CLIMATE PREDICTION EXPERIMENT FOR TROPICAL CYCLONE GENESIS FREQUENCY USING THE LARGE-SCALE CIRCULATION FORECAST BY A COUPLED GLOBAL CIRCULATION MODEL

Based on an analysis of the relationship between the tropical cyclone genesis frequency and large-scale circulation anomaly in NCEP reanalysis, large-scale atmosphere circulation information forecast by the JAMSTEC SINTEX-F coupled model is used to build a statistical model to predict the cyclogenesis frequency over the South China Sea and the western North Pacific. The SINTEX-F coupled model has relatively good prediction skill for some circulation features associated with the cyclogenesis frequency including sea level pressure, wind vertical shear, Intertropical Convergence Zone and cross-equatorial air flows. Predictors derived from these large-scale circulations have good relationships with the cyclogenesis frequency over the South China Sea and the western North Pacific. A multivariate linear regression(MLR) model is further designed using these predictors. This model shows good prediction skill with the anomaly correlation coefficient reaching, based on the cross validation, 0.71 between the observed and predicted cyclogenesis frequency. However, it also shows relatively large prediction errors in extreme tropical cyclone years(1994 and 1998, for example).

Large-scale circulation features associated with the heat wave over Northeast China in summer 2018

In late July and early August 2018,Northeast China suffered from extremely high temperatures,with the maxium temperature anomaly exceeding 6°C.In this study,the large-scale circulation features associated with this heat wave over Northeast China are analyzed using station temperature data and NCEP–NCAR reanalysis data.The results indicate that strong anomalous positive geopotential height centers existed from the lower to upper levels over Northeast China,and the related downward motions were directly responsible for the extreme high-temperature anomalies.The northwestward shift of the western Pacific subtropical high(WPSH)and the northeastward shift of the South Asian high concurrently reinforced the geopotential height anomalies and descending flow over Northeast China.In addition,an anomalous Pacific–Japan pattern in the lower troposphere led to the northwestward shift of the WPSH,jointly favoring the anomalous geopotential height over Northeast China.Two wave trains emanating from the Atlantic region propagated eastwards along high latitudes and midlatitudes,respectively,and converged over Northeast China,leading to the enhancement of the geopotential height anomalies.

Drought variability and its connection with large-scale atmospheric circulations in Haihe River Basin

Drought is one of the most widespread and devastating extreme climate events when water availability is significantly below normal levels for a long period.In recent years,the Haihe River Basin has been threatened by intensified droughts.Therefore,characterization of droughts in the basin is of great importance for sustainable water resources management.In this study,two multi-scalar drought indices,the standardized precipitation evapotranspiration index(SPEI)with potential evapotranspiration calculated by the PenmaneMonteith equation and the standardized precipitation index(SPI),were used to evaluate the spatiotemporal variations of drought characteristics from 1961 to 2017 in the Haihe River Basin.In addition,the large-scale atmospheric circulation patterns were used to further explore the potential links between drought trends and climatic anomalies.An increasing tendency in drought duration was detected over the Haihe River Basin with frequent drought events occurring in the period from 1997 to 2003.The results derived from both SPEI and SPI demonstrated that summer droughts were significantly intensified.The analysis of large-scale atmospheric circulation patterns indicated that the intensified summer droughts could be attributed to the positive geopotential height anomalies in Asian mid-high latitudes and the insufficient water vapor fluxes transported from the south.©2021 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Interannual Variation of Tropical Night Frequency in Beijing and Associated Large-Scale Circulation Background

This study examined the variability in frequency of tropical night occurrence （i.e., minimum air tem- perature 25℃） in Beijing, using a homogenized daily temperature dataset during the period 1960–2008. Our results show that tropical nights occur most frequently in late July and early August, which is consis- tent with relatively high air humidity associated with the rainy season in Beijing. In addition, year-to-year variation of tropical night occurrence indicates that the tropical nights have appeared much more frequently since 1994, which can be illustrated by the yearly days of tropical nights averaged over two periods： 9.2 days of tropical nights per year during 1994–2008 versus 3.15 days during 1960–1993. These features of tropical night variations suggest a distinction between tropical nights and extreme heat in Beijing. We further investigated the large-scale circulations associated with the year-to-year variation of tropical night occurrence in July and August, when tropical nights appear most frequently and occupy 95% of the annual sum. After comparing the results in the two reanalysis datasets （NCEP/NCAR and ERA-40） and considering the possible effects of decadal change in the frequency of tropical nights that occurred around 1993/94, we conclude that on the interannual time scale, the cyclonic anomaly with a barotropic structure centered over Beijing is responsible for less frequent tropical nights, and the anticyclonic anomaly is responsible for more frequent occurrence of tropical nights over Beijing.

