滑动窗区空间相关系数加权集合方法及其在IPCC-AR4多模式集合模拟和预测中的应用

本文根据政府间气候变化委员会(IPCC)第四次评估报告(AR4)(简称IPCC-AR4)中22个耦合模式对20世纪气候模拟(20C3M)结果中20世纪晚期亚洲夏季风降水的模拟所显示出各模式模拟能力的较大空间差异,提出了一种滑动窗区空间相关系数来量化表征这种空间差异特征,结果表明,该系数明显优于传统空间相关系数,其空间分布能够较为细致地描述各模式对较小区域模拟性能的空间差异特征。在此基础上,本文提出以这种滑动窗区空间相关系数作为各模式的权重系数进行加权集合平均,并称之为滑动窗区空间相关系数加权集合方法。利用该方法对IPCC-AR422个耦合模式所模拟的20世纪晚期亚洲夏季风降水进行加权集合平均,并将其结果与传统空间相关系数加权集合平均以及等权重多模式集合平均结果进行比较,表明了利用本文所提出的加权集合方法对20世纪晚期亚洲夏季风降水的集合模拟结果明显优于简单的等权重多模式集合平均结果以及传统空间相关系数加权集合平均结果。鉴于此原因,本文利用此方法对在A1B(各种能源均衡发展)排放情景下IPCC-AR4中22个耦合模式所模拟的21世纪各时期亚洲夏季风降水演变趋势进行集合预测。其结果表明:在A1B排放情景下,从21世纪中期(2045～2065年)开始南亚夏季风降水将比20世纪晚期明显增强;而东亚夏季风降水相对于20世纪晚期的变化呈现出从南到北经向三极子型异常分布特征,即华南和华北地区夏季风降水增多,而长江流域夏季风降水相对于20世纪晚期没有太大变化。并且,结果还表明亚洲夏季风降水异常这种变化趋势可以延续到21世纪晚期。

Shift of the principal mode of Pan-Asian monsoon summer precipitation in terms of spatial pattern

This paper documents that the principal mode of Pan-Asian monsoon summer precipitation experienced a prominent interdecadal shift around 1992/1993 in terms of spatial pattern and major driving factors. During 1979-1992 （Period 1, P1）, Pan-Asian monsoon summer precipitation anomalies mainly display a meridional dipole pattern from north to south, whereas in the period 1993-2016 （Period 2, P2）, it shows a meridional tripole pattern instead. The summer precipitation in P1 is primarily associated with a combination of the developing phase （central-eastern Pacific type） and decaying phase （eastern Pacific type） of El Nino-Southem Oscillation （ENSO）; while in P2, it is mainly associated with the decaying phase of central-eastern-Pacific-type ENSO.

Intensified East Asian summer monsoon and associated precipitation mode shift under the 1.5 ℃ global warming target

In this study, the East Asian summer climate changes under the 1.5 ℃ global warming （1.5 GW） target in 30 simulations derived from 15 coupled models within the Coupled Model Intercomparison Program phase 5 （CMIP5） are examined. Compared with the current summer climate （1975-2005）, both surface air temperature and precipitation increase significantly over the East Asian continent during the 1.5 GW period （average period 2021-2051）. In northeastern China this is particularly pronounced with regional averaged precipitation increases of more than 7.2%, which is greater than that for the whole East Asian continent （approximately 4.2%）. Due to stronger enhancement of precipitation north of 40°N, the leading empirical orthogonal function （EOF） mode of summer precipitation over the East Asian continent changes from tripolar-like mode to dipole mode. As there is stronger surface warming over the East Asian continent than that over surrounding ocean, the land-sea thermal contrast is enhanced during the 1.5 GW period. As a result, the monsoon circulation in the lower troposphere is significantly strengthened, which causes the increased summer precipitation over the East Asian continent. In addition, larger interannual variabilities of East Asian summer monsoon circulation and associated precipitation are also suggested for the 1.5 GW period.

