Observations of Hurricane David (1979) using the microwave sounding unit
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Observations of Hurricane David (1979) using the microwave sounding unit

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Observations of Hurricane David (1979) using the microwave sounding unit


  • Description:
    The Microwave Sounding Unit was first launched October 13, 1978, aboard TIROS-N, as a component of an operational sounding system. The sounder consists of four oxygen channels (50.30, 53.74, 54.96, 57.95 GHz) with a horizontal resolution of 110 km at nadir. This study reports on the microwave measurements obtained for Hurricane David at four 12-h intervals, beginning September 3, 1979, when David was in the Florida Strait, until 48-h later when it approached the Georgia coast.

    Comparisons are made between the brightness temperature measurements for the three highest frequency channels (called "sounding" channels) and the values computed from radiosonde data. Precipitation effects are only evident in the lowest peaking (700 mb) sounding channel at 53.74 GHz. At 54.96 GHz, the measurements display the magnitude and spatial extent of the hurricanes warm-core anomaly near 300 mb. The highest sounding channel at 57.95 GHz responds to temperatures around 100 mb and displays a strong north-south gradient corresponding to the latitudinal variation in tropopause height. For this channel, the influence of the hurricane appears minimal, although there is a greater disparity with the radiosonde computations than for the lower sounding channels.

    In addition to the individual spot measurements, comparisons are also made between the radial derivative of brightness temperature for the 54.96-GHz channel and the derivatives estimated using radiosonde winds. Measurements and simulations demonstrate that the brightness temperature derivative is correlated with the winds between 700 and 500 mb. Horizontal smoothing resulting from the instrument's 110-km resolution degrades the gradient information near the hurricane center more than the spot measurements of brightness temperature.

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