Effect of condensation latent heat release on the relative vorticity tendency in extratropical cyclones: a case study

Abstract

Taking an extratropical cyclone that produced extreme precipitation as the research object, this paper calculates the contribution of condensation latent heat release (LHR) to relative vorticity tendency based on the complete-form vertical vorticity tendency equation. The results show that the heating rate of convectional condensation LHR can reach up to about 40 times that of stable condensation LHR. Both the stable and convectional heating centers are higher than 700 hPa, which would cause ∂Q/∂z > 0 and a positive vorticity source in the lower troposphere. The vertical gradient of stable condensation LHR contributes little to the growth of relative vorticity, while the relative vorticity tendency associated with the vertical gradient of convectional condensation LHR can be an order of magnitude higher than the former. The positive vorticity source is always located right below the latent heating center, and its maximum value can always be found in the lower troposphere. Convectional LHR is the primary factor for cyclone development from the perspective of diabatic heating. The horizontal gradient of total condensation LHR can contribute about 65% of the actual vorticity growth, but the effect of the vertical gradient of convectional condensation (LHR) can reach twice as much. The adiabatic heating from LHR can cause vorticity tendency directly. However, it can also change the vertical and horizontal gradient of potential temperature, which can further induce vorticity tendency.