. The thermodynamic parameters such as relative humidity and potential intensity in general play a minor role, except that the latter helps promote northward advance during the early TC season. The change of the environmental parameters is closely linked to the sub‐seasonal evolution of the monsoon trough and subtropical high in the western North Pacific. Maximum synoptic‐scale variability also experiences a similar meridional shift, contributing to the TC genesis location shift. [ABSTRACT FROM AUTHOR]

Strong winds have evident impacts on the environment and the society. It can affect the dispersion of air pollutants, land erosion, and damage buildings, representing a severe hazard to people and properties. However, the changes and variabilities of extreme winds are still largely unknown, especially in global high-elevation regions, e.g., the Tibetan Plateau. This study analyses for the first-time changes in extreme wind speed over the Tibetan Plateau using homogenized near-surface daily maximum wind speed observations for 1973–2020. Results show that the daily maximum wind speed has significantly decreased in most stations during 1973–2020, with the largest decline in magnitude observed in spring. The frequency of daily maximum wind speed exceeding the 95% percentile shows a similar slowdown pattern. The detected decline is linked to large-scale atmospheric circulation, particularly to changes in the patterns of westerly and monsoon, which explain 35%~57% of daily maximum wind speed anomaly variations. Furthermore, this study reveals that changes in (a) geostrophic wind, (b) the instability of atmospheric thermal stratification, (c) vertical wind shear, and (d) Tibetan Plateau low vortex also contributes to the observed decreasing trends of daily maximum wind speed. [ABSTRACT FROM AUTHOR]

Measuring boundary layer stratification, wind shear, and turbulence remains challenging for wind resource assessment. In particular, larger eddy scales have the greatest impact on turbine load fluctuations, and there are few in situ methods to observe them adequately. Satellite remote sensing using synthetic aperture radar (SAR) is an alternative approach. In this study, eddy‐related signatures in 704 high‐resolution images are related to stratification through a bulk Richardson number (Ri$$ Ri $$) measured by a buoy near Martha's Vineyard, the US epicenter of offshore wind. Variations in SAR‐observed atmospheric boundary layer eddies, or lack of them, correspond to specific Ri$$ Ri $$ regimes. Accounting for strong vertical wind shear, typically under stable stratification, is critical for energy production and turbine loads, and SAR directly identifies these conditions by the absence of energetic eddies. SAR also provides a regional climatology of atmospheric stratification for offshore wind assessment, complementing other observations, and with potential application worldwide. [ABSTRACT FROM AUTHOR]

Nuclear war would cause massive amounts of smoke from its associated explosions and fires that would subsequently inject copious amounts of aerosols into the stratosphere. There would also be considerable changes to the global climate system, threatening human health and sustainability. Our work reveals a reduction of global‐scale tropical cyclones (TCs) from a simulation of a nuclear war scenario that could produce ∼150 million tons of smoke. In response to nuclear war, there would be spatially uneven cooling that would result in an anomalous sea surface temperature (SST) gradient pattern. Associated with this would be an anomalous zonal vertical circulation, tending to suppress upward motion and increase vertical wind shear over all TC main development regions, largely explaining the observed TC reduction at regional and global scales. This study improves our understanding of the impact of nuclear war on the TC environment. Plain Language Summary: The topic of potential nuclear war has come to the forefront recently given the context of the Ukraine war. The smoke and soot released into the atmosphere from nuclear explosions and subsequent fires would dramatically affect both global and regional climates. By blocking solar radiation, these particles could trigger significant global cooling, disrupting the atmospheric circulation and altering oceanic conditions. This work shows a consistent decrease in global‐scale tropical cyclones (TCs) in the simulation of nuclear war between the United States and Russia with a release of 150 Tg black carbon. In addition to unfavorable thermodynamic conditions caused by large‐scale cooling, we examine the potential driver mechanisms of the global reduction in TCs in response to nuclear war. Due to the spatially uneven cooling, there would be an anomalous sea surface temperature gradient, as well as low‐level westerly anomalies. Near the tropopause, the reduced pole–equator temperature gradient induces strong upper‐level easterly anomalies. The anomalous zonal winds could further alter the zonal vertical circulation, reducing global TCs via decreases in upward motion and increases in vertical wind shear. This study improves our understanding of the impact of nuclear war on the TC environment as well as the large‐scale atmospheric and oceanic environment. Key Points: Simulations of nuclear war show a consistent decrease in global tropical cyclone frequencySpatially uneven cooling causes an anomalous sea surface temperature gradient and changes the zonal vertical circulationIncrease wind shear and reduced upward velocity are the primary drivers of the tropical cyclone reduction [ABSTRACT FROM AUTHOR]

The Sporadic E layer or Es is an ionospheric phenomenon characterized by enhancements in electron density within 90–120 km above the Earth's surface. Based on the wind shear theory, the formation of Es layers is associated with vertical shears in the horizontal wind, in the presence of the Earth's magnetic field. This study explores the role of planetary waves on inducing these vertical shears and subsequently shaping Es layers. Our investigations benefit from a large amount of data facilitated by the FORMOSAT‐7/COSMIC2 and Spire missions, which offer extensive global coverage. A wave analysis is applied to the Es intensity as represented by the S4 index derived from radio occultation measurements, in search of potential planetary wave signatures. Additionally, measurements from Aura/MLS are used to analyze corresponding spectra for the geopotential height, enabling a comparative examination of planetary wave signatures in the Es layer and geopotential height variations. The findings reveal westward and eastward wave components with specific wavenumbers and periods, suggesting the involvement of westward propagating quasi 6‐day, quasi 4‐day planetary waves, and eastward propagating Kelvin waves with a period of around 3 days in Es layer formation at low latitudes. Key Points: Spatial‐temporal analysis of FORMOSAT‐7/COSMIC2 & Spire radio occultation data shows influence of planetary waves on Es layer formationWestward propagating planetary waves, particularly the 6‐day and 4‐day wave (wavenumber 1 and 2), impact Es layer intensity at low latitudesThe study reveals the involvement of eastward propagating ultrafast Kelvin waves also play a role for low‐latitude Es [ABSTRACT FROM AUTHOR]

The parameterization of subgrid‐scale processes such as boundary layer (PBL) turbulence introduces uncertainty in Earth System Model (ESM) results. This uncertainty can contribute to or exacerbate existing biases in representing key physical processes. This study analyzes the influence of tunable parameters in an experimental version of the Cloud Layers Unified by Binormals (CLUBBX) scheme. CLUBB is the operational PBL parameterization in the Community Atmosphere Model version 6 (CAM6), the atmospheric component of the Community ESM version 2 (CESM2). We perform the Morris one‐at‐a‐time (MOAT) parameter sensitivity analysis using short‐term (3‐day), initialized hindcasts of CAM6‐CLUBBX with 24 unique initial conditions. Several input parameters modulating vertical momentum flux appear most influential for various regionally‐averaged quantities, namely surface stress and shortwave cloud forcing (SWCF). These parameter sensitivities have a spatial dependence, with parameters governing momentum flux most influential in regions of high vertical wind shear (e.g., the mid‐latitude storm tracks). We next evaluate several experimental 20‐year simulations of CAM6‐CLUBBX with targeted parameter perturbations. We find that parameter perturbations produce similar physical mechanisms in both short‐term and long‐term simulations, but these physical responses can be muted due to nonlinear feedbacks manifesting over time scales longer than 3 days, thus causing differences in how output metrics respond in the long‐term simulations. Analysis of turbulent fluxes in CLUBBX indicates that the influential parameters affect vertical fluxes of heat, moisture, and momentum, providing physical pathways for the sensitivities identified in this study. Plain Language Summary: Models struggle with certain aspects of predicting the Earth's current and future climate. To achieve better predictions in the future, it is important to understand which parts of the model need to be improved. This study explores how changing certain model characteristics influences what the model outputs. We find that changing how the model estimates small‐scale motions in the atmosphere improves the model's accuracy. Furthermore, these changes affect both short‐term (several days) and long‐term (several decades) model simulations. The results of this study can help scientists understand the physical behavior of climate models and help inform future improvements to enhance model accuracy. Key Points: A computationally‐efficient sensitivity analysis identifies key parameters and physical mechanisms for global climate propertiesCertain parameter sensitivities in short‐term, initialized hindcasts are consistent with those seen in multidecadal climate simulationsParameters governing the degree of turbulent mixing in the presence of vertical wind shear are influential for surface stress representation [ABSTRACT FROM AUTHOR]

This research paper discusses a case study of Kelvin-Helmholtz (KH) waves in the atmosphere, specifically focusing on a KH wave event observed above Dubrovnik, Croatia on October 9, 2015. The authors conducted a numerical simulation using the Weather Research and Forecasting (WRF) model to analyze the atmospheric conditions that led to this particular KH event. The simulation suggested the presence of KH waves at altitudes corresponding to the observed KH clouds, and revealed a sheared layer in the middle troposphere and a saturated layer at a specific altitude, providing further evidence of the association between the KH clouds and the favorable conditions for KH waves. The article concludes that the WRF model has the potential to simulate even shorter wavelengths of KH waves with a finer grid resolution. [Extracted from the article]

