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The mechanism of convective cell initiation and regeneration in the Bandung Basin ( 107. 35 ∘ E - 107. 95 ∘ E ; 6. 75 ∘ S - 7. 25 ∘ S ), Indonesia, is investigated using a Weather Research and Forecasting model. Based on the Cumulative Distribution Function and Regeneration Index, model simulations were conducted using case studies in February–March 2019. Upslope wind flows to the mountain peak in north and south of the basin due to solar heating, carrying water vapor from the bottom of the basin. Therefore, low-level convergence is formed due to the convergence of winds from the bottom of the basin and from outside the basin. The low-level convergence causes the developing updraft, makes atmosphere unstable, and generates convective initiation. The convective system will be developed in the mountains region, produced precipitation, and formed cold pools on the surface. The cold pool will fall down the slopes and convective activity from the mountains will continue to the bottom of the basin. The convective system's outflow causes the cold pool to move in the west–east direction. The cold pool will collide with warmer air from the opposite direction, resulting in an updraft at the cold pool leading edge, and convection will be re-initiated (convective regeneration) in the Bandung Basin, with the new convective system tending to move eastward. [ABSTRACT FROM AUTHOR]

Antarctic coastal surface winds affect ice‐sheet stability, sea ice, and local ecosystems. The strongest coastal winds are especially important due to the nonlinear relationship between wind speed and wind stress. We investigate the dynamics of extreme coastal winds using a simplified momentum budget calculated across the period 2010–2020 from the ERA5 reanalysis. The pressure‐gradient forcing term in the budget is decomposed into a large‐scale component and one associated with the temperature deficit layer. The role of budget terms across the coastal sector is compared for weak and strong winds. We then calculate composites of the top 100 easterly wind events across six east Antarctic coastal sectors, identifying terms responsible for the evolution of coastal extremes. A simple balance of terms exists offshore, dominated by large‐scale forcing, contrasting with the complex balance in the onshore sector where katabatic forcing is large. Large‐scale forcing explains 57% of offshore coastal wind‐speed variance overall, improving to 81% when budget terms associated with the temperature deficit layer and horizontal advection are included, with significant regional variation. The residual term plays an increasingly active role as wind speed increases. Extremes in all coastal sectors are associated with a synoptic‐scale transient dipole of pressure anomalies driving warm‐air advection. Although katabatic forcing is a very large term in magnitude, it is found to play a passive role, declining as wind speeds increase during extreme conditions. In some regions, an anomalous southerly component develops during extremes, which we attribute to an ageostrophic barrier wind. This research underscores the major role for large‐scale forcing in Antarctica's coastal winds, but also reveals a significant regional locally driven component. The results have implications for improving numerical model simulations of coastal easterlies and for studying their impacts on ocean circulation, sea ice, and ice‐shelf basal melt. [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]

The diagonal squall line that passed through the Korean Peninsula on the 18 May 2020 was examined using wind data retrieved from multiple Doppler radar synthesis focusing on its kinematic and dynamic aspects. The low-level jet, along with warm and moist air in the lower level, served as the primary source of moisture supply during the initiation and formation process. The presence of a cold pool accompanying the squall line played a role in retaining moisture at the surface. As the squall line approached the Korean Peninsula, the convective bands in the northern segment (NS) and southern segment (SS) of the squall line exhibited distinct evolutionary patterns. The vertical wind shear in the NS area was more pronounced compared to that in the SS. The ascending inflow associated with the tilted updraft in the NS reached an altitude of 7 km, whereas it was only up to 4 km in the SS. The difference was caused by the strong descending rear flow, which obstructed the ascending inflow and let to significant updraft in the SS. [ABSTRACT FROM AUTHOR]

The response of the oceanic surface layer to atmospheric shallow convection is explored using realistic atmospheric large eddy simulations coupled with an oceanic 1D model with high vertical resolution. The effects of cloud shading, rain, and enhanced heat loss due to gust fronts on the edge of cold pools and their interactions are investigated in a case study of the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden–Julian Oscillation experiment in the tropical Indian Ocean, during a suppressed phase of the Madden–Julian Oscillation. Conditions of low surface wind and strong solar heating result in diurnal warming of the oceanic surface of 2 °C over a depth of 1 m. Analysis of specific periods covering the diurnal cycle shows the contrasting effects of cloud shading, rain, and turbulent heat fluxes under the cold pools on the sea temperature at the surface and below. On the one hand, decreasing the solar radiation (cloud shading) results in slight cooling extended horizontally and penetrating down to 1–2 m depth, depending on the time of the day. On the other hand, turbulent heat fluxes enhanced up to 300 W·$$ \cdotp $$m −2$$ {}^{-2} $$ by gusts and freshwater lenses due to rain act together and more locally. They isolate and strongly cool a thin inner layer at the surface, which eventually destabilizes the surface layer and propagates the cooling downward. The exact relative part and efficiency of these processes depend on the time evolution of the thermal stratification and vertical turbulent mixing in the oceanic upper layer. Surface cooling of up to −$$ - $$0.5 °C may occur in a few tens of minutes and last for several hours, significantly mitigating the effects of diurnal warming over large extents. [ABSTRACT FROM AUTHOR]

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Previous studies have demonstrated that cold pools play a pivotal role in the initiation and organization of convection, yet their influence on the evolution of gust fronts (GFs) remains inadequately understood. A destructive wind event associated with a rearward gust front (RGF; 8 grade gale after passing GF) and a prior gust front (PGF; 10 grade gale before passing GF) over the north coast of China on 10 June 2016 was analyzed. Using multiple forms of observation data, as well as the four-dimensional Variational Doppler Radar Data Assimilation System (VDRAS), we found that the depth and intensity of the cold pool in RGF are relatively shallower and weaker, leading to a correspondingly reduced strength in both outflow and convergence. In contrast, the enhanced vertical shear and boundary northeaster inflow of PGF generate intensified and more organized downdrafts, resulting in a deeper cold pool, robust outflow, and convergence. Two schematic models were proposed to explain the discrepancy between GFs and associated cold pools. We further show that there is an internal correlation between meso-γ-scale vortices (MVs) and cold pools, the collision of MVs strengthened low-level convergence and updraft between these two GFs. Moreover, the consolidation of the two cold pools exacerbates low-layer instability and rotation, generating an intense horizontal vorticity that leads to rapid convective storm intensification. These findings offer novel insights into the diversity of GFs and associated cold pools. [ABSTRACT FROM AUTHOR]

A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China, leading to heavy precipitation. We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10-13, 2022. The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing. In contrast, the northern rain belt was related to low-level horizontal shear and the surface-level front. The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt. The convective cell propagated east over the coastal area, where there was a large temperature gradient. The bow-shaped echo in this region may be closely related to the rear-inflow jet. By contrast, the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear, with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain. The terrain blocked the movement of the cold pool, resulting in the stagnation of the frontal convective cell at an early stage. Subsequently, a meso-γ-scale vortex formed during the rapid movement of the convective cell, corresponding to an enhancement of precipitation. The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt, even though both resulted in comparable hourly rainfalls. These results help us better understand the characteristics of double rain belts over South China. [ABSTRACT FROM AUTHOR]

From 17 to 22 July 2021, the "21·7" extreme rainfall event ("21·7" ERE) hit Henan Province, breaking the record for mainland China with a maximum hourly rainfall of 201.9 mm at the Zhengzhou station. The long-lived (20 h) mesoscale Huang-Huai vortex (HHV) was an important system that directly affected the major rainfall stage, including the extreme hourly rainfall. This study investigates the formation and development mechanism of the HHV, as well as its association with the simulation of extreme hourly rainfall through numerical simulations. The simulated rainfall and radar composite reflectivity were in good agreement with the observations, thus effectively reproducing the generation and developmental process of the HHV. The analysis results showed that the HHV initially formed at 850 hPa on 19 July at 1800 UTC and eventually developed to 550 hPa. The positive feedback formed by the horizontal convergence and vertical vorticity transport was the main mechanism leading to the generation and deepening of the HHV. The stretching effect (STR) term played an absolutely dominant role in the increase in the vorticity tendency, and it primarily originated from the coupling effect of boundary layer jets (BLJs) and synoptic-weather-system-related low-level jets (SLLJs). The accurate simulation of the HHV allowed the early rainfall to reasonably reproduce the surface cold pool near the Zhengzhou station, and then the cooperation of the SLLJs, the BLJs, and the cold pool made the simulated extreme hourly rainfall exactly close to the Zhengzhou station, but with a weaker intensity, due to the fact that the HHV moved northeastward after its formation, resulting in a narrow range of southerly flow in southern Henan, which is not conducive to convective triggering in the southerly flow. [ABSTRACT FROM AUTHOR]

