In the early 21st century, Southwest China (SWC) frequently experienced extreme droughts and severe haze pollution events. Although the meteorological causes of these extreme droughts have been widely investigated, previous studies have yet to understand the causes of haze pollution events over SWC. Moreover, the associations between winter atmospheric teleconnections during drought and haze pollution event across SWC has received negligible attention and therefore warrants investigation. This study examines the associations between the atmospheric teleconnections with respect to winter droughts and winter haze pollution over SWC. Our main conclusions are as follows. (1) Winter precipitation and winter haze days (WHD) over SWC had three major fluctuations from 1959 to 2016. (2) The atmospheric circulation pattern over the Eurasian (EU) continent associated with WHD over SWC resembled that of winter droughts over SWC, where both can be characterized by an EU teleconnection pattern. The Arctic Oscillation (AO) mainly induced the atmospheric circulation pattern over the EU continent that is associated with WHD over SWC. (3) The sea surface temperature (SST) and low circulation anomalies in the Pacific and north Atlantic associated with WHD were similar to those associated with winter droughts over SWC. La Nina events and negative phases of the North Atlantic Oscillation (NAO) may induce winter drought and increase the WHD over SWC. (4) Compared with winter drought over SWC, the variation in the WHD was more complex and the factors affecting WHD were more diverse, and winter drought and its related atmospheric circulations were important factors that induced haze pollution over SWC. Overall, this study not only fills a gap in the literature with respect to the associations between the atmospheric teleconnections of winter drought and winter haze pollution over SWC, but also provides an important scientific basis for the development of potential predictions of local monthly haze pollution, which improves the forecast accuracy of local short-term haze pollution and enriches the theoretical understanding of the meteorological causes of local haze pollution. (C) 2020 Elsevier B.V. All rights reserved.

In this study, the instability of extreme temperatures is defined as the degree of perturbation of the spatial and temporal distribution of extreme temperatures, which is to show the uncertainty of the intensity and occurrence of extreme temperatures in China. Based on identifying the extreme temperatures and by analyzing their variability, we refer to the entropy value in the entropy weight method to study the instability of extreme temperatures. The results show that TXx (annual maximum value of daily maximum temperature) and TNn (annual minimum value of daily minimum temperature) in China increased at 0.18 degrees C/10 year and 0.52 degrees C/10 year, respectively, from 1966 to 2015. The interannual data of TXx' occurrence (CTXx) and TNn' occurrence (CTNn), which are used to identify the timing of extreme temperatures, advance at 0.538 d/10 year and 1.02 d/10 year, respectively. In summary, extreme low-temperature changes are more sensitive to global warming. The results of extreme temperature instability show that the relative instability region of TXx is located in the middle and lower reaches of the Yangtze River basin, and the relative instability region of TNn is concentrated in the Yangtze River, Yellow River, Langtang River source area and parts of Tibet. The relative instability region of CTXx instability is distributed between 105 degrees E and 120 degrees E south of the 30 degrees N latitude line, while the distribution of CTNn instability region is more scattered; the TXx's instability intensity is higher than TNn's, and CTXx's instability intensity is higher than CTNn's. We further investigate the factors affecting extreme climate instability. We also find that the increase in mean temperature and the change in the intensity of the El Nino phenomenon has significant effects on extreme temperature instability.

In the hydrological year 2022/2023, the glaciers in the Qilian Mountains experienced unprecedented mass loss. The glacier -wide mass balance was -1,188 mm w.e., in contrast to -350 mm of average mass balance since 1990 over the Bailanghe Glacier No. 12 in the middle of Qilian Mountains. The temperature during 2022-2023 reached the highest value ever recorded, second only to 2022, while at the same time the precipitation amount was less compared to other year since 2000, which together led to the strongest glacier mass loss during 2022-2023. The atmospheric circulation analysis shows that the high temperature in the Qilian Mountains in 2023 was jointly caused by the Arctic air mass and East Asian monsoon.

Regional atmospheric circulation patterns affect haze pollution and they change in the warming climate. Here, the characteristics of atmospheric circulation anomalies conducive to extreme haze occurrence in China and their historical and future trends are examined based on surface observations, reanalysis data, aerosol source tagging technique, and multimodel intercomparison results. December 2016 and 2017 are identified as the worst months of haze pollution over northern and southern China, featuring weakened and strengthened prevailing winds, respectively. During 1980-2019, the atmospheric pattern similar to December 2016 decreased, while that similar to 2017 increased, suggesting that severe haze formation mechanism in eastern China has been shifting from causes of local accumulation to regional transport processes. In the future, climate change under the sustainable and intermediate development scenarios are the ideal paths to reduce haze in China, while high social vulnerability and radiative forcing would cause a severe damage to the environment.

