~525 m

~800 m

~1200 m

C enter for S evere W eather R esearch

DOW Radar in Galveston, Texas. Hurricane Ike (2008)

Correlation of structural damage with individual wind streaksHurricane Gustav (2008)

Dual-Doppler analysis

Hurricanes Intercepted by DOW Radars 1996-2008

Hurricane Ike (2008)

FINE-SCALE RADAR OBSERVATIONS

OF BOUNDARY LAYER STRUCTURES

IN LANDFALLING HURRICANES

Karen Kosiba, Joshua Wurman, Paul C. RobinsonCenter for Severe Weather Research

Forrest MastersUniversity of Florida

FRANCES

1454:201454:191454:181454:171454:131448:53

Individual Wind Streak Damages Building (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 (black circle and arrow.).

10 km

Some Pods Co-located with FCMP towers

5 km

~ 9 s1 km

1453:49 1453:57 1454:04

Above: Screen captures of video taken of roof collapse ~5 m from DOW. Collapse begins at about 1454:13 UTC

Radar reflectivity (left) and DOW-measured Doppler velocity (right) from within the eye of Hurricane Ike. Red circles denote mesovortices.

Above, left: Deployment of DOW6 (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

Texas City

Galveston

Above: Wind trace at East Galveston seawall.

Above: DOW, Tower, and Pod positions

Analysis of Eyewall Mesovortices and Surface WindfieldCharacteristics of Hurricane Boundary Layers (HBLs) across several DOW-intercepted landfalls

Above: 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.

Above: Vertical cross-sections. The vertical depth of the boundary layer features is ~0.5km

Left: 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.

Left: 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.

Evolution of Boundary Layer Streak Wavelengths (Above.) FFT analyses at 0049 and 0149, indicating features with dominant spatial scales of 1400 m and 700-800 m..

Hurricane Ivan (2004)Hurricane Frances (2004) Dual-Doppler Analysis

Barrier Island Affects Boundary Layer Streak Wavelengths: FFT analyses from 2300-0200 (Above.) At each time two scales of features are always present: 0.8 and 1.1-1.3 km. Additionally, at 00, a 0.6 km scale is present and at 02, there appear to be small-scale < 0.6 km features, which potentially have been smoothed out or are unresolved by the current wind synthesis. Larger wavelength features (> 2km) are more evident at earlier times.Below: 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.

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.

Above: 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.

Hurricane Rita (2005)

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DOW Radar Winds Are Corrected for Surface Roughness (Left):(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.

2D wind mapping using DOW data and surface roughness

Winds and Streak Intensity Increases at Landfall (Right): Doppler velocities observed by DOW3 in hurricane Rita as a function of time. Boundary layer streaks increase in intensity as the eyewall approaches land.

1 km

a

b

Winds lower in built up residential area

Winds higher in open area

Left: FFT wavelength analysis illustrating dominant wavelengths of ~525 m, ~800 m and ~1200 m.

Left: (a) Doppler velocities at a 1.2 degrees elevation angle and (b) the corresponding velocities when reduced to 10m AGL using open exposure and corrected for observation angle. Reduced winds can used to create 2D wind maps based on land usage and compared to surface observations.

DOW Winds Corrected to 10 m AGLAbove: 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, left) shown.

Supported by National Science

Foundation grants 0734001, 0910737, 0328421, 0329522,

and the National Geographic

Society

Barrier Island Affects Boundary Layer Structure: 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 denote the boundaries of the barrier island. Wavelengths of the perturbation winds are smaller leeward of the barrier island than windward of the barrier island.

Radar-based Maximum Hurricane Winds Over Built-up and Open Areas