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1.
Diurnal variation in the initiation of rainfall over the Indian subcontinent during two different monsoon seasons of 2008 and 2009 总被引：1，自引：1，他引：0
In the present study, the diurnal variations in the time of initiation of rainfall, during two contrasting monsoon seasons of 2008 (below normal) and 2009 (normal) over the Indian subcontinent and surrounding oceanic areas has been analyzed. Harmonic analysis was used to detect the spatial variation of the diurnal cycle of the time of initiation of rainfall, as obtained at half-hourly intervals from the Kalpana 1 satellite. In general, the diurnal cycle in the time of initiation is strongest in regions where convective clouds are predominant, while it is weaker in regions where the clouds are predominantly stratiform with long-lived medium to high cloud cover. In the interior of the subcontinent, the time of maximum mainly occurred in the afternoon to evening hours, with a distinct southeast to northwest gradation. Substantial spatial variations were detected in the diurnal patterns between a normal and below normal monsoon years. Spatially, rainfall is initiated later in 2009 compared to 2008 over most of the interior of the Indian subcontinent. The most distinct difference was observed over the core monsoon region in central India, where the diurnal patterns were stronger in 2009 compared to 2008. On the other hand, over the oceans surrounding the Indian subcontinent, the initiation times are generally earlier in 2009. 相似文献
2.
In this study, the observed CMORPH precipitation data from 1998 to 2015 are used to analyze diurnal variation of global precipitation. The results reveal that the strong diurnal signals of precipitation occur over equatorial continental areas where the annual precipitation centers are located. The phase of diurnal variation of global precipitation reveals a distinct land-sea contrast with nocturnal peaks at sea and afternoon maxima over continents. The analysis of six selected area reveals that precipitation peak over equatorial land areas occur in afternoon and maximum diurnal signals appear in autumn or winter. Eastern equatorial Intertropical Convergence Zone (ITCZ) barely shows diurnal signals in the entire year. Precipitation over Sichuan Basin and northwestern Pacific shows nocturnal peak and the maximum diurnal amplitude in summer. Precipitation over coastal areas off eastern China shows an afternoon peak and the largest diurnal amplitude in summer. 相似文献
3.
The NOAA daily outgoing longwave radiation (OLR) and the Global
Precipitation Climatology Project （GPCP） daily precipitation data are used
to study the variation of dominant convection modes and their relationships
over Asia, the Indian Ocean, and the western Pacific Ocean during the
summers from 1997 to 2004. Major findings are as follows: (1) Regression
analysis with the OLR indicates the convective variations over Asian monsoon
region are more closely associated with the convective activities over the
western subtropical Pacific (WSP) than with those over the northern tropical
Indian Ocean (NTIO). (2) The EOF analysis of OLR indicates the first mode
(EOF1) exhibits the out-of-phase variations between eastern China and India,
and between eastern China and the WSP. The OLR EOF1 primarily exhibits
seasonal and even longer-term variations. (3) The OLR EOF2 mostly displays
in-phase convective variations over India, the Bay of Bengal, and
southeastern China. A wavelet analysis reveals intraseasonal variation (ISV)
features in 2000, 2001, 2002, and 2004. However, the effective ISV does not
take place in every year and it seems to occur only when the centers of an
east--west oriented dipole reach enough intensity over the tropical Indian
and western Pacific Oceans. (4) The spatial patterns of OLR EOF3 are more
complicated than those of EOF1 and EOF2, and an effective ISV is noted from
1999 to 2004. The OLR EOF3 implies there is added complexity of the OLR
pattern when the effective ISV occurs. (5) The correlation analysis suggests
the precipitation over India is more closely associated with the ISV,
seasonal variations, and even longer-term variations than precipitation
occurring over eastern China. 相似文献
4.
