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Aim: Integration of macroecology and palaeoecology is an important trend in understanding rapidly changing marine ecosystems. However, the spatial mismatch between these two data types has led to difficulties in interpretation, particularly for short-lived phytoplankton and their microfossils. Fronts are narrow transition zones between distinct water masses and play an essential role in partitioning phytoplankton assemblages in the ocean. Whether they also delimit microfossil assemblages deposited at the sea floor is unclear. We examined the correlation between quasi-stationary mesoscale fronts and the spatial distribution of microfossils (diatoms, dinoflagellates and silicoflagellates) in the Bohai, Yellow and East China Seas, to establish a causal link between microfossil assemblages and the factors controlling pelagic species assemblages on continental shelves. Location: China. Time period: 2003–2015. Major taxa studied: Phytoplankton. Methods: Front locations were determined using gradient analysis of monthly satellite sea surface temperature (SST) for 2003–2015. Microfossil assemblages were classified using two-way indicator species analysis of the relative abundance of 345 species collected from surface sediments at 126 sites. The relationships between frontal patterns and microfossil assemblages were evaluated by superimposing maps of front location, microfossil distribution and environmental features in the main water masses and by canonical correspondence analysis. Results: Ten major fronts and four primary microfossil assemblages were identified. Analyses of the spatial patterns of fronts, microfossil assemblages, SST, salinity and nutrients revealed that the fronts partitioned the microfossils into assemblage types corresponding to the physicochemical features of the water masses. Main conclusions: Microfossil species assemblages and their indicator species are separated by mesoscale fronts and are correlated with water properties. Producing base maps of microfossil assemblages in relationship to SST fronts enables examination of the importance of quasi-stationary mesoscale fronts in constructing microfossil patterns on continental shelves. The results displayed potential for the interpretation sediment core data and their integration with the macroecological context.

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.

The relationship between a synoptic-scale, upper-level cold vortex and a meso-α scale polar low (PL) over the Sea of Japan, and the role played by low-level baroclinicity in the development of the PL were investigated. We examined three PLs from the perspective of potential vorticity (PV) and energy budgets, using mesoscale analysis data with a horizontal resolution of ~11 km. During the development stage of each PLs, a meso-α scale upper-level PV (UPV) anomaly, which intrudes to around the 700-600 hPa level and which is just a part of a synoptic-scale PV anomaly accompanying the cold vortex, moved to the west side of a low-level PL. The PL was located in a wide region of low static stability in the lower troposphere. These conditions suggested that the synoptic-scale cold vortex, accompanied by a cold dome and the different scales of UPV anomalies, played a role in creating a favourable environment for the PL development. One of the common characteristics of the PL cases studied here was that, in contrast to the low-level PL, the upper-level disturbance associated with the meso-α scale UPV anomaly showed no development at all. This is likely because of the mobile UPV anomaly cut off from its source. Low-level baroclinicity, which varied with time, was an important factor in differentiating the PL shape and the energy sources necessary for PL development. Furthermore, the strength of baroclinicity, through its enhancement of mesoscale fronts and convection, affected diabatic processes, as well as baroclinic development.

Observations from the summer Arctic Ocean Experiment 2001 (AOE-2001) are analysed with a focus on the interactions between mesoscale and boundary-layer dynamics. Wavelet analyses of surface-pressure variations show daylong periods with different characteristics, some featuring episodes of pronounced high-frequency surface-pressure variability, here hypothesized to be caused by trapped gravity waves. These episodes are accompanied by enhanced boundary-layer turbulence and an enhanced spectral gap, but with only minor influence on the surface stress. During these episodes, mesoscale phenomena were often encountered and usually identified as front-like features in the boundary layer, with a peak in drizzle followed by changing temperature. These phenomena resemble synoptic fronts, though they are generally shallow, shorter-lasting, have no signs of frontal clouds, and do not imply a change in air mass. Based on this analysis, we hypothesize that the root cause of the episodes with high-frequency surface-pressure variance are shallow, mesoscale fronts moving across the pack ice. They may be formed due to local-to-regional horizontal contrasts, for example, between air with different lifetimes over the Arctic or with perturbations in the cloud field causing differential cooling of the boundary layer. Thermal contrasts sharpen as the air is transported with the mean flow. The propagating mesoscale fronts excite gravity waves, which affect the boundary-layer turbulence and also seem to favour entrainment of free tropospheric air into the boundary layer.

SST fronts at the mesoscale eddy edge (ME fronts) were investigated from 2007–2017 in the northern South China Sea (NSCS) based on an automatic method using satellite sea level anomaly (SLA) and SST data. The relative probabilities between the number of anticyclonic/cyclonic ME fronts (AEF/CEF) and the number of anticyclones/cyclones reached 20%. The northeastern and southwestern parts of these anticyclones had more fronts than the northwestern and southeastern parts, although CEFs were nearly equally distributed in all directions. The number of ME fronts had remarkable seasonal variations, while the eddy kinetic energy (EKE) showed no seasonal variations. The total EKE at the ME fronts was three times of that within the MEs, and it was much stronger in AEFs than in CEFs. The interannual variability in the number of ME fronts and EKE had no significant correlation with the El Niño-Southern Oscillation (ENSO) index. Possible mechanisms of ME fronts were discussed, but the contributions of mesoscale eddies to SST fronts need to be quantified in future studies.

