Radar Meteorology – A First Course

Radar Meteorology – A First Course

Radar, an acronym for RAdio Detection And Ranging, was initially developed to remotely detect aircraft and ships. During the 1930s, military applications of radar for aircraft detection were explored by Britain, Germany, and the USA, but the devices available were limited to very low frequencies and low power output. In 1940, the British invented the cavity magnetron, a device that permitted radars to operate at higher frequencies and high power output. The new, secret radars employing the cavity magnetron gave the Allies a distinct advantage throughout World War II—the capability to detect aircraft and ships at long ranges. Studies of atmospheric phenomenon with radar began almost as soon as the first radars were used. These studies were initiated because weather and atmospheric echoes represented undesirable “clutter” that hampered detection of military targets.

Following the war, the first large weather-related field campaign with non-military application, the Thunderstorm Project, was organized to study coastal and inland thunderstorms. Data from this and other projects stimulated interest in a national network of weather radars. Enthusiasm for a national network was spurred by efforts to estimate precipitation from radar measurements. The discovery of the hook echo and its association with a tornado led to widespread optimism that tornadoes may be identified with radar. Following the war, several surplus military radars were adapted for weather observation. These were replaced beginning in 1957 by the Weather Surveillance Radar (WSR-57), which became the backbone of the U.S. National Weather Service radar network until the Weather Surveillance Radar-1988 Doppler (WSR-88D) Doppler radars were installed three decades later.

The advent of digital technology, the rapid growth in the number of scientists in the field of radarmeteorology, and the availability of research radars to the general meteorological community led to dramatic advances in radar meteorological research. A fundamental change that spurred the revolution was the advance in digital technology. A basic problem facing radar scientists was the large volume of data generated by radars. A typical pulsed Doppler radar system, for example, samples data at rates as high as three million samples per second. This amount of data is impractical to store—the data must be processed in real time to reduce its volume and convert it to useful forms. Beginning in the early 1970s, advances in data storage technology, digital displays, computer hardware and software, and processing algorithms all made it possible to collect, process, store, and view data at a rate equal to the rate of data ingest. A key advance was the development of efficient software to process the data stream from Doppler radars. This development occurred at about the same time that the hardware became available to implement it, leading to rapid advances in Doppler measurements.

Doppler radars were soon developed with antennas that rotate in azimuth and elevation so that the full hemisphere around the radar could be observed. A network of Doppler radars, the WSR-88D network, was installed throughout the USA in the early 1990s to monitor severe weather. Countries of the European Union and China have also installed Doppler radar networks for storm monitoring. Mobile, airborne, spaceborne, and dual-polarization meteorological research radars were developed in the decades of the 1980s, 1990s, and 2000s for specialized applications. The WSR-88D radars were upgraded in 2011–2012 to employ polarization technology.

Early studies of “weather clutter” with the first-generation radars of the 1940s have evolved today into a complete scientific discipline called radar meteorology. Today, radar scientists worldwide meet regularly to learn about the latest advances in the science and to decide how best to employ these advances to better protect the public from weather hazards. With the development of the Internet and smart phone technology, displays of virtually all radar variables from the WSR-88D radars are now available in near real time to anyone in the world within range of a cell phone tower. Radar data are displayed regularly on television news, and ordinary people with no meteorological training “check the radar” every morning before venturing out into a rainy day.

So why study radar meteorology? The answer is straightforward—radar is the only tool with which we can observe the detailed structure of storms. Radar allows operational meteorologists to routinely detect tornadoes and flash floods in sufficient time to warn the public to seek shelter. Weather radars used by air traffic control provide controllers with the information to warn approaching and departing aircraft about microbursts and wind shear events. Meteorologists use radar to discriminate precipitation type in winter and determine the onset, end, and type of winter weather to be expected.

Atmospheric scientists use radar for a wide range of research, from diagnosing the circulations in hurricane eyewalls to investigating convective initiation along the Great Plains dry line. Radar data are now assimilated into numerical models used in research and forecasting. Radar is a critical tool in hydrological research.

In future decades, radar will be a key component of emerging science frontiers in the atmospheric sciences. Global climate change impacts will drive scientific research—the predicted increase and impact of extreme events, for example, will demand a greater focus on these events by the radar research community. New frontiers will continue to be forged in tropical and extra-tropical cyclone research, studies of convective, tropical and winter weather systems, measurement of rain and snowfall, and detection of floods. New technologies will be exploited to measure atmospheric properties such as water vapor and particle types in clouds. A diversity of radar technologies—and trained individuals to employ them—will be needed to accomplish this research. Capabilities will extend across the full range of current technologies—Doppler and polarization diversity, standard and phased array antennas, and multiple wavelengths—to yet-to-be-invented technologies. Radars will be deployed on a wide array of platforms such as aircraft, ships, and trucks to nearby locations as well as remote regions of the earth. The future of radar meteorology is vibrant and exciting—and studying radar meteorology gives you the tools to be part of the adventure.

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