The seasonal and diurnal variations of cloud systems are profoundly affected by the large-scale and local environments. In this study, a one-year-long simulation was conducted using a two-dimensional cloud-resolving model over the Eastern Tibetan Plateau (ETP) and two subregions of Eastern China: Southern East China and Central East China. Deep convective clouds (DCCs) rarely occur in the cold season over ETP, whereas DCCs appear in Eastern China throughout the year, and the ETP DCCs are approximately 20%?30% shallower than those over Eastern China. Most strong rainfall events (precipitation intensity, PI> 2.5 mm h?1) in Eastern China are related to warm-season DCCs with ice cloud processes. Because of the high elevation of the ETP, the warm-season freezing level is lower than in Eastern China, providing favorable conditions for ice cloud processes. DCCs are responsible for the diurnal variations of warm-season rainfall in all three regions. Warm-season DCCs over the ETP have the greatest total cloud water content and frequency in the afternoon, resulting in an afternoon rainfall peak. In addition, rainfall events in the ETP also exhibit a nocturnal peak in spring, summer, and autumn due to DCCs. Strong surface heat fluxes around noon can trigger or promote DCCs in spring, summer, and autumn over the ETP but produce only cumulus clouds in winter due to the cold and dry environment. 相似文献
5.
基于1979～2018年观测的向外长波辐射（outgoing longwave radiation, OLR）资料和其他多种再分析资料,发现西太平洋暖池对流存在3类显著的月际变化。第一类为OLR在6月和8月为负异常而7月为正异常;第二类与第一类完全相反;第三类为OLR在6～7月为正异常,8月为负异常。3类月际变化与ENSO循环的背景有关,前两类发生在较弱的La Ni?a年和El Ni?o发展年,与春季暖池海温异常有关。当前一个月海温偏高时,后一个月对流偏强,造成局地海温降低,偏低的海温又反过来抑制了后一个月的对流发展,因此暖池地区局地海气相互作用在这两类月际变化中起到关键作用。与前两类不同的是,第三类月际变化发生在El Ni?o衰减年,与春季热带印度洋海温偏高有关。热带印度洋海温偏高造成印度附近对流在6～7月间增强,通过东传Kelvin波抑制了暖池对流发展。同时,印度附近对流偏强造成8月印度洋海温降低和对流减弱,对暖池对流的影响因而减弱。另一方面,6～7月暖池对流偏弱造成8月暖池海温升高,结果造成暖池对流增强。因此,第三类月际变化受到热带印度洋强迫以及暖池地区局地海气相互作用的共同影响。 相似文献
6.
利用外逸长波辐射 (outgoing longwave radiation, OLR) 资料分析了热带对流季内振荡 (ISO) 强度的季节变化及年际异常特征, 重点研究其与海表温度的关系。结果表明:最强的OLR季内振荡主要位于高海表温度 (SST) 区, 即热带印度洋和热带西太平洋区域, 终年存在, 冬、春季最强, 振荡中心偏于夏半球。OLR季内振荡强度年际异常显著区域是热带中东太平洋区域、西北太平洋区域和西南太平洋区域, 它与SST年际异常存在局地正相关关系, 伴随环流的辐合辐散, 并与ENSO事件关系密切。另外, El Ni?o事件发生之前, 热带印度洋和热带西太平区域OLR季内振荡增强, 其中心随事件的发展逐渐东移, 事件发生后这两个区域ISO减弱, 这与OLR季内振荡强度年际异常显著的区域具有内在连贯性。海表温度是决定OLR季内振荡强度季节变化、年际异常的一个关键因子。 相似文献
7.
热带地区云量日变化的气候特征 总被引：3，自引：0，他引：3
利用国际卫星云气候计划（ISCCP）1984—2003年共20年云量资料,统计分析了热带地区的云量日变化特征,研究结果表明,云量峰值时间和变化幅度在全球的分布都较为均匀,而海陆差异明显。高云和低云在变化机制上相对独立,其云量日变化并非同步。全球云量日变化由4类基本形式组成,分别为洋面高云型、陆面高云型、洋面低云型和陆面低云型。高云日变化与地表辐射加热状况密切相关,其形式在洋面和陆面类似,均为早晨出现云量最小值而午后到达云量峰值。相比于洋面,陆面高云的峰值在夜间持续时间较长,可发展至更为稳定深厚的云系。低云多在局地5时附近出现云量峰值,18时左右达到云量极小值,其中陆面低云在12时出现第二峰值。 相似文献
8.
