Mass and Energy Budgets of a 1 km High Atmospheric Box over the GATE C-Scale Triangle during Undisturbed and Disturbed Weather Conditions

Abstract

Using vertical wind, temperature and humidity profiles in the C-scale triangle during GATE from 2?5 September 1974, the budgets of mass, latent heat and dry and moist static energy are calculated in the lowest kilometer of the atmosphere. The computations are performed for intervals of 3?6 h. Using radar pictures the results are classified as ?undisturbed? or ?disturbed? with respect to the convective activity. The horizontal flow near the sea surface is nearly always convergent. During disturbed situations the low-level convergence (?10?4 s?1) is about one order of magnitude larger than during undisturbed conditions. When relating the convection (radar echo covergage) to the low-level convergence it is found that a certain background value of convergence must be exceeded before radar echoes (raining convection) develop and that the convection reacts with a delay of 3?4 h to variations of the low-level divergence. During disturbed situations the subgrid-scale flux of moist static energy at the sea surface is about 30% greater than during undisturbed conditions. The flux is constant with height in undisturbed conditions but increases with height in disturbed situations. At cloud base the subgrid-scale flux of moist static energy is about twice as large in disturbed conditions (180 W m?2) as in undisturbed conditions (100 W m?2).