2000: On calculating vertical motions in isentropic coordinates

Output from a mesoscale numerical model is used to calculate all three terms of the W equation in isentropic space. Previously, it was thought that, in the presence of diabatic heating, the local pressure tendency term and the diabatic heating term would generally offset one another; that being the case, the transport term was expected to give an accurate representation of the vertical motion field. Calculations of all three terms of the isentropic W equation for four case studies demonstrate that the local pressure tendency and diabatic heating terms do not always offset, and that the transport term alone, while typically of the correct sign; may underestimate the total We by two-thirds. This study employed model output from simulations of four meso-a to synoptic-scale precipitation systems: two associated with strong extratropical cyclogenesis, and two forced primarily by jet streak dynamics. A representative isentropic surface was chosen, upon which each term of the we equation was calculated. 1