The eastern North Pacific right whale (NPRW) is the most endangered population of whale and has been observed north of its core feeding ground in recent years with low sea ice extent. Sea ice and water temperature are important drivers for zooplankton dynamics within the whale's core feeding ground in the southeastern Bering Sea, seasonally forming stable fronts along the shelf that give rise to distinct zooplankton communities. A northward shift in NPRW distribution driven by changing distribution of prey resources could put this species at increased risk of entanglement and vessel strikes. We modeled the abundance of NPRW prey, Calanus glacialis, Neocalanus, and Thysanoessa species, using a dynamic biophysical food web model of nine zooplankton guilds in the Bering shelf zooplankton community during a period of warming (2006–2016). This model is unique among prior zooplankton studies from the region in that it includes density dependence, thereby allowing us to ask whether species interactions influence zooplankton dynamics. Modeling confirmed the importance of sea ice and ocean temperature to zooplankton dynamics in the region. Density‐independent growth drove community dynamics, while dependent factors were comparatively minimal. Overall, Calanus responded to environment terms, with the strength and direction of response driven by copepodite stage. Neocalanus and Thysanoessa responses were weaker, likely due to their primary occurrence on the outer shelf. We also modeled the steady‐state (equilibrium) abundance of Calanus in conditions with and without wind gusts to test whether advection of outer shelf species might disrupt the steady‐state dynamics of Calanus abundance; the results did not support disruption. Given the annual fall sampling design, we interpret our results as follows: low‐ice‐extent winters induced stronger spring winds and weakened fronts on the shelf, thereby advecting some outer shelf species into the study region; increased development rates in these warm conditions influenced the proportion of C. glacialis copepodite stages over the season. Residual correlation suggests missing drivers, possibly predators, and phytoplankton bloom composition. Given the continued loss of sea ice in the region and projected continued warming, our findings suggest that C. glacialis will move northward, and thus, whales may move northward to continue targeting them. [ABSTRACT FROM AUTHOR]

Many mobile marine taxa are changing their distributions in response to climate change. Such movements pose a challenge to fisheries monitoring and management, particularly in systems where climate‐adaptive and ecosystem‐based management objectives are emphasized. While shifts in species distributions can be discerned from long‐term fisheries‐independent monitoring data, distilling coherent patterns across space and time from such datasets can be challenging, particularly for transboundary stocks. One approach for identifying dominant patterns of spatiotemporal variation that has been widely used in physical atmospheric and oceanographic studies is empirical orthogonal function (EOF) analysis, wherein spatiotemporal variation is separated into time‐series of annual factor loadings and spatial response maps. Here, we apply an extension of EOF analysis that has been modified for compatibility with biological sampling data to a combined US–Russian fisheries‐independent survey dataset that spans the eastern (United States) and western (Russia) Bering Sea shelf to estimate dominant patterns of spatiotemporal variation for 10 groundfish species at a shelf‐wide scale. EOF identified one axis of variability that was coherent with the extent of cold (≤0°C) near‐bottom waters (the cold pool) previously shown to be a key influence on species distributions and ecosystem structure for the Bering Sea. However, the leading axis of variability identified by our EOF analysis was characterized by low frequency changes in the distributions of several species over longer time scales. Our analysis has important implications for predicting variation in species distributions over time and demonstrates a widely applicable method for leveraging combined fisheries‐independent survey datasets to characterize community‐level responses to ecosystem change at basin‐wide scales. [ABSTRACT FROM AUTHOR]

Abstract A heavy rainfall event caused by mesoscale convective systems (MCSs) resulted in flooding over areas of Davao City in Mindanao Island, Philippines, on 03 May 2017. The event occurred during the summer season (April–May) under weak large-scale conditions. This study investigated the initiation and development of MCSs by performing high-resolution numerical simulations with the finest grid spacing of 200 m, using the Weather Research and Forecasting (WRF) model. It was found that the merging of two meso- $$\beta$$ β scale convective systems over the west and east of Mount Apo caused the flood-producing rainfall in the Davao area. Results show that the west meso- $$\beta$$ β scale convective system formed over the basin area in Mindanao Island due to moisture advection from sea breeze circulation. In addition, the concave geometry of the Mindanao basin assisted in accumulating moisture which made the basin favorable for convection development. Meanwhile, the precipitating downdrafts generated cold pools wherein the continuous convergence of multiple outflow boundaries resulted in the further development and maintenance of the MCS over the basin. While the east meso- $$\beta$$ β scale convective system developed over the Davao area due to the interaction between southeasterlies (ambient trade winds) and Mount Apo terrain. Merging of the MCSs resulted in the development of a larger meso- $$\beta$$ β scale system. Eventually, the larger meso- $$\beta$$ β scale convective system split and splitted MCSs weakened over time.

High‐resolution air‐sea observations collected by a suite of remotely‐piloted uncrewed surface vehicles (USV) provide new insight on surface latent and sensible heat fluxes associated with convective cold pools over the eastern Pacific Intertropical Convergence Zone (ITCZ). Convective cold pools are linked to isolated, heavily precipitating cells over the ocean that yield downdrafts of evaporatively‐cooled air that spreads out horizontally in all directions and are characterized by strong air temperature gradients and horizontal wind speeds. Cold pool frontal signatures are identified based on air temperature depression criteria of −1.5°C in 10 min or less, resulting in a total of 276 events observed within the eastern Pacific ITCZ across 590 total seadays of data from 10 drones over the course of 3 years. Composite analysis reveals enhanced latent and sensible heat fluxes from the ocean to the atmosphere immediately following the frontal passage, and a decomposition of the bulk flux formulas indicates that variations in latent heat flux are largely influenced by the anomalous wind field (i.e., the cold pool gust front) acting on the mean background air‐sea moisture gradient, while variations in sensible heat flux are largely influenced by the mean background wind acting on the anomalous air‐sea temperature gradient (i.e., the cold pool temperature front). High‐frequency variations in wind speed and velocity are further explored in the context of "gustiness" and averaging intervals used in bulk flux algorithms. A case study is also presented for a convective cold pool event captured by a traveling mesoscale network, or mesonet, of USVs. Plain Language Summary: New 1‐min measurements of oceanic and atmospheric variables collected by automated observing platforms, Saildrone uncrewed surface vehicles, are used to explore convective cold pools over the stormy region of the northern hemisphere eastern tropical Pacific ocean. Convective cold pools are domes of cold air near the surface that form underneath intensely raining thunderstorms. The cold pool boundary (or front) separates the cold, dry air within the dome from the warm, moist air of the surrounding environment, and thus qualifying events are identified based on temperature drops of −1.5°C in 10 min or less in the 1‐min saildrone data. Results based on 276 cold pool events observed between 10 drones over 3 years reveal that increasing wind speed and decreasing air temperature associated with the cold pool front largely contribute to enhanced air‐sea heat fluxes (i.e., exchanges of energy) from the ocean to the atmosphere, highlighting the importance of high‐resolution (i.e., 1‐min) observations to capture variations on small time and space scales. A cold pool event observed by multiple saildrones is also explored, and wind measurements from a single saildrone are further investigated in the context of a "gustiness" parameter used in the bulk flux equations. Key Points: High‐resolution uncrewed surface vehicles measurements provide new insight on sub‐grid/sub‐footprint variability associated with convective cold poolsConvective cold pool fronts modulate latent heat fluxes primarily through mechanical forcing by the anomalous wind fieldConvective cold pool fronts modulate sensible heat fluxes primarily through thermodynamic forcing by the anomalous temperature gradient [ABSTRACT FROM AUTHOR]

