Guoxiong Wu - Academia.edu (original) (raw)

Papers by Guoxiong Wu

Atmospheric and Oceanic Science Letters, Jun 2, 2017

High computational performance is extremely important for climate system models, especially in ul... more High computational performance is extremely important for climate system models, especially in ultra-high-resolution model development. In this study, the computational performance of the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL) was comprehensively evaluated on Tianhe-2, which was the world's top-ranked supercomputer from June 2013 to May 2016. The standardized Atmospheric Model Inter-comparison Project (AMIP) type of experiment was carried out that focused on the computational performance of each node as well as the simulation year per day (SYPD), the running cost speedup, and the scalability of the FAMIL. The results indicated that (1) based on five indexes (CPU usage, percentage of CPU kernel mode that occupies CPU time and of message passing waiting time (CPU_SW), code vectorization (VEC), average of Gflops (Gflops_ AVE), and peak of Gflops (Gflops_PK)), FAMIL shows excellent computational performance on every Tianhe-2 computing node; (2) considering SYPD and the cost speedup of FAMIL systematically, the optimal Message Passing Interface (MPI) numbers of processors (MNPs) choice appears when FAMIL use 384 and 1536 MNPs for C96 (100 km) and C384 (25 km), respectively; and (3) FAMIL shows positive scalability with increased threads to drive the model. Considering the fast network speed and acceleration card in the MIC architecture on Tianhe-2, there is still significant room to improve the computational performance of FAMIL. 摘要 高性能计算指标对于气候模式的发展，尤其是高分辨率气候模式的发展至关重要。本文系统 性的评估了IAP／LASG新一代有限体积大气环流模式FAMIL在Tianhe-2超算平台上的计算性能。 通过标准的AMIP试验，本文重点评估FAMIL在每个节点的高性能指标、每天所积分的模式年 (SYPD)、计算成本加速比、可扩展性五方面的性能。结果表明：1) FAMIL在CPU使用率、CPU 节点间信息传输等待时间、代码向量化、Gflops平均值、Gflops峰值五个方面表现出优异性 能。2) 综合考虑SYPD和计算成本加速比，对于C96(100km)和C384(25km)水平分辨率的FAMIL 积分，最优进程使用数(MNPs)分别为384和1536。3) FAMIL具有良好的可扩展性，并且随着 Tianhe-2网络传输速度的提升及MIC加速的使用，FAMIL的计算新能可以进一步得到提升。

Journal of Climate, Nov 15, 2022

An extreme drought occurred over Southeast China (SEC) in August 2019. We demonstrate synergistic... more An extreme drought occurred over Southeast China (SEC) in August 2019. We demonstrate synergistic effects of midlatitude and tropical circulation on this extreme event and highlight the impacts of the coupling and locking of two cyclones at different latitudes, which are otherwise ignored. We propose the relaying roles of the Tibetan Plateau (TP) and western North Pacific in connection with the tropical convection and SEC precipitation. The equivalent-barotropic anticyclone over the TP and lower-tropospheric cyclone over the western North Pacific both resulted from the positive Indian Ocean dipole and El Niño Modoki. The equivalent-barotropic cyclone over Northeast China originated from the dispersion of Rossby waves upstream along the subtropical waveguide associated with the North Atlantic tripole sea surface temperature anomaly pattern and the Rossby wave response to the TP precipitation deficiency. Further, they jointly contributed to this drought by inducing strong northerly wind anomalies in the entire troposphere over East China. These anomalous northerly winds led to decreased warm moisture from the south and substantial sinking motions, which inhibited the occurrence of the SEC local convection and precipitation. The SEC precipitation is closely related to convection over the Maritime Continent from a climate perspective. This relationship is verified by observations, linear baroclinic model experiments, and general circulation model sensitivity experiments with and without the TP, in which precipitation anomalies over the southern TP and Philippine Sea play important bridge roles. The results will advance the prediction of the SEC extreme drought events.

npj climate and atmospheric science, Mar 28, 2022

The Tibetan Plateau (TP) is known as one of the most sensitive regions to climate change, and it ... more The Tibetan Plateau (TP) is known as one of the most sensitive regions to climate change, and it has experienced accelerated warming in recent decades. However, to what degree the TP warming amplification relates to remote forcing such as sea ice loss in the Arctic sea ice remains unclear. Here, we found that the decline of sea ice concentration over the Barents-Kara Sea (BKS) could account for 18-32% of the winter warming over the TP by comparing observational data and ensemble experiments from an atmospheric general circulation model. The reduced BKS sea ice and resultant upward turbulent heat fluxes can intensify a Rossby wave train propagating equatorward to the TP. As a result, the enhanced southwesterlies towards the TP strengthen the warm advection over most parts of the TP and lead to TP warming. In addition, an atmospheric teleconnection between the Arctic and the TP also exists in the interannual variability. That is, a tripole mode in air temperature, with warm centers in the Arctic and TP but a cold center in the mid-high latitudes of the Eurasian continent in between. Our results imply that the BKS sea ice loss could intensify such a tripole mode and thus enhancing the winter TP warming.

