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171.
树轮降水记录及东亚夏季风强弱变化——以内蒙古包头地区为例 总被引:23,自引:0,他引:23
在精确交叉定年的基础上 ,依据树木年轮宽度指标 ,分别精确重建了中国内蒙古包头地区过去 2 6 0a来 2— 7月上旬及 6— 8月上旬降水总量 ,方差解释量分别达到 42 6 0 %和 32 6 0 % ,并与历史记载进行了良好的对比。通过 6— 8月上旬降水总量所反应的干湿时段的分析 ,研究了东亚夏季风10 0 10 1a尺度的强弱变化历史。发现在过去近 2 6 0a中 ,东亚夏季风经历了 8次较强和 8次较弱的发展过程。同时周期分析表明 ,6— 8月上旬降水存在 12 6 3,7 5 ,5 115 2 2 ,4 5 34 6 2 ,3 16 3 5 3a的准周期。 相似文献
172.
我国东部夏季降水百年雨型的多时间尺度变化特征研究 总被引:8,自引:4,他引:8
本文用1900-1950年的我国实测的与内插的降水、气温资料,结合近代先进的统计方法对立了1900-1950年我国东部夏季降水雨型序列,并将其与已有的近48年(1951-1998年)的夏季雨型序列相衔接,进而研究了近百年我国夏季雨带的演变规律及其与ENSO的关系,此外,还研究了百年夏季雨型与大气活动中心在基本态时间尺度上的关系,研究了北太平洋涛动和我国夏季降水的关系。 相似文献
173.
The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM)
of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved
treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization
of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction
of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon
forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August)
of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988).
Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes
in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more
predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable
increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became
more intense with the introduction of changes in the operational forecasting system.
Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with
the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10).
The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment
of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports
of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have
enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities
have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts
to improve the formulations of physical processes for further reduction of systematic forecast errors. 相似文献
174.
Nityanand Singh 《Journal of Earth System Science》1995,104(1):1-36
Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation
in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm
isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area
(monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered
as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics
of the summer monsoon dry area (SMDA) are reported.
To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area
and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global
surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere,
April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant
correlation.
A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested
in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges
whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura
(Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724.
Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding
year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May
as independent parameters. 相似文献
175.
176.
177.
春季海温对中国夏季降水影响的诊断研究和预测试验 总被引:9,自引:2,他引:9
文中利用季降水异常集合的典型相关预测模式 ,以全球春季 (3~ 5月 )海温场作为因子场 ,对中国夏季降水场进行了诊断研究 ,并对 1998,1999及 2 0 0 0年这几个典型的中国夏季降水进行了回报试验。结果表明 ,春季海温与中国夏季降水之间存在较好的关系 ,春季海温在较大程度上决定了中国夏季降水雨带及其分布类型。考虑面积因子的集合典型相关预测方案对中国夏季降水具有较强的回报能力 ,此模式不仅能诊断出降水场和海温场中一些比较典型的空间模态和时间变化规律 ,而且可以再现 1998和 2 0 0 0年中国大部分地区的旱涝灾害。揭示了全球春季海温的异常变化在中国夏季 (6~ 8月 )降水异常中的作用。 相似文献
178.
The δ18O variations in an 80.36 m ice core retrieved in the accumulation zone of the East Rongbuk Glacier, Mount Qomolangma (Everest), is not consistent with changes of air temperature from both southern and northern slopes of Himalayas, as well as these of the temperature anomalies over the Northern Hemisphere. The negative relationship between the δ18O and the net accumulation records of the ice core suggests the "amount effect" of summer precipitation on the δ18O values in the region. Therefore, the δ18O records of the East Rongbuk ice core should be a proxy of Indian Summer Monsoon intensity, which shows lower δ18O values during strong monsoon phases and higher values during weak phases. 相似文献
179.
Runoff and peak flows in four experimental catchments with different land uses are analyzed for summer periods. The catchments have a rainy temperate climate with annual precipitations between 2000 and 2500 mm, 70% of which is concentrated in the winter period between May and August. The final harvest of the forest plantation in one of these catchments generated increases in summer runoff. Also, differences between the maximum instantaneous discharge and the flow at the beginning of the storm then almost duplicated those registered in rainfall events of similar magnitude when the catchment was fully forested. Runoff analysis in this catchment is difficult because the two post-harvesting summer periods are much wetter than the two pre-harvesting ones but a double mass analysis shows the effect of harvesting clearly. In a paired catchment study, low cover in one of the two neighbour catchments explains higher direct runoff and base flows although lower maximum instantaneous specific discharge occurred in the less vegetated but larger catchment. Low vegetation cover explains increases in summer flows, although the size, topography, rainfall conditions, road density, extent of affected area and runoff generation processes play an important role in the hydrological effects of different land uses. 相似文献
180.
东亚冬季风强度异常与夏季500hPa环流及我国气候异常的关系 总被引:5,自引:0,他引:5
利用一个耦合海气模式,用数值试验方法分析了1982/1983ENSO期间的暖池和赤道事带的相互使用对大气表面流场和散度的影响。结果指出,ENSO高峰期和成熟期SPCZ比ITCZ更重要;ENSO的形成初期和衰减期SPCZ和ITCZ同样重要。 相似文献