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1.
利用西藏地区1980-2013年夏季降水量资料、NCEP再分析资料等,分析了西藏地区夏季降水主模态季节内变化特征,尤其是盛夏7和8月降水异常对应的大尺度环流特征和影响系统。结果表明:西藏夏季降水存在明显的季节内变化,6和7月降水主模态的时间系数变化具有较好的持续性,而7和8月降水主模态的时间系数的相关关系明显减弱。西藏地区7和8月降水偏多年,西藏地区上游低层纬向风场均呈西风异常,但是水汽来源有差异;同时欧亚中高纬地区对流层中高层环流存在显著差异。西藏7月降水与南亚高压强度存在显著负相关关系,南亚高压偏强/弱时,降水偏少/多。西藏8月降水与南亚高压的位置关系更密切,南亚高压偏南/北,降水偏多/少。 相似文献
2.
以2003年6月29日-7月11日淮河流域梅雨期强降水为研究对象,采用ERAInterim再分析资料和站点降水资料,综合分析该期间慢降水时段水汽收支。结果表明：降水主要来自低层水汽辐合的贡献,而与低空急流相联系的水汽辐合具有显著的日变化,即后半夜至凌晨最大,午后最小,并由此造成了梅雨期强降水独特的日变化特征,最强降水出现在后半夜至凌晨;蒸发主要集中在白天,夜晚很小,数值约为降水量的15％,表明局地水循环的重要作用。针对淮河流域强降水区进行的水汽收支计算表明,水汽收支方程左、右两边数值在整个强降水时段具有较好的一致性,相关系数为0．77;对整个强降水期取时间平均,获得的水汽收支方程左、右两端数值的偏差为18％。 相似文献
3.
Comparison of Daily Extreme Temperatures over Eastern China and South Korea between 1996–2005 总被引：1，自引：1，他引：0
This paper examined the decadal mean, seasonal cycle, and interannual variations of mean and extreme temperatures using daily temperature and relative humidity data from 589 stations over eastern China and South Korea between 1996–2005. The results show that the decadal mean Tm (mean daily mean temperature) and the TNn (minimum daily minimum temperature) increase from north to south; the opposite spatial gradient is found in the DTR (diurnal temperature range); the value of the DTR over South Korea is in- b... 相似文献
4.
区域数值预报系统在北京地区的降水日变化预报偏差特征及成因分析 总被引：1，自引：0，他引：1
为了研究北京快速更新循环同化预报系统(BJ-RUCv2.0)在北京地区降水日变化的预报偏差特征及其成因,利用2012—2015年夏季BJ-RUCv2.0系统第2重区域(3 km分辨率)预报结果和北京地区122个自动气象站逐时观测数据以及观象台探空观测资料,分析模式对北京地区降水日变化预报偏差的区域性特征和传播特征,研究模式局地环流预报偏差特征及其对降水预报偏差的可能反馈机制。研究结果表明,BJ-RUCv2.0系统多个更新循环的预报在北京平原地区均存在夜间降水漏报问题,降水预报偏差表现为模式预报降水在西部山区降水偏多,预报降水雨带难以在平原地区增强发展,造成了模式降水在傍晚山区偏多而夜间平原地区降水明显偏少。通过分析模式局地环流预报偏差及其响应机制发现,由于白天平原地区近地层偏暖偏干,山区底层偏冷中层偏湿,造成了山区-平原地区间的温度梯度强度偏强且强温差出现时间提前,西部山区午后降水偏多;由于平原地区地面气温预报持续偏高,入夜后偏北风难以到达平原地区,造成了山区-平原间的地形辐合线位置偏北,影响山区降水雨带向平原地区移动,同时平原地区近地层内水汽持续偏低,抑制降水雨带在东移过程中的发展,造成模式在平原地区夜间降水预报容易出现漏报。模式冷启动所用的GFS资料土壤湿度在北京平原地区明显小于实际观测,是模式预报偏暖偏干的可能原因之一。 相似文献
5.
