HURRICANE GENESIS: A science review by Mark Betancourt in Air & Space Smithsonian

I’ve enjoyed Air & Space magazine for years, but an in-depth article by Mark Betancourt in the August 2015 issue goes above and beyond. I expect informative technology reviews and personal interest articles sating my inborn curiosity in aviation and space developments, but this story is one of the best science reviews I’ve read in a popular magazine.

Mr. Betancourt elucidates the state and the art of hurricane science, describing the methods and tools used to ask and answer the important questions. Of course, that’s how scientists operate, figuring out how to devise and conduct the tests required to solve the unknowns. Here we have the story of hurricane genesis focused on those tools and techniques climate scientists have used in the past as well as the new methods used today. But this story goes even further, into the future, laying out the questions we need to answer about how hurricanes begin.

KatrinaEyewall_NOAA
Eye wall of Hurricane Katrina from NOAA aircraft

Betancourt does all this without forgetting how Air & Space magazine adroitly grabs reader’s attention with personal stories about real people. So we read about the first pilot to penetrate a hurricane in an airplane. Joseph Duckworth, an Army Air Corps flight instructor and unusually skilled instrument pilot, was eager to show his British student pilots the capabilities of the AT-6 Texan aircraft they liked to ridicule. In July, 1943, he flew an AT-6 into a hurricane off Texas’ Gulf Coast, and returned unscathed. A fascinated colleague asked Duckworth to take him into the hurricane on a repeat of his daring flight. He did so, again returning safely.
AT-6 Texans
Restored AT-6 Texans flying at Oshkosh, July, 2015

Thus began the era of aircraft flying into a hurricane to take measurements of its strength and movement. P-3 Orions and C-130s have done it now for years, but here we taste the future with details of large and small drones used to study hurricanes up close.

p3_Orion_NOAA
NOAA WP-3D Orion Hurricane Hunter

GlobalHawk_NASA
Global Hawk outfitted for hurricane duty with NOAA

The large drone is the Global Hawk, 44’ long with a wingspan of 130’, weighing as much as 32,000 pounds and able to stay aloft in and above a hurricane for 18 hours. The Global Hawk is big enough to release dropsondes that fall through the storm sending back measurements.

coyote_NOAA
Coyote drone dropped into hurricanes by NOAA

At the other end is the Coyote, a three-foot long handheld drone with a six-foot wingspan weighing just seven pounds and capable of short two-hour flights through a hurricane. The Coyote is itself deployed from a manned P-3 Orion Hurricane Hunter.

The Genesis Part

Along with the personal interest stories and latest technology updates, Mr. Betancourt delivers sound science surrounding the still mysterious forces that coalesce to create a hurricane. He starts with three things we understand, evaporation, convection, and condensation. Water evaporates from the warm ocean surface making the air at the ocean’s surface less dense, causing it to rise – convection. As it rises, the air cools and the evaporated water molecules begin to condense into small droplets. When the droplets grow larger gravity forces them to fall back into warmer air below. When this happens, the droplets partially evaporate, cooling the air around them. This newly cooled air continues to fall, being heavier than the warmer air below. This is a classic downburst of rain and cool air, and it replaces the warm surface air mass that fed convection in the first place. Further evaporation and convection is stopped, and the storm is over.

I knew about evaporation, convection, condensation, even downbursts. But I didn’t know downbursts kill the storm.

What does this have to do with the mystery surrounding the genesis of a hurricane? As a cluster of convective storms come together, the middle layer of air through which rain falls becomes too warm and humid for the raindrops to evaporate, so there is no cooling. The downburst stops, or never really gets going, and rather then being cut off, the storms continue to grow bigger. More evaporation leads to more convection across a broad swath of the ocean surface as the storms coalesce and strengthen. A low pressure center builds as the warm air rises en masse. Cool, dry, and dense air from outside the low pressure center rushes inward from all directions, pushing the warm moist air up faster, allowing more evaporation to occur at the warm ocean’s surface, pushing more convection and ever lower pressure. The inward rushing air speeds up, further increasing surface evaporation and convection, and a positive feedback loop leads to a stronger and stronger storm. Bingo, a hurricane is born.

Unanswered questions include what causes a cluster of storms to coalesce rather than stay isolated and dissipate as they normally do, and what is the role of warm ocean surface waters? But thanks to this well-designed story that focuses on the tools, techniques, and unknowns surrounding the birth of hurricanes, those questions come forth with clarity. That’s how science operates. What’s rare is to see this in-the-field process of scientific investigation form the basic structure of a compelling story.

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