Influence of surface characteristics on the development of cumulus cloud fields

There is growing evidence that changes in land surface characteristics and heterogeneity affect mesoscale circulations, resulting in changes of surface temperature, soil moisture and precipitation. Landuse change has a strong effect upon boundary layer convection, which alters the nature of cumulus cloud fields through modulation of the surface energy budget. The presence of vegetation alters the surface radiation budget and the moisture and heat fluxes, and it also affects surface roughness.

This study investigates the effect of vegetation on cumulus cloud fields. Formation and growth of cumulus cloud fields are simulated using Colorado State University Regional Atmospheric Modeling System (CSU RAMS) for variety of atmospheric and surface conditions. A large banana plantation in Costa Rica which is surrounded by forests is used as a specific study area. Satellite data shows this deforested area having far less cumulus cloud activity than neighboring forested regions. Also changes in cloud cover, cloud base and top height are found as clouds advect from forested into deforested areas. There is a transition zone over which cloud field properties change when they are advected over sharp forest/agricultural boundaries. Sensitivity studies show that the presence of forest causes the earlier onset of convection, and vigor of convection is higher over forested areas compared to deforested areas. For extreme cases, the RAMS simulations show differences of up to 800m in cloud thickness, 1.5gm/kg in liquid water content and 2kg/m2 in liquid water path when surface is changed from evergreen forest to grassland.