Mechanism of Diabatic Heating on Precipitation and the Track of a Tibetan Plateau Vortex over the Eastern Slope of the Tibetan Plateau

Existing studies contend that latent heating(LH)will replace sensible heating(SH)to become the dominant factor affecting the development of the Tibetan Plateau vortex(TPV)after it moves off the Tibetan Plateau(TP).However,in the process of the TPV moving off the TP requires that the airmass traverse the eastern slope of the Tibetan Plateau(ESTP)where the topography and diabatic heating(DH)conditions rapidly change.How LH gradually replaces SH to become the dominant factor in the development of the TPV over the ESTP is still not very clear.In this paper,an analysis of a typical case of a TPV with a long life history over the ESTP is performed by using multi-sourced meteorological data and model simulations.The results show that SH from the TP surface can change the TPV-associated precipitation distribution by temperature advection after the TPV moves off the TP.The LH can then directly promote the development of the TPV and has a certain guiding effect on the track of the TPV.The SH can control the active area of LH by changing the falling area of the TPV-associated precipitation,so it still plays a key role in the development and tracking of the TPV even though it has moved out of the main body of the TP.

Interannual Variability of Late-spring Circulation and Diabatic Heating over the Tibetan Plateau Associated with Indian Ocean Forcing

The thermal forcing of the Tibetan Plateau （TP） during boreal spring, which involves surface sensible heating, latent heating released by convection and radiation flux heat, is critical for the seasonal and subseasonal variation of the East Asian summer monsoon. Distinct from the situation in March and April when the TP thermal forcing is modulated by the sea surface temperature anomaly （SSTA） in the North Atlantic, the present study shows that it is altered mainly by the SSTA in the Indian Ocean Basin Mode （IOBM） in May, according to in-situ observations over the TP and MERRA reanalysis data. In the positive phase of the IOBM, a local Hadley circulation is enhanced, with its ascending branch over the southwestern Indian Ocean and a descending one over the southeastern TP, leading to suppressed precipitation and weaker latent heat over the eastern TP. Meanwhile, stronger westerly flow and surface sensible heating emerges over much of the TP, along with slight variations in local net radiation flux due to cancellation between its components. The opposite trends occur in the negative phase of the IOBM. Moreover, the main associated physical processes can be validated by a series of sensitivity experiments based on an atmospheric general circulation model, FAMIL. Therefore, rather than influenced by the remote SSTAs of the northern Atlantic in the early spring, the thermal forcing of the TP is altered by the Indian Ocean SSTA in the late spring on an interannual timescale.

Global Response to Tropical Diabatic Heating Variability in Boreal Winter

Global teleconnections associated with tropical convective activities were investigated, based on monthly data of 29 Northern Hemisphere winters： December, January, February, and March （DJFM）. First, EOF analyses were performed on the outgoing longwave radiation （OLR） data to characterize the convective ac tivity variability in the tropical Indian Ocean and the western Pacific. The first EOF mode of the convective activity was highly correlated with the ENSO. The second EOF mode had an east–west dipole structure, and the third EOF mode had three convective activity centers. Two distinct teleconnection patterns were identified that were associated, respectively, with the second and third EOF modes. A global primitive equation model was used to investigate the physical mechanism that causes the global circulation anoma lies. The model responses to anomalous tropical thermal forcings that mimic the EOF patterns matched the general features of the observed circulation anomalies well, and they were mainly controlled by linear processes. The importance of convective activities in the tropical Indian Ocean and western Pacific to the extended and longrange forecasting capability in the extratropics is discussed.

Can Current AGCMs Reproduce Historical Changes in the Atmospheric Diabatic Heating over the Tibetan Plateau?

