首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献，搜索用时 578 毫秒
1.
Spatio-temporal variations of water vapor optical depth in the lower troposphere (450-3850 m) over Punt (18o32’N, 73o51’E, 559 m Above Mean Sea Level), India have been studied over a period of five years. The mean ver-tical structure showed that the moisture content is greatest at the lowest level and decreases with increasing altitude, except in the south-west monsoon season (June to September) where an increase upto 950 m has been found. Optical depths are maximum in the monsoon season. The increase from pre-monsoon (March-May) to monsoon season in moisture content on an average is by about 58% in the above altitude range. The temporal variations in surface Rela-tive Humidity and optical depth at 450 m show positive correlation. The amplitude of seasonal oscillation is the larg-est at 1465 m altitude. The time-height cross-sections of water vapor optical depths in the lower troposphere showed a contrast between years of good and bad monsoon.  相似文献   

2.
Apparent moisture sink and water vapor transport flux are calculated by using NCAR/NCEP reanalyzed daily data for water vapor and wind fields at various levels from 1980 to 1989.With the aid of EOF analysis method,temporal and spatial characteristics of moisture budgets over Asian and Australian monsoon regions are studied.The results show that there is apparent seasonal transition of moistrue sink and water vapor transport between Asian monsoon region and Australian monsoon region.In winter,the Asian monsoon region is a moisture source,in which three cross-equatorial water vapor transport channels in the “continent bridge“,at 80°E and 40°E～50° transport water vapor to the Australian monsoon region and southern Indian Ocean which are moistrue sinks.In summer,Australian Monsoon region anmd southern Indian Ocean are moistrue sources and by the three cross-equatorial transport channels water vapor is transport to the Asian monsoon region which is a moisture sink.In spring and autumn,ITCZ is the main moisture sink and there is no apparent water vapor transport between Asian monsoon region and Australian monsoon region.  相似文献   

3.
In summer, water vapor over the eastern China monsoon region(ECMR) comes mainly from low latitudes and is modulated by tropical cyclone(TC) activity in East Asia(EA). This study examines the variability of water vapor transport over the ECMR, especially of the moisture inflow via the southern and eastern boundaries. The results of composite and correlation analyses, using data from 1979 to 2010, reveal significant differences in moisture budgets along the boundaries between TC days and non-TC days. Almost 80% of the water vapor transport via the eastern boundary occurs during TC days, while at the southern boundary most inflow occurs on non-TC days. The ratio of the total water vapor transport between TC and non-TC days is about 4:6. In addition, the El Nio–Southern Oscillation(ENSO) exhibits a remarkable influence on moisture transport over EA and the contributions of moisture inflow on TC days increase(reduce) in El Nio(La Nia) years. Moreover,different types of TCs, based on their tracks, have different effects on the moisture budgets along the southern and eastern boundaries. When TCs enter EA(but not the ECMR), they favor the moisture inflow via the eastern boundary and hinder the moisture inflow via the southern boundary. After TCs enter the ECMR, the inhibition of moisture inflow via the southern boundary will be weakened, and more water vapor can be brought into the ECMR. For some recurving TCs with an increase in TC activity in the midlatitudes, the influence is uncertain in different cases. The results herein suggest that TC activity is an important factor that influences the boundary moisture budgets in the ECMR.  相似文献   

4.
Using the US Climate Prediction Center(CPC)soil moisture dataset and the observed precipitation over China together with the NCEP/NCAR reanalysis wind and air temperature,the relationship between June precipitation over mid-lower reaches of the Yangtze River basin(MLR-YRB)and spring soil moisture over the East Asian monsoon region was explored,with the signal of the ENSO effect on precipitation removed.A significant positive correlation was found between the mean June precipitation and the preceding soilmoisture over the MRL-YRB.The possible response mechanism for this relationship was also investigated.It is found that when the soil over the MRL-YRB is wetter(drier) than normal in April and May,theair temperature in the lower troposphere over this region in May is lower(higher) than normal,and this temperature effect leads to a decrease(increase) in the temperature contrast between the land and the sea.Generally,a decrease(increase) in the land-sea temperature contrast leads to weaker(stronger) East Asian summer monsoon in June.Southerly(northerly)wind anomalies at 850 hPa then show up in the south of the Yangtze River basin while northerly(southerly)wind anomalies dominate in the north.These anomalies lead to the convergence(divergence) of wind and water vapor and hence gives rise to more(less) precipitation in June over the MLR-YRB.  相似文献   

