Hurricane Imaging Radiometer (HIRAD) Wind Speed Retrievals and Validation Using Dropsondes

Area of Science:

• Meteorology
• Remote Sensing
• Oceanography

Background:

• Accurate measurement of tropical cyclone wind speeds is crucial for forecasting and understanding storm intensity.
• Existing remote sensing technologies have limitations in providing high-resolution surface wind data.
• The Hurricane Imaging Radiometer (HIRAD) offers a potential advancement in observing these critical parameters.

Purpose of the Study:

• To generate and validate surface wind speed retrievals using Hurricane Imaging Radiometer (HIRAD) data.
• To assess the performance of HIRAD wind speed retrievals against dropsonde measurements.
• To characterize the accuracy and biases of HIRAD retrievals across different wind speed regimes.

Main Methods:

• Utilized HIRAD measurements from flights over four tropical cyclones in 2015.
• Developed procedures for creating brightness temperature maps for wind speed and rain rate retrieval.
• Employed an iterative retrieval approach tailored to HIRAD's measurement characteristics.
• Validated retrievals using 636 dropsondes from the Tropical Cyclone Intensity (TCI) experiment.

Main Results:

• HIRAD wind speed retrievals demonstrated very small bias for winds tropical storm strength (≥17.5 m s⁻¹) or greater.
• Reduced sensitivity and a small positive bias (~2 m s⁻¹) were observed for winds weaker than tropical storm strength.
• Root mean square differences ranged from 4.1 m s⁻¹ (below tropical storm strength) to 6.3 m s⁻¹ (hurricane strength).
• Mean absolute differences were lowest for hurricane strength winds (4.8 m s⁻¹, 12%).

Conclusions:

• HIRAD provides reliable surface wind speed estimates for tropical storm and hurricane strength winds.
• The instrument shows potential for improving hurricane intensity monitoring and research.
• Further investigation is needed for HIRAD's performance in very weak wind conditions.