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The impacts of global warming on Meiyu-Baiu extreme rainfall and the associated mid-latitude synoptic-scale weather systems over the Eastern China (EC) and the Baiu rainband (Bu) regions in East Asia have been examined, based on simulations from the 20-km Meteorological Research Institute atmospheric general circulation model (MRI-AGCM3.2S). This model was demonstrated to give realistic Asian extreme rainfall, when compared with data from the Tropical Rainfall Measuring Mission (TRMM). Here we used a novel wave-selection algorithm based on the 300hPa wind, in order to identify upper-level propagating wave signals in conjunction with the occurrence of extreme precipitation in either EC or Bu. The same algorithm was applied for both the present (1979-2003) and future (2075-2099) climate simulations from the AGCM, so as to infer the impacts of global warming on the behavior of these systems. Results show robust decrease of intensity of systems influencing both Bu and EC in the future warmer climate. Their corresponding low-to-mid level circulation, as revealed by vertical velocity, temperature advection and sea-level pressure composites, was also found to be weakened. This is likely related to changes in the background circulation in future over the East Asian mid-latitude zone, such as the widespread increment of the seasonal mean static stability at 500 hPa. However, the wave-associated precipitation over these regions was enhanced in the future climate simulations. This can be attributed to more strong intensity rainfall, which increases as the background temperature in these regions warms, largely following the Clausius-Clapeyron relation. Therefore, changes of wave-related extreme precipitation in EC and Bu are mainly controlled by the thermodynamic effect; the latter appears to be much stronger than the potential impacts due to the slight weakening of these weather systems.

It is well known that rapid changes in tropical cyclone motion occur during interaction with extratropical waves. While the translation speed has received much attention in the published literature, acceleration has not. Using a large data sample of Atlantic tropical cyclones, we formally examine the composite synoptic-scale patterns associated with tangential and curvature components of their acceleration. During periods of rapid tangential acceleration, the composite tropical cyclone moves poleward between an upstream trough and downstream ridge of a developing extratropical wavepacket. The two systems subsequently merge in a manner that is consistent with extratropical transition. During rapid curvature acceleration, a prominent downstream ridge promotes recurvature of the tropical cyclone. In contrast, during rapid tangential or curvature deceleration, a ridge is located directly poleward of the tropical cyclone. Locally, this arrangement takes the form of a cyclone-anticyclone vortex pair somewhat akin to a dipole block. On average, the tangential acceleration peaks 18 hours prior to extratropical transition while the curvature acceleration peaks at recurvature. These findings confirm that rapid acceleration of tropical cyclones is mediated by interaction with extratropical baroclinic waves. Furthermore, The tails of the distribution of acceleration and translation speed show a robust reduction over the past 5 decades. We speculate that these trends may reflect the poleward shift and weakening of extratropical Rossby waves.

Droughts in the orography dominated mid-to-high elevation Himalaya have serious impact on the agrarian economy and biodiversity of the region. Temporally and spatially limited weather records from the Himalaya restrict our understanding on the socioeconomic impact of droughts in long-term perspective. In view of this, high-resolution proxies are required to develop long-term drought records from the data scarce Himalayan region. To fill this void, we developed February–May (FMAM) 4-month standardized precipitation-evapotranspiration index (SPEI4-May), a metric of drought, extending back to AD 1773 using ring-width chronology of Himalayan cedar (Cedrus deodara (Roxb.) G. Don) from Chakrata region of Garhwal, Uttarakhand, western Himalaya. The calibration model (1969–2016) captured 43% of the variance in the observed SPEI series. The SPEI reconstruction revealed high year-to-year and inter-decadal variation with 1774 (SPEI -3.11) and 1787 (SPEI +2.13) being the driest and the wettest years, respectively. The five year mean of reconstructed SPEI revealed droughts in 1818–1822, 1798–1802, 1813–1817, 1793–1797, 1958–1962 and pluvials in 1783–1787, 1838–1842, 1788–1792, 1933–1937, 1808–1812. A comparison of present SPEI reconstruction with other available tree-ring based precipitation and drought records from the western Himalayan region revealed synoptic scale features represented in our data. The findings underscore that a wide network of such large tree-ring based drought records from the data scarce Himalayan region should be very useful to understand the spatial distribution of droughts.

Wind and solar electricity generation is projected to expand substantially over the next several decades due both to rapid cost declines as well as regulation designed to achieve climate targets. With increasing reliance on wind and solar generation, future energy systems may be vulnerable to previously underappreciated synoptic-scale variations characterized by low wind and/or surface solar radiation. Here we use western North America as a case study region to investigate the historical meteorology of weekly-scale “droughts” in potential wind power, potential solar power and their compound occurrence. We also investigate the covariability between wind and solar droughts with potential stresses on energy demand due to temperature deviations away human comfort levels. We find that wind power drought weeks tend to occur in late summer and are characterized by a mid-level atmospheric ridge centered over British Columbia and high sea level pressure on the lee side of the Rockies. Solar power drought weeks tend to occur near winter solstice when the seasonal minimum in incoming solar radiation co-occurs with the tendency for mid-level troughs and low pressure systems over the U.S. southwest. Compound wind and solar power drought weeks consist of the aforementioned synoptic pattern associated with wind droughts occurring near winter solstice when the solar resource is at its seasonal minimum. We find that wind drought weeks are associated with high solar power (and vice versa) both seasonally and in terms of synoptic meteorology, which supports the notion that wind and solar power generation can play complementary roles in a diversified energy portfolio at synoptic spatiotemporal scales over Western North America.

The present study focuses on changes in synoptic-scale waves (SSWs) over the northwest Pacific (NWP) during boreal summer and compares them with intraseasonal oscillations (ISOs). The results show that the intensity of eddy kinetic energy (EKE)-based SSWs (2–10-day period) has greater climatological means and interannual variations than the 10–20-day and 30–60-day ISOs. Additionally, the distribution of the SSWs is similar to that of the 10–20-day ISO, which shows a greater amplitude in the monsoon trough region. Further investigation reveals that the EKE-based SSW intensity over the South China Sea-tropical NWP region, where the greatest SSW activity occurs, is positively correlated with central Pacific (CP) warming. The EKE-based SSW intensity tends to be higher in years of developing CP warming. The influences of the Indian Ocean sea surface temperature (SST) are limited and show a weak correlation with the EKE-based SSW intensity over the key region (5° N–20° N, 115° E–155° E). In turn, the SSWs have impacts on local SST anomalies, with active SSWs leading to SST cooling. CP warming induces a favorable environment for SSW origination over CP and SSW development in the monsoon trough region. Concurrent with the CP warming-associated easterly vertical wind shear, upward vertical motion and abundant moisture supply, significant synoptic-scale EKE conversion occurs over the key region, which indicates its dominant role in influencing the SSW intensity. The influences of CP warming on SSW intensity over the NWP demonstrate the potential of the El Nino Modoki index for predicting interannual variations in SSW intensity. Moreover, considering that influences related to SSWs bear a resemblance to the 10–20-day ISOs, future research should take into account the contributions of SSWs to avoid overestimating the impact from ISOs.

