Journal of Geophysical Research: Atmospheres最新文献

Raindrop fall speed increases with raindrop size. Because larger raindrops fall through a given layer of the atmosphere more quickly compared to smaller raindrops, they spend less time in the layer and, therefore, have less time to be acted on and advected by the storm-relative winds. This results in hydrometeor size sorting which impacts the polarimetric radar variables such as differential reflectivity $��\left(Z_{�D�R�}\right)�$ and specific differential phase $��\left(K_{�D�P�}\right)�$. Previous work has shown a strong correlation between the mean storm-relative wind in the sorting layer and the separation between regions of enhanced $��Z_{�D�R�}�$ and $��K_{�D�P�}�$ at the bottom of the sorting layer. This study leverages this finding, along with a simple size sorting model, to construct radar-derived estimates of the storm-relative wind profile. The radar-derived “pseudo-hodographs” are well-correlated with the magnitude and direction of the corresponding storm-relative wind profiles. Further, these radar-derived estimates of the storm-relative winds are used to calculate estimates of shear and storm-relative helicity, which also exhibit a strong correlation.

Using the ERA5 reanalysis data, we analyzed the impacts of the Arctic stratospheric polar vortex weakening on Ural Blocking (UB). The results indicate that UB activities are suppressed following the weakening of the polar vortex. Specifically, the probability of UB is significantly reduced, with a maximum decrease of 30% observed around day 24 following the polar vortex weakening. The average life cycle of UB shortens by approximately one day. The amplitude of UB, as measured by the negative potential vorticity (PV) anomalies over the Urals, experiences a significant decrease, particularly with the presence of positive PV anomalies on the western side of Urals. Further analysis indicates that the suppression of UB following the weakened polar vortex is closely linked to both the equatorward horizontal transport of high-PV air over the Arctic across the dynamic tropopause, and the anomalous increase in static stability over the Urals resulting from a descent of the isentropic surface near the tropopause. Finally, we evaluate the relative roles of the polar vortex weakening and the negative phase of the Arctic Oscillation (AO) in suppressing the development of UB. Our analysis reveals that the impacts of the weak polar vortex on the suppression of UB are stronger and more long-lasting compared to the negative AO, suggesting that the impacts of the weakened polar vortex on UB cannot be simply explained by the AO response.

Meteoroids of sub-milligram sizes burn up high in the Earth's atmosphere and cause streaks of plasma trails detectable by meteor radars. The altitude at which these trails, or meteors, form depends on a number of factors including atmospheric density and the astronomical source populations from which these meteoroids originate. A previous study has shown that the altitude of these meteors is affected by long-term linear trends and the 11-year solar cycle related to changes in our atmosphere. In this work, we examine how shorter diurnal and seasonal variations in the altitude distribution of meteors are dependent on the geographical location at which the measurements are performed. We use meteoroid altitude data from 18 independent meteor radar stations at a broad range of latitudes and investigate whether there are local time (LT) and seasonal variations in the altitude of the peak meteor height, defined as the majority detection altitude of all meteors within a certain period, which differ from those expected purely from the variation in the visibility of their astronomical source. We find a consistent LT and seasonal response for the Northern Hemisphere locations regardless of latitude. However, the Southern Hemisphere locations exhibit much greater LT and seasonal variation. In particular, we find a complex response in the four stations located within the Southern Andes region, which indicates that the strong dynamical atmospheric activity, such as the gravity waves prevalent here, disrupts, and masks the seasonality and dependence on the astronomical sources.

Under global warming, the convective heating over the western Pacific (WP) has exhibited a significantly intensifying trend during the boreal spring, while the surface air temperatures in the Middle East (ME) have increased more rapidly than those in other tropical regions. Are these climate phenomena of the two regions physically connected? If yes, what are the responsible dynamical mechanisms involved? Utilizing the ERA5 reanalysis data and model simulations, this study reveals a significant seesaw variation in the convection and temperature trends between WP and ME. When convective heating intensifies over the WP, the ME tends to be drier and hotter during the spring, and vice versa. A further investigation indicates that the enhanced WP convective heating can induce anticyclonic circulation anomalies in the upper and middle troposphere over the Iranian and Tibetan plateaus. These anomalous high pressures extend westward, exhibiting a barotropic structure, which leads to stronger sinking motions, reduced cloud cover, and increased surface solar radiation over the ME. Consequently, these conditions result in drier and hotter soils and an increase in heatwave days in the ME. This study provides useful information for enhancing our understanding of the role of tropical WP climate change in influencing the upstream climate conditions with a focus on the ME.

