青藏高原地面加热场日变化对亚洲季风区大气环流的影响

利用1982-1996年每天两次的NCEP丙分析资料，研究青藏高原地面加热场的日变化对亚洲季风区环流的影响。结果表明；青藏高原地面加热场的日变化是引起亚洲季风区大气环流日变化的主要因子，青藏高原地区，阿拉伯海，盂加拉湾和菲律宾附近地区是四个主要的日变化显著区，青藏高原地区是垂直运动的负值日变化中心，其它三个区域的日变化与青藏高原地区的日变化有反相关系，这种特征一年四季都存在，但各显著区域范围的大小，中心位置及环流日变化的强度随季节有不同程度的变化，青藏高原加热场日变化对我国东部地区环流的影响主要发生在夏季。     

中国近40年来雾的研究

自1958年以来,中国一直重视人工消雾试验和雾的物理学研究。文中总结了40余年来中国在人工消雾、雾的物理化学特性、雾生消物理过程研究等方面的成就,介绍了雾与生态环境之间的紧密关系及雾数值模式研究的发展过程和取得的重要成果。雾是贴地层空气中悬浮着大量水滴或冰晶微粒而使水平能见距离降到1km以内的天气现象。它不仅对水陆空交通有不利影响,而且对工农业生产和人民身体健康也带来了严重危害。纯净雾水也有有利的一面,比如云南省南部的雾对生产高质量的茶叶及发展橡胶林十分有利。对一些干旱地区还可“雾中取水”。近些年来发现,雾与生态环境关系密切,研究雾可为保护生态环境提供科学依据。     

ANALYSIS OF THE MICROPHYSICAL STRUCTURE OF RADIATION FOG IN XUANEN MOUNTAINOUS REGION OF HUBEI, CHINA

Based on data of radiation fog events in Xuanen, Hubei province, 2010, this paper analyzes the microphysical process and evolution characteristics of radiation fogs with complicated substrate in the upper and middle reaches of the Yangtze River, and compares them with findings in other areas. Results are as follows: radiation fog in Xuanen is evidently weaker in droplet number concentration and liquid water content than land fogs in other areas. Its liquid water content fluctuates obviously, 0.01g/ m3 with visibility of 1,000 meters, which is quite different from that in urban areas, but similar to the Nanling Mountains. Bi-modal droplet distribution is likely to occur in Xuanen mountain radiation fog (MRF) events. Statistical analysis shows that the observed droplet size distribution can be piecewise described well by the Gamma distribution. There is a positive correlation between liquid water content, fog droplet concentration and mean radius, especially in the development and dissipation stage. Condensation growth and droplet evaporation are major processes of Xuanen MRF. The dissipation time coincided with the time when the grass temperature reached the peak value, which indicated that dew evaporation is a key role in maintaining Xuanen MRF. In the early stage of dense fog’s growth, droplets with diameter of over 20 micrometers can be observed with visibility of 800-1,000m, which might be caused by the transportation of low cloud droplets to earth’s surface by turbulence. Big droplets in the initial stage correspond to higher water content, leading to the higher observed value of water content of Xuanen MRF.     

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed byusing daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stationsfrom January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well asTBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset dateof summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than thenormal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and thenpropagated westward and northward.The convection over east and west parts of TP shows thatthere is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches ofYangtze River is formed by the westward propagation of convection over subtropical westernPacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lagcorrelation between the convection over the middle and western TP and that over the subtropicalwestern Pacific and southern China.Therefore it can be inferred that a feedback zonal circulationwith a quasi two-three week oscillation exists between the ascending region of TP and descendingregion of subtropical western Pacific,i.e.the convection over TP may affect the subtropical highover western Pacific and vice versa.     

1980年6月9日长江口地区平流辐射雾的数值模拟

本文用二维非定常数值模式模拟了1980年6月9日长江口地区海雾向上海地区平流而形成的平流雾个例,其中讨论了盛行风、海陆环流对海雾的影响,结果与实况近于一致。     

青藏高原大气热源和冬春积雪与中国东部降水的年代际变化关系

利用NCEP 1950—2004年逐日再分析资料,采用倒算法,对青藏高原大气热源的长期变化进行了计算,结果发现,青藏高原及附近地区上空大气春夏季热源在过去50年里,尤其是最近20年,表现为持续减弱的趋势。而1960—2004年青藏高原50站的冬春雪深却出现了增加,尤其是春季雪深在1977年出现了由少到多的突变。用SVD方法对高原积雪和高原大气热源关系的分析表明,二者存在非常显著的反相关关系,即高原冬春积雪偏多,高原大气春夏季热源偏弱。高原大气春夏季热源和中国160站降水的SVD分析表明,高原大气春夏季热源和夏季长江中下游降水呈反相关,与华南和华北降水呈正相关;而高原冬春积雪和中国160站降水的SVD分析显示,高原冬春积雪和夏季长江流域降水呈显著正相关,与华南和华北降水呈反相关。在年代际尺度上,青藏高原大气热源和冬春积雪与中国东部降水型的年代际变化(南涝北旱)有很好的相关。最后讨论了青藏高原大气热源影响中国东部降水的机制。青藏高原春夏季热源减弱,使得海陆热力差异减小,致使东亚夏季风强度减弱,输送到华北的水汽减少,而到达长江流域的水汽却增加;同时,高原热源减弱,使得副热带高压偏西,夏季雨带在长江流域维持更长时间。导致近20年来长江流域降水偏多,华北偏少,形成"南涝北旱"雨型。高原冬春积雪的增加,降低了地表温度,减弱了地面热源,并进而使得青藏高原及附近地区大气热源减弱。     

