On the Z DR, small raindrops are evident by low Z DR (darker blue pixels), while larger, convective drops are evident in the western eye-wall evident by higher values of Z DR. On the Z e image above, concentric ring-like bands of heavy precipitation are seen with an intense band within the western eye-wall. A two-panel radar image of the Z e and Z DR, from left to right respectively, as Hurricane Irma moved north of Puerto Rico on September 6th, 2017. hail) cannot be discerned through the sole use of Z e. However, the exact precipitation features (i.e. The higher the echoes, measured in decibels (dBZ), the greater the intensity of precipitation. This is the most universal weather radar product used by meteorologists and the public alike. The above image is a PPI scan from the Equivalent Reflectivity Factor (Z e). High values of dBZ (~45dBZ) were detected in the western eye-wall, where the heaviest precipitation was occurring at the time. Tropical Cyclone Radar Imagery Equivalent Reflectivity Factor (Z e) imagery of Hurricane Harvey as it made landfall near Rockport, Texas, on August 26th, 2017. Now that we have established some basic understanding of the functionality behind a WSR-88D, we can dive into some fascinating and unique imagery that has occurred over the past several years. Graphic compiled by: Harrison Sincavageĭual-polarimetric variables such as the Differential Reflectivity (Z DR), Correlation Coefficient (ρ HV or CC), and the Specific Differential Phase (K DP/ϕ DP) must be utilized to obtain a full analysis of the types of echoes involved on the Z e imagery. While we will not delve into the specifics behind these polarimetric radar variables, the images including polarimetric radar will be shown in a relevant manner. After a multitude of processes within the radar, the backscattered information is processed onto the radar displays we see daily. A portion of the scattered beam travels back to the radar and is captured through the antenna (or receiver). Upon passing through the raindrop, the beam scatters due to electromagnetic energy. As the beam travels across the medium, it passes through a falling raindrop (light blue). The blue ovals are the beam emitted in the horizontal and the green ovals are the beam emitted in the vertical plane along a given medium. A cartoon illustrating the functionality of a polarimetric weather radar as it rotates about its axis. After a multitude of complex processes within the radar, it is displayed into the imagery that we see on a daily basis. This portion of the beam that returns to the radar is captured through the receiver (which is also the same antenna that emitted the signal). Image of the KOUN research radar at the NOAA Radar Operations Center in Norman, Oklahoma. These emitted pulses travel at the speed of light and when they pass through an object such as a raindrop, a portion of the beam returns to the radar due to scattering. Since the implementation of polarimetric radar, Doppler radars work by emitting pulses in both the horizontal and vertical plane. The use of the polarimetric radar variables has been a crucial element in weather forecasting operations, research, and in public consumption.ĭoppler weather radars rotate about their axis, and are Planned Position Indicators (PPIs). In 2013, the entire WSR-88D network was upgraded to dual-polarization capabilities, meaning that the Doppler radar can emit pulses in both the horizontal and vertical plane. The National Weather Service’s Weather Surveillance Radar-1988 Doppler (WSR-88D) network across the United States consists of 155 Doppler radar sites operated by the National Oceanic and Atmospheric Administration (NOAA).
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