The heat wave that is baking America is being called a “heat dome”.
A better name would be “Hadley’s Horrible High” or “The Attack of the Hadley Cell”.
Whatever it’s called, it means sweat, misery and higher electrical bills when you crank up the air conditioner.
George Hadley was an 18th century scientist who noted that:
- Hot air rises,
- Cold air sinks, and
- The rotation of the Earth affects winds.
Tropical air circulation – a Hadley Cell
Source: Wikipedia http://en.wikipedia.org/wiki/File:HadleyCross-sec.jpg
It all sounds harmless doesn’t it? Now his name has been given to the circulation pattern of tropical air, a Hadley cell. It is this swirl of tropical air that causes hurricanes, monsoons and heat waves. Unfortunately this tropic pattern shifts north during summer and the heat that would normally be blasting the South visits the Midwest.
Here’s how the Hadley cell works:
- The area where the sun is shining directly over head gets hot. Hot air rises. The warm air rises and cools until the moisture in the atmosphere rains out. This band of rising air and rain produces low air pressure and tropical storms.
- The rotation of the Earth steers winds away from the equators toward the poles.
- As the tropical air drifts through the high atmosphere, further and further north, (or south if it is south of the equator) it cools off. Cold air sinks. At around 30°N it sinks. This area where the air is plunging downward is called a high pressure area. It blasts away any clouds and moisture and the sun bakes the area so that it is very hot and dry.
- Winds blow away from the high pressure and the general flow is from the 30° latitude back towards the equator.
This tropical circulation produces tropical climate – jungles around the equator, deserts around the 30° highs and monsoons with wet and dry seasons in between.
Unfortunately, that tropical Hadley cell is not staying south of 30° where it belongs. As your elementary teacher taught you, the Earth is tilted towards the sun in summer time. This means that on June 20, the sun is beating directly down at 23° north. The whole Hadley cell circulation shifts north. The atmospheric high, and the heat it causes shifts north. Instead of beating down on Arizona, it drifts north into the Great Plains.
Hadley cells – Stormy lows in the tropics and cloudless heat waves in the Great Plains.
SOURCE: © Browning Newsletter on a satellite photo from NASA
So if you feel blasted by the heat, you’re right! You are being blasted by tropical air. The news is calling this area of high pressure a heat dome, but it’s more accurately a heat bomb, brought to you by your friendly Hadley cell. You are under attack – so go inside and take shelter by the first air conditioner that you can find.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin  and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.