Present Situations and Suggestions for Large-scale Development of Chenopodium quinoa Willd.

In this paper,based on the study of Chenopodium quinoa Willd.planting,it is concluded that the current situations of large-scale development of C.quinoa Willd.include the following four aspects:first,the research on C.quinoa Willd.varieties needs to be strengthened;second,it is insufficient to master the training environment and cultivation techniques;third,the large-scale planting of C.quinoa Willd.is not enough;fourth,the degree of mechanization of C.quinoa Willd.planting is not enough.In view of the above situation,this paper puts forward the following effective suggestions to strengthen the large-scale development of C.quinoa Willd.:the first is to increase the investment in C.quinoa Willd.variety research;the second is to strengthen the analysis of introduction and screening of C.quinoa Willd.varieties;the third is to study the best planting environment and cultivation techniques of C.quinoa Willd.;the fourth is to increase the scale of mechanized production of C.quinoa Willd.;the fifth is to increase the research and development of C.quinoa Willd.related products and their deep processing technology.

An Eddy-Permitting Oceanic General Circulation Model and Its Preliminary Evaluation

An eddy-permitting, quasi-global oceanic general circulation model, LICOM (LASG/IAP (State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics) Climate System Ocean Model), with a uniform grid of 0.5? × 0.5? is established. Forced by wind stresses from Hellerman and Rosenstain (1983), a 40-yr integration is conducted with sea surface temperature and salinity being restored to the Levitus 94 datasets. The evaluation of the annual mean climatology of the LICOM control run shows that the large-scale circulation can be well reproduced. A comparison between the LICOM control run and a parallel integration of L30T63, which has the same framework but a coarse resolution, is also made to con?rm the impact of resolution on the model performance. On account of the reduction of horizontal viscosity with the enhancement of the horizontal resolution, LICOM improves the simulation with respect to not only the intensity of the large scale circulations, but also the magnitude and structure of the Equatorial Undercurrent and South Equatorial Current. Taking advantage of the ?ne grid size, the pathway of the Indonesian Through?ow (ITF) is better represented in LICOM than in L30T63. The transport of ITF in LICOM is more convergent in the upper layer. As a consequence, the Indian Ocean tends to get warmer in LICOM. The poleward heat transports for both the global and individual basins are also signi?cantly improved in LICOM. A decomposed analysis indicates that the transport due to the barotropic gyre, which primarily stands for the barotropic e?ect of the western boundary currents, plays a crucial role in making the di?erence.

Relationships between the Oxygen Isotopes in East Asian Stalagmites and Large-Scale Atmospheric and Oceanic Modes

The stalagmite δ18O record is known to be associated with the climate, but the specifics of the relationship remain unclear. It may not represent variation in air temperature or precipitation, but instead reflect integral changes of monsoon circulation, especially water vapor sources(the so-called "circulation effect"). Since large-scale atmospheric-oceanic modes such as the Atlantic Multidecadal Oscillation(AMO), Pacific Decadal Oscillation(PDO), and North Atlantic Oscillation(NAO) exert significant effects on Asian monsoon, in this paper the authors investigate the relationships of the East Asian stalagmite δ18O record with these modes. The last three centuries form the focus of our study, for which the authors use reconstructed as well as instrumental data. Considering the impacts of human activity, our analysis is conducted with respect to two periods—the pre- and post-industrial periods. The results show significant lead-lag connections: a positive correlation peaks when the PDO leads East Asian stalagmite δ18O by 3 years, which is persistent over the past 300 years; while the relationships of the AMO and NAO with the East Asian stalagmite δ18O record show significant differences in the post-industrial relative to the pre-industrial period. This implies that the East Asian stalagmite δ18O record may primarily reflect the PDO signal.

Circulation-Enhanced Tank Heating Using Shallow Profile Coil Bundles

Heavy fuel oils require heated tanks to facilitate their transportation and processing.This paper proposes and investigates threeand four-level heating coil bundles.Numerical study revealed that powerful large-scale circulation of the heated fluid enhances heat transfer,delivering 16.7%and 23%improvements to the average heat transfer coefficient for the three-and four-level bundles,respectively.Furthermore,this circulation improves oil mixing and limits the variation in bulk oil temperature to-0.3 to+1.3°C from the average.The study also quantified oil flow velocity near the bottom of the tank.The time-averaged horizontal components of velocity,estimated 25 mm and 50 mm above the bottom of the tank,exceed 2 mm/s and 4 mm/s,respectively.The proposed heating coil bundles feature a compact design that reduces the material and labor costs of construction and that,by occupying only a small portion of the bottom of the tank,improves accessibility,maintenance,and cleaning.