利用2014-2018年5-10月贵州西南部的黔西南州、六盘水市、安顺市以及黔南州长顺县、惠水县、罗甸县共20个气象观测站小时降水资料,分析近5 a 5-10月贵州省西南部突发性暴雨的时空变化,结果表明:突发性暴雨呈逐年减少的趋势;月际变化特征为6月"爆发",7月"回落",而8月略增,9-10月呈不断减少趋势;具有白天少、夜间多的日变化特征,且突发性暴雨的高发时段主要是在午后至凌晨。从各等级小时降水骤增量的站次空间分布情况来看,突发性暴雨空间分布与地形分布具有较好的对应关系,骤增等级大时,主要出现在北盘江河谷一带,而镇宁一直是一个高发中心。从突发性暴雨站次的整个时空演变来看,5月从东南部开始,6月兴义和六枝成为南北两个高发中心,7月总体减少,中部为多发中心,8月略有增加,分布呈现出南北盘江河谷一带多发;从逐年的演变来看,"突发性"的特点在地域分布上也有体现,每一年的分布情况均不相同。 相似文献
6.
内蒙古半干旱草原能量物质交换的微气象方法估算 总被引：15，自引：1，他引：14
根据1998年5～8月和1999年8月在中国科学院内蒙古草原生态系统定位试验站进行微气象观测的资料,作者分析了该地区能量平衡及其各分量的基本特征.结果表明:(1)净辐射通量的转化形式有明显的季节性变化,5～6月份,净辐射能大部分用于感热交换,而后期则多用于潜热交换,5～8月份的日波文比值分别为1.26,1.42,0 41和0.20.(2)观测期间,波文比的日变化特征表现为,早晚变化大不稳定,而白天则相对稳定.(3)用涡度相关方法观测的感热和潜热通量之和与同期的净辐射相比较,前者的结果偏小1 5%左右,两种方法观测到的潜热通量的差异达平均35%左右.(4)半干旱草原CO2通量有明显的日变化,在生长旺期,白天CO2通量强度可达到1.5 mg s-1m-2以上,但在生长后期,1998年和1999年8月份的白天CO2通量强度分别为0.38 mg s-1m-2和0.2 mg s-1m-2左右;其差异与草地土壤水分和植物长势有关. 相似文献
7.
《Atmospheric Research》2006,79(3-4):166-181
The change of cloud droplet spectra can modify the microphysics and radiative processes of the atmosphere, which in turn affects surface precipitation. In this paper, the impact of cloud droplet spectral change (CDSC) on mesoscale precipitation is studied by simulating two cases, a South China Storm on June 8, 1998 and a Yangtze River Storm on July 22, 2002, and employing the MM5V3 with newly developed, dual-parameterized explicit moisture scheme coupled to. The results show that CDSC has a slight influence on rainfall distribution/pattern, but can significantly change the precipitation intensity, especially the position and intensity of the precipitation centers. The effects of CDSC are more distinct in the daytime and have an obvious diurnal cycle on rain rate. Precipitation increase (decrease) due to CDSC is ascribed to the relative upper radiative cooling (heating) and lower radiative heating (cooling) in the daytime atmosphere. 相似文献
8.
Atmospheric moisture budget and its regulation of the summer (June–July–August) precipitation over the Southeastern United State (SE U.S.) were examined during 1948–2007 using PRECipitation REConstruction over Land and multiple reanalysis datasets. The analysis shows that the interannual variation of SE U.S. summer precipitation can be largely explained by the leading Empirical Orthogonal Function mode showing a spatially homogenous sub-continental scale pattern. Consequently, areal-averaged precipitation was investigated to focus on the large-scale rainfall changes over the SE U.S. The wavelet analysis identifies an increased 2–4 year power spectrum in recent 30 years (1978–2007), suggesting an intensification of the interannual variability. Analysis of the atmospheric moisture budget indicates that the increase in precipitation variability is mainly caused by moisture transport, which exhibits a similar increase in the 2–4 year power spectrum for the same period. Moisture transport, in turn, is largely controlled by the seasonal mean component rather than the subseasonal-scale eddies. Furthermore, our results indicate that dynamic processes (atmospheric circulation) are more important than thermodynamic processes (specific humidity) in regulating the interannual variation of moisture transport. Specifically, the North Atlantic Subtropical High western ridge position is found to be a primary regulator, with the ridge in the northwest (southwest) corresponding to anomalous moisture divergence (convergence) over the SE U.S. Changes in moisture transport consistent with the increased frequency of these two ridge types in recent 30 years favor the intensification of summer precipitation variability. 相似文献
9.