Extreme precipitation events have been occurring frequently worldwide, and their causative factors and convection initiation (CI) mechanisms have been attracting more and more attention in recent years. As a comprehensive study on the CI mechanisms of extreme rainstorms over the northern slope of the Kunlun Mountains (KLM), Xinjiang, based on both observational and high tempo-spatial numerical simulation, the major findings of this work are as follows: A cold pool (CP) was formed in the northwestern Tarim Basin under the influence of early precipitation evaporation, and it moved towards the northern slope of the KLM several hours before the CI. With the movement of the CP, a significant vertical temperature gradient was formed close to the leading edge of the CP, thereby enhancing local convective instability (up to ~10 PVU). In addition, the vertical shear of the horizontal winds at the leading edge of the CP led to a notable increase in the baroclinic component of moist potential vorticity, thus reinforcing the local conditional symmetric instability (up to ~8 PVU), providing another important unstable energy for the CI. In addition, the combined effect of the convergent lifting of a boundary layer jet (BLJ, the maximum wind speed below 1 km exceeding 10 m s−1) and the significant frontogenetical forcing (up to ~100 × 10−8 K m−1 s−1) at the leading edge of the CP were the causes of the release of the unstable energies. Further analysis of the frontogenetical forcing associated with the CP indicates that the convergence (up to ~2 × 10−3 s−1), diabatic heating and slantwise terms (indicates the baroclinicity and inhomogeneity of the vertical momentum in horizontal direction) were the major contributors, whereas the deformation term at the leading edge of the CP provided a relatively weaker contribution. [ABSTRACT FROM AUTHOR]

Cold pools that form from existing convection can generate new clouds nearby, a process that has been suggested to contribute to cloud organization. However, some disagreement exists on the role of cold pools in cloud organization over tropical oceans, and much remains to be understood on how this role depends on the state of large‐scale disturbances such as the Madden‐Julian Oscillation (MJO). This study addresses this question by examining the intraseasonal variability in the properties of cold pools and their effects on convection triggering using observations. The unique set of surface meteorology data and ground‐based radars deployed during the DYNAMO/AMIE field campaign are used to identify cold pools and the associated spatiotemporal evolution of rainfall. The results suggest that cold pools enhance rainfall at their expected speed of 3–8 m s−1, which includes the Doppler‐shifting effect by the background wind. The cold pools also enhance rainfall mainly within a 20 km radius, especially in the direction of boundary‐layer vertical wind shear. However, gravity waves appear to contribute predominantly to the propagation of convection over a wider range of distances due to their faster propagation speeds. The interface of convection triggering and propagation at different speeds of cold pools and gravity waves seems to contribute to cloud organization. The effectiveness of cold pools and gravity waves on cloud organization also depends highly on the MJO due to the combined effects of changes in environmental humidity and boundary to lower‐tropospheric wind. Plain Language Summary: High‐density air that forms due to evaporative cooling of rainfall and downward injection of colder air aloft spreads horizontally, a phenomenon known as a cold pool. The spreading edges of cold pools initiate new cumulus clouds by lifting humid air, which is thought to cluster cumulus clouds that can merge and form larger clouds. However, the importance of cold pools in cloud clustering remains debated. This study uses a unique combination of observational data collected during a field campaign deployed over the Indian Ocean to examine the effect of cold pools on cloud clustering. The results provide observational evidence that cold pools support cloud formation within a 20 km radius of the identified cold pools, helping the clustering of clouds within a limited distance. In addition to cold pools, gravity waves that form from cumulus clouds mainly lead to the propagation and formation of cumulus clouds over longer distances due to their faster propagation speeds. The formation of cumulus clouds over a varying range of distances due to different propagation speeds of cold pools and gravity waves seems critical to the clustering of clouds. However, their effectiveness on cloud formation depends on atmospheric conditions set by intraseasonal variability. Key Points: Precipitation‐induced cold pools are observed to enhance rainfall within 20 km through interactions with boundary‐layer vertical wind shearWhile cold pools trigger convection within a limited distance, gravity waves mainly propagate convection over a wider range of distancesThe cold pools and gravity waves together lead to cloud organization, but their effectiveness depends on the large‐scale environment [ABSTRACT FROM AUTHOR]

The diagonal squall line that passed through the Korean Peninsula on the 18 May 2020 was examined using wind data retrieved from multiple Doppler radar synthesis focusing on its kinematic and dynamic aspects. The low-level jet, along with warm and moist air in the lower level, served as the primary source of moisture supply during the initiation and formation process. The presence of a cold pool accompanying the squall line played a role in retaining moisture at the surface. As the squall line approached the Korean Peninsula, the convective bands in the northern segment (NS) and southern segment (SS) of the squall line exhibited distinct evolutionary patterns. The vertical wind shear in the NS area was more pronounced compared to that in the SS. The ascending inflow associated with the tilted updraft in the NS reached an altitude of 7 km, whereas it was only up to 4 km in the SS. The difference was caused by the strong descending rear flow, which obstructed the ascending inflow and let to significant updraft in the SS.

Previous studies have demonstrated that cold pools play a pivotal role in the initiation and organization of convection, yet their influence on the evolution of gust fronts (GFs) remains inadequately understood. A destructive wind event associated with a rearward gust front (RGF; 8 grade gale after passing GF) and a prior gust front (PGF; 10 grade gale before passing GF) over the north coast of China on 10 June 2016 was analyzed. Using multiple forms of observation data, as well as the four-dimensional Variational Doppler Radar Data Assimilation System (VDRAS), we found that the depth and intensity of the cold pool in RGF are relatively shallower and weaker, leading to a correspondingly reduced strength in both outflow and convergence. In contrast, the enhanced vertical shear and boundary northeaster inflow of PGF generate intensified and more organized downdrafts, resulting in a deeper cold pool, robust outflow, and convergence. Two schematic models were proposed to explain the discrepancy between GFs and associated cold pools. We further show that there is an internal correlation between meso-γ-scale vortices (MVs) and cold pools, the collision of MVs strengthened low-level convergence and updraft between these two GFs. Moreover, the consolidation of the two cold pools exacerbates low-layer instability and rotation, generating an intense horizontal vorticity that leads to rapid convective storm intensification. These findings offer novel insights into the diversity of GFs and associated cold pools.

Objective: The worldwide pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants remains a health threat. As sports event-related outbreaks due to long-range airborne transmission in ventilation have been reported, the present study aimed to quantify infection risk using available data and apply the results to an outbreak in an ice hockey arena. Methods: A mathematical modeling approach was used to estimate the risk of airborne infection. Results: A quantum was defined as the dose of airborne droplet nuclei required to cause infection in 63% of susceptible persons. The estimated quanta emission rate per infector showed a log-normal distribution with a geometric mean (GM) of 28.81, geometric deviation (GD) of 5.78, and median of 22.65 quanta/h. The estimated average time-average quanta concentration (Cavg; quanta/m3) showed a log-normal distribution with a GM of 0.08, GD of 5.80, and median of 0.06. The outdoor ventilation rate per infected person for the scenario showed a log-normal distribution with a GM of 710.96, GD of 6.22, and median of 169.17 m3/h. A higher Cavg value indicated exposure to SARS-CoV-2 due to the lower ventilation r ate in the a rena a nd the l arge expiratory volume of athletes caused by intensive exercise. [ABSTRACT FROM AUTHOR]