Numerous studies focus on the impacts of ENSO diversity on tropical cyclone (TC) activities in the western North Pacific (WNP). In recent years, there is a growing threat of landfalling and northward-moving TCs in East Asia, accompanying an increase in central Pacific (CP) El Niño. Here, we aim to discover variations in landfalling TCs during various types of CP El Niño (CP-I and CP-II El Niño). It is found that significant changes in landfalling and going northward TCs over East Asia north 20°N are modulated by CP-I El Niño. During CP-I El Niño, TCs tend to landfall more often over the mainland of China with longer duration, moving distance, and stronger power dissipation index (PDI) after landfall and increased TC-induced rainfall, due to favorable conditions (beneficial steering flow, weak vertical wind shear, increased specific humidity, increased soil moisture, and temperature), especially significant over the northeastern part. The situation over the mainland of China is reversed during eastern Pacific (EP) El Niño and CP-II El Niño, with a significant decrease in the characteristics with corresponding unfavorable environments. Over the Korean Peninsula and Japan, the frequency of TC landfalls, as well as the duration and the moving distance after landfall, exhibits greater levels during CP-I and CP-II El Niño than during EP El Niño due to favorable steering flow, and thus, TC-induced rainfall enhances correspondingly. Regarding the PDI over the Korean Peninsula and Japan, it remains relatively consistent across all El Niño types. However, a notable increase in the PDI during EP El Niño could be attributed to the higher intensity of TCs prior to landfall. [ABSTRACT FROM AUTHOR]

The variety of produced variables at the surface and atmospheric pressure levels, appropriate resolution, and global coverage of the ERA5 reanalysis data have led its consideration both in numerous climate research studies and for predicting atmospheric parameters. The initial step in using reanalysis data involves its verification using observational data. Despite the scattered nature of measuring stations, observational data remains a practical dataset for this purpose, particularly in investigating thunderstorms. In this research, we have verified the accuracy of ERA5 reanalysis data in estimating of two convective parameters: the Lifted Index (LI) and Vertical Wind Shear (WVSH). To achieve this, we analyzed radiosonde data from nine stations across Iran (including Tabriz, Mashhad, Tehran, Kermanshah, Isfahan, Ahvaz, Kerman, Shiraz and Zahedan stations) in the period of 1990-2020. Statistical indicators were employed for comparison between the reanalysis data and observational data. Several constraints were applied to the data. For instance, both temperature and dew point profiles should be measured simultaneously. Profiles that terminated below the 6 km above the ground or provided data at fewer than 10 pressure levels were excluded. Additionally, some constrains were utilized to quality control wind and temperature gradients. Specifically: (I) Profiles were removed if the lapse rate in the mid-troposphere exceeded 9 K/km, (II) Profiles were excluded if the lapse rate in the low-troposphere exceeded 11 K/km, (III) Profiles were discarded if VWSH-1000 exceeded 35 m/s, (IV) Profiles were omitted if VWSH-3000 exceeded 45 m/s and (V) Profiles were removed if VWSH-6000 exceeded 70 m/s. The VWSH was calculated across three layers at altitudes of 1000, 3000 and 6000 meters from the surface. Investigations were conducted on daily, monthly, seasonal and long-term time scales. On a monthly scale, the minimum (maximum) root mean square errors (RMSE) for VWSH-1000, VWSH-3000, and VWSH-6000 were approximately 3 (8.5), 3.36 (9.84), and 4 (20) m/s, respectively. The results showed that the ERA5 reanalysis data consistently underestimated the value of VWSH-1000 across all stations (except Ahvaz station in recent years). The estimation of VWSH-3000 and VWSH-6000 parameters exhibited both overestimation and underestimation in different months. Notably, the highest error in ERA5 data for VWSH-6000 occurred during January. Across most stations, the largest errors were observed during cold months (particularly for the VWSH-6000 parameter), while the smallest errors occurred during warm months. In conclusion, the results suggest that as the height of the investigated layer increases, the performance of ERA5 in generating the considered VWSH parameters at the stations improves, especially in recent years. A comparison between reanalysis-LI and observational-LI indicatedes that the highest (lowest) error occurs during warm (cold) months of the year. Throughout the study period, the reanalysis data produced an error of at least 10 K (at Zahedan station) and up to 15 K (at Tehran station) in LI estimation. Except for Ahvaz station, LI was consistently underestimated across all stations. The monthly mean of reanalysis-LI reflected more unstable conditions, whereas the observed values indicated a more stable atmosphere. Consequently, reanalysis-LI may not be a suitable metric for distinguishing stability and instability in the considered stations. However, in Mashhad and Tehran stations, there were consistencies between the trend of annual average values from reanalysis and observational data. In other stations, this agreement becomes evident in recent years. However, in some stations, the annual average value of reanalysis LI has overcome the observations, while in others, it is the opposite. [ABSTRACT FROM AUTHOR]

Latent heating modifies the jet stream by modifying the vertical geostrophic wind shear, thereby altering the potential for baroclinic development. Hence, correctly representing diabatic effects is important for modelling the mid-latitude atmospheric circulation and variability. However, the direct effects of diabatic heating remain poorly understood. For example, there is no consensus on the effect of latent heating on the cross-jet temperature contrast. We show that this disagreement is attributable to the choice of spatio-temporal averaging. Jet representations relying on averaged wind tend to have the strongest latent heating on the cold flank of the jet, thus weakening the cross-jet temperature contrast. In contrast, jet representations reflecting the two-dimensional instantaneous wind field have the strongest latent heating on the warm flank of the jet. Furthermore, we show that latent heating primarily occurs on the warm flank of poleward directed instantaneous jets, which is the case for all storm tracks and seasons. [ABSTRACT FROM AUTHOR]

The wind dynamo in the ionosphere leads to differential motion of ions and electrons, which in turn sets up electric fields and currents. Observations show that daytime lower thermospheric horizontal winds have large vertical gradients. Numerical modeling conducted approximately 50 years ago demonstrated that the zonal wind shears in the ∼130–180 km altitude range can generate off‐equatorial relative minima (dips) in the daytime height‐integrated eastward current density, appearing as westward sidebands north and south of the equatorial electrojet (EEJ). This study observationally confirms this connection for the first time by combining Ionospheric CONnection explorer zonal wind profiles and Swarm latitudinal zonal currents. We demonstrate observationally that the magnitude of the EEJ sideband current is proportional to the strength of westward turning winds with altitude in the Pedersen conductivity dominated region. Additional numerical experiments explain the importance of wind shear in different altitude regions in generating the sideband current. This study contributes to the better understanding of the neutral wind effect on the local current generation. Plain Language Summary: The winds in the E‐region ionosphere push the plasma in the presence of Earth's magnetic field, causing ions and electrons to move separately, producing electric current. The low‐latitude ionospheric current system consists of an intense eastward current at the magnetic equator (called Equatorial Electro‐Jet (EEJ)) and off‐equatorial reduced eastward or relative westward currents (EEJ sideband currents) in both hemispheres. Modeling studies have shown that the altitudinal gradient of the zonal wind is related to the strength of the EEJ sideband currents. However, observational studies to validate these results have been missing to this date. This study utilizes simultaneous observations from Ionospheric CONnection explorer and Swarm satellites to provide insights on the connection between low‐latitude winds and currents, which will improve our understanding of the causes of daytime ionospheric variability. Key Points: First observational evidence of effect of zonal wind gradients at ∼130–180 km on low‐latitude Equatorial Electro‐Jet sideband currentsThe altitude variation of the zonal wind gradient modulates the latitudinal variation of EEJ sideband currentsWith increasing westward wind shear, the strength of low‐latitude Equatorial Electro‐Jet sideband current increases [ABSTRACT FROM AUTHOR]

The downshear‐left enhancement of tropical cyclone rainfall has been demonstrated previously, but the radial dependence of this effect was not analyzed in detail. This study quantifies the progressive upwind shift of the wavenumber‐1 maximum rain position with radius relative to the vertical wind shear direction. This shift is visualized as a distinctive upwind spiral of the maximum. It is shown that this spiral pattern is generally observed across various storm intensities, shear strength, and ocean basins. Detailed examination revealed that the maximum downwind deflection angle of the wavenumber‐1 rain maximum relative to the shear direction is smaller for tropical storms than hurricanes, but insensitive to hurricane intensity. It is proposed that the spirality is produced by a continuous decline in angular advection of air parcels with radius. The stability of the deflection angle in hurricanes may be accounted for by a corresponding increase in vertical ascent under strengthening angular flow. Plain Language Summary: Tropical cyclones (TCs) can produce torrential rainfall that generates floods, causing significant socio‐economic losses. Understanding the spatial structure of the TC rain field is crucial for improving disaster preparedness. The TC rain field can be thought of as the combination of a symmetric and an asymmetric part. By using a technique called Fourier decomposition, we can break down the asymmetric part into individual wavenumber components. The first component, wavenumber‐1 (WN‐1), is dominant and tends to be larger in the downshear quadrants under vertical wind shear. Using 21 years of global WN‐1 rain fields, we produced composite images aligned with the shear direction. We discovered that the positions at which the WN‐1 maximum occurs progressively shift upwind with increasing distance from the TC center, forming a spiral. We provided the first quantification of the observed spirals and showed that this is a general pattern that exists across different TC intensities, shear strength, and ocean basins. We also identified detailed changes in the pattern with storm intensity and introduced simple models as a first attempt to comprehend these changes. The findings can improve weather forecasts and risk predictions, making us better prepared for hazards associated with TC rainfall. Key Points: There exists a general and progressive upwind shift in the wavenumber‐1 maximum with radius in global shear‐relative rainfall compositesMaximum downwind deflection of the wavenumber‐1 maxima rises with storm intensity up to Category 1 on the Saffir–Simpson Hurricane ScaleLinearity between the angular velocity and the vertical velocity of the storm may stabilize the downwind deflection beyond Category 1 [ABSTRACT FROM AUTHOR]