Accurately predicting the volatilities of molecules in aerosols is challenging but crucial for understanding the atmospheric effects of aerosols. We used negative and positive ion electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to identify differences in the molecular compositions of gas and particle phase samples from urban atmosphere. We aimed to identify intrinsic chemical parameters that determine and predict the organic aerosol volatility. We found higher average molecular weights, carbon mass percentages, and double bond equivalents (DBE) but lower average O/C ratios and oxygen mass percentages in the particle phase than the gas phase. We identified DBE, which display a significant negative correlation with volatility, as a key parameter. We proposed to improve the previous model for predicting organic aerosol volatility by incorporating DBE as a new variant; and the result showed that this subsequently improved the accuracy of the model, particularly for compounds with minimal or no heteroatoms (0–2) such as hydrocarbons (CH). The revised model offers insights into the contributions of DBE, carbon, nitrogen, oxygen, and sulfur atoms to the volatilities of diverse organic molecules in aerosols and could be applied to improve our understanding of the phase distributions of volatile organic compounds in the ambient air.

Stratospheric transit time distributions (age-of-air spectra) are estimated using time series of satellite water vapor (H₂O) measurements from the Microwave Limb Sounder over 2004 to 2021 assuming stationary transport. Latitude-altitude dependent spectra are derived from correlations of interannual H₂O anomalies with respect to the tropical tropopause source region, fitted with an inverse Gaussian distribution function. The reconstructions accurately capture interannual H₂O variability in the “tropical pipe” and near-global lower stratosphere, regions of relatively fast transport (∼1–2 years) in the Brewer-Dobson circulation. The calculations provide novel observational estimates of the corresponding “short transit-time” part of the age spectrum in these regions, including the mode. However, the H₂O results do not constrain the longer transit-time “tail” of the age spectra, and the mean age of air and spectral widths are systematically underestimated compared to other data. We compare observational results with parallel calculations applied to the WACCM chemistry-climate model and the CLaMS chemistry-transport model, and additionally evaluate the method in CLaMS by comparing with spectra from idealized pulse tracers. Because the age spectra accurately capture H₂O interannual variations originating from the tropical tropopause, they can be used to identify “other” sources of variability in the lower stratosphere, and we use these calculations to quantify H₂O anomalies in the Southern Hemisphere linked to the Australian New Years fires in early 2020 and the Hunga volcanic eruption in 2022.

Unraveling plausible future rainfall change (ΔPr) patterns is crucial for tailoring societies' responses to climate change-induced hazards. This study compares rainfall projections from the regionally coupled ocean model (ROM) and its atmospheric component, the regional atmospheric model REMO, over Central Equatorial Africa (CEA). Both models are forced by the Earth system model MPI-ESM-LR following the Representative Concentration Pathway 8.5. Results reveal increased rainfall across most of CEA, with ROM projecting more widespread and intensified wetting than REMO, although REMO produces more precipitation under future conditions, underscoring the influence of historical biases on REMO's projection. Examining processes underpinning changes unveils strong controls of sea and land surface temperature changes in ΔPr differences between the two models. Specifically, ROM mitigates warming more over the Atlantic than over CEA landmass compared to REMO, inducing enhancement of the Congo Basin cell and increased precipitable water content through specific humidity, affecting deep convection. Both models project enhanced Sahel and Kalahari thermal lows, with ROM better depicting the Kalahari low's warmer nature than the Sahel low. The resulting temperature gradients strengthen the northern and southern shallow meridional Hadley overturning circulation. ROM simulates the wetter conditions than REMO, attributed to its weaker northern Hadley Cell, which restricts the likelihood of northward moisture divergence toward the Sahel. Additionally, differences in mid-tropospheric moisture convergence differentiate between ROM and REMO's wetness relative to the historical period and under future conditions. ROM projections are more plausible, in association with the reliability of its added value under the historical climate and mechanisms underlying Δpr.

