On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984-2000

[摘要] In the present paper, we have calculated the outgoing longwave radiation atthe top of the atmosphere (OLR at TOA) using a deterministic radiationtransfer model, cloud data from ISCCP-D, and atmospheric temperature andhumidity data from NCEP/NCAR reanalysis, for the seventeen-year period1984-2000. We constructed anomaly time-series of the OLR at TOA, as well asof all of the key input climatological data, averaged in the tropical regionbetween 20°N and 20°S. We compared the anomaly time-series of themodel calculated OLR at TOA with that obtained from the ERBE S-10N (WFOV NFedition 2) non-scanner measurements. The model results display very similarseasonal and inter-annual variability as the ERBS data, and indicate adecadal increase of OLR at TOA of 1.9±0.2Wm^-2/decade, which islower than that displayed by the ERBS time-series (3.5±0.3Wm^-2).Analysis of the inter-annual and long-term variability of the variousparameters determining the OLR at TOA, showed that the most importantcontribution to the observed trend comes from a decrease in high-level cloudcover over the period 1984-2000, followed by an apparent drying of the uppertroposphere and a decrease in low-level cloudiness. Opposite but smalltrends are introduced by a decrease in low-level cloud top pressure, anapparent cooling of the lower stratosphere (at the 50mbar level) and a smalldecadal increase in mid-level cloud cover.

[学科分类] 大气科学