Spatial fields of outgoing long wave radiation (OLR) spectrum variance of the 1979-2016 austral summer months in southern Brazil are analyzed on different timescales: synoptic, sub-monthly, and intra-seasonal. Variability fields differ both in intensity and location and highlight dominant convection cycles in the study area. The results show that the amplitude of sub-monthly variability is greater than that of the other scales in the southeastern region of Brazil, while the synoptic scale prevails in the southern region. The above-mentioned scales show greater amplitudes over the western Pacific Ocean where the Madden-Julian Oscillation plays an important role, along the South Pacific Convergence Zone, and over the storm track areas over the South Pacific Ocean. The influence of spectral OLR scale interaction is also analyzed, associated to the occurrence of two intense rainfall events over the southeastern Brazil in the austral summers of 2011 and 2014 when the South Atlantic Convergence Zone (SACZ) was active in both events. The results obtained suggest that spectral OLR scale interaction takes place in such way that it strengthens the SACZ, since the spatial pattern footprints of the two to eight-day timescale (synoptic), 10 to 30-day timescale (sub-monthly) and 30 to 60-day timescale (intra-seasonal) overlap in the study region.

The present study investigates the factors that affect the year-to-year change in the intensity of synoptic-scale variability (SSV) over the tropical western North Pacific (TWNP) during boreal summer and fall. It is found that the intensity of the TWNP SSV in summer is associated with the equatorial central-eastern Pacific sea surface temperature (SST) anomalies that modulate the background fields through a Rossby wave response both in the source region and along the propagation path of the synoptic-scale disturbances. In fall, the intensity of the TWNP SSV is related to an SST anomaly pattern with opposite anomalies in the equatorial central Pacific and TWNP that modulates the background fields from the equatorial central Pacific to TWNP. However, the equatorial central Pacific SST anomalies alone fail to change the intensity of the TWNP SSV as the induced background field changes are limited to the equatorial central Pacific. It is shown that tropical western Pacific SST anomalies may induce notable changes in the intensity of the TWNP SSV. The relation of the TWNP SSV to the equatorial eastern Pacific SST is weak due to opposite SST anomalies in different types of years. Both seasonal mean and intraseasonal flows provide sources of barotropic energy for the change in the intensity of the TWNP synoptic-scale disturbances in summer. Seasonal mean flow has a main contribution to the barotropic energy conversion for the change in the intensity of the TWNP synoptic-scale disturbances in fall.

International audience; The input of mechanical power to the ocean due to the surface wind-stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from satellites observations. Its dependence on the coarse-graining range of the atmospheric and oceanic velocity in space from 0.5 o to 10 o and time from 6h to 40 days is determined. In the area of the Gulf Stream and the Kuroshio extensions the dependence of the power-input on space-time coarse-graining varies over tenfold for the coarse-graining considered. It decreases over twofold for the Gulf Stream extension and threefold for the Kuroshio extension, when the coarse-graining length-scale passes from a few degrees to 0.5 o at a temporal coarse-graining scale of a few days. It increases over threefold in the Gulf Stream and the Kuroshio extensions when the coarse-graining passes from several days to 6h at a spatial coarse-graining of a few degrees. The power input is found to increase monotonically with shorter coarse-graining in time. Its variation with coarse-graining in space has no definite sign. Results show that including the dynamics at scales below a few degrees reduces considerably the power input by air-sea interaction in regions of strongly non-linear ocean currents. When the ocean velocities are not considered in the shear calculation the power-input is considerably (up to threefold) increased. The dependence of the power input on coarse-graining in space and time is close to being multiplicatively separable in all regions and for most of the coarse-graining domain considered.

Variability of surface water masses of the Laptev and the East Siberian seas in August–September 2018 is studied using in situ and satellite data. In situ data were collected during the ARKTIKA-2018 expedition and then complemented with satellite-derived sea surface temperature (SST), salinity (SSS), sea surface height, wind speed, and sea ice concentration. The estimation of SSS fields is challenging in high-latitude regions, and the precision of soil moisture and ocean salinity (SMOS) SSS retrieval is improved by applying a threshold on SSS weekly error. For the first time in this region, the validity of DMI (Danish Meteorological Institute) SST and SMOS SSS products is thoroughly studied using ARKTIKA-2018 expedition continuous thermosalinograph measurements and conductivity–temperature–depth (CTD) casts. They are found to be adequate to describe large surface gradients in this region. Surface gradients and mixing of the river and the sea water in the ice-free and ice-covered areas are described with a special attention to the marginal ice zone at a synoptic scale. We suggest that the freshwater is pushed northward, close to the marginal ice zone (MIZ) and under the sea ice, which is confirmed by the oxygen isotope analysis. The SST-SSS diagram based on satellite estimates shows the possibility of investigating the surface water mass transformation at a synoptic scale and reveals the presence of river water on the shelf of the East Siberian Sea. The Ekman transport is calculated to better understand the pathway of surface water displacement on the shelf and beyond.

Haze episodes, characterised by extremely high aerosol concentrations and a reduction in visibility to less than 10 km, are a frequent occurrence in wintertime Beijing, despite policy interventions leading to an overall improvement in average annual air quality. The main drivers in the onset of haze episodes in wintertime Beijing are changing synoptic conditions, however, aerosol-radiation interactions and their feedback on boundary layer meteorology are thought to play an essential role in the intensity and longevity of haze episodes. In this study we use a coupled LES aerosol-radiation model (UCLALES-SALSA), which we have recently configured for the urban environment of Beijing. The model's high resolution and control over meteorological and aerosol conditions as well as atmospheric processes means we can directly elucidate and quantify the importance of specific aspects of the aerosol-radiation-meteorology feedback in the cumulative stage of Beijing haze. The main results presented here show (a) synoptic scale meteorology has a larger impact on boundary layer suppression than high aerosol concentrations and (b) unlike previous results obtained using regional models or observationally driven analyses, there is no threshold value at which the aerosol-radiation-meteorology feedback has a significant effect on PBL height. Rather, our work shows that for the aerosol composition in this case study, the role of the feedback effect in reducing PBL height increases under shallow boundary layer conditions and with increasing pollution loading in an almost linear fashion. This lack of a threshold found for our case study has important policy implications since interventions based on such a value will not result in large reductions associated with turning off the feedback process. Furthermore, this work directly shows that although the right synoptic changes are a prerequisite for pollution episodes in Beijing, local and regional emissions drive increases in aerosol load that are sufficient to initiate the aerosol feedback loop. This further drives suppression of the boundary layer top and promotes stagnation of air and increased stability, which can be self-sustaining. This results in higher surface aerosol concentrations for extended periods of time, with severe consequences for human health [Lv et al., Atmos. Environ., 2016, 124, 98-108; Wang et al., Atmos. Chem. Phys., 2019, 19(10), 6949-6967].

