Wednesday, 12 February 2003: 5:00 PM
Evaluation of climate model simulations of HIRS water-vapor channel radiances
Simulations of the HIRS 6.7 µm (water vapor) radiances, computed within the Hadley Centre atmospheric climate model (HadAM3) are compared with the observations over the period 1979-1998. The model is forced with observed sea surface temperature and sea-ice fields. HadAM3 overestimates the HIRS 6.7 µm brightness temperature (T6.7) over regions of strong descending motion, particularly over the southern hemisphere. Some of the discrepancy between model and observed T6.7 are related to the clear-sky sampling differences between the model diagnostic and the measured quantity. The interannual variation of T6.7 over tropical oceans is of similar magnitude in the model and observations suggesting small changes in upper tropospheric humidity over the period. Peaks in T6.7 during 1983 and 1998 coincide with strong El Niń o events. The effect on the simulations of prescribing volcanic, solar and greenhouse gas forcing and observed ozone variations is assessed.