Atmospheric Science Letters最新文献

Sea breezes penetrate inland more than 100 km. Using 7 years of meteorological observations, we have identified 470 cases of deep inland (>100 km) penetrating sea breezes at the Savannah River Site between March and October (27% of days) of 2015–2021. We compared measurements of temperature, dewpoint temperature, incoming solar radiation, cloud fraction, and lightning on days of sea breeze initiation, the day after the sea breeze passage, and all other nonsea breeze (NSB) days for these 8 months over the 7 years. Days of sea breeze initiation were found to have lower cloud fraction, higher temperature, and greater incoming solar radiation compared with NSB days. Variations occurred by time of year as days after the sea breeze passage were found to have higher dewpoint temperature than NSB days in the spring. Lightning density measurements indicated that residual sea breeze conditions could drive earlier initiation of deep convection on days following the sea breeze than normal non sea breeze days. This data set provides a 7-year record of sea breezes which can be leveraged for future studies.

In recent years, there has been a notable increase in the consumption of fossil energy, leading to a significant rise in environmental pollution, particularly in China due to its rapid development. This has resulted in the frequent occurrence of large-scale fog and haze weather, highlighting the urgent need for environmental protection measures. To gain insights into the atmospheric conditions in China, an analysis was conducted on the wet deposition of polycyclic aromatic hydrocarbons (PAHs) in a remote region of Central South China from 2014 to 2017. The study revealed that the average concentrations and peak values of Ʃ₁₆PAHs in 2014 and 2015 were considerably higher than those observed in 2016 and 2017. Furthermore, it was found that five-ring PAH species were the predominant components during 2014 and 2015, indicating a shift in the main sources of PAHs. The peaks of Ʃ₁₆PAHs were predominantly detected in samples collected during light rain in the winter, specifically on days without heavy rainfall. This can be attributed to the absence of heavy rain, which would otherwise reduce the concentration of air pollutants. Consequently, contaminants accumulated in the air are easily enriched in rainwater. The concentrations of Ʃ₁₅Alkyl-PAHs also exhibited a significant correlation with the number of rainfall days. Notably, a much higher annual average concentration of Ʃ₁₅Alkyl-PAHs was observed in 2017, which experienced fewer rainfall days. Coal combustion, petroleum sources, and vehicular emissions accounted for 58%, 12%, and 30% of the PAHs in the air, respectively. Despite improvements in air quality in China since 2016, it is crucial to address the elevated concentrations of PAHs in the atmosphere, particularly under adverse meteorological conditions characterized by reduced rainfall.

Ensemble forecasting systems provide useful insight into the uncertainty in the prediction of the atmosphere. However, most analysis considers ensembles in latitude, longitude, and time. Here, the vertical aspects of the spread-skill relation are considered in a convective-scale ensemble via comparisons with radiosonde ascents. The specific focus is on the impact of stratifying the spread-skill relation by radiosonde drift. The drift acts as a proxy for the mobility of the atmosphere. The overall spread-skill relation shows the temperature has a better relation than the dewpoint. However, the total variance comparisons between model and observations indicates that the dewpoint is underspread throughout the atmosphere, whilst the temperature is overspread through the lower atmosphere and underspread aloft. This suggests that the model bias is influencing the spread-skill relation. Stratifying these results by the radiosonde drift indicates that the spread-skill relation, and model bias, for both temperature and dewpoint degrades with increased mobility. For the most mobile situations, the ensemble is underspread throughout the atmosphere. These results have implications for ensemble design in terms of the role and influence of the driving ensemble in regional systems as more mobile situations will have a stronger dependence on the lateral boundary conditions. Longer term it may also imply that different strategies are required depending on the mobility of the synoptic conditions. Therefore, it argues for more consideration of “on-demand” ensemble forecasting systems to allow a fairer representation of the uncertainty in different situations.