This study investigates the synoptic-scale flows associated with extreme rainfall systems over the Asian–Australian monsoon region (90°E–160°E and 12°S–27°N). On the basis of the statistics of the 17-year Precipitation Radar observations from Tropical Rainfall Measurement Mission, a total of 916 extreme systems, with both the horizontal size and maximum rainfall intensity exceeding the 99.9th percentiles of the tropical rainfall systems, are identified over this region. The synoptic wind pattern and rainfall distribution surrounding each system are classified into four major types: vortex, coastal, coastal with vortex, and none of above, with each accounting for 44%, 29%, 7%, and 20%, respectively. The vortex type occurs mainly over the off-equatorial areas in boreal summer. The coast-related types show significant seasonal variations in their occurrence, with high frequency in the Bay of Bengal in boreal summer and on the west side of Borneo and Sumatra in boreal winter. The none-of-the-above type occurs mostly over the open ocean, and in boreal winter, these events are mainly associated with the cold surge events. The environment analysis shows that coast-related extremes in the warm season are found within the areas where high total water vapor and low-level vertical wind shear occur frequently. Despite the different synoptic environments, these extremes show a similar internal structure, with broad stratiform and wide convective core (WCC) rain. Furthermore, the maximum rain rate is located mostly over the convective area, near the convective–stratiform boundary in the system. Our results highlight the critical role of the strength and direction of synoptic flows in the generation of extreme rainfall systems near coastal areas. With the enhancement of the low-level vertical wind shear and moisture by the synoptic flow, the coastal convection triggered diurnally has a higher chance to organize into mesoscale convective systems and hence a higher probability to produce extreme rainfall.

Fifty years ago, in 1970, open ocean eddies of the synoptic scale were experimentally found during the expedition within the Soviet Oceanographic Program Polygon–70 carried out in the subtropical zone of the North Atlantic. This turned out to be one of the most significant events in oceanology of the twentieth century. Unlike the previously known similar circulation structures that usually separated from large-scale jet streams, the newly discovered eddies were free, that is, they had essential inertial wave character. The velocities in such eddies often exceeded the mean mesoscale ocean current velocity. By analogy with cyclones and anticyclones in the atmosphere, free eddies of the open ocean, which have spatial and temporal scales similar to the atmospheric eddy formations, were called SYNOPTIC eddies. This term is used in the Russian literature. The history of the Polygon–70 experiment and its main results are described. Brief information is given about other major international and that of Shirshov Institute of Oceanology “polygon” programs for the study of mesoscale eddies.

In authors’ previous studies, the role of distinctive mean states in the western North Pacific (WNP) and North Atlantic (NA) in affecting tropical cyclone (TC) size was investigated. In this study, the effect of different synoptic scale perturbation types in the two basins on TC size is further investigated. Numerical model experiments with an initial synoptic wave train (SWT) and easterly wave (EW) environmental condition show that the former (latter) leads to the development of a larger (smaller) TC at an equilibrium state. The physical mechanism responsible for the difference is revealed. Compared with the EW, the surface wind speed of the SWT is larger. Therefore, the SWT generates more moisture in the outer region than EW through surface evaporation process. This favors the development of stronger convection in the outer region. The enhanced convection leads to greater diabatic heating, which lower the local sea level pressure (SLP), which changes surface radial pressure gradients in the inner-core and outer-core of the vortex. On the one hand, the falling of the SLP decreases the surface radial pressure gradient in the inner-core. As a result, the radial wind is weakened and then the radius of maximum wind (RMW) extends outwards after initial contraction. On the other hand, the lower SLP increases the radial pressure gradient in the outer region, strengthening the radial wind outside. The wind convergence favors stronger development of convection in the outer region. Through this positive feedback, inflow in the outer region is further strengthened. This accelerates local tangential wind and thus enlarges the TC size.

This is the first study concerning the assimilation of the INSAT-3D/3DR radiance in the Hurricane Weather Research and Forecasting (HWRF) model and assesses its credibility to improve track, intensity, and precipitation forecasts of tropical cyclone (TC) Titli that occurred over the Bay of Bengal (BoB), which showed rapid intensification (RI) and weakening through its lifetime. The inbuilt Gridpoint Statistical Interpolation (GSI) method is used with a 3-D variational (3DVAR) configuration. Three sets of numerical experiments such as control (CNTL) (no assimilation), Global Telecommunication System (GTS) (observations from GTS network), and INSAT-3D/3DR (INSAT-3D/3DR sounder radiance data and GTS observations) were carried out with seven different initializations. The radiance analysis reproduced the initial vortex and the prominent synoptic scale features associated with TC Titli. The average root-mean-square errors (RMSE) of the analysis were relatively lower in the INSAT-3D/3DR compared to the CNTL and GTS. The HWRF performance is enhanced for track simulation, with improvements in mean landfall position errors by 40%–70% and 26%–52% for the INSAT-3D/3DR and GTS runs, respectively. The assimilation of radiance data has a positive impact on the simulation of warm core and thermodynamic structures, which has led to a more accurate intensity prediction (by 30–47%) over the CNTL. The assimilation run could realistically simulate the RI and weakening phases of the TC. A cold dry air intrusion is also observed when associated with the weakening. The study highlights the need to incorporate INSAT-3D/3DR radiances for improved TC predictions over the BoB basin.

Environments of tornadic and non‐tornadic narrow cold frontal rainbands (NCFRs) are investigated using ERA‐Interim reanalyses for a sample of 114 events over the UK and Ireland (44 tornadic). The results offer a practical tool for prediction of the likelihood of tornadoes in these potentially high‐impact events. Of 22 analysed parameters, a bulk measure of shear vorticity, and the front‐normal wind component on the cold side of the front, yield the best discrimination between event classes, showing significantly larger values in tornadic events. A generalised measure of tornado probability (p(TN)) is obtained using the distribution of points within the two‐dimensional parameter space defined by these parameters. Synoptic situations commonly associated with tornadic NCFRs are identified and conceptual models describing the large‐scale evolution are developed. Most events are associated with developing secondary cyclones (i.e. frontal waves) along trailing cold fronts (≥54.5%), generally within west to south‐westerly large scale flow. Another significant class of event corresponds to situations where a strong mid‐ to upper‐level jet streak cuts across the front within an amplifying large‐scale flow pattern (upstream ridge building and downstream trough extension), generally within north‐westerly flow (27.3%). In frontal waves, tornadoes occurred relatively early in the wave's development and just down‐front of the wave centre, where rapid increases in p(TN) occurred as the wave amplified. In north‐westerly flow cases, tornadoes occurred along a well‐defined NCFR bulge close to where the mid‐ to upper‐level jet streak and an associated positive PV anomaly intersected the front. Analysis of a high‐tornadic subset of tornadic events (NCFRs producing ≥7 tornadoes) revealed an even stronger association with frontal waves (72.2% of cases), suggesting that the highest‐impact events are usually associated with secondary cyclogenesis. The possible relevance of identified environmental parameters to candidate vortex‐genesis and tornadogenesis mechanisms within NCFRs and quasi‐linear convective systems is discussed.

