Doppler radar and profiler observations of boundary evolution and collision

The kinematic and thermodynamic characteristics of outflow boundaries, their interactions with one another, and the head-to-head collision of two mature gust fronts are investigated using Doppler radar data and data from the multi-sensor Mobile Integrated Profiling System (MIPS) on 16 June, 2003 during the BAMEX field campaign. The pre-collision boundary layer contained horizontal convective rolls (HCRs) aligned parallel to the approaching outflow boundaries. Environmental conditions and the kinematic structures of boundaries are inferred by a mobile sounding unit (MGLASS), the Sioux Falls (SD) WSR-88D radar, and the MIPS 915 MHz profiler and Doppler sodar. Surface observations and the 12-channel microwave radiometer are used to investigate thermodynamic structures of boundaries. A radar fineline analysis suggests that convective initiation or storm intensification occurred in only several locations along the rather extensive collision line.

The post collision boundaries assumed bore-like characteristics that persisted for more than 2 hours. Detailed MIPS profiler observations and two-dimensional wind field analyses performed on the WSR-88D data suggest that the interacting outflow boundaries are dynamically similar to laboratory simulated density currents. The aftermath of the collision boundary and its interaction with a new gust front were observed by the MIPS instruments. An oscillatory behavior in Signal-to-Noise-Ratio (SNR) and mean vertical velocities in the elevated boundary were measured. The MIPS 915 MHz profiler measured 2 m/s updrafts and 4-6 m/s downdrafts with 180 degree phase difference as a gust front and elevated gust front (post-collision boundary) passed over. During the gust frontal passage, maximum convergence and divergence over the 1.5 km depth was found to be , respectively. The height of the gust front acquired by profiler is also confirmed by aerosol enhancement observed by ceilometer.