A heavy rainfall event caused by mesoscale convective systems (MCSs) resulted in flooding over areas of Davao City in Mindanao Island, Philippines, on 03 May 2017. The event occurred during the summer season (April–May) under weak large-scale conditions. This study investigated the initiation and development of MCSs by performing high-resolution numerical simulations with the finest grid spacing of 200 m, using the Weather Research and Forecasting (WRF) model. It was found that the merging of two meso- β scale convective systems over the west and east of Mount Apo caused the flood-producing rainfall in the Davao area. Results show that the west meso- β scale convective system formed over the basin area in Mindanao Island due to moisture advection from sea breeze circulation. In addition, the concave geometry of the Mindanao basin assisted in accumulating moisture which made the basin favorable for convection development. Meanwhile, the precipitating downdrafts generated cold pools wherein the continuous convergence of multiple outflow boundaries resulted in the further development and maintenance of the MCS over the basin. While the east meso- β scale convective system developed over the Davao area due to the interaction between southeasterlies (ambient trade winds) and Mount Apo terrain. Merging of the MCSs resulted in the development of a larger meso- β scale system. Eventually, the larger meso- β scale convective system split and splitted MCSs weakened over time. [ABSTRACT FROM AUTHOR]

A short-time rainstorm exceeding the extreme historical rainfall occurred in the Jinnan District of Tianjin, China, on 3 July 2022. Due to the concentrated time period of precipitation, it caused serious water accumulation in the Jinnan District. The purpose of this paper is to study the weather mechanism of this extreme rainstorm in the Jinan District of Tianjin. By analyzing the fine observation facts, we can obtain the mesoscale weather characteristics and environmental conditions of the process. The results provide a reference for similar weather forecasting and warning in the future. Based on the 1 min interval precipitation observation data, the ERA5 reanalysis data, the CINRAD-SA radar reflectivity data of Tanggu, the cloud-top brightness temperature data of the Fengyun-4A satellite, and the Variational Doppler Radar Analysis System data, we comprehensively analyzed a record-breaking extreme rainfall process in Tianjin on 3 July 2022. The results show that the extreme rainfall process presents prominent mesoscale weather characteristics, with high precipitation intensity in a short-term period. This process is influenced by multi-scale weather systems, including the 500 hPa upper-level trough and the long-distance water vapor transport by Typhoon Chaba. The rainstorm event is caused by the combined actions of cold pool outflow produced by the upstream precipitation, the easterly disturbance in the boundary layer, the mesoscale temperature front, and the ground convergence line. Specifically, the ground convergence line is formed by the northerly wind of the cold pool outflow and the warm and moist southerly airflow from the ocean, and the temperature front is caused by the horizontal thermal difference of the underlying surface. Both the ground convergence line and temperature front contribute considerably to the triggering of mesoscale convection. The mesoscale secondary circulation is formed in the meridional direction by the meso-γ-scale convergence and its interaction with strong velocity in front of the trough, contributing to the development and maintenance of vertical motion in the Jinnan region of Tianjin and thereby leading to the occurrence and development of this extreme heavy rainfall process. [ABSTRACT FROM AUTHOR]

We reviewed various physical and biological manifestations of an unprecedented large-scale water temperature anomaly that emerged in the Northeast Pacific in late 2013. The anomaly dubbed "The Blob" persisted through 2014–2016, with some signs of its persistence through 2017–2018 and a possible reemergence in 2019. The tentative timeline of The Blob's successive appearances around the Northeast Pacific is suggestive of its advection by currents around the Gulf of Alaska, along the Aleutians, into the Bering Sea, and eventually to the Bering Strait. During the initial phase of The Blob's development in 2013–2014, advection along the Polar Front might have played a certain role. The extreme persistence and magnitude of The Blob resulted in numerous and sometimes dramatic ecosystem responses in the eastern Bering Sea. The multi-year duration of The Blob might have preconditioned the Bering Sea for the record low seasonal sea ice extent during the winter of 2017–2018 and the disappearance of the cold pool in 2016 and 2018 that profoundly affected zooplankton, invertebrates, fishes, seabirds, and marine mammals. A comparison of the time series of population responses across trophic levels suggests that The Blob lowered primary production during spring, increased production of small copepods and jellyfish, and reduced the efficiency of energy transfer to higher trophic levels. While the Bering Sea's water temperature, seasonal sea ice, and cold pool seem to return to the long-term mean state in 2022, it remains to be seen if the Bering Sea ecosystem will completely recover. The two most likely alternative scenarios envision either irreversible changes or hysteresis recovery. [ABSTRACT FROM AUTHOR]

The structure and evolution of a cold front that produced a tornadic narrow cold‐frontal rainband (NCFR) over the UK on 20 November 2013 is explored using reanalysis data, high‐resolution model simulations and observations. Physical links are found to exist across a range of spatiotemporal scales, through which the evolving large‐scale flow field exerts an influence on the timing and location of miso‐scale vortex genesis, and therefore the potential for tornado genesis. The synoptic‐scale flow pattern exhibited amplification, consisting of upstream ridge building and downstream trough extension. A prominent jet streak and associated positive potential vorticity (PV) anomaly and tropopause fold moved rapidly southeastward on the rear flank of the extending upper‐level trough, the leading edge of these features eventually overspreading the surface cold front over the UK. Increasing 850 hPa frontogenesis occurred underneath the left exit of the jet streak and associated, intensifying, PV anomaly. A filament of dry, high‐PV air was extruded from the overlying tropopause fold within an intensifying front‐transverse circulation in this region. This dry filament eventually penetrated to low levels immediately behind the front, where it undercut the upper, rearward parts of the wide cold‐frontal precipitation band. Model fields and observations suggest that diabatic cooling, associated with sublimation of solid hydrometeors falling into the dry filament, led to the development of local downdraft and near‐surface divergence maxima and a prominent cold pool immediately behind the surface cold front over central England. Increases in horizontal convergence, updraft speed, and horizontal temperature gradients along the frontal boundary immediately ahead of the cold pool resulted in development of a locally well‐defined cold front and associated NCFR, where the surface front was formerly (and elsewhere continued to be) relatively weak. Tornadoes occurred in association with miso‐scale vortices that developed rapidly along an intensifying vertical vortex sheet at the NCFR. [ABSTRACT FROM AUTHOR]

This study attempts to investigate how future sea surface temperature increases will affect the size (radius of gale-force [17 m   s − 1 ] wind at 10 m height; i.e., R17) evolution of tropical cyclones that undergo extratropical transition (ET) through sensitivity experiments of sea surface temperature (SST) for Typhoon Songda (2016) in the northwestern Pacific. Two numerical experiments were carried out, including a control simulation (control) and a sensitivity experiment (SST4.5) with SST increased by 4.5 degrees in the entire domain. The results showed that Songda tended to be stronger and larger with projected higher SSTs. Moreover, the momentum equation for tangential wind was utilized to study the mechanism of R17 evolution in different SST scenarios, in which the radial absolute vorticity flux term played a dominant role in generating a positive tendency of tangential wind. The results indicate that before ET, higher SSTs in the entire domain led to more active rainbands in both inner-core and outer-core regions. As a result, stronger secondary circulation and low-level inflow extended outward, and the absolute angular momentum (AAM) importing from the outer region increased, which led to a larger R17 in SST4.5. During the ET, the peripheral baroclinically driven frontal convection induced extensive boundary layer inflow, which accelerated the tangential flow in the outer frontal region through strong inward AAM transport. However, due to the lower latitude of the cyclone and the strong frontolysis at the outer side of the cold pool in SST4.5, the peripheral frontal convection reached the location of R17 later; thus, the increase in the cyclone size lagged behind that in the control. [ABSTRACT FROM AUTHOR]

From 17 to 22 July 2021, the “21·7” extreme rainfall event (“21·7” ERE) hit Henan Province, breaking the record for mainland China with a maximum hourly rainfall of 201.9 mm at the Zhengzhou station. The long-lived (20 h) mesoscale Huang-Huai vortex (HHV) was an important system that directly affected the major rainfall stage, including the extreme hourly rainfall. This study investigates the formation and development mechanism of the HHV, as well as its association with the simulation of extreme hourly rainfall through numerical simulations. The simulated rainfall and radar composite reflectivity were in good agreement with the observations, thus effectively reproducing the generation and developmental process of the HHV. The analysis results showed that the HHV initially formed at 850 hPa on 19 July at 1800 UTC and eventually developed to 550 hPa. The positive feedback formed by the horizontal convergence and vertical vorticity transport was the main mechanism leading to the generation and deepening of the HHV. The stretching effect (STR) term played an absolutely dominant role in the increase in the vorticity tendency, and it primarily originated from the coupling effect of boundary layer jets (BLJs) and synoptic-weather-system-related low-level jets (SLLJs). The accurate simulation of the HHV allowed the early rainfall to reasonably reproduce the surface cold pool near the Zhengzhou station, and then the cooperation of the SLLJs, the BLJs, and the cold pool made the simulated extreme hourly rainfall exactly close to the Zhengzhou station, but with a weaker intensity, due to the fact that the HHV moved northeastward after its formation, resulting in a narrow range of southerly flow in southern Henan, which is not conducive to convective triggering in the southerly flow.