Mesoscale Convective Systems (MCSs) play a critical role in tropical rainfall patterns and circulations. To reduce persistent biases and improve understanding of the climate system, international groups have called for unprecedented investment in global convection–permitting (CP) climate models. It is essential such models accurately represent MCSs, and in particular environmental interactions such as dynamical control by wind shear. We show that in representative current generation CP simulations, MCS updraft entrainment decreases with shear, leading to a realistic increase of extreme rainfall. We find the control of environmental shear extends to mean storm rainfall and anvil heights. The simulation of these effects depends strongly on model physics in both CP and parameterized models. We show that in West Africa, MCS shear response influences the zonal distribution of storm diabatic heating, modifying upscale impacts of convection. Our results demonstrate key tests for focused process–based assessment of CP model fidelity. Plain Language Summary: Movements of tropical air are driven by interactions between large, continental–scale circulations and localized deep convection — cells of ascending moist air reaching to the tropopause. These cells can aggregate to form Mesoscale Convective Systems (MCSs), long–lived thunderstorm clusters with large cold cloud shields that dominate tropical rainfall and atmospheric heating, forcing air circulations. Meanwhile, the strength of MCS rainfall depends on local atmospheric conditions. Such local process interactions occur on scales much smaller than typical global climate model grid spacings (>25 km), thus requiring a sub–grid parameterization of deep convection that introduces model biases. Here we show that kilometer–scale models can realistically capture the response of MCSs to local atmospheric moisture and wind conditions. A realistic response to the wind field relies on models showing variable mixing of dry environmental air into convective updrafts, with reduced rates for stronger vertical wind shear. We find that this wind (i.e., dynamical) control on MCSs explains patterns of mean rainfall biases in West Africa and influences atmospheric heating, likely mediating MCSs' upscale impacts on tropical circulations. Our results provide vital process–based methods for verifying the added value of explicitly representing convective storms in novel kilometer–scale global models. Key Points: Convection‐permitting models can capture the response of Mesoscale Convective Systems to both moisture and shear in West AfricaStrong shear gives larger cores, reduced entrainment and greater maximum and mean storm rainfall; this is missed in a parameterized modelShear response has upscale impacts through control of zonal distribution of biases in storm mean rainfall and diabatic heating [ABSTRACT FROM AUTHOR]

The occurrence of tropical cyclones (TCs) in the Horn of Africa and nearby areas is for the first time examined to document their contribution to local rainfall and their trends over the period 1990–2020. An average 1.5 TC (of any intensity) per year was observed over the Western Arabian Sea, with two asymmetrical seasons, namely May–June (30% of cyclonic days) and September–December (70%). Case studies reveal that in many instances, TC‐related rainfall extends beyond 500 km from the TC center, and that substantial rains occur one to 2 days after the lifecycle of the TC. Despite their rarity, in the otherwise arid to semi‐arid context characteristic of the region, TCs contribute in both seasons to a very high percentage of total rainfall (up to 30%–60%) over the northwestern Arabian Sea, the Gulf of Aden and their coastlines. Over inland northern Somalia, contributions are much lower. TCs disproportionately contribute to some of the most intense daily falls, which are often higher than the mean annual rainfall. A strong increase in the number of TCs is found from 1990 to 2020, hence their enhanced contribution to local rainfall. This increase is associated with a warmer eastern/southern Arabian Sea, a decrease in vertical wind shear, and a strong increase in tropospheric moisture content. Plain Language Summary: The role played by tropical cyclones in local rainfall in the Horn of Africa and nearby areas is for the first time examined. An average 1.5 cyclones (of any intensity) per year is observed over the Western Arabian Sea. They occur in two different seasons: May–June (30% of cyclonic days) and September–December (70%). Despite their rarity, these cyclones affect a region which displays arid to semi‐arid climates, hence they contribute to a very high percentage of total rainfall (30%–60%) over the northwestern Arabian Sea, the Gulf of Aden and their coastlines. Over inland northern Somalia, contributions are lower. Many of the most intense rainfall events are related to cyclones, with daily rainfall sometimes higher than the mean annual rainfall. There has been a strong increase in the number of cyclones from 1990 to 2020, and they contribute more to local rainfall. This increase is associated with a warmer Arabian Sea, a change in the wind flow and a higher moisture content. Key Points: An average 1.5 tropical cyclones occur annually in the Western Arabian Sea, 70% of them in September–December, the rest in May–JuneThey strongly contribute (30%–60%) to rainfall over the northwestern Arabian Sea, the Gulf of Aden and their coastlinesTheir frequency sharply increased from 1990 to 2020, resulting in a 11% rise of their contribution to the Gulf of Aden precipitation [ABSTRACT FROM AUTHOR]

Based on the ERA5 reanalysis data and the surface observations from automatic weather stations, a comparative analysis has been conducted to investigate the differences in heavy rainfall distributions caused by two landfalling tropical cyclones (TCs): LUPIT (2109) and LISA (9610). The two TCs have similar tracks, intensity and landing points, but show different asymmetric features in their rainstorm location relative to their tracks. The results indicate that the TC rainfall differences are mainly caused by different rainstorm formation mechanisms. The wind shear contributes most to the rainstorm of LISA, while land-sea contrast and topographical effect are the main factors of LUPIT rainstorm. Under the influence of strong environmental vertical wind shear and the weak cold air invasion from the west, the circulation center of LISA tilts westward with height, which cooperates with the low-level water vapor convergence and vertical ascending movement on the western side of the TC center to jointly cause the heavy rainstorm to the west of LISA center. In contrast, LUPIT has weak environmental vertical wind shear and no obvious structure tilting with height. Topographic effect plays a crucial role in causing the heavy rainstorm on the north of TC center. The southeasterly jet is blocked by the Taimu Mountain in the northeastern Fujian Province, and the strong ascending motion caused by the terrain-induced convergence appears to the north of LUPIT center. In addition, the moisture convergence is more pronounced in the north and weaker in the south. The intrusion of weak cold air from the east to the coastal areas of central-northern Fujian, and the moisture-convergence distribution, jointly cause the heavy rainstorm to the north of LUPIT. [ABSTRACT FROM AUTHOR]

Rainfall associated with landfalling tropical cyclones (TCs) along the Northern Vietnam coast is examined to develop an asymmetric parametric TC‐induced rainfall model starting from the axisymmetric Rain‐Climatology and Persistence (R‐CLIPER) model. We recalibrated the R‐CLIPER model (original R‐CLIPER denoted as NHC) against observed rainfall patterns of 14 landfalling TCs from 2001 to 2021 in the Northern Vietnam coast, while relaxing the model's underlying linear relationships. The recalibrated R‐CLIPER (denoted as Fit‐Ax), still axisymmetric, suggests that some parameters are better correlated with the normalized maximum wind speed using logarithmic and exponential relationships. Fit‐Ax reduces the 12‐hr total rainfall overall root‐mean‐square errors (RMSEs) and Bias magnitudes in the before‐ and after‐landfall periods from NHC for the entire 500‐km TC domain. We further redistribute the Fit‐Ax rainfall intensity across the four quadrants with respect to the TC forward motion to account for the observed large asymmetry in quadrant rainfall (version denoted as Fit‐As). The vertical wind shear (VWS) and landfall (before or after) are considered in this redistribution. Fit‐As generally outperforms Fit‐Ax and NHC in reproducing the observed rainfall distribution for the 14 TCs. At the quadrant level, both Fit‐Ax and Fit‐As show significant improvement in Bias over NHC. Fit‐As is further better overall in RMSE and Skill when weighted by quadrant rainfall volume. In pattern matching, Fit‐As produces the best grid‐averaged Pearson correlation coefficients for 11 TCs. In addition, its equitable threat scores (ETSs) are best beyond the 20‐mm rainfall threshold, with the maximum of 0.299 at the 90‐mm rainfall threshold. Thus, our locally fitted asymmetric rainfall model demonstrates improved capability in reproducing the historical TC‐induced rainfall along the Northern Vietnam coast. [ABSTRACT FROM AUTHOR]

The jet stream is a primary factor contributing to turbulence, especially for upper-level aircraft. This study utilized pilot reports and ERA5 data from 2023 to investigate the relationship between upper-level turbulence and the East Asian westerly jet (EAJ). The results indicate that approximately 45.9% of upper-level aircraft turbulence occurs within the jet stream, with the lowest proportion in August and the highest in January. Additionally, the strongest vertical wind shear (VMS) is found concentrated in the lower part of the jet stream core, particularly in the South–Down part of the jet stream, where upper-level aircraft turbulence occurs most frequently (27.1%). The most turbulent area is located between 30–40° N and 110–120° E, with the main air routes experiencing turbulence being the Henan sections of G212 and B208. From a seasonal perspective, there is less frequent occurrence of upper-level aircraft turbulence in summer and autumn but more in winter and spring. The EAJ volume increases with the strengthening of the jet core wind speed, with the jet core regions being most distinct at altitudes of 200~300 hPa. Meanwhile, the jet stream intensity index peaks at 70.6 m/s in January and reaches its lowest value of 7.1 m/s in August. The jet stream axis shifts southward in winter and northward in summer, reaching the southernmost position in December at 32.2° N and the northernmost position in August at 43.5° N. Furthermore, the VMS at turbulence points within the jet stream is higher than that at the turbulence points outside the jet stream, and the Richardson number (RI) is lower. Moreover, the temporal distribution of upper-level aircraft turbulence is primarily determined by the location and intensity of the jet stream, of which the jet stream intensity index provides guidance and thus serves as a reliable indicator. [ABSTRACT FROM AUTHOR]

