Evolution and dynamics of a late-stage squall line that occurred on 20 February 1993 during TOGA COARE

Airborne Doppler and flight-level data are used to document the structure a nd evolution of portions of a late-stage horseshoe-shaped squall line syste m and its effect on vertical momentum and mass transports. This system, whi ch occurred on 20 February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment, was similar to many previous ly studied, but had some unique features. First, a slow-moving transverse b and, which formed the southern leg of the horseshoe, drew most of its low-l evel updraft air from the squall-line stratiform region on its north side r ather than the "environment" to the south. Second, a long-lived cell with m any properties similar to a midlatitude supercell, formed 150 km to the rea r of the squall line. This cell was tracked for 4 h, as it propagated into and then through the cold pool, and finally dissipated as it encountered th e convection forming the northern edge of the horseshoe. Finally, as the sq uall line was dissipating, a new convective band formed well to its rear. The transverse band and the long-lived cell are discussed in this paper. Qu adruple-Doppler radar data, made possible by tightly coordinated flights by the two NOAA P3s, are used to document the flow with unprecedented accurac y. At lower levels, the transverse band flow structure is that of a two-dim ensional convective band feeding on its north side, with vertical fluxes of mass and horizontal momentum a good match to the predictions of the Moncri eff archetype model. At upper levels, the transverse band flow is strongly influenced by the squall line, whose westward-tilting updraft leads-to much larger Vertical velocities than predicted by the model. The long-lived cel l, though weak, has supercell-like properties in addition to its longevity, including an updraft rotating in the sense expected from the environmental hodograph and an origin in an environment whose Richardson number falls wi thin the Weisman-Klemp "supercell" regime.