The Role of Latent Heat Release in the Evolution of a Weak Extratropical Cyclone

Abstract

A study of the sensitivity of a weak winter extratropical cyclone to latent heat release (LHR) is presented using 48-h simulations of the cyclone's evolution derived from three versions of the LFM model: a MOIST simulation in which full model physics was employed, a DRY simulation in which all latent heating was removed, and a DOUBLE MOIST simulation in which the effect of latent heating on the temperature field was doubled. Results indicate that a deepening cyclone occurs in the DOUBLE MOIST simulation, a near steady-state cyclone in the MOIST simulation, and a filling cyclone in the DRY simulation. Thus, for this case the presence and intensity of LHR is of critical importance to this cyclone's intensification. In addition, using height tendency diagnoses, it is concluded that for this case in the lower troposphere the dominant LHR influence is direct, through the explicit diabatic heating forcing in the height tendency equation. In contrast, in the middle and upper troposphere this direct LHR role is no longer dominant, but rather shares its importance with the indirect effect, represented by the influence of LHR on the dynamical forcing mechanisms.