Is the Tropical Atmosphere Conditionally Unstable?

We examine the mean and standard deviation of the bouyancy of lifted boundary layer parcels from a large sample of soundings from the western equatorial Pacific. The inclusion of condensate loading in the definition of buoyancy is emphasized as is the precise originating level of parcels in the subcloud layer. We confirm the observation of Betts that those parts of the tropical atmosphere experiencing deep convection are nearly neutral to adiabatic parcel ascent from the subcloud layer when adiabatic condensate loading is included in the definition of buoyancy. Parcels lifted from the top of the subcloud layer are more nearly neutral than those originating near the surface, and atmospheres with higher levels of free convection (LFCs) are closer to neutral than those with low LFCs. We explore possible reasons for these observations and discuss their implications for tropical meteorology.