A study on the simulation of carbon and water fluxes of Dangxiong alpine meadow and its response to climate change

The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of the Tibetan Plateau,is a typical example.To understand the carbon and water fluxes,water use efficiency(WUE),and their responses to future climate change for the alpine meadow ecosystem in the Dangxiong area,two parameter estimation methods,the Model-independent Parameter Estimation(PEST)and the Dynamic Dimensions Search(DDS),were used to optimize the Biome-BGC model.Then,the gross primary productivity(GPP)and evapotranspiration(ET)were simulated.The results show that the DDS parameter calibration method has a better performance.The annual GPP and ET show an increasing trend,while the WUE shows a decreasing trend.Meanwhile,ET and GPP reach their peaks in July and August,respectively,and WUE shows a“dual-peak”pattern,reaching peaks in May and November.Furthermore,according to the simulation results for the next nearly 100 years,the ensemble average GPP and ET exhibit a significant increasing trend,and the growth rate under the SSP5–8.5 scenario is greater than that under the SSP2–4.5 scenario.WUE shows an increasing trend under the SSP2–4.5 scenario and a significant increasing trend under the SSP5–8.5 scenario.This study has important scientific significance for carbon and water cycle prediction and vegetation ecological protection on the Tibetan Plateau.

A comparative study of the land-atmosphere energy and water exchanges over the Tibetan Plateau and the Yangtze River Region

正确认识不同区域能量和水分循环特征是研究局地地气相互作用及准确预测区域天气,气候变化的关键.为了研究属于干旱/半干旱气候的青藏高原(TP)和湿润/半湿润气候的长江流域(YRR)之间地表能量和水分交换的异同,本文对比分析了两个区域8个不同地表类型(包括高山荒漠,高山草地,(平原)城市和(平原)草地等)观测站点的地表辐射和能量通量数据.结果显示:(1)TP由于高原大气层稀薄且空气洁净,年平均入射短波辐射为251.3W m^(-2),是YRR的1.7倍.加之高原地表反照率高导致反射辐射(59.6 W m^(-2))是YRR的2.87倍.入射及出射的长波辐射为231.5和338.0 W m^(-2),分别为YRR的0.64和0.83.而两个区域的净辐射差异不大;(2)草地站更多的潜热释放使得地表总加热效率高于城市和高山荒漠,TP和YRR的草地站的年平均潜热分别为35.0和38.8 W m^(-2),而植被稀疏且土壤干燥的高山荒漠地区感热最大,年平均感热为42.1 W m^(-2);其次是城市下垫面,其年平均感热为37.7 W m^(-2).研究结果揭示了不同气候背景下典型下垫面地气相互作用特征,为地气相互作用过程深入分析奠定了基础.

Intensified haze formation and meteorological feedback by complex terrain in the North China Plain region

华北平原地区冬季雾霾污染频发,本研究结合地面观测,卫星反演和大气动力-化学耦合模拟发现,该地区复杂地形加剧了细颗粒物污染及其与大气边界层之间的相互作用.一方面,复杂地形导致污染在山麓平原积聚,加强迎风坡上升气流.在污染事件中,污染层易被抬升至1-2公里高度,高空较强的氧化能力利于二次气溶胶生成;另一方面,地形导致的污染层抬升和二次生成进一步加强气溶胶-边界层相互作用,削弱垂直扩散并加剧近地面大气污染.

A Study on the Assessment and Integration of Multi-Source Evapotranspiration Products over the Tibetan Plateau

Evapotranspiration(ET)is a crucial variable in the terrestrial water,carbon,and energy cycles.At present,a large number of multi source ET products exist.Due to sparse observations,however,great challenges exist in the evaluation and integration of ET products in remote and complex areas such as the Tibetan Plateau(TP).In this paper,the applicability of the multiple collocation(MC)method over the TP is evaluated for the first time,and the uncertainty of multisource ET products(based on reanalysis,remote sensing,and land surface models)is further analyzed,which provides a theoretical basis for ET data fusion.The results show that 1)ET uncertainties quantified via the MC method are lower in RS-based ET products(5.95 vs.7.06 mm month^(-1))than in LSM ET products(10.22 vs.17.97 mm month^(-1))and reanalysis ET estimates(7.27 vs.12.26 mm month-1).2)A multisource evapotranspiration(MET)dataset is generated at a monthly temporal scale with a spatial resolution of 0.25°across the TP during 2005-15.MET has better performance than any individual product.3)Based on the fusion product,the total ET amount over the TP and its patterns of spatiotemporal variability are clearly identified.The annual total ET over the entire TP is approximately 380.60 mm.Additionally,an increasing trend of 1.59±0.85 mm yr^(-1)over the TP is shown during 2005-15.This study provides a basis for future studies on water and energy cycles and water resource management over the TP and surrounding regions.