The significant socioeconomic impact of extreme flooding provides an incentive to improve our understanding of flood drivers. In this study, floods that occurred in northern Xinjiang from 2006 to 2011 were divided into three categories: rainstorm-type, warming-type, and mixed-type. These three types of floods primarily occurred from April to July, with most occurring in May and June. Through analysis of the atmospheric circulation evolution process of the three types of floods, it can be concluded that when a rainstorm-type flood occurs, northern Xinjiang is affected by an anomalous cyclone that forms in front of the strengthened trough over northern Europe. Anomalous cyclones provide favorable conditions for precipitation, which is conducive to rainstorm-type floods. As for the warming-type flood event, northern Xinjiang is affected by an anomalous anticyclone formed by the eastward movement of the blocking system in the middle of the Eurasian continent. Before the third type of mixed flood event occurred, northern Xinjiang was affected by an anomalous cyclone formed by energy propagation along the northwesterly wind belt. In addition, the energy propagating along the westerly wind belt along the southern road is conducive to the formation of a high-pressure ridge in southern Xinjiang. In addition, the analysis of temperature conditions indicates that the daily maximum temperature showed a warming trend from 5 to 1 day before the warming-type and mixed-type flood event occurred. These results provide valuable insights for flood risk management by identifying atmospheric circulation patterns and temperature conditions associated with floods in northern Xinjiang.

Tianjin, one of the four municipalities in China, is the eastern gate of the capital city of Beijing and is of great socioeconomic importance. When rainstorms attack Tianjin, urban flooding often occurs due to the dense river network, well-developed water system and flat terrain. In this study, the source analysis of water vapor in rainstorm processes in Tianjin during 2012–2020 is conducted based on the moisture source attribution method, and the PyTrajector and HYSPLIT softwares. Then, the evolution characteristics of rainstorms in Tianjin are investigated. The results show that the rainstorm water-vapor sources in Tianjin city can be roughly divided into four directions. The west and southwest directions are the main source, which contribute about 89% of the water vapor to the rainstorms. For heavy rainstorm, the water vapor from the southwest direction contributes about 60%, which is larger than that of rainstorm. The southwest direction is the main water vapor source of heavy rainstorm in Tianjin and has the main effect on the water vapor fluctuations during heavy rainstorm. For the more hazardous extraordinary rainstorm, the water vapor from the southwest direction occupies an even larger proportion (74.3%). The annual total rainstorm precipitation in Tianjin city in 2012 was more than that in common years, and this is mainly due to the anomalous increase of water vapor from the southwest direction. This result further indicates that the annual total rainstorm precipitation in Tianjin is mainly influenced by the water vapor from the southwest direction. This study reveals that the majority of rainstorm in Tianjin originates from the western and southwestern directions, but significant heavy rainstorm events in Tianjin are particularly influenced by moisture from the southwestern direction. This research holds crucial implications not only for meteorological and water resource management in Tianjin but also provides valuable insights for global urban flood risk studies.

Greece is characterized by a significant warming trend in recent decades, accompanied by increasing frequency, intensity, and duration of heat waves (HWs). A particularly devastating HW that affected the country was the late July/early August 2021 event (JA2021HW), which lasted for 9 days (July 28–August 5). Focusing on the hottest day of the event (August 3), the main characteristics of JA2021HW are presented in the current study, using model reanalysis data and up to 11-year observations derived from the dense network of ground-based weather stations operated by the Meteo Unit at the National Observatory of Athens (NOA). This analysis highlights the severity of JA2021HW, especially in the central and southernmost regions of Greece. Most importantly, the impact of the direct effect of anthropogenic greenhouse gases to the examined extreme event, in terms of intensity and probability of occurrence, is examined by employing a regional 31-member ensemble (ENS) modeling approach based on Weather Research and Forecasting (WRF) model, which is operationally used by NOA/Meteo. Firstly, WRF is validated under 7-day lead-time ENS simulations with current-state greenhouse gas (GHG) concentrations (GHG_2021 ENS), showing a robust model performance in replicating the JA2021HW's magnitude on August 3rd. Then, 7-day lead-time ENS simulations with the GHG concentrations reduced to the pre-industrial (1854) levels (GHG_1854 ENS) are performed and compared to the GHG_2021 ENS experiment. The results reveal a contribution of the immediate anthropogenic warming due to the increased GHG concentrations to the JA2021HW intensity in West and South continental and insular Greece, which can be important in the framework of the human health impacts of extreme temperatures. For the event's occurrence probability, no robust evidence of any change could be derived. These statements are partially constrained by the fact that only the direct GHG effect on the timescale of a few days was examined.