Recent studies have demonstrated a persistent decreasing trend in the spring sensible heat(SH) source over the Tibetan Plateau(TP) during the past three decades. By comparing simulations from nine state-of-the-art atmospheric general circulation models(AGCMs) driven by historical forcing fields with both observational data and five reanalysis datasets, the authors found that the AGCMs are unable to reproduce the change in the SH flux over the TP. This deficiency arises because the observed decreasing trend in SH flux depends primarily on the change in surface wind speed according to the bulk formula, whereas in the models it is also influenced largely by changes in the land-air temperature difference related to the systematic cold bias. In addition, an obvious discrepancy exists in other aspects of the diabatic heating simulated by the models, suggesting that a significant improvement is required in the physical schemes associated with land surface processes and diabatic heating over the complicated topography.

Diabatic Processes and the Generation of the Low-Level Potential Vorticity Anomaly of a Rainstorm in Saudi Arabia

The diabatic heating is calculated, using the thermodynamic equation in isobaric coordinates, of a heavy rainstorm that developed over Jeddah, Saudi Arabia on 25 November 2009. Throughout the period of study, the horizontal heat advection is the dominant term and the vertical advection term is opposed by the adiabatic one. The contribution of the local temperature term to the change in diabatic heating is relatively very minimal. The presence of the Red Sea and its adjacent mountains suggest that the diabatic heating in the lower atmosphere on that rainy day is primarily due to the latent heat released by convection. The dynamics of the studied case is also investigated in terms of isobaric Potential Vorticity (PV). The results show that the heating region coincides with the location of the low-level PV anomaly. Ertel’s Potential Vorticity (EPV) generation estimates imply that condensation supplies a large enough source of moisture to account for the presence of the low-level EPV anomaly. The low-level diabatic heating-produced PV assisted in amplifying the surface thermal wave early in the rainstorm development and in the upper-level wave during the later stages of the system’s growth.

THE DIABATIC WAVES IN BAROTROPIC MODEL

The equations of barotropic model are used to discuss the effects of diabatic factors such as heat-ing of convective condensation, evaporation-wind feedback and CISK on the Rossby wave and the Kelvin wave. In low latitudes we have obtained the angular frequency and analyzed the period and stability of waves. The result shows the existence of the diabatic factors not only enlarges the period of adiabatic waves but also changes the stability of waves. Thus we think that the so-called intraseasonal oscillation and some other low-frequency oscillations are a kind of diabatic waves which are important factors producing the long-term weather changes and short-term climatic evolution.

NUMERICAL EXPERIMENTS OF THE INFLUENCE OF DIABATIC HEATING ON TROPICAL CYCLONE ASYMMETRIC STRUCTURE

Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetric The result shows that the diabatic heating has important effects on the asymmetric structure in addition to the roll of the β term and nonlinear advection term in its formation. It again confirms the conclusion that the diabatic heating is a possible mechanism responsible for such structures in the tropical cyclone.

Interaction of diabatic processes, large-scale eddies and the mean atmospheric circulation over the Atlantic, Arctic and Eurasia

In the last decade, the atmospheric part of the climate system experienced a shift from pronounced zonal to stronger meridional flow configurations and regionally diverse changes and trends. The climate system shows complex interactions and nonlinear behavior, manifested in global warming, rising ocean temperatures and the retreat of Arctic sea ice. Although atmospheric trends and changes are observed, underlying processes are not well understood. In this study we diagnose the interaction of large-scale atmospheric eddies and the mean flow with respect to diabatic heating and cooling processes that impact on the atmospheric advection of heat. For this purpose, three-dimensional Eliassen-Palm flux theory is used in combination with an analysis of the thermodynamic equation, diabatic heating and cooling and heat advection. The most recent decades of observed winter climate are evaluated in terms of climatology and trends over the Atlantic, Arctic and Eurasia. The change of the atmospheric circulation and related processes differ between early and late winter. In early winter, the interaction of macro-turbulent eddies with the mean flow is inhibited at the Atlantic jet stream entrance region and atmospheric heat is meridionally advected into the Arctic, both related to strong high pressure anomalies. In late winter, these anomalies are inverted and a negative phase of the Arctic Oscillation with a more wavy mean flow and a tendency towards stronger meridionalization is observed.