Changes in Regional Heavy Rainfall Events in China during 1961–2012

A new technique for identifying regional climate events, the Objective Identification Technique for Regional Extreme Events（OITREE）, was applied to investigate the characteristics of regional heavy rainfall events in China during the period1961–2012. In total, 373 regional heavy rainfall events（RHREs） were identified during the past 52 years. The East Asian summer monsoon（EASM） had an important influence on the annual variations of China＇s RHRE activities, with a significant relationship between the intensity of the RHREs and the intensity of the Mei-yu. Although the increase in the frequency of those RHREs was not significant, China experienced more severe and extreme regional rainfall events in the 1990 s. The middle and lower reaches of the Yangtze River and the northern part of South China were the regions in the country most susceptible to extreme precipitation events. Some stations showed significant increasing trends in the southern part of the middle and lower reaches of the Yangtze River and the northern part of South China, while parts of North China, regions between Guangxi and Guangdong, and northern Sichuan showed decreasing trends in the accumulated intensity of RHREs.The spatial distribution of the linear trends of events＇ accumulated intensity displayed a similar so-called ＂southern flooding and northern drought＂ pattern over eastern China in recent decades.

Comparisons of Three-Dimensional Variational Data Assimilation and Model Output Statistics in Improving Atmospheric Chemistry Forecasts

Atmospheric chemistry models usually perform badly in forecasting wintertime air pollution because of their uncertainties. Generally, such uncertainties can be decreased effectively by techniques such as data assimilation（DA） and model output statistics（MOS）. However, the relative importance and combined effects of the two techniques have not been clarified. Here,a one-month air quality forecast with the Weather Research and Forecasting-Chemistry（WRF-Chem） model was carried out in a virtually operational setup focusing on Hebei Province, China. Meanwhile, three-dimensional variational（3 DVar） DA and MOS based on one-dimensional Kalman filtering were implemented separately and simultaneously to investigate their performance in improving the model forecast. Comparison with observations shows that the chemistry forecast with MOS outperforms that with 3 DVar DA, which could be seen in all the species tested over the whole 72 forecast hours. Combined use of both techniques does not guarantee a better forecast than MOS only, with the improvements and degradations being small and appearing rather randomly. Results indicate that the implementation of MOS is more suitable than 3 DVar DA in improving the operational forecasting ability of WRF-Chem.

Vertical structure of variabilities in the tropical easterly jet and associated factors

热带东风急流为热带上对流层-下平流层内夏季出现的一支强东风带,其垂直范围为300-70hPa,目前其垂直结构的变化特征有待研究.本文利用经验正交函数分解研究了热带东风急流纬向垂直剖面的主要模态。第一模态表现为垂直方向上急流强度的一致变化.ENSO对第一模态的年际分量具有主导贡献,而大西洋年代际振荡和太平洋年代际振荡可能调制其年代际分量第二模态表现为热带东风急流垂直位移的年际变化.热带平流层准两年振荡不同位相的相继下传既可以直接影响对流层顶的纬向风异常,也可以通过改变海洋性大陆附近的对流异常影响热带东风急流的垂直位置.

Subseasonal reversal of haze pollution over the North China Plain

中国近几十年来频受雾霾污染问题困扰,其中华北平原作为排放最密集的区域之一,常遭遇不同尺度的严重雾霾污染本文利用30余年的能见度和颗粒物(PM_(2.5))观测数据,发现了华北平原地区在秋季和早冬时雾霾污染在次季节尺度上“跷跷板式”反向变化的关系.研究发现,当9-10月污染较轻(重)时,11-12月的污染倾向于加重(减轻).这种突然的变化与局地和大尺度环流的反向变化有关,污染较重的月份常伴随有更高的相对湿度,更低的边界层高度和近地面风速以及低层的南风异常,均不利于污染的垂直和水平扩散和传输,从而导致了次季节尺度上霾污染的加重,进一步的研究发现环流场的突然转向与在次季节尺度上活跃的中纬度波列的传播密切相关,而此波列可能主要与大西洋海温转变及引起的EA/WR遥相关型有关,这一次季节反向变化为霾污染多尺度变率预测提供了新的理解,同时为华北地区年度空气质量达标的短期目标提供了具有可行性的参考方法.