5.
The 20-year (1976-1995) daily radiosonde data at 17 stations in the tropical western Pacific was ana lyzed. The analysis shows that the atmosphere is more humid in a warmer climate on seasonal, inter-annual and long-term (20-year) time scales, implying a positive water vapor feedback. The vertical structure of the long-term trends in relative humidity (RH) is distinct from that on short-term (seasonal and inter-annual) time scales, suggesting that observed water vapor changes on short time scales could not be considered as a surrogate of long-term climate change. The increasing trend of RH (3%-5%/decade) in the upper troposphere is stronger than that in the lower troposphere (1%-2% / decade). Such vertical structure would amplify positive water vapor feedback in comparison to the common assumption of constant RH changes vertically. The empirical orthogonal function (EOF) analysis of vertical structure of RH variations shows distinct features of the vertical structure of the first three EOFs. The first three EOFs are optimal for repre sentation of water vapor profiles and provide some hints on physical mechanisms responsible for observed humidity variability. Vaisala radiosondes were used at nine stations, and VIZ radiosondes used at other eight stations. The Vaisala data are corrected for temperature-dependence error using the correction scheme developed by NCAR / ATD and Vaisala. The comparison of Vaisala and VIZ data shows that the VIZ-measured RHs after October 1993 have a moist bias of ～ 10% at RHs ＜ 20%. During 1976-1995, several changes in cluding both instruments and reporting practice have been made at Vaisala stations and introduce errors to long-term RH variations.  相似文献   

6.
The spatial and temporal distributions of the stable isotopes such as HD16O (or 1H2H16O, or HDO) and H218O in atmospheric water vapor are related to evaporation in source places, vapor condensation during transport, and vapor convergence and divergence, and thus provide useful information for investigation and understanding of the global water cycle. This paper analyzes spatiotemporal variations of the content of iso- tope HDO (i.e., δD), in atmospheric water vapor, namely, δDv, and the relationship of δDv with atmospheric humidity and temperature at different levels in the troposphere, using the HDO and H2O data retrieved from the Tropospheric Emission Spectrometer (TES) at seven pressure levels from 825 to 100 hPa. The results indicate that δDv has a clear zonal distribution in the troposphere and a good correspondence with atmospheric precipitable water. The results also show that δDv decreases logarithmically with atmospheric pressure and presents a decreasing trend from the equator to high latitudes and from lands to oceans. Sea- sonal changes of δDv exhibit regional differences. The spatial distribution and seasonal variation of δDv in the low troposphere are consistent with those in the middle troposphere, but opposite situations occur from the upper troposphere to the lower stratosphere. The correlation between δDv and temperature has a similar distribution pattern to the correlation between δDv and precipitable water in the troposphere. The stable isotope HDO in water vapor (δDv), compared with that in precipitation (δDp), is of some differences in spatial distribution and seasonal variation, and in its relationship with temperature and humidity, in- dicating that the impacts of stable isotopic fractionation and atmospheric circulation on the two types of stable isotopes are different.  相似文献   