A STUDY ON TYPHOON MOVEMENT PART──Ⅰ：THE EFFECT OF DIABATIC HEATING AND HORIZONTAL TEMPERATURE DISTRIBUTION

ＡＳＴＵＤＹＯＮＴＹＰＨＯＯＮＭＯＶＥＭＥＮＴＰＡＲＴⅠ：ＴＨＥＥＦＦＥＣＴＯＦＤＩＡＢＡＴＩＣＨＥＡＴＩＮＧＡＮＤＨＯＲＩＺＯＮＴＡＬＴＥＭＰＥＲＡＴＵＲＥＤＩＳＴＲＩＢＵＴＩＯＮ￥ＨｅＨａｉｙａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＡｔｍｏｓｐｈｅｒｉｃＳ...

The Role of Topography and Diabatic Heating in the Formation of Dipole Blocking in the Atmosphere

In this paper, the nonlinear stationary waves forced by topography and diabatic heating are investigated. It is pointed out that (1) the nonlinear interaction of different stationary waves forced only by topography might form dipole blocking in the atmosphere, this might explain the dipole blocking appeared in the Pacific and Atlantic regions; (2) the dipole blocking could not be caused by the nonlinear interaction of the different stationary waves forced by the diabatic heating alone; (3) the nonlinear interaction of the diffferent stationary waves forced by both topography and diabatic heating could initiate dipole blocking in the atmosphere. In winter, the dipole blocking mainly occurs in the west regions of the Pacific and the Atlantic, and the heat source over the western part of the two oceans is advantageous to the formation of dipole blocking in the west of two oceans. However, in summer, the dipole blocking could be formed in the east part of the two oceans, and the heat source over the eastern part of two continents is favourable for the formation of dipole blocking in the east regions of two oceans.

Influence of rainfall-induced diabatic heating on southern rainfall-northern haze over eastern China in early February 2023

In early February 2023,there was severe haze on the North China Plain(NCP)that was contemporaneous with heavy rainfall over southern China,which was known as southern rainfall-northern haze(SR-NH).Based on observational and reanalysis data,the meteorological causes of this SR-NH event are investigated in this study using correlation analysis,dynamic diagnostics and numerical experiments.The results show that the anticyclonic anomaly in the Pacific Northwest(also referred to as the northeast Asian anomalous anticyclone)is responsible for the SR-NH.On the one hand,this anticyclonic anomaly leads to persistent rainfall over southern China by causing strong ascending motion in conjunction with an anomalous cyclone over the Chinese mainland and transporting large amounts of water vapor there.On the other hand,it weakens the climatological northerly winds of the NCP through the southeasterly flow,worsening the horizontal diffusion conditions of pollutants.Additionally,the atmospheric stability and relative humidity over the NCP are significantly increased by this anticyclonic anomaly.These conditions result in higher PM2.5concentrations over the NCP.Additional results suggest that this anticyclonic anomaly is related to diabatic heating released by rainfall in southern China,which not only intensifies the rainfall process there(with a contribution of 11.5%)but also induces an anticyclonic anomaly in the upper troposphere of the Pacific Northwest(i.e.,200 hPa).The rainfall-related anticyclonic anomaly reinforces the anticyclonic anomaly in the Pacific Northwest caused by large-scale circulation(with a contribution of 27%)and thus affects haze over the NCP.This study provides a new reference for understanding the contribution of rainfall in southern China to haze over the NCP.

Diagnostic Study of an Extreme Explosive Cyclone over the Kuroshio/Kuroshio Extension Region

Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-April)was studied to reveal the variations of the key factors at different explosive-developing stages.This EC had weak low-level baroclinicity,mid-level cyclonic-vorticity advection,and strong low-level water vapor convergence at the initial explosive-developing stage.The low-level baroclinicity and mid-level cyclonic-vorticity advection increased substantially during the maximum-deepening-rate stage.The diagnostic analyses using the Zwack-Okossi equation showed that diabatic heating was the main contributor to the initial rapid intensification of this EC.The cyclonic-vorticity advection and warm-air advection enhanced rapidly in the middle and upper troposphere and contributed to the maximum rapid intensification,whereas the diabatic heating weakened slightly in the mid-low troposphere.The relative contribution of the diabatic heating decreased from the initial explosive-developing stage to the maximum-deepening-rate stage due to the enhancement of other factors(the cyclonic-vorticity advection and warm-air advection).Furthermore,the physical factors contributing to this EC varied with the explosive-developing stage.The non-key factors at the initial explosive-developing stage need attention to forecast the rapid intensification.