Influence of Atmospheric Particulate Matter on Ozone in Nanjing,China:Observational Study and Mechanistic Analysis

Particulate matter with diameters of 2.5 μm or smaller(PM_(2.5)) and ozone(O_3) are major pollutants in the urban atmosphere. PM_(2.5) can affect O_3 by altering the photolysis rate and heterogeneous reactions. However, these two processes and their relative importance remain uncertain. In this paper, with Nanjing in China as the target city, we investigate the characteristics and mechanism of interactions between particles and O_3 based on ground observations and numerical modeling.In 2008, the average concentrations of PM_(2.5) and O_3 at Caochangmen station are 64.6 ± 47.4 μg m^(-3) and 24.6 ± 22.8 ppb,respectively, while at Pukou station they are 94.1 ± 63.4 μg m^(-3) and 16.9 ± 14.9 ppb. The correlation coefficient between PM_(2.5) and O_3 is -0.46. In order to understand the reaction between PM_(2.5) and O_3, we construct a box model, in which an aerosol optical property model, ultraviolet radiation model, gas phase chemistry model, and heterogeneous chemistry model,are coupled. The model is employed to investigate the relative contribution of the aforementioned two processes, which vary under different particle concentrations, scattering capability and VOCs/NOxratios(VOCs: volatile organic compounds;NOx: nitric oxide and nitrogen dioxide). Generally, photolysis rate effect can cause a greater O_3 reduction when the particle concentrations are higher, while heterogeneous reactions dominate O_3 reduction with low-level particle concentrations.Moreover, in typical VOC-sensitive regions, O_3 can even be increased by heterogeneous reactions. In Nanjing, both processes lead to O_3 reduction, and photolysis rate effect is dominant. Our study underscores the importance of photolysis rate effect and heterogeneous reactions for O_3, and such interaction processes should be fully considered in future atmospheric chemistry modeling.

Causes of the Extreme Hot Midsummer in Central and South China during 2017:Role of the Western Tropical Pacific Warming

This study investigates why an extreme hot midsummer occurred in Central and South China(CSC) during 2017. It is shown that the western North Pacific subtropical high(WNPSH) was abnormally intensified and westward-extending,resulting in anomalous high pressure and consequent extreme heat over CSC. The abnormal WNPSH was favored by the warming of the western tropical Pacific(WTP), which was unrelated to ENSO and manifested its own individual effect.The WTP warming enhanced the convection in-situ and led to anomalous high pressure over CSC via a local meridional circulation. The influence of the WTP was confirmed by CAM4 model experiments. A comparison between the 2017 midsummer and 2010 midsummer(with a stronger WNPSH but weaker extreme heat) indicated that the influence of the WNPSH on extreme heat can be modulated by the associated precipitation in the northwestern flank.The role of the WTP was verified by regression analyses on the interannual variation of the WTP sea surface temperature anomaly(SSTA). On the other hand, the WTP has undergone prominent warming during the past few decades, resulting from decadal to long-term changes and favoring extreme warm conditions. Through a mechanism similar to the interannual variation, the decadal to long-term changes have reinforced the influence of WTP warming on the temperature over CSC,contributing to the more frequent hot midsummers recently. It is estimated that more than 50% of the temperature anomaly over CSC in the 2017 midsummer was due to the WTP warming, and 40% was related to the decadal to long-term changes of the WTP SSTA.

Advantages of the latest Los Alamos Sea-Ice Model(CICE):evaluation of the simulated spatiotemporal variation of Arctic sea ice

