SFMR Surface Wind Undersampling over the Tropical Cyclone Life Cycle

Surface wind speeds in tropical cyclones are important for defining current intensity and intensification. Traditionally, airborne observations provide the best information about the surface wind speeds, with the Stepped Frequency Microwave Radiometer (SFMR) providing a key role in obtaining such da...

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Bibliographic Details
Published in:Monthly weather review 2019-01, Vol.147 (1), p.247-268
Main Authors: Klotz, Bradley W., Nolan, David S.
Format: Article
Language:English
Subjects:
Airborne observation
Aircraft
Cyclones
Data assimilation
Estimates
Experiments
Hurricane tracking
Hurricanes
Life cycle
Life cycle analysis
Life cycles
Lookup tables
Maximum winds
Microwave radiometers
Precipitation
Radiometers
Simulation
Surface wind
Tropical climate
Tropical cyclone intensities
Tropical cyclones
Tropical depressions
Tropical storms
Wind
Wind speed
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Summary:Surface wind speeds in tropical cyclones are important for defining current intensity and intensification. Traditionally, airborne observations provide the best information about the surface wind speeds, with the Stepped Frequency Microwave Radiometer (SFMR) providing a key role in obtaining such data. However, the flight patterns conducted by hurricane hunter aircraft are limited in their azimuthal coverage of the surface wind field, resulting in an undersampling of the wind field and consequent underestimation of the peak 10-m wind speed. A previous study provided quantitative estimates of the average underestimate for a very strong hurricane. However, no broader guidance on applying a correction based on undersampling has been presented in detail. To accomplish this task, a modified observing system simulation experiment with five hurricane simulations is used to perform a statistical evaluation of the peak wind speed underestimate over different stages of the tropical cyclone life cycle. Analysis of numerous simulated flights highlights prominent relationships between wind speed undersampling and storm size, where size is defined by the radius of maximum wind speed (RMW). For example, an intense hurricane with small RMW needs negligible correction, while a large-RMW tropical storm requires a 16%–19% change. A lookup table of undersampling correction factors as a function of peak SFMR wind speed and RMW is provided to assist the tropical cyclone operations community. Implications for hurricane best track intensity estimates are also discussed using real data from past Atlantic hurricane seasons.
ISSN:0027-0644
1520-0493
DOI:10.1175/MWR-D-18-0296.1