Evolving Perspectives on Abrupt Seasonal Changes of the General Circulation

Professor Duzheng YE（Tu-cheng YEH） was decades ahead of his time in proposing a model experiment to investigate whether abrupt seasonal changes of the general circulation can arise through circulation feedbacks alone, unrelated to underlying inhomogeneities at the lower boundary. Here, we introduce Professor YEH＇s ideas during the 1950 s and 1960 s on the general circulation and summarize the results and suggestions of Yeh et al.（1959） on abrupt seasonal changes. We then review recent advances in understanding abrupt seasonal changes arising from model experiments like those proposed by Yeh et al.（1959）. The model experiments show that circulation feedbacks can indeed give rise to abrupt seasonal transitions.In these transitions, large-scale eddies that originate in midlatitudes and interact with the zonal mean flow and meridional overturning circulations in the tropics play central roles.

Countermeasures and Investigation of Land Circulation in Less Developed Agricultural Area of Henan Province,China

Some places in Henan Province are investigated by using sample surveys and interviews. Result shows that land circulation in less developed agricultural area of Henan Province has the characteristics of small scale,single form,short period,and circulation land in economic core region. Problems in land circulation are as follows:slow transfer of rural surplus labor force,hard implementation of fundamental land circulation,complicated mentality towards rural land circulation,many misgivings about land circulation,the unformed social service system of land circulation,and imperfect agricultural risk prevention mechanism for circulated land use. Based on the characteristics of land circulation,suggestions for promoting the land circulation of less developed agricultural areas are put forward in order to solve the problems in land circulation and to lay the foundation for effective implementation of land circulation,such as speeding up the development of urbanization,developing the circulation of collective land,effectively implementing the laws and regulations of rural collective land circulation,transferring land according to law,establishing market mechanism of agricultural land circulation,promoting the agricultural industrialization,establishing market mechanism of agricultural land circulation,promoting the agricultural industrialization,energetically readjusting rural industrial structure,and developing economy with local characteristics.

The interannual periodicity of precipitation and its links to the large-scale circulations over the Third Pole

To understand the spatio-temporal variability of precipitation(P)in the Third Pole region(centered on the Tibetan Plateau-TP),it is necessary to quantify the interannual periodicity of P and its relationship with large-scale circulations.In this study,Morlet wavelet transform was used to detect significant(p<0.05)periodic characteristics in P data from meteorological stations in four climate domains in the Third Pole,and to reveal the major large-scale circulations that triggered the variability of periodic P,in addition to bringing large amounts of water vapour.The wavelet transform results were as follows.(1)Significant quasiperiodicity varied from 2 to 11 years.The high-frequency variability mode(2 to 6 years quasi-periods)was universal,and the low-frequency variability mode(7 to 11 years quasi-periods)was rare,occurring mainly in the westerlies and Indian monsoon domains.(2)The majority of periods were base periods(53%),followed by two-base periods.Almost all stations in the Third Pole(95%)showed one or two periods.(3)Periodicity was widely detected in the majority of years(84%).(4)The power spectra of P in the four domains were dominated by statistically significant high-frequency oscillations(ie.,with short periodicity).(5)Large-scale circulations directly and indirectly influenced the periodic P variability in the different domains.The mode of P variability in the different domains was influenced by interactions between large-scale circulation features and not only by the dominant circulation and its control of water vapour transport.The results of this study will contribute to better understanding of the causal mechanisms associated with P variability,which is important for hydrological science and waterresourcemanagement.