The effects of horizontal resolution on the simulation of tropical cyclones were studied using th... more The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences FGOALS-f3 climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Both the low-resolution (approximately 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (approximately 25 km resolution) FGOALS-f3 (FGOALS-f3-H) model were used to achieve the standard Tier1 experiment required by the HighResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with the exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated with the observation firstly. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. The seasonal cycles of the number of tropical cyclones increased by about 50% at the higher resolution and better matched the observed values in the peak month, especially in the eastern Pacific, northern Atlantic, southern Indian and southern Pacific oceans. The simulated variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins on the interannual timescale. The characteristics of the tropical cyclones (e.g., the average lifetime, the wind-pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the Madden-Julian oscillation from FGOALS-f3-H contributed to the realistic simulation of tropical cyclones. The genesis

Advances in Atmospheric Sciences, Jan 12, 2022

The influences of interannual surface potential vorticity forcing over the Tibetan Plateau (TP) o... more The influences of interannual surface potential vorticity forcing over the Tibetan Plateau (TP) on East Asian summer rainfall (EASR) and upper-level circulation are explored in this study. The results show that the interannual EASR and associated circulations are closely related to the surface potential vorticity negative uniform leading mode (PVNUM) over the TP. When the PVNUM is in the positive phase, more rainfall occurs in the Yangtze River valley, South Korea, Japan, and part of northern China, less rainfall occurs in southern China, and vice versa. A possible mechanism by which PVNUM affects EASR is proposed. Unstable air induced by the positive phase of PVNUM could stimulate significant upward motion and a lower-level anomalous cyclone over the TP. As a result, a dipole heating mode with anomalous cooling over the southwestern TP and anomalous heating over the southeastern TP is generated. Sensitivity experiment results regarding this dipole heating mode indicate that anomalous cooling over the southwestern TP leads to local and northeastern Asian negative height anomalies, while anomalous heating over the southeastern TP leads to local positive height anomalies. These results greatly resemble the realistic circulation pattern associated with EASR. Further analysis indicates that the anomalous water vapor transport associated with this anomalous circulation pattern is responsible for the anomalous EASR. Consequently, changes in surface potential vorticity forcing over the TP can induce changes in EASR.

Atmospheric and Oceanic Science Letters, Mar 18, 2019

It is important to be able to characterize the thermal conditions over the equatorial Indian Ocea... more It is important to be able to characterize the thermal conditions over the equatorial Indian Ocean for both weather forecasting and climate prediction. This study compared the equatorial eastern Indian Ocean (EEIO) temperature and relative humidity profiles from three reanalysis products (JRA-55, MERRA2, and FGOALS-f2) with shipboard global positioning system (GPS) sounding measurements obtained during the Eastern Indian Ocean Open Cruise in spring 2018. The FGOALS-f2 reanalysis product is based on the initialization module of a sub-seasonal to seasonal prediction system with a nudging-based data assimilation method. The results indicated that: (1) both JRA-55 and MERRA2 were reliable in characterizing the temperature profile from 850 to 600 hPa, with a maximum deviation of about <0.5°C. Both datasets showed a large negative deviation below 825 hPa, with a maximum bias of about 2°C at 1000 hPa and 1.5°C at 900 hPa, respectively. (2) JRA-55 showed good performance in characterizing the relative humidity profile above 850 hPa, with a maximum deviation of < 8%, while it showed much wetter conditions below 850 hPa. MERRA2 overestimated the relative humidity in the middle to lower troposphere, with a maximum deviation of about 15% at 925 hPa. (3) The FGOALS-f2 reanalysis product more accurately reproduced the temperature profile in the marine atmospheric boundary layer over the EEIO than that in JRA-55 and MERRA2, but showed much wetter conditions than the GPS sounding observations, with a maximum deviation of up to 20% at 600 hPa. Future applications of GPS sounding datasets are discussed.

National Science Review, Feb 6, 2020

Journal of Climate, Mar 1, 2023

As the highest and most extensive plateau in the world, the Tibetan Plateau (TP) has remarkable e... more As the highest and most extensive plateau in the world, the Tibetan Plateau (TP) has remarkable effects on global climate. Through coupled model sensitivity experiments with and without the TP, we show that the TP can affect the Arctic directly via orography-forced stationary waves, and influence the Antarctic indirectly via stationary waves forced by sea surface temperature (SST) in the Indian Ocean. These far-reaching impacts occur mainly in wintertime. The fast atmospheric processes play an important role; particularly, the midlatitude westerly flow, which is stronger and closer to the equator in winter, provides a favorable condition for the eastward and poleward energy propagation of the forced waves. In the Northern Hemisphere, removing the TP causes a wave train traveling from the Asian continent to the North America-Atlantic Ocean region, resulting in intensified westerlies and thus an enhancement of stratospheric polar vortex and Arctic cooling. The pathways are northeastward directly in the upper level due to the background westerlies, while they are eastward and then northeastward in the lower level, modulated by the winter monsoon. To the south, the TP perturbation causes an anomalous cross-equatorial flow, leading to an anomalous SST dipole pattern in the Indian Ocean in the austral winter; this generates stationary waves propagating energy southeastward from the tropical Indian Ocean to the Antarctic, resulting in a Rossby wave train circulating around the Antarctic. Our study identifies the seasonality and pathways of the TP affecting the polar regions, which may help to understand the role of the TP in the future climate changes in polar regions.

Advances in Atmospheric Sciences, Jul 3, 2019

The outputs of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System... more The outputs of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L) model for the baseline experiment of the Atmospheric Model Intercomparison Project simulation in the Diagnostic, Evaluation and Characterization of Klima common experiments of phase 6 of the Coupled Model Intercomparison Project (CMIP6) are described in this paper. The CAS FGOALS-f3-L model, experiment settings, and outputs are all given. In total, there are three ensemble experiments over the period 1979-2014, which are performed with different initial states. The model outputs contain a total of 37 variables and include the required three-hourly mean, six-hourly transient, daily and monthly mean datasets. The baseline performances of the model are validated at different time scales. The preliminary evaluation suggests that the CAS FGOALS-f3-L model can capture the basic patterns of atmospheric circulation and precipitation well, including the propagation of the Madden-Julian Oscillation, activities of tropical cyclones, and the characterization of extreme precipitation. These datasets contribute to the benchmark of current model behaviors for the desired continuity of CMIP.