This study utilized the WRF model to investigate the track evolution and rapid intensification (RI) of Typhoon Doksuri (2023) as it moved across the Luzon Strait and through the South China Sea (SCS). The simulation results indicate that Doksuri has a smaller track sensitivity to the use of different physics schemes, while having a greater intensity sensitivity. Sensitivity numerical experiments with different physics schemes can well capture its northwestward movement in the first two days, but they predict less westward track deflection as the typhoon moves across the Luzon Strait and through the SCS. Moreover, all the experiments successfully simulated Doksuri's RI, albeit with quite different rates and a time lag of 12 h. Among different combinations of physics schemes, there exists an optimal set of cumulus parameterization and cloud microphysics schemes for track and intensity predictions. Doksuri's track changes as the typhoon moved across the Luzon Strait and through the SCS were influenced by the topographic effects of the terrain of the Philippines and Taiwan, to different extents. The track changes of Doksuri are explained by the wavenumber-one potential vorticity (PV) tendency budget from different physical processes, highlighting that the horizontal PV advection dominates the PV tendency throughout most of the simulation time due to the offset of vertical PV advection and differential diabatic heating. In addition, this study applies the extended Sawyer–Eliassen (SE) equation to compare the transverse circulations of the typhoon induced by various forcing sources. The SE solution indicates that radial inflow was largely driven in the lower-tropospheric vortex by strong diabatic heating, while being significantly enhanced in the lower boundary layer due to turbulent friction. All other physical forcing terms were relatively insignificant for the induced transverse circulation. The coordinated radial inflow at low levels may have led to the eyewall development in unbalanced dynamics. Intense diabatic heating thus was vital to the severe RI of Doksuri under a weak vertical wind shear. [ABSTRACT FROM AUTHOR]

The tropical cyclone genesis frequency (TCGF) is an essential metric for gauging the performance of climate models. Previous evaluations on CMIP family models usually employ one realization for each model and show their diversities in performance. The single model initial condition large ensemble experiments provide a unique opportunity to quantify how internal variability may affect the model evaluation skill. Here, taking the TCGF in the Western North Pacific (WNP) as an example, we use two genesis potential indices as proxies to evaluate the performance of the FGOALS-g3 large ensemble simulation with 110 members. We show that while internal variability does not have a significant influence on the TCGF mean state evaluation, the TCGF-ENSO (El Niño–Southern Oscillation) relationship is significantly modulated by the decadal scale internal variability. For mean state simulation, the FGOALS-g3 large ensembles show reasonable performance in the simulation of TCGF spatial pattern but have differences compared with ERA5 in magnitude. Physical process analysis indicates that compared with ERA5, nearly all dynamic terms are more unfavorable for tropical cyclogenesis due to the cold sea surface temperature anomalies in the midlatitude, while the thermodynamic terms are more conducive to more TCs. For interannual variability, the ENSO-TCGF connection is significantly modulated by the tropical Pacific decadal variability (TPDV) mode by influencing the vertical wind shear in the WNP. Particularly, the model simulation skill depends on the choice of genesis potential indices. Our finding highlights the importance of considering decadal-scale internal variability in the evaluation of interannual ENSO-TCGF variability. [ABSTRACT FROM AUTHOR]

The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa. [ABSTRACT FROM AUTHOR]

The 2023 Atlantic hurricane season was above normal, producing 20 named storms, 7 hurricanes, 3 major hurricanes, and seasonal accumulated cyclone energy that exceeded the 1991–2020 average. Hurricane Idalia was the most damaging hurricane of the year, making landfall as a Category 3 hurricane in Florida, resulting in eight direct fatalities and 3.6 billion U.S. dollars in damage. The above-normal 2023 hurricane season occurred during a strong El Niño event. El Niño events tend to be associated with increased vertical wind shear across the Caribbean and tropical Atlantic, yet vertical wind shear during the peak hurricane season months of August–October was well below normal. The primary driver of the above-normal season was likely record warm tropical Atlantic sea surface temperatures (SSTs), which effectively counteracted some of the canonical impacts of El Niño. The extremely warm tropical Atlantic and Caribbean were associated with weaker-than-normal trade winds driven by an anomalously weak subtropical ridge, resulting in a positive wind–evaporation–SST feedback. We tested atmospheric circulation sensitivity to SSTs in both the tropical and subtropical Pacific and the Atlantic using the atmospheric component of the Community Earth System Model, version 2.3. We found that the extremely warm Atlantic was the primary driver of the reduced vertical wind shear relative to other moderate/strong El Niño events. The concentrated warmth in the eastern tropical Pacific in August–October may have contributed to increased levels of vertical wind shear than if the warming had been more evenly spread across the eastern and central tropical Pacific. SIGNIFICANCE STATEMENT: The 2023 Atlantic hurricane season produced above-normal activity despite strong El Niño conditions. The season had 20 named storms, along with 7 hurricanes and 3 major hurricanes. Normally, El Niño decreases Atlantic hurricane activity due to increases in vertical wind shear. In 2023, vertical wind shear was below average, likely driven by the record warm tropical Atlantic and Caribbean Sea surface temperatures which led to tropical circulation patterns that were considerably different from the atmospheric flow typically observed during El Niño events. This manuscript also uses a state-of-the-art climate model to investigate the impacts of Atlantic and Pacific SST configurations on Atlantic vertical wind shear patterns. [ABSTRACT FROM AUTHOR]

Tropical cyclone intensification is simulated with a cloud-resolving model under idealized conditions of constant SST and unidirectional environmental vertical wind shear maximized in the middle troposphere. The intensification process commonly involves a sharp transition to relatively fast spinup before the surface vortex achieves hurricane-force winds in the azimuthal mean. The vast majority of transitions fall into one of two categories labeled S and A. Type S transitions initiate quasi-symmetric modes of fast spinup. They occur in tropical cyclones after a major reduction of tilt and substantial azimuthal spreading of inner-core convection. The lead-up also entails gradual contractions of the radii of maximum wind speed rm and maximum precipitation. Type A transitions begin before an asymmetric tropical cyclone becomes vertically aligned. Instead of enabling the transition, alignment is an essential part of the initially asymmetric mode of fast spinup that follows. On average, type S transitions occur well after and type A transitions occur once the cyclonically rotating tilt vector becomes perpendicular to the shear vector. Prominent temporal peaks of lower-tropospheric CAPE and low-to-midlevel relative humidity averaged over the entire inner core of the low-level vortex characteristically coincide with type S but not with type A transitions. Prominent temporal peaks of precipitation and midlevel vertical mass flux in the meso-β-scale vicinity of the convergence center characteristically coincide with type A but not with type S transitions. Despite such differences, in both cases, the transitions tend not to begin before the distance between the low-level convergence and vortex centers divided by rm reduces to unity. [ABSTRACT FROM AUTHOR]

We analyze the gravity waves (GWs) from the ground to the thermosphere during 11–14 January 2016 using the nudged HI Altitude Mechanistic general Circulation Model. We find that the entrance, core and exit regions of the polar vortex jet are important for generating primary GWs and amplifying GWs from below. These primary GWs dissipate in the upper stratosphere/lower mesosphere and deposit momentum there; the atmosphere responds by generating secondary GWs. This process is repeated, resulting in medium to large‐scale higher‐order, thermospheric GWs. We find that the amplitudes of the secondary/higher‐order GWs from sources below the polar vortex jet are exponentially magnified. The higher‐order, thermospheric GWs have concentric ring, arc‐like and planar structures, and spread out latitudinally to 10 − 90°N. Those GWs with the largest amplitudes propagate against the background wind. Some of the higher‐order GWs generated over Europe propagate over the Arctic region then southward over the US to ∼15–20°N daily at ∼14 − 24 UT (∼9 − 16 LT) due to the favorable background wind. These GWs have horizontal wavelengths λH ∼ 200 − 2,200 km, horizontal phase speeds cH ∼ 165 − 260 m/s, and periods τr ∼ 0.3 − 2.4 hr. Such GWs could be misidentified as being generated by auroral activity. The large‐scale, higher‐order GWs are generated in the lower thermosphere and propagate southwestward daily across the northern mid‐thermosphere at ∼8–16 LT with λH ∼ 3,000 km and cH ∼ 650 m/s. We compare the simulated GWs with those observed by AIRS, VIIRS/DNB, lidar and meteor radars and find reasonable to good agreement. Thus the polar vortex jet is important for facilitating the global generation of medium to large‐scale, higher‐order thermospheric GWs via multi‐step vertical coupling. Plain Language Summary: Gravity waves (GWs) are perturbations in the Earth's atmosphere created by various processes. When a GW breaks, it imparts momentum to the atmosphere, which in turn can become unbalanced and generate secondary GWs. The same process happens at higher altitudes where the secondary GWs break, thereby generating higher‐order GWs. We simulate the primary, secondary and higher‐order GWs on 11–14 January 2016 using a GW‐resolving whole atmosphere model. We find that the entrance, core and exit regions of the jet that encircles the polar vortex generate primary GWs. In addition, the polar vortex jet magnifies the amplitudes of higher‐order GWs from sources below the jet, such as mountain waves. The resulting higher‐order GWs have horizontal wavelengths of hundreds to thousands of km with concentric ring, arc‐like and planar structures in the thermosphere. We compare the simulated GWs with AIRS, VIIRS/DNB, lidar, and meteor radar observations and find reasonable to good agreement. Key Points: The vertical shear of the horizontal wind in the entrance, core and exit regions of the polar vortex jet generate GWs in the stratosphereHigher‐order GWs generated over Europe and Asia propagate over the Arctic then southward over the CONUS at ∼9 − 16 LT due to favorable windsLarge‐scale GWs with λH ∼ 3,000 km and cH ∼ 650 m/s propagate southwestward across the northern thermosphere at ∼8–16 LT [ABSTRACT FROM AUTHOR]

