What is the contribution of air mass in determining the climate of a place?
Answers
An air mass is a large unit of the lower atmosphere defined by common physical characteristics, such as temperature and humidity, at any given altitude, and one that remains discrete and identifiable as it moves. These giant parcels -- often better than 1,600 kilometers (1,000 miles) broad -- exert significant meteorological and climatic influence, transporting characteristics of their regions of origin through the territory they move over. Thresholds of adjacent air masses also form fronts, along which much of the world’s major weather action travels.
Air-Mass Basics
The zones that birth air masses, which are most prevalent in the tropics, subtropics and high latitudes, are called “source regions.” They’re typically areas of relatively uniform surface -- tracts of ocean, desert or snow-covered plains, for example -- which experience generally weak winds, the kind of stable conditions that allow parcels of atmosphere to assume physical characteristics from the underlying water or land. These source regions and their prevailing temperature, humidity and stability features help classify the world’s major air masses, which include continental-polar, or cP, maritime-polar, or mP, continental-tropical, cT, maritime-tropical, mT, and Arctic/Antarctic, A.
Movement
An air mass may sit over its source region for long periods of time, or it may migrate. An air mass on the move begins to transform as it passes over new landscapes, while at the same time retaining enough of its original conditions to alter local weather. For example, a cP air mass originating from the tundra of northern Canada may push southward during the winter. It brings frigid temperatures to the central United States, even as it warms up somewhat on its journey across lower latitudes. While dry in its source region, such an air mass often picks up substantial moisture during an early-winter transit of the Great Lakes, allowing it to dump so-called lake effect snow on leeward coasts. Different air masses don’t easily merge with one another; they clash uneasily in the atmospheric frontiers called fronts.
Weather and Climate
Weather describes the day-to-day meteorological conditions -- precipitation, temperature, wind and the like -- of a certain site. A thunderstorm along a frontal boundary is a weather event. Climate, meanwhile, represents the long-term annual patterns of those meteorological conditions -- the seasonal fluctuations of rainfall in a given region, for example. While the major, readily observable effects of air masses are mostly in the realm of daily weather, the reliability of air-mass incursions in many regions make them important contributors to regional climate conditions.