1. Hurricane Frances (2004) Hurricane Rita (2005) Hurricane Ike (2008) Supported by National Science Foundation grants 0734001, 0910737, 0328421, 0329522, and the National Geographic Society FINE-SCALE RADAR OBSERVATIONS OF BOUNDARY LAYER STRUCTURES IN LANDFALLING HURRICANES Karen Kosiba, Joshua Wurman, Paul C. Robinson Center for Severe Weather Research Forrest Masters University of Florida 5 km Above, left: Deployment of DOW 6 (green star), two mobile mesonets (pink squares) and ten PODs (aqua circles) during the landfall of Hurricane Ike. Arrow denotes path of center of eye. Above, right: Positions of DOW6 and PODs relative to the observed propagation of two distinct mesovortices occurring 06:02:37-06:18:02Z (brown circles, north of DOW 6) and 06:35:29-07:06:22Z (red circles) embedded within the eyewall of Hurricane Ike. 5 km 10 km Above: Radar reflectivity (left) and DOW-measured Doppler velocity (right) from within the eye of Hurricane Ike. Red circles denote mesovortices. Left: (a) Doppler velocities at a 1.2-degree elevation angle and (b) the corresponding velocities when reduced to 10m AGL using open exposure and corrected for observation angle. Reduced winds can be used to create 2D wind maps based on land usage and compared to surface observations. Left: Intercomparison between DOW and 10 m tower winds. DOW winds are corrected for observation angle, exposure of towers (which varies depending on wind direction), and altitude of radar observations. Comparison with T0 tower (on map above) shown. 2D wind mapping using DOW data and surface roughness Analysis of eyewall mesovortices and surface windfield Dual-Doppler Analysis Hurricanes Intercepted by DOW Radars 1996-2008 DOW Radar in Galveston, Texas. Hurricane Ike (2008) Above: Doppler velocities observed by DOW3 in hurricane Rita as a function of time. Boundary layer streaks increase in intensity as the eyewall approaches land. Above: FFT wavelength analysis illustrating dominant wavelengths of ~525 m, ~800 m and ~1200 m. ~525 m ~800 m ~1200 m a b Right: (a) Surface roughness values based on land usage for Port Arthur, TX and (b) the corresponding 3-hour maximum wind speed at 10 m AGL based on the DOW wind measurements. a b Winds lower in built up residential area Winds higher in open area Positions of DOW2, DOW3, and the dual-Doppler domain. Fort Pierc e, Flori da Hutchins on Island Texas City Galveston Supported by National Science Foundation grants 0734001, 0910737, 0328421, 0329522, and the National Geographic Society FINE-SCALE RADAR OBSERVATIONS OF BOUNDARY LAYER STRUCTURES IN LANDFALLING HURRICANES Karen Kosiba, Joshua Wurman, Paul Robinson Center for Severe Weather Research Forrest Masters University of Florida Above: FFT analyses, windward of the barrier island, from 2300-0200 UTC on the 12.5 km x 12.5 km domain. At each time, two scales of features are always present: 0.8 and 1.1-1.3 km. Additionally, at 00 UTC, a 0.6 km scale is present and at 02 UTC, there appear to be small-scale 2km) are more evident at earlier times. Above: Dual-Doppler analysis of Ivan at 160 m AGL The black line denotes the location of the FFT analyses and vertical cross-sections presented below. During this time period, coherent structures were mostly larger than those present in Frances. Above: FFT analyses indicating the presence of features with dominant spatial scales of 1400 m and 700-800 m. Left: Vertical cross- sections. The vertical depth of the boundary layer features is ~0.5km Correlation of structural damage with individual wind streaks Hurricane Gustav (2008) Above: DOW scans every 8 s through an individual wind gust as it destroys a building. Data indicate leading edge of the most intense portion of the wind-streak/gust impacts DOW and building at 1454:13 UTC. Above: Deployment locations of DOW6 and five PODs (aqua circles) relative to path of Gustav’s eye. 10 km Some Pods Co-located with FCMP towers 5 km Above: DOW, Tower, and Pod positions ~ 9 s 1 km 14:53:49 14:53:57 14:54:04 14:54:2014:54:1914:54:1814:54:1714:54:1314:48:53 Left: Video captures of roof collapse ~5 m from DOW. Collapse begins at about 1454:13 UTC Hurricane Ivan (2004) Above: Vertical cross-sections at the locations of the FFT analyses (black lines in top left figure). Vectors indicate the vertical motion and the color contours indicate the magnitude of the perturbation winds. Dual Doppler analysis of Hurricane Frances at 100 m AGL on a 12.5 x 12.5 km domain using 40 m horizontal grid spacing (Above). A smaller (5.5 km x 5.5 km), finer-scale (horizontal grid spacing of 20 m) was used to investigate the boundary layer structure leeward of the barrier island (Below). Horizontal perturbation winds are depicted with vectors and colored contours (yellow/red outbound, green/blue inbound). The thin, black lines denotes the boundaries of the barrier island. Wavelengths of the perturbation winds are smaller leeward of the barrier island than windward of the barrier island. Above: Mean winds as a function of height. During this 1-hour time period, the BL height was approximately 1.4 km AGL. Peak tangential velocities occurred ~ 1.2 km AGL. Right: Examples of perturbation winds in six different hurricanes. The perturbations are weaker in Ivan, Isabel and Ike than in Frances, Georges and Gustav at the times shown. Characteristics of Hurricane Boundary Layers across several DOW-intercepted landfalls Right: Mean radial (solid) and tangential (dashed) wind profiles as a function of height. Height profiles of the mean radial winds in Frances indicate that data were within the boundary layer. Tangential winds peaked around 4-500 m AGL for all times, before slowly decreasing. Above: Wind trace at East Galveston seawall Above: FFT analyses, leeward of the barrier island, from 2300-0200 UTC on the 5.5 km x 5.5 km domain. At each time, two scales of features are always present: 0.75 and 0.5 km. Additionally, at 23 and 02 UTC, a feature of wavelength < 0.4 km scale is present. FFT cross-section