Paper on how tropical cyclones can intensify in high shear published in Monthly Weather Review

When the wind within about 150 miles of the center of a tropical cyclone (what we call the near environment) is very different at the bottom and the top of the storm (what we call wind shear), the storm usually weakens, especially if the storm is already weak. However, sometimes this doesn’t happen, and the storm can intensify. The ways that this can happen are studied using radar data from NOAA hurricane hunter aircraft and data from dropsondes (that measure wind, temperature, humidity and moisture as they fall from the aircraft to the ocean surface) released from drone aircraft flying at a very high altitude (about 55,000 ft above the ocean).

Important Conclusions:

1. When water vapor in the atmosphere forms clouds, heat is released. Tropical cyclones are usually made up of strong thunderstorm clouds that reach high into the atmosphere and release tremendous amounts of heat. These thunderstorms require warm air in the lowest 5000 ft and cool air above 20,000 ft to allow rising air to remain less dense than their environment and continue to rise (what we call buoyancy). When many thunderstorms occur in the same location for several days, however, the heat released above 20,000 ft warms the air and reduces buoyancy, so most of the thunderstorms that develop do not extend as high in the atmosphere as before. Because these thunderstorms are shallow, the heat is then released in the low levels of the atmosphere.
2. When air gets warmer, like from heating from developing thunderstorms, it gets less dense, so its pressure falls. If this occurs over a large enough area, a circulation forms. The process described above creates these circulations. The shallow thunderstorms create a circulation in the low levels (lowest 5000 ft) of the atmosphere. However, the older, deeper convection also leaves a circulation in the middle levels (about 15,000 ft). When the low-level and mid-level circulations are in the same place (what we call aligned), the tropical cyclone can intensify.
3. This is the first time that this process, which we have seen before in computer modeling studies) has been documented in observations.

   See the study at https://journals.ametsoc.org/doi/abs/10.1175/MWR-D-19-0315.1.