An Analysis of the Low Moving Speed of Landfalling Typhoon In-Fa in 2021

The movement speed of Typhoon In-Fa(2021)was notably slow,at 10 km h-1or less,for over 20 hours following its landfall in Zhejiang,China,in contrast to other typhoons that have made landfall.This study examines the factors contributing to the slow movement of Typhoon In-Fa,including the steering flow,diabatic heating,vertical wind shear(VWS),and surface synoptic situation,by comparing it with Typhoons Yagi(2018)and Rumbia(2018)which followed similar tracks.The findings reveal that the movement speed of Typhoons Yagi and Rumbia is most closely associated with their respective 500 h Pa environmental winds,with a steering flow of 10^(-12)m s^(-1).In contrast,Typhoon InFa’s movement speed is most strongly correlated with the 850 h Pa environmental wind field,with a steering flow speed of only 2 m s^(-1).Furthermore,as Typhoon In-Fa moves northwest after landfall,its intensity is slightly greater than that of Typhoons Yagi and Rumbia,and the pressure gradient in front of Typhoon In-Fa is notably smaller,leading to its slow movement.Additionally,the precipitation distribution of Typhoon In-Fa differs from that of the other two typhoons,resulting in a weak asymmetry of wavenumber-1 diabatic heating,which indirectly affects its movement speed.Further analysis indicates that VWS can alter the typhoon’s structure,weaken its intensity,and ultimately impact its movement.

Seasonal Prediction of Indian Summer Monsoon Using WRF: A Dynamical Downscaling Perspective

Seasonal forecasting of the Indian summer monsoon by dynamically downscaling the CFSv2 output using a high resolution WRF model over the hindcast period of 1982-2008 has been performed in this study. The April start ensemble mean of the CFSv2 has been used to provide the initial and lateral boundary conditions for driving the WRF. The WRF model is integrated from 1st May through 1st October for each monsoon season. The analysis suggests that the WRF exhibits potential skill in improving the rainfall skill as well as the seasonal pattern and minimizes the meteorological errors as compared to the parent CFSv2 model. The rainfall pattern is simulated quite closer to the observation (IMD) in the WRF model over CFSv2 especially over the significant rainfall regions of India such as the Western Ghats and the central India. Probability distributions of the rainfall show that the rainfall is improved with the WRF. However, the WRF simulates copious amounts of rainfall over the eastern coast of India. Surface and upper air meteorological parameters show that the WRF model improves the simulation of the lower level and upper-level winds, MSLP, CAPE and PBL height. The specific humidity profiles show substantial improvement along the vertical column of the atmosphere which can be directly related to the net precipitable water. The CFSv2 underestimates the specific humidity along the vertical which is corrected by the WRF model. Over the Bay of Bengal, the WRF model overestimates the CAPE and specific humidity which may be attributed to the copious amount of rainfall along the eastern coast of India. Residual heating profiles also show that the WRF improves the thermodynamics of the atmosphere over 700 hPa and 400 hPa levels which helps in improving the rainfall simulation. Improvement in the land surface fluxes is also witnessed in the WRF model.