Advances in Atmospheric Sciences, May 7, 2021

Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplificat... more Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplification Model Intercomparison Project (PAMIP) were carried out by the model group of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L). Eight groups of experiments forced by different combinations of the sea surface temperature (SST) and sea ice concentration (SIC) for pre-industrial, present-day, and future conditions were performed and published. The time-lag method was used to generate the 100 ensemble members, with each member integrating from 1 April 2000 to 30 June 2001 and the first two months as the spin-up period. The basic model responses of the surface air temperature (SAT) and precipitation were documented. The results indicate that Arctic amplification is mainly caused by Arctic SIC forcing changes. The SAT responses to the Arctic SIC decrease alone show an obvious increase over high latitudes, which is similar to the results from the combined forcing of SST and SIC. However, the change in global precipitation is dominated by the changes in the global SST rather than SIC, partly because tropical precipitation is mainly driven by local SST changes. The uncertainty of the model responses was also investigated through the analysis of the large-ensemble members. The relative roles of SST and SIC, together with their combined influence on Arctic amplification, are also discussed. All of these model datasets will contribute to PAMIP multi-model analysis and improve the understanding of polar amplification.

Geoscientific Model Development, Oct 12, 2021

The effects of horizontal resolution on the simulation of tropical cyclones were studied using th... more The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences Flexible Global Ocean-Atmosphere-Land System Finite-Volume version 3 (FGOALS-f3) climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project phase 6 (CMIP6). Both the lowresolution (about 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (about 25 km resolution) FGOALS-f3 (FGOALS-f3-H) models were used to achieve the standard Tier 1 experiment required by High-ResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with the exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated using observations. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. Although the number of tropical cyclones increased by about 50 % at the higher resolution and better matched the observed values in the peak month, both FGOALS-f3-L and FGOALS-f3-H appear to replicate the timing of the seasonal cycle of tropical cyclones. The simulated average and interannual variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins. The characteristics of tropical cyclones (e.g., the average lifetime, the wind-pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the response between the El Niño-Southern Oscillation and the number of tropical cyclones and the accumulated cyclone energy in FGOALS-f3 contributed to the realistic simulation of tropical cyclones. The genesis potential index and the vorticity, relative humidity, maximum potential intensity and the wind Published by Copernicus Publications on behalf of the European Geosciences Union. 6114 J. Li et al.: Effect of horizontal resolution on the simulation of tropical cyclones shear terms were used to diagnose the effects of resolution. We discuss the current insufficiencies and future directions of improvement for the simulation of tropical cyclones and the potential applications of the FGOALS-f3-H model in the subseasonal to seasonal prediction of tropical cyclones.

Global Climate Impacts of Land‐surface and Atmospheric Processes over the Tibetan Plateau

Reviews of Geophysics, Aug 9, 2023

The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanical... more The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanically and thermally affects air masses or airflows. Moreover, the TP provides a key channel for substance transport between the troposphere and the stratosphere. This study reviews recent advances in research regarding land–atmosphere coupling processes over the TP. The TP experiences climate warming and wetting. Climate warming has caused glacier retreat, permafrost degradation, and a general increase in vegetation density, while climate wetting has led to a significant increase in the number of major lakes, primarily through increased precipitation. Local and regional climates are affected by interactions between the land and the atmosphere. Namely, the TP drives surface pollutants to the upper troposphere in an Asian summer monsoon (ASM) anticyclone circulation, before spreading to the lower stratosphere. Further, the thermal forcing of the TP plays an essential role in the ASM. TP forcing can modulate hemispheric‐scale atmospheric circulations across all seasons. The TP interacts with remote oceans through a forced atmospheric response and is substantially affected by the evolution of the Earth's climate via promoting Atlantic meridional overturning circulation and eliminating Pacific meridional overturning circulation. The extensive influence of the TP is facilitated by its coupling with the ASM in the summer; whereas its winter influence on climate mainly occurs through Rossby waves. The observed increasing trends of temperature and precipitation over the TP are projected to continue throughout the 21st century.

Climate Dynamics, Jan 31, 2022

At midnight on 27-28 June 2016, a Tibetan Plateau (TP) Vortex (TPV) generated over the western TP... more At midnight on 27-28 June 2016, a Tibetan Plateau (TP) Vortex (TPV) generated over the western TP that subsequently caused a downstream record-breaking rainstorm and extremely severe natural disaster. Based on reanalysis data and satellite imagery, this study investigates the formation of this TPV from a potential vorticity (PV) perspective. Results show that, in late June 2016, a remarkable circulation anomaly occurred over the TP and its peripheral area, with easterly flow in the middle and lower troposphere developing in the subtropical zone, replacing the normal westerly flow there. Its forefront merged with the southwesterly flow from the west and penetrated and converged over the western TP where the surface was warmer than normal, forming a low-level jet and downward slantwise isentropic surfaces in-situ. When the air parcel slid down the slantwise isentropic surface, its vertical relative vorticity developed owing to slantwise vorticity development associated with PV restructuring. At the same time, the penetrating southwesterly flow brought abundant water vapor to the western TP and induced increasing sub-cloud entropy and air ascent there. Low-layer cloud formed and the cloud liquid water content increased. The strong latent heat that was released in association with the formation of cloud produced strong diabatic heating near 400 hPa at night and strong PV generation below. The normal diurnal variation was interrupted and the vortex was generated near the surface. These results demonstrate that, against a favorable circulation background, both adiabatic and diabatic PV processes are crucial for TPV genesis.

