Climatology is the study of the long-term state of the atmosphere, or climate. The long-term state of the atmosphere is a function of a variety of interacting elements. They are:
- Solar radiation
- Air masses
- Pressure systems (and cyclone belts)
- Ocean Currents
Solar radiation is probably the most important element of climate. Solar radiation first and foremost heats the Earth's surface which in turn determines the temperature of the air above. The receipt of solar radiation drives evaporation, so long as there is water available. Heating of the air determines its stability, which affects cloud development and precipitation. Unequal heating of the Earth's surface creates pressure gradients that result in wind. So you see, just about all the characteristics of climate can be traced back to the receipt of solar radiation.
Air masses as an element of climate subsumes the characteristics of temperature, humidity, and stability. Location relative to source regions of air masses in part determines the variation of the day-to-day weather and long-term climate of a place. For instance, the stormy climate of the midlatitudes is a product of lying in the boundary zone of greatly contrasting air masses called the polar front.
Pressure systems have a direct impact on the precipitation characteristics of different climate regions. In general, places dominated by low pressure tend to be moist, while those dominated by high pressure are dry. The seasonality of precipitation is affected by the seasonal movement of global and regional pressure systems. Climates located at 10o to 15o of latitude experience a significant wet period when dominated by the Intertropical Convergence Zone and a dry period when the Subtropical High moves into this region. Likewise, the climate of Asia is impacted by the annual fluctuation of wind direction due to the monsoon. Pressure dominance also affects the receipt of solar radiation. Places dominated by high pressure tend to lack cloud cover and hence receive significant amounts of sunshine, especially in the low latitudes.
Ocean currents greatly affect the temperature and precipitation of a climate. Those climates bordering cold currents tend to be drier as the cold ocean water helps stabilize the air and inhibit cloud formation and precipitation. Air traveling over cold ocean currents lose energy to the water and thus moderate the temperature of nearby coastal locations. Air masses traveling over warm ocean currents promote instability and precipitation. Additionally, the warm ocean water keeps air temperatures somewhat warmer than locations just inland from the coast during the winter.
Topography affects climate in a variety of ways. The orientation of mountains to the prevailing wind affects precipitation. Windward slopes, those facing into the wind, experience more precipitation due to orographic uplift of the air. Leeward sides of mountains are in the rain shadow and thus receive less precipitation. Air temperatures are affected by slope and orientation as slopes facing into the Sun will be warmer than those facing away. Temperature also decreases as one moves toward higher elevations. Mountains have nearly the same affect as latitude does on climate. On tall mountains a zonation of climate occurs as you move towards higher elevation.