Why are Deserts so dry?

SAHARA DESERT in North Africa

Key places today…

• North Africa

• Sahara Desert

• Atlantic Ocean

• Canary Islands

• Morocco

• Atlas Mountains

High PRESSURE or anticyclone

Air sinks

Air warms

Moisture evaporates

Clear blue skies and dry weather

Deserts are areas of permanent HIGH PRESSURE

1.

Deserts lie on the West side of continents….

In zones where the prevailing winds come from the east.

2.

Saharan sand blown off to the west by easterly winds.

The cold ocean current : THE CANARY CURRENT

3.

Canary Islands - fog

‘It was pretty cold and windy in the damp fog’

San Francisco coast California –

Also gets fogs.

Moisture condenses out of the air over cold oceans

3.

RELIEF RAINFALL and RAIN SHADOW

Atlantic Ocean Atlas Mountains Sahara Desert

RAIN in Morocco

Sahara Desert

Rain near Equator

R

E

L

I

E

F

R

A

I

N

F

A

L

L

Rain Shadow effect here

Sahara Desert Begins

Relief Rainfall Here

Warm dry air sinks down into the Sahara…

… making it a desert

The Relief Rainfall and the Rain Shadow happens in the dry SW USA too.