In this paper, the characteristics of a squall line that occurred in central and northern Zhejiang on 21 July 2022 are analyzed by using S-band dual-polarization radar, X-band phased array radar data, wind retrieval, lightning location and ERA5 reanalysis data. The results show that: The squall line affected the area for up to 6 hours, causing large-scale winds of 8-10 levels along the way. The pressure surge ahead of the strong winds and precipitation at the extremely strong wind station served as a precursor to extreme winds. The squall line occurred under the control of the subtropical high. The dry and cold air at the bottom of the high-level cold vortex invaded, with the high-energy and high humidity in the low-level forming an unstable layer structure, which provided favourable environmental conditions for the generation and maintenance of the squall line. The observation of the S-band dual polarisation radar showed that the evolution of squall lines went through processes such as initiation, merging, growth, maturity, and disappearance. The initial convection was formed in the mesoscale convergence lines in the northwest and east of Hangzhou. Strong storms in the northwest of Hangzhou moved faster than those in the east, leading to the rapid merging and development of the two into squall lines. After the squall line entered the south bank of the Hangzhou Bay, the storm outflow overlapped with the mesoscale convergence centre on the south bank of the Hangzhou Bay, leading to the rapid development of the squall line to its mature stage. In addition, the growth of vertical wind shear was also conducive to the rapid development of the squall line. Strong winds often occurred in areas with dense cloud flashes. The X-band phased array radar could finely detect the vertical structure of strong cells before and after extreme winds occurred. The development of ZDR and KDP columns in mature strong cells represented storm intensification, and the rapid decline of the echo centroid could indicate surface winds. The falling and dragging of precipitation particles intensified the sinking motion, which further enhanced the strong winds. The configuration of inclined upward and downward airflow in strong squall lines ensured that the falling of precipitation particles did not affect the upward airflow, which was beneficial for the development and maintenance of storms. The oblique sinking airflow met the near-surface environmental wind, triggering the development of frontal convection, which was conducive to the propagation of squall lines downstream.

Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone (TC) under the influence of an environment with either uniform flow, vertical wind shear (VWS), or both. Results show that rainwater is enhanced to the right of the motion in the outer rainband, but such enhancement occurs in the upshear-left area of the inner-core region. Additionally, due to the asymmetries introduced by environmental flow, wavenumber-1 temperature and height anomalies develop at a radius of ~1000 km in the upper levels. A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears, and asymmetric horizontal winds emerge, which, in turn, changes the storm-scale (within 400 km) VWS. Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s–1 and is located downshear of the storm-scale VWS in all the experiments with environmental flow. In the outer rainbands, the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant. These results extend upon the findings of previous studies in three aspects: (1) The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS; (2) The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow, resulting in changes in the storm-scale VWS pattern within the TC area; (3) The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS. [ABSTRACT FROM AUTHOR]

The unique Tropical cyclone (TC) Fantala appeared in the central Indian Ocean (12.4°S, 73.5°E) at 00Z on April 11 in 2016 and moved northwestward along the northeast of Madagascar at 18 Z on April 15. Then, two incomprehensible turnbacks formed a unique TC track. The dynamic mechanisms of the three turnbacks were first studied based on remote sensing and multisource reanalysis data. The results reveal that the wind field with upper divergence and lower convergence promotes the development of Fantala. The anticyclone high pressure on the middle level atmosphere is an important factor for TC turnbacks. On 15 April, the TC made the first turnback to turn northwest due to the southward anticyclone weakened to moving northwest. On 18 April, the TC made the second turnback along the anticyclone edge due to the northern high-pressure and southern low-pressure trough. On 22 April, the TC made the third turnback because the anticyclonic high press center broke into two small independent anticyclonic centers in the southwest and northeast, which created a barrier band and pushed the northern TC to move to the northwest. Meanwhile, the vertical wind shear (VWS) also provides favorable conditions for TC turnbacks. On April 18, the middle atmosphere of the TC was affected by strong easterly shear and weak southerly shear, and the second turnback was completed. On April 22, the middle level environment was affected by strong westerly shear and weak north shear, and the third turnback was completed. Additionally, heat transport from the ocean to the atmosphere provides favorable conditions for TC development. On April 18, The maximum mean latent heat flux over northeastern Madagascar was 112.94 W/m2, Tropical Cyclone Heat Potential was 39.05 kJ/cm2, and the maximum wind speed at the center of the TC was 155 kts. On April 22, The heat transfer from the equator increased by 18.08 W/m2 compared with the latent heat on 21 April, the Tropical Cyclone Heat Potential was 33.30 kJ/cm2, the maximum wind speed in the TC center was 90 kts, the high PV centerspread down from 850 mb to 900 mb. This study deepens the understanding of track forecasting during the development of a TC. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TCs), especially intense TCs, pose serious threats to life and property particularly in the affected coastal regions. Understanding the factors determining the TC intensification rate (IR) remains a great challenge. This study identifies the dominant factors responsible for the observed significant increase in TC IR over the western North Pacific in recent decades using the energetically based dynamical system model of TC intensification. It is found that the environmental dynamical efficiency mainly contributed by vertical wind shear and upper‐level divergence is responsible for the long‐term changes in TC IR during the strong TC stage, but it played a secondary role in the long‐term changes in IR during the weak TC stage. The latter were primarily contributed by the maximum potential intensity, which is primarily determined by sea surface temperature. Results also strongly suggest that global warming is the primary driver of the long‐term changes in TC IR. Plain Language Summary: Tropical cyclone (TC) intensification is closely associated with the extent of damage caused by these storms. The TC intensification rate (IR) over the western North Pacific (WNP), particularly in tropical regions, has shown a significant increasing trend in recent decades. This study employs an energetically based dynamical system model of TC intensification to quantitatively unveil factors driving the long‐term changes in TC IR over the WNP. Results show that the thermodynamic and dynamic factors exhibit different effects at different stages of TCs. The maximum potential intensity is found to be the most important factor contributing to the long‐term changes in TC IR at the weak TC stage, while the environmental dynamical efficiency, mainly governed by vertical wind shear and upper‐level divergence, plays the predominant role at the strong TC stage. Although the long‐term changes in TC IR over the WNP result from a combination of global warming and internal climate variabilities, global warming is the primary driver of the long‐term changes in TC IR based on quantitative analysis. The Atlantic Multidecadal Oscillation exhibits a secondary influence, while the Pacific Decadal Oscillation contributes little. These results can help enhance forecasting capabilities and future projections of TC activities. Key Points: The environmental dynamical efficiency dominantly controls the long‐term changes in TC intensification rate during the strong TC stageDuring the weak TC stage, the long‐term changes in intensification rate are primarily driven by the maximum potential intensityGlobal warming is the primary driver of the long‐term changes in TC intensification rate [ABSTRACT FROM AUTHOR]

Grasping the physical interactions when two tropical cyclones (TCs) (TC) are in proximity is essential for boosting the accuracy of TC forecasts. This study dissects an uncommon scenario wherein the merging with Tropical Depression 13 W significantly hastened the rapid weakening of Super Typhoon Hinnamnor (2022), utilizing comparative experiments with and without 13 W in simulation's initial field. The findings reveal strong correlations between the merger, amplified environmental vertical wind shear (VWS), and Hinnamnor's consecutive weakening, unfolding in two stages— "top‐down" (Stage 1) and "bottom‐up" weakening (Stage 2) stage. In Stage 1, 13 W led to downdrafts from upper level, hindering the eyewall updrafts and weakening the warm core. In Stage 2, 13 W merged into Hinnamnor's outer rainband, introduced low‐entropy air into the boundary layer and also vied with the eyewall for energy. This research emphasizes that even minor, less‐intense vortices can have profound impacts on the rapid intensity change in TCs. Plain Language Summary: A tropical cyclone (TC)'s intensity and track can be affected by the atmospheric vortices through binary interaction (i.e., Fujiwhara effect). Yet little study has illustrated the merger of TCs with large differences in intensity and size, as well as how it impacts the TC structure and intensity. This study examines the rapid weakening of Super Typhoon Hinnamnor (2022) during its interaction with the tropical depression named 13 W, by two numerical experiments—with and without the existence of 13 W in the initial field. The results find that the merger‐induced increase in environmental vertical wind shear and outer rainband effect caused by 13 W contributed to Hinnamnor's weakening. The process unfolds in two stages. In the first stage, the 13 W in upshear quadrants induced downdrafts from the upper level, disrupting Hinnamnor's eyewall updrafts and diminishing the warm core from top to down. In the second stage, the 13 W in downshear quadrants merged into Hinnamnor's outer rainband, increasing the infusion of low‐entropy air into boundary layer, in turn weakening Hinnamnor from bottom to upper level. This research demonstrates the rainband effect from the other TC during binary interaction, and underlines the attention on impacts from weak and small vortices in TC operational forecasting. Key Points: The merger with Tropical Depression 13 W amplified lower environmental wind and vertical wind shear, leading to Hinnamnor's further weakeningIn early "top‐down" weakening, the 13 W in upshear induced downdrafts, diminishing Hinnamnor's eyewall updrafts and warm coreIn later "bottom‐up" weakening, the 13 W in downshear merged into Hinnamnor's outer rainband, reducing the entropy of boundary layer inflow [ABSTRACT FROM AUTHOR]