Chunmei Zhu David W. Pierce Tim P. Barnett Andrew W. Wood Dennis P. Lettenmaier 《Climatic change》2004,62(1-3):45-74
The ability of the Parallel Climate Model (PCM) to reproduce the mean and variability of hydrologically relevant climate variables was evaluated by comparing PCM historical climate runs with observations over temporal scales from sub-daily to annual. The domain was the continental U.S, and the model spatial resolution was T42 (about 2.8 degrees latitude by longitude). The climate variables evaluated include precipitation, surface air temperature, net surface solar radiation, soil moisture, and snow water equivalent. The results show that PCM has a winter dry bias in the Pacific Northwest and a summer wet bias in the central plains. The diurnal precipitation variation in summer is much stronger than observed, with an afternoon maximum in summer precipitation over much of the U.S. interior, in contrast with an observed nocturnal maximum in parts of the interior. PCM has a cold bias in annual mean temperature over most of the U.S., with deviations as large as ?8 K. The PCM daily temperature range is lower than observed, especiallyin the central U.S. PCM generally overestimates the net solar radiation over most of the U.S, although the diurnal cycle is simulated well in spring, summer and winter. In autumn PCM has a pronounced noontime peak in solar radiation that differs by 5–10% from observations. PCM'ssimulated soil moisture is less variable than that of a sophisticated land-surface hydrology model, especially in the interior of the country. PCM simulates the wetter conditions over the southeastern U.S. and California during warm (El Niño) events, but shifts the drier conditions in the PacificNorthwest northward and underestimates their magnitude. The temperature response to the North Pacific Oscillation is generally captured by PCM, but the amplitude of this response is overestimated by a factor of about two. 相似文献
10.
Kyu-Myong Kim William K.-M. Lau Yogesh C. Sud Gregory K. Walker 《Climate Dynamics》2010,35(1):115-126
Effects of aerosol radiative forcing on the diurnal and seasonal cycles of precipitation over West Africa and eastern Atlantic
Ocean are investigated for the boreal summer season: June–July–August. An eight year (2000–2007) average of GCM simulated
rainfall data is compared with the corresponding TRMM rainfall data. The comparison shows that the amplitude of the diurnal
cycles of rainfall over land and ocean are reasonably well simulated. Over land, the phase of the simulated diurnal cycle
of precipitation peaks several hours earlier than that of the TRMM data. Corresponding differences over the ocean(s) are relatively
smaller. Some of the key features of the aerosol induced model simulated field anomalies are: (a) aerosol direct radiative
forcing which increases the atmospheric stability and reduces the daytime moist convection and convective precipitation; (b)
the aerosol induced changes in the diurnal cycle of precipitation are out of phase with those of the TRMM data over land,
but are in-phase over the ocean; (c) aerosols reduce the amplitude of the diurnal cycle of precipitation over land and enhance
it over ocean. However, the phase of the diurnal cycle is not affected much by the aerosol radiative forcing both over land
and ocean. During the boreal summer, aerosol radiative forcing and induced circulation and precipitation cool the Sahel and
the southern part of Sahara desert more than the adjacent areas to the north and south, thereby shifting the peak meridional
temperature gradient northward. Consequently, an anomalous easterly jet is found north of its climatological location. This
anomalous jet is associated with increased cyclonic circulation to the south of its axis, resulting in an anomalous monsoon
rain belt in the Sahel. 相似文献
11.
Summary Chaco jet events (CJEs) are a subset of South American low-level jet events to the east of the Andes, characterized by enhanced
poleward penetration and by a strong impact on precipitation over southeastern South America. The present study uses the Eta
model short range weather forecasts produced operationally in the Brazilian Center for Weather Forecasts and Climate Studies
(Centro de Previs?o de Tempo e Estudos Climáticos, CPTEC) to characterize the CJEs and the related precipitation during the
1997–1998 warm season.
An enhanced diurnal cycle in precipitation with respect to that found during the warm season mean can be recognized during
CJEs in Eta/CPTEC model output, with preference for a nocturnal maximum over southern Brazil, Uruguay, and the central part
of northern Argentina, and a daytime maximum near high topography (northwestern Argentina, the Brazilian Planalto). The analysis
of thermodynamic and dynamic forcing appearing during CJEs, helps to explain the modeled precipitation cycle: the nocturnal
maximum is mostly explained by enhanced low-level convergence at night, while the diurnal one is mainly a response to radiative
warming. Boundary-layer convergence, and convective instability, present within the CJEs environment, work together to provide
both dynamic forcing and potential for convection. The simulated precipitation cycle is complemented with surface observations
of “current weather” that corroborate the main oscillations found in simulated precipitation. 相似文献
12.