On June 30 and July 1, 2020, the southern region of Brazil was the scene of an explosive cyclogenesis that directly impacted society, causing, material, economic and social damage and human fatalities. In the present work, the objective is to characterize the genesis of the absolute maximum gusts (=20 m/s) that occurred during that extreme meteorological event. From this, it was possible to differentiate two main groups with distinct gusts: one of convective origin and the other, nonconvective. In addition to the different genesis, the geographic coverage and the period in which the absolute maximum gusts occurred in each group, attest that although affected by the extratropical cyclone, the relative position to it was preponderant. A cold front system caused a squall line that was responsible for the absolute maximum gusts belonging to the first group, which, given the wide-ranging conditions (from the southern portion of the Paraná State to the north of the Rio Grande do Sul), could be treated by using the meteorological term derecho. In the second group, that is, nonconvective gusts, the intense pressure gradient given by the deepening of the extratropical (explosive) cyclone over the ocean, conditioned absolute maximum gusts in the coastal strip, especially in Rio Grande do Sul State. [ABSTRACT FROM AUTHOR]

Extreme precipitation events have been occurring frequently worldwide, and their causative factors and convection initiation (CI) mechanisms have been attracting more and more attention in recent years. As a comprehensive study on the CI mechanisms of extreme rainstorms over the northern slope of the Kunlun Mountains (KLM), Xinjiang, based on both observational and high tempo-spatial numerical simulation, the major findings of this work are as follows: A cold pool (CP) was formed in the northwestern Tarim Basin under the influence of early precipitation evaporation, and it moved towards the northern slope of the KLM several hours before the CI. With the movement of the CP, a significant vertical temperature gradient was formed close to the leading edge of the CP, thereby enhancing local convective instability (up to ~10 PVU). In addition, the vertical shear of the horizontal winds at the leading edge of the CP led to a notable increase in the baroclinic component of moist potential vorticity, thus reinforcing the local conditional symmetric instability (up to ~8 PVU), providing another important unstable energy for the CI. In addition, the combined effect of the convergent lifting of a boundary layer jet (BLJ, the maximum wind speed below 1 km exceeding 10 m s−1) and the significant frontogenetical forcing (up to ~100 × 10−8 K m−1 s−1) at the leading edge of the CP were the causes of the release of the unstable energies. Further analysis of the frontogenetical forcing associated with the CP indicates that the convergence (up to ~2 × 10−3 s−1), diabatic heating and slantwise terms (indicates the baroclinicity and inhomogeneity of the vertical momentum in horizontal direction) were the major contributors, whereas the deformation term at the leading edge of the CP provided a relatively weaker contribution.

Abstract Mesoscale convective systems (MCS) contribute about half of the world's precipitation and create flash flooding as well as other extreme weather events. Despite steady progress in research of these systems in the last several decades, better theoretical understanding is still needed to understand their dynamical organizations and to improve their forecasts in numerical models. By using the Moncrieff‐Green horizontal vorticity equation, this paper presents an analytical model of one type of MCS, the steady‐state squall lines. It describes the organization, propagation, and properties of mesoscale circulations of two‐dimensional steady‐state convective systems under sheared environment. Far‐side solutions are formulated to illustrate the underlying physical processes of squall line flows. Numerical procedures are described to solve the model under general environmental conditions. The model leads to the following prediction of squall line properties: Given the environmental profiles of wind and convective available potential energy (CAPE), the propagation speed, the depths and mass fluxes of the tilted ascending front‐to‐rear flow, the overturning updraft, and the descending rear inflow of the squall line can be all determined from the cold pool buoyancy or CAPE. The squall lines are therefore self‐organized dynamical systems that have limited degrees of freedom in their properties. The model advances the theoretical understanding of how mesoscale flow components interact to sustain organized convection. It provides a new tool to interpret squall line systems in high resolution models and to parameterize them in climate models.

Using automatic station observation data, Doppler radar data, ERA-5 0.25°×0.25° reanalysis data and WRF numerical simulation data, we analyzed the mesoscale environmental conditions, the mesoscale convective systems triggering and maintenance mechanisms of one warm-sector heavy rainfall process in the Wuling Mountains of Chongqing on May 19-20, 2018. The results were as follows: (1) There was no obvious cold air forcing in this process, the baroclinicity is weak, but the boundary layer had high temperature and humidity, and the atmosphere stratification was extremely unstable. (2) The evolution of the mid- and small-scale convective systems of the heavy precipitation in Shiqiao mainly had three stages: the convections scattered into east-west zonal flow, the rainfall near Shiqiao remained quasi-stationary after the break of the zonal flow, and the northeast-southwest zonal flow reconstructed rapidly. (3) The convergence line which distributed along the Wuling Mountains, triggered the thunderstorm. The strong echo of convective cell moved and strengthened along the convergence line, contributing to the formation of the "train effect". (4) The strong thunderstorm cold pool on the eastern mountain top of Shiqiao flowed down the mountain, working together with the warm and humid air currents and topography to maintain the strong precipitation in Shiqiao. (5) Topography played an important role in this heavy precipitation process. The easterly wind near the ground interacted with the mountains in the west of Shiqiao to form a small local cyclonic vortex, which made significant contribution to triggering precipitation. Moreover, due to the blocking effect of the mountains in the east of Shiqiao, the speed of the topographic vortex slowed down, which was conducive to the maintenance of precipitation. [ABSTRACT FROM AUTHOR]

Nocturnal spatial variation of temperature, wind, and turbulence over microtopography is generally poorly understood. Low amplitude microtopography covers much of the Earth's surface and, with very stable conditions, can produce significant spatial variations of temperature and turbulence. We examine such variations over gentle terrain that include two shallow gullies that feed into a small valley. The gullies are covered by a sub-network of seven flux stations that is embedded within a larger network that covers the valley. The measurements indicate that gullies of only 2–5-m depth and 100-m width can often lead to spatial variations of temperature of several kelvin or more. Such variations depend on ambient wind speed and direction and the near-surface stratification. We investigate the surprising importance of microscale lee turbulence occurring over the gentle microtopography with slopes of only 5%. Near-surface stratification unexpectedly tends to increase with surface elevation on the slopes. We examine the potential causes of this puzzling behaviour of the near-surface stratification. [ABSTRACT FROM AUTHOR]

The impact of radar and surface data assimilation on the forecast of a nocturnal squall line initiated above the stable boundary layer in the Yangtze–Huaihe River is investigated by the Weather Research and Forecasting (WRF) model and its three-dimensional variational assimilation system (WRFDA 3DVar). Results show that the assimilation of radar and surface data can improve the prediction of the convection initiation time, height and vertical ascending motion during the early stage of the squall line formation by adjusting the thermodynamic structure, circulation patterns, water vapor conditions and hydrometeor mixing ratios. Although the radar and surface data assimilation can improve the forecast of the location of the squall line to a certain extent, the squall line is stronger in the radar data assimilation than that in the surface data assimilation, leading to stronger radar reflectivity and heavier precipitation. The assimilation of both radar and surface data has a more positive impact on the forecast skill than the assimilation of either type of data. Moreover, during the mature stage of the squall line, radar and surface data assimilation can enhance the intensity of the surface cold pool. Specifically, radar data assimilation or assimilating the two data simultaneously can produce a stronger cold pool than only assimilating surface data, which is more conducive to the maintenance and development of the squall line. [ABSTRACT FROM AUTHOR]

