Aircraft Observations in Hurricanes: Instrumentation and Intensity Estimates

WP-3D Orion Instrumentation Aft Doppler radar WP-3D Orion Instrumentation Flight level instruments (gust probe) SFMR Flight level instruments Lower Fuselage radar

Instruments and Data Dual Doppler radars. Dual Doppler radar analysis. 3-D wind and reflectivity fields, so good for research. Limited range horizontally. Not resolve boundary layer well. Good view of inner core circulation and maximum winds sustained on vortex scale. Accurate.

Instruments and Data Lower fuselage radar. Large range. Reflectivity field. Good for navigation.

Instruments and Data Flight level data. High spatial resolution. Accurate, except for some wetting errors at times in eyewall. Temp, Dewpoint, Wind, Pressure (est). Stepped Frequency Microwave Radiometer (SFMR) data. High spatial resolution but often inaccurate. Attempt to measure 10-m winds.

Instruments and Data Dropsondes. High spatial resolution, but poor aerial coverage. Expensive. Very dependent upon placement, such as if stuck in an updraft or downdraft. Very interesting data, but difficult to piece together. Accurate. Temp, Dewpoint, Wind, Pressure.

Satellites DT estimates from IR (last presentation) Microwave estimates of rainfall and 10 m wind circulations (last presentation)

Saffir-Simpson Scale Now, only used to measure wind. Formerly used average wind-pressure relationship found for hurricanes in North Atlantic. Storms at higher latitudes and large storms typically display a lower wind speed than the central pressure would indicate from the following table.

Saffir-Simpson Scale

Intensity estimation Estimate maximum sustained surface wind speed (10 m above ground) for a wind anywhere in the vortex (typically represents a 1 or 2-min interval) Take highest estimates from each instrument: dropsondes, flight level data, SFMR, satellite Estimated to nearest 5 kt and rounded so last digit is a “0” or a “5” Remember, if coverage is fairly spotty (common), an addition of 3-5 kt for the aircraft estimates may be good, as other locations in the storm may have greater wind speeds than those sampled from limited aircraft coverage.

Eyewall Penetrations Aircraft typically complete figure-4 patterns to sample each quadrant in order for intensity estimations. y x

Intensity estimation Flight level reduction: typically take about 90% of flight level value for maximum sustained surface wind speed. Dropsondes: if values for all quadrants available at 10 m, take the max value found. Often, peak wind in jet just above PBL, where surface wind is often 80% of that maximum; on average, slightly less in right quadrants and slightly more in left quadrants, though left quadrant winds will still be weaker, usually.

Intensity estimation SFMR takes surface wind speed estimate from emitted sea foam characteristics. Seem to saturate quite often at high wind speeds (135 kt or so) and often produce low biases in cat-4 and 5 hurricanes. Remember, an addition of 3-5 kt or so is often wise to apply to the value measured by each aircraft instrument in order to estimate an expected maximum sustained surface wind speed.

Thank You.