Last week Dr. Robin Tanamachi of National Severe Storm Labs spoke to my local IEEE Section about scientific storm chasing. Part of her job is to get near tornadoes and take scientific data on them, mostly using radar.
Storm chasing has had a recent surge in hobbyist interest. It’s not illegal, but there are informal rules of storm chasing safety and etiquette. Because of the recent interest there are often long streams of cars on rural roads near the path of a tornado.
Police response to controlling traffic and dealing with storm chasers varies from place to place. A tornado traveling through a particular city or county is such a rare event that local authorities usually don’t have a pre-set policy toward storm chaser traffic. Usually police are tolerant of storm chasers, especially ones like Dr. Tanamachi who are doing scientific research, but she knows of one case in which a researcher was detained because the police suspected he was a looter because of the video camera and chainsaw (for cutting through fallen trees) in his car.
The idea of chasing storms with radar equipment was pioneered by Dr. Wurman and Dr. Bluestein in the mid 90s. Prior to that, researchers used data from the nearest weather radar tower. Physically chasing tornadoes was strictly a hobbyist activity.
Weather radar looks at amplitude to determine precipitation density. Starting in the late 80s, radar began including doppler shift to work out raindrop speed. Most radar antennas are horizontally polarized because, contrary to common depiction, raindrops are shaped more like hamburger buns. New radar systems take horizontally and vertically polarized data and measure the correlation to work out raindrop shape.
Radar towers are located in most major cities and cover most of the country except for some unpopulated areas on the Rocky Mountains. Radar is line-of-sight, so at long range it is capable of detected high-altitude raindrops only. There is a program called Collaborative Adaptive Sensing of the Atmosphere (CASA) to install radar towers between major cities to provide low altitude precipitation information.
Taking portable radar equipment directly to the site of a tornado provides even more resolution. The width of the radar beam varies from 0.18 to 3.0 degrees, depending on the radar system. This means at close range, researchers can aim the antenna at different elevations to get a view at different altitudes.
Dr. Tanamachi’s research involves looking at doppler radar sweeps at different altitudes. Comparing wind speed with altitude provides a better picture of how tornadoes work. On interesting finding from this work is that some tornadoes spaced a few minutes apart are actually part of the same vortex whose strength is varying. Only when it’s strong enough for a condensation funnel cloud to occur can it be visually recognized as a tornado.
There are new radar systems that use beamforming instead of a physical antenna. This allows the radar to collect data from different directions without waiting for the antenna to rotate. The systems cost around a billion dollars. Based on the low prices of Wi-Fi chipsets that support MIMO, which requires similar DSP processing power to beamforming, I suspect the price of this radar will drop rapidly.
A Thrilling Job?
I asked Dr. Tanamachi about the thrill-seeking element of her job. She says she simply has to ignore fear, excitement, or any emotion when doing her work. She has to collect data that researchers with fixed towers cannot get and use it for novel research. Seeking to go closer to a tornado than necessary or being afraid to approach a tornado would interfere with her ability to get data.
She has only had one close call with a tornado. It was at night and a navigation mistake led her to truck to pass right by a tornado. People like to talk to her about this, but they don’t realize having a close call with a tornado is an on-the-job error in her work.
Although she tries to stay several miles from tornadoes when collecting data, occasional close exposure to tornados is invariably part of a scientific storm chaser’s job. It’s only at the end of the day when data has been collected and everyone is safely away from the storm that she and her team can think about the beauty and excitement of the severe weather they experience.
The video below shows a typical storm chase, which maintains a safe distance from the tornado.