Man‐Li C. Wu 《大气与海洋》2013,51(1):150-174
Abstract Global precipitation estimates using satellite data are derived using difference fields of outgoing long‐wave radiation (OLR). The difference fields consist of clear OLR minus cloudy OLR, which is a measure of long‐wave cloud radiative forcing at the top of the earth‐atmosphere system; and clear daytime OLR minus clear night‐time OLR, which is a measure of the diurnal variation of surface heating. All geophysical parameters used to compute OLR are derived from an analysis of the HIRS2/MSU sounding data. The derived global precipitation estimates show good agreement with collocated raingauge data over land. The correlation coefficient between the precipitation estimates derived using difference fields of OLR and raingauge data over land is about 0.65 for the FGGEyear. The correlation coefficient between precipitation estimates derived using difference fields of OLR and the GOES Precipitation Index (GPI) fraction is about 0.914 from 30°S to 30°N for July 1983, and between the precipitation estimates derived using difference fields of OLR and the difference field of atmospheric reflectance is about 0.86. Using one set of coefficients, global precipitation fields are derived for each 10‐day period and each month of the FGGE year (from December 1978 to November 1979). These fields contain rich information on seasonal variations. 相似文献
9.
中国大陆降水日变化研究进展 总被引：32，自引：4，他引：28
文章概述了中国大陆降水日变化的最新研究成果,给出了中国大陆降水日变化的整体图像,指出目前数值模式模拟降水日变化的局限性,为及时了解和掌握降水日变化研究进展、开展相关科学研究和进行降水预报服务提供了有价值的科学依据和参考。现有研究表明：（1）中国大陆夏季降水日变化的区域特征明显。在夏季,东南和东北地区的降水日峰值主要集中在下午;西南地区多在午夜达到降水峰值;长江中上游地区的降水多出现在清晨;中东部地区清晨、午后双峰并存;青藏高原大部分地区是下午和午夜峰值并存。（2）降水日变化存在季节差异和季节内演变。冷季降水日峰值时刻的区域差异较暖季明显减小,在冷季南方大部分地区都表现为清晨峰值;中东部地区暖季降水日变化随季风雨带的南北进退表现出清晰的季节内演变,季风活跃（间断）期的日降水峰值多发生在清晨（下午）。（3）持续性降水和局地短时降水的云结构特性以及降水日峰值出现时间存在显著差异。持续性降水以层状云特性为主,地表降水和降水廓线的峰值大多位于午夜后至清晨;短时降水以对流降水为主,峰值时间则多出现在下午至午夜前。（4）降水日变化涉及不同尺度的山-谷风、海-陆风和大气环流的综合影响,涉及复杂的云雨形成和演变过程,对流层低层环流日变化对降水日变化的区域差异亦有重要影响。（5）目前数值模式对中国降水日变化的模拟能力有限,且模拟结果具有很强的模式依赖性,仅仅提高模式水平分辨率并不能总是达到改善模拟结果的目的,关键是要减少存在于降水相关的物理过程参数化方案中的不确定性问题。 相似文献
10.
根据美国NOAA卫星观测得到的射出长波辐射资料(Outgoing Longwave Radiation,简称OLR)，分析了西藏高原及其附近地区各月的辐射气候特征，指出:高原冬、春季节OLR主要反映了高原下垫面温度的季节变化，高原夏季为雨季，OLR与降水之间存在较好的负相关。印度季风爆发前后的OLR演变特征反映出中、低纬大气环流调整对高原雨季形成及降水分布的影响。旱涝年OLR合成分析表明:高原夏季降水与赤道印度洋反Walker环流强弱、印度季风槽、副热带高压及西太平洋暖池区对流强度、位置变化有密切的关系。 相似文献
11.
本文使用1979年1月至1984年12月射出长波辐射(OLR)资料,对热带地区低频振荡的一些特性进行了研究,认为正常年份30—60天振荡的合成功率谱最强,El Nino年最弱。低频波活动冬夏差异较大,其年际变化大值区冬季在赤道地区,夏季位置偏北,位于印度洋和西太平洋。就六年平均而言,低频波在西太平洋及印度洋地区有明显的经向传播,赤道地区低频波的纬向传播主要集中在北半球夏季。此外,30—60天OLR滤波场的强弱与印度季风的爆发和减弱有较好的对应关系。 相似文献
12.