7.
In this paper, we mainly summarize and review the progresses in recent climatological studies (by CMSR, IAP/CAS and some associated domestic and international institutions) on the interannual and interdecadal variabilities of monsoon troughs and their impacts on tropical cyclones and typhoons (TCs) geneses over the western North Pacific Ocean. The climatological characteristics of monsoon troughs and four types of circulation patterns favorable to TCs genesis over the western North Pacific Ocean in summer and autumn are given in this paper. It is also shown in this paper that the monsoon trough over the western North Pacific Ocean has obvious interannual and interdecadal variabilities. Especially, it is revealed in this paper that the interannual and interdecadal variabilities of the monsoon trough over the western North Pacific Ocean influence the TCs genesis not only through the impact on distributions of the vorticity in the lower troposphere and the divergence in the upper troposphere, the water vapor in the mid- and lower troposphere and the vertical shear of wind fields between the upper and lower troposphere over the western North Pacific Ocean, but also through the dynamical effects of the transition between convectively coupled tropical waves and providing disturbance energy. Besides, some climatological problems associated with TCs activity over the western North Pacific Ocean that need to be studied further are also pointed out in this paper.  相似文献   

8.
By using a reverse computation method and the NCEP/NCAR daily reanalysis data from 1960 to 2004, the atmospheric heat source （AHS） was calculated and analyzed. The results show that AHS over the Tibetan Plateau （TP） and its neighboring areas takes on a persistent downtrend in spring and summer during the foregone 50 years, especially the latest 20 years. Snow depth at 50 stations over the TP in winter and spring presents an increase, especially the spring snow depth exhibits a sharp increase in the late 1970s. A close negative correlation exists between snow cover and AHS over the TP and its neighboring areas, as revealed by an SVD analysis, namely if there is more snow over the TP in winter and spring, then the weaker AHS would appear over the TP in spring and summer. The SVD analysis between AHS over the TP in spring and summer and rainfall at 160 stations indicates that the former has a negative correlation with summer precipitation in the middle and lower reaches of the Yangtze River, and a positive correlation with that in South China and North China. The SVD analysis of both snow cover over the TP in winter and spring and rainfall at the same 160 stations indicates that the former has a marked positive correlation with precipitation in the middle and lower reaches of the Yangtze River, and a reversed correlation in South China and North China. On the decadal scale, the AHS and winter and spring snow cover over the TP have a close correlation with the decadal precipitation pattern shift （southern flood and northern drought） in East China. The mechanism on how the AHS over the TP influences rainfall in East China is discussed. The weakening of AHS over the TP in spring and summer reduces the thermodynamic difference between ocean and continent, leading to a weaker East Asian summer monsoon, which brings more water vapor to the Yangtze River Valley and less water vapor to North China. Meanwhile, the weakening of AHS over the TP renders the position of the subtropical high further westward and the r  相似文献   

9.
The timing of the South Asian High (SAH) establishment over the Indochina Peninsula (IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-central China in summer are investigated by using NCEP/NCAR daily reanalysis data, outgoing longwave radiation (OLR) data and the daily precipitation data from 753 weather stations in China. It is found that the transitions of the zonal wind vertical shear and convection establishment over tropical Asia are earlier (later) in the years of early (late) establishment of SAH. In the lower troposphere, anti-cyclonic (cyclonic) anomaly circulation dominates the equatorial Indian Ocean. Correspondingly, the tropical Asian summer monsoon establishes earlier (later). Furthermore, the atmospheric circulation and the water vapor transport in the years of advanced SAH establishment are significantly different from the delayed years in Asia in summer. Out-of-phase distribution of precipitation in eastern-central China will appear with a weak (strong) SAH and western Pacific subtropical high, strong (weak) ascending motion in the area south of Yangtze River but weak (strong) ascending motion in the area north of it, and cyclonic (anti-cyclonic) water vapor flux anomaly circulation from the eastern-central China to western Pacific. Accordingly, the timing of the SAH establishment at the upper levels of IP is indicative of the subsequent onset of the tropical Asian summer monsoon and the flood-drought pattern over eastern-central China in summer.  相似文献   