The Holocene, starting approximately 11.7 cal ka, is characterized by distinct periods of warming and cooling. Despite these known climate events, few temperature proxy data exist in the northwestern Atlantic Ocean. One potential record of past water temperatures is preserved in the marine fossil record. Shell growth of ocean quahogs (Arctica islandica), a long-lived bivalve, can provide records of past environmental conditions. Arctica islandica habitat includes the Mid-Atlantic Bight (MAB), an area rapidly warming as a consequence of climate change. The Cold Pool, a bottom-trapped water mass on the outer continental shelf within the MAB, rarely rises above 15°C. Ocean quahogs inhabiting the MAB are confined to the Cold Pool as a consequence of an upper thermal limit for the species of ~15–16°C. Recently, dead A. islandica shells were discovered outside of the species' present-day range, suggesting that the Cold Pool once extended further inshore than now observed. Shells collected off the Delmarva Peninsula were radiocarbon-dated to identify the timing of habitation and biogeographic range shifts. Dead shell ages range from 4400 to 60 cal BP, including ages representing four major Holocene cold events. Nearly absent from this record are shells from the intermittent warm periods. Radiocarbon ages indicate that ocean quahogs, contemporaneous with the present MAB populations, were living inshore of their present-day distribution during the past 200 years. This overlap suggests the initiation of a recent biogeographic range shift that occurred as a result of a regression of the Cold Pool following the Little Ice Age. [ABSTRACT FROM AUTHOR]

In this study, multi‐source data, especially weather radar data, were used in the analysis of structural features and evolution of a squall line‐like rainband (SLLR) of a linear mesoscale convective system (MCS) in the eastern slope of the Taihang Mountains on 12 and 13 August 2018 and reached the following conclusions: (a) The SLLR, located in north of the linear MCS, exhibited a significant horizontal gradient of reflectivity and large vertical extension. The front‐to‐rear flow that appeared between the surface and the stratosphere was lifted upward immediately in front of a cold pool that formed rearward‐tilting updrafts. (b) As the SLLR passed over, surface meteorological quantities changed drastically, coinciding with the heavy precipitation. (c) The SLLR, when propagating northeastward, showed a complex convective development of sequential intensification, weakening, and re‐intensification within a 2.5‐hr period. The temporal intensification was related not only to the development of a low‐level rear‐inflow jet but also to the dynamic interaction between the vertical environmental wind shear and the cold pool. The lifted rear‐inflow jet, which formed over a vertically stacked horizontal vorticity couplet behind the leading edge, provides a reasonable explanation for the intensification of the SLLR, resulting in the reduction of the cold pool circulation and enhancement of the convective updraft. Topographic forcing might play a crucial role in the re‐intensification of the SLLR, which suggests the importance of the cold pool and topography in structural features and convective evolution of the squall line‐like rain bands. Key Points: The squall line‐like rainband (SLLR) in a linear mesoscale convective system exhibited the characteristics of the typical squall lineThe SLLR was associated with a complex convective development of sequential intensification, weakening, and re‐intensificationThe cold pool and topography play crucial roles in structural features and convective evolution of the SLLR [ABSTRACT FROM AUTHOR]

This study investigated the relevant processes responsible for differences of convective precipitation caused by land-surface resolution. The simulations were performed with the ICOsahedral Nonhydrostatic model (ICON) with grid spacing of 156 m and Large Eddy Simulation physics. Regions of different orographic complexity, days with weak synoptic forcing and favourable convective conditions were selected. The resolution of land-surface properties (soil type, vegetation) and/or the orography was reduced from 156 to 5000 m. Analyses are based on backward trajectories (Lagrangian Analysis Tool (LAGRANTO)), heat budget and convective organisation potential (COP) calculations. On average, the relative difference of areal mean daily precipitation at 1250 and 5000 m land-surface resolutions compared to 156 m were 6% and 15%, respectively. No consistent dependency of precipitation on orography or land-surface properties was found. Both factors impact convective initiation over areas with embedded mesoscale-sized land-surface heterogeneities. The position of convective precipitation was often influenced by the resolution of orography. Coarsening from 156 to 5000 m considerably changed the location of wind convergence and associated convection initiation. It also affects the onset times of clouds (<20 min) and precipitation (≈1 h). Cloud aggregation and microphysical processes proved to be important for further development towards convective precipitation. [ABSTRACT FROM AUTHOR]

Based on conventional observation data, automatic weather station data and CINRAD-SA Doppler radar data, we analyzed the weather background, environmental conditions, development mechanism and the gale that caused for the squall line event on 27 May 2018 in Guangxi. Results show that the cold tongue at 500hPa superimposed with the warm ridge in the lower layer built a strong stratification instability structure, with a high value of CAPE, which provided a favorable environment for the development of the squall line. The mesoscale convergence line located at the coast of Guangxi was the trigger mechanism for the initial convection system that finally leaded to the formation of the squall line system. The warm and moist inflow from the lower layer of the squall line reached the top of the storm and diverged. The cold and dry air inflow from the rear of the middle layer strengthened the downdraft within the squall line. The downdraft outflow formed convergence on the front side of the storm to trigger new convection. The self-organization structure of the squall line was formed by the inflow and outflow stagger. These were the important reasons for maintenance and development of the squall line under the condition of weak vertical wind shear. The main reason of strong wind was the density current caused by the merger and strengthening of surface cold pools.

Abstract In this study, multi‐source data, especially weather radar data, were used in the analysis of structural features and evolution of a squall line‐like rainband (SLLR) of a linear mesoscale convective system (MCS) in the eastern slope of the Taihang Mountains on 12 and 13 August 2018 and reached the following conclusions: (a) The SLLR, located in north of the linear MCS, exhibited a significant horizontal gradient of reflectivity and large vertical extension. The front‐to‐rear flow that appeared between the surface and the stratosphere was lifted upward immediately in front of a cold pool that formed rearward‐tilting updrafts. (b) As the SLLR passed over, surface meteorological quantities changed drastically, coinciding with the heavy precipitation. (c) The SLLR, when propagating northeastward, showed a complex convective development of sequential intensification, weakening, and re‐intensification within a 2.5‐hr period. The temporal intensification was related not only to the development of a low‐level rear‐inflow jet but also to the dynamic interaction between the vertical environmental wind shear and the cold pool. The lifted rear‐inflow jet, which formed over a vertically stacked horizontal vorticity couplet behind the leading edge, provides a reasonable explanation for the intensification of the SLLR, resulting in the reduction of the cold pool circulation and enhancement of the convective updraft. Topographic forcing might play a crucial role in the re‐intensification of the SLLR, which suggests the importance of the cold pool and topography in structural features and convective evolution of the squall line‐like rain bands.