Bomb cyclones, or explosive cyclones, are rapidly-intensifying extratropical weather systems that are often associated with extreme wind and precipitation. The projection of bomb cyclones is crucial for climate change risk assessment given their severe impacts on society and environment. This study investigates the projected changes in bomb cyclone activity between historical (1950–2014) and future (2015–2050) periods using the HighResMIP-PRIMAVERA multimodel ensemble. In the North Pacific (NP), the ensemble projects a 0.40° northward shift of bomb cyclone activity, with notably less events around Japan. An eastward shift of bomb cyclone activity is projected in the North Atlantic (NA) with a marked decline in the northwestern part. In the Southern Hemisphere (SH), bomb cyclones are projected to shift poleward by 0.49°, with little change in the total number of events. In all three analysis regions, the projected changes in bomb cyclone activity are associated with changes in lower-tropospheric baroclinicity, with the major contributor being vertical wind shear and static stability in the NP and the SH, respectively. Furthermore, we identify close relationships between the projected bomb cyclone changes and mean-flow changes in the NP and SH, with the shift of mid-latitude jet latitude significantly correlated with the projected decline and poleward shift of bomb cyclone activity. In the SH, the cooling of the polar lower stratosphere also contributes to the projected poleward movement. These results are not strongly dependent on model horizontal resolution, although higher-resolution models generally have a larger number of bomb cyclones. [ABSTRACT FROM AUTHOR]

A recent study published in the Bulletin of the American Meteorological Society examines the impact of global warming on typhoons in the East China Sea. The study focuses on the case of Typhoon Hinnamnor, which struck South Korea in September 2022. The researchers found that the unusually warm surface water in the East China Sea contributed to the intensification of the typhoon. Using observational data and climate model simulations, they determined that human activities have made such warm water conditions at least five times more likely. The study suggests that as global warming continues, typhoons in the region may become stronger, but it does not establish whether they will become more or less frequent. [Extracted from the article]

Jiangsu is a province in China and has the highest frequency of tornado occurrences. Studying the meteorological background and mechanisms of tornado formation is crucial for predicting tornado events and preventing the resulting disasters. This paper analyzed the meteorological background, instability mechanisms, and lifting conditions of the two Enhanced Fujita Scale level 2 (EF2) and above tornadoes that occurred in southern Jiangsu on 14 May 2021 ("5.14") and 6 July 2020 ("7.06") using ERA5 reanalysis data. Detailed analyses of the internal structure of tornado storms were conducted using Changzhou and Qingpu radar data. The results showed that (1) both tornadoes occurred in warm and moist areas ahead of upper-level troughs with significant dry air transport following the cold troughs. The continuous strengthening of low-level warm and moist advection was crucial in maintaining potential instability and triggering tornado vortices. The 14 May tornado formed within a low-level shear line and a warm area of a surface trough, while the 6 July tornado occurred at the end of a low-level jet stream, north of the eastern section of a quasi-stationary front. (2) The convective available potential energy (CAPE) and K indices for both tornado processes were very close (391 for "5.14" and 378 for "7.06"), with the lifting condensation level (LCL) near the ground. The "5.14" showed greater instability and more favorable thermodynamic conditions, with deep southwesterly jets at the mid-level shear line producing rotation under strong convergent action (convergence center value exceeding −1 ×   10 − 4 s − 1 ). In contrast, the "7.06" was driven by super-low-level jet stream pulsations and wind direction convergence under the influence of the Meiyu Front (convergence center value exceeding −1.5 ×   10 − 4   s − 1 ), resulting in intense lifting and vertical vorticity triggered by a surface convergence line. (3) The "5.14" tornado process involved a supercell storm over a surface dry line experiencing tilting due to strong vertical wind shear, which led to the formation of smaller cyclonic vortices near a hook echo that developed into a tornado. The "7.06" developed on a bow echo structure within a mesoscale convective system formed over the Meiyu Front, where dry air subsidence, entrainment, and convergence of the southeast jet stream triggered a "miniature" supercell. The relevant research results provide a reference for the prediction and early warning of tornadoes. [ABSTRACT FROM AUTHOR]

Continuous wavelet transform (CWT) is a commonly used mathematical tool when it comes to the time–frequency (or distance–wavenumber) analysis of non-stationary signals that is used in a variety of research areas. In this work, we use the CWT to investigate signatures of atmospheric internal gravity waves (GWs) as observed in vertical temperature profiles obtained, for instance, by lidar. The focus is laid on the determination of vertical wavelengths of dominant GWs. According to linear GW theory, these wavelengths are a function of horizontal wind speed, and hence, vertical wind shear causes shifts in the evolution of the vertical wavelength. The resulting signal fulfills the criteria of a chirp. Using complex Morlet wavelets, we apply CWT to test mountain wave signals modeling wind shear of up to 5m s-1km-1 and investigate the capabilities and limitations. We find that the sensitivity of the CWT decreases for large chirp rates, i.e., strong wind shear. For a fourth-order Morlet wavelet, edge effects become dominant at a vertical wind shear of 3.4m s-1km-1. For higher-order wavelets, edge effects dominate at even smaller values. In addition, we investigate the effect of GW amplitudes growing exponentially with altitude on the determination of vertical wavelengths. It becomes evident that in the case of conservative amplitude growth, spectral leakage leads to artificially enhanced spectral power at lower altitudes. Therefore, we recommend normalizing the GW signal before the wavelet analysis and before the determination of vertical wavelengths. Finally, the cascading of receiver channels, which is typical of middle-atmosphere lidar measurements, results in an exponential sawtooth-like pattern of measurement uncertainties as a function of altitude. With the help of Monte Carlo simulations, we compute a wavelet noise spectrum and determine significance levels, which enable the reliable determination of vertical wavelengths. Finally, the insights obtained from the analysis of artificial chirps are used to analyze and interpret real GW measurements from the Compact Rayleigh Autonomous Lidar in April 2018 in Río Grande, Argentina. Comparison of commonly used analyses and our suggested wavelet analysis demonstrate improvements in the accuracy of determined wavelengths. For future analyses, we suggest the usage of a fourth-order Morlet wavelet, normalization of GW amplitudes before wavelet analysis, and computation of the significance level based on measurement uncertainties. [ABSTRACT FROM AUTHOR]

The planetary boundary layer (PBL) over the Tibetan Plateau (TP) exerts a significant influence on regional and global climate, while its vertical structures of turbulence and evolution features remain poorly understood, largely due to the scarcity of observations. This study examines the vertical profile of and daytime variation in the turbulence dissipation rate (ε) in the PBL and free troposphere over the TP using the high-resolution (6 min and 120 m) measurements from a radar wind profiler (RWP) network, combined with hourly data from ERA5 during the period from 1 September 2022 to 31 October 2023. Observational analyses show that the magnitude of ε below 3 km under all-sky conditions exhibits a large spatial discrepancy over the six RWP stations over the TP. Particularly, the values of ε at Minfeng and Jiuquan over the northern TP and at Dingri (alternately Tingri) over the southern TP are roughly an order of magnitude greater than those at Lijiang, Ganzi (alternately Garzê), and Hongyuan over the eastern TP. This could be partially attributed to the difference in land cover across the six RWP stations. In terms of the diurnal variation, ε rapidly intensifies from 09:00 local standard time (LST) to 14:00 LST and then gradually levels off in the late afternoon. Under clear-sky conditions, both ε and the planetary boundary layer height (zi) are greater compared with cloudy-sky conditions, which could be due to the cooling effect of clouds, which reduces the solar irradiation reaching the surface. In the lower PBL (0.3 ≤ z/zi ≤ 0.5), where z is the height above ground level, the dominant influential factor in the development of turbulence is the surface–air temperature difference (Ts-Ta). By comparison, in the upper PBL (0.6 ≤ z/zi ≤ 1.0), both Ts-Ta and vertical wind shear (VWS) affect the development of turbulence. Above the PBL (1.0 < z/zi ≤ 2.0), the shear production resulting from VWS dominates the variation in turbulence. Under cloudy-sky conditions, the reduced Ts-Ta and weakened surface sensible heat flux tend to inhibit the turbulent motion in the PBL. On the other hand, the strong VWS induced by clouds enhances the turbulence above the PBL. The findings obtained here underscore the importance of the RWP network in revealing the fine-scale structures of the PBL over the TP and gaining new insight into the PBL evolution. [ABSTRACT FROM AUTHOR]

Utilizing observational data from the Xiamen radar station during the warm season of 2015–2018 (May to September), this study employs a convective storm identification algorithm to statistically analyze the spatiotemporal distribution, diurnal propagation, and seasonal variability of convective storms over the southeastern coast of China. Key findings include: (1) Significant monthly variations in convective storm frequency, with peaks in August over land areas of Zhangzhou and Xiamen's northwest, and offshore southeast of Xiamen. Seasonal circulation patterns, particularly the subtropical high and northern high-level troughs, drive these variations. (2) Large-scale convective storms are most frequent, while small-scale ones are less common. Mid-deep convective storms dominate, particularly in southern Zhangzhou and southwestern mountainous Quanzhou, whereas shallow convective storms are rare and scattered. High-frequency areas correlate with higher terrain, underscoring the influence of topography on storm occurrence and development. (3) Hovmöller plots reveal a bimodal diurnal pattern in propagation of storms for July and August, with peaks in the daytime and late night. Daytime storms propagate from coastal to higher terrain areas, while nighttime storms maybe driven by enhanced vertical wind shear. These findings enhance the understanding of convective storms in the region and highlight the crucial role of the circulation background, terrain, and prevailing wind directions in the spatiotemporal characteristics of warm season convective storms in southeastern China. [ABSTRACT FROM AUTHOR]