Differences in Variations of Long-Lived and Short-Lived Summer Heat Waves during 1981-2020 over Eastern China and Their Corresponding Large-Scale Circulation Anomalies

Using daily maximum temperature(Tmax)data from 516 observation stations in eastern China from 1981 to 2020,this study employed a relative threshold method to define short-and long-lived heat waves(HWs)by considering regional climate differences to investigate the spatial characteristics and evolution of large-scale circulation during summer HWs.The results demonstrated spatial disparities in the frequency distribution of HWs of different durations and differences in the magnitude of duration and intensity between short-and long-lived HWs.Empirical orthogonal function analysis revealed three dominant spatial modes for both short-and long-lived HWs.The first mode showed that short-lived HWs occur prominently in both northern and southern regions,whereas long-lived HWs mainly occur in the northern region.The second mode was characterized by a meridional dipole pattern in both cases.The third mode exhibited a quadrupole pattern for short-lived HWs and a tripole pattern for long-lived HWs.Differences in the center locations of anomalies in the 500-hPa geopotential height and 850-hPa wind fields significantly influenced the temperature and precipitation anomaly distribution of typical HWs by affecting the warm column in the lower troposphere,cloud distribution,and moisture transport.Moreover,the atmospheric circulation evolution processes of typical HWs associated with the different modes of long-and short-lived HWs were linked to distinct teleconnection patterns.During the three modes of long-lived(short-lived)HWs,there was stronger(weaker)wave flux activity with multiple(single)propagation paths.Stronger westward Atlantic wave train activity at 300 hPa triggered the synergistic action of meridional and zonal wave fluxes,favoring the strengthening and maintenance of positive anomalies in geopotential height of 500 hPa.This may have contributed to the formation of long-lived HWs.These findings provide valuable insights to enhance our understanding and prediction of summer HWs.

Extreme large-scale atmospheric circulation associated with the“21·7”Henan flood

From July 19 to 21,2021,Henan,a province in northern China(NC),was affected by severe flooding(referred to hereafter as“21·7”)caused by a prolonged record-breaking extreme precipitation(EP)event.Understanding the extremes of the large-scale circulation pattern during“21·7”is essential for predicting EP events and preventing future disasters.In this study,daily atmospheric large-scale circulations over NC in the summers from 1979 to 2021 were investigated using the circulation classification method of an obliquely rotated principal component analysis in T-mode(PCT).The geopotential heights at 500 hPa and 925 hPa were applied successively in classification.Among the nine summer circulation patterns found at 500 hPa,the three days of“21·7”belonged to the Type 8 pattern,which had the second highest probability of EP days among all patterns.It was characterized by a southeasterly wind toward North China Plain driven by a dipole geopotential height field,with the West Pacific subtropical high(WPSH)extending far north to 30°N and low pressure to the south near NC.Tropical cyclones(TCs)occurred on 72.5%of EP days,in which larger amounts of precipitation and a longer duration of EP days were found along the mountains in NC,as compared with other patterns.The distribution of EP events under this pattern was mainly influenced by the location of the low pressure at 925 hPa in the dipole.The subtype 8-3 circulation,with low pressure in the east of Taiwan Island,included“21·7”and accounted for 1.6%of all summer days.Typhoon In-fa,together with the WPSH,gave rise to intense column integrated moisture flux convergence(IMFC)via the southeasterly wind to Henan,which occurred continuously during the 3 days of“21·7”,resulting in the largest(second largest)mean IMFC among 3 consecutive EP days under type 8(all types)during the past 43 summers in NC.Further analysis revealed that the large-scale dynamic process could not completely explain the record-breaking EP during“21·7”,indicating possible contributions of other dynamic processes related to meso-scale convective storms.

MM5 Simulations of the China Regional Climate During the LGM.Ⅱ:Influence of Change of Land Area,Vegetation,and Large-scale Circulation Background

Using a regional climate model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate the relative LGM climate response to changes of land-sea distribution, vegetation, and large-scale circulation background over China. Model results show that compared with the present climate, the fluctuations of sea-land distribution in eastern Asia during the LGM result in the temperature decrease in winter and increase in summer. It has significant impact on the temperature and precipitation in the east coastal region of China. The impact on precipitation in the east coastal region of China is the most significant one, with 25%-50% decrease in the total precipitation change during the LGM. On the other hand, the changes in sea-land distribution have less influence on the climate of inland and western part of China. During the LGM, significant changes in vegetation result in temperature alternating with winter increase and summer decrease, but differences in the annual mean temperature are minor. During the LGM, the global climate, i.e., the large-scale circulation background has changed significantly. These changes have significant influences on temperature and precipitation over China. They result in considerable temperature decreases in this area, and direct the primary patterns and characteristics of temperature changes. Results display that, northeastern China has the greatest temperature decrease, and the temperature decrease in the Tibetan Plateau is larger than in the eastern part of China located at the same latitude. Moreover, the change of large-scale circulation background also controls the pattern of precipitation change. Results also show that, most of the changes in precipitation over western and northeastern parts of China are the consequences of changing large-scale circulation background, of which 50%-75% of precipitation changes over northern and eastern China are the results of changes in large-scale circulation background. Over China, the LGM climate responses to different mechanisms in order of strength from strong to weak are, the large-scale circulation pattern, sea- land distribution, vegetation, CO2 concentration, and earth orbital parameters.