选取了甘肃平凉地区2015-2019年6-8月发生的27次短时强降水事件。利用自动站逐小时降水资料和高空探测资料,按照短时强降水阈值分类统计法和常规天气分析方法对甘肃平凉地区夏季短时强降水时空分布、影响天气系统及大气环境背景进行了统计分析。结果表明：6月短时强降水频次少,强降水高发区为六盘山山区;7月频次明显增多,活跃地区为静宁、崇信、泾川一带;8月频次及强度达到峰值,密集区为平凉北部的崆峒山区、崇信南部河谷地带。6月短时强降水日变化呈现单峰型特征,以午后居多,1 h降水量在20-30 mm段发生频次最高,占6月频次的80%以上;7月和8月日变化呈多峰型结构,夜间短时强降水频次增多,1 h降水量大于30 mm的频次显著增加,约占7月和8月总频次的40%。分析总结了平凉地区短时强降水天气类型,即高空低槽类、副热带高压类、西北气流类。另外,对表征动力、水汽、不稳定条件的环境参数统计分析,结果显示K指数、CAPE、T850-T500、Q850、θse-850等物理量平均特征值对平凉地区强降水预报有较好的指示意义。 相似文献
13.
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
14.
Previous studies suggest that the Pacific Decadal Oscillation (PDO) modulates annual and summer precipitation patterns over East China. In this study, the effect of the PDO on monthly precipitation anomalies over this region is investigated. The new results show that the effect is month-dependent. The well-known North–South dipole patterns of annual precipitation are dominated by the July–August precipitation. In other months, the corresponding patterns vary in strength, position, and even shape. For example, the May and June precipitation patterns show opposite signs to the July–August or annual mean patterns, whereas the September–December monthly precipitation anomalies show a triple pattern. Monthly precipitation patterns over East China are largely determined by large-scale moisture transport controlled by atmospheric circulation. The PDO affects East China precipitation patterns by modulating the large-scale circulation pattern. 相似文献
15.
Ensemble regional model simulations over the central US with 30-km resolution are analyzed to investigate the physical processes of projected precipitation changes in the mid-twenty-first century under greenhouse gas forcing. An atmospheric moisture balance is constructed, and changes in the diurnal cycle are evaluated. Wetter conditions over the central US in April and May occur most strongly in the afternoon and evening, supported primarily by moisture convergence by transient eddy activity, indicating enhanced daytime convection. In June, increased rainfall over the northern Great Plains is strongest from 0000 to 0600 LT. It is supported by positive changes in stationary meridional moisture convergence related to a strengthening of the GPLLJ accompanied by an intensification of the western extension of the North Atlantic subtropical high. In the Midwest, decreased rainfall is strongest at 1500 LT and 0000 LT. Both a suppression of daytime convection as well as changes in the zonal flow in the GPLLJ exit region are important. Future drying over the northern Great Plains in summer is triggered by weakened daytime convection, and persists throughout August and September when a deficit in soil moisture develops and land–atmosphere feedbacks become increasingly important. 相似文献
16.
基于青藏高原春季感热异常信号的中国东部夏季降水统计预测模型 总被引：3，自引：0，他引：3
使用1980-2014年由青藏高原中东部的地面气象观测台站观测资料计算得到的地表感热通量以及中国东部高分辨率的降水格点资料,在年代际变化和年际变率两个时间尺度上,使用最大协方差分析方法研究了青藏高原春季感热与中国东部夏季6、7和8月降水的关系,基于最大协方差关联因子的时间尺度分解回归分析方法建立了一个降水统计预测模型。青藏高原春季感热的各个关联预报因子与中国东部夏季各月降水的相关分析表明,在年代际成分中,6、7和8月在中国东部绝大部分地区均存在显著相关,方差贡献分别为75.6%、99.9%和79.7%;在年际成分中,相关区域在6月是华南地区、华北沿海地区和江淮流域,7月是华南地区西南部、长江流域、东北地区东南部和黄河中下游地区,8月是东北地区和华南地区西部,方差贡献分别为42.7%、43.4%和32.0%。预测模型的解释方差分析和后报试验检验表明,7月对整个中国东部地区预测效果最好,6月主要在长江以南地区,而8月主要在东北地区和华南地区西部预测效果较好。该预测模型能很好描述青藏高原春季感热与中国东部夏季各月降水的关联性,并对局地降水实现较好的定量预测,具有在短期气候预测业务应用的价值。 相似文献
17.