This study assesses the ability of six European seasonal forecast models to simulate the observed teleconnection between ENSO and tropical cyclones (TCs) over the North Atlantic. While the models generally capture the basin-wide observed link, its magnitude is overestimated in all forecast models compared to reanalysis. Furthermore, the ENSO-TC relationship in the Caribbean is poorly simulated. It is shown that incorrect forecasting of wind shear appears to affect the representation of the teleconnection in some models, however it is not a completely sufficient explanation for the overestimation of the link.

The vertical profile of the wind structure of translating tropical cyclones, including the associated azimuthal asymmetry, has been the subject of existing theoretical and observational studies using dropsondes. Most of these studies are based on data collected from relatively strong cyclones over the Atlantic. Here we explore the tropical cyclone boundary layer wind profile of mainly relatively weak landfalling cyclones near Hong Kong. We find that decaying tropical storms have a much larger mid- to low-level inflow angle than those that are intensifying or in steady-state. The inflow angles of intensifying, steady-state and decaying tropical storms converge towards the top of the boundary layer. The wind speed reduces through the boundary layer in a similar way in all three cases. The combination of these factors means that decaying tropical storms have stronger inflow than intensifying and steady-state ones. We attribute these local effects to remote enhanced surface friction over land when the storms are weakening.

This study investigates the adjustment of large-scale localized buoyancy anomalies in mid-latitude regions and the nonlinear evolution of associated condensation patterns in both adiabatic and moist-convective environments. This investigation is carried out utilizing the two-layer idealized moist-convective thermal rotating shallow water (mcTRSW) model. Our investigation reveals that the presence of a circular positive potential temperature anomaly in the lower layer initiates an anticyclonic high-pressure rotation, accompanied by a negative buoyancy anomaly in the upper layer, resulting in an anisotropic northeast–southwest tilted circulation of heat flux. The evolution of eddy heat fluxes, such as poleward heat flux, energy, and meridional elongation of the buoyancy field, heavily depends on the perturbation's strength, size, and vertical structure. The heatwave initiates atmospheric instability, leading to precipitation systems such as rain bands and asymmetric latent heat release due to moist convection in a diabatic environment. This creates a comma cloud pattern in the upper troposphere and a comma-shaped buoyancy anomaly in the lower layer, accompanied by the emission of inertia gravity waves. The southern and eastern sectors of the buoyancy anomaly show an upward flux, generating a stronger cross-equatorial flow and inertia-gravity waves in a southward and eastward direction. Furthermore, the simulations reveal a similar asymmetric pattern of total condensed liquid water content distribution, accompanied by the intensification of moist convection as rain bands. This intensification is more pronounced in barotropic structures than in baroclinic configurations with stagnant upper layers. This study highlights the importance of considering moist convection and its effects on atmospheric and oceanic flows in mid-latitude regions, as well as the role of buoyancy anomalies in generating heatwaves and precipitation patterns.

East Africa is highly vulnerable to extreme weather events, such as droughts and floods. Skillful seasonal forecasts exist for the October–November–December short rains, enabling informed decisions, whereas seasonal forecasts for the March–April–May (MAM) long rains have historically had low skill, limiting preparation capacity. Therefore, improved long rains prediction is a high priority and would contribute to climate change resilience in the region. Recent work has highlighted how lower-troposphere Congo zonal winds in MAM strongly impact regional moisture fluxes and the long rains total precipitation. We therefore approach long rains predictability through the predictability of the Congo winds. We analyze a set of hindcasts from a dynamical prediction system that is able to reproduce the long rains—Congo winds relationship in its individual ensemble members. Encouragingly, in observations, the strength of MAM Congo zonal winds and East Africa rainfall show substantial correlation with the MAM Atlantic (including North Atlantic Oscillation, NAO) and Indo-Pacific variability, suggestive of ocean influence and potential predictability. However, these features are replaced by different teleconnections in the hindcast ensemble mean fields. This is also true for NAO linkage to Congo winds, despite correct representation in individual members, and good skill in hindcasting the NAO itself. The net effect is strongly negative skill for the Congo winds. We explore statistical correction methods, including using the Congo zonal wind as an anchor index in a signal-to-noise calibration for the long rains. This is considered a demonstration of concept, for subsequent implementation using models with better Congo zonal wind skill. Indeed, the clear signals found in the Atlantic (including Mediterranean) and Indo-Pacific, studied here both in observations and a dynamical prediction system, motivate evaluation of these features across other prediction systems, and offer the prospect of improved physically-informed long rains dynamical predictions.