A synergetic approach for quantitative analysis of high‐resolution ocean synthetic aperture radar (SAR) and imaging spectrometer data, including the infrared (IR) channels, is suggested. This approach first clearly demonstrates that sea surface roughness anomalies derived from Sun glitter imagery compare very well to SAR roughness anomalies. As further revealed using these fine‐resolution (∼1 km) observations, the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature (SST) field. To quantitatively interpret SAR and optical (in visible and IR ranges) images, equations are derived to relate the “surface roughness” signatures to the upper ocean flow characteristics. As developed, a direct link between surface observations and divergence of the sea surface current field is anticipated. From these satellite observations, intense cross‐frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the SST field. As a plausible mechanism, it is suggested that interactions of the wind‐driven upper layer with the quasi‐geostrophic current field (via Ekman advective and mixing mechanisms) result in the generation of secondary ageostrophic circulation, producing convergence and divergence of the surface currents. The proposed synergetic approach combining SST, Sun glitter brightness, and radar backscatter anomalies, possibly augmented by other satellite data (e.g., altimetry, scatterometry, ocean color), can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence/divergence (upwelling/downwelling). This, in turn, establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two‐dimensional satellite surface expressions. Key Points Synergistic approach for quantitative analysis of ocean SAR and optical data SAR and Sun glitter imagery of mesoscale ocean currents Surface roughness anomalies trace current divergence

Heavy rainfall that occurred at the south coast of China on 10–11 May 2014 was associated with a synoptic-system-related low-level jet (SLLJ) and a boundary layer jet (BLJ). To clarify the role of the double low-level jets in convection initiation (CI), we perform convective-permitting simulations using a nonhydrostatic mesoscale model. The simulations reproduce the occurrence location and mesoscale evolution of new convective cells as well as their small-scale wavelike structures at the elevated layers, which are generally consistent with radar observations despite some differences in their orientation. The nighttime BLJ over the northern South China Sea strengthens the convergence at ~950 hPa near the coast where the BLJ’s northern terminus reaches the coastal terrain. Meanwhile, the SLLJ to the south of the inland cold front provides divergence at ~700 hPa near the SLLJ’s entrance region. Such low-level convergence and midlevel divergence collectively produce strong mesoscale lifting for CI at the coast. In addition to the enhanced mesoscale lifting, the double low-level jets also provide favorable conditions for the superimposed small-scale disturbances that can serve as effective moistening mechanisms of the lower troposphere during CI. In a sensitivity experiment with coastal terrain removed, CI still occurs near the coast but is delayed and weaker compared to the control run. This latter experiment suggests that double low-level jets and their coupling indeed exert key effects on CI, while the BLJ colliding with terrain may enhance coastal convergence for amplifying CI. These findings provide new insights into the occurrence of coastal heavy rainfall in the warm sector far ahead of the fronts.

Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean–atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air–sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air–sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontal-scale air–sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air–sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air–sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air–sea interaction research.

The structure and diurnal evolution of long-lived, eastward-propagating mesoscale convective vortices (MCVs) along typical summertime mei-yu fronts over the east China plains are investigated through composite analysis of a 30-day semi-idealized simulation. The simulation uses lateral boundary conditions that vary only diurnally in time using analyses of recurring MCV events during 1–10 July 2007. Hence, the behavior of convection and vorticity follows a closely repeating diurnal cycle for each day during the simulation. Assisted by the eastward extension of enhanced vorticity anomalies from the Sichuan basin, the incipient MCV forms in the morning hours over the immediate lee (east) of the central China mountain ranges (stage 1). From local afternoon to early evening, as the MCV moves over the plains, convection weakens in the daytime downward branch of the mountain–plains solenoid. This allows the upper-level and lower-level portions of the vortex to partially decouple, and for convection to shift to the east-southeast side of the surface vortex (stage 2). Immediately after sunset, convection reinvigorates above the low-level MCV center as a result of moistening and destabilization from a combination of radiative forcing and an intensified low-level jet. This intensifies the MCV to maturity (stage 3). The mature MCV eventually evolves into an occluding subsynoptic cyclone with strong convection across all sectors of the low-level vorticity center during the subsequent day’s morning hours along the east China coastal plains before it moves offshore (stage 4).

Over the course of his career, Fuqing Zhang drew vital new insights into the dynamics of meteorologically significant mesoscale gravity waves (MGWs), including their generation by unbalanced jet streaks, their interaction with fronts and organized precipitation, and their importance in midlatitude weather and predictability. Zhang was the first to deeply examine “spontaneous balance adjustment”—the process by which MGWs are continuously emitted as baroclinic growth drives the upper-level flow out of balance. Through his pioneering numerical model investigation of the large-amplitude MGW event of 4 January 1994, he additionally demonstrated the critical role of MGW–moist convection interaction in wave amplification. Zhang’s curiosity-turned-passion in atmospheric science covered a vast range of topics and led to the birth of new branches of research in mesoscale meteorology and numerical weather prediction. Yet, it was his earliest studies into midlatitude MGWs and their significant impacts on hazardous weather that first inspired him. Such MGWs serve as the focus of this review, wherein we seek to pay tribute to his groundbreaking contributions, review our current understanding, and highlight critical open science issues. Chief among such issues is the nature of MGW amplification through feedback with moist convection, which continues to elude a complete understanding. The pressing nature of this subject is underscored by the continued failure of operational numerical forecast models to adequately predict most large-amplitude MGW events. Further research into such issues therefore presents a valuable opportunity to improve the understanding and forecasting of this high-impact weather phenomenon, and in turn, to preserve the spirit of Zhang’s dedication to this subject.