Enhanced Asian warming increases Arctic amplification

Environmental Research Letters, Mar 1, 2023

The Arctic has been experiencing prominent warming amplification. However, despite anthropogenic ... more The Arctic has been experiencing prominent warming amplification. However, despite anthropogenic emissions and oceanic variability, whether Arctic amplification has a connection with land in the lower latitudes remains unknown. Here, we newly identify enhanced Asian warming as a factor underlying Arctic amplification. The simulations demonstrate that enhanced Asian warming contributes 22% of the wintertime amplified warming over the Barents–Kara Seas (BKS). We demonstrate that Asian warming remotely affects the Arctic by affecting poleward atmospheric heat and moisture transport. The external anomalous heat and moisture further trigger local feedbacks concerning sea ice-albedo feedback and changes in longwave radiation and evaporation, thus facilitating BKS warming amplification. The capacitor effect of the Arctic Ocean further modulates the seasonality of BKS warming via turbulent heat flux exchange between the atmosphere and ocean. Moreover, anomalous Rossby wave trains are responsible for the anomalous atmospheric circulations favoring the atmospheric heat and moisture transport into BKS. Our findings illuminate a new factor from remote lower latitudes affecting Arctic climate change.

Analyses of the Dynamic Effects on Winter Circulation of the Two Main Mountains in the Northern HEMISPHERE--II.VERTICAL Propagation of Planetary Waves

Journal of meteorological research, 1992

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed ... more A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate thevertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal meanflow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo-cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbationcaused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow isvery weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagatingwaves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up-wards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-Pcross-sections obtained from both observational data and simulated results also demonstrate that waves excited by theRocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,inaddition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by theTibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetratesthe tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wavepropagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains inthe Northern Hemisphere.

Quantification of Seasonal and Interannual Variations of the Tibetan Plateau Surface Thermodynamic Forcing Based on the Potential Vorticity

Geophysical Research Letters, Mar 8, 2022

In this study, a new index based on the potential vorticity (PV) framework is proposed for the qu... more In this study, a new index based on the potential vorticity (PV) framework is proposed for the quantification of the Tibetan Plateau (TP) surface thermodynamic and dynamic forcing. The results show that the derived TP surface PV (SPV) includes the topographical effect, near‐surface absolute vorticity, and land–air potential temperature differences. The climatological annual cycle of the SPV suggests that the TP transitions from a cooling to a heating source in April. The SPV reaches a maximum from June to August, which is consistent with the evolution of the Asian summer monsoon precipitation. Further analysis suggests that the intensified SPV in the boreal summer results in a low‐level cyclonic circulation anomaly associated with increased precipitation over the southeastern slope of the TP and South China and decreased precipitation over the Indian Ocean. In winter, the intensified SPV is associated with local cold air and divergence at the TP surface.

Abnormal warm sea‐surface temperature in the Indian Ocean, active potential vorticity over the Tibetan Plateau, and severe flooding along the Yangtze River in summer 2020

Quarterly Journal of the Royal Meteorological Society, 2022

Excessive precipitation was observed throughout the Yangtze River Valley during the record‐breaki... more Excessive precipitation was observed throughout the Yangtze River Valley during the record‐breaking Meiyu season in 2020. However, the mechanism of extreme precipitation over the upper reaches of the Yangtze River remains unclear. Our results show that the activities of high potential vorticity (PV) systems during their eastward propagation over the eastern Tibetan Plateau (TP) should be responsible for the above‐normal rainfall not only over western China but also over eastern China. The activity of high‐PV systems is characterized by a prominent diurnal cycle, and their formation is closely related to the thermal contrast between the near‐surface and lower atmosphere. In the morning, surface sensible heating increases sharply after sunrise, leading to a decrease in diabatic heating with height. Accordingly, PV weakens in the lower atmosphere, and the formation of high‐PV systems reaches a minimum. An increase in turbulence increases near‐surface evaporation, which in turn reduces surface diabatic heating. At the same time, cloud formation increases diabatic heating at approximately 400 hPa. Consequently, the thermal contrast below 400 hPa leads to an increase in diabatic heating with height, favoring the generation of high‐PV systems. Compared with the climatology, an excessive water vapor supply from the anomalous anticyclone over the northern Bay of Bengal, forced by the Indian Ocean warming in 2020, contributes to a stronger thermal contrast and enhanced activity of high‐PV systems over the TP. The arrival timing of high‐PV systems at the eastern flank of the TP plays an important role in the subsequent development of these systems. Early arrival in the afternoon or evening is generally accompanied by air convergence and sufficient water vapor supply downstream of the TP, which favors the systems moving off the TP and influencing precipitation downstream.

Climate Research, Oct 20, 2014

An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is ... more An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is used in an atmospheric general circulation model to investigate anthropogenic aerosol radiative forcing (RF) with a focus on East Asia. Compared to the pre-industrial era, the calculated strongest global mean direct RF (DRF) of −0.30 W m −2 at the all-sky top of the atmosphere (TOA) occurs in the 1980s and an indirect cloud albedo forcing (CAF) of −0.67 W m −2 in the 2000s; a maximum atmospheric DRF of 0.48 W m −2 , mainly by black carbon absorption, is found in the 2010s. Much larger aerosol DRF and CAF values are distributed over East Asia until the 2010s, and the negative surface and positive atmospheric DRF in Eastern China is even projected to maintain a magnitude of 5.0 W m −2 until the 2030s. Increasing East Asian aerosol loading has shifted the anthropogenic aerosol RF centers to lower latitudes in the Northern Hemisphere since the 1980s, and this trend is more severe under future mid-and high-range emission scenarios. Further results indicate that larger DRF values over East Asia can be partly attributed to climatological summer atmospheric moisture that is higher relative to Norther American and European regions, which enhances the aerosol hygroscopic effect, then strengthens aerosol optical depth and DRF at clear-sky TOA and surface, and even influences their long-term changes. The observational comparisons reveal that present day simulated surface concentrations of key anthropogenic aerosol species and resulting optical depth are highly underestimated in Eastern China. Further research on simulated meteorology and aerosol features is therefore recommended to reduce the uncertainties in estimating aerosol RF over East Asia.

