Airborne Doppler radar observations of the MAP SOP IOP14 (3 November 1999) convective storms over the Apennine mountains

One of the principal scientific objectives of "Wet MAP" was to investigate the mechanism of orographically generated heavy precipitation events with special emphasis on their dynamics, microphysics and hydrological consequences (especially flooding). Specifically, the SOP was to provide data sets to distinguish the relative roles of orographic, baroclinic, and convective dynamics in the airflow producing precipitation over complex terrain (mountains).

During IOP 14 of the MAP SOP, the NOAA P-3 and NCAR Electra aircraft conducted flight patterns in and around strong convective storms located over the Apennine terrain along the western coast of Italy. The airborne Doppler radar data from the NOAA P-3 has been processed to provide three-dimensional wind fields that illustrate the kinematic structure of the convection located over the seaward facing slopes of the Apennine mountains. The aircraft flew "box" patterns surrounding the storms as well as a 1000 ft altitude pass along the coast to sample the character of the inflowing air. These storms produced heavy rain and the mesoscale convective system that contained the individual storms was relatively stationary during the period of aircraft investigation. The Doppler radar data was synthesized to Cartesian grids using a digital topographic data base to assist in removing the deleterious effects of ground clutter.

The Doppler radar derived winds and reflectivity fields indicate a complex structure of airflow within the storms. Specifically, storms tended to generate over the coastal regions in response to a strong convergence region produced by shallow downslope winds (presumably) produced as part of the storm outflow with the prevailing onshore environmental winds. Storms thus generated along the coastal plain then detrained cloud material in the prevailing upper level flow, and help produce precipitation along the higher slopes through a “feeder-seeder” mechanism.

The presentation will illustrate this conceptual model of precipitation formation behavior through reflectivity and wind cross sections, and trajectory analyses based on the Doppler-derived three-dimensional wind fields.