Interannual variability of outgoing longwave radiation as observed by AIRS and CERES

摘要

The paper examines spatial anomaly time series of outgoing longwave radiation (OLR) and Clear Sky OLR (OLR_(CLR)) as determined using observations from CERES Terra and AIRS over the time period September 2002 through June 2011. We find excellent agreement of the two OLR data sets in almost every detail down to the 1 × 1 spatial grid point level. The extremely close agreement of OLR anomaly time series derived from observations by two different instruments implies high stability of both sets of results. Anomalies of global mean, and especially tropical mean, OLR are shown to be strongly correlated with an El Nio Index. These correlations explain that the recent global and tropical mean decreases in OLR over the time period studied are primarily the result of a transition from an El Nio condition at the beginning of the data record to La Nia conditions toward the end of the data period. We show that the close correlation of mean OLR anomalies with the El Nio Index can be well accounted for by temporal changes of OLR within two spatial regions, one to the east of, and one to the west of, the NOAA Nio-4 region. Anomalies of OLR in these two spatial regions are both strongly correlated with the El Nio Index as a result of the strong anticorrelation of anomalies of cloud cover and midtropospheric water vapor in these two regions with the El Nio Index.