Four typical double-moment cloud microphysical schemes (Milbrandt, Morrison, NSSL and WDM6) in WRF (Weather Research and Forecasting) are used to investigate the impact of the different schemes on the simulation of a straight squall line evolving into a bow-shaped one in East China on 15 April 2016. Although simulations with Milbrandt, Morrison and WDM6 schemes can produce bow-shaped squall lines, only the WDM6 scheme can simulate the evolution process of the straight squall line to a bow-shaped one well. The simulation results with the NSSL scheme produce a broken straight squall line. The possible reason is that the range and intensity of cold pools and the rear inflows are different among the four schemes when the observed squall line evolves into a standard bow-shaped squall line. The mixing ratio and number concentration of rain water with the WDM6 scheme is largest in strong convective areas, and the cold pool and rear inflow are also strongest among the four schemes. Compared with the WDM6 scheme, the mixing ratio and number concentration of rain water are less with the Milbrandt and Morrison schemes. Also, the cold pool and rear inflow with the Milbrandt scheme are weaker than for the WDM6 scheme but stronger than those with the Morrison scheme. The rainwater mixing ratio is very low and no obvious cold pool and rear inflow exist with the NSSL scheme. [ABSTRACT FROM AUTHOR]

Abstract Background The detection efficiency of ultrasonic transmitters is seasonally variable, requiring long-term studies to evaluate key environmental features that mask, alter speed, bend, or reflect transmissions. The US Southern Mid-Atlantic Bight shelf is characterized by a strong summer thermocline capping remnant winter water, known as the Cold Pool, and a well-mixed water column in other seasons. To investigate the effects of interactions between temperature stratification and storm-induced noise on transmission detectability, we conducted a year-long range test of 69-kHz acoustic transmitters in the bottom waters of the US Southern Mid-Atlantic Bight. We used generalized additive models and cross-validation to develop and evaluate a predictive model of detection efficiency and visualize variability in detection distance throughout the year of deployment. Results The most-predictive model contained the effects of temperature stratification and ambient noise, predicting that stratification results in a 33% increase in detectability and 56% increase in detection distance. The model had an overall error rate of 17.1% and an 18.7% error at a distance of 800 m, predicting 17% detectability at median ambient noise when the water column was not stratified and > 50% when the difference between surface and bottom temperatures was greater than 4.2 °C. The distance at 50% detectability increased with the formation of the Cold Pool during spring, increasing by nearly 300 m over 3 days. All seasons were associated with storm-induced reductions in overall detectability and distance at 50% detectability. Conclusion Thermal stratification within the Southern Mid-Atlantic Bight increases bottom water ultrasonic transmitter detection distance and reduces the impact of surface noise. This effect leads to a seasonal increase in detection distance from the late-spring through the summer. To our knowledge, this study is the first to report and quantify an increase in detection range as a result of temperature stratification, likely due to placing transmitters and receivers on the same side of a strong thermocline.

A short-time rainstorm exceeding the extreme historical rainfall occurred in the Jinnan District of Tianjin, China, on 3 July 2022. Due to the concentrated time period of precipitation, it caused serious water accumulation in the Jinnan District. The purpose of this paper is to study the weather mechanism of this extreme rainstorm in the Jinan District of Tianjin. By analyzing the fine observation facts, we can obtain the mesoscale weather characteristics and environmental conditions of the process. The results provide a reference for similar weather forecasting and warning in the future. Based on the 1 min interval precipitation observation data, the ERA5 reanalysis data, the CINRAD-SA radar reflectivity data of Tanggu, the cloud-top brightness temperature data of the Fengyun-4A satellite, and the Variational Doppler Radar Analysis System data, we comprehensively analyzed a record-breaking extreme rainfall process in Tianjin on 3 July 2022. The results show that the extreme rainfall process presents prominent mesoscale weather characteristics, with high precipitation intensity in a short-term period. This process is influenced by multi-scale weather systems, including the 500 hPa upper-level trough and the long-distance water vapor transport by Typhoon Chaba. The rainstorm event is caused by the combined actions of cold pool outflow produced by the upstream precipitation, the easterly disturbance in the boundary layer, the mesoscale temperature front, and the ground convergence line. Specifically, the ground convergence line is formed by the northerly wind of the cold pool outflow and the warm and moist southerly airflow from the ocean, and the temperature front is caused by the horizontal thermal difference of the underlying surface. Both the ground convergence line and temperature front contribute considerably to the triggering of mesoscale convection. The mesoscale secondary circulation is formed in the meridional direction by the meso-γ-scale convergence and its interaction with strong velocity in front of the trough, contributing to the development and maintenance of vertical motion in the Jinnan region of Tianjin and thereby leading to the occurrence and development of this extreme heavy rainfall process.

An isolated convection was unexpectedly initiated in the evening of 1 August 2019 around the Tianjin urban region (TUR), which happened at some distance from the shear line at lower level and the preexisting convection to the South, analyzed by using ERA5 reanalysis data and observations from surface weather stations, and a S-band radar. The results show that, 42 min before the initiation of the convection, the atmospheric thermodynamic conditions around TUR were favorable for the initiation of the isolated convection, although the southerly and vertical shear of the horizontal wind at the lower level was weak. A sea-breeze front approached the TUR and continued to move West, leading to the triggering of the isolated convection in the context of the urban humid heat island (UHHI) effect. Subsequently, the gust front, which was formed between the cold pool away from the TUR and the warm and humid air of the UHHI, moved northward, approached the convection, and collided with sea breeze front, resulting in five reflectivity centers of isolated convection being merged and the convection's development. Finally, the isolated convection split into two convections that moved away from the TUR and disappeared at 20:36 Beijing Time. The isolated convection was initiated and developed by the interaction of the sea breeze front and gust front in the context of the UHHI effect. The sea breeze front triggered the isolated convection around TUR in the context of the UHHI effect, and the gust front produced by the early convective storms to the south played a vital role in the development of the isolated convection. [ABSTRACT FROM AUTHOR]

The Cold Pool feature of the Middle Atlantic Bight (MAB) is a body of cold bottom water that develops in the spring and persists through the summer‐autumn months. It is maintained by northerly currents and can be traced back to Arctic water masses. The Cold Pool provides habitat for many boreal species at latitudes far south of their normal range and plays an important role in the population dynamics of lower and upper trophic level organisms. Here, we describe changes in the extent and thermal properties of the Cold Pool using both observations and models. Two indices are developed based on a gridded, interpolated bottom temperature dataset; the first is a mean temperature indicator, and the second is a spatial extent indicator. The temperature indicator showed a significant increasing trend over the study period 1968–2019 and a single change point in 2008. Similarly, the area indicator declined significantly, also displaying a change point in 2008. Cold Pool maximum temperature and minimum size were observed in 2017, which is also known as a heatwave year in the MAB. The indices presented here support the view of a rapidly warming Cold Pool that is being limited in its spatial extent. Changes in Cold Pool hydrography will likely affect boreal species distributions and total ecosystem productivity. [ABSTRACT FROM AUTHOR]

We explore whether and how the land characteristics, especially surface drag, affect the squall line, in an idealized modeling framework. We find that the balance between the ambient low‐level shear and cold‐pool‐induced shear in the squall line can be modified by surface drag: it not only changes the ambient shear if near‐surface environmental wind is nonzero, but also reduces the cold‐pool‐induced shear by both weakening the low‐level wind and deepening the cold pool. The land surface impact on squall lines is larger with lower convective available potential energy (CAPE), partly because of stronger convection with higher CAPE. The cold pool intensity (vertically integrated negative buoyancy) could not explain the reduced cold pool shear induced by the land. Furthermore, land characteristics—such as roughness lengths—help maintain the shear balance and potentially make the squall line long‐lived, suggesting that they be included in convective (or cold pool) parameterizations to improve climate and Earth system models. Key Points: Surface drag affects squall lines by weakening near‐surface wind and deepening the cold poolThe widely used cold pool intensity no longer characterizes the cold‐pool‐induced shear when surface drag is includedDynamical effects of the land surface are missed in thermodynamic‐based cold pool parameterizations [ABSTRACT FROM AUTHOR]

A double‐moment version of the SBU‐YLIN cloud microphysical scheme in WRF is introduced. It predicts the mass and number mixing ratios of cloud droplet, rain, cloud ice, and precipitating ice. In addition, a number of physical processes, like rain evaporation, collection between rain and snow are also optimized in the new scheme. The scheme is evaluated and compared with the original one‐moment scheme for a squall line case. We found that the double‐moment approach gives a better representation of rain evaporation, which is critical for the development, morphology, and evolution of the simulated squall line, especially for the enhanced trailing stratiform cloud and leading convective line. The relationship between key microphysical processes and squall line dynamics is investigated to identify the driving mechanisms of the descending rear inflow, cold pool, and slantwise updraft. Furthermore, formation of the transition zone in the simulated squall line strongly depends on the flexible description of ice particle properties, such as size, degree of riming and fall speed. Plain Language Summary: A double‐moment version of the SBU‐YLIN cloud microphysical scheme in WRF is introduced and evaluated. The scheme improves a squall line simulation in terms of the shape and structure of the squall line with enhanced stratiform precipitation. The improvement is mainly related to more realistic rain evaporation and flexible description of ice particle properties. Close interactions between cloud and precipitation physics and dynamics is key for the development, maintenance and movement of squall lines. Key Points: A double‐moment version of the SBU‐YLIN scheme is introducedThe scheme improves the simulation of a squall line in terms of the transition zone and stratiform precipitationRain evaporation and flexible description of ice particles are critical for a realistic simulation [ABSTRACT FROM AUTHOR]

