Profiler and Scanning Radar Observations of a Tropical Ocean Squall

A wind profiler, a vertically pointing S-Band radar, and a C-Band scanning radar were deployed on the JAMSTEC research vessel, the Mirai, near the equatorial Pacific island of Nauru for the Nauru99 campaign. This large campaign, sponsored by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program made intensive observations of the atmosphere and ocean in this area using a variety of instruments from ships and other platforms. The wind profiler used was MAPR (Multiple Antenna Profiler Radar) an advanced UHF profiler that uses spaced antenna techniques to make wind measurements on time scales of a minute or less, much faster than conventional DBS (Doppler Beam Swinging) profilers. This system also supplies continuous measurements in the vertical, which allows uninterrupted observations of vertical motion within and in the vicinity of convection.

Conditions were generally suppressed for the campaign (carried out in June of 1999) with only occasional convective activity observed. This paper will present an interesting example where mesoscale lifting was observed ahead of a squall line. The lifting took place ahead of the surface gust front and serves to create more favorable conditions for the continued propagation of the squall line. The lifting is consistent with recent theoretical work on gravity wave response to convective heating and cooling.

The rapid wind measurement capability of MAPR also allowed it to observe gusts in excess of 50 knots in the upper part of the system. Comparing the observations of MAPR and S-Band system (which was supplied by NOAA/ETL) allows characteristics of the rain to be determined and these are compared to the scanning radar observations and measurements of a disdrometer at the surface.