The Los Alamos Sea-Ice Model(CICE)is one of the most popular sea-ice models.All versions of it have been the main sea-ice module coupled to climate system models.Therefore,evaluating their simulation capability is an important step in developing climate system models.Compared with observations and previous versions(CICE4.0 and CICE5.0),the advantages of CICE6.0(the latest version)are analyzed in this paper.It is found that CICE6.0 has the minimum interannual errors,and the seasonal cycle it simulates is the most consistent with observations.CICE4.0 overestimates winter sea-ice and underestimates summer sea-ice severely.Meanwhile,the errors of CICE5.0 in winter are larger than for the other versions.The main attention is paid to the perennial ice and the seasonal ice.The spatial distribution of root-mean-square errors indicates that the simulated errors are distributed in the Atlantic sector and the outer Arctic.Both CICE4.0 and CICE5.0 underestimate the concentration of the perennial ice and overestimate that of the seasonal ice in these areas.Meanwhile,CICE6.0 solves this problem commendably.Moreover,the decadal trends it simulates are comparatively the best,especially in the central Arctic sea.The other versions underestimate the decadal trend of the perennial ice and overestimate that of the seasonal ice.In addition,an index used to objectively describe the difference in the spatial distribution between the simulation and observation shows that CICE6.0 produces the best simulated spatial distribution.

A southward withdrawal of the northern edge of the East Asian summer monsoon around the early1990s

The northern edge of the East Asian summer monsoon （EASM） is identified using the pentad total column water vapor obtained from ERA-Interim reanalysis data during 1979-2015.Empirical orthogonal function analysis is applied to study the meridional displacement of the northern edge of the EASM during the study period,and the results show an interdecadal southward shift around 1993/1994 and an indistinct northward displacement after 2007/2008.To focus on the interdecadal change around 1993/1994,composite analysis using the difference between 1979-1993 and 1994-2007 is employed.Through examination of the differences between these two periods,a significant anticyclonic anomaly is found over Mongolia,suggesting a pronounced interdecadal weakening of the Mongolian low during 1994-2007.Thus,northward advancement of the EASM may have been prevented by the anomalous northerly flow to the east of the weakened Mongolian low after 1993.Further study shows that the interdecadal weakening of the Mongolian low might be attributable to the meridional inhomogeneity of surface warming over the northern part of East Asia.Previous studies suggest that such meridional inhomogeneity would lead to a reduction in local atmospheric baroclinicity,and thus the suppression of extratropical cyclone activity over Mongolia,resulting in a southward withdrawal of the northern edge of the EASM on the interdecadal timescale.

Strengthening the three-dimensional comprehensive observation system of multi-layer interaction on the Tibetan Plateau to cope with the warming and wetting trend

Changes in the water cycle on the Tibetan Plateau(TP)have a significant impact on local agricultural production and livelihoods and its downstream regions.Against the background of widely reported warming and wetting,the hydrological cycle has accelerated and the likelihood of extreme weather events and natural disasters occurring(i.e.,snowstorms,floods,landslides,mudslides,and ice avalanches)has also intensified,especially in the highelevation mountainous regions.Thus,an accurate estimation of the intensity and variation of each component of the water cycle is an urgent scientific question for the assessment of plateau environmental changes.Following the transformation and movement of water between the atmosphere,biosphere and hydrosphere,the authors highlight the urgent need to strengthen the three-dimensional comprehensive observation system(including the eddy covariance system;planetary boundary layer tower;profile measurements of temperature,humidity,and wind by microwave radiometers,wind profiler,and radiosonde system;and cloud and precipitation radars)in the TP region and propose a practical implementation plan.The construction of such a three-dimensional observation system is expected to promote the study of environmental changes and natural hazards prevention.

Vortex Rossby Waves in Asymmetric Basic Flow of Typhoons

Wave ray theory is employed to study features of propagation pathways（rays） of vortex Rossby waves in typhoons with asymmetric basic flow, where the tangential asymmetric basic flow is constructed by superimposing the wavenumber-1 perturbation flow on the symmetric basic flow, and the radial basic flow is derived from the non-divergence equation. Results show that, in a certain distance, the influences of the asymmetry in the basic flow on group velocities and slopes of rays of vortex Rossby waves are mainly concentrated near the radius of maximum wind（RMW）, whereas it decreases outside the RMW. The distributions of radial and tangential group velocities of the vortex Rossby waves in the asymmetric basic flow are closely related to the azimuth location of the maximum speed of the asymmetric basic flow, and the importance of radial and tangential basic flow on the group velocities would change with radius. In addition, the stronger asymmetry in the basic flow always corresponds to faster outward energy propagation of vortex Rossby waves. In short, the group velocities, and thereby the wave energy propagation and vortex Rossby wave ray slope in typhoons, would be changed by the asymmetry of the basic flow.

