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

D. Hatzidimitriou (1, 2) , I. Vardavas (1, 2) , K. G. Pavlakis (2) , N. Hatzianastassiou (2, 3) , C. Matsoukas (2) , E. Drakakis (2, 4)

1 Department of Physics [Heraklion]
2 Foundation for Research and Technology-Hellas
3 Department of Physics
4 Department of Electrical Engineering

In the present paper, we have calculated the outgoing longwave radiation at the top of the atmosphere (OLR at TOA) using a deterministic radiation transfer model, cloud data from ISCCP-D, and atmospheric temperature and humidity data from NCEP/NCAR reanalysis, for the seventeen-year period 1984-2000. We constructed anomaly time-series of the OLR at TOA, as well as of all of the key input climatological data, averaged in the tropical region between 20°N and 20°S. We compared the anomaly time-series of the model calculated OLR at TOA with that obtained from the ERBE S-10N (WFOV NF edition 2) non-scanner measurements. The model results display very similar seasonal and inter-annual variability as the ERBS data, and indicate a decadal increase of OLR at TOA of 1.9±0.2Wm^-2/decade, which is lower than that displayed by the ERBS time-series (3.5±0.3Wm^-2). Analysis of the inter-annual and long-term variability of the various parameters determining the OLR at TOA, showed that the most important contribution to the observed trend comes from a decrease in high-level cloud cover over the period 1984-2000, followed by an apparent drying of the upper troposphere and a decrease in low-level cloudiness. Opposite but small trends are introduced by a decrease in low-level cloud top pressure, an apparent cooling of the lower stratosphere (at the 50mbar level) and a small decadal increase in mid-level cloud cover.

Domaines: Océan, Atmosphère

D. Hatzidimitriou, I. Vardavas, K. G. Pavlakis, N. Hatzianastassiou, C. Matsoukas, et al.. On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984-2000. Atmospheric Chemistry and Physics, 2004, 4 (5), pp.1419-1425. ⟨hal-00295491⟩