Journal of the Atmospheric Sciences, Dec 1, 1992

Atmospheric and Oceanic Science Letters, Jun 2, 2017

High computational performance is extremely important for climate system models, especially in ul... more High computational performance is extremely important for climate system models, especially in ultra-high-resolution model development. In this study, the computational performance of the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL) was comprehensively evaluated on Tianhe-2, which was the world's top-ranked supercomputer from June 2013 to May 2016. The standardized Atmospheric Model Inter-comparison Project (AMIP) type of experiment was carried out that focused on the computational performance of each node as well as the simulation year per day (SYPD), the running cost speedup, and the scalability of the FAMIL. The results indicated that (1) based on five indexes (CPU usage, percentage of CPU kernel mode that occupies CPU time and of message passing waiting time (CPU_SW), code vectorization (VEC), average of Gflops (Gflops_ AVE), and peak of Gflops (Gflops_PK)), FAMIL shows excellent computational performance on every Tianhe-2 computing node; (2) considering SYPD and the cost speedup of FAMIL systematically, the optimal Message Passing Interface (MPI) numbers of processors (MNPs) choice appears when FAMIL use 384 and 1536 MNPs for C96 (100 km) and C384 (25 km), respectively; and (3) FAMIL shows positive scalability with increased threads to drive the model. Considering the fast network speed and acceleration card in the MIC architecture on Tianhe-2, there is still significant room to improve the computational performance of FAMIL. 摘要 高性能计算指标对于气候模式的发展，尤其是高分辨率气候模式的发展至关重要。本文系统 性的评估了IAP／LASG新一代有限体积大气环流模式FAMIL在Tianhe-2超算平台上的计算性能。 通过标准的AMIP试验，本文重点评估FAMIL在每个节点的高性能指标、每天所积分的模式年 (SYPD)、计算成本加速比、可扩展性五方面的性能。结果表明：1) FAMIL在CPU使用率、CPU 节点间信息传输等待时间、代码向量化、Gflops平均值、Gflops峰值五个方面表现出优异性 能。2) 综合考虑SYPD和计算成本加速比，对于C96(100km)和C384(25km)水平分辨率的FAMIL 积分，最优进程使用数(MNPs)分别为384和1536。3) FAMIL具有良好的可扩展性，并且随着 Tianhe-2网络传输速度的提升及MIC加速的使用，FAMIL的计算新能可以进一步得到提升。

Journal of Climate, Nov 15, 2022

An extreme drought occurred over Southeast China (SEC) in August 2019. We demonstrate synergistic... more An extreme drought occurred over Southeast China (SEC) in August 2019. We demonstrate synergistic effects of midlatitude and tropical circulation on this extreme event and highlight the impacts of the coupling and locking of two cyclones at different latitudes, which are otherwise ignored. We propose the relaying roles of the Tibetan Plateau (TP) and western North Pacific in connection with the tropical convection and SEC precipitation. The equivalent-barotropic anticyclone over the TP and lower-tropospheric cyclone over the western North Pacific both resulted from the positive Indian Ocean dipole and El Niño Modoki. The equivalent-barotropic cyclone over Northeast China originated from the dispersion of Rossby waves upstream along the subtropical waveguide associated with the North Atlantic tripole sea surface temperature anomaly pattern and the Rossby wave response to the TP precipitation deficiency. Further, they jointly contributed to this drought by inducing strong northerly wind anomalies in the entire troposphere over East China. These anomalous northerly winds led to decreased warm moisture from the south and substantial sinking motions, which inhibited the occurrence of the SEC local convection and precipitation. The SEC precipitation is closely related to convection over the Maritime Continent from a climate perspective. This relationship is verified by observations, linear baroclinic model experiments, and general circulation model sensitivity experiments with and without the TP, in which precipitation anomalies over the southern TP and Philippine Sea play important bridge roles. The results will advance the prediction of the SEC extreme drought events.

npj climate and atmospheric science, Mar 28, 2022

The Tibetan Plateau (TP) is known as one of the most sensitive regions to climate change, and it ... more The Tibetan Plateau (TP) is known as one of the most sensitive regions to climate change, and it has experienced accelerated warming in recent decades. However, to what degree the TP warming amplification relates to remote forcing such as sea ice loss in the Arctic sea ice remains unclear. Here, we found that the decline of sea ice concentration over the Barents-Kara Sea (BKS) could account for 18-32% of the winter warming over the TP by comparing observational data and ensemble experiments from an atmospheric general circulation model. The reduced BKS sea ice and resultant upward turbulent heat fluxes can intensify a Rossby wave train propagating equatorward to the TP. As a result, the enhanced southwesterlies towards the TP strengthen the warm advection over most parts of the TP and lead to TP warming. In addition, an atmospheric teleconnection between the Arctic and the TP also exists in the interannual variability. That is, a tripole mode in air temperature, with warm centers in the Arctic and TP but a cold center in the mid-high latitudes of the Eurasian continent in between. Our results imply that the BKS sea ice loss could intensify such a tripole mode and thus enhancing the winter TP warming.