Severe local storm (SLS) activity is known to occur within specific thermodynamic and kinematic environments. These environments are commonly associated with key synoptic-scale features--including southerly Great Plains low-level jets, drylines, elevated mixed layers, and extratropical cyclones--that link the large-scale climate to SLS environments. This work analyzes spatiotemporal distributions of both the environmental parameters and synoptic-scale features in ERA5 reanalysis and in Community Atmosphere Model version 6 (CAM6) during 1980--2014 over North America. Compared to radiosondes, ERA5 successfully reproduces SLS environments, with strong spatiotemporal correlations and low biases, especially over the Great Plains. Both ERA5 and CAM6 reproduce the climatology of SLS environments over the central United States as well as its strong seasonal and diurnal cycles. ERA5 and CAM6 also reproduce the climatological occurrence of the synoptic-scale features, with the distribution pattern similar to that of SLS environments. Compared to ERA5, CAM6 exhibits a high bias in Convective Available Potential Energy over the eastern United States primarily due to a high bias in surface moisture, and to a lesser extent, storm-relative helicity due to enhanced low-level winds. Composite analysis indicates consistent synoptic anomaly patterns favorable for significant SLS environments over much of the eastern half of the United States in both ERA5 and CAM6, though the pattern differs for the southeastern United States. Overall, results indicate that both ERA5 and CAM6 are capable of reproducing SLS environments as well as the synoptic-scale features and transient events that generate them., 25 pages, 15 figures

Made available in DSpace on 2022-04-29T08:33:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-02-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Petrobras The South Atlantic Ocean (SAO) is characterized by the development of different types of synoptic scale cyclones, which affect the weather and climate of South America. For the first time, we obtained the long term trend of subtropical cyclones (SCs) climatology over the SAO through two ensembles under RCP8.5 scenario. Regional Climate Model version 4 (RegCM4) projections were driven by three global climate models (GCMs) from CMIP5. SCs are obtained by applying three algorithms: (1) for tracking all cyclones based on relative vorticity; (2) to describe the thermal structure of the cyclones; and (3) for selecting only the SCs. Ensemble means are able to capture the main SCs characteristics shown by ERA-Interim reanalysis in the present climate (1979–2005), such as the main region of formation (near the southeastern Brazilian coast), track density, seasonality (higher frequency in austral summer) and lifetime (~ 3 days). The RegCM4 and GCMs ensembles project a negative and statistically significant trend in the frequency of SCs in the future climate (2050–2080) near the southeastern coast of Brazil. The projections also indicate a greater negative trend of SCs than for all cyclones. This would be a response to the future increase in the mean sea level pressure (expansion of South Atlantic subtropical anticyclone), which in turn leads to a change in the low-level circulation acting to decrease the moisture transport to the main region of SCs development. Though the SCs frequency will decrease in the future, they are projected to be more intense due to stronger convective forcing. Departamento de Ciências Atmosféricas Instituto de Astronomia Geofísica e Ciências Atmosféricas Universidade de São Paulo, SP Instituto de Recursos Naturais Universidade Federal de Itajubá, MG Bauru Meteorological Centre (IPMET) Faculdade de Ciências Universidade Estadual Paulista (Unesp), SP Bauru Meteorological Centre (IPMET) Faculdade de Ciências Universidade Estadual Paulista (Unesp), SP

Meteorology and emissions play very important roles in the concentrations of air pollutants during severe haze/smog periods. This study compares the impacts of synoptic meteorology and nationwide/local emissions during high PM10 multi-event and non-event days in the Seoul Metropolitan Area (SMA). The multi-event and non-event cases were selected based on daily mean PM10 concentrations in Seoul from January 2014 to March 2019. The multi-event cases in spring and winter were closely associated with weak synoptic winds, while that in autumn was due to the strong winds at the rear side of a strong cold front, which induced the Asian dust event in northeastern China and Korea. The multi-event case in spring was found to be mainly due to series of migratory anticyclones, while winter case was due to the stagnant system after northerly winds. The surrounding low pressure systems as well as high pressure systems could be important to determine whether the synoptic systems would be stagnant or not. The fractional contributions of SMA emissions to the mean PM10 and PM2.5 concentrations were 24%-35% and 22%-35% for the multi-event cases, respectively. The contributions to the maximum PM10 and PM2.5 concentrations were larger than those to the mean concentrations by 16%-23% and 19%-26% for the multi-event cases, respectively.

This study used the dynamic synthetic analysis method to analyze the causes of attenuated heavy rainfall from a westward moving typhoon after landfall over Fujian by focusing on the genetic diagrgnosis of the strongest 12 h rainstorms based on typhoon data obtained from the Shanghai Typhoon Institute, precipitation data from Fujian Province, and NCEP reanalysis data from the United States. The results showed that: (1) the environmental field of the westward moving typhoon benefits the long-term maintenance of convergence in coastal areas, which provides synoptic scale forcing for rainstorm intensification along the southeastern coast; (2) the southwest jet in the boundary layer transports warm water vapor from low latitudes into the eastern circulation of typhoon; the water vapor peak occurs 6 h before the strongest rainstorm and can be used as a reference index to predict heavy rainstorms; (3) the high altitude strong divergence center is located at 100–150 hPa, and the strong convergence center is located near 925–950 hPa in the boundary layer, which is higher (lower) than the 200 hPa divergence layer (850 hPa convergence layer) commonly used in professional work; (4) warm and wet advection in the boundary layer transports unstable energy and weak cold air southward, strengthens the baroclinic pressure, increases the latent heat flux on the sea surface, and plays a significant role in triggering and developing mesoscale convective clouds along the southeast coast.

Heavy precipitation events are increasingly concerned because their significant contribution to annual precipitation in the Northwestern China, which might be related to invasion of summer monsoon moisture. It is interest whether or not the same is Jade Pass as being outside the control of the Asian summer monsoon. In this work, six heavy precipitation events were selected based on the 95 percentiles of the daily precipitation at the 12 weather stations around the Jade Pass from 1970–2000, with consideration of the influences of elevation. The event on June 19th, 2013 was chosen for a detailed examination due to the fact that the day has a large-scale precipitation as revealed by a gridded precipitation dataset over a large region. Using a Weather Research and Forecasting Model (WRF) simulation with high spatiotemporal resolution and in situ isotopic tracing (δ18O, δD), under a large-scale heavy precipitation event, this study provides ambitious view at the synoptic scale. A dramatic decrease in the δ18O, δD and deuterium (d)-excess of precipitation, very high relative humidity (98%), and reduced air temperature indicate that the precipitation was a result of long-distance-transported monsoon vapor. In addition, the slope of the local water meteoric line (LWML) of the precipitation for this event was very close to that of the global meteoric water line (GWML), indicating the source of moisture was from the ocean. Meanwhile, the WRF simulation confirms that the precipitation at the Jade Pass was not caused by local convection, but by summer monsoon. Both WRF simulation and isotopic tracing support the view that the monsoon moisture could invade Jade Pass at the synoptic scale and impact on precipitation, which need be further investigated.

