Journal of Geophysical Research: Atmospheres最新文献

This study examines the influence of shallow cumulus clouds on the excessive summertime heat in the Houston-Galveston metropolitan area, a coastal urban area in the warm Southeast United States. Specifically, it aims to improve our understanding of how both the clouds and the relatively cool, moist afternoon sea breeze impact the Urban Heat Island (UHI) and Heat Index (HI). During the warm season, the afternoon sea breeze phenomenon in this coastal city acts as a natural air conditioner for city residents, facilitating the dispersion of moisture, heat, and pollutants. To investigate the relationship among urbanization, clouds, and land-sea interactions, we conducted cloud- and urban-resolving simulations at a 900 m grid resolution and perform simulation scenarios aiming to isolate urbanization, clouds and land-sea circulations. Results show that urbanization correlates with the presence of shallow cumulus clouds, higher cloud bases, and increased cloud duration over the Galveston-Houston region compared to rural areas. These urban clouds benefit from the enhanced moist static energy that is favored by intensifying vertical mixing and moisture flux convergence. Urbanization raises the mean HI while mitigating its afternoon HI high. We found that the urban circulation dome overwhelms the sensitivity of the sea breeze to the urbanization. Instead, the influence of urbanization on cloud enhancement emerges as a crucial pathway responsible for reducing the high afternoon HI values. Moreover, uncertainties in SSTs are closely linked to the sensitivities of land-sea circulations, which in turn modulate UHI and HI.

The study on the characteristic and the parameterization of cloud droplet effective radius (r_e) is important for the optimization of warm cloud microphysical schemes in numerical models. Based on numerical simulations combined with the four aircraft observations of stratiform warm clouds in Jiangxi, China, this work investigated their microphysical properties, focusing on the evolutionary pattern and the parameterization of r_e, as well as the correlation between r_e and the number concentration (N_c) of cloud droplet and liquid water path (LWP). It is found that there is a negative correlation between r_e and N_c, and the rate of the decrease could be increased by 2–4 times with a strengthening of collision-coalescence process. What's more, the direct introduction of collision-coalescence is conducted based on the existing r_e parameterization schemes, and the results show that it can perform well in most of collision-coalescence intensities. It is also found that LWP is positively correlated with r_e when r_e is less than 12 μm, after which the relationship changes to a negative correlation due to the impact of rainfall intensity.

The historical global temperature record is an essential data product for quantifying the variability and change of the Earth system. In recent years, better characterization of observational uncertainty in global and hemispheric trends has become available, but the methodologies are not necessarily applicable to analyses at smaller regional areas, or monthly or seasonal means, where station sparsity and other systematic issues contribute to greater uncertainty. This study presents a gridded uncertainty ensemble of historical surface temperature anomalies from the Goddard Institute for Space Studies (GISS) Surface Temperature (GISTEMP) product. This ensemble characterizes the complex spatial and temporal correlation structure of uncertainty, enabling better uncertainty propagation for climate and applied science in applications of historical temperature products at spatial scales from global to regional and temporal scales from centennial to monthly. This work details the methodology for generating the uncertainty ensemble, presents key statistics of the uncertainty evolution over space and time, and provides best practices for using the uncertainty ensemble in future studies. Summary statistics from the uncertainty ensemble agree well with the previous GISTEMP global uncertainty assessment, providing confidence in both.

We report observations of non-methane volatile organic compounds (VOCs) at an urban site in Guangzhou, China, and analyzed the seasonally contrasting composition, diurnal patterns, and sources of VOCs driven by the Asian Monsoon weather. In July, southerly low-level jets and coastal recirculation coincided with a large enhancement of light alkanes and alkenes along with methyl tert-butyl ether from urban transportation. Diurnal profiles of propanal and methyl vinyl ketone followed isoprene and O₃, suggesting a common biogenic origin and fast photochemical production. In October, dominating northerly descending dry air mass led to a 10-fold increase in acetone and methyl ethyl ketone, suggesting a large free tropospheric reservoir and abundant precursors of these ketones. Enhanced source apportionment aided by a comprehensive emission speciation data set identified five classes of VOCs from a much larger pool of local and regional emission sources than reported from previous studies. Seasonal transition of VOCs offers unique natural constraint for the chemistry and sources of VOCs in this and other similar regions, which warrants future long term measurements and advanced modeling and analysis.