Seasonal sea ice plays a key role in shaping the ecosystem dynamics of the eastern Bering Sea shelf. In particular, it leads to the formation of a characteristic pool of cold water that covers the bottom of the shelf from winter through summer; the extent of this cold pool is often used as a management index for distribution, productivity, recruitment, and survival of commercially important fish and shellfish species. Here, we quantify our ability to seasonally forecast interannual variability in Bering Sea bottom temperature and sea ice extent. Retrospective forecast simulations from two global forecast models are downscaled using a regional ocean model; the retrospective forecast simulations include 9‐month to 12‐month forecasts spanning 1982–2010. We find that dynamic forecasting can predict summer bottom temperatures across the eastern Bering Sea shelf with lead times of up to 4 months. The majority of the prediction skill derives from the persistence signal, and a persistence forecast is comparably skillful to the dynamic forecast at these lead times. However, forecast skill of sea ice advance and retreat is low when a forecast model is initialized before or during the ice season (October–February); this limits the ability of either dynamic or persistence models to predict summer bottom temperatures when initialized across the late fall to early spring months. Plain Language Summary: The Bering Sea region is home to a large number of important fisheries. Fluctuations in fish distribution, abundance, and productivity can be influenced by environmental factors; in the Bering Sea, the temperature of the deep shelf water can affect where groundfish are located, how much of their preferred prey is available, and how many juvenile fish and shellfish survive each year. In this study, we test whether we can successfully predict whether bottom water will be colder or warmer than average in a given year. We do this by running forecast models for previous years and comparing the model output to observations collected during the same period. We find that we can skillfully predict summer bottom temperature if we start a forecast four or fewer months in advance of the summer period. However, beginning the forecast during the winter (when sea ice is present) or during the prior fall results in low skill. The 4‐month forecasts can be useful when planning for summer surveys and to provide advance notice to the North Pacific Fishery Management Council of any unusual summer conditions that may affect the quotas they set for the upcoming fishing seasons. Key Points: Dynamic forecasting with a regional model can predict summer bottom temperature on the eastern Bering Sea shelf 3–4 months in advanceMost of the bottom temperature predictability comes from persistence; a multi‐model dynamic forecast may extend predictability 1–2 monthsSea ice presents a prediction barrier, with low sea ice and bottom temp. Skill if forecasts begin before or during the ice season (October–February) [ABSTRACT FROM AUTHOR]

Abstract Background Extreme weather events, including hurricanes, have considerable biological, ecological, and anthropogenic impacts. Hurricane Irene caused substantial economic damage when it hit the Mid-Atlantic Bight (MAB) off of the eastern United States in August of 2011. The MAB is highly stratified during the summer when a strong thermocline separates warm, surface water from deep, cold water, and this oceanographic phenomenon makes modeling hurricane strength difficult. Loggerhead sea turtles (Caretta caretta) forage in the MAB primarily during the stratified season and their dive behavior to the bottom allows them to experience the oceanographic conditions of the entire water column. Methods In this study, we analyzed the movements and dive behavior of juvenile and adult-sized loggerhead sea turtles (n = 18) that were foraging in the MAB as Hurricane Irene moved through the region. The satellite tags deployed on these turtles transmitted location data and dive behavior as well as sea surface temperature (SST) and temperature-depth profiles during this time. Results Behavioral and environmental shifts were observed during and after the hurricane compared to conditions before the storm. During the hurricane, most of the turtles (n = 15) moved north of their pre-storm foraging grounds. Following the storm, some turtles left their established foraging sites (n = 8) moving south by 7.3–135.0 km, and for the others that remained (n = 10), 12% of the observed dives were longer (0.54–1.11 h) than dives observed before the storm. The in situ data collected by the turtle-borne tags captured the cooling of the SST (Mean difference = 4.47°C) and the deepening of the thermocline relative to the pre-storm conditions. Conclusions Some of the loggerhead behavior observed relative to a passing hurricane differed from the regular pattern of seasonal movement expected for turtles that forage in the MAB. These data documented the shifts in sea turtle behavior and distribution during an ecosystem-level perturbation and the recorded in situ data demonstrated that loggerheads observe environmental changes to the entire water column, including during extreme weather events.

In the afternoon of 24 July 2016,a local short-term heavy rainfall occurred in Dagang of Tianjin. The maximum rainfall intensity was 95 mm·h-1,which broke the extreme record in the past ten years. The formation environment and structure of the supercell thunderstorm which caused the short-term heavy rainfall are qualitatively and quantitatively analyzed by using a variety of observation data from automatic station,sounding,radar,microwave radiometer,etc. The results show that:(1) The evolution of supercell is that ground convergence line triggers the generation of old thunderstorms,cold pool outflow boundary triggers the generation of new thunderstorms,and new thunderstorms merge,develop and strengthen into supercell. (2) Three hours before the extreme heavy rainfall,the sea breeze from the Bohai is cold and wet,which played the role of "cold cushion" and vapor transport. (3) Super cells exhibit high centroid development with strong echo cores migrating to the right with increasing altitude. The bounded weak echo area,the backward inflow gap and the drape structure are obvious. The weak mesocyclone maintains four volume scans,with a rotation speed 16 m·s-1,a diameter of the core 40 km and a spreading height 13 km,which is always in the parcel of heavy rainfall. Before the radar echo parameter V50 (volume of reflectivity greater than 50 dBz) reaches its maximum,the echo variable parameter FV50 (change of strong echo volume of 50 dBz in 6 min) appears a sudden drop,which has warning significance for the development of supercells. (4) Within 6 minutes,the heavy precipitation corresponds well with the vertical decline rate of vapor density,the effective thickness and the effective area of the unit in the lower levels.

Abstract A double‐moment version of the SBU‐YLIN cloud microphysical scheme in WRF is introduced. It predicts the mass and number mixing ratios of cloud droplet, rain, cloud ice, and precipitating ice. In addition, a number of physical processes, like rain evaporation, collection between rain and snow are also optimized in the new scheme. The scheme is evaluated and compared with the original one‐moment scheme for a squall line case. We found that the double‐moment approach gives a better representation of rain evaporation, which is critical for the development, morphology, and evolution of the simulated squall line, especially for the enhanced trailing stratiform cloud and leading convective line. The relationship between key microphysical processes and squall line dynamics is investigated to identify the driving mechanisms of the descending rear inflow, cold pool, and slantwise updraft. Furthermore, formation of the transition zone in the simulated squall line strongly depends on the flexible description of ice particle properties, such as size, degree of riming and fall speed.

The impact of radar and surface data assimilation on the forecast of a nocturnal squall line initiated above the stable boundary layer in the Yangtze–Huaihe River is investigated by the Weather Research and Forecasting (WRF) model and its three-dimensional variational assimilation system (WRFDA 3DVar). Results show that the assimilation of radar and surface data can improve the prediction of the convection initiation time, height and vertical ascending motion during the early stage of the squall line formation by adjusting the thermodynamic structure, circulation patterns, water vapor conditions and hydrometeor mixing ratios. Although the radar and surface data assimilation can improve the forecast of the location of the squall line to a certain extent, the squall line is stronger in the radar data assimilation than that in the surface data assimilation, leading to stronger radar reflectivity and heavier precipitation. The assimilation of both radar and surface data has a more positive impact on the forecast skill than the assimilation of either type of data. Moreover, during the mature stage of the squall line, radar and surface data assimilation can enhance the intensity of the surface cold pool. Specifically, radar data assimilation or assimilating the two data simultaneously can produce a stronger cold pool than only assimilating surface data, which is more conducive to the maintenance and development of the squall line.