On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984-2000 D. Hatzidimitriou1,2, I. Vardavas1,2, K. G. Pavlakis2, N. Hatzianastassiou2,3, C. Matsoukas2, and E. Drakakis2,4 1Department of Physics, University of Crete, Heraklion, Crete, Greece 2Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece 3Department of Physics, University of Ioannina, Greece 4Department of Electrical Engineering, Technological Educational Institute of Crete, Greece
Abstract. 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.
Citation: Hatzidimitriou, D., Vardavas, I., Pavlakis, K. G., Hatzianastassiou, N., Matsoukas, C., and Drakakis, E.: On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984-2000, Atmos. Chem. Phys., 4, 1419-1425, doi:10.5194/acp-4-1419-2004, 2004.