本文利用NOAA13年月平均格点资料分析了冬夏热带副热带射出长波辐射(OLR)的气候特征及其遥相关结构。结果表明,OLR场的高低值带有明显的季节变动,低值带中心从冬至夏由赤道西太平洋地区向西北移至孟加拉湾,高值带从冬至夏北移约10—15个纬度,但东南太平洋高值区的位置无明显季节变动。 遥相关结构分析表明,冬夏季节OLR场分别有8个遥相关关键区,它们之间存在着较强的同时性遥相关联系。冬季遥相关型主要由位于赤道低纬度“印度洋—西太平洋—东太平洋—大西洋”的纬向2波式遥相关和在太平洋中部、东亚地区,南北半球副热带与赤道地区的经向负遥相关型组成。夏季OLR遥相关关键区主要分布在孟加拉湾至赤道西太平洋、东太平洋与低纬度大西洋和中纬度东亚沿海与北美大陆,构成低纬度和中纬度两类纬向正遥相关型。进一步分析发现,冬夏OLR遥相关型的年际变化较好地揭示了OLR场异常与ENSO、低纬度Walker、Hadley环流等海—气系统异常的整体联系。 相似文献
13.
Based on LIS/OTD gridded lightning climatology data, ERA5 reanalysis data, and MODIS atmosphere monthly global products, we examined latitudinal and daily variations of lightning activity over land, offshore areas, open sea, and all marine areas (i.e., the aggregate of open sea and offshore areas) for different seasons over the Pacific Ocean and the adjacent land areas at 65°N-50°S, 99°E-78°W, and analysed the relationships of lightning activity with CAPE (Convective Available Potential Energy) and AOD (Aerosol Optical Depth). At any given latitude, the lightning density is the highest over land, followed by offshore areas, all marine areas and the open sea in sequence. The lightning density over land is approximately an order of magnitude greater than that over all marine areas. Lightning activity over land, offshore areas, open sea, and all marine areas varies with season. The diurnal variation of lightning density over land has a single-peak pattern. Over the offshore area, open sea, and all marine areas, lightning densities have two maxima per day. The magnitude of the daily variation in mean lightning density is the largest over land and the smallest over the open sea. The lightning density over the Pacific Ocean and adjacent land areas is significantly and positively correlated with CAPE. The correlation is the strongest over land and the weakest over the open sea. Cloud Base Height (CBH) may affect the efficiency of CAPE conversion to updraft. CAPE has a positive effect on lightning activity and has a greater impact on land than on the ocean. Over the sea, both CAPE and AOD can contribute to lightning activity, but the magnitudes of the influence of CAPE and AOD on lightning activity remain to be determined. Lightning activity over land and sea is a result of the combined action of AOD and CAPE. 相似文献
14.
Diurnal variations of circulation and precipitation in the vicinity of the Tibetan Plateau in early summer 总被引：2，自引：2，他引：0
A regional climate model (RCM) has been applied to simulate the diurnal variations of the Asian summer monsoon during the
early summer period. The ERA40 reanalysis data and the TRMM precipitation data are used to evaluate the performance of the
model. The 5-year simulations show that the RCM could simulate well the diurnal cycle of the monsoon circulation over the
region. A strong diurnal variation of circulation over the Tibetan Plateau (TP) can be observed at the 500-hPa level, with
strong convergence and upward motion in the late afternoon. The diurnal variation of the 500-hPa relative vorticity over the
TP associated with the corresponding diurnal variation of convergence may lead to the formation of a prominent plateau-scale
cyclonic circulation over the TP during the evening to midnight period. The simulated diurnal variation of precipitation over
land is generally better than that over the ocean, particularly over the regions close to the TP such as the Bangladesh region
in the southern flank of the TP, where the well-known nocturnal maximum in precipitation is well captured by the RCM. However,
the late-afternoon maximum in precipitation over the Southeast Asia region is not well simulated by the RCM. The model results
suggest that the diurnal variation of precipitation over the southern flank of the TP is associated with the strong diurnal
variation in the circulation over the TP. 相似文献
15.
