A radar characterization of the tradewind boundary layer

The Rain In Cumulus over the Ocean (RICO) experiment occurred during winter 2004/2005 with operations based on the islands of Antigua and Barbuda. The over-riding purpose of RICO was to determine the mechanisms which contribute to the initiation and the longevity of the trade wind fair weather cumuli. In an effort to characterize the environment, soundings were launched on average four times per day. In addition to these soundings, two sets of six dropsondes were also released from the NCAR C-130 during most research flights. They were deployed from roughly 5000 m height as the plane traversed circles which were around 60 km in diameter. What these dropsonde sets revealed was the expected low variability in the temperature profile, but surprisingly high variability in the relative humidity profile. Horizontally measured standard deviations of relative humidity on the order of 10% or more were typical across a single set of dropsondes. Given the great variability in the moisture profile, it is difficult to determine the appropriate environmental context for the tradewind clouds studied from soundings alone. In fact, attempting to do so may hinder the investigation into their initiation and longevity - especially since the high degree of moisture variability may be the key to both.

In an effort to spatially and temporally augment the sounding characterization of the environmental moisture profile, use can be made of SPOLk-a radar data. Methodologies were developed to use Fourier analysis to characterize the roll structure which dominates the lowest kilometer of the atmosphere and wavelet analysis to characterize the layered humidity structure of the atmosphere extending from cloud base to the top of the boundary layer. In addition, the extreme versatility of both these techniques in conjunction with the large radar data set allow for environmental comparisons of the atmosphere both ahead of and behind any cloud fields passing through a subset of the radar domain. Results from these analyses will be presented.