Climate & Radiation Branch Special Seminar: Joel Susskind

The time period September 2002 through February 2010, observed by both AIRS and CERES, is marked by substantial decreasing OLR trends on the order of -0.1 W/m2/yr averaged over the globe, and -0.2 W/m2/yr averaged over the tropics. There are very  large  spatial variations of these  trends however, with local values ranging from -2.6 W/m2/yr to +3.0 W/m2/yr in the tropics. The spatial patterns of OLR trends over this time period, as observed by CERES and computed using AIRS retrieved geophysical parameters, are in essentially perfect agreement with each other, as are the anomaly time series averaged over different spatial regions. This essentially perfect agreement of OLR anomalies and trends derived from observations by two different instruments, in totally independent and different manners, implies that both sets of results must be highly accurate. The agreement of anomalies and trends of OLR as observed by CERES and computed from AIRS derived products also indirectly validates the anomalies and trends of the AIRS derived surface and atmospheric products as well.                                
 
We use anomalies and trends of the AIRS Science Team Version 5 products over the 8-year time period September 2002 through August 2010 to explain the cause of the large negative trend of global OLR over this time period. The beginning of the time period under study, late 2002, corresponds to the end of a strong El Niño period. Tropical OLR began to decrease significantly at the onset of a strong La Niña in mid-2007. AIRS products show that cloudiness and mid-tropospheric water vapor began to increase in the tropics at roughly the same time, especially in the region 8°N through 20°S latitude extending eastward from 140°W through 40°E longitude, with a corresponding very large drop in OLR in this region, which we call Region 1. Late 2009 is characterized by a strong El-Niño, with a corresponding change in sign of observed tropical water vapor, cloud cover, and OLR anomalies. We show that OLR anomalies in Region 1 are highly correlated with the values of an El Nino index evaluated 4 months previously, as are anomalies of water vapor and cloud cover in this region. If one excludes the area of Region 1 from the statistics, area mean OLR trends over the rest of the tropics are essentially zero over the time period under study, and the negative OLR trend averaged over the rest of the globe is substantially reduced.
 
The seminar will be comprised of three parts: 1) a brief description of the characteristics of AIRS and the AIRS Science Team Version 5 retrieval algorithm; 2) an inter-comparison of anomalies and trends of CERES and AIRS OLR products: and 3) attribution of recent global and tropical anomalies and trends of OLR to the effects of El Niño/ La Niña oscillations over the 8 year time period September 2002 through August 2010.
 
Branch Seminar Series Coordinators:
Lazaros.Oraiopoulos@nasa.gov
Charles.K.Gatebe@nasa.gov