Momentum Budgets of a Subtropical Squall Line Determined from Dual-Doppler Data

Abstract

A thermodynamic retrieval method was employed to investigate some stwctural atures of a subtropical squall line during IOP-2.. Dual-Doppler data, centered at 0040, 0043, 0046, 0049, and 0052 LST 17 May 1987, were objectively analyzed in the horizontal domain of 45 k by 25 km using 1 km grid spacing. There were 10 analysis levels in the vertical ranging om 0.3 to 8.8 km. Vertical velocities were com­ puted from the anelastic continuity equation by integrating downward with variational adjustment. Fields of deviation perturbation pressure and temperature were retrieved om the Doppler derived winds us­ ing the three momentum equations; These elds were subjected to · internal consistency checks to determine the level of con dence be re interpretation.
Results show that the vertical transport of horizontal momentum normal to the line is downward corresponding to the west-tilted con­ vective updrafts, while the line-parallel component results in an up­ ward momentum transport. Momentum b u dget calculations show that the horizontal and vertical ux convergences/divergences of horizontal momentum by the mean and eddy motions contribtite largely to the growth/decay of mean horizontal mornentum. These ndings are in qualitative agreement with those of tropical squall lines during COPT 8L The dynamic interaction between t.he mesoscale convective system and its environment can be studied using the momentum budget equa­ tions and vertical uxes of horizontal momentum estimated from the Doppler derived winds.

Read 822 times