Jets in the upper troposphere constitute a cornerstone of both synoptic meteorology and climate dynamics, providing a direct link between weather and midlatitude climate variability. Conventionally, jet variability is often inferred indirectly through the variability of geopotential or sea level pressure. As recent findings pointed to physical discrepancies of this interpretation for the Southern Hemisphere, this study presents a global overview of jet variability based on automated jet detections in the upper troposphere. Consistent with previous studies, most ocean basins are dominated by variability patterns comprising either a latitudinal shift of the jet or a so-called pulsing, a broadening/narrowing of the jet distribution without a change in the mean position. Whereas previous studies generally associate a mode of storm track variability with either shifting or pulsing, jet-based variability patterns frequently represent a transition from shifting to pulsing, or vice versa, across the respective ocean basin. In the Northern Hemisphere, jet variability is consistent with geopotential variability, confirming earlier analyses. In the Southern Hemisphere, however, the variability of geopotential and jets often indicates different modes of variability. Notable exceptions are the consistent dominant modes of jet and geopotential variability in the South Pacific and, to a lesser extent, the south Indian Ocean during winter, as well as the dominant modes in the South Atlantic and south Indian Ocean during summer. Finally, tropical variability is shown to modulate the jet distribution in the Northern Hemisphere, which is in line with previous results. The response in the Southern Hemispheric, however, is shown to be markedly different.

Nine tornado outbreaks (days with three or more tornadoes) have occurred in the United Kingdom from quasi-linear convective systems (QLCSs) in the 16 years between 2004 and 2019. Of the nine outbreaks, eight can be classified into two synoptic categories: type 1 and type 2. Synoptic categories are derived from the location of the parent extratropical cyclone and the orientation of the surface front associated with the QLCS. Environmental differences between the categories are assessed using ERA5 reanalysis data. Type 1 events are characterized by a confluent 500-hPa trough from the west, meridional cold front, strong cross-frontal wind veer (about 90°), cross-frontal temperature decrease of 2°–4°C, prefrontal 2-m dewpoint temperatures of 12°–14°C, a prefrontal low-level jet, and prefrontal 0–1- and 0–3-km bulk shears of 15 and 25 m s−1, respectively. In contrast, type 2 events are characterized by a diffluent 500-hPa trough from the northwest, zonal front, weaker cross-frontal wind veer (≤45°), much smaller cross-frontal temperature decrease, lower prefrontal 2-m dewpoint temperatures of 6°–10°C, and weaker prefrontal 0–1- and 0–3-km bulk shears of 10 and 15 m s−1, respectively. Analysis of the Met Office radar reflectivity mosaics revealed that narrow cold-frontal rainbands developed in all type 1 events and subsequently displayed precipitation core-and-gap structures. Conversely, type 2 events did not develop narrow cold-frontal rainbands, although precipitation cores developed sporadically within the wide cold-frontal rainband. Type 1 events produced tornadoes 2–4 h after core-and-gap development, whereas type 2 events produced tornadoes within 1 h of forming cores and gaps. All events produced tornadoes during a relatively short time period (1–3 h).

The present work aims at better understanding regional climate–aerosol interactions by studying the relationships between aerosols and synoptic atmospheric circulation over the Euro-Mediterranean region. Two 40-year simulations (1979–2018) have been carried out with version 6.3 of the Centre National de Recherches Météorologiques (National Centre for Meteorological Research) – Aire Limitée Adaptation dynamique Développement InterNational (CNRM-ALADIN) regional climate model, one using interactive aerosols and the other one without any aerosol. The simulation with aerosols has been evaluated in terms of different climate and aerosol parameters. This evaluation shows a good agreement between the model and observations, significant improvements compared to the previous model version and consequently the relevance of using this model for the study of climate–aerosol interactions over this region. A first attempt to explain the climate variability of aerosols is based on the use of the North Atlantic Oscillation (NAO) index. The latter explains a significant part of the interannual variability, notably in winter for the export of dust aerosols over the Atlantic Ocean and the eastern Mediterranean, and in summer for the positive anomalies of anthropogenic aerosols over western Europe. This index is however not sufficient to fully understand the variations of aerosols in this region, notably at daily scale. The use of “weather regimes”, namely persisting meteorological patterns, stable at synoptic scale for a few days, provides a relevant description of atmospheric circulation, which drives the emission, transport and deposition of aerosols. The four weather regimes usually defined in this area in winter and in summer bring significant information to answer this question. The blocking and NAO+ regimes are largely favourable to strong aerosol effects on shortwave surface radiation and near-surface temperature, either because of higher aerosol loads or because of weaker cloud fraction, which reinforces the direct aerosol effect. Inversely, the NAO− and Atlantic Ridge regimes are unfavourable to aerosol radiative effects, because of weaker aerosol concentrations and increased cloud cover. This study thus puts forward the strong dependence of aerosol loads on the synoptic circulation from interannual to daily scales and, as a consequence, the important modulation of the aerosol effects on shortwave surface radiation and near-surface temperature by atmospheric circulation. The role of cloud cover is essential in this modulation as shown by the use of weather regimes.

The role of synoptic-scale cyclones in the trends and variability of Arctic sea ice conditions has remained uncertain. In recognition, we conduct a systematic investigation of how sea-ice concentration (SIC) changes with cyclone passage, including all individual storms that pass over any part of the region's ice pack. For all seasons, especially summer and autumn, we find a pattern of higher ice concentration after a region is influenced by a cyclone compared to when it is not, primarily due to thermodynamic effects. During warm months, cyclones appear to slow the general day-to-day decline in concentration; in cold months, cyclones augment the day-to-day increase. These relationships are changing over time, with cyclone-associated concentration changes becoming less distinct from overall changes. Cyclone effects on ice divergence are spatially variable; computed fields are noisy. In summer, these dynamic effects of cyclone passage generally decrease SIC, but are outweighed by the thermodynamic effects (e.g., reductions in air temperature, shortwave radiation). In autumn, cyclone-associated concentration changes are not as easily explained by observed cyclone conditions. Key questions remain regarding the extent to which our findings are influenced by artifacts of surface melt and weather effects on the passive microwave retrievals.

A polar–subtropical jet superposition represents a dynamical and thermodynamic environment conducive to the production of high-impact weather. Prior work indicates that the synoptic-scale environments that support the development of North American jet superpositions vary depending on the case under consideration. This variability motivates an analysis of the range of synoptic–dynamic mechanisms that operate within a double-jet environment to produce North American jet superpositions. This study identifies North American jet superposition events during November–March 1979–2010 and subsequently classifies those events into three characteristic event types. “Polar dominant” events are those during which only the polar jet is characterized by a substantial excursion from its climatological latitude band, “subtropical dominant” events are those during which only the subtropical jet is characterized by a substantial excursion from its climatological latitude band, and “hybrid” events are those characterized by a mutual excursion of both jets from their respective climatological latitude bands. The analysis indicates that North American jet superposition events occur most often during November and December, and subtropical dominant events are the most frequent event type for all months considered. Composite analyses constructed for each event type reveal the consistent role that descent plays in restructuring the tropopause beneath the jet-entrance region prior to jet superposition. The composite analyses further show that surface cyclogenesis and widespread precipitation lead the development of subtropical dominant events and contribute to jet superposition via their associated divergent circulations and diabatic heating, whereas surface cyclogenesis and widespread precipitation tend to peak at the time of superposition and well downstream of polar dominant events.

