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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerab... more Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerable spring top-of-the-atmosphere (TOA) radiative cooling over Southeast China (SEC) is very likely related to upstream orography forcing. Here we investigate the mechanical and thermal forcings of Asian large-scale orography, particularly the Tibetan Plateau (TP), on downstream East Asian cloud amount and atmospheric radiation budget during March-April using the Global Monsoons Model Intercomparison Project simulations. The thermal forcing drives significant surface heating and a low-level cyclone over the TP, pumping low-level air to the middle troposphere. Ascent and water vapor convergence triggered by the thermal forcing favor air condensation, low-middle clouds, and resultant strong spring cloud radiative cooling over SEC. Moreover, the thermal forcing moves the position of cloud radiative cooling westward toward the TP. The TP's blocking role weakens low-level westerlies over SEC, but its deflecting role increases downstream highlevel westerlies, dynamically favoring cloud formation over SEC and the eastward ocean. In addition, the TP can force ascent and increase cloud amounts over the western and central TP. The thermal forcing contributes to 57.1% of total cloud amount and 47.6% of TOA cloud radiative cooling induced by the combined orography forcing over SEC while the mechanical one accounts for 79.4% and 95.8% of the counterparts over the ocean to the east of SEC. Our results indicate that Asian large-scale orography shapes the contemporary geographical distribution of spring East Asian cloud amount and atmospheric radiation budget to a large extent. SIGNIFICANCE STATEMENT: Clouds tied to large-scale topography and circulation exhibit some remarkable geographical distributions. The global strongest cloud radiative cooling, with an intensity of up to 290 W m 22 , occurs over Southeast China (SEC) during March-April. The primary purpose of this study is to understand the influences of Asian large-scale orography, particularly the Tibetan Plateau (TP), on this unique climatic phenomenon using the latest climate model simulations. Our results show that Asian large-scale orography forcing significantly increases ascent, low-middle cloud formation, and resultant strong spring cloud radiative cooling over SEC and downstream ocean. The sensible-heat-driven air pump induced by the TP's thermal forcing maintains strong cloud radiative cooling over SEC. This study provides valuable insights that link Asian large-scale orography forcing to downstream cloud-radiation characteristics.
To study the effects of the uplift of Qinghai-Xizang Plateau(QXP) on Asian atmospheric general ci... more To study the effects of the uplift of Qinghai-Xizang Plateau(QXP) on Asian atmospheric general circulation in spring and summer,the experiments with and without QXP are performed respectively(called TP-Experiment and NTP-Experiment hereafter) for 10 years using an atmospheric general circulation model with rhomboidal truncation(R42L9).Comparing the results of TP Experiment with NTP-Experiment,it is showed that the Asian atmospheric general circulation has a strong response to the uplift of QXP.The QXP split the westerlies and force them to flow around it in lower level.There are two branches of the westerlies,one flow to the north and the other to the south of the Plateau.The northern branch strengthen cold air go down southward to Eastern Asia.The intensity of southern branch enhances because of weaken heating of the QXP in spring.The enhanced southern branch transport moisture to southernChina.Meeting of cold and warm air in southern China causes heavy rain in there in spring.In summer,cyclonic circulation caused by the QXP strong heating source in lower level enhances the Eastern Asia summer monsoon on the east side of QXP and make it develop northward.However,the sensible heat air pumping of QXP bring negative vorticity and divergence over southern Asia in lowew level,and decrease the precipitation in there in summer.So the southern Asia summer monsoon weakens with the uplift of QXP.Another thermal influence of the QXP is reflected in upper level.The negative vorticity sources over the Plateau generated by the QXPheatingstrengthen the Iranhigh at 200 hPa in a remote way.
In Part I the authors have shown that heating sources in spring over the Tibetan Plateau (TP), an... more In Part I the authors have shown that heating sources in spring over the Tibetan Plateau (TP), and in particular the sensible heat flux (SHF), exhibit a significant weakening trend since the mid-1980s that is induced mainly by decreased surface wind speed. The possible reason of such a change is further investigated in Part II by analyzing historical observations and the NCEP/Department of Energy (DOE) reanalysis. The steady declining trend in the surface wind speed over the TP after the 1970s arises mainly from the zonal component. Since the mean altitude of the TP is about 600 hPa and the surface flow is controlled by the East Asian subtropical westerly jet (EASWJ) for most parts of the year, the substantial tropospheric warming in the mid-and high latitudes to the north of the plateau results in a decrease of the meridional pressure gradient in the subtropics. As a result, the EASWJ and the surface winds over the TP are decelerated. Moreover, changes of the general circulation in the twentieth century simulated by 16 coupled climate models driven by natural and anthropogenic forcings are examined. Intercomparison results suggest that sulfate aerosol indirect effects and ozone may be important in reproducing the weakening trend in EASWJ. Although nearly half of the models can successfully reproduce the observed trends in the EASWJ during the last two decades, there is an obvious spread in simulation of the spatial patterns of twentieth-century tropospheric temperatures, suggesting significant room still exists for improvement of the current state-of-theart coupled climate models.