A Climatological Perspective on Extratropical Synoptic-Scale Transient Eddy Activity Response to Western Pacific Tropical Cyclones

An observational study focusing on the contribution of tropical cyclones(TCs)that form over the western North Pacific(WNP)to the synoptic-scale transient eddy activity(STEA)over the North Pacific during the boreal autumn and early winter in the period 1979–2019 is presented in this paper.Statistical results show that WNP TCs entering the midlatitudinal North Pacific provide significant positive effects on the pentad mean strength of STEA,which is primarily concentrated over the Kuroshio/Oyashio Extensions(KOE)and regions from east of Japan to 160°W in the lower and midto-upper troposphere,respectively.TC intensity is highly indicative of the subsequent STEA with a correlation coefficient of 0.37/0.33/0.45 at 300 hPa/500 hPa/850 hPa exceeding the 99%confidence level for the period 1979–2019.The strength of STEA in the upper troposphere associated with TCs presents a more significant linear growth with TC intensity than that at the mid-to-lower levels after the cyclones enter the KOE region,suggesting that the impact of TCs on STEA gradually increases with height.Further analyses reveal that the contribution of TCs accounts for 4%–6%of the total STEA change over the KOE region during the late autumn and early winter.In addition,the influence of TCs on STEA experienced an interdecadal decrease from the early 2000 s through the early 2010 s.

Role of tropical cyclones over the western North Pacific in the East Asian summer monsoon system

Precipitation observations collected at weather stations in eastern China, the NCEP/NCAR reanalysis data, the tropical cyclone(TC) Best Track Dataset, and a sensitivity numerical experiment were used in the present study to investigate the role in the East Asian summer monsoon(EASM) system played by frequent TC activities over the western North Pacific(WNP). Results indicated that, in active TC years, the EASM is stronger and the southerly winds in the lower troposphere advance farther north and reach higher latitudes.Meanwhile, the monsoon rain belt remains in the lower and middle reaches of the Yangtze River valley for a relatively short period,leading to less precipitation there. Both the western Pacific subtropical high and the South Asian high weaken with the northward shift of the ridgelines for both high-pressure systems as well as the East Asian subtropical upper-level jet. Therefore, the impacts of frequent TC activities over the WNP on each individual component of the EASM are in phase with those of the stronger EASM itself, amplifying features of the already strengthened EASM.

Estimations of Land Surface Characteristic Parameters and Turbulent Heat Fluxes over the Tibetan Plateau Based on FY-4A/AGRI Data

Accurate estimates of land surface characteristic parameters and turbulent heat fluxes play an important role in the understanding of land-atmosphere interaction. In this study, Fengyun-4A (FY-4A) Advanced Geostationary Radiation Imager (AGRI) satellite data and the China Land Data Assimilation System (CLDAS) meteorological forcing dataset CLDAS-V2.0 were applied for the retrieval of broadband albedo, land surface temperature (LST), radiation flux components, and turbulent heat fluxes over the Tibetan Plateau (TP). The FY-4A/AGRI and CLDAS-V2.0 data from 12 March 2018 to 30 April 2018 were first used to estimate the hourly turbulent heat fluxes over the TP. The time series data of in-situ measurements from the Tibetan Observation and Research Platform were divided into two halves-one for developing retrieval algorithms for broadband albedo and LST based on FY-4A, and the other for the cross validation. Results show the root-mean-square errors (RMSEs) of the FY-4A retrieved broadband albedo and LST were 0.0309 and 3.85 K, respectively, which verifies the applicability of the retrieval method. The RMSEs of the downwelling/upwelling shortwave radiation flux and downwelling/upwelling longwave radiation flux were 138.87/32.78 W m^(−2) and 51.55/17.92 W m^(−2), respectively, and the RMSEs of net radiation flux, sensible heat flux, and latent heat flux were 58.88 W m^(−2), 82.56 W m^(−2) and 72.46 W m^(−2), respectively. The spatial distributions and diurnal variations of LST and turbulent heat fluxes were further analyzed in detail.