Precipitation in high-mountain regions is characterized by a strong heterogeneity due to complex interaction between atmospheric circulation and steep topography, however, extremely rare network of high elevation stations hampers the adequate high resolution regional climate modeling. In this study we present new data of precipitation directly measured in high-mountain catchment, on the continental glacier (East Sayan Range, south of East Siberia) during the summer periods of 2015–2017 using automatic weather station. The precipitation record was compared with near located weather stations and ERA Interim and NCEP/NCAR reanalysis data. Precipitation mode similar to the glacier site was found at the stations located west and northwest, while ERA Interim and NCEP/NCAR reanalysis data underestimated the precipitation by 40 % and 70 %, respectively. Atmospheric circulation patterns in days with precipitation were analyzed by using mean sea level pressure, geopotential height at 700 and 500 hPa and classification of macro scale atmospheric processes of the Northern Hemisphere by Dzerdzeevskii. Summer precipitation was mostly associated with meridional southern group of large scale circulation the Northern Hemisphere, while at synoptic scale it basically fell in cyclonic (49 % of precipitation) and low-gradient cyclonic (30 %) baric fields. Six typical atmospheric circulation patterns over the East Sayan were identified for days with precipitation. The sources and atmospheric moisture transfer to the glacier was defined by using the HYSPLIT trajectory model. The most of summer precipitation (70 %) was related with western cyclones, while about 25 % of rainfalls (mainly of moderate to strong intensity) was originated from the south-east (Pacific monsoon influence).

Accurate simulation and prediction of intense precipitation events require better understanding of their physical mechanisms. This study uses Yaan—a place with regional maximum rainfall in central China—to investigate the cause and process of intense precipitation. Hourly rain gauge records and the new ERA5 reanalysis are used to characterize the evolution process of warm season intense regional rainfall events (RREs) in Yaan and its associated three-dimensional circulation. Results show that before the start of the Yaan intense RREs, moderate rainfall amount (frequency) appears northeast of the key region. The rainfall then moves southward in the following several hours along the eastern periphery of the Tibetan Plateau where it reaches peak. It then moves to and end up in the south and southeast Sichuan Basin. The progression of the RREs is found to be associated with a counter-clockwise rotation of anomalous surface winds associated with a developing mesoscale surface low-pressure center, which is further associated with the southeastward progression of a large-scale synoptic scale wave. The easterly phase of the winds in the counter-clockwise rotation causes upslope motion perpendicularly toward the terrain that leads to maximum rainfall. The findings illustrate how large-scale circulations, mesoscale systems, and specific topographic features interact to create the RREs evolution in Yaan.

Previous investigations have documented relationships between global-scale forcings and Northeast United States moisture conditions, yet the physical pathways from global-scale forcing to sub-regional moisture deficit or surplus are not well understood. This research uses eigenvector-based regionalization to confirm the existence of sub-regional moisture environments within the Northeast. Synoptic classification is used to derive daily weather types that impact these moisture environments, and evaluate the relationship between global and synoptic scales. The Palmer Drought Severity Index (PDSI) regionalization identifies 3 sub-regions across the Northeast with homogeneous moisture conditions including New England, the Eastern Great Lakes, and Mid-Atlantic Regions. All 3 regions’ PDSI conditions are predominantly associated with variations in precipitation, rather than thermal characteristics. The frequency of key precipitation-associated synoptic types can inform PDSI variability in the regions, where drier conditions are observed during growing seasons with a reduced frequency of precipitation-inducing synoptic types and an enhanced frequency of dry synoptic types. Variations in the frequencies of these synoptic types are partially explained by the phase of the various teleconnection patterns. In the case of the New England region, 14% of the variance in PDSI is explained by the frequency of synoptic type D2, and 12% of the variance in D2 is explained by variations in the Summer Atmospheric Drought Index. The New England region became significantly wetter (positive PDSI) from 1950 to 2016. This study suggests a partial cause of this trend is the increased and decreased frequencies of wet and dry synoptic types, respectively, both related to the phase of the Summer Atmospheric Drought Index.

South Asian monsoon exhibits multiscale spatiotemporal variability. Analyzing the nature and behavior of numerical weather forecast error associated with these space-time heterogeneities will eventually help in improving the models. We investigate the spatiotemporal error characteristics of the National Centre for Medium-Range Weather Forecasting (NCMRWF) Global Forecast System (NGFS) model over South Asian land and ocean separately. Although error grows with lead-time, it saturates within 3–5 days of forecast initiation. The saturated error is only about 15–25% higher than that of day-1, indicating that most of the error accumulates within first 24-h of forecast. Increase in error over oceanic regions is due to an increase in the area with high error at all precipitation ranges with large day-to-day variability. However, over land error growth is primarily confined at locations of high mean precipitation. Decomposition of error arising due to intensity and phase variations reveals that about 90% of it arises from the model’s inability to capture phase of precipitation at various timescales. We show that NGFS cannot capture synoptic scale variations ($$

In this study, power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China. Two heavy rainfall episodes are selected during the months of April−June 2008−15, which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances, respectively. Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea (SCS) at the quasi-biweekly scale with 15.1% variance contributions, and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastward-moving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastward-propagating anticyclonic anomaly from higher latitudes with 35.2% variance contribution. In contrast, the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasi-monthly scale with 23.2% variance contributions to the total rainfall variance, which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China, respectively. At the synoptic scale, it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3% variance contributions. In both cases, the lower-tropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions; it is the above synoptic, quasi-biweekly or quasi-monthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China.

Stable oxygen isotopes in precipitation contain meaningful environmental information on a synoptic scale and can be applied to diagnose hydrometeorological processes. A series of rainstorms occurred at the southern Tianshan Mountains during the period from May to June 2013, and the event-based precipitation was sampled along the mountain range from west to east. Based on δ18O values in precipitation samples as well as the corresponding meteorological parameters, the moisture transport paths during the sampling period were identified. In late-May (stage 1), isotopes in precipitation collected generally showed a depleting trend. In mid-June (stage 2), there was no coherent trend of isotopes in precipitation for these stations, and only isotope values in Aksu showed a continually depleting trend. Checking other meteorological proxies during the sampling period, the event-based precipitation isotopes sensitively reflected the moisture process. In central Asia, both the westerly and monsoon moisture can be delivered to cause extreme precipitation events, and the isotopic information provides an alternative tool to investigate the atmospheric processes.