The precipitation over the eastern Tibetan Plateau (ETP, here defined as 29°–38°N, 91°–103°E) usu... more The precipitation over the eastern Tibetan Plateau (ETP, here defined as 29°–38°N, 91°–103°E) usually exhibits significant subseasonal variation during boreal summer. As the hot spot of land‐air interaction, the influences of ETP surface soil temperature (Tsoil) on the local precipitation through subseasonal land‐air interaction are still unclear but urgently needed for improving subseasonal prediction. Based on station and reanalysis datasets of 1979–2018, this study identifies the evident quasi‐biweekly (QBW) (9–30 days) periodic signal of ETP surface Tsoil variation during the early summer (May–June), which results from the anomalies of southeastward propagating mid‐latitude QBW waves in the mid‐to‐upper troposphere. The observational results further show that the maximum positive anomaly of precipitation over the ETP lags the warmest surface Tsoil by one phase at the QBW timescale, indicating that the warming surface Tsoil could enhance the subseasonal precipitation. The numeric...
Using a variety of CloudSat/CALIPSO products, this study synergistically examines the performance... more Using a variety of CloudSat/CALIPSO products, this study synergistically examines the performance of clouds and their radiative effects (CRE) for models participating in CMIP6. Results show virtually all models overestimate the net cooling effect of clouds, which is caused by the overestimation of shortwave CRE and the underestimation of longwave CRE. By dividing clouds into regimes jointly sorted by cloud water path and cloud cover, we found models commonly underestimate the relative frequency of occurrence (RFO) for clouds that are geometrically thick, and the bias of RFO is dominant over that of within‐regime CRE in an error decomposition of total CRE. This results in underestimations of CRE in geometrically thick clouds, which are partially offset by overestimations in the remaining cloud regimes, leading to the globally averaged CRE being less biased. The consideration of regime‐based CRE gives important information that could be used for correction of cloud parameterization in models.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerab... more Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerable spring top-of-the-atmosphere (TOA) radiative cooling over Southeast China (SEC) is very likely related to upstream orography forcing. Here we investigate the mechanical and thermal forcings of Asian large-scale orography, particularly the Tibetan Plateau (TP), on downstream East Asian cloud amount and atmospheric radiation budget during March-April using the Global Monsoons Model Intercomparison Project simulations. The thermal forcing drives significant surface heating and a low-level cyclone over the TP, pumping low-level air to the middle troposphere. Ascent and water vapor convergence triggered by the thermal forcing favor air condensation, low-middle clouds, and resultant strong spring cloud radiative cooling over SEC. Moreover, the thermal forcing moves the position of cloud radiative cooling westward toward the TP. The TP's blocking role weakens low-level westerlies over SEC, but its deflecting role increases downstream highlevel westerlies, dynamically favoring cloud formation over SEC and the eastward ocean. In addition, the TP can force ascent and increase cloud amounts over the western and central TP. The thermal forcing contributes to 57.1% of total cloud amount and 47.6% of TOA cloud radiative cooling induced by the combined orography forcing over SEC while the mechanical one accounts for 79.4% and 95.8% of the counterparts over the ocean to the east of SEC. Our results indicate that Asian large-scale orography shapes the contemporary geographical distribution of spring East Asian cloud amount and atmospheric radiation budget to a large extent. SIGNIFICANCE STATEMENT: Clouds tied to large-scale topography and circulation exhibit some remarkable geographical distributions. The global strongest cloud radiative cooling, with an intensity of up to 290 W m 22 , occurs over Southeast China (SEC) during March-April. The primary purpose of this study is to understand the influences of Asian large-scale orography, particularly the Tibetan Plateau (TP), on this unique climatic phenomenon using the latest climate model simulations. Our results show that Asian large-scale orography forcing significantly increases ascent, low-middle cloud formation, and resultant strong spring cloud radiative cooling over SEC and downstream ocean. The sensible-heat-driven air pump induced by the TP's thermal forcing maintains strong cloud radiative cooling over SEC. This study provides valuable insights that link Asian large-scale orography forcing to downstream cloud-radiation characteristics.
