DISCUSSION: The Global Precipitation Measurement (GPM) Core Satellite was launched in 2014 as a joint project between NASA and the Japan Aerospace and Exploration Agency (JAXA). The two primary instruments carried on the satellite are the GPM Microwave Imager and the Dual-Frequency Precipitation Radar (DPR). The GMI measures naturally emitted radiation in 13 channels, while the DPR measures scattered radiation at two microwave frequencies. The combination of information from these instruments provides critical information necessary to create a globally-consistent measure of precipitation. Rain gauges and ground-based radar are useful tools for estimating precipitation, but these are only available on land and coverage is not uniform. Only from a satellite can a truly consistent, global measure of precipitation be obtained. The GPM mission actually consists of a constellation of satellites, but the GPM Core Satellite provides the basis against which all the other satellite instruments are compared or calibrated against.
Hurricane Walaka is currently a Category 1 hurricane located northwest of Hawaii. The storm formed southwest of Hawaii and moved west of the islands without any direct impacts there. The storm is currently weakening as it moves over cooler water and into the mid-latitude westerlies. When the storm was still an intensifying tropical storm on 30 September, the GPM satellite passed over the storm center. The above figure shows a 3-D depiction of the 17-dBZ surface from the Ku Band of the DPR instrument. This basically shows how the precipitation is distributed around the storm and in the vertical. The figure also shows the intense and deep (up to 8.5 miles [13.7 km] above the sea surface) convection in the southeastern and northwestern section of the eyewall of the storm. The DPR also observed intense rainfall in a rainband northeast of the storm center with an estimated rain rate of nearly 6.5 inches (165 mm) per hour. Without satellite microwave instruments, acquiring estimates of such intense rainfall in the middle of the ocean would be much more difficult if not impossible.
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© 2018 Meteorologist Dr. Ken Leppert II