Satellite-Monitored Snow Cover in the Climate System - Satellite-based Applications on Climate Change - page 180

the northern annual mode (Thompson et al. 2000 ), typhoons over the western Pacific
(Xie et al. 2005 ), and the outbreak of cold waves at middle latitudes (Vavrus 2007 ).
Over 100 years ago, Blanford ( 1884 ) first suggested that the variability of continental
snow cover might exert a thermal forcing on the land surface and consequently
influence the Asian summer monsoon and its rainfall. Based on Blanford's hypothesis,
Walker ( 1910 ) found a negative correlation between Himalayan snow depth at the end
of May and the amount of summer rainfall over India. Hahn and Shukla ( 1976 )first
used modern observations to confirm an apparent relationship between the Eurasian
snow cover and the Indian monsoon rainfall based on NOAA/NESDIS snow mappings
derived from satellite visible imagery. There have been many empirical studies focused
on this relationship between winter/spring snow cover and the Indian summer monsoon
rainfall (Bamzai and Shukla 1999 ; Dey and Kumar 1983 ; Dickson 1984 ;Hahnand
Shukla 1976 ; Kripalani and Kulkarni 1999 ; Parthasarathy and Yang 1995 ; Sankar-Rao
et al. 1996 ;Yang 1996 ).
In particular, the snow cover over the Tibetan Plateau (TP) is believed to exert
a significant influence on the summer rainfall over East Asia (EA). As EA is located
in the downstream region of the TP, the snow-cover anomalies over the TP could
exert a stronger thermal forcing on the East Asian Summer Monsoon (EASM).
Chen and Yan ( 1979 , 1981 ) first found that positive snow depth anomalies over the
Tibetan Plateau in boreal winter-spring are accompanied by above normal
May-June rainfall in southern China. Other observational studies (Chen et al.
2000 ; Wu and Qian 2003 ), however, suggested a negative correlation between
Tibetan winter snow depth and subsequent summer precipitation over southern
China, but indicated a positive correlation over the Yangtze River Basin (YRB).
Chen and Wu ( 2000 ) obtained positive correlations over the Yangtze River region
but negative correlations in South China for JJA. It has also been found that the
correlation of rainfall with the Tibetan Plateau winter snow depth has a pronounced
change from July to August and the correlation for JJA rainfall differs from that for
May-June (Chen and Wu 2000 ). Although the snow-cover connection with EASM
is not very robust, snow cover is applied as one of four key predictors besides
ENSO, subtropical high, and blocking for short-range climate prediction at
National Climate Center of China (Xu and Li 2010 ;Zhao 1999 ).
Aside from the monsoon, other linkages between snow cover and atmospheric
circulation have been discovered by numerous observation studies. Studies show
that excessive summer-autumn snow coverage over Eurasia favors unusually cold
winters over Europe and the USA, due to forcing of the negative phase of Arctic
oscillation (Cohen and Entekhabi 1999 ). Subsequent studies confirmed the physical
mechanism of this relationship (Cohen and Saito 2003 ; Gong et al. 2002 , 2004a ;
Saito et al. 2001 ): early-season snow-cover anomalies trigger vertically propagating
planetary waves that quickly alter the stratospheric polar vortex. These observa-
tional linkages between snow cover and atmospheric circulation have motivated
efforts for seasonal climate forecasts based on snow anomalies.
In addition to being a climate predictor, snow cover also has profound ecological
and societal impact on the hydrosphere since snowpack strongly affects the