To study the effects of the uplift of Qinghai-Xizang Plateau(QXP) on Asian atmospheric general ci... more To study the effects of the uplift of Qinghai-Xizang Plateau(QXP) on Asian atmospheric general circulation in spring and summer,the experiments with and without QXP are performed respectively(called TP-Experiment and NTP-Experiment hereafter) for 10 years using an atmospheric general circulation model with rhomboidal truncation(R42L9).Comparing the results of TP Experiment with NTP-Experiment,it is showed that the Asian atmospheric general circulation has a strong response to the uplift of QXP.The QXP split the westerlies and force them to flow around it in lower level.There are two branches of the westerlies,one flow to the north and the other to the south of the Plateau.The northern branch strengthen cold air go down southward to Eastern Asia.The intensity of southern branch enhances because of weaken heating of the QXP in spring.The enhanced southern branch transport moisture to southernChina.Meeting of cold and warm air in southern China causes heavy rain in there in spring.In summer,cyclonic circulation caused by the QXP strong heating source in lower level enhances the Eastern Asia summer monsoon on the east side of QXP and make it develop northward.However,the sensible heat air pumping of QXP bring negative vorticity and divergence over southern Asia in lowew level,and decrease the precipitation in there in summer.So the southern Asia summer monsoon weakens with the uplift of QXP.Another thermal influence of the QXP is reflected in upper level.The negative vorticity sources over the Plateau generated by the QXPheatingstrengthen the Iranhigh at 200 hPa in a remote way.
In Part I the authors have shown that heating sources in spring over the Tibetan Plateau (TP), an... more In Part I the authors have shown that heating sources in spring over the Tibetan Plateau (TP), and in particular the sensible heat flux (SHF), exhibit a significant weakening trend since the mid-1980s that is induced mainly by decreased surface wind speed. The possible reason of such a change is further investigated in Part II by analyzing historical observations and the NCEP/Department of Energy (DOE) reanalysis. The steady declining trend in the surface wind speed over the TP after the 1970s arises mainly from the zonal component. Since the mean altitude of the TP is about 600 hPa and the surface flow is controlled by the East Asian subtropical westerly jet (EASWJ) for most parts of the year, the substantial tropospheric warming in the mid-and high latitudes to the north of the plateau results in a decrease of the meridional pressure gradient in the subtropics. As a result, the EASWJ and the surface winds over the TP are decelerated. Moreover, changes of the general circulation in the twentieth century simulated by 16 coupled climate models driven by natural and anthropogenic forcings are examined. Intercomparison results suggest that sulfate aerosol indirect effects and ozone may be important in reproducing the weakening trend in EASWJ. Although nearly half of the models can successfully reproduce the observed trends in the EASWJ during the last two decades, there is an obvious spread in simulation of the spatial patterns of twentieth-century tropospheric temperatures, suggesting significant room still exists for improvement of the current state-of-theart coupled climate models.
The precipitation over the eastern Tibetan Plateau (ETP, here defined as 29°–38°N, 91°–103°E) usu... more The precipitation over the eastern Tibetan Plateau (ETP, here defined as 29°–38°N, 91°–103°E) usually exhibits significant subseasonal variation during boreal summer. As the hot spot of land‐air interaction, the influences of ETP surface soil temperature (Tsoil) on the local precipitation through subseasonal land‐air interaction are still unclear but urgently needed for improving subseasonal prediction. Based on station and reanalysis datasets of 1979–2018, this study identifies the evident quasi‐biweekly (QBW) (9–30 days) periodic signal of ETP surface Tsoil variation during the early summer (May–June), which results from the anomalies of southeastward propagating mid‐latitude QBW waves in the mid‐to‐upper troposphere. The observational results further show that the maximum positive anomaly of precipitation over the ETP lags the warmest surface Tsoil by one phase at the QBW timescale, indicating that the warming surface Tsoil could enhance the subseasonal precipitation. The numeric...
Using a variety of CloudSat/CALIPSO products, this study synergistically examines the performance... more Using a variety of CloudSat/CALIPSO products, this study synergistically examines the performance of clouds and their radiative effects (CRE) for models participating in CMIP6. Results show virtually all models overestimate the net cooling effect of clouds, which is caused by the overestimation of shortwave CRE and the underestimation of longwave CRE. By dividing clouds into regimes jointly sorted by cloud water path and cloud cover, we found models commonly underestimate the relative frequency of occurrence (RFO) for clouds that are geometrically thick, and the bias of RFO is dominant over that of within‐regime CRE in an error decomposition of total CRE. This results in underestimations of CRE in geometrically thick clouds, which are partially offset by overestimations in the remaining cloud regimes, leading to the globally averaged CRE being less biased. The consideration of regime‐based CRE gives important information that could be used for correction of cloud parameterization in models.
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