Mr. Kevin Nolen
Penncrest High School
Media, PA

 Air has both mass
(weight) and density
(thickness), causing its pressure.
 “High" is an area where the air pressure is higher than the surrounding air.
 A "low” is where it's lower. It’s all relative.

 High-pressure is thicker and heavier, so it descends.
 As air descends, it warms, which inhibits the formation of clouds.
 This is why high pressure is often associated with good weather.

 Low pressure is thinner and lighter, so it rises.
 As air rises it cools, the humidity (moisture) condenses and it rains.
 This is why low pressure is associated with bad weather.
Thanks to: http://www.usatoday.com/weather/tg/whighlow/ whighlow.htm

Air masses flow from high pressure to low pressure.

Air masses are deflected as a result of the earth’s rotation.

Air masses over land heat and cool faster than air masses over water.

Summer Day at the Beach: Sea Breeze
 The air over the land heats up and expands causing it to become lose pressure and rise.
 This rising air is replaced with moist, high-pressure air from over the ocean.
Note: Breezes are described by the direction they come from.

Summer Evening at the Beach: Land Breeze
 The air over the land cools faster than the air over the ocean.
 The air gets cooler and compresses
(gains pressure) and blows to the ocean.

Differential Heating and the Indian Subcontinent
Since the Indian
Ocean is bounded to the north by the largest landmass on the planet, the effects of differential heating are intense.
Thanks: http://www.crseo.ucsb.edu/esrg/I
OM2/Differential_Heating.html

 A monsoon is a seasonal wind that dominates the climate of South Asia.
 The word “monsoon” means “season” in Arabic.
 There are two monsoons: the wet monsoon of summer and the dry monsoon of winter.

 The wet monsoon arrives in late May or early June.
 Warm, dry, lowpressure air masses form over the subcontinent.
 Cool, moist, highpressure air masses flow in from the sea.

 The dry monsoon arrives in October.
 Warm, moist, lowpressure air masses form over the sea.
 Cool, dry, high-pressure air masses form over the subcontinent and flow toward the sea.