Diurnal variations of precipitation over the South China Sea 总被引：1，自引：0，他引：1
In this study, the diurnal variations of precipitation and related mechanisms over the South China Sea (SCS) are studied using the TRMM and other auxiliary atmospheric data. We have found that: (1) the amplitude and peak time of the diurnal precipitation over SCS exhibit remarkable regional features and seasonal variations. Diurnal variations are robust all the year around over the southern SCS especially over the Kalimantan Island and its offshore area. Over the middle to northern SCS, however, diurnal variations are noticeable only in the summer and autumn; (2) over the northern SCS precipitation peaks in early morning, while over the southern SCS it has two diurnal peaks: one in the early morning and another in the late afternoon; (3) the diurnal variations of precipitation over the SCS are related to the activity of the SCS summer monsoon and the ENSO events. The late afternoon precipitation increases remarkably after the onset of the SCS summer monsoon over the northern SCS. The early-morning rainfall peak is much more significant during La Nina years than during El Nino years; (4) the land–sea breeze is responsible for the diurnal cycle over the Kalimantan Island and its offshore area while the “static radiation–convection” mechanisms may result in the early-morning rainfall peak over the SCS. 相似文献
16.
This study investigates diurnal variations of precipitation during May–August, 1998–2012, over the steep slopes of the Himalayas and adjacent regions(flat Gangetic Plains–FGP, foothills of the Himalayas–FHH, the steep slope of the southern Himalayas–SSSH, and the Himalayas-Tibetan Plateau tableland–HTPT). Diurnal variations are analyzed at the pixel level utilizing collocated TRMM precipitation radar and visible infrared data. The results indicate that rain parameters(including rain frequency, rain rate, and storm top altitude) are predominantly characterized by afternoon maxima and morning minima at HTPT and FGP, whereas, maximum rain parameters at FHH typically occur in the early morning. Rain parameters at SSSH are characterized by double peaks;one in the afternoon and one at midnight. Over HTPT and FGP,convective activity is strongest in the afternoon with the thickest crystallization layer. Over FHH, the vertical structure of precipitation develops most vigorously in the early morning when the most intense collision and growth of precipitation particles occurs. Over SSSH, moist convection is stronger in the afternoon and at midnight with strong mixing of ice and water particles. The results of harmonic analysis show that rain bands move southward from lower elevation of SSSH to FHH with apparent southward propagation of the harmonic phase from midnight to early morning. Moreover, the strongest diurnal harmonic is located at HTPT, having a diurnal harmonic percentage variance of up to 90%. Large-scale atmospheric circulation patterns exhibit obvious diurnal variability and correspond well to the distribution of precipitation. 相似文献
17.
Kathrin Wapler 《Meteorology and Atmospheric Physics》2013,122(3-4):175-184
A 6-year analysis (including data of 36 million strokes) of the spatial and temporal occurrence of lightning strokes in Germany and neighbouring areas is presented. The analysis on a high-resolution grid with spatial resolution of 1 km allows assessing the local risk of lightning and studying local effects, e.g. the influence of orography on the occurrence of thunderstorms. The analysis reveals spatial and temporal patterns: the highest number of lightning strokes occurs in the pre-alpine region of southern Germany, further local maxima exists in low mountain ranges. The lowest number of lightning strokes is present in areas of the North Sea and Baltic Sea. Despite a high year-to-year variability of lightning rates, on average a clear annual cycle (maximum June to August) and diurnal cycle (maximum in the afternoon) are present. In addition to this well-known annual and diurnal pattern, the analysis shows that those are intertwined: the diurnal cycle has an annual cycle, visible in the time of daily maximum which occurs later in the afternoon in summer compared to spring and autumn. Furthermore, the annual cycle of lightning is varying geographically, e.g. offshore and coastal regions show a lower amplitude of the annual cycle and a later maximum (autumn) compared to inland (mountainous) regions. In addition, the annual and diurnal cycles of lightning attributes are analysed. The analysis reveals rising height of inner-cloud lightning during the year with a maximum in late summer. 相似文献
18.