Anomalous Features of Extreme Meiyu in 2020 over the Yangtze-Huai River Basin and Attribution to Large-Scale Circulations

Extremely anomalous features of Meiyu in 2020 over the Yangtze-Huai River basin(YHRB)and associated causes in perspective of the large-scale circulation are investigated in this study,based on the Meiyu operational monitoring information and daily data of precipitation,global atmospheric reanalysis,and sea surface temperature(SST).The main results are as follows.(1)The 2020 YHRB Meiyu exhibits extremely anomalous characteristics,which are the most prominent since the 1980 s.The 2020 Meiyu season features the fourth earliest onset,the third latest retreat,the longest duration,the maximum Meiyu rainfall,the strongest mean rainfall intensity,and the maximum number of stations/days with rainstorm.(2)The extremely long duration of the 2020 Meiyu season lies in the farily early onset and late retreat of Meiyu in this particular year.The early onset of Meiyu is due to the earlier-than-normal first northward shift and migration of the key influential systems including the northwestern Pacific subtropical high(NWPSH)and the South Asian high(SAH)along with the East Asian summer monsoon,induced by weak cold air activities from late May to early mid-June.However,the extremely late retreat of Meiyu is because of later-than-normal second northward shift of the associated large-scale circulation systems accompanied with strong cold air activities,and extremely weak and southward located ITCZ over Northwest Pacific in July.(3)The extremely more than normal Meiyu rainfall is represented by its long duration and strong rainfall intensity.The latter is likely attributed to extreme anomalies of water vapor convergence and vertical ascending motion over the YHRB,resulting from the compound effects of the westward extended and enlarged NWPSH,the eastward extended and expanded SAH,and the strong water vapor transport associated with the low-level southerly wind.The extremely warm SST in the tropical Indian Ocean seems to be the key factor to induce the above-mentioned anomalous large-scale circulations.The results from this study serve to improve understanding of formation mechanisms of the extreme Meiyu in China and may help forecasters to extract useful large-scale circulation features from numerical model products to improve medium-extended-range operational forecasts.

Changes in Persistent Precipitation in Northwest China and Related Large-Scale Circulation Features

Based on China's daily precipitation data of 2415 stations and ERA5 hourly reanalysis data from 1961 to 2019, the station-based and regional precipitation events over Northwest China(NWC) are identified and sorted into persistent precipitation(PP, duration ≥ 2 days) events and non-persistent precipitation(NPP, duration = 1 day) events;and then changes in the persistence structure of the PP and NPP events over NWC and the long-term mean adjustment of the related large-scale circulation configuration are analyzed. The results show that PP and NPP both witness an increasing trend over most parts of NWC. In terms of the total precipitation at most stations and the regional mean, contributions from PP have been increasing, while those from NPP have been decreasing. This demonstrates that the wetting trend in NWC is mainly caused by the increase in PP. Through analyzing the large-scale circulation corresponding to regional PP events at several representative levels, we found that the westerly jet at 200 hPa, the ridge/trough systems at 500 hPa, and the Mongolian low at sea level are the key circulation systems responsible for regional PP events over NWC. As for long-term mean changes after and before 1990(a shifting point recognized by previous studies), it is found that the extent of the South Asian high becomes larger and the westerly jet shifts northward by approximately 1.5 degrees in the upper troposphere. The ridge near the Ural Mountains and the ridge downstream of NWC strengthen by approximately 10–30 hPa at 500 hPa. Furthermore, the difference between the Mongolian low trough and its surrounding high pressure increases by approximately 2 hPa at the sea level. The combinations of circulation changes from upper to lower levels facilitate the strengthening of ascending motions. These adjustments in circulations create more favorable conditions for PP to occur over NWC in the last three decades.