The effects of horizontal resolution on the simulation of tropical cyclones were studied using th... more The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences FGOALS-f3 climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Both the low-resolution (approximately 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (approximately 25 km resolution) FGOALS-f3 (FGOALS-f3-H) model were used to achieve the standard Tier1 experiment required by the HighResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with the exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated with the observation firstly. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. The seasonal cycles of the number of tropical cyclones increased by about 50% at the higher resolution and better matched the observed values in the peak month, especially in the eastern Pacific, northern Atlantic, southern Indian and southern Pacific oceans. The simulated variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins on the interannual timescale. The characteristics of the tropical cyclones (e.g., the average lifetime, the wind-pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the Madden-Julian oscillation from FGOALS-f3-H contributed to the realistic simulation of tropical cyclones. The genesis

Advances in Atmospheric Sciences, Jan 12, 2022

The influences of interannual surface potential vorticity forcing over the Tibetan Plateau (TP) o... more The influences of interannual surface potential vorticity forcing over the Tibetan Plateau (TP) on East Asian summer rainfall (EASR) and upper-level circulation are explored in this study. The results show that the interannual EASR and associated circulations are closely related to the surface potential vorticity negative uniform leading mode (PVNUM) over the TP. When the PVNUM is in the positive phase, more rainfall occurs in the Yangtze River valley, South Korea, Japan, and part of northern China, less rainfall occurs in southern China, and vice versa. A possible mechanism by which PVNUM affects EASR is proposed. Unstable air induced by the positive phase of PVNUM could stimulate significant upward motion and a lower-level anomalous cyclone over the TP. As a result, a dipole heating mode with anomalous cooling over the southwestern TP and anomalous heating over the southeastern TP is generated. Sensitivity experiment results regarding this dipole heating mode indicate that anomalous cooling over the southwestern TP leads to local and northeastern Asian negative height anomalies, while anomalous heating over the southeastern TP leads to local positive height anomalies. These results greatly resemble the realistic circulation pattern associated with EASR. Further analysis indicates that the anomalous water vapor transport associated with this anomalous circulation pattern is responsible for the anomalous EASR. Consequently, changes in surface potential vorticity forcing over the TP can induce changes in EASR.

Atmospheric and Oceanic Science Letters, Mar 18, 2019

It is important to be able to characterize the thermal conditions over the equatorial Indian Ocea... more It is important to be able to characterize the thermal conditions over the equatorial Indian Ocean for both weather forecasting and climate prediction. This study compared the equatorial eastern Indian Ocean (EEIO) temperature and relative humidity profiles from three reanalysis products (JRA-55, MERRA2, and FGOALS-f2) with shipboard global positioning system (GPS) sounding measurements obtained during the Eastern Indian Ocean Open Cruise in spring 2018. The FGOALS-f2 reanalysis product is based on the initialization module of a sub-seasonal to seasonal prediction system with a nudging-based data assimilation method. The results indicated that: (1) both JRA-55 and MERRA2 were reliable in characterizing the temperature profile from 850 to 600 hPa, with a maximum deviation of about <0.5°C. Both datasets showed a large negative deviation below 825 hPa, with a maximum bias of about 2°C at 1000 hPa and 1.5°C at 900 hPa, respectively. (2) JRA-55 showed good performance in characterizing the relative humidity profile above 850 hPa, with a maximum deviation of < 8%, while it showed much wetter conditions below 850 hPa. MERRA2 overestimated the relative humidity in the middle to lower troposphere, with a maximum deviation of about 15% at 925 hPa. (3) The FGOALS-f2 reanalysis product more accurately reproduced the temperature profile in the marine atmospheric boundary layer over the EEIO than that in JRA-55 and MERRA2, but showed much wetter conditions than the GPS sounding observations, with a maximum deviation of up to 20% at 600 hPa. Future applications of GPS sounding datasets are discussed.

National Science Review, Feb 6, 2020

Journal of Climate, Mar 1, 2023

As the highest and most extensive plateau in the world, the Tibetan Plateau (TP) has remarkable e... more As the highest and most extensive plateau in the world, the Tibetan Plateau (TP) has remarkable effects on global climate. Through coupled model sensitivity experiments with and without the TP, we show that the TP can affect the Arctic directly via orography-forced stationary waves, and influence the Antarctic indirectly via stationary waves forced by sea surface temperature (SST) in the Indian Ocean. These far-reaching impacts occur mainly in wintertime. The fast atmospheric processes play an important role; particularly, the midlatitude westerly flow, which is stronger and closer to the equator in winter, provides a favorable condition for the eastward and poleward energy propagation of the forced waves. In the Northern Hemisphere, removing the TP causes a wave train traveling from the Asian continent to the North America-Atlantic Ocean region, resulting in intensified westerlies and thus an enhancement of stratospheric polar vortex and Arctic cooling. The pathways are northeastward directly in the upper level due to the background westerlies, while they are eastward and then northeastward in the lower level, modulated by the winter monsoon. To the south, the TP perturbation causes an anomalous cross-equatorial flow, leading to an anomalous SST dipole pattern in the Indian Ocean in the austral winter; this generates stationary waves propagating energy southeastward from the tropical Indian Ocean to the Antarctic, resulting in a Rossby wave train circulating around the Antarctic. Our study identifies the seasonality and pathways of the TP affecting the polar regions, which may help to understand the role of the TP in the future climate changes in polar regions.

Advances in Atmospheric Sciences, Jul 3, 2019

The outputs of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System... more The outputs of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L) model for the baseline experiment of the Atmospheric Model Intercomparison Project simulation in the Diagnostic, Evaluation and Characterization of Klima common experiments of phase 6 of the Coupled Model Intercomparison Project (CMIP6) are described in this paper. The CAS FGOALS-f3-L model, experiment settings, and outputs are all given. In total, there are three ensemble experiments over the period 1979-2014, which are performed with different initial states. The model outputs contain a total of 37 variables and include the required three-hourly mean, six-hourly transient, daily and monthly mean datasets. The baseline performances of the model are validated at different time scales. The preliminary evaluation suggests that the CAS FGOALS-f3-L model can capture the basic patterns of atmospheric circulation and precipitation well, including the propagation of the Madden-Julian Oscillation, activities of tropical cyclones, and the characterization of extreme precipitation. These datasets contribute to the benchmark of current model behaviors for the desired continuity of CMIP.

