Chapter 6: Arizona Climate and Riparian Areas

Large-Scale Atmospheric Controls on Arizona Climate

    • Arizona is located geographically close to a belt of high-pressure systems that circle the globe.
    • An idealized circulation called a Hadley cell produces sinking and warming air (high pressure systems) around 30° north and south latitude.
    • These subtropical high pressure systems produce warm and sunny conditions and typically arid climates.
    • Arizona is influenced by the Pacific high and the Bermuda high.
    • Winter circulation pattern (left map below):
      • Winter precipitation typically comes from low pressure systems that enter Arizona from the west or northwest.
      • The Pacific subtropical high pressure system retreats with the approach of low pressure systems from the west.
      • These systems bring moisture from the Pacific and usually cooler temperatures from a northwest flow. The combination of cooler temperatures and precipitation can mean accumulating snows for higher elevation locations.
    • Summer circulation pattern (right map below):
      • Summer monsoon precipitation requires a flow of moisture from the south-southeast.
      • A south-southeast flow over Arizona is coupled with the strengthening of the Bermuda subtropical high pressure system across Mexico.

    

Figure 6.4. Average flow patterns and moisture airmass boundaries for winter (left) and summer (right).