Near-Ground Boundary Layer Observations from Hurricanes Frances and Ivan (2004)

Abstract eng:
Two meteorologically-instrumented towers were placed in the paths of Hurricanes Frances and Ivan (2004) by a faculty member and a group of undergraduate students as part of a pilot project at the University of Louisiana at Monroe (ULM). The students who participated were able to gain valuable hands-on research experience. The towers are both 2 m in height, and are compact enough to be transferred to the coastline in an automobile. Each tower is equipped with meteorological instrumentation and a datalogger. In a cooperative effort with other universities such as Texas Tech University (TTU) and Jackson State University, sites were selected with the aim of studying the coastal wind transition zone that exists landward near the coastline within the onshore flow of landfalling tropical cyclones [1]. All tower locations were within or in the vicinity of the eyewall at landfall, and turbulence parameters (turbulence intensities, roughness lengths, and gust factors) were determined in post-storm analysis. Wind speed at 10 m AGL was estimated using roughness lengths in combination with Wieringa’s [2, 3] exposure adjustment technique. The estimates during Ivan reveal a threshold roughness where the adjustment technique breaks down. Roughness was also observed to decrease in both storms with progression closer to the center of circulation. It is hypothesized that the decrease occurs due to changes in atmospheric stability, rather than a true decrease in roughness. Some visual observations of the destruction associated with Hurricane Frances are also presented.

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