青藏高原季风期降水的日变化 总被引：7，自引：0，他引：7
利用1998年夏季GAME－TIBET IOT期间的探空、降水和雷达资料分析了季风期降水和CAPE、LCL热力参量的日变化及其之间的关系。降水的日变化很明显，最大的降水和CAPE的最大值出现在同一时间段。6km和8.5km高度内的大气层结在大部分时间是不稳定的。0400－0800时间内6km以下9km以上的稳定层结阻碍了对流系统的发展，降水的日变化与这些热力参数的日变化有关。同时，利用三维云模式模拟了降水的日变化和水汽及温度对降水的影响，云模式再现了降水和回波强度的最大和最小值，晚上低层的高湿度是影响降水的重要因素。 相似文献
19.
This paper summarizes the recent progress in studies of the diurnal variation of precipitation over con- tiguous China. The main results are as follows. （1） The rainfall diurnal variation over contiguous China presents distinct regional features. In summer, precipitation peaks in the late afternoon over the south- ern inland China and northeastern China, while it peaks around midnight over southwestern China. In the upper and middle reaches of Yangtze River valley, precipitation occurs mostly in the early morning. Summer precipitation over the central eastern China （most regions of the Tibetan Plateau） has two diurnal peaks, i.e., one in the early morning （midnight） and the other in the late afternoon. （2） The rainfall diurnal variation experiences obvious seasonal and sub-seasonal evolutions. In cold seasons, the regional contrast of rainfall diurnal peaks decreases, with an early morning maximum over most of the southern China. Over the central eastern China, diurnal monsoon rainfall shows sub-seasonal variations with the movement of summer monsoon systems. The rainfall peak mainly occurs in the early morning （late afternoon） during the active （break） monsoon period. （3） Cloud properties and occurrence time of rainfall diurnal peaks are different for long- and short-duration rainfall events. Long-duration rainfall events are dominated by strat- iform precipitation, with the maximum surface rain rate and the highest profile occurring in the late night to early morning, while short-duration rainfall events are more related to convective precipitation, with the maximum surface rain rate and the highest profile occurring between the late afternoon and early night. （4） The rainfall diurnal variation is influenced by multi-scale mountain-valley and land-sea breezes as well as large-scale atmospheric circulation, and involves complicated formation and evolution of cloud and rainfall systems. The diurnal cycle of winds in the lower troposphere also contributes to the regional differences 相似文献
20.
Two competing cloud-radiative feedbacks identified in previous studies i.e., cloud albedo feedback and the super greenhouse effect, are examined in a sensitivity study with a global coupled ocean-atmosphere general circulation model. Cloud albedo feedback is strengthened in a sensitivity experiment by lowering the sea-surface temperature (SST) threshold in the specified cloud albedo feedback scheme. This simple parameterization requires coincident warm SSTs and deep convection for upper-level cloud albedos to increase. The enhanced cloud albedo feedback in the sensitivity experiment results in decreased maximum values of SST and cooler surface temperatures over most areas of the planet. There is also a cooling of the tropical troposphere with attendant global changes of atmospheric circulation reminiscent of those observed during La Niña or cold events in the Southern Oscillation. The strengthening of the cloud albedo feedback only occurs over warm tropical oceans (e.g., the western Pacific warm pool), where there is increased albedo, decreased absorbed solar radiation at the surface, stronger surface westerlies, enhanced westward currents, lower temperatures, and decreased precipitation and evaporation. However, the weakened convection over the tropical western Pacific Ocean alters the large-scale circulation in the tropics such that there is increased upper-level divergence over tropical land areas and the tropical Indian Ocean. This results in increased precipitation in those regions and intensified monsoonal regimes. The enhanced precipitation over tropical land areas produces increased clouds and albedo and wetter and cooler land surfaces. These additional contributions to decreased absorbed solar input at the surface combine with similar changes over the tropical oceans to produce the global cooling associated with the stronger cloud albedo feedback. Increased low-level moisture convergence and precipitation over the tropical Indian Ocean enhance slightly the super greenhouse effect there. But the stronger cloud albedo feedback is still the dominant effect, although cooling of SSTs in that region is less than in the tropical western Pacific Ocean. The sensitivity experiment demonstrates how a regional change of radiative forcing is quickly transmitted globally through a combination of radiative and dynamical processes in the coupled model. This study points to the uncertainties involved with the parameterization of cloud albedo and the major implications of such parameterizations concerning the maximum values of SST, global climate sensitivity, and climate change.Support is provided by the Office of Health and Environmental Research of the U.S. Department of Energy, as part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献