Ziyue Guo Juan Fang Xuguang Sun Jie Tang Yi Yang Jianping Tang 《Climate Dynamics》2020,54(3):1329-1349
With a decadal long period (1998–2010) climate simulation using the Weather Research and Forecasting model at convection-permitting resolution (4 km) (WRF_CPM), the diurnal cycles of precipitation amount (PA), frequency (PF) and intensity (PI) and their related large-scale atmospheric circulations over eastern China are analyzed. The simulations are further compared against the CN05.1, CMORPH v1.0 and the ECMWF Re-Analysis Interim (ERAIN). Results show that WRF_CPM can reasonably represent the observed seasonal rainfall and the atmospheric circulations. As for the features at a sub-daily scale, WRF_CPM is superior at reproducing the diurnal amplitude of PF that is similar to PA in terms of the spatial distribution. Moreover, the diurnal peak timing of summer PF and PA over the three sub-regions, i.e., North China (NC), Yangtze-Huaihe River basin (YHR) and South China (SC), can be properly reproduced by WRF_CPM. The observed precipitation systems exhibit obvious eastward propagation from the Plateau to its downstream, which may be due to the solenoid circulations associated with the low-level anomalous wind and moisture convergence. However, they are almost overestimated by WRF_CPM and in turn causing overestimated precipitation along YHR. The early morning precipitation in WRF_CPM has a larger fraction than CMORPH, which is related to the overestimated nocturnal low-level jet. Whereas, due to the solar heating and the land-sea breezes, the late-afternoon precipitation peak is mainly located along the coasts of eastern China, which matches well with the vertical motion in WRF_CPM. 相似文献
18.
使用2007—2017年京津冀地区156个气象站暖季（5—9月）逐小时降水观测数据,根据地形将研究区域分为6个分区,分析各分区降水量季节内变化和日变化特征,结果表明：1）京津冀的多雨区主要位于沿燕山南麓到太行山,存在多个降雨中心。2）各分区降水量季节内特征总体表现为单峰型,即7月降水量最大,7月第3候至8月第4候是主汛期,8月降水量次之,5月最少。3）降水呈夜间多,白天少的特点,7月初之前的前汛期降水多发生在16—21时;主汛期降水呈双峰型,峰值在17—22时,次峰值出现在00—07时;8月中旬以后的后汛期多夜间降水,峰值多出现在00—08时。4）高原山区多短历时降水,长历时累计降水对季节降水贡献率大值区位于平原地区,而持续性降水贡献率大值位于太行山区和燕山迎风坡的西部。 相似文献
19.
Effects of an Urban Park and Residential Area on the Atmospheric CO2 Concentration and Flux in Seoul, Korea 总被引：1，自引：0，他引：1
The CO2 concentrations and fluxes over an urban forest site (Namsan) and an urban residential region (Boramae) in Seoul, Korea, during the non-growing season (2–4 March 2011), the growing season (10–12 June 2011), and the late-growing season (22–24 September 2011) were analyzed. The CO2 concentrations of two sites showed nearly the same diurnal variation, with a maximum value occurring during the night and a minimum value occurring during daytime, as well as the same seasonal variation, with a maximum value during the non-growing season (early spring) and a minimum value during the growing season (summer). The CO2 flux over the urban forest did not show any typical diurnal variation during the non-growing season, but did show diurnal variation with a small positive value during the night and a large negative value during daytime in the growing and late-growing seasons due to photosynthesis in the urban forest. The CO2 flux over the urban residential region showed a positive daily mean value for all periods, with large values during the non-growing season and small values during the growing season, and it also showed diurnal variation with two maxima at 0600–1000 LST and 1800–2400 LST, and two minima at 0300-0600 LST and 1100-1500 LST, and was strongly correlated with the use of liquefied natural gas for cooking and heating by surrounding houses. 相似文献
20.
利用RegCM3模式对青藏高原1991—2000年10年夏季（6~8月）的地面气温和降水进行了模拟, 其模拟结果与CRU资料的对比分析表明: RegCM3模式的模拟能再现高原地面气温和降水的基本特征, 特别是气温, 能捕捉到高原北部夏季升温明显高于南部, 东北部升温最大; 在夏季3个月中, 模拟结果和CRU在6月份最为吻合, 7月份两者均为夏季气温最高月份和升温幅度最大月份, 8月份两者相差较大。RegCM3模式能够模拟出高原降水分布的基本特征和主要干湿中心, 由于高原降水的复杂性和模式对降水描述能力的不足, 降水模拟要差于气温。 相似文献