Advances in Atmospheric Sciences, May 7, 2021

Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplificat... more Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplification Model Intercomparison Project (PAMIP) were carried out by the model group of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L). Eight groups of experiments forced by different combinations of the sea surface temperature (SST) and sea ice concentration (SIC) for pre-industrial, present-day, and future conditions were performed and published. The time-lag method was used to generate the 100 ensemble members, with each member integrating from 1 April 2000 to 30 June 2001 and the first two months as the spin-up period. The basic model responses of the surface air temperature (SAT) and precipitation were documented. The results indicate that Arctic amplification is mainly caused by Arctic SIC forcing changes. The SAT responses to the Arctic SIC decrease alone show an obvious increase over high latitudes, which is similar to the results from the combined forcing of SST and SIC. However, the change in global precipitation is dominated by the changes in the global SST rather than SIC, partly because tropical precipitation is mainly driven by local SST changes. The uncertainty of the model responses was also investigated through the analysis of the large-ensemble members. The relative roles of SST and SIC, together with their combined influence on Arctic amplification, are also discussed. All of these model datasets will contribute to PAMIP multi-model analysis and improve the understanding of polar amplification.

Geoscientific Model Development, Oct 12, 2021

The effects of horizontal resolution on the simulation of tropical cyclones were studied using th... more The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences Flexible Global Ocean-Atmosphere-Land System Finite-Volume version 3 (FGOALS-f3) climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project phase 6 (CMIP6). Both the lowresolution (about 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (about 25 km resolution) FGOALS-f3 (FGOALS-f3-H) models were used to achieve the standard Tier 1 experiment required by High-ResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with the exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated using observations. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. Although the number of tropical cyclones increased by about 50 % at the higher resolution and better matched the observed values in the peak month, both FGOALS-f3-L and FGOALS-f3-H appear to replicate the timing of the seasonal cycle of tropical cyclones. The simulated average and interannual variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins. The characteristics of tropical cyclones (e.g., the average lifetime, the wind-pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the response between the El Niño-Southern Oscillation and the number of tropical cyclones and the accumulated cyclone energy in FGOALS-f3 contributed to the realistic simulation of tropical cyclones. The genesis potential index and the vorticity, relative humidity, maximum potential intensity and the wind Published by Copernicus Publications on behalf of the European Geosciences Union. 6114 J. Li et al.: Effect of horizontal resolution on the simulation of tropical cyclones shear terms were used to diagnose the effects of resolution. We discuss the current insufficiencies and future directions of improvement for the simulation of tropical cyclones and the potential applications of the FGOALS-f3-H model in the subseasonal to seasonal prediction of tropical cyclones.

Global Climate Impacts of Land‐surface and Atmospheric Processes over the Tibetan Plateau

Reviews of Geophysics, Aug 9, 2023

The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanical... more The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanically and thermally affects air masses or airflows. Moreover, the TP provides a key channel for substance transport between the troposphere and the stratosphere. This study reviews recent advances in research regarding land–atmosphere coupling processes over the TP. The TP experiences climate warming and wetting. Climate warming has caused glacier retreat, permafrost degradation, and a general increase in vegetation density, while climate wetting has led to a significant increase in the number of major lakes, primarily through increased precipitation. Local and regional climates are affected by interactions between the land and the atmosphere. Namely, the TP drives surface pollutants to the upper troposphere in an Asian summer monsoon (ASM) anticyclone circulation, before spreading to the lower stratosphere. Further, the thermal forcing of the TP plays an essential role in the ASM. TP forcing can modulate hemispheric‐scale atmospheric circulations across all seasons. The TP interacts with remote oceans through a forced atmospheric response and is substantially affected by the evolution of the Earth's climate via promoting Atlantic meridional overturning circulation and eliminating Pacific meridional overturning circulation. The extensive influence of the TP is facilitated by its coupling with the ASM in the summer; whereas its winter influence on climate mainly occurs through Rossby waves. The observed increasing trends of temperature and precipitation over the TP are projected to continue throughout the 21st century.

Climate Dynamics, Jan 31, 2022

At midnight on 27-28 June 2016, a Tibetan Plateau (TP) Vortex (TPV) generated over the western TP... more At midnight on 27-28 June 2016, a Tibetan Plateau (TP) Vortex (TPV) generated over the western TP that subsequently caused a downstream record-breaking rainstorm and extremely severe natural disaster. Based on reanalysis data and satellite imagery, this study investigates the formation of this TPV from a potential vorticity (PV) perspective. Results show that, in late June 2016, a remarkable circulation anomaly occurred over the TP and its peripheral area, with easterly flow in the middle and lower troposphere developing in the subtropical zone, replacing the normal westerly flow there. Its forefront merged with the southwesterly flow from the west and penetrated and converged over the western TP where the surface was warmer than normal, forming a low-level jet and downward slantwise isentropic surfaces in-situ. When the air parcel slid down the slantwise isentropic surface, its vertical relative vorticity developed owing to slantwise vorticity development associated with PV restructuring. At the same time, the penetrating southwesterly flow brought abundant water vapor to the western TP and induced increasing sub-cloud entropy and air ascent there. Low-layer cloud formed and the cloud liquid water content increased. The strong latent heat that was released in association with the formation of cloud produced strong diabatic heating near 400 hPa at night and strong PV generation below. The normal diurnal variation was interrupted and the vortex was generated near the surface. These results demonstrate that, against a favorable circulation background, both adiabatic and diabatic PV processes are crucial for TPV genesis.