Ozone pollution in China is influenced by meteorological processes on multiple scales. Using regression analysis and weather classification, we statistically assess the impacts of local and synoptic meteorology on daily variability in surface ozone in eastern China in summer during 2013–2018. In this period, summertime surface ozone in eastern China (20–42∘ N, 110–130∘ E) is among the highest in the world, with regional means of 73.1 and 114.7 µg m−3, respectively, in daily mean and daily maximum 8 h average. Through developing a multiple linear regression (MLR) model driven by local and synoptic weather factors, we establish a quantitative linkage between the daily mean ozone concentrations and meteorology in the study region. The meteorology described by the MLR can explain ∼43 % of the daily variability in summertime surface ozone across eastern China. Among local meteorological factors, relative humidity is the most influential variable in the center and south of eastern China, including the Yangtze River Delta and the Pearl River Delta regions, while temperature is the most influential variable in the north, covering the Beijing–Tianjin–Hebei region. To further examine the synoptic influence of weather conditions explicitly, six predominant synoptic weather patterns (SWPs) over eastern China in summer are objectively identified using the self-organizing map clustering technique. The six SWPs are formed under the integral influence of the East Asian summer monsoon, the western Pacific subtropical high, the Meiyu front, and the typhoon activities. On average, regionally, two SWPs bring about positive ozone anomalies (1.1 µg m−3 or 1.7 % and 2.7 µg m−3 or 4.6 %), when eastern China is under a weak cyclone system or under the prevailing southerly wind. The impact of SWPs on the daily variability in surface ozone varies largely within eastern China. The maximum impact can reach ±8 µg m−3 or ±16 % of the daily mean in some areas. A combination of the regression and the clustering approaches suggests a strong performance of the MLR in predicting the sensitivity of surface ozone in eastern China to the variation of synoptic weather. Our assessment highlights the importance of meteorology in modulating ozone pollution over China.

Satellite SAR images are an essential source of information on mesoscale and sub-mesoscale dynamic phenomena in the ocean with a resolution of 4–1000 m. They can be obtained irrespective of cloudin...

Synoptic meteorology is a branch of meteorology that uses synoptic weather observations and charts for the diagnosis, study, and forecasting of weather. Weather refers to the specific state of the atmosphere near the Earth’s surface during a short period of time. The spatial distribution of meteorological elements in the atmosphere can be represented by a variety of transient weather phenomena, which are caused by weather systems of different spatial and temporal scales. Weather is closely related to people’s life, and its development and evolution have always been the focus of atmospheric scientific research and operation. The development of synoptic meteorology is closely related to the development of observation systems, dynamical theories and numerical models. In China, observation networks have been built since the early 1950s. Up to now, a comprehensive meteorological observation system based on ground, air and space has been established. In particular, the development of a new generation of dense radar networks, the development of the Fengyun satellite series and the implementation of a series of large field experiments have brought our understanding of weather from large-scale environment to thermal dynamics, cloud microphysical structure and evolution characteristics of meso and micro-scale weather systems. The development of observation has also promoted the development of theory, numerical model and simulation. In the early days, China mainly used foreign numerical models. Lately, China has developed numerical model systems with independent intellectual property rights. Based on the results of high-resolution numerical simulations, in-depth understanding of the initiation and evolution mechanism and predictability of weather at different scales has been obtained. Synoptic meteorology has gradually changed from an initially independent development to a multidisciplinary approach, and the interaction between weather and the change of climate and environment has become a hot and frontier topic in atmospheric science. This paper reviews the important scientific and technological achievements made in China over the past 70 years in the fields of synoptic meteorology based on the literatures in China and abroad, from six aspects respectively including atmospheric dynamics, synoptic-scale weather, typhoon and tropical weather, severe convective weather, numerical weather prediction and data assimilation, weather and climate, atmospheric physics and atmospheric environment.

The Indo-Gangetic Plains (IGPs) are densely populated and agriculturally productive areas with strong interannual and intraseasonal rainfall variability. The intraseasonal rainfall variability over IGPs is due to variation in sea surface temperature in the equatorial Indian Ocean. The intense rainfall activity over IGPs is mainly convection-driven, which may be linked with Madden–Julian Oscillation (MJO). The threshold for exceptionally heavy rainfall during the period 1979–2012 is based on the analysis of heavy rainfall episodes (percentage departure in daily rainfall (PDR ≥ 700%). The thresholds for extremely strong MJO events show highest departure in MJO amplitude (PDA ≤ 200%). The present study aims to find the simultaneous relationship between 60 and 30-day cycles of rainfall variability over IGPs and linked with MJO amplitude variability for the period 1979–2012. Further, the 30-day cycle of rainfall variability is elaborately studied for different phases of MJO. The monthly and daily variability of IGPs rainfall as well as MJO amplitude is analysed to find important intense rainfall and MJO events. The results suggest that the monthly rainfall variability is caused due to synoptic scale weather systems like monsoon trough oscillation and corresponding pressure fluctuations over IGPs. The exceptionally intense rainfall activity during onset and retreat phases is observed to be associated with MJO phases 6–8. The intense rainfall activity during active-break phase is observed to be associated with MJO phases 3–5. The intense rainfall events during break phase are observed along foothills of Himalaya. The day-to-day rainfall variability is due to interaction between monsoon circulation and MJO.

Mesoscale convective systems (MCS) are difficult to forecast due to their inherent unpredictability and development from scales that are sub grid in typical global models. Here the impacts of model representation of convection on MCS structure and downstream forecast evolution are examined using two configurations of the Met Office Unified Model: the convection‐permitting (4.4‐km grid spacing) limited area Euro4 and convection‐parametrizing (25‐km grid spacing) Global configurations. MCSs are associated with a characteristic potential vorticity (PV) structure: a positive PV anomaly in the mid troposphere and negative PV anomalies above and to the side of it. Convection‐permitting models produce larger amplitude MCS PV anomalies than convection‐parametrizing models. These differences are shown to persist after coarse graining the output from a Euro4 simulation to the 25‐km grid spacing of the Global configuration for a case study from July 2012, and are largest in magnitude and extent in the upper troposphere. The effect of the poor representation of this PV structure by convection‐parametrizing models on forecasts is investigated by adding ‘MCS perturbations’, calculated as differences between the coarse‐grained Euro4 and the Global outputs, to five‐day Global configuration forecasts. Upper‐level MCS perturbations lead to greater forecast differences than those at middle levels, though using perturbations at all levels yields the greatest impact. For the first 36 hours differences grow on the convective scale related to the MCS and its influence on a developing UK cyclone, despite perturbation amplitudes initially reducing. Subsequently, differences grow rapidly onto the synoptic scale and by five days impact the entire northern hemisphere. MCS perturbations slow the eastward movement of Rossby waves due to ridge amplification. Thus, perturbing convection‐parametrizing models to include PV anomalies associated with MCSs produces synoptic‐scale forecast differences implying that the mis‐representation of the PV structures associated with MCSs are a potential source of forecast errors.