Based on glacio-meteorological records, 7 years of in-situ mass balance data, and a temperature-index model, the long-term annual and seasonal mass balances of Shiyi Glacier in the northeast Tibetan Plateau (TP) were reconstructed from 1963/64 to 2016/17. Variations were then linked to local climatic and macroscale circulation changes. The model was calibrated based on in-situ mass balance data and was driven by daily air temperature and precipitation data recorded at nearby alpine meteorological stations. The results show that the reconstructed annual mass balance experienced an overall downward trend over the past 54 years, with a remarkably high mass loss rate during 1990/91-2016/17. Analysis of mass balance sensitivity and local climatic changes shows that the pronounced mass loss since the 1990s can be mainly attributed to cumulative positive temperature increases caused by air temperature increases and prolongation of the ablation season. From the perspective of macroscale circulation, the reconstructed annual mass balance values correlate well with zonal wind speeds (June to September) in the glacierized region. For the positive/negative phase of the annual mass balance, an inverse spatial pattern in relation to geopotential height change (low/high-pressure centres) and corresponding conversion of cyclonic/anti-cyclonic circulation were present in northern hemisphere mid-latitudes. Comparative analysis of existing long-term mass balance series over the TP indicates that asynchronous climatic changes in the different glacierized regions led to inconsistent interannual fluctuations in glacier mass balance.

Anthropogenic aerosols partially mask the greenhouse warming and cause the reduction in Asian summer monsoon precipitation and circulation. By decomposing the atmospheric change into the direct atmospheric response to radiative forcing and sea surface temperature (SST)-mediated change, the physical mechanisms for anthropogenic-aerosol-induced changes in the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM) are diagnosed. Using coupled and atmospheric general circulation models, this study shows that the aerosol-induced troposphere cooling over Asian land regions generates anomalous sinking motion between 20 degrees and 40 degrees N and weakens the EASM north of 20 degrees N without SST change. The decreased EASM precipitation and the attendant wind changes are largely due to this direct atmospheric response to radiative forcing, although the aerosol-induced North Pacific SST cooling also contributes. The SST-mediated change dominates the aerosol-induced SASM response, with contributions from both the north-south interhemispheric SST gradient and the local SST cooling pattern over the tropical Indian Ocean. Specifically, with large meridional gradient, the zonal-mean SST cooling pattern is most important for the Asian summer monsoon response to anthropogenic aerosol forcing, resulting in a reorganization of the regional meridional atmospheric overturning circulation. While uncertainty in aerosol radiative forcing has been emphasized in the literature, our results show that the intermodel spread is as large in the SST effect on summer monsoon rainfall, calling for more research into the ocean-atmosphere coupling.

The large uncertainty in estimating the global aerosol radiative forcing (ARF) is one of the major challenges the climate community faces for climate projection. While the global-mean ARF may affect global quantities such as surface temperature, its spatial distribution may result in local thermodynamical and, thus, dynamical changes. Future changes in aerosol emissions distribution could further modulate the atmospheric circulation. Here, the effects of the spatial distribution of the direct anthropogenic ARF are studied using an idealized global circulation model, forced by a range of estimated-ARF amplitudes, based on the Copernicus Atmosphere Monitoring Service data. The spatial distribution of the estimated-ARF is globally decomposed, and the effects of the different modes on the circulation are studied. The most dominant spatial distribution feature is the cooling of the Northern Hemisphere in comparison to the Southern Hemisphere. This induces a negative meridional temperature gradient around the equator, which modulates the mean fields in the tropics. The ITCZ weakens and shifts southward, and the Northern (Southern) Hemisphere Hadley cell strengthens (weakens). The localization of the ARF in the Northern Hemisphere midlatitudes shifts the subtropical jet poleward and strengthens both the eddy-driven jet and Ferrel cell, because of the weakening of high-latitude eddy fluxes. Finally, the larger aerosol concentration in Asia compared to North America results in an equatorial superrotating jet. Understanding the effects of the different modes on the general circulation may help elucidate the circulation's future response to the projected changes in ARF distribution.

