Large-scale interannual variability of monthly outgoing longwave radiation anomalies over the global tropics
- Climate Analysis Center, Washington, DC (United States)
- Office of Climate and Atmospheric Research, Rockville, MD (United States)
This study examines the broad aspects of large-scale interannual and long-term variability in the monthly mean outgoing longwave radiation (OLR) data over the global tropics. The data is from NOAA's polar-orbiting satellites. Rotated principal component analysis (RPCA) has been performed on monthly OLR anomalies over the global tropics (30[degrees]-30[degrees]S) on a 10[degrees] longitude by 5[degrees] latitude grid for the period from June 1974 through March 1989, excluding calendar year 1978. The leading rotated principal components have been tested for robustness and reproducibility. The spatial-loading pattern and the time series for the first principal component ([open quotes]canonical ENSO[close quotes] mode) represent the major large-scale features in the tropics during the typical phase of the major warm and cold events in the tropical Pacific. The characteristics of the dramatic 1982/83 warm event that were different from the canonical ENSO mode completely dominate the second RPC (termed the 1982/83 mode). The third and fourth leading RPCs appear to describe the changes in the satellite-observing system. Of the six leading modes considered, the [open quotes]nonphysical[close quotes] modes (3 and 4) accounted for more than 40% of the explained variance over North Africa and northeastern South America. The physical modes (1, 2, 5, and 6) explained more than 70% of the variance in the central equatorial and eastern Pacific Ocean. While the eigenmodes that result from unrotated principal component analysis are sensitive to small changes in analysis domain and period, those of the rotated analysis are fairly stable. However, the [open quotes] 1982/83 mode,[close quotes] is unique to the analysis period (1974-89). The results of the sensitivity analysis do not provide strong support of the claim by other authors that the decade of the 1980s, as compared to the 1970s, experienced enhanced levels of convective activity in the tropical Pacific and Indian oceans.
- OSTI ID:
- 6597573
- Journal Information:
- Journal of Climate; (United States), Vol. 5:4; ISSN 0894-8755
- Country of Publication:
- United States
- Language:
- English
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