Weather radar, also known as weather surveillance radar (WSR), is a specialized type of radar used by meteorologists and hydrologists to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). It emit radio waves or microwaves which bounce off rain or snow in the atmosphere and detect the reflected signals. The intensity of the reflected wave helps determine the size of the precipitation particles. By tracking the movement of precipitation echoes on the radar scope, radars can detect approaching rainfall, potentially hazardous storms and help predict weather.
How Radar Works
Weather Radar system consists of an antenna and a transmitter/receiver housed in a rotating dome. The antenna rotates usually at speeds between 8-24 rpm and emits short pulses of radio waves/microwaves in a broad conical beam. As the beam strikes raindrops, snowflakes or other targets in the atmosphere, some of the energy is scattered back towards the antenna. The receiver part detects these echoes and measures their strength and time delay between transmission and reception. Using these parameters, the radar computes the distance, intensity and speed of the precipitation or weather system. Modern radars use Doppler radar which can detect radial motion of targets by analyzing Doppler shifts in the returned signal. This helps forecasters distinguish between precipitation that is moving towards or away from the radar.
Data Interpretation
The radar data is used to generate images called radar scans which are overlaid on digital maps to depict the location and intensity of storms. Bright colors like red, yellow and green represent heavy precipitation while lighter blues indicate weaker echoes. Meteorologists analyze these scans to detect developing storms, estimate rainfall amounts, track storm movements and identity unique weather signatures. For example, a hook echo is characteristic of supercell thunderstorms and indicates strong rotation with chances of tornadoes. Shear lines separating rain areas signify gust fronts and help locate the leading edge of storm outflows. By monitoring changes in successive scans, forecasters can stay ahead of hazardous weather and issue timely advisories.
Range and Resolution
The range of radars varies from operational radar but they typically have a detection range of 150-230 miles. However, detection capabilities decrease significantly beyond 100 miles. Radar resolution also declines with distance as the beam widens. Close-in targets may be resolved at 1 degree or less while targets 100 mi away have resolutions of 5-10 degrees. New dual polarization radar systems provide higher resolution data by transmitting two orthogonal signals that can distinguish large rain drops from small ones, melting precipitation and even bird activity. This helps improve quantitative precipitation estimation.
Applications and Benefits
Weather radar data is crucial for detecting, tracking and nowcasting convective storms including thunderstorms, hurricanes, winter storms etc. It forms the backbone of real-time severe storm warning operations at national weather centers. Radar-indicated storms are routinely used by meteorologists to issue warnings for tornados, large hail and damaging winds. Aviation meteorologists utilize radar maps for tracking storms near airports and rerouting planes if necessary. Hydrologists use quantitative precipitation estimates from radar to initialize watershed and rainfall-runoff models leading to better flood forecasts. Municipalities rely on radar to plan road clearing during winter snowstorms. Ordinary citizens also access radar via smart devices and television to monitor weather approaching their area. In summary, it is a powerful remote sensing tool that enhances public safety during hazardous weather.
Limitations and Sources of Error
While very useful, weather radar data has some limitations that can introduce errors in analysis and forecasts if not properly accounted for. One major source is beam blocking and beam overshooting. Tall terrain features like mountains can block the radar beam from detecting precipitation on the other side. Conversely, beam overshooting causes precipitation to be estimated above its actual height resulting in misplaced echoes. Other causes of error include anomalous propagation, second trip echoes, biological scatterers and hardware/software issues. Moreover, radar cannot differentiate between rain, snow and hail. It also struggles to observe precipitation lightly loaded with water like drizzle. Combined with resolution loss at long distances, radar readings become less reliable beyond 100-150 miles. Operators must be mindful of these limitations to make the most accurate use of weather radar.
Dual-Polarization Techniques
To address some of the shortcomings, NEXRAD Doppler radars are being upgraded nationwide to dual polarization mode. In addition to ordinary horizontal transmit and receive, DP radars can switch between transmitting horizontal and vertical signals. This allows parameters like differential reflectivity (ZDR) and correlation coefficient (rhv) to be measured. ZDR provides information on size, shape and orientation of hydrometers. Oriented drops have higher horizontal reflectivity while spheroidal ice scatter more vertically. Rhv measures randomness of scatters to distinguish precipitation from biological/mechanical targets. Dual-pol is significantly improving quantitative precipitation estimates, hail detection, melting layer diagnosis and wind profiles. It also helps forecast initiation and dissipation of precipitation more confidently. The additional dual-polarization variables from radar are revolutionizing many applications of weather surveillance radars.
In the weather radar has become indispensable for detecting storms, issuing timely warnings and nowcasting hazardous weather. Though not perfect, continuous technological enhancements like Doppler and dual-polarization are significantly enhancing the utility of radar for meteorological and hydrological purposes. When used judiciously along with other observing systems like satellite, radar data provides vital information about precipitation location, movement and intensity on time scales important for forecasting and emergency response. Understanding radar fundamentals, limitations as well as innovative techniques helps extract maximum value from this important remote sensing technology for protecting lives and property.
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Ravina Pandya, Content Writer, has a strong foothold in the market research industry. She specializes in writing well-researched articles from different industries, including food and beverages, information and technology, healthcare, chemical and materials, etc. (https://www.linkedin.com/in/ravina-pandya-1a3984191)