Study of a Horizontal Shear Line over the Qinghai–Tibetan Plateau and the Impact of Diabatic Heating on Its Evolution

Based on the 4 times daily 0.75°× 0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal （east-west-oriented） shear line （TSL） during 15-19 August 2015 and the effect of diabatic heating on its evolution were analyzed. The results show that the TSL possessed a vertical thickness of up to 1.5 km （approxim-ately 600-450 hPa）, and was baroclinic in nature. Weak ascending motions occurred near the TSL, accompanied with more significant gradients in dew point temperature than in temperature. The TSL was characterized by diurnal vari- ations in its appearance and structure. It was relatively full in shape （broken） and was the lowest （highest） in vertical extent at 0000 （1800） UTC, and veered clockwise （anticlockwise） dttring 0000--0600 （1200-1800） UTC. When the north-south span of the TSL increased, it was prone to fracturing; and it disappeared when the dew point temperat-ure gradients to its either side decreased. When the TSL moved northward （southward）, its western （eastern） section broke up, while the eastern （western） section inclined to regenerate or merge. The TSL tended to move towards the positive vorticity areas with significant increases in vorticity. When the positive vorticity center moved down, the height of TSL decreased. Further analysis shows that the plateau surface heating dominated the vorticity attribute of the TSL and its movement, with different contributions from local variation, horizontal advection, and vertical advec-tion of the diabatic heating to the TSL at different heights.

Wave-mean flow interaction and its relationship with the atmospheric energy cycle with diabatic heating

Based on the traditional theory of wave mean flow interaction, an improved quasi-geostrophic Eliassen-Palm flux with diabatic heating included is deduced. It is shown that there exists an intrinsic relation between the atmospheric energy cycle derived by Lorenz and the wave energy transfer derived by Eliassen and Palm. From this relation it becomes clear that the energy propagation process of large-scale stationary wave is indeed a part of Lorenz energy cycle, and the energy transform from mean flow to wave equals the global mass integral of the divergence of local wave energy flux or the global integral of local wave energy. The diagnostic results by using NCEP/NCAR reanalysis data suggest that the classical adiabatic Eliassen-Palm flux relation can present only the wintertime wave energy transformation. For other seasons, however, the diabatic effect must be taken into account.

The Diabatic Heating and the Generation of Available Potential Energy: Results from NCEP Reanalysis

In the existing studies on the atmospheric energy cycle, the attention to thegeneration of available potential energy (APE) is restricted to its global mean value. Thegeographical distributions of the generation of APE and its mechanism of formation are investigatedby using the three-dimensional NCEP/NCAR diabatic heating reanalysis in this study. The results showthat the contributions from sensible heating and net radiation to the generation of zonal andtime-mean APE (G_Z) are mainly located in high and middle latitudes with an opposite sign, while thelatent heating shows a dominant effect on G_Z mainly in the tropics and high latitudes where thecontributions from the middle and upper tropospheres are also contrary to that from the lowtroposphere. In high latitudes, the G_Z is much stronger for the Winter Hemisphere than for theSummer Hemisphere, and this is consistent with the asymmetrical feature shown by the reservoir ofzonal and time-mean APE in two hemispheres, which suggests that the generation of APE plays afundamental role in maintaining the APE in the global atmospheric energy cycle. The samecontributions to the generation of stationary eddy APE (G_(SE)) from the different regions relatedto the maintenance of longitudinal temperature contrast are likely arisen by different physics.Specifically, the positive contributions to G_(SE) from the latent heating in the western tropicalPacific and from the sensible heating over land are dominated by the heating at warm regions,whereas those from the latent heating in the eastern tropical Pacific and from the sensitive heatingover the oceans are dominated by the cooling at cold regions. Thus, our findings provide anobservational estimate of the generation of eddy APE to identify the regional contributions in theclimate simulations because it might be correct for the wrong reasons in the general circulationmodel (GCM). The largest positive contributions to the generation of transient eddy APE (G_(TE)) arefound to be at middle latitudes in the middle and upper tropospheres, where reside the strong localcontributions to the baroclinic conversion from transient eddy APE to transient eddy kinetic energyand the resulting transient eddy kinetic energy.

