Into the Storm

Today we are (virtually) piloting an airplane into a storm.
Generally, this is considered a bad idea. But if we want to understand and better predict the impact of storms, we have to learn more about them–and we need some way to get measurements of the storms in order to do that.
Since 2009, a small reconnaissance aircraft has been used for data collection around Hong Kong International Airport. The plane is equipped with a meteorological set of instruments which measure wind, temperature, relative humidity, and pressure; in a sense, a weather station with engines. Starting in 2011, this same aircraft has been flown above the northern part of the South China Sea, into typhoons (the name for hurricanes in the Northwestern Pacific). That brings us to today’s article, “Weather Observations by Aircraft Reconnaissance Inside Severe Typhoon Utor“, written by P.W. Chan, W.K. Wong, and K.K. Hon, published in 2014 in the journal Weather.
On August 13, 2013, the plane was flown into Severe Typhoon Utor, the strongest storm it had yet entered, and with a longer, lower flight path than usual, gathering data the entire time.
A satellite image of Hurricane Isabel in September 2013. Courtesy of National Oceanic and Atmospheric Administration.
A satellite image of Hurricane Isabel in September 2013. Courtesy of National Oceanic and Atmospheric Administration.
The wind speeds recorded by the plane changed direction–from the northwest, to a southeastern origin, experienced at opposite sides of the typhoon. Spikes in the wind speed were recorded while the plane crossed areas of convection, but generally the winds were 35 to 40 meters per second (78 to 89 mph) compared to the estimated 48.9 meters per second (109 mph) that had been predicted. When possible, wind speeds were compared with oil rigs and weather buoys in the same area, and were consistent with the plane’s instruments.
An important metric in meteorology is pressure. That’s why large Ls and Hs appear on your screen when the seven-day forecast is done, signifying areas of low and high pressure. Pressure is the measure of force per area–when standing outside, the weight of the air above you. At sea level, this is usually about 101,325 Pascals. At the center of the storm was the lowest mean sea level pressure, which when calculated was 97,370 Pascals–larger than the estimated 94,100 Pascals–both notably lower than the standard. These types of storms are low-pressure systems, so this is not surprising.
The eye of the storm is easy to see when the winds switch directions around the eye. However, this was also seen about 50 kilometers (31 miles) southwest of the eye of Severe Typhoon Utor. The systems and measurements were double checked, and the ‘secondary circulation system’ seems real, not just a strange hiccup in the data. It lines up with an outer rain band. These are uncommon, and the authors do not know of any described in existing literature, so there will be a lot more research into this particular result.
Also found was the gale-force radius–the distance from the eye in which winds were at gale-force strength (generally starting at 14 meters per second, or 31 miles per hour). This was 290 kilometers (180 miles), though six hours later, as the storm progressed, was measured to be 350 kilometers (about 217.5 miles). This is consistent with estimations made by satellite observations.
The turbulence–the unsteady, sometimes swirling motion of the air–was found using winds measured to have a vertical direction of travel. Inside the storm, it was quite turbulent; outside, it was moderately to severely turbulent as well.
Data from this flight, and others into different storms, has aided the typhoon warning service in Hong Kong, and the data helps analysis and forecasting of the storms. With each flight, we are closer to understanding these storms and what to expect from them.

 

Bibliography
Chan, P. W., W. K. Wong, and K. K. Hon. “Weather observations by aircraft reconnaissance inside Severe Typhoon Utor.” Weather 69.8 (2014): 199-202.
Today’s main article.
National Oceanic and Atmospheric Administration. What is the difference between a hurricane, a cyclone, and a typhoon?  NOAA/National Ocean Service, 10 Oct. 2014. Web.
A webpage on the NOAA site discussing hurricanes/typhoons. Also the source of the image used in this post.
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