川西高原冰雹时空分布特征及大冰雹环境条件分析

选取2001—2016年川西高原31个县市气象站逐月冰雹日、3个探空站资料及ERA5逐小时再分析资料,分析川西高原冰雹时空分布特征及冰雹发生的天气背景和环境条件。结果表明:(1)近16 a川西高原冰雹日数总体呈减少趋势,高海拔降雹次数多于较低海拔地区。降雹频率分布曲线呈双峰偏态型,阿坝州的峰值出现在5月和9月,甘孜州出现在6月和9月。降雹主要发生时段为11—21时,占比95.5%,峰值出现在15时和17时。冰雹直径<5 mm冰雹占年降雹的72%以上。(2)连续冰雹天气的发生多伴随有高原低值系统的东移,黄淮低涡西侧的切变是影响夏季阿坝地区的重要天气系统之一。不同季节阿坝北部的大冰雹天气均是在高原低值系统的影响下发生,春、夏季大冰雹个例受明显的冷空气或冷平流的影响。(3)大冰雹个例中,-20℃层高度为7.2~8.6 km,0℃层高度距离地面4 km左右,对流有效位能CAPE≥980 J·kg^(-1)。无论春夏还是秋季,红原大冰雹个例的中低层温差(T600~400 hPa)≥21℃且600~400 hPa垂直风切变达到15~21 m·s^(-1),有利于形成高度组织化的对流风暴。

2021年10月山西一次罕见持续性强降水过程物理机制分析

利用气象观测资料、NCEP/NCAR 1°×1°×再分析以及GDAS等资料,对2021年10月2—7日山西持续性强降水天气过程进行分析。结果表明:稳定的乌拉尔山低槽后部冷空气扩散,中纬度短波槽东移,与副热带高压外围西南暖湿气流持续交汇,高低空急流耦合形成强烈上升运动,低层切变线和地面辐合线稳定维持,及低层水汽不断输送并形成辐合,为持续性强降水的发生发展提供有利的动力和水汽条件。强降水过程分为对流性降水和稳定性降水2个阶段,2个阶段水汽输送通道的源地、路径、高度存在明显差异,但水汽输送贡献率均为对流层中低层山西南侧的水汽输送占主导地位。降水开始前,对流层中上层存在对称不稳定,大气可降水量明显跃增;对流性降水阶段,干空气不断入侵,对流不稳定快速建立与释放,对流层中低层水汽辐合区与强上升气流配合,导致山西出现强对流天气。地形的阻挡、抬升及地形收缩作用对局地极端强降水有增幅作用。

甘肃河东夏季区域性短时强降水环流形势分类特征

甘肃河东地区短时强降水易致灾,预报预警难度大。利用2010-2021年夏季加密观测站逐小时降水资料和NCEP/NCAR再分析资料,筛选出甘肃河东50次区域性短时强降水天气过程,基于这些天气过程的500 hPa位势高度距平场,使用K均值客观聚类分析和主观天气学检验相结合的方法进行天气尺度环流形势分类,并通过合成分析和中尺度对流天气环境场条件分析方法构建不同类型的天气尺度系统配置概念模型。结果表明:(1)甘肃河东区域性短时强降水的天气尺度环流形势可分为高原槽东移型、副高边缘西南气流型、两高切变型和西北气流型四类。(2)副高边缘西南气流型引发的区域性短时强降水次数最多,两高切变型和高原槽东移型发生频率相当,西北气流型发生次数最少。(3)四种类型的环流形势在天气系统配置、抬升条件、水汽条件和不稳定条件等方面存在显著差异。高原槽东移型、副高边缘西南气流型、两高切变型三种类型发生时西太平洋副热带高压(以下简称西太副高)所处的位置逐渐向西向北推进,水汽条件和不稳定条件逐渐趋好,当高空槽引导冷空气东移南下,斜压锋生形成大范围短时强降水。高原槽东移型抬升条件最好,短时强降水落区偏南;两高切变型冷空气偏北且主要由对流层低层侵入,短时强降水落区偏北;副高边缘西南气流型冷暖气团交汇最剧烈,斜压锋生最强,短时强降水范围及强度也更大。西北气流型的动力条件和水汽条件是四类中最差的,但强烈的中高层干冷平流叠加低层暖湿气流或温度暖脊形成了四类中最好的不稳定条件,短时强降水落区较分散。

三统河流域一次局地极端暴雨特征

文章选取三统河流域常规气象观测数据、ERA5再分析资料、风云卫星及雷达产品等,对2022-06-29—2022-06-30通化市柳河县高台村局地极端暴雨过程进行分析。结果表明:此次极端降水发生在深厚高空槽前配合低空较强气旋切变影响下,在暖区温湿条件较好的前期环境中受副高后部低层暖湿切变的触发产生;中低层深厚的水汽饱和层和不稳定能量的增大为极端暴雨的持续提供了水汽和动力条件,表现为强烈的“列车效应”。研究结果旨在为局地暴雨的短时临近预警叫应工作提供一定参考。