In this study, the performance of 24 Coupled Model Intercomparison Project Phase 6 (CMIP6) models in simulating the dynamic processes of Arctic sea ice concentration (SIC)- and El Niño-Southern Oscillation (ENSO)- forced teleconnection during winter is subjectively and objectively evaluated. The Arctic SIC-forced teleconnection is associated with a warm Arctic-cold Eurasian pattern of surface temperature (T2m), a low Arctic-high Eurasian pattern of sea level pressure (SLP), and a southeastward propagating wave-train originating from Arctic in the upper troposphere. The ENSO-forced teleconnection is associated with a poleward propagating wave-train originating from tropical Pacific in the upper troposphere, a low North Pacific-high Arctic pattern of SLP, and a cold North Pacific-warm Greenland pattern of T2m. The metrics of Taylor skill scores and Distance between indices of simulation and observation (DISO) are used to objectively and quantitatively evaluate the performance of models. The results of subjective and objective evaluation are essentially consistent. The CanESM5, MPI-ESM1-2-HR, EC-Earth3, and MRI-ESM2-0 models have the best performance in simulating the Arctic SIC-forced teleconnection. The CESM2, ACCESS-CM2, NESM3, NorESM2-MM, CAS-ESM2-0, MRI-ESM2-0 models have the best performance in simulating the ENSO-forced teleconnection. The two best-performing multi-model ensembles well reproduce the dynamic processes of the Arctic SIC- and ENSO- forced teleconnection. The diversity of model performance is attributed to the different skills of different models in simulating the interannual variability of Arctic SIC, the anomalous deep warm high over the Barents-Kara Seas, the interannual variability of tropical Pacific SSTs, and the wave number of poleward propagating Rossby waves.

This study investigates thermal circulations on Reunion Island (21°07’S 55°32’E), focusing on the complex terrain of the region. Observations from the BIO-MAÏDO campaign, along with 2 days of high-resolution simulation using the MesoNH model, were analyzed to understand the thermally-driven mechanisms. This simulation was conducted with a horizontal resolution of 100 m and employed a vertically stretched grid, achieving a resolution of 1 m at the lowest levels. Two distinct wind regimes were identified, characterized by katabatic flows prevailing within a 30 m thick layer during nighttime, and an anabatic flow manifesting within a layer spanning from 150 to 200 m during the daytime. The simulation was confirmed through validation with surface measurements, and thus enabling a detailed study of thermal breeze circulations. Results reveal that the intensity of trade winds significantly influences the development of thermal circulations. Complex layered structures in the atmosphere were also identified. At an intensity of 7 m s⁻¹, trade winds impede the development of thermal circulations atop the slope, and result in the emergence of a convergence zone between local and regional circulations. The analysis of the breeze establishment period indicates that the katabatic flow stabilizes in 35 min, quicker than the anabatic flow, which takes 110 min. Momentum and heat budget analysis provide insights into the primary drivers of thermal circulations: buoyancy acceleration, influenced by local surface heating during anabatic flow onset, and local surface cooling during katabatic flow onset.

Volatile organic compounds (VOCs) are important atmospheric species that regulate the formation of both ozone and secondary organic aerosol. Compared with continental environments, VOC species, concentration and origins in marine environments were much less understood. Here, we conducted a 2-month VOCs measurement using a proton-transfer-reaction mass spectrometer during the cruise of DongFangHong III research vessel over the eastern oceanic areas of China in winter 2019. According to the location of DongFangHong III, we divided our cruise into five regions: Qingdao port (QD), Zhoushan port (ZS), Bohai Sea (BHS), Yellow Sea (YS), and East China Sea (ECS). For most individual VOCs, their concentration exhibited the trend of ZS > QD > BHS > YS > ECS. A decreasing tendency was also found when the measurement location was progressively farther away from the coastline. Further, we performed Positive Matrix Factorization and retrieved five distinct VOC sources, including shipping emission, DongFangHong III emission, regional background, aged transport, and port and nearshore emission. Contributions of these five factors varied depending on the location, influenced by emission, atmospheric oxidation, and meteorological conditions. In addition, the inland anthropogenic sources were found to have a larger contribution than oceanic ones. Overall, by conducting in situ measurements of VOCs and source apportionment, this study complements the lack of information on the speciation, abundance, and sources of VOCs in the marine environment of China.

