Story by Lance Quackenbush
Edited by Francis Lavigne-Theriault
Weather impacts us in our daily lives. The forecast you see on your weather app, on TV or on the computer allows us to plan out our daily and weekly routines. In addition, the radar app on your phone allows you to see if rain or snow is coming in real time. But how does radar work and how effective is it at seeing severe weather?
What is Radar?
The word RADAR stands for RAdio Detection And Ranging, which outlines the physical processes that the unit does. A radar sends out a pulse of microwave energy, which is a type of radio wave. When the pulse of energy hits precipitation (rain, hail, sleet, snow, etc), the radio wave is reflected back to the radar. The time it takes for the pulse to get to the radar and back tells the user how far away the precipitation is, as well as other information about the wind speeds occurring in the "target" the radar is looking at.
Canada's National Radar Upgrade
In February 2017, Canada announced an upgrade to its national network of Doppler radars, which featured a change in the type of radars being used. The old radars used what is called a C-band wavelength, which has a wavelength of around 5 cm. The upgraded radars used a wavelength twice as long as of the old radars at around 10 cm, which is known as an S-Band wavelength. The higher powered S-Band radars can detect storms that are behind other storms much better, whereas the C-Band radars have trouble detecting the storms due to being lower energy (a storm can scatter a lot of the energy and make other storms seem weaker behind a strong storm, lowering reflectivity values and rainfall estimates even though the storm may be equally as strong as the first storm the C-band radar detects).
Dual-Polarization
In addition, the new upgraded radars use a technology called dual-polarization, in which the beam changes angles and can in essence scan precipitation (in the vertical and horizontal with alteration of the radio waves) such as rain, snow, freezing rain, and see what the structure of the precipitation is. This allows for the type of precipitation to be determined, particularly in winter storms where there are quick transitions between rain and snow, as well as mixed-precipitation. In the summer, knowing the size and shape of precipitation can also allow meteorologists to determine if a severe thunderstorm has large hail within it, in addition to seeing areas of high-reflectivity on radar.
Extended Range
One more key change between the old and new radars is the effective range of detecting precipitation and winds from the radar site. The C-band radars had an effective Doppler range of around 120 km, whereas the S-Band radars can see double that at 240 km. This is very important as there is a limited number of radars in Canada as it’s a large country. The ability to have extended range allows for the detection of precipitation and severe weather, much like what was observed in Calgary this summer when a tornado warned storm moved through parts of the city. Another example of what the range combined with dual polarization can do is determine if a storm at long-range is severe.
More Frequent Radar Updates
The expanded range and dual-polarization also has one more advantage for the public: more radar scans per hour. The old C-Band radar images were published once every 10 minutes. The new radars update every 6 minutes, allowing for 4 extra public radar updates every hour. This allows for users to make more informed decisions and know when precipitation, or even dangerous weather may be coming. The investment by the Canadian Government was important for weather forecasting and will allow meteorologists to issue timely warnings to the public so that lives and property can be protected when severe or adverse weather approaches.
Example of S-Band Radar in Action
An example of this occurred in Manitoba north of Foxwarren in 2019. The dual-polarization radar detected a thunderstorm at long range, which had high reflectivity values. Based on the shape of the hygrometers, the radar determined that there was large hail within the thunderstorm, which was verified by the public via storm reports. Knowing large hail is occurring in a particular storms allows for warnings to be issued earlier and gives the public extra time to protect their property and life. In addition, the dual-polarization radar does a great job in determining rainfall rates, which can allow for more accurate warnings when flash floods may occur. This justifies investments in these radar sites.
The extended range can allow for detection of tornadoes in rural areas that may have otherwise been undetected by the older radars. For example, The Northern Tornadoes Project (NTP) oftentimes find tornadoes using satellite imagery that have been missed by conventional radar. Having the new S-Band radars can allow for a higher detection rate of supercell thunderstorms.
For more information on Canada’s Radar Upgrades, visit: https://www.canada.ca/en/environment-climate-change/services/weather-general-tools-resources/radar-overview/modernizing-network.html#wb-auto-5
References
NOAA. (2016, June 15). Dual Polarization Technology. Retrieved from https://www.weather.gov/hun/radar_dual_pole
Laramée, S., et al. (2019, November 18). Replacement of the Canadian Weather Radar Network - CMOS Bulletin. Retrieved from https://bulletin.cmos.ca/canadian-weather-radar-network/