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- Author or Editor: David L. Randel x
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Abstract
Detailed comparisons are made between the climate simulated by a seasonal version of the NCAR Community Climate Mode) (CCM1) at 12 level, R15 spectral resolution, and that revealed by ECMWF operational analyses over 1980–86 truncated to a similar resolution. A variety of circulation statistics are presented to reveal the spatial character and seasonality of CCM1 biases in temperatures, winds, and wave flux quantities. CCM1 biases are typical of current climate models run at similar resolution. Interrelationships between the above biases are a focus of this study, in particular using wave-mean flow interaction diagnostics.
CCM1 exhibits a westerly zonal wind bias in the tropics and a lack of westerlies in the high latitude Southern Hemisphere (SH). The tropical zonal mean meridional circulation (Hadley cell) in the model is approximately a factor of two too weak. The poleward eddy heat flux is accurately simulated, but the poleward eddy momentum flux is severely underestimated, particularly in the SH. There is a resulting excessive large-scale wave drag in the model extratropical upper troposphere, in qualitative agreement with the weak model high latitude westerlies (and temperature bias patterns). Conversely, the model tropical zonal wind bias does not appear to be related to influences by large-scale waves. Wave flux biases are compared for stationary and transient statistics; model stationary waves are in good agreement with observations, while the largest relative momentum flux error is found for higher frequency transient waves.
Abstract
Detailed comparisons are made between the climate simulated by a seasonal version of the NCAR Community Climate Mode) (CCM1) at 12 level, R15 spectral resolution, and that revealed by ECMWF operational analyses over 1980–86 truncated to a similar resolution. A variety of circulation statistics are presented to reveal the spatial character and seasonality of CCM1 biases in temperatures, winds, and wave flux quantities. CCM1 biases are typical of current climate models run at similar resolution. Interrelationships between the above biases are a focus of this study, in particular using wave-mean flow interaction diagnostics.
CCM1 exhibits a westerly zonal wind bias in the tropics and a lack of westerlies in the high latitude Southern Hemisphere (SH). The tropical zonal mean meridional circulation (Hadley cell) in the model is approximately a factor of two too weak. The poleward eddy heat flux is accurately simulated, but the poleward eddy momentum flux is severely underestimated, particularly in the SH. There is a resulting excessive large-scale wave drag in the model extratropical upper troposphere, in qualitative agreement with the weak model high latitude westerlies (and temperature bias patterns). Conversely, the model tropical zonal wind bias does not appear to be related to influences by large-scale waves. Wave flux biases are compared for stationary and transient statistics; model stationary waves are in good agreement with observations, while the largest relative momentum flux error is found for higher frequency transient waves.
Abstract
The interannual variability of the top of the atmosphere net radiation budget as measured from the Nimbus- 7 Earth Radiation Budget instruments was calculated for an eight yew period 1979–1986. The largest fluctuations are shown to occur in three tropical areas. the Atlantic off the west emit of Africa, the eastern Pacific near South America, and the western Pacific northeast of Indonesia. The variability in the Atlantic was 20% greater than in the eastern Pacific and 35% greater than in the Indonesian area. The maximum anomalies in these two Pacific regions occurred during the El Niño year 1982–1983, while the maximum Atlantic anomalies. south of the Gulf of Guinea, were during 1984. An independent dataset of derived cloud type and amount from the Temperature Humidity Infrared Radiometer (THIR) and the Total Ozone Mapping Spectrometer (TOMS) instruments shows interannual changes in multilevel convective cloud systems have a minimal effect of the net balance. However changes in middle and low clouds drastically effect the balance, and are the most likely cause of the maximum radiation balance variability in the Gulf of Guinea region. This observed interannual variation of the top of the atmosphere net balance, reported in the present study, denotes the most variable “cloud radiative forcing” situation observed to date.
Abstract
The interannual variability of the top of the atmosphere net radiation budget as measured from the Nimbus- 7 Earth Radiation Budget instruments was calculated for an eight yew period 1979–1986. The largest fluctuations are shown to occur in three tropical areas. the Atlantic off the west emit of Africa, the eastern Pacific near South America, and the western Pacific northeast of Indonesia. The variability in the Atlantic was 20% greater than in the eastern Pacific and 35% greater than in the Indonesian area. The maximum anomalies in these two Pacific regions occurred during the El Niño year 1982–1983, while the maximum Atlantic anomalies. south of the Gulf of Guinea, were during 1984. An independent dataset of derived cloud type and amount from the Temperature Humidity Infrared Radiometer (THIR) and the Total Ozone Mapping Spectrometer (TOMS) instruments shows interannual changes in multilevel convective cloud systems have a minimal effect of the net balance. However changes in middle and low clouds drastically effect the balance, and are the most likely cause of the maximum radiation balance variability in the Gulf of Guinea region. This observed interannual variation of the top of the atmosphere net balance, reported in the present study, denotes the most variable “cloud radiative forcing” situation observed to date.
