Observed Relationships between Global Precipitation and Surface Temperature on Inter-annual and Longer Time Scales
Robert F. Adler, ESSIC, University of Maryland, College Park and NASA/GSFC, Greenbelt, MD; and G. Gu and G. J. Huffman
Associations between global and regional precipitation and surface temperature anomalies on inter-annual and longer time scales are examined for the period of 1979-2006 using the GPCP precipitation product. Positive (negative) correlations are generally observed between these two variables over tropical oceans (lands). ENSO is the dominant factor in these interannual, tropical relations. Away from the tropics, particularly in the northern hemisphere mid-high latitudes, this correlation relationship becomes much more complicated with positive and negative values of correlation tending to appear over both ocean and land. These relations may be associated with the effects from both ENSO and the Arctic Oscillation (AO). In particular a strong seasonal variation in the correlation patterns tends to occur in the northern hemisphere mid-high latitudes.
Possible relationships between the long-term changes (trends) in global precipitation and surface temperature are also assessed. Most intense long-term, linear changes in annual-mean rainfall anomalies during the data record tend to be within the tropics, as do their largest interannual variances. For surface temperature however, both the strongest linear changes and largest variances are observed in the northern hemisphere mid-high latitudes, with much weaker temperature changes in the tropical region and southern hemisphere. Northward increase of land surface fraction coverage may be a major reason. Regional variations in both variables are further described.
Finally, the ratios between the linear changes in zonal-mean rainfall and temperature anomalies over the period are estimated. Globally, the calculation results in a +2.3%/C precipitation change, although the magnitude is sensitive to small errors in the precipitation data set and to the length of record used for the calculation. The long-term temperature-precipitation relations are also compared to the inter-annual variations of the same ratio in a zonally-averaged sense, and are shown to have similar profiles, except for over tropical land areas. These similarities and differences may reflect how temperature-precipitation processes on these two time scales are related and provide the basis for further evaluation through the data sets and models. Possible physical bases for these variations, both inter-annual and long-term will be discussed.
Session 6, Global dynamics and processes
Tuesday, 13 January 2009, 1:30 PM-3:00 PM, Room 129A
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