Written by Kristine Flacké Haualand from the Bjerknes Centre and the Geophysical Institute at the University of Bergen.
Midlatitude cyclones are often associated with moist processes related to clouds, ocean, and rain.
In cyclones, there is a lot of moist air that ascends and condenses into clouds. When clouds form, latent heat is released, which fuels midlatitude cyclones and enhances their development.
The reason is related to the latent cooling that occurs when rain evaporates on its way down to the surface. While air at lower levels cools, it gets heavier, causing a weakening of cyclone ascent.
The weakened ascent is associated with less cloud condensation, and therefore also less enhancement and cyclone growth. Evaporation of rain is therefore indirectly weakening cyclone growth through its modification of cloud condensation.
Haualand, K.F. and Spengler, T. (2019): How does latent cooling affect baroclinic development in an idealized framework? Journal of Atmospheric Sciences, https://doi.org/10.1175/JAS-D-18-0372.1