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER*

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed by using daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stations from January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well as TBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically 6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to 2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset date of summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than the normal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and then propagated westward and northward.The convection over east and west parts of TP shows that there is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches of Yangtze River is formed by the westward propagation of convection over subtropical western Pacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lag correlation between the convection over the middle and western TP and that over the subtropical western Pacific and southern China.Therefore it can be inferred that a feedback zonal circulation with a quasi two-three week oscillation exists between the ascending region of TP and descending region of subtropical western Pacific,i.e.the convection over TP may affect the subtropical high over western Pacific and vice versa.     

NUMERICAL EXPERIMENTS ON THE INFLUENCES OF GENERAL CIRCULATION ANOMALY OVER THE TIBETAN PLATEAU AND SURFACE ALBEDO CHANGE IN NORTHWEST CHINA ON SUMMER PRECIPITATION

An advanced three-level global atmospheric general circulation model has been used to studythe summer precipitation anomaly in Northwest China.based on the synoptic fact and thestatistical analysis of the precipitation,the surface albedo in Northwest China,and the synopticsystems over the Tibetan(Qinghai-Xizang)Plateau.The results show that either the anticycloneintensified over the plateau or the surface alhedo enhanced in Northwest China results in summerprecipitation reduction east of Northwest China.Especially.when both of them appearsimultaneously,summer precipitation was obviously reduced and severe drought occurred in mostareas of Northwest China.Moreover.the simulated difference of precipitation rate of NorthwestChina is similar to the actural precipitation distribution in Northwest China in 1995,which is themost severe drought year in Northwest China in the past fifty years.So the tendency in droughtseverity intensified,drought frequency accelerated,drought persistence period extended,anddrought areas expanded in Northwest China in recent years is maybe a result of the influences ofhuman activities(e.g.vegetation was reduced,and desertification worsened)on droughtcirculation pattens over the Tibetan Plateau.     

南海及其邻近地区夏季风爆发的特征及其机制的初步研究

利用ＯＬＲ和ＴＢＢ资料,提出一个指标,确定了１９７５～１９９３年间南海夏季风爆发日期,发现与风向转变的日期比较一致。在此基础上,讨论了南海夏季风爆发的过程。随后,还讨论了南海夏季风爆发与海温异常、高原热状况和海陆温差变化的关系,发现它与４月份南海、东太平洋赤道以及３０～４０°ＮＳＳＴＡ有关,与海陆温差由冬季的冷陆暖海转变到热陆冷海有关。     

CHARACTERISTICS OF UT/LS CARBON MONOXIDE INTRASEASONAL OSCILLATIONS AND THEIR IMPACT FACTORS OVER THE TIBETAN PLATEAU AND ITS ADJACENT AREAS IN SUMMER

The study presented herein investigated the main characteristics of carbon monoxideintraseasonal variability and evaluated its possible impact factors using the upper troposphere and lowerstratosphere (UT/LS) Aura Microwave Limb Sounder (MLS) observations over Tibetan Plateau and itsadjacent areas in summer (June to August) of 2005 and 2006. Observations show a persistent constituentextreme extending up into the UT/LS throughout summer, as well as a temporally reversed phase variationbetween the carbon monoxide and ozone in UT/LS. The intraseasonal oscillations (ISOs) of carbonmonoxide during summer are investigated by using methods of wavelet and band pass filter analysis. It isfound that ISOs over the Tibetan Plateau have periods of 10 to 20 days and 30 to 60 days. The formermainly appeared in upper troposphere while the latter in lower stratosphere. Further analysis shows thatthese two periods of ISOs in UT/LS are mainly in phase to the activities of convection over the south of theplateau and the variation of South Asia High, respectively. The above two factors and their dynamicalcoupling may be responsible for the tracer ISOs at different levels.     