10.
Three sampling cross sections along the south path starting from the Tropics through the vapor passage in the Yunnan-Guizhou Plateau to the middle-low reaches of the Yangtze River, the north path from West China, via North China, to Japan under the westerlies, and the plateau path from South Asia over the Himalayas to the northern Tibetan Plateau, are set up, based on the IAEA (International Atomic Energy Agency)/WMO global survey network and sampling sites on the Tibetan Plateau. The variations, and the relationship with precipitation and temperature, of the δ18O in precipitation along the three cross sections are analyzed and compared. Along the south path, the seasonal differences of mean δ18O in precipitation are small at the stations located in the Tropics, but increase markedly from Bangkok towards the north, with the δ18O in the rainy season smaller than inthe dry season. The δ18O values in precipitation fluctuate on the whole, which shows that there are different vapor sources. Along the north path, the seasonal differences of the mean δ18O in precipitation for the stations in the west of Zhengzhou are all greater than in the east of Zhengzhou. During the cold half of the year, the mean δ18O in precipitation reaches its minimum at Urumqi with the lowest temperature due to the wide, cold high pressure over Mongolia, then increases gradually with longitude, and remains at roughly the same level at the stations eastward from Zhengzhou. During the warm half of the year, the δ18O values in precipitation are lower in the east than in the west, markedly influenced by the summer monsoon over East Asia. Along the plateau path, the mean δ18O values in precipitation in the rainy season are correspondingly high in the southern parts of the Indian subcontinent, and then decrease gradually with latitude. A sharp depletion of the stable isotopic compositions in precipitation takes place due to the very strong rainout of the stable isotopic compositions in vapor in the process of lifting over the southern slope of the Himalayas. The low level of the δ18O in precipitation is from Nyalam to the Tanggula Mountains during the rainy season,but δ18O increases persistently with increasing latitude from the Tanggula Mountains to the northern Tibetan Plateau because of the replenishment of vapor with relatively heavy stable isotopic compositions originating from the inner plateau. During the dry season, the mean δ18O values in precipitation basically decrease along the path from the south to the north. Generally, the mean δ18O in precipitation during the rainy season is lower than in the dry season for the regions controlled by the monsoons over South Asia or the plateau, and opposite for the regions without a monsoon or with a weak monsoon.  相似文献   

11.
采用水平分辨率1°×1°的NCEP 再分析资料、1°×1°的NCEP GDAS资料和2.5°×2.5°的NOAA大气环流资料, 结合NOAA HYSPLIT v4.8轨迹模式对0604号热带风暴“Bilis”整个生命史的水汽输送特征进行模拟分析, 并分析了“Bilis”暴雨增幅前和增幅后的水汽输送轨迹及不同来源的水汽贡献。结果表明, “Bilis”整个活动过程中主要有四支水汽输送通道, 分别是源自索马里、孟加拉湾、120°E 越赤道气流和东太平洋的水汽, 其中源自索马里和孟加拉湾的西南水汽输送(偏南水汽通道)占主导地位, 120°E 越赤道气流和东太平洋的水汽是西南水汽随着“Bilis”环流逆时针旋转, 自环流中心东北侧进入雨区(东北水汽通道), 是低压环流与偏南风相互作用的结果。其中, 偏南通道水汽大部分输送到850 hPa以下的低层, 自环流北侧输入的水汽则主要输送到暴雨区上空850 hPa以上。对比暴雨增幅前后各通道的水汽贡献率发现, 孟加拉湾西南气流输送的低纬水汽对此次暴雨增幅的形成、发展起重要作用。  相似文献   

12.
This paper presents a Raman lidar for measuring tropospheric water vapor profiles over Hefei(31.9°N,117.17°E),China.Intercomparisons of water vapor mixing ratio obtained by this Raman lidar and GZZ-59 type radiosonde observations show the good agreements when relative humidity is higher than 20%.Typical vertical profiles and seasonal variations of water vapor mixing ratio distribution are reported.Many observation eases indicate that the high moisture layer corresponds to large aerosol scattering ratios in the lower troposphere.  相似文献   

