Journal of Geophysical Research: Atmospheres最新文献

Unprecedented heatwaves accompanying severe droughts hit South Europe in May‒July 2022. From the interdisciplinary perspective, this study revealed that the extreme climate events can intensify European energy crisis through pushing up electricity demand and limiting renewable energy supply that makes up more than one-third of gross electricity consumption in the European Union (EU). The record-high electricity demand over South Europe in May‒July was closely associated with the long-lasting extreme heatwaves. On the other hand, the anomalous high-pressure system over Europe contributed to the severe heatwaves and the shortage of renewable power generation, for instance, through affecting the wind speed. The wind power generation over South Europe was reduced by the anomalous anticyclone which weakened low-tropospheric prevailing northwesterly wind. The results indicate a potential intensive conflict between the increasing power demand and the decreasing renewable power generation in Europe that are induced simultaneously by the extreme heatwaves. Therefore, it is suggested that the energy sectors' resilience to extreme climate events should be well built as the EU sets to significantly increase the renewable energy target to meet the goal of climate-neutral by 2050.

Atmospheric blocking is closely linked to the occurrence of extreme weather events. However, low-resolution Earth system models often underestimate the frequency of blocking, undermining confidence in future projections. In this study, we use the high-resolution Community Earth System Model (CESM-HR; 25 km atm and 10 km ocean) to show that CESM-HR reduces biases in atmospheric blocking for both winter and summer, particularly for events lasting longer than 10 days. This improvement is partly due to reduced sea surface temperature biases at higher resolution. Additionally, applying a bias correction to the 500 hPa geopotential height further enhances blocking frequency simulations, highlighting the crucial role of the mean state. Under the Representative Concentration Pathway 8.5 scenario, CESM-HR projects a decrease in wintertime blocking over regions such as the Euro-Atlantic and Chukchi-Alaska, consistent with previous studies. In contrast, summer blocking is expected to become more frequent and persistent, driven by weakened zonal winds. The blocking center shifts from historical locations over Scandinavia and eastern Russia to central Eurasia, significantly increasing blocking over the Ural region. Summer blocking frequency over the Scandinavia-Ural region may eventually surpass historical winter blocking over the Euro-Atlantic. This increase in summer blocking could exacerbate summer heatwaves in a warming climate, making severe heatwaves, like those observed recently, more common in the future.

Past North Atlantic abrupt cold events have the potential to provide insights into the future climatic response to the slowdown of the Atlantic meridional overturning circulation (AMOC). This study explores spring temperature changes on the southern Tibetan Plateau during the 8.2 ka cold event through simulations forced by North Atlantic freshwater hosing. Simulation results reveal anomalous warming on the southern Tibetan Plateau due to hosing-induced AMOC slowdown. This warming was primary caused by the increase of net solar flux and the presence of an anomalous warm anticyclone over the Tibetan Plateau. The enhanced net solar flux resulted from the decrease in snowfall, which led to a reduction in albedo. The snowfall was mainly reduced by the decrease in westerly moisture transport, resulting from weakened lower-level westerlies induced by AMOC-driven climate variabilities over the North Atlantic and tropical Indian Ocean. The warm anticyclone was induced by the anomalous vertical northerly shear over the southeastern Tibetan Plateau, which resulted from enhanced diabatic heating released by Asian monsoon rainfall. Asian monsoon rainfall increased due to anomalous lower-level cyclone over the tropical Indian Ocean. This anomalous cyclone was induced by the Mastuno-Gill response over the tropical Indian Ocean and amplified by a wave train propagating from the North Atlantic, both of which were resulted from the AMOC slowdown. The AMOC weakening is likely to play an important role in the recent and ongoing amplification of spring warming on the southern Tibetan Plateau.