Experimental 15-day-lead statistical forecast of intraseasonal summer monsoon rainfall over Eastern China

This study utilizes daily Asian Precipitation–Highly-Resolved Observational Data Integration Towards Evaluation（APHRODITE）gridded rainfall and the U.S.National Centers for Environmental PredictionDepartment of Energy reanalysis II products to examine the intraseasonal oscillations（ISOs）of rainfall over Eastern China during each summer of 1996,2002,and 2006.These three cases represent three typical spatial patterns of intraseasonal rainfall anomalies over Eastern China,with the strongest intraseasonal rainfall occurring over the middle and lower Yangtze Basin,southern Yangtze Basin,and Southeast China,respectively.The intraseasonal rainfall anomalies over Eastern China are dominated by both 30–60-and 10–20-day ISOs in each summer and are further modulated by the boreal summer ISOs（BSISOs）over the entire Asian summer monsoon region.The objective of this study is thus to apply the Bayesian wavelet-banding（WB）scheme to predicting intraseasonal rainfall over Eastern China.Several key factors associated with BSISOs are selected as predictors to experimentally develop a 15-day-lead statistical forecast.The forecast results show promise for the intraseasonal rainfall anomalies over Eastern China.Correlations generally greater than or equal to 0.6 are noted between the observed and predicted ISOs of rainfall over the major intraseasonal activity centers during each of the three summers.Such a high forecasting skill on intraseasonal timescales over various areas in Eastern China demonstrates the general usefulness of the WB scheme.

Diurnal variations of summer precipitation over the Asian monsoon region as revealed by TRMM satellite data

Climatological characteristics of diurnal variations in summer precipitation over the Asian monsoon region are comprehensively investigated based on the Tropical Rainfall Measuring Mission(TRMM) satellite data during 1998-2008.The topographic influence on the diurnal variations and phase propagations of maximum precipitation are identified according to spatiotemporal distributions of the amplitude and peak time of the diurnal precipitation.The amplitude and phase of diurnal precipitation show a distinct geographical pattern.Significant diurnal variations occur over most of continental and coastal areas including the Maritime Continent,with the relative amplitude exceeding 40%,indicating that the precipitation peak is 1.4 times the 24-h mean.Over the landside coasts such as southeastern China and Indochina Peninsula,the relative amplitude is even greater than 100%.Although the diurnal variations of summer precipitation over the continental areas are characterized by an afternoon peak(1500-1800 Local Solar Time(LST)),over the central Indochina Peninsula and central and southern Indian Peninsula the diurnal phase is delayed to after 2100 LST,suggesting the diurnal behaviors over these areas different from the general continental areas.The weak diurnal variations with relative amplitudes less than 40% exist mainly over oceanic areas in the western Pacific and most of Indian Ocean,with the rainfall peak mainly occurring from midnight to early morning(0000-0600 LST),indicating a typical oceanic regime characterized by an early morning peak.However,apparent exceptions occur over the South China Sea(SCS),Bay of Bengal(BOB),and eastern Arabian Sea,with the rainfall peak occurring in daytime(0900-1500 LST).Prominent meridional propagations of the diurnal phase exist in South Asia and East Asia.Along the eastern Indian Peninsula,there is not only the southward phase propagation with the peak occurring around 25°N but also the northward phase propagation with the peak beginning with the southernmost continent,and both reach the central Indian continent to finish.Along the same longitudes where southern China and Kalimantan are located,the diurnal phase of the former propagates from the oceanic area(northern SCS) toward the inland continent,while the phase of the latter propagates from the land area toward the outside sea,showing a landward or seaward coastal diurnal regime.A distinct zonal propagation of the diurnal phase is observed over the BOB oceanic area.The maximum precipitation zone originates from the land-sea boundary of the eastern coast of the Indian peninsula at around 0300 LST,and then propagates eastward with increasing time to reach the eastern coast of the BOB on 1800 LST,finally migrates into the Indochina continent on about 2100 LST.