Response of a General Circulation Model to a Change in Cold Solar Forcing: Model Feedbacks and Comparison with Satellite Data
Abstract
The response of a general circulation model to a change in its treatment of cloud solar forcing is investigated. Radiation field data from the forecast model of the Navy Operational Global Atmospheric Prediction System for five Julys (1979-1983) are presented in an investigation of the effect of a change from grid cell averaged clouds to maximally overlapping clouds in the model's solar radiation scheme. The model results are compared with Nimbus 7 Earth Radiation Budget top of the atmosphere (TOA) solar and longwave irradiances and with derived surface irradiance data. Although the maximal overlap scheme performs considerably better than the grid cell averaging scheme (reducing maximum deficiencies in TOA and surface solar irradiance by over 100 W m-2), significant errors remain. The simulated correlation between TOA net solar and longwave irradiance improves at low latitudes in the northern hemisphere, with little change at higher latitudes. This improved correlation is consistent with the greater consistency between the treatments of solar and longwave cloud radiative forcing brought to the model by the new solar radiation scheme. The change in the radiation treatment is shown to have the greatest direct effect on solar radiation over convective regions, a consequence of the scarcity of optically thick clouds produced by the model's cloud parameterization in other regions. The model responds with an increase in convective activity over land and an increase in the flux of moisture from sea to land. Planetary cooling over the oceans increases because of a decrease in cloud cover.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 20, 1994
- Accession Number
- ADA286177
Entities
People
- Beth Chertock
- James A. Rideout
- Ronald Gelaro
Organizations
- United States Naval Research Laboratory