Enhanced Asian warming increases Arctic amplification

Environmental Research Letters, Mar 1, 2023

The Arctic has been experiencing prominent warming amplification. However, despite anthropogenic ... more The Arctic has been experiencing prominent warming amplification. However, despite anthropogenic emissions and oceanic variability, whether Arctic amplification has a connection with land in the lower latitudes remains unknown. Here, we newly identify enhanced Asian warming as a factor underlying Arctic amplification. The simulations demonstrate that enhanced Asian warming contributes 22% of the wintertime amplified warming over the Barents–Kara Seas (BKS). We demonstrate that Asian warming remotely affects the Arctic by affecting poleward atmospheric heat and moisture transport. The external anomalous heat and moisture further trigger local feedbacks concerning sea ice-albedo feedback and changes in longwave radiation and evaporation, thus facilitating BKS warming amplification. The capacitor effect of the Arctic Ocean further modulates the seasonality of BKS warming via turbulent heat flux exchange between the atmosphere and ocean. Moreover, anomalous Rossby wave trains are responsible for the anomalous atmospheric circulations favoring the atmospheric heat and moisture transport into BKS. Our findings illuminate a new factor from remote lower latitudes affecting Arctic climate change.

Analyses of the Dynamic Effects on Winter Circulation of the Two Main Mountains in the Northern HEMISPHERE--II.VERTICAL Propagation of Planetary Waves

Journal of meteorological research, 1992

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed ... more A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate thevertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal meanflow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo-cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbationcaused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow isvery weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagatingwaves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up-wards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-Pcross-sections obtained from both observational data and simulated results also demonstrate that waves excited by theRocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,inaddition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by theTibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetratesthe tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wavepropagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains inthe Northern Hemisphere.

Quantification of Seasonal and Interannual Variations of the Tibetan Plateau Surface Thermodynamic Forcing Based on the Potential Vorticity

Geophysical Research Letters, Mar 8, 2022

In this study, a new index based on the potential vorticity (PV) framework is proposed for the qu... more In this study, a new index based on the potential vorticity (PV) framework is proposed for the quantification of the Tibetan Plateau (TP) surface thermodynamic and dynamic forcing. The results show that the derived TP surface PV (SPV) includes the topographical effect, near‐surface absolute vorticity, and land–air potential temperature differences. The climatological annual cycle of the SPV suggests that the TP transitions from a cooling to a heating source in April. The SPV reaches a maximum from June to August, which is consistent with the evolution of the Asian summer monsoon precipitation. Further analysis suggests that the intensified SPV in the boreal summer results in a low‐level cyclonic circulation anomaly associated with increased precipitation over the southeastern slope of the TP and South China and decreased precipitation over the Indian Ocean. In winter, the intensified SPV is associated with local cold air and divergence at the TP surface.

Abnormal warm sea‐surface temperature in the Indian Ocean, active potential vorticity over the Tibetan Plateau, and severe flooding along the Yangtze River in summer 2020

Quarterly Journal of the Royal Meteorological Society, 2022

Excessive precipitation was observed throughout the Yangtze River Valley during the record‐breaki... more Excessive precipitation was observed throughout the Yangtze River Valley during the record‐breaking Meiyu season in 2020. However, the mechanism of extreme precipitation over the upper reaches of the Yangtze River remains unclear. Our results show that the activities of high potential vorticity (PV) systems during their eastward propagation over the eastern Tibetan Plateau (TP) should be responsible for the above‐normal rainfall not only over western China but also over eastern China. The activity of high‐PV systems is characterized by a prominent diurnal cycle, and their formation is closely related to the thermal contrast between the near‐surface and lower atmosphere. In the morning, surface sensible heating increases sharply after sunrise, leading to a decrease in diabatic heating with height. Accordingly, PV weakens in the lower atmosphere, and the formation of high‐PV systems reaches a minimum. An increase in turbulence increases near‐surface evaporation, which in turn reduces surface diabatic heating. At the same time, cloud formation increases diabatic heating at approximately 400 hPa. Consequently, the thermal contrast below 400 hPa leads to an increase in diabatic heating with height, favoring the generation of high‐PV systems. Compared with the climatology, an excessive water vapor supply from the anomalous anticyclone over the northern Bay of Bengal, forced by the Indian Ocean warming in 2020, contributes to a stronger thermal contrast and enhanced activity of high‐PV systems over the TP. The arrival timing of high‐PV systems at the eastern flank of the TP plays an important role in the subsequent development of these systems. Early arrival in the afternoon or evening is generally accompanied by air convergence and sufficient water vapor supply downstream of the TP, which favors the systems moving off the TP and influencing precipitation downstream.

Climate Research, Oct 20, 2014

An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is ... more An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is used in an atmospheric general circulation model to investigate anthropogenic aerosol radiative forcing (RF) with a focus on East Asia. Compared to the pre-industrial era, the calculated strongest global mean direct RF (DRF) of −0.30 W m −2 at the all-sky top of the atmosphere (TOA) occurs in the 1980s and an indirect cloud albedo forcing (CAF) of −0.67 W m −2 in the 2000s; a maximum atmospheric DRF of 0.48 W m −2 , mainly by black carbon absorption, is found in the 2010s. Much larger aerosol DRF and CAF values are distributed over East Asia until the 2010s, and the negative surface and positive atmospheric DRF in Eastern China is even projected to maintain a magnitude of 5.0 W m −2 until the 2030s. Increasing East Asian aerosol loading has shifted the anthropogenic aerosol RF centers to lower latitudes in the Northern Hemisphere since the 1980s, and this trend is more severe under future mid-and high-range emission scenarios. Further results indicate that larger DRF values over East Asia can be partly attributed to climatological summer atmospheric moisture that is higher relative to Norther American and European regions, which enhances the aerosol hygroscopic effect, then strengthens aerosol optical depth and DRF at clear-sky TOA and surface, and even influences their long-term changes. The observational comparisons reveal that present day simulated surface concentrations of key anthropogenic aerosol species and resulting optical depth are highly underestimated in Eastern China. Further research on simulated meteorology and aerosol features is therefore recommended to reduce the uncertainties in estimating aerosol RF over East Asia.

Journal of the Atmospheric Sciences, Dec 1, 1992