Air Temperature Patterns

Introduction

Air temperature is a measure of the heat content of the air. One can think of it as a measure of the average speed or kinetic energy level of molecules. The temperature of our atmosphere is controlled by a complex set of interactions between the biosphere, lithosphere and atmosphere. Energy is constantly being exchanged between the surface and the air above a place, as well as circulating around the globe. In this lecture we'll first look at look at what controls the air temperature at a particular place by examining radiation and energy exchanges between the earth and air above. Then we'll see how the global circulation of air and water affect air temperature.

Air Temperature

Definition: measure of the average speed or kinetic energy level of air molecules.

Controls over air temperature at a place

• Radiation transfers

• Sensible heat transfer

• Location with respect to water bodies (Continentality)

• Air mass movement

Radiation transfer and temperature

• Solar radiation - principle source of heating the surface.

• Longwave terrestrial radiation - source for heating the air.

• Lag period

  • Daily lag - Amount of time between maximum insolation and air temperature on a daily basis.

  • Seasonal lag - Amount of time between maximum insolation and air temperature on a seasonal basis.

  
  

• Radiation, Cloud Cover and Air Temperature

  • Clouds good absorbers of longwave terrestrial radiation.

  • Cloudless evenings - coldest temperatures

  • Desert locations - large daily temperature range

Air Temperature and sensible heat

• Sensible Heat - energy used to heat air above surface

• Sensible heat flux depends on:

  • surface temperature/vertical temperature gradient.

  • air turbulence

Air Temperature and water bodies

• Properties that effect water temperature

  • Transparency

  • Q* allocated to latent heat flux

  • Ability to circulate

  • Specific heat

• Impact on air temperatures

  • Air temperature is lower.

  • Temperature ranges are smaller

  • Seasonal temperature lags are longer

Air Temperature and Air Mass Movement

• Air Mass - vast pool of air, covering thousands of square kilometers, having about the same humidity and temperature characteristics over its horizontal extent. (See USA Today Interactive North America Air Mass map)

Air Mass Source Regions

• Some air mass types:

  • Maritime Tropical (mT)

    • Originates over the tropical oceans

    • Warm and Moist

  • Continental Polar (cP)

    • Originates over high latitude continents (about 60 degrees north)

    • Cold and dry

  • Maritime Polar (mP)

    • Originates over mid to high latitude oceans.

    • Cool and moist

• Influence of air masses on temperature at a place.

  • Depends on location with respect to the source of the air mass

  • Depends on the trajectory (direction of movement) of the air mass away from the source

Global Patterns of Air Temperature

Can you.....

• describe the relationship between incoming solar radiation, outgoing energy, and air temperature on a daily and seasonal basis for a midlatitude continental location?

• describe why coastal locations have cooler air temperatures than places located in the interior of a continent?

• describe how temperature ranges vary as you move from west to east across a midlatitude continent?