Tuesday, 24 January 2017
Soil moisture is robust factor in climate system, which has feedback to atmosphere. The processes of frozen soil thawing and snow melting can greatly influence spring soil moisture (SSM). The impacts of SSM anomalies on sequent climate are supposed to contain the information of snow anomalies in the preceding winter/spring. Variability of SSM is also determined by the preceding summer precipitation through the freezing-thawing process in the Northern Hemisphere (NH). Land surface models (LSMs) generally perform not well in the process of soil frozen thawing, the errors between observation and LSM simulations is obvious. Spatial-temporal characteristics of SSM revealed by Global Land Data Assimilation System (GLDA) show a large variability in NH in spring. European and Northern American continent are regions for significant variability of SSM. Correlation analysis and simulations show that the changes of SSM in those two regions relate well to the subsequent summer precipitation, which Soil moisture on the contribution of precipitation is second only to the ocean. We propose a mechanism schematic of impact for soil moisture on subsequent summer precipitation, that is: the part of soil moisture actually comes from the preceding summer precipitation sealed by soil frozen in winter, with temperature increasing in spring, frozen soil begins thawing, the soil moisture increases and exchanges with atmosphere, thus effect atmospheric circulation via diabatic heating, further leads precipitation anomaly in summer.
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