Ensemble forecasts are run operationally to determine forecast uncertainty arising from initial condition, model physics and boundary condition uncertainty. However, global configuration ensembles, which use a convection parametrization scheme, may miss uncertainty because of the misrepresentation of intense convection by such schemes. Here the impacts of the misrepresentation of Mesoscale Convective Systems (MCSs) on downstream ensemble forecast skill and evolution are determined for a case study. MCS perturbations (calculated from the difference between output from convection-parametrizing and convection-permitting Met Office model configurations) are added to six members of a global configuration ensemble created by downscaling forecasts from the global version of the Met Office Global and Regional Ensemble Prediction System. For the first 36 h differences grow on the convective scale related to the MCSs leading to systematic deepening of a developing UK cyclone, although there is damping of the perturbations found in root mean square difference calculations between the forecasts with and without the perturbations (particularly in mean sea level pressure). Subsequently, differences grow rapidly onto the synoptic scale and by five days impact the entire northern hemisphere. The MCS perturbations can have systematic effects on the ensemble forecasts (e.g. a systematic displacement of a downstream cyclone is found), but for this case, there is no discernible change in forecast skill as measured by root mean square error of the ensemble means and the effects of the MCS perturbations are smaller than those generated by the initial condition perturbations. The spread of the combined ensemble (the two ensembles with and without the MCS perturbations) is larger than that of the individual ensembles. Thus, perturbing convection-parametrizing models to include PV anomalies associated with MCSs represented in convection-permitting forecasts, or idealised representations of them, produces alternative realisations to those generated by initial condition perturbations and has the potential to be useful operationally.

The present study deals with the analysis of synoptic conditions that led to floods in the Sheonath river basin, which is the largest tributary of the Mahanadi river basin. To identify the flooding events a flood disaster database Dartmouth Flood Observatory is used and archives from this source were examined and flooding years were identified as 1994, 2005 and 2007. To verify the flood events derived from the database, data of streamflow is used, which is available at five locations in the river basin. The effect of flooding was observed in one of these five stations. The Synoptic conditions were constructed for the aforementioned flood events using geopotential height anomalies at 500 and 850 hPa pressure levels and Sea Level Pressure data. These conditions were studied three days before the flood event. It was observed that all the three flood events had a low-pressure system developing over the northwestern Bay of Bengal as the common feature. However, each synoptic system of each flood event has a different pathway of dissipation. After establishing the synoptic conditions that led to flooding, the ENSO (Sea Surface Temperature Anomalies-SSTA) and streamflow relationship are examined by the correlation approach. It was observed that the streamflow in this river basin is weakly correlated with SSTA. The Sheonath river basin doesn’t experience frequent flooding, nevertheless, it is essential to study the meteorological aspects of flooding that involve the evolution of pressure patterns, change in atmospheric moisture and occurrence of precipitation that will provide a better understanding of the atmospheric drivers of floods.

The article describes the technology of express analysis of images and videos, recorded by coastal video monitoring systems, developed by the authors. Its main feature is its ability to measure or evaluate in real time the signals of sea waves, sea level fluctuations, variations of underwater currents, etc., on video recordings or streaming video from coastal cameras. The real-time mode is achieved due to processing video information read not from files, but from the graphic memory of the screen. Measurements of sea signals can be carried out continuously for a long time, up to several days, with high sampling rate, up to 16 Hz, at several points of the observed water area simultaneously. This potentially allows studying the entire spectrum of wave movements, from short waves with periods of 0.3–0.5 s to multi-day fluctuations at the sea level of a synoptic scale. The paper provides examples of the use of this technology for analyzing images and videos obtained in the network of scientific video monitoring of the Peter the Great Bay (Sea of Japan/East Sea), deployed by the authors.

The extreme heat event that hit the Pacific Northwest (Oregon, Washington, southern British Columbia) at the end of June 2021 was 3 °C greater than the previous Seattle record of 39 °C, larger extremes of 49 °C were observed further inland that were 6 °C above previous record. There were hundreds of deaths over the region and loss of marine life and forests. At the large scale prior to the event, the polar vortex was split over the Arctic. A polar vortex instability center formed over the Bering Sea and then extended southward along the west coast of North America. The associated tropospheric trough (low geopotential heights) established a multi-day synoptic scale Omega Block (west-east oriented low/high/low geopotential heights) centered over the Pacific Northwest. Warming was sustained in the region due to subsidence/adiabatic heating and solar radiation, which were the main reasons for such large temperature extremes. The seasonal transition at the end of spring suggests the possibility of a southern excursion of a polar vortex/jet stream pair. Both the Pacific Northwest event in 2021 and the Siberian heatwave climax in June 2020 may be examples of crossing a critical state in large-scale atmospheric circulation variability.

High-resolution model simulations and radar observations are used to investigate the onset of vortex-genesis in a tornadic narrow cold-frontal rain band (NCFR). The timing and location of vortex-genesis was strongly constrained by a developing frontal wave, which tracked northeast across the United Kingdom and Ireland on 17 October 2011. In the simulations, vortices occurred preferentially during the early stages of wave development and just down-front of the wave centre, where large increases in vertical vorticity occurred in concert with decreases in the cross-frontal confluence. Vortex-genesis ceased as the frontal wave matured, due to the onset of frontal fracture. Two distinct scales of vortex-genesis are documented: primary vortex-genesis on the meso-γ-scale, and secondary vortex-genesis on the miso-scale. We show that horizontal shearing instability is the most likely vortex-genesis mechanism, consistent with previous theoretical work on the stability of vertical vortex strips in the presence of horizontal stretching deformation. Secondary vortices occurred along the braid regions between primary vortices where the shear zone became particularly narrow and intense. In the model, these vortices developed extremely rapidly (from small perturbations to maximum vertical vorticity in 5–15 min) and the strongest exhibited near-surface vertical vorticity maxima approaching 10−1 s−1. Vortices of both scales were associated with characteristic local perturbations in the NCFR and we show, by comparison with radar reflectivity data, that primary and secondary vortices were likely present in the real NCFR. Tornado reports were associated with small NCFR perturbations like those associated with the secondary vortices in the model simulations. Analysis of the sub-structure of individual simulated vortices suggests that tornado-genesis is most likely within a region of intense near-surface vertical vorticity stretching at the north or northwest flank of the secondary vortices. publishedVersion

Alberta Clippers (clippers) have long been associated with lake-effect snow (LES) events due to their frequent passage over the Great Lakes basin. However, not all clippers produce LES, and no research has inquired into which synoptic fields most influence LES formation. This study analyzes clippers during non-LES situations to further knowledge on which atmospheric variables most regulate LES development on the synoptic scale. As no such database currently exists, a clipper repository is developed using National Centers for Environmental Prediction Reanalysis data. The repository is then cross referenced with a previously developed LES repository to identify clippers responsible for LES. Composite synoptic-scale patterns were then constructed on the remaining non-LES clippers to identify synoptic conditions that ultimately inhibited LES formation. This analysis is supplemented by an assessment of lake surface conditions in each composite to evaluate how influential the lake characteristics were in the suppression of LES activity. In total, 51 non-LES clippers were identified, tracked, and separated into three composite map types that exhibited unique storm track and spatial characteristics. Permutation testing revealed that lake surface conditions were not significantly (p ≤ 0.05) different between LES and non-LES associated clippers implying the main LES inhibition factors were meteorological.