Memory And Climate Effects Of Soil Moisture

The memory and climate effects of soil moisture(SM)are the focus and hotspot in climate research.Especially for the Tibetan plateau(TP),the diabatic heating caused by the phase change of soil water has important influences on weather,climate and general circulation characteristics over local area and whole Asia region,which is a worthy scientific question.In this study,the time-space distribution characteristics of global SM and the relationship between SM and climate are analyzed using GLDAS SM assimilation data based on statistical diagnosis method and numerical simulation method,this study analyzes the time-space distribution characteristics of global SM and the relationship between SM and climate by use of GLDAS SM assimilation data.Firstly,the quality of GLDAS SM data in global land is tested.Taking the TP as an example,the errors of GLDAS SM data and its main causes are analyzed.And on this basis,we investigate the time-space distribution characteristics of SM by use of GLDAS SM data.A temperature-humidity index is defined by use of precipitation and air temperature to analyze the relation between global SM and local climate.On the basis of diagnostic analysis,two sensitivity tests by mesosclae numerical model are designed to investigate the effects of the SM in late spring on the subsequent weather over TP.The main conclusions are as follows:(1)The variation tendency of GLDAS SM(0-10cm)is basically consistent with observational data over the TP,although existing the deviation in magnitude in non-frozen period(April to October).The inaccuracy of precipitation in GLDAS driven data is the main reason leading to GLDAS SM errors in non-frozen period.GLDAS SM errors mainly show up in the changes of SM along with the temperature,especially in the freezing–thawing process in frozen period(November to March).And the errors of GLDAS SM in frozen period reveals that the faultiness of the freezing–thawing parameterization scheme and the errors from surface temperature in the GLDAS model,particularly for the process of phase change,simulation of SM is almost incondite.(2)On a global scale,GLDAS SM data has good correlation with observational data.SM memory that calculated by use of GLDAS SM data has obvious seasonal variation and spatial distribution difference.The temporal scale of global SM memory varies from 20 days to 110 days.The SM memory of humid and high mountain areas is longer than that of arid area in the shallow soil.And the memory of arid area in the deep soil is longer than the memory in shallow soil.The longest SM memory occurs in spring in the Northern Hemisphere and the memory in summer in the Southern Hemisphere.(3)SM memory quantifies the sustainability of soil moisture anomalies,which implies SM can “remember” the effects of previous climate,and also can continue to affect the subsequent climate.Precipitation and temperature,as the climate factors closely contacted with SM change,have different effects on the SM in different regions and seasons.The summer and autumn precipitation in the Northern Hemisphere are the main sources of soil moisture.In the mid-high latitudes of the Northern Hemisphere and the TP,the increase of SM is mainly dependent on the thaw of permafrost active layer and snow caused by temperature rising in the spring and winter.The summer and autumn precipitation,which were saved by infiltration and the freeze of permafrost active layer,are the main sources of soil moisture in the spring of next year,and the middle layer soil(10~100 cm)is the main reservoir layer of precipitation.Similarly,the rise of temperature in summer and autumn can accelerate the thaw of soil and increase of SM in the spring of next year,and the rise of temperature in spring is beneficial to the increase of SM in summer.In mid-low latitudes and the Southern Hemisphere,SM mainly increases with the increase of precipitation and decreases with the increase of temperature.The soil of middle and deep layers mainly stores the information of temperature and precipitation in the previous season.That is to say the SM of mid and deep layer increases with the increase of precipitation and the decrease of temperature of previous season.(4)The SM of the Northern Hemisphere significantly increases in spring.The increase of local SM is beneficial to the increase of subsequent precipitation at low latitudes,but the relationship between local SM and subsequent precipitation is inferior.The influence of mid layer SM on the subsequent precipitation is important on seasonal scales,and the influence of shallow layer SM on the subsequent precipitation is crucial on day-month scales.There is a negative correlation between the SM in spring and the temperature in summer in most arid regions,and is a positive correlation in high latitudes.(5)Numerical simulation results show that the changes of the SM in late spring have an effect on the subsequent weather by mainly through influencing the diabatic heating and water vapor transport over the TP.When the SM increases in late spring,the surface latent heat flux and upward water-vapor flux increases and the temperature reduces,the surface sensible heat flux decreases.The 500 hPa geopotential height increased on the TP and the 200 hPa geopotential height decreased on the TP and even China.Thus the precipitation increases,and the precipitation duration becomes longer on the northwest TP.When SM decreases in late spring,these changes are opposite to the situation of SM increase.Thus the precipitation increases,and the precipitation duration becomes longer on the southeast TP;and the precipitation decreases,and the duration becomes shorter in the northwest TP.