A Study Of Soil Moisture-Precipitation Coupling Strength In China

The research about the land-atmosphere interaction will help understanding the complicated exchanges of energy and water between land and atmosphere, and improving the parameterization schemes in model. The quantitative impact of land surface on precipitation is one of the main indicators to reflect the land–atmosphere coupling characteristics, and furthermore soil moisture plays an important role in land surface processes. Therefore, soil moisture-precipitation coupling is one of the core issues of the land–atmosphere coupling. In China, the research for land–atmosphere quantitative coupling strength is less. Due to the incomplete soil moisture observations and a series of complicated middle processes of soil moisture on the precipitation, the results of quantitative study on soil moisture and precipitation are different.Two popular research methods of diagnosing the coupling strength are selected in this paper to study the coupling characteristics between soil moisture and precipitation in China. We start with the viewpoint of two intermediate processes involved in the influence of soil moisture on precipitation. And based on GLDAS data and 12 sets of CMIP5 model outputs, the characteristics of soil moisture–precipitation coupling are indirectly investigated by analyzing the land surface coupling index(ILH), the coupling index(ILCL) between latent heat flux and the lifting condensation level(ZLCL), and ZLCL itself. Then, the decadal variations of the summer coupling indices are analyzed in four representative regions for the period 1958–2013 and — under the RCP4.5 radiative forcing scenario — the period 2006–2055. After that, the correlations between the Arctic Oscillation Index, El Nino and land surface coupling index are analyzed. Finally, we select two summers as simulation periods respectively in strong and weak coupling years with no El Nino, i.e., 2000 and 2005 based on the results of statistics, and a nested grid is introduced in the strong coupling area. A series of controlled tests and the sensitivity tests of precipitation to soil moisture are carried out to directly diagnose coupling strength.The statistical results show that: from 1958 to 2013, the larger summer ILH values were located around the Yin Mountains in Inner Mongolia, and in parts of Xinjiang and Qinghai provinces. The decadal variations of the summer coupling indices decreased in the following order: North China, South China, central Inner Mongolia, and Northwest China. Abrupt change in the indices was found in the mid-1970 s to mid-1980 s. From 2006 to 2055, the region projected to feature larger ILH on average is still near the Yin Mountains. Compared with the historical period(1958–2005), ILH is projected to increase near the central region of Xinjiang Province and around the Yin Mountains, while the degree of coupling in Guangxi and Guangdong provinces is shown to reduce. In terms of decadal variation in the period 2006–2055, North China is projected to be the strongest coupling region and South China the weakest(from 2026 to 2035). Meanwhile, in Northwest China, few changes are projected to occur, and ILH in central Inner Mongolia is shown to gradually increase. Weak coupling is in El Nino year, but not necessarily the coupling is weak in El Nino years.Based on the diagnostic results of the mesoscale model WRF on the coupling strength of China in two summers of 2000 and 2005, it is found that with the increase of time scale precipitation time series, the coupling signal of soil moisture and precipitation gradually becomes weake, and the value of ?? reaches a peak at the time scale of 6 hour. And Shandong province, Shanxi province, Hebei province, Tianjin, Beijing, southern central area of Inner Mongolia are the high value region of coupling strength in China. As for nesting area, in July is the strongest coupling in 2000, while in August is in 2005. The common strong coupling centers of the 2000 and 2005 summer are located in southern of Beijing, Tianjin, most of Shandong province, Baotou, Hohhot, and Wulanchabu of Inner Mongolia province. By means of simulation, the new scattered areas with very strong coupling are found which can not be resolved by the GLDAS data. Which is mostly distributed in the Qinghai Tibet Plateau, Yunnan province, midwest of Sichuan province, western of Guizhou province and southeast coast. The coupling strength and the large value area in the summer of 2000 are larger than that these in 2005, which is consistent with the GLDAS data analysis.The common strong coupling region from the two diagnosis methods is in South Central Inner Mongolia. Meanwhile, and in June, the common coupling area also includes parts of Shandong province.