The art of cloud parameterization in GCMs has evolved steadily in complexity from prescribed cloud properties, to diagnostic schemes, to prognosed schemes (see reviews by Randall and Fowler et al. Therefore, parameterization of stratiform clouds is an important aspect of General Circulation Models (GCMs). The atmospheric LW warming, together with vertical gradients in its heating profile, play an important role in tropical large-scale circulations such as the Hadley circulation, the Walker circulation and the tropical intraseasonal oscillation. The surface SW cooling is important for regulating the tropical sea surface temperature. Although the SW CRF and LW CRF nearly cancel, SW cooling acts mainly at the surface while LW warming acts mainly on the atmosphere.
Climate change modeling studies also show that, in different models, changes in stratiform cloud properties lead to different changes in LW CRF and SW CRF, because of their associated cloud fraction feedback and cloud optical depth feedback (e.g., Charlock Somerville and Remer see review by Del Genio and Wolf ). The upper tropospheric stratiform clouds (anvil and cirrus clouds) associated with tropical deep convection are important to the earth's radiation budgets because of their large longwave (LW) and shortwave (SW) cloud radiative forcing (CRF Interestingly, the seasonal-mean LW CRF and SW CRF nearly cancel each other in current climate, but this delicate balance between two big terms is sensitive to the stratiform cloud properties, and breaking of the balance is observed when stratiform cloud properties change, for example, during a strong El Niño event, and in the tropical intraseasonal oscillation. Cloud radiation feedback is well recognized as a key uncertainty in predicting any potential future climate change. Current climate models lack these effects. Such cloud also reflects shortwave radiation, reducing surface downward flux (energy input to the ocean) by 10s of Wm −2. In typical convecting conditions, shear-induced additional cloudiness can reduce outgoing longwave radiation (OLR) by 10s of Wm −2, implying longwave radiative changes on the order of 10% of the total latent heating. Wind shear affects cloud-radiative fluxes, through both the cloud fraction and optical thickness, in a strong and systematic way. This study further examines wind shear effects on cloud properties (including cloud fraction and cloud optical depth) and associated top of atmosphere (TOA) and surface radiative fluxes, using observations from the Tropical Ocean Global Atmosphere program's Coupled Ocean Atmosphere Response Experiment (TOGA COARE) experiment and long-term satellite measurements. Several recent observational studies indicate that vertical wind shear is an important factor affecting stratiform cloud fraction and cloud overlap. Upper tropospheric stratiform clouds associated with deep convection are important to global radiation budgets and to cloud-radiation feedbacks on climate variability and change.
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