全新世中国夏季降水量变化的两种模态

根据气候模拟的夏季降水量及古气候湿润度代用资料，指出全新世中国夏季降水量变化存在两种模态。模态1：降水量异常的中心为一个东北－西南向的带； 从东北、内蒙东部、经华北、河套到青藏高原为一正异常中心。模拟结果的EOF分析表明这种模态占模拟的全新世中国夏季降水量变化总方差的75.8%。全新世降水量变化的模拟主要考虑地球轨道要素，其中岁差起着重要作用。因此，这个模态可以称为岁差模。岁差模主要反映近万年全新世降水变化的趋势。模态2：降水量异常分布在中国东部(100°E以东)自北向南表现为负－正－负分布。负异常在内蒙中部到华北，正异常在黄河中游、淮河、到长江流域，江南部分地区又有负异常。这与模拟的大西洋热盐环流减弱所造成的中国夏季降水量异常分布一致。因此，这个模态可能与全新世的气候突变有关，称为气候突变模。覆盖中国的80个代用资料序列给出的9kaB.P.和4kaB.P.干湿分布，证明早全新世气候湿润，晚全新世气候干旱。这种变化趋势主要反映了岁差的影响。同时，4kaB.P.虽然干旱分布广泛，但是长江流域、关中地区到高原东部则有若干气候湿润的指示。这表明4kaB.P.同时受岁差及气候突变的影响。

TWO MODES OF SUMMER PRECIPITATION VARIATION OF HOLOCENE IN CHINA

Two modes of summer precipitation variation of Holocene in China were identified according to climate modeling and palaeo-climatic humidity data,Mode 1 has such a feature given by EOF_1 of palaeo-climate modeling: positive precipitation anomaly centers are distributed in a NE-SW extended zone from North East China, Eastern Inner Mongolia, North China, the Great Bend of the Yellow River to the Tibet Plateau. This mode is correlated closely to the solar radiation change controlled mainly by precession in Holocene. It can be used to interpret 75.8% of the total variance of the modeled summer precipitation variation of Holocene. The modeling indicates that the average precipitation in whole China has a decrease of about 10% from Early to Late Holocene. This mode is called the precession mode. Mode 2 represents as a negative-positive-negative distribution of precipitation anomaly from north to south in East China (east of 100°E) : negative precipitation anomalies in North China, positive anomalies in the middle reach of the Yellow River, the Huai River, and the Yangtze River Valley, and negative anomalies in parts south of the Yangtze River. This mode is similar in a great extent to the modeled pattern of summer precipitation anomaly of China by reducing of the Atlantic thermohaline Circulation. This mode might be related to climate abrupt change during Holocene,so it is called the abrupt change mode. Palaeo-climatic humidity data in 80 sites throughout China support the identification of the two modes. A wet climate occurred in 9kaB. P., whereas a dry climate occurred in 4kaB. P., suggesting an impact of precession. The dry climate of 4kaB. P. Was widespread, but the Yangtze River valley, the Central Shaanxi plain and the east part of the Tibet Plateau were wet. These suggest that there were influences of both precession and climate abrupt change in that time.