SPATIO-TEMPORAL VARIATION OF ACTUAL EVAPOTRANSPIRATION AND ITS RELATION WITH CLIMATE PARAMETERS IN THE PEARL RIVER BASIN, CHINA

Spatio-temporal variation of actual evapotranspiration (ETa) in the Pearl River basin from 1961 to 2010 are analyzed based on daily data from 60 national observed stations. ETa is calculated by the Advection-Aridity model (AA model) in the current study, and Mann–Kendall test (MK) and Inverse Distance Weighted interpolation method (IDW) were applied to detect the trends and spatial variation pattern. The relations of ETa with climate parameters and radiation / dynamic terms are analyzed by Person correlation method. Our findings are shown as follows: 1) Mean annual ETa in the Pearl River basin is about 665.6 mm/a. It has significantly decreased in 1961–2010 at a rate of -24.3 mm/10a. Seasonally, negative trends of summer and autumn ETa are higher than that of spring and winter. 2) The value of ETa is higher in the southeast coastal area than in the northwest region of the Pearl River basin, while the latter has shown the strongest negative trend. 3) Negative trends of ETa in the Pearl River basin are most probably due to decreasing radiation term and increasing dynamic term. The decrease of the radiation term is related with declining diurnal temperature range and sunshine duration, and rising atmospheric pressure as well. The contribution of dynamic term comes from increasing average temperature, maximum and minimum temperatures in the basin. Meanwhile, the decreasing average wind speed weakens dynamic term and finally, to a certain extent, it slows down the negative trend of the ETa.     

NUMERICAL SIMULATION OF THE IMPACT OF LATENT HEAT FLUX ANOMALY IN THE TROPICAL WESTERN PACIFIC ON PRECIPITATION OVER SOUTH CHINA IN JUNES

Based on composite analysis and numerical simulations using a regional climate model （RegCM3）, this paper analyzed the impact of the LHF anomaly in the tropical western Pacific on the precipitation over the south of China in June. The results are as follows. （1） Correlation analysis shows that the SC precipitation in June is negatively correlated with the LHF of the tropical western Pacific in May and June, especially in May. The SC precipitation in June appears to negatively correlate with low-level relative vorticity in the abnormal area of LHF in the tropical western Pacific. （2） The LHF anomaly in the tropical western Pacific is a vital factor affecting the flood and drought of SC in June. A conceptual model goes like this： When the LHF in the tropical western Pacific is abnormally increased （decreased）, an anomalous cyclone （anticyclone） circulation is formed at the low-level troposphere to its northwest. As a result, an anomalous northeast （southwest） air flow affects the south of China, being disadvantageous （advantageous） to the transportation of water vapor to the region. Meanwhile, there is an anomalous anticyclone （cyclone） at the low-level troposphere and an anomalous cyclone （anticyclone） circulation at the high-level troposphere in the region, which is advantageous for downdraft （updraft） there. Therefore a virtual circulation forms updraft （downdraft） in the anomalous area of LHF and downdraft （updraft） in the south of China, which finally leads to the drought （flood） in the region.     

THE TEMPORAL AND SPATIAL VARIATION OF STABLE ISOTOPES IN PRECIPITATION ON THE TIBETAN PLATEAU AND ITS ADJACENT REGIONS*

The temporal and spatial variation on the stable isotopic compositions in precipitation and the relationship with temperature,precipitation and vapor sources are analyzed for the Tibetan Plateau and its adjacent regions.There is no temperature effect in the southern Tibetan Plateau and South Asia.Amount effect has been observed at a few sampling stations that account for about a half of the statistical stations.However,the seasonal variations on the stable isotopic compositions in precipitation at those stations are inconsistent with that of precipitation intensity.There is notable temperature effect in the middle and northern Tibetan Plateau and its adjacent Northwest China.It has been observed that the seasonal variations of the δ¹⁸O in precipitation are almost consistent with those of air temperature in these regions.Because vapor is directly originated from lowlatitude oceans,the relative heavy δ¹⁸O with small variation characterizes the rainfall in South Asia.A sharp depletion of the stable isotopic compositions in precipitation takes place from Kyangjin on the southern slop of the Himalayas to the Tanggula Mountains in the middle Plateau.The δ¹⁸O reaches minimum due to very strong rainout of the vapor from oceans as the vapor rises over the Himalayas.From the Tanggula Mountains to the northern Tibetan Plateau,the δ¹⁸O in precipitation increases with increasing latitude and the is otopic situation in the northern Plateau istransferred into Northwest China with little disruption.     

青藏高原冬季积雪异常和长江中下游主汛期旱涝及其与环流关系的研究

在对青藏高原冬季异常积雪资料进行了综合分析的基础上 ,用 3种方法对长江中下游的旱涝指标进行了综合评定 ,计算了高原积雪日数和深度资料与长江中下游 6～ 8月降水量之间的相关系数 ,结果表明 ,青藏高原冬季积雪异常与长江中下游流域的旱涝呈正相关关系 ,最大正相关区主要位于江南北部。通过对冬季北半球 50 0 h Pa高度场、OLR、SSTA资料的合成分析以及对夏季风指数的联系揭示表明 ,高原多雪和少雪所反映出的环流特征显著不同。讨论了异常积雪 -大气 -海洋 -雨带相互之间的可能联系 ,给出了一个初步与青藏高原冬季积雪相联系的长江中下游旱涝物理过程概念模型 ,进而为短期气候监测、预测提供参数线索。