13.
Summary ?The dependence of aerosol optical depth on wavelength as well as the fit of the ?ngstr?m approximation have been investigated under different air masses at a sub-Arctic location (Abisko, Sweden; 68° 21′ N, 18° 49′ E) and a tropical environment (Ife, Nigeria; 7° 30′ N, 4° 31′ E). The study is based on spectral data acquired with a high resolution spectral radiometer (spectral range: 300–1100 nm) in absorption-free regions. The wavelength dependence of the aerosols under different air mass conditions at the sub-arctic location offer significant contrasts to aerosols of Saharan origin at Ife. A general characteristic of the aerosol optical depth spectra after the Pinatubo volcanic eruption was a much weaker wavelength dependence relative to pre-Pinatubo conditions. Categorising the features of the optical depth spectra according to their wavelength dependence, three main groups were observed at Abisko, while two main classes have been discussed for the harmattan season in the tropical climate of Ife and environs. For the first two groups in Abisko (and the first group at Ife), aerosol optical depth generally decreased with wavelength while the third group (second group at Ife) exhibited strong curvatures. The correlation coefficient obtained from the regression equation of the ?ngstr?m equation, has been shown to be a good index of the general fit of the ?ngstr?m approximation for the three groups at Abisko, but much weaker for the harmattan conditions at the tropical location. Although the probability of systematic deviations from the ?ngstr?m law is highest under intense harmattan conditions with considerably high β and low α, it has been observed that the ?ngstr?m fit was good in many highly turbid conditions at the tropical site. Hence, apart from the level of turbidity, the applicability of the ?ngstr?m approximation is strongly dependent on aerosol characteristics and source region. Formerly Adeyefa. Received May 18, 2001; revised June 20, 2002; accepted August 5, 2002  相似文献   

14.
Lidar Measurements of Aerosols in the Tropical Atmosphere   总被引：3，自引：0，他引：3  
Measurements of atmospheric aerosols and trace gases using the Laser radar (lidar) techniques, have been in pro-gress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18o32’N, 73o51’E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal va-riation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected me-teorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles ob-tained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol lay-ers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.  相似文献   

15.
Synoptic Features of the Second Meiyu Period in 1998 over China   总被引：10，自引：0，他引：10  
1. IntroductionThe Meiyu, translated as plum rain, is a majorannual rainfall event over the Yangtze River Basin inChina and southern Japan in June and July. Theheavy rainfall is mainly caused by a quasi-stationaryfront, known as the Meiyu front, extended from east-ern China to southern Japan (Tao, 1958; Matsumotoet al., 1971; Akiyama, 1990; Gao et al, 1990). Studiesof Zhang and Zhang (1990) and Chen et al. (1998)pointed that the Meiyu front is one of the most signif-icant circulation s…  相似文献   

16.
 This study presents the monthly climatology and variability of the historical soviet snow depth data. This data set was developed under the bilateral data exchange agreement between United States of America and the former Union of Soviet Socialist Republics. The original data is for 284 stations for periods varying from 1881 upto 1985. The seasonal cycle of the mean snow depth has been presented both as spatial maps and as averages over key locations. The deepest snow (=80 cms/day) areas are found over Siberia (in Particular over 80′–100 ′E, 55′–70 ′N) during March. Over the course of the annual cycle average snow depth over this region changes dramatically from about 10 cms in October to about 80 cms in March. The variability is presented in the form of spatial maps of standard deviation. To investigate the interaction of snow depth with Indian monsoon rainfall (IMR), lag and lead correlation coefficients are computed. Results reveal that the winter-time snow depth over western Eurasia surrounding Moscow (eastern Eurasia in central Siberia) shows significant negative (positive) relationship with subsequent IMR. Following the monsoon the signs of relationship reverse over both the regions. This correlation structure is indicative of a midlatitude longwave pattern with an anomalous ridge (trough) over Asia during the winter prior to a strong (weak) monsoon. As the time progresses from winter to spring, the coherent areas of significant relationship show southeastward propagation. Empirical orthogonal function analysis of the snow depth reveal that the first mode describes a dipole-type structure with one centre around Moscow and the other over central Siberia, depicting similar pattern as the spatial correlation structure. The decadal-scale IMR variations seem to be more associated with the Northern Hemisphere midlatitude snow depth variations rather than with the tropical ENSO (El Nino Southern Oscillation) variability. Received: 16 March 1998 / Accepted: 24 December 1998  相似文献   

