Extended Abstract (764K)J3.5
A stratified diagnosis of the Indian monsoon—Eurasian snow cover relationship
J. Fasullo, PAOS, University of Colorado, Boulder, CO
This study attempts to reconcile inconsistencies between modeling studies of the Indian monsoon-Eurasian snow cover relationship, which support the Blanford (1884) hypothesis, and recent diagnostic studies, which have largely failed to show a negative correlation between Eurasian snow cover and All-India Rainfall (AIR). Recently released Version 2 NESDIS/NOAA satellite-based retrievals of snow cover are used. A focus is given to diagnosing a) spatial and temporal complexity in the Eurasian snow cover distribution, b) the role of ENSO in modulating the snow cover-AIR relationship, and c) the spatial distribution of the rainfall association within India.
With these goals in mind, the climatological distribution of snow cover and its interannual variability are first assessed. While snow cover is largest in northern Eurasia, its variability is most pronounced in southwestern Asia between the Black and Caspian Seas, and across the northern Indian, Himalayan, and Tibetan Plateau (NIHT) regions. AIR is found to exhibit a very weak correlation with both DJF and MAM snow cover averaged over Eurasia and regions of large snow cover variability near India.
Patterns of snow cover anomalies associated with both ENSO and anomalous monsoon seasons are then examined in a composite analysis. Spatial complexity in snow cover anomalies during both anomalous monsoon years and ENSO events is shown to be large. The composites suggest that many idealized simulations of the monsoon snow-cover interaction are based on forcings that are not generally reflective of variations in nature. Moreover, as the association between ENSO and snow cover is found to be strong across much of Eurasia, ENSO’s influence on the monsoon-snow cover relationship over the climatological record is strongly suggested. When correlations between snow cover and monsoon intensity are calculated for regions neighboring India during anomalous monsoon seasons in which ENSO is weak (AM-neutral years), robust and statistically significant negative correlations are found. Specifically, snow cover over both the Southwest Asian and NIHT regions is found to correlate strongly with AIR during spring and winter, respectively. While snow cover over the entirety of Eurasia is also found to exhibit a modest correlation with AIR during AM-Neutral years, the correlation results largely from anomalies in northern Eurasia that are distant from India and are therefore probably unrelated to the Blanford hypothesis.
The spatial pattern of rainfall anomalies within India is also investigated. It is found that correlations between district rainfall and snow cover in the SW Asia and NIHT regions during ENSO are largely insignificant while during AM-Neutral years, significant negative correlations are found across central and northern India, in modest agreement with model simulations that show the strongest rainfall response in northern India. Together, the findings support the existence of the Blanford hypothesis while suggesting that the influence of the land surface can be overwhelmed by ENSO. A new conceptual model of the monsoon-snow cover relationship that builds on the Blanford hypothesis is thus proposed to better explain its apparent absence from diagnostic studies that use mean Eurasian snow cover over the entire available data record.
Joint Session 3, Land-Atmosphere Interactions (Joint with the 15th Symp. on Global Change and Climate Variations and 18th Conf on Hydrology; Room 609/610)
Tuesday, 13 January 2004, 8:30 AM-12:15 PM, Room 609/610
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