Measuring the temperature of lightning is a fundamental part of understanding the evolution of the plasma channel, and it is also crucial to quantify its chemical and energetic impacts in the atmosphere. Nonetheless, due to complications that have both to do with the complexity of the source and required equipment, this has only been done in a few studies to date. Here we report on the design and implementation of an instrument to perform simultaneous, multi-band optical and radio observations of lightning, which aims to provide a fast and simple way to routinely measure its temperature. The primary instrument includes photometers to measure temperature and electric field sensors to identify lightning sub-processes. Data are analyzed in tandem with 2D and 3D lightning location information. To measure the temperature, the photometer array includes 3 channels equipped with narrowband filters (1 nm) centered at bright atomic oxygen lines in the near-infrared, and temperature is given from the relative intensity of optical emissions across the 3 channels. We found the average peak temperature of 44 negative cloud-to-ground lightning return strokes to be 17,600 K. Additionally, the peak temperature had no apparent correlation to the peak current. Comparisons between 777 nm observations from the ground and from space by the Geostationary Lightning Mapper (GLM) emphasize the picture that the instruments in these two vantage points tend to see different portions of the lightning flash. They also reveal that dart leaders play a key role in the interpretation of lightning observations from space.

Due to the impact of various climate systems, including the Asian Summer Monsoon (ASM) and westerlies, it is challenging to identify specific climate variables from the ice core δ¹⁸O records of the Tibetan Plateau (TP). Here, we disentangle the major climate modes by applying the singular spectrum analysis method to a δ¹⁸O time series in a shallow ice core retrieved from central TP. This method allows us to identify three major climate modes: the trend component, the El Niño Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). The trend component mainly reflects warming in the middle and upper troposphere over the south of the TP rather than the low land surface temperature changes. Furthermore, we found that water vapor δ¹⁸O in these upper atmospheric layers positively correlates with temperature. We propose that the up-and-over transport of such water vapor to the TP contributes to the temperature signal in the ice core δ¹⁸O record, which also helps understand the increasing trend in TP ice core δ¹⁸O records during the last deglaciation. ENSO and PDO affect the intensity of the ASM through two phases: warm phases tend to weaken the monsoon, leading to higher δ¹⁸O values, whereas cool phases strengthen the monsoon, resulting in lower δ¹⁸O values. Our findings suggest that multiple climate forcings can have their specific isotopic imprints in isotopic archives and highlight the importance of analyzing the integrated effects of diverse climatic drivers. The analyses also shed light on separating different climate signals from paleoclimate records.

Using radiosonde and ERA5 reanalysis data, we investigated the spatial and temporal variations in the tropopause and tropopause inversion layer (TIL) in the Antarctic region during the 2002 and 2019 southern sudden stratospheric warming (SSW) events and the mechanism involved. Following these SSW events there was a sharper TIL and a warmer and lower tropopause. After the onset of rapid warming during the major SSW event in 2002 and the minor SSW event in 2019, the magnitudes of these anomalies increased and reached their respective first peaks. The anomalies increased and peaked again following the early final breakdown of the polar vortex (i.e., the switch to summer circulation). During the SSW events and final breakdown of the polar vortex in 2002 and 2019, stratospheric residual mean circulation, which was driven by planetary waves, was the primary cause of these anomalies. The adiabatic heating of the anomalous downwelling residual mean circulation above the tropopause led to a decrease in the tropopause height and a warming of the tropopause temperature. It also led to increased static stability near the tropopause by dynamical heating, which represented a strengthened TIL. In addition, approximately 4% and 1.9% of the strengthening of the TIL in 2002 and 2019, respectively, can be attributed to the increased anticyclonic circulation at the tropopause.