17.
阿利曼  王君  冯锦明  李秀连 《大气科学》2016,40(5):1073-1088
本文利用1979～2014年NCEP-DOE日平均再分析资料和中国区域2375份航空器空中颠簸报告资料,研究中国东部区域高空颠簸的时空分布特征及其与热带中东太平洋海温异常（简称“海温异常”;空间范围:5°S～5°N,120°～170°W）的关系以及产生这种关系的可能原因。结果表明:中国东部地区高空颠簸与东亚副热带西风急流之间存在显著时空相关关系,其原因是高空纬向风引起的垂直风切变是构成高空颠簸时空分布的主导因素。中国东部夏季高空颠簸与海温异常存在正相关关系;冬季呈现南北两个正负相关区:以30°N为界,北部区域存在显著的负相关,南部区存在显著的正相关,在30°N急流轴附近区域无显著相关关系。海温异常影响中国高空颠簸时空分布的可能原因是海温变化引起对流层高层温度出现异常,进而影响温度的经向梯度,导致东亚副热带西风急流强度和位置出现异常（夏季,急流轴南侧出现西风异常;冬季,急流轴北侧出现东风异常,南侧出现西风异常）。高空纬向风的变化导致纬向风的垂直梯度和经向梯度出现异常,最终影响高空颠簸的时空分布特征。对流层高层温度的异常变化可能是由与热带海温异常相关的平流层水汽变化所引起。  相似文献   

18.
程龙  刘海文  周天军  朱玉祥 《大气科学》2013,37(6):1326-1336
利用地面观测资料和NCEP/NCAR再分析资料集,使用相关分析、合成分析等方法,在将地面风分为东南季风和西南季风的基础上,分析了近30余年来盛夏东亚季风频率的年代际变化特征。结果表明:盛夏东南季风、西南季风频率和前期春季青藏高原积雪均在21世纪初期发生了显著的年代际变化;东南季风、西南季风频率由较少改变为较多,春季青藏高原积雪则由深变浅。由于青藏高原积雪厚度发生了年代际变浅,说明青藏高原发生了年代际变暖和南亚高压变强,南亚高压的年代际变强,使得其下游对流层低层(18°~28°N,108°~118°E)的反气旋性环流异常增强,有利于东亚西南季风频率的增加;同时,由于高原发生湿反馈作用,使得淮河地区降水发生年代际变多,由Sverdrup涡度平衡关系,降水的异常增多通过潜热释放,使得东亚副热带高压异常加强,而副热带高压异常变强则有利于盛夏东亚东南季风频率发生年代际增加。  相似文献   

19.
夏季亚洲季风区是对流层向平流层物质输送的主要通道,其对平流层水汽的变化有重要贡献。以往的研究表明亚洲季风区向平流层的水汽传输主要在青藏高原及周边地区。本文利用多年平均的逐日ERAi、MERRA再分析数据和微波临边观测仪（Microwave Limb Sounder,MLS）数据,首先对比分析夏季青藏高原周边上空水汽的分布特征,再利用再分析资料分析了对流层—平流层水汽传输的特征。结果表明:青藏高原周边特定的等熵面和对流层顶结构分布有利于水汽向平流层的绝热输送;在南亚高压的东北侧,从青藏高原到中太平洋地区,340~360 K层次存在最为显著的水汽向平流层的纬向等熵绝热输送通道,7~8月平均输送强度可达约7×103 kg s-1。此外,在伊朗高原及南亚高压的西部,350~360 K层次也存在一支水汽向平流层的经向等熵绝热输送通道,但强度相对较弱（约2.5×103 kg s-1）。在青藏高原南侧370~380 K层次存在强的水汽向平流层的非绝热输送,主要由深对流和大尺度上升运动引起,7~8月平均输送强度约0.4×103 kg s-1。落基山以东到大西洋西部,350~360 K层次存在水汽向平流层的纬向等熵绝热输送通道,但强度也弱得多（约2.5×103 kg s-1）。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号