The eastward displacement of Southwest Vortices (SWVs) profoundly impacts the precipitation in the middle and lower reaches of the Yangtze River Basin (YRB) in summer. At present, the feedback mechanism of latent heating on the persistent eastward movement of SWVs under the influence of the orographic effect of the second-step terrain in China remains unclear. Therefore, this study focused on clarifying the relationship between orographic effects and the mechanisms governing the persistent eastward movements of SWVs, as well as the feedback effect of latent heating on the eastward-moving SWVs. In this study, it is revealed that discontinuous maintenance of closed vortex circulation occurs when eastward-moving SWVs pass over the second-step terrain region. Specifically, eastward-moving SWVs first experience dissolution on the windward side, followed by substantial reconstruction of closed vortex circulation on the leeward side when passing over the second-step terrain region. Moreover, the reconstruction of closed vortex circulation on the leeward side is closely associated with the feedback effect of latent heating, and the microphysical property of cold clouds identified during the vortex intensification determines the dual-peak feature observed in the vertical constitution of the total latent heating, which is related to two major phase-transition processes: the condensation of water vapor into liquid-phase hydrometeors (LCP_vapor) process and the desublimation of water vapor into ice-phase hydrometeors (LSP_vapor) process. From a potential vorticity (PV) perspective, latent heating promotes the genesis of PV anomalies, which accordingly facilitates the maintenance of a positive “vorticity tower” (i.e., total budget of vorticity) via the tilting effect and the horizontal advection effect of local vorticity. Further sensitivity experiments of latent heating indicated that latent heating associated with the LCP_vapor process fulfills a more important role in sustaining the positive “vorticity tower” than does that associated with the LSP_vapor process during the vortex intensification.

Arctic cyclones are key drivers of sea ice and ocean variability. During the 2019–2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, joint observations of the coupled air-ice-ocean system were collected at multiple spatial scales. Here, we present observations of a strong mid-winter cyclone that impacted the MOSAiC site as it drifted in the central Arctic pack ice. The sea ice dynamical response showed spatial structure at the scale of the evolving and translating cyclonic wind field. Internal ice stress and ocean stress play significant roles, resulting in timing offsets between the atmospheric forcing and the ice response and post-cyclone inertial ringing in the ice and ocean. Ice motion in response to the wind field then forces the upper ocean currents through frictional drag. The strongest impacts to the sea ice and ocean from the passing cyclone occur as a result of the surface impacts of a strong atmospheric low-level jet (LLJ) behind the trailing cold front and changing wind directions between the warm-sector LLJ and post cold-frontal LLJ. Impacts of the cyclone are prolonged through the coupled ice-ocean inertial response. Local impacts of the approximately 120 km wide LLJ occur over a 12 hr period or less and at scales of a kilometer to a few tens of kilometers, meaning that these impacts occur at combined smaller spatial scales and faster time scales than most satellite observations and coupled Earth system models can resolve.

Dry- and wet-bulb temperature (T_d and T_w) are usually to define heatwaves (HWs) which have been enhanced under anthropogenic climate change (ACC) and urbanization. However, responses of various types of HWs (i.e., dry HWs, only high T_d; humid HWs, only high T_w; hybrid HWs, both high T_d and T_w; total HWs, high T_d or T_w), to ACC and urbanization remain unknown. In this study, both observations and simulations show significantly increasing occurrence probability of total HWs over China during 1971–2020, whereas this increase is mainly reflected in hybrid HWs, followed by dry HWs and humid HWs. 68.2%–93.0% of the observed increases in the above four types of HWs can be attributed to ACC; on the other hand, urbanization tends to suppress humid HWs but enhance dry HWs, as a result of contributing to the increase of hybrid HWs by 10.9%. Under future ACC, total HWs are projected to be more frequent as expected, which is mainly sourced from the increasing hybrid HWs because dry/humid HWs are projected to be steady/downward. As a consequence, urban population exposure to ACC-induced total HWs would remarkably increase to 83.55 billion person-days by the 2090s, 89.5% of which can be attributed to hybrid HWs. Urbanization would amplify this population exposure of ACC-induced hybrid HWs from 74.79 billion person-days to 110.9 billion person-days. Our results underscore the importance of improving understanding of hybrid HWs in urban areas and developing targeted adaptation planning on a warmer planet.