Spatial and temporal variations of light rain events over China and the mid-high latitudes of the Northern Hemisphere

Abstract

Based on observed daily precipitation data, monthly gridded radiosonde upper air temperature and sea surface temperature data from the UK Met Office Hadley Centre, monthly surface air temperature from the Climatic Research Unit at the University of East Anglia and the NCEP/NCAR monthly reanalysis data, this study investigates the spatial and temporal variations of light rain events over China and the mid-high latitudes of the Northern Hemisphere during 1961-2010, and discusses the relationship between the change of light rain events and atmospheric stability, sea surface temperature and atmospheric circulation. The light rain events over East China display a decreasing trend of 3.0%/10 a in summer and winter half years. Over Northwest China, an increasing trend of 4.1%/10 a is found in winter half years, but there is no trend in summer half years. Using empirical orthogonal function (EOF) analysis, it is found that the first two principal components of light rain events over the mid-high latitudes of the Northern Hemisphere show long time scale variations in summer and winter half years. The first EOF modes (EOF1s) for summer and winter half years both depict a long-term increase in light rain events over North America and Southern Europe as well as Northwest China (except in summer half years), and a long-term decrease over most of the Eurasia (Central Europe, Eastern Europe, North Asia and East China). The second EOF mode (EOF2) for summer half year shows that light rain events increase over North America, Southern Europe and South China, but decrease over Eurasia north of 45°N from 1961 to early 1980s, while the trends reverse from late 1980s to 2010. The second EOF mode (EOF2) for winter half years indicates that light rain events increase over North America and South and North China, but decrease over Eurasia north of 40°N from 1961 to early 1980s, while the trends reverse from late 1980s to 2009. Correlation analysis and linear regression analysis suggest that EOF1s may be related to the change in atmospheric static stability associated with global warming, and EOF2s are possibly linked to the AMO. light rain, the mid-high latitudes of the Northern Hemisphere, EOF, atmospheric stability, global warming Citation: Huang G, Wen G H. Spatial and temporal variations of light rain events over China and the mid-high latitudes of the Northern Hemisphere.

Opposite Trends in Light Rain Days over Western and Eastern China from 1960 to 2014

“…The work of Qian, et al [23], Fu, et al [34], Huang and Wen [25], and Liu, et al [35] attributed the reduction of light rain days over eastern China to increases in lower-tropospheric temperatures that were capable of one or more of the following: (1) increasing the dew-point temperature; (2) causing a rise in the condensation height of precipitable clouds and reducing cloudage; and (3) weakening atmospheric stability and strengthening upward motion such that precipitation intensity increased and light rain events decreased. Nevertheless, universal increases in lower-tropospheric temperature cannot explain increasing trends in light rain events over western China.…”

“…From 1973 to 2009, decreasing trends for light rain events have been observed in North America, Europe, and Asia, especially in eastern Asia [22]. Previous studies have led researchers to conclude that light precipitation days have significantly decreased over eastern China (east of 100 • E) [8,21,[23][24][25][26].…”

“…Research conducted based on the Weather Research and Forecasting (WRF) simulations model by Wu et al [27] indicated that soil moisture-atmospheric coupling was important for explaining variations in summer light precipitation events over eastern Asia. Huang and Wen [25] argued that global warming weakens atmospheric stability such that upward motion strengthens while precipitation intensity increases and light rain events decrease.…”

Possible Causes for Spatial and Temporal Variation of Warm Season Precipitation in Xinjiang from 1960–2014

“…Of all of the potential causes for decreases in light precipitation, an increase in lower-tropospheric temperatures is considered to be the main factor. Lower-tropospheric temperature increases the dew-point temperature, causes a rise in the condensation height of precipitable clouds, and reduces cloudiness, weakens atmospheric stability, and strengthens upward motion [28,29,32,34]. A study by Wu et al [33] for eastern China indicated that both lower-tropospheric warming and specific humidity were responsible for variations in light rain days during the warm season.…”

“…Light precipitation requires additional time to soak into soils, leaving less water for surface runoff [2], and this characteristic of light precipitation is important for abating droughts in the arid region of Xinjiang. In the past, studies have focused on decreasing light precipitation days over eastern China [28][29][30][31][32][33]. Of all of the potential causes for decreases in light precipitation, an increase in lower-tropospheric temperatures is considered to be the main factor.…”