Effect of Cloud-Precipitation-Ocean Mixed Layer Feedback on Drag Coefficient
Abstract
From similarity theory, the drag and thermal exchange coefficients (C(D), C(H), and C(E)) for 10m above the ocean surface depend on the atmospheric stability parameter (z/L(alpha)) where L(alpha) the Obukhov length scale for the atmospheric surface layer. Cloud, precipitation, and ocean mixed layer (OML) thermodynamical feedback affects the atmospheric stability parameter in two ways. Clouds reduce the incoming solar radiation at the ocean surface by scattering and absorption, which cools (relatively) the ocean mixed layer. The OML cooling lowers the sensible and latent heat fluxes from the ocean surface, which increases the atmospheric stability parameter. On the other hand, precipitation from the clouds dilutes the surface salinity, stabilizing the upper ocean, and reducing OML deepening. The ocean mixed layer may be caused to shallow if the downward surface buoyance flux is sufficiently enhanced by the precipitation. When the ocean surface receives a downward net surface heat flux, the reduction in the OML depth will increase the sea surface temperature (SST) by concentrating the net radiation plus heat fluxed downward across the sea surface into a thinner layer. The increase of SST augments the sensible and latent heat fluxes from the ocean surface, which decreases the atmospheric stability parameter. On the other hand, when the ocean surface has a net surface heat loss, the reduction in the OML depth will decrease SST due to the decrease of the thermal inertia. The decrease of SST reduces the sensible and latent heat fluxes from the ocean surface, which increases the atmospheric stability parameter. The variation of atmospheric stability parameter in turn changes the drag and thermal exchange coefficients. In this study, a simple coupled cloud-precipitation- ocean mixed layer model proposed by Chu et. al. (1990) and Chu and Garwood (1991) is used to compute the time rate change of drag and thermal exchange coefficients caused by this mechanism.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1992
- Accession Number
- ADA530531
Entities
People
- Peter Cheng Chu
- Roland W. Garwood Jr.
Organizations
- Naval Postgraduate School