Global Precipitation Analysis
Robert F. Adler, Guojun Gu
October 26, 2012 15:25:50
Description of Problem
The objective is to analyze precipitation data from the Global Precipitation Climatology Project (GPCP) and other sources to understand interannual to interdecadal/long-term variations in global and regional precipitation.
Scientific Objectives and Approach
Global precipitation data sets are analyzed along with other data sets and model outputs to better understand variations in mean precipitation and extremes on a variety of spatial and temporal time scales.
The effects of ENSO and two large tropical volcanic eruptions (El Chichón, March 1982; Mt. Pinatubo, June 1991) are examined for the period of 1979-2008 using various satellite- and station-based observations of precipitation, surface and atmospheric temperature, and tropospheric water vapor content. By focusing on the responses in the time series of tropical and global means over land, ocean, and land and ocean combined, we provide a detailed observational comparison of how these two phenomena, represented by Nino 3.4 and the tropical mean stratospheric aerosol optical thickness (), respectively, influence precipitation, temperature, and water vapor variations.
Strong same-sign ENSO signals appear in tropical and global mean (surface and tropospheric) temperature over both land and ocean. However, ENSO only has very weak impact on tropical and global mean (land+ocean) precipitation, though intense anomalies are readily seen in the time series of precipitation averaged over either land or ocean. In contrast, the two volcanoes decreased not only tropical and global mean surface and tropospheric temperature, but also tropical and global mean (land+ocean) precipitation. The differences between the responses to ENSO and volcanic eruptions are further examined by means of lag-correlation analyses. The ENSO-related peak responses in oceanic precipitation and sea surface temperature (SST) have the same time lags with Nino 3.4, two (four) months for the tropical (global) means. Tropical and global mean tropospheric water vapor over ocean (and land) generally follows surface temperature. However, land precipitation responds to ENSO much faster than temperature, suggesting a certain time needed for surface energy adjustment there following ENSO-related circulation and precipitation anomalies. Weak ENSO signals in the tropical and global mean mid-lower tropospheric atmospheric (dry) static instability are also discovered, seeming to be consistent with weak ENSO responses in the tropical and global (land+ocean) mean precipitation. For volcanic eruptions, tropical and global mean precipitation over either ocean or land responds faster than (surface and atmospheric) temperature and tropospheric water vapor averaged over the same areas, suggesting that precipitation change is more sensitive to volcanic-related solar forcing. The volcanic-related precipitation variations are further shown to be related to the changes in the mid-lower tropospheric atmospheric (dry) instability.
Refereed Journal Publications
Gu, G., and R. F. Adler, 2011: Precipitation and temperature variations on the interannual time scale: Assessing the impact of ENSO and volcanic eruptions. J. Climate (in press)
Other Publications and Conferences
Gu, G., and R. F. Adler, 2010: Comparing the ENSO and volcanic effects on the evolution of precipitation and temperature anomalies during the period of 1979-2008. AGU 2010 Fall Meeting. San Francisco, California, December 13-17, 2010.
Gu, G., and R. F. Adler, 2010: Seasonal-to-interannual precipitation variability: Observations versus reanalysis outputs. Evaluation of Reanalyses-Developing and Integrated Earth System Analysis (IESA) Capability, UCAR-JOSS. Baltimore, Maryland, November 1-3, 2010.
Gu, G., and R. F. Adler, 2010: Exploring the relationships between precipitation and surface temperature using satellite-based observations. 17th Conference on Satellite Meteorology, American Meteorological Society. Annapolis, Maryland, September 27-30, 2010.