Research / Research Highlights

What controls variations in atmospheric humidity, CAPE, and precipitation?

Submitter

Romps, David — Lawrence Berkeley National Laboratory

Area of Research

Atmospheric Thermodynamics and Vertical Structures

Journal Reference

Romps D 2020. "Ascending columns,WTG, and convective aggregation." Journal of the Atmospheric Sciences, 78(2), 10.1175/JAS-D-20-0041.1.

Science

Analytic solutions are derived for the relative humidity, lapse rate, and precipitation rate of an atmospheric column with mean ascent. By comparison with ARM data, it is shown that these solutions cannot be used to explain variations of humidity, CAPE, and precipitation as has been argued in the literature, but they can be used to understand the mean tropical lapse rate and some of the basic properties of a convectively aggregated atmosphere (e.g., its higher relative humidity in the convecting patches, lower relative humidity overall, and smaller lapse rate).

Impact

Much of the earlier theoretical work on the tropical atmosphere has used radiative-convective equilibrium (RCE) as a toy model. These new solutions get closer to an appropriate framework by modeling the intensely convecting regions (like the ITCZ) that actually control the tropical atmosphere's thermal structure.

Summary

It has been argued that a certain connection between humidity and the lapse rate (moderated by convection's sensitivity to humidity via entrainment) can explain the co-variability of relative humidity, CAPE, and precipitation in the tropics. With the solutions derived here, it is shown that such an interpretation is strongly contradicted by the tropics' observed weak temperature gradient (WTG).