Compound hazards involving tropical cyclones and extreme heat (“TC-heat”) have rarely been examined in prior research. Peripheral subsidence associated with cyclones can warm an area to varying degrees, depending on the cyclone's strength and position. Meanwhile, the peripheral airflow also overwhelmed the land-sea breeze circulation system in coastal cities and favored downwind urbanized heat advection on the Southern China coastline. Here, we systematically applied ERA5 global reanalysis data, local surface-level observations, MODIS-based land-cover data and HYSPLIT backward trajectories to evaluate how the position of distant TCs may divert the monsoon system and foster the surface heat advection from upwind urban agglomerate amplifying air temperature in downwind coastline. The analysis suggests when a distant TC is situated in a favorable area (the vicinity of Taiwan and Luzon Strait) at roughly 500–1,250 km to the east of Hong Kong, it forms a unique meteorological condition which allows the surface heat transport from the Greater Bay Area to Hong Kong, reflecting that regional build-up of heat could be an important mechanism for producing local heat extremes.

In the Atacama Desert, one of the driest places on Earth, the persistent absence of water preserves the record of environmental change, making it an invaluable proxy for studying the evolution of life on Earth. Due to the scarcity of in situ measurements and difficulties in satellite remote sensing, information on precipitation characteristics is limited even for the present climate. Guided by a case study of extreme precipitation in late January 2019, we derive a conceptual framework to explain how moisture transport combined with the diurnal circulation produces rainfall. We found a synoptic-scale weather pattern that we named “moist northerlies” (MNs) based on surface observations, reanalysis, and high-resolution simulation. During an MN event, moisture transport from the tropical Pacific is observed in the lower free-troposphere in the forefront of an 850 hPa low-pressure offshore Atacama. The diurnal circulation along the western Andean slope transports the moist free tropospheric air above the marine boundary layer inland, triggering clouds and storms. A trough over the southeast Pacific and a southward displaced Bolivian High seem to drive the MNs dynamically. Long-term observations (1960–2020) show that most of the rainy days in the hyperarid core (75%) are triggered by MNs, occurring more frequently during neutral/La Niña conditions and phases 7-8-1 of the Madden-Julian oscillation (MJO). A trend analysis (1991–2020) reveals that summer water vapor along the west coast of South America has increased rapidly due to the MNs, enhancing summer rainfall in Atacama. The implications of climate change and other climate variability modes are discussed.

The spring-high temperature events (SHTE) over northeast China (NEC) and the related local atmospheric factors including cloud cover, radiation flux, and soil moisture exhibited an increased interannual variability after 1992/93. Correlation analyses reveal that both the North Atlantic quadrupole sea surface temperature anomalies (NAQSSTA) and the spring Siberian snow depth (SSSD) had a stronger linkage with SHTE since the early 1990s. Additionally, the interannual variability of SSSD also showed an interdecadal increase, which is a key factor in the changes of interannual variability of SHTE. Further analyses showed that the NAQSSTA could excite Rossby wave via increasing low-level atmospheric baroclinicity during 1993–2017. One branch of the wave trains propagated eastward and the other branch propagated northeastward through the Siberian high latitudes, which eventually reached NEC together and resulted in local anomalous anticyclonic circulation and sinking motion. The latter branch could contribute to the low geopotential height and cyclonic anomalies over the Siberian high latitudes, which further favored the increase of snow depth there. Subsequently, the positive snow anomalies facilitate the more occurrences of SHTE by exacerbating the meridional thickness gradient between the polar region and mid-latitudes and then limiting the Arctic cold air to invade into the south. Meanwhile, the positive polar-Eurasian pattern (POL) associated with higher SSSD could guide the Rossby wave train originating from the North Atlantic to propagate northeastward, which is consistent with the SHTE-related wave train path after 1992/93. Model results further reproduce the physical processes that linking the NAQSSTA with SHTE.