An online coupled regional climate-chemistry model called RegCCMS is used to investigate the interactions between anthropogenic aerosols and the East Asian summer monsoon (EASM) over East Asia. The simulation results show that the mean aerosol loading and optical depth over the region are 17.87mg/m(2) and 0.25, respectively. Sulfate and black carbon (BC) account for approximately 61.2% and 7.8% of the total aerosols, respectively. The regional mean radiative forcing (RF) is approximately -3.64, -0.55, and +0.88W/m(2) at the top of the atmosphere for the total aerosol effect, the total aerosol direct effect, and the BC direct effect, respectively. The surface direct RF of BC accounts for approximately 31% of the total RF of all aerosols. Because of the total aerosol effect, both the energy budgets and air temperature are considerably reduced in the region with high aerosol loadings, leading to decreases in the land-ocean air temperature gradient in summer. The total column-absorbed solar radiation and surface air temperature decrease by 8.4W/m(2) and 0.31K, respectively. This cooling effect weakens horizontal and vertical atmospheric circulations over East Asia. The wind speed at 850hPa decreases by 0.18m/s, and the precipitation decreases by 0.29mm/d. The small responses of solar radiation, air temperature, and atmospheric circulations to the BC warming effect are opposite to those of the total aerosol effect. The BC-induced enhancement of atmospheric circulation can increase local floods in south China, while droughts in north China may worsen in response to the BC semidirect effect. The total aerosol effect is much more significant than the BC direct effect. The East Asian summer monsoon becomes weaker due to the total aerosol effect. However, this weakness could be partially offset by the BC warming effect. Sensitivity analyses further indicate that the influence of aerosols on the EASM might be more substantial in years when the southerlies or southwesterlies at 850hPa are weak compared with years when the winds are strong. Changes in the EASM can induce variations in the distribution and magnitude of aerosols. Aerosols in the lower troposphere over the region can increase by 3.07 and 1.04 mu g/m(3) due to the total aerosol effect and the BC warming effect, respectively.

Aerosols play important roles in the climate system and one of key issues is to quantitatively investigate their radiative forcing (RF). Anthropogenic RF due to black carbon (BC) and sulfate relative to 1850 s is therefore investigated in this study using an atmospheric general climate model (AGCM) and the aerosol dataset simulated by an atmospheric chemistry transport model. To calculate the instantaneous aerosol RF, meteorological fields are simulated, by the AGCM. The AGCM used in this study is developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The long-term three-dimensional black carbon and sulfate fields are taken from the simulation from the NCAR CAM Chemistry model. The dataset covers the period from the 1850s to 2100, and each 10-year set of results is averaged to produce the decadal mean. The decades of 1850-1859 and 2000-2009 represent the pre-industry (PI) and present day (PD), respectively. Cloud albedo forcing (CAF) is calculated from a diagnose scheme. The anthropogenic aerosols and the associated direct RF are estimated as the differences between a specified decade and the PI. The aerosol RF is obtained using a double radiation call method, in which the radiation scheme is called twice at each radiation time step. The GHGs, ozone, and solar forcing are fixed at present levels. The sea surface temperature and sea ice are from the prescribed climatology. This study shows that the present global annual mean anthropogenic sulfate all-sky direct and cloud albedo RF is estimated to be -0.37 and -0.98 W.m(-2), respectively; BC RF at all-sky top of atmosphere (TOA) and in the atmospheric column is calculated to be 0.16 and 0.47 W.m(-2), respectively. The present strongest RF due to above aerosols occurs in Eastern China, where sulfate direct and indirect RF exceeds -2.0 and -4.0 W.m(-2), respectively, and BC RF at TOA and column atmosphere is up to 2.0 and 5.0 W.m(-2), respectively. Furthermore, the estimated aerosol RF over East Asia still continuously increases and the maximum values are projected to occur in the 2010s. The projected stronger RF over Eastern China will even last until the 2030s. Thus, sulfate and BC from East Asia is projected to contribute more proportion to the global aerosol RF under future middle and high emission scenarios. The analysis in this study also indicates that the stronger summer atmospheric moisture over East Asia tends to intensify aerosol optical depth and direct clear-sky RF due to hydrophilic sulfate aerosol; moreover, cloud effects not only strengthen BC direct RF at all-sky TOA but also influence seasonal features of sulfate cloud albedo forcing over East Asia. Climatological characteristics over East Asia lead to the corresponding differences in aerosol RF compared to European and Northern American regions. The BC and sulfate RF and their possible time evolution are investigated in this paper. Many valuable results are obtained as mentioned above. However, the estimation of aerosol RF in the AGCM is determined by many factors and still faces large uncertainties. The first uncertainty arises from aerosol loading. Compared to surface measurements in Eastern China, the simulated BC and sulfate surface concentrations are much weaker and spatial correlations are also not high. These biases lead to our estimated present RF due to BC and sulfate likely lower than the actual values in East Asia. Other uncertainties are caused by simulated model meteorological fields and aerosol radiative parameterizations, such as atmospheric moisture, clouds and aerosol optical properties. So, it is suggested in our work that improvements of current climate models associated with aerosol processes and meteorological fields, which help to obtain more reasonable East Asian aerosol RF.