Summer precipitation in the Southeast United States (SEUS) is classified into three categories—light, moderate, and heavy—using a Bayesian statistical model. We find that heavy rainfall events explain most of the interannual variance of summertime cumulative precipitation in the region, influencing regional hydroclimate patterns. For each rainfall category, we track the respective moisture sources using the 2-Layers Water Accounting Model driven by reanalysis data. We find that the Atlantic Ocean is the primary moisture source across all rainfall categories and becomes more important with increasing rainfall intensity. Conversely, land moisture contributions decrease with rainfall intensity. In the case of heavy rainfall, the moisture originating from the Atlantic Ocean is transported to the SEUS via a southeastward positioning of the North Atlantic Subtropical High (NASH) Western Ridge. The ample supply of moisture fluxes is further propelled by reduced surface pressure which promotes ascending motion in the SEUS. Analysis of mid-troposphere circulation indicates that this anomalous low-pressure might stem from wave trains originating over the North Pacific Ocean. Thus, heavy rainfall events involve increased Atlantic Ocean moisture fluxes directed by the NASH to the SEUS, which, in turn, is modulated by anomalous atmospheric circulation produced over the Pacific Ocean. Furthermore, we observe that the heavy and moderate (light) rainfall event frequency has increased (decreased) by five days throughout the 1970–2019 analysis period.

Refractory black carbon (rBC) is a primary aerosol species, produced through incomplete combustion, that absorbs sunlight and contributes to positive radiative forcing. The overall climate effect of rBC depends on its spatial distribution and atmospheric lifetime, both of which are impacted by the efficiency with which rBC is transported or removed by convective systems. These processes are poorly constrained by observations. It is especially interesting to investigate rBC transport efficiency through the Asian Summer Monsoon (ASM) since this meteorological pattern delivers vast quantities of boundary layer air from Asia, where rBC emissions are high to the upper troposphere/lower stratosphere (UT/LS) where the lifetime of rBC is expected to be long. Here, we present in situ observations of rBC made during the Asian Summer Monsoon Chemistry and Climate Impact Project of summer, 2022. We use observed relationships between rBC and CO in ASM outflow to show that rBC is removed nearly completely (>98%) from uplifted air and that rBC concentrations in ASM outflow are statistically indistinguishable from the UT/LS background. We compare observed rBC and CO concentrations to those expected based on two chemical transport models and find that the models reproduce CO to within a factor of 2 at all altitudes whereas rBC is overpredicted by a factor of 20–100 at altitudes associated with ASM outflow. We find that the rBC particles in recently convected air have thinner coatings than those found in the UTLS background, suggesting transport of a small number of rBC particles that are negligible for concentration.

We use trace gas profiles from Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) satellite measurements and the TOMCAT three-dimensional chemical transport model to diagnose stratospheric trends in O₃, HCl and N₂O. We find that the 2004–2021 ACE-FTS trends exhibit a clear lower stratosphere (LS) interhemispheric asymmetry with positive (negative) O₃ and N₂O (HCl) trends in the Southern Hemisphere (SH), and trends of opposite sign in the Northern Hemisphere (NH). The trends are larger for the shorter time period of 2004–2018. TOMCAT qualitatively agrees with the ACE-FTS LS N₂O and HCl trends, confirming that transport variability drives such patterns, despite some discrepancies for O₃. An additional model simulation is used to quantify the sensitivity of O₃ to long-term changes in chlorine and bromine and thus determine the chemical contribution of the spatially varying halogen trends to both observed and modeled O₃ trends. Overall, the recent dynamically induced variation in mid-latitude LS halogen abundance has, through chemical feedback, accentuated the O₃ recovery signal in the SH and delayed it in the NH, reflecting the enhanced dynamical variability of the NH. These results further indicate the complexities that exist in the search for the signal of ozone recovery in the mid-latitude LS.

The update to the deep convection parameterization in the energy exascale Earth system model version 2 (E3SMv2) makes the simulated quasi-biennial oscillation (QBO) have a shorter period than without the update when other tunable parameters the same since the update makes convection more intense but less frequent while leaving the time-mean convective heating tendency almost unchanged. Amplitudes of momentum fluxes of parameterized gravity waves (GWs) are intensified since they are determined by the square of convective heating tendency. In addition, stronger planetary waves are simulated in E3SMv2 with the convection scheme update, partially due to the tropospheric precipitation change. Furthermore, there is evidence that planetary waves are intensified in the stratosphere due to the dissipation of enhanced parameterized GWs. These factors are found to be responsible for modulating the QBO simulated in E3SMv2.