Using FY-2G satellite data, Aircraft Meteorological Data Relay (AMDAR) downlink data, and the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate (ERA5) dataset, we analyzed the circulation, thermal, and dynamic characteristics of the convective aircraft turbulence over Australia in the Southern Hemisphere. The results show that the near-convective clouds turbulence (NCCT) in the Southern Hemisphere mostly occurred in front of deep warm high-pressure ridges in mid-latitude regions and on the left side of the axis of the subtropical westerly jet stream. The isotherms in this area were relatively dense (i.e., large gradients), and the wind speed was high, with strong horizontal and/or vertical cyclonic wind shear. In addition, the NCCT usually occurred near the zero-divergence or zero-vorticity line and in areas with large vertical wind speed gradients. There were also strong vertical and horizontal wind shears in this area, which could easily trigger severe turbulence. Furthermore, the NCCT in the Southern Hemisphere mostly occurred at the intersection of cold and warm temperature advections (i.e., near the zero-temperature advection line), and the turbulence point was located near the high-altitude frontal zone where there was a strong gradient of cold and warm advections. There was temperature inversion with pseudo-equivalent potential temperatures in the middle and lower troposphere on the warmer side of the turbulence point. The unstable stratification of cold air at the top and warm air at the bottom was conducive to triggering convection from the ground, forming strong convective clouds, and causing severe turbulence. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between sea ice concentration (SIC) in the Arctic Ocean and the Boreal Summer Intraseasonal Oscillation (BSISO) from 1991 to 2020 and its underlying mechanism. A significantly positive (negative) correlation was found between the frequency of phase 7 (3) of BSISO1 (30–60 d) and the preceding winter SIC, which is located the north of the East Siberian-Beaufort Sea (ESBS). Compared with low-SIC years, the conditions including northeasterly vertical wind shear, an enhanced ascending branch of the anomalous Walker circulation, an eastward water vapour transport channel, and an increased humidity gradient induce active convection over the Philippine Sea in high-SIC years, which benefits (hinders) to phase 7 (3) of BSISO1. The positive SIC anomaly during the transition from winter to spring influences local temperature and pressure through anomalous local sensible heat flux. This anomaly induces wave activity flux from the ESBS, which converges over the Bering Sea, enhancing the Aleutian Low (AL). Subsequently, the AL triggers an anomalous subtropical anticyclone through wave-mean flow interaction in the North Pacific. Due to southerly wind stress and increased sea surface heat flux, positive sea surface temperature anomalies near Japan persist in the summer, heating the lower troposphere and increasing baroclinicity. Significant positive geopotential heights and anticyclone anomalies occur over Japan, accompanied by a negative vorticity anomaly. The enhanced ascending motion over the Philippine Sea, facilitated by Ekman pumping, favours convection and influences the frequency of phases 7 and 3. [ABSTRACT FROM AUTHOR]

Convective-permitting ensemble simulations are used to understand the roles of thermodynamic and dynamic processes in changing intense storms over the West African Sahel due to increases in atmospheric greenhouse gas concentrations. Ensemble simulations with 16 members represent recent August conditions during the height of the boreal summer monsoon season over the Sahel. They are compared with 5 Future-Warming ensemble simulations with increased greenhouse gas concentrations under the late-21st -century high-emission SSP5-8.5 scenario and initial/boundary conditions from the Current-Climate data plus the multi-model mean anomalies derived from CMIP6 experiments. The Current-Climate simulations reproduce observed precipitation and environmental conditions over the Sahel well. The frequency of heavy rainfall events with 24-hr rainfall > 77 mm (the 99.9th percentile) increases by 38.2% in the Future-Warming simulations. While the low- to mid-level vertical wind shear increases in the Future-Warming simulations, we find no significant correlations between the environmental shear strength and peak storm rain rates. In contrast, lower (middle) tropospheric moisture and temperature are correlated (anticorrelated) with peak rain rates and/or the maximum updraft velocity of intense events, consistent with significant correlations between the increased atmospheric instability and storm intensity. Thus, thermodynamic processes and not dynamical (shear-related) processes dominate the rainfall intensification over the Sahel in the simulations. Nevertheless, the enhanced shear strength is associated with larger rain-shield areas and propagation speeds of intense storms in Future-Warming. Wind shear strength is also correlated with pre-storm atmospheric instability, which grows less/more under strong/weak shear with greenhouse gas increases and is relevant for sub/super Clausius-Clapeyron scaling of precipitation. [ABSTRACT FROM AUTHOR]

This study investigates long‐term trends related to the mature stage duration of tropical cyclones (TCs) over the western North Pacific (WNP) during June–November between 1982 and 2021. There is a significant shortening in the mean duration of the WNP mature TC stage, which is defined as the period when a TC is within 5 kt of its lifetime maximum intensity. This shortening is induced by a significant (weak) poleward migration in the starting (ending) location of the WNP mature TC stage, which can be further explained by changes in environmental conditions. From 1982 to 2021, there have been significant increases in maximum potential intensity and 700–500‐hPa relative humidity over most of the WNP, which has broadly expanded the TC‐favorable area poleward. Consequently, WNP TCs can start their mature stages and reach their lifetime maximum intensities at higher latitudes. By contrast, there are only weak changes in 850‐hPa relative vorticity and 850–200‐hPa vertical wind shear (VWS). Given the dominant role of VWS in modulating the TC weakening rate, the TC‐suppressive area over the subtropical WNP has shown lesser changes, thus leading to insignificant changes in the ending location of the mature TC stage. [ABSTRACT FROM AUTHOR]

Coupling the Weather Research and Forecasting (WRF) model with wind farm parameterization can be effective in examining the performance of large-scale wind farms. However, the current scheme is not suitable for floating wind turbines. In this study, a new scheme is developed for floating wind farm parameterization (FWFP) in the WRF model. The impacts of the side columns of a semi-submersible floating wind turbine on waves are first parameterized in the spectral wave model (SWAN) where the key idea is to consider both inertial and drag forces on side columns. A machine learning model is trained using results from idealized high-resolution SWAN simulations and then implemented in the WRF to form the FWFP. The difference between our new scheme and the original scheme in a realistic case is investigated using a coupled atmosphere–wave model. The results show that the original scheme has a lower power output in most of the grids with an average of 12 % compared to the FWFP scheme. The upstream wind speed is increased slightly compared to the original scheme (<0.4 m s -1), while the downstream wind speed is decreased but by a much larger magnitude (<1.8 m s -1). The distribution of the difference in turbulent kinetic energy (TKE) corresponds well to that of the wind speed, and the TKE budget reveals that the difference in TKE in the rotor region between the two schemes is mainly due to vertical wind shear. This demonstrates that the FWFP is necessary for both predicting the wind power and evaluating the impact of floating wind farms on the surrounding environment. [ABSTRACT FROM AUTHOR]

Precipitation from tropical cyclones (TCs) can cause massive damage from inland floods and is becoming more intense under a warming climate. However, knowledge gaps still exist in changes of spatial patterns in heavy TC precipitation. Here we define a metric, DIST30, as the mean radial distance from centers of clustered heavy rainfall cells (> 30 mm/3 h) to TC center, representing the footprint of heavy TC precipitation. There is significant global increase in DIST30 at a rate of 0.34 km/year. Increases of DIST30 cover 59.87% of total TC impact areas, with growth especially strong in the Western North Pacific, Northern Atlantic, and Southern Pacific. The XGBoost machine learning model showed that monthly DIST30 variability is majorly controlled by TC maximum wind speed, location, sea surface temperature, vertical wind shear, and total water column vapor. TC poleward migration in the Northern Hemisphere contributes substantially to the DIST30 upward trend globally. The tropical cyclone (TC) precipitation footprint has expanded globally. Interpretable machine learning reveals that this footprint is majorly controlled by TC wind speed, location, sea surface temperature, wind shear, and total water column vapor. [ABSTRACT FROM AUTHOR]

The frequency and power dissipation index (PDI) of tropical cyclones (TCs) in the North Indian Ocean (NIO) has dramatically grown over the last 10 years, according to our analysis utilizing the European Centre for Medium Range Weather Forecasts reanalysis version‐5 (ERA5) dataset and the India Meteorological Department (IMD) best track data over the period 1982–2021. Our findings indicate that the recent increase in the post‐monsoon TC PDI over NIO is caused by a reduction in wind shear and an increase in convective available potential energy over the Bay of Bengal. The importance of improving our understanding and developing more accurate predictions of the TCs activity has increased as TCs become more frequent and intense owing to the effects of global warming. This study therefore develops TC prediction models for frequency and PDI over NIO for various lead times that vary from 2 to 8 months in addition to the trend analysis employing the ERA5 and IMD best track data. The potential predictors used in proposed model are surface temperature (2 m temperature over land and sea surface temperature over oceanic regions), vertical wind shear, winds (zonal, meridional), geopotential height and temperature at different pressure levels during January–August. The developed models are remarkably accurate (skill is ~94%) in forecasting TCs frequency and PDI. The proposed models outperform the best performing models that are already in use for long‐range TC activity prediction. With a lead‐time as long as up to 8 months, this effort is the first to investigate the possibility of forecasting the frequency and PDI of post‐monsoon TC activity over the NIO with good accuracy. Therefore, the developed models show an operational potential for seasonal TC activity forecast over the NIO. [ABSTRACT FROM AUTHOR]

