QUASI-LAGRANGIAN MEASUREMENTS IN CONVECTIVE BOUNDARY-LAYER PLUMES ANDTHEIR IMPLICATIONS FOR THE CALCULATION OF CAPE

Measurements were made to determine the level of origin of air parcels participating in natural convection. Lagrangian measurements of conse rvative variables are ideal for this purpose. A simple remotely pilote d vehicle was developed to make in situ measurements of pressure, temp erature, and humidity in the convective boundary layer. These quasi-la grangian measurements clearly show that convective plumes originate in the superadiabatic surface layer. The observed boundary layer plumes have virtual temperature excesses of about 0.4 K in a tropical region (Orlando, Florida) and of about 1.5 K in a desert region (Albuquerque, New Mexico). The water vapor contribution to parcel buoyancy was appr eciable in Orlando but in Albuquerque was insignificant. These observa tions indicate that convective available potential energy should be de termined by adiabatically lifting air parcels from the surface layer, at screen level.