Hurricane Hunters and Observations
In the Atlantic basin, there are two main groups responsible for flying planes into hurricanes to take measurements such as wind speed and air pressure in order to better understand the current state of tropical cyclones. Those two groups are the Air Force Reserve and NOAA scientists. Whenever a tropical cyclone in the Atlantic basin poses a legitimate threat to life and property, the Hurricane Hunters will perform flights through the center of the tropical cyclone, gathering scientific data.
The video above was taken while a Hurricane Hunters flight was within the eye of Hurricane Dorian in 2019 and shows the strong convection in the eyewall surrounding the eye. These thick clouds building up along the edge of the eye are often referred to as the “stadium effect” because they resemble stadium seating as they branch out away from the eye. This effect is usually only observed in the strongest tropical cyclones.
Equipped on the Hurricane Hunters planes are multiple observation instruments, including Doppler radar and the Stepped-Frequency Microwave Radiometer. The SFMR measures the surface brightness temperature from the surface of the sea water. As winds within the tropical cyclone increase, the sea water becomes choppier with more waves, and the microwave radiation given off by the sea water is more diffuse. In addition, heavy rain between the SFMR and the sea surface will attenuate, or weaken, the signal produced by the SFMR. Because of these two effects, the SFMR can provide an estimate for the rainfall rate and the near-surface wind speed within tropical cyclones. This is the primary instrument used to determine the wind speeds associated with a tropical cyclone.
Hurricane Hunters flights also release instruments known as “dropsondes” into different parts of tropical cyclones in order to estimate their intensity. These dropsondes are released through a pressurized tube within the aircraft and include an instrument package which measures air temperature, dew point temperature, air pressure, and wind speed. Dropsondes can be useful for getting direct measurements of wind speeds and air pressure near the surface, where it is too dangerous for the planes to fly. The HH aircraft typically fly within tropical cyclones at an altitude between 8,000 and 10,000 feet, which is both safely above the strongest winds and would give the pilots plenty of time to react in case of an emergency.
In addition to the flights with the C-130 and P-3 aircraft through the eyewall and eye of tropical cyclones, the Hurricane Hunters also operate high-altitude flights with a cruising altitude of 45,000 feet, well above the tropical cyclone, to collect data from the upper atmosphere, which may affect the hurricane’s track and intensity. These high-altitude flights are taken with a Gulfstream IV plane specially equipped with instruments measuring pressure, temperature, and humidity as well as computers which process the data before sending it to the National Hurricane Center for analysis.