Quality control (QC) of HaiYang-2B (HY-2B) satellite data is mainly based on the observation process, which remains uncertain for data assimilation (DA). The data in operation have not been widely used in numerical weather prediction. To ensure HY-2B data meet the theoretical assumptions for DA applications, the iterated reweighted minimum covariance determinant (IRMCD) QC method was studied in HY-2B data based on the typhoon "Chanba". The statistical results showed that most of the outliers were eliminated, and the observation increment distribution of the HY-2B data after QC (QCed) was closer to a Gaussian distribution than the raw data. The kurtosis and skewness of the QCed data were much closer to zero. The QCed track demonstrated the lowest accumulated error and the best intensity in typhoon assimilation, and the QCed intensity was closest to the observation during the nearshore enhancement, exhibiting the strongest intensity among the experiment. Further analysis revealed that the improvement was accompanied by a significant reduction in vertical wind shear during the nearshore enhancement of the typhoon. The QCed moisture flux divergence and vertical velocity in the upper layer increased significantly, which promoted the upward transport of momentum in the lower layers and contributed to the maintenance of the typhoon's barotropic structure. Compared with the assimilation of raw data, the effective removal of outliers using the IRMCD algorithm significantly improved the simulation results for typhoons. [ABSTRACT FROM AUTHOR]

With increasing air and sea temperatures, the thermodynamic environments over the oceans are becoming more favourable for the development of intense tropical cyclones (TCs) with rapid intensification (RI). The South China coastal region consists of highly densely populated cities, especially over the Pearl River Delta (PRD) region. Intense TCs maintaining their strength or the RI of TCs close to the coastal region can present substantial forecasting challenges and have significant potential impacts on the coastal population. This study investigates the effect of sea-surface and sub-surface temperatures and salinity on the intensification of five TCs, namely Super Typhoon Hato in 2017, Super Typhoon Mangkhut in 2018, and Typhoon Talim, Super Typhoon Saola, and Severe Typhoon Koinu in 2023, which have significantly affected the South China coastal region and triggered high TC warning signals in Hong Kong in the past few years. This analysis utilised the Hong Kong Observatory's TC best-track and intensity data, along with sea temperature and salinity profiles generated using the China Ocean ReAnalysis version 2 (CORA2) product from the National Marine Data and Information Service of China. It was found that high sea-surface temperatures (SST) of 30 °C or above for a depth of about 20 m, low sea-surface salinity (SSS) levels of 33.8 psu or below for a depth of at least 20 m, and strong salinity stratification of at least 0.6 psu per 100 m depth might offer useful hints for predicting the RI of TCs over the western North Pacific and the South China Sea (SCS) in operational forecasting, while noting other contributing environmental factors and synoptic flow patterns conducive to RI. This study represents the first documentation of sub-surface salinity's impact on some intense TCs traversing the SCS during 2017–2023 based on an observational study. Our aim is to supplement operational techniques for forecasting RI with some quantitative guidance based on upper-level ocean observations of temperatures and salinity, on top of well-known but more rapidly changing dynamical factors like low-level convergence, weak vertical wind shear, and upper-level divergent outflow, as forecasted with numerical weather prediction models. This study will also encourage further research to refine the analysis of quantitative contributions from different RI factors and the identification of essential features for developing AI models as one way to improve the forecasting of TC RI before the TC makes landfall near the PRD, with due consideration given to the effect of freshwater river discharge from the Pearl River. [ABSTRACT FROM AUTHOR]

In the present study, a severe squall line (SL) was analyzed by using intensive observational surface data and radar monitoring products. In this process, mesoscale convergence lines, such as the sea breeze front (SBF), gust front and dry line, served as the main triggering and strengthening factors. The transition from convection triggering to the formation of the initial shape was mainly affected by the convergence line of the SBF, which combined with thermal convection to form the main parts of the SL. In the later stage, the convergence line of the gust front merged with other convergence lines to form a series of strong convective cells. The SBF had good indicative significance in terms of severe convective weather warnings. The suitable conditions of heat, water vapor and vertical wind shear on the Shandong Peninsula were beneficial to the maintenance of the SL. Before SL occurrence, tropopause folding strengthened, which consequently enhanced the baroclinic property in the middle and upper troposphere. The high sensible heat flux at the surface easily produced a positive potential vorticity anomaly in the low layer, resulting in convective instability, which was conducive to the maintenance of these processes. In the system, when precipitation particles passed through the unsaturated air layer, they underwent strong evaporation, melting or sublimation, and the cooling effect formed negative buoyancy, which accelerated the sinking of the air and promoted the sustained development of the surface gale. Together with the development of lowlevel mesocyclones, the air pressure decreased rapidly, which was conducive to gale initiation. [ABSTRACT FROM AUTHOR]

One of the most important parameters in meteorology is the mean wind profile in the tropical cyclone boundary layer. The vertical profile of wind speed and wind direction were measured during the period of the Nisarga cyclone from May 31st, 2020, to June 5th, 2020, using the newly installed Phased Array Doppler Sodar system at the Center for Space and Atmospheric Science (CSAS), Sanjay Ghodawat University, Kolhapur (16.74° N, 74.37° E; near India's western coast). Our analysis revealed that the maximum mean wind speed was 17 m/s on June 3, 2020, at 10:00 IST. It also shows the change in wind direction from southwest to southeast on June 2 and 3, 2020. Daily high-resolution reanalysis data in the domain, 0-25°N, 65-110°E, during the period from May 31st to June 5th, 2020, revealed the variation of the atmospheric pressure of the Nisarga cyclone from 1000 to 1008 hPa, sea surface temperature (SST) between 30 ℃ and 31 ℃, outgoing longwave radiation (OLR) between 100 and 240 Wm-2, wind speed between 3 and 15 m/s, and low values of vertical wind shear (VWS) were observed to the north of Nisarga track. These observations may provide more insights for the study of boundary layer turbulence during cyclonic activities. [ABSTRACT FROM AUTHOR]

Large ground-based solar telescopes are equipped with adaptive optics systems to correct wavefront distortions induced in the turbulent atmosphere. The design of the adaptive optics system strongly depends on the vertical profiles of the optical turbulence. In particular, the characteristics of the optical turbulence determine the design of tomographic adaptive optics systems, which provide image correction within a wide field of view. In the article, a new method to estimate reference optical turbulence characteristics from Era-5 reanalysis assimilated data is presented. This method is based on the dependence of the air refractive index structure constant |$C_n^2$| on the vertical shears of wind speed as well as the outer scale of turbulence L0. The L0 parameter is estimated by minimization of the dispersion between the modeled and measured values of the refractive index structure constant |$C_n^2$| within the surface layer. For the first time, parametrization coefficients and reference profiles of optical turbulence averaged for the period 1940–2022 are calculated for the Large Solar Vacuum Telescope (LSVT) site. The calculated optical turbulence profiles are representative; these profiles correspond to typical changes of the measured values of the Fried parameter, the isoplanatic angle, and the outer scale of turbulence at the LSVT site. The model turbulence profiles are verified taking into account the Shack–Hartmann wavefront sensor measurements at the LSVT. The higher accuracy of estimation of the optical turbulence characteristics makes it possible to refine parameters relevant to the LSVT adaptive optics system. The obtained results can be used in order to develop high-resolution solar adaptive optics technologies as applied to ground-based telescopes including those using the principles of atmospheric tomography. [ABSTRACT FROM AUTHOR]

Tropical cyclones have resulted in casualties and economic losses in the areas surrounding the Bay of Bengal (BoB). Thus, a comprehensive investigation of these tropical cyclones holds vital implications for disaster preparedness and mitigation. This paper compares the occurrence of storms in the last two decades, i.e., 2002–2011 and 2012–2021, and results reveal that such storms exhibited predominantly a northwesterly track towards the northwestern BoB, with a severer intensity but equal total storm frequencies. Over the past decade, a southeast-northwest pathway (SNP) was identified, demonstrating a higher incidence of severe tropical cyclones (STC, with lifetime maximum intensity ≥ 64 knots) over the BoB. Further analysis of the changes in the environmental conditions between these two decades indicates that a southeasterly anomaly in the steering flow contributed to the formation of the SNP. During the same period, the more favorable oceanic conditions during the last decade, including higher sea surface temperatures, a greater upper ocean heat content, a thicker warm water layer, and a thicker barrier layer beneath the SNP, favored the development of these storms by providing more heat energy to the storms. The atmospheric conditions, including increased air-sea heat fluxes, moisture, and instability within the lower troposphere, as well as reduced vertical wind shear, facilitated the development of convection within these storm systems. These favorable conditions improved the potential for storm development into STCs and elevated the risk of the northwestern BoB being impacted by more destructive storms. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) size and intensity define the potential destructiveness in the land-falling region. This study investigates the inter-relationships between size parameters (radius of maximum wind, Rmax; 34-knots wind, R34; and TC-fullness, TCF) and intensity. The best-track (size and intensity) data is obtained from the Joint Typhoon Warning Center during 2002–2021. The frequently observed R34, Rmax, and TCF are 100–150 km, 20–60 km, and 0.8, respectively for NIO TCs. Intensity and TCF are more strongly related (0.7) than R34 (0.5) and Rmax (0.6). Analysis shows that size changes are weakly related to intensity changes (0.37–0.39). Diagnostic analysis has been conducted to address possible reasons for different TC groups 1) TCs with no size variation with intensity (Group-1), (2) both increase (Group-2), (3) size increases with no intensity change (Group-3), (4) Initial more size (Group-4). The dry air intrusion outside the eyewall in Group-1 TCs in low vertical wind shear condition limit rain-bands development, enabling moisture convergence into the primary eyewall that helps maintain storm intensity without R34 increase. Strong surface fluxes in the primary eyewall region support convection and absolute angular momentum (AAM) at upper and lower levels, which boosts size and intensity in Group-2 TCs. Strong and broader surface fluxes and vertical velocities may create rain-bands or secondary-eyewall, causing bigger TCs with limited intensification in Group-3 TCs. Larger initial TC vortices maintain wider and intense surface fluxes, vertical velocities, and AAM in the TC inner and outer cores, supporting the maintenance of larger TC size in Group-4. [ABSTRACT FROM AUTHOR]