The radar dish inside is 28 ft (8.5 m) across. Nā‘ālehu radome, 39 ft (about 12 m) in diameter. This capability was especially useful at night when direct visual observations were not possible. Although not strictly weather clouds, these plumes of rock, mineral, and glass particles behaved a lot like normal meteorological clouds: they rose through the atmosphere, mixing with or punching through the existing weather cloud deck, and then drifted downwind.īy examining the radar snapshot of the clouds within minutes of formation, NWS and HVO could estimate the maximum height of the cloud and then use a computer model to visualize where the cloud would move and how much ash might fall. Data from the Nā‘ālehu installation assisted the USGS Hawaiian Volcano Observatory (HVO), NWS, and other agencies to rapidly detect and characterize ash clouds that erupted from Kīlauea Volcano's Halema‘uma‘u Crater repeatedly in May and June. In 2018, this radar provided an additional service to Hawaii residents. These data are used daily by weather forecasters, mariners, and anyone wanting helpful information on weather conditions and related hazards such as thunderstorms, hail, tornadoes, heavy rain, or flash flooding. The strength of the return signals (known as reflectivity) are directly related to size and concentration of reflectors (usually rain droplets or ice particles). Radar is a very useful tool because it penetrates clouds where the radar energy bounces off particles within the atmosphere and returns to the antenna. Data are displayed for all to see on a NOAA website. In the case of station PHWA, or the Nā‘ālehu radar, this extends from well southwest of South Point sweeping counterclockwise northeast off Cape Kumukahi and Hilo Bay. Around the clock, the resulting information, maps and animations of the intensity of radar returns from the atmosphere extending more than 100 miles (161 km) from the site. The radar's job is to scan the atmosphere rapidly in all directions to locate and track weather clouds. It is one of two such facilities on the Island of Hawai‘i the other sits atop Kohala to the north. The curious white orb is the radome (housing) of the South Hawaii or Nā‘ālehu Weather Surveillance Doppler radar installation owned by the Federal Aviation Administration (FAA) and operated by the National Oceanic and Atmospheric Administration (NOAA)'s National Weather Service (NWS). Data could also be displayed in cross section to estimate the height of the cloud. Reflectivity is the amount of transmitted power returned to the radar receiver, and because it occurs over a wide range, a logarithmic (or decibel, dBZ) scale is used. Colors indicate the different echo intensities or reflectivity. The colors scale is radar reflectivity, a measure of the size of the particles and their concentration within the ash cloud.
This image is a slice through the cloud at an altitude of 14,000 ft (4 km) above sea level at 4:12 a.m., HST.
Radar image of the eruption of ash from Halema‘uma‘u Crater.
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