摘要:本文首先利用中国气象局国家气象信息中心提供的中国732个站点观测的土壤体积含水量，评估了CLM4.5（Community Land Model version 4.5）在CFSR（Climate Forecast System Reanalysis）近地面大气数据驱动下模拟的逐月土壤湿度（记为CLM4.5-CFSR），然后基于CLM4.5-CFSR比较了皮尔逊相关法和自相关法计算得到的1980～2009年中国地区土壤湿度记忆性的区域及季节分布特征，量化了土壤湿度的记忆能力，研究了降水频率、降水强度和近地表气温分别对土壤湿度记忆性的影响。结果表明：CLM4.5-CFSR能较好地反映出大部分地区月时间尺度上土壤湿度的变化特征。两种方法描述的土壤湿度记忆性的空间分布特征相似，但季节特征不同。不同深度土壤湿度的记忆时长相差不大，在0.85～2.2个月不等，其中内蒙古东北部较大，新疆西南部较小。春季，较湿的土壤记忆性也较强。当降水频率较低时，其对蒸发速率较大的地区土壤湿度的记忆性影响很小，当降水强度较大时，它会迅速补充土壤散失的水分，破坏初始时刻土壤的干湿状态，引起其记忆性减弱。近地表气温变化主要通过影响土壤的蒸发过程减弱土壤湿度的记忆性。未来可利用气候模式开展数值敏感性试验对本文得到的结论进行机理研究，为进一步提高季节和季节内尺度的降水预报提供依据。
关键词:土壤湿度/
记忆性/
降水频率/
降水强度/
近地表气温
Abstract:This study first uses the volumetric soil water content data from 732 stations in China, as provided by the National Meteorological Information Center (NMIC) at the China Meteorological Administration (CMA), to evaluate the simulations of the Community Land Model version 4.5 (CLM4.5) driven by Climate Forecast System Reanalysis (CFSR) near surface meteorological data (referred as to CLM4.5-CFSR). Then the CLM4.5-CFSR is used to investigate the spatial-temporal characteristics of soil moisture memory in China region during 1980–2009. The soil moisture memory is calculated by both Pearson correlation method and autocorrelation method. The effects of precipitation frequency, precipitation intensity and near-surface temperature on soil moisture memory are then explored. The results show that CLM4.5-CFSR can reflect the soil moisture changes on the monthly time scale in China. The spatial distributions of soil moisture memory from two methods are similar, but their seasonal characteristics are different. The soil moisture memory duration does not vary very much with soil depth, ranging from 0.85–2.2 months across China with relatively larger magnitude in the northeast of the Inner Mongolia, while smaller in the southwest of Xinjiang Province. In spring, the wetter the soil, the longer the soil moisture memory. When the precipitation frequency is low, it has little effect on soil moisture memory in areas where the evaporation rate is high. When the precipitation intensity is high, soil moisture memory will be shortened by it because it can replenish the soil water rapidly and destroy the initially dry or wet conditions of the soil. Changes in the near-surface temperature will shorten the soil moisture memory through its effect on the soil evaporation. In the future, it is necessary to carry out climate model sensitivity experiments to gain insights on physical mechanisms associated with the conclusions obtained in the current study, which in turn to provide a basis for further improvements of the seasonal and intraseasonal precipitation prediction.
Key words:Soil moisture/
Memory/
Precipitation frequency/
Precipitation intensity/
Near-surface temperature
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