An interdecadal decrease in extreme heat days in August over Northeast China around the early 1990s

Northeast China(NEC)witnessed an interdecadal increase in summer extreme heat days(EHDs)around the mid-1990s.The current study reveals that this interdecadal increase only occurs in June and July,while August features a unique interdecadal decrease in EHDs around the early 1990s.Plausible reasons for the interdecadal decrease in EHDs in August are further investigated.Results show that the interdecadal decrease in EHDs in August is due to the deceased variability of daily maximum temperature(Tmax).Overall,the variation of the Tmax over NEC in August is modulated by the Eurasian teleconnection pattern,Silk Road pattern,and East AsiaPacific pattern.However,the influence of the Silk Road pattern dramatically weakens after the early 1990s because the meridional wind variability along the westerly jet significantly decreases.The weakened influence of the Silk Road pattern contributes to the decreased Tmax variability over NEC.Meanwhile,the convection over the western North Pacific,which accompanies the East Asia-Pacific pattern,presents a significant decrease in variance after the early 1990s,further decreasing the Tmax variability over NEC.

Relationship between cross-equatorial flows over the Bay of Bengal and Australia in boreal summer:Role of tropical diabatic heating

The interannual variability of cross-equatorial flows(CEFs)over the Asian–Australian monsoon(AAM)region during boreal summer was analyzed by applying the empirical orthogonal function(EOF)method to the meridional wind at 925 h Pa.The first mode(EOF1)exhibits an in-phase relationship among different CEF channels over the AAM region,which has received much attention owing to its tight linkage with ENSO.By contrast,the second mode(EOF2)possesses an out-of-phase relationship between the Bay of Bengal(BOB)CEF(90°E)and Australian CEF,among which the New Guinea CEF near 150°E shows the most significant opposite correlation with the BOB CEF.Observational and numerical model results suggest that the equatorially asymmetric heat source(sink)over the western(eastern)Maritime Continent,closely associated with the in-situ sea surface temperature anomaly,can induce cross-equatorial northerly(southerly)flow into the heating hemisphere,which dominates the out-of-phase relationship between the BOB and New Guinea CEFs.Furthermore,an equatorially symmetric heating over the central Pacific may indirectly change the CEFs by modulating the zonal atmospheric circulation near the Maritime Continent.

Summer extreme precipitation patterns and synoptic-scale circulation precursors over the Tibetan Plateau

In the context of global warming,the extreme summer precipitation over the Tibetan Plateau(TP)has changed significantly.In this study,the summer(June–August)extreme precipitation on the TP was classified into three spatial types by applying the K-means clustering method to the Third Pole Region long time-series high-resolution(1/30°)precipitation dataset(TPHi Pr,1979–2020).The characteristics of the circulation anomalies and precursors corresponding to the extreme precipitation on the TP in summer during 1979–2020 were investigated.The results showed that the summer extreme precipitation of the TP can be categorized into northwestern(NW),southeastern(SE),and southern Himalayan(HS)types based on extreme precipitation thresholds.The NW and SE types are mainly influenced by anomalous signals in the mid-to-high latitude regions upstream of them,whereas the HS type is controlled by the localized subtropical anomalous circulation.On the 8th day before the onset of the NW type,an anomalous cyclone was observed in the western Atlantic Ocean(60°W,50°N),which triggered the west-to-east quasi-latitudinal propagation of Rossby waves.On the onset day of the NW type,the upper troposphere showed positive-negative-positive geopotential height anomalies along the latitudinal 40°N from the Caspian Sea,the western part of Xinjiang,to the northeastern TP.Moisture entered from the Arabian Sea along the southeastern edge of the anomalous cyclone on the southwestern TP and converged in the northwestern TP.Compared to the NW type,the precursors of the SE type appeared at higher latitudes and were more intense.On the 8th day before the onset of the SE type,an anomalous cyclone occurred near Greenland(60°W,70°N)and excited Rossby waves propagating southeastward.On the onset day of the SE type,the upper troposphere showed negative-positive-negative geopotential height anomalies across Eurasia from the Ural Mountains and the Iranian Plateau to the northern TP in the northwest-southeast direction and entered the southeastern TP from the Bay of Bengal along the southeastern edge of the anomalous cyclone in the southern TP.On the 6th day before the onset of the HS type,the anomalously high pressure in the middle and lower layers of the low-latitude region extended westward,and a significant anticyclonic anomalous circulation occurred on the southern TP on the onset day of the HS type,enabling the delivery of moisture from the Bay of Bengal to the southern foothills of the Himalayas.Additionally,an anomalous cyclone perched in the northeastern TP at a geopotential height of 200 h Pa strengthened westerly winds in the southern TP and contributed to the maintenance of the anticyclonic system on the southern TP.