Relationship Between the Western Pacific Subtropical High and the Subtropical East Asian Diabatic Heating During South China Heavy Rains in June 2005

Based on the daily NCEP/NCAR reanalysis data,the position variation of the western Pacific subtropical high（WPSH） in June 2005 and its relation to the diabatic heating in the subtropical East Asia are analyzed using the complete vertical vorticity equation.The results show that the position variation of the WPSH is indeed associated with the diabatic heating in the subtropical East Asian areas.In comparison with June climatology,stronger heating on the north side of the WPSH and relatively weak ITCZ（intertropical convergence zone） convection on the south side of the WPSH occurred in June 2005.Along with the northward movement of the WPSH,the convective latent heating extended northward from the south side of the WPSH.The heating to the west of the WPSH was generally greater than that inside the WPSH,and each significant enhancement of the heating field corresponded to a subsequent westward extension of the WPSH.In the mid troposphere,the vertical variation of heating on the north of the WPSH was greater than the climatology,which is unfavorable for the northward movement of the WPSH.On the other hand,the vertical variation of heating south of the WPSH was largely smaller than the climatology,which is favorable for the anomalous increase of anticyclonic vorticity,leading to the southward retreat of the WPSH.Before the westward extension of the WPSH in late June 2005,the vertical variation of heating rates to（in） the west（east） of the WPSH was largely higher（lower） than the climatology,which is in favor of the increase of anticyclonic（cyclonic） vorticity to（in） the west（east） of the WPSH,inducing the subsequent westward extension of the WPSH.Similar features appeared in the lower troposphere.In a word,the heating on the north-south,east-west of the WPSH worked together,resulting in the WPSH extending more southward and westward in June 2005,which is favorable to the maintenance of the rainbelt in South China.

Effect of Horizontal Nonuniformity of Diabatic Heating on Tropical Cyclone Intensity and Structure

The effect of the horizontal variation of diabatic heating on the tropicalcyclone intensity and structure is studied in this paper. According to the potential vorticity (PV)equation in axis-symmetric cylindrical coordinates, PV disturbance caused by the radial differenceof diabatic heating is positive (negative) inside (outside) the maximum heating radius, implyingthat the radial nonuniformity of diabatic heating should contribute positively to the intensity of atropical cyclone while negatively to its size. A primitive equation model is then used to get somequantitative ideas on the problem. Results show that the modeled tropical cyclone weakens by about20% but is larger in size if the effect of horizontal variety of convective heating is excluded inthermodynamic and dynamic equations. The PV disturbance originated from the horizontal nonuniformityof diabatic heating is positive inside the maximum heating radius and negative outside, inconsistent with the PV equation analyses. The maximum disturbance (both negative and positive)appears around the maximum heating level and their magnitude is comparable to that generated byvertical variance of heating. It is concluded that the effect of the horizontal heat nonuniformityon the intensity and structure of TC cannot be neglected.

IMPACTS OF DIABATIC PHYSICS PARAMETERIZATION SCHEMES ON MESOSCALE HEAVY RAINFALL SHORTRANGE SIMULATION

Based on the non-hydrostatic version of Mesoscale Model version 5 (MMS) and the data sets of four heavy rainfall scenarios occurring in August 2001 in China,this paper investigates the impacts of diabatic physical processes on predictions of dynamic and thermodynamic elements of heavy rainfall in China,deeply analyzes the effects of convective schemes on mesoscale heavy rain simulations and discusses the feasibility of using model physics perturbations in ensemble simulation of heavy rain,The results show that diabatic physical processes have little impact on the short-range prediction of geopotential height.However,planetary boundary layer schemes and convective schemes have significant influence on moisture divergence flux,vertical velocity,and unstable stratification,which are the three basic conditions of torrential rain.The forecast deviations in different convection schemes increase rapidly in the first 12 h time periods of simulation and the deviation structures are well correlated to that of sub-grid scale rainfall,while in the later periods of simulation with less correlation.Diabatie physical processes influence the structure and evolution of the simulations.For the rain storm events with a homogeneous thermal environmental condition in China.the numerical model ensembles could be created by perturbing the planetary parameterization scheme and convective parameterization.