When two different air masses meet, the boundary zone between them is called a front and the process of formation of the fronts is known as frontogenesis. There are four types of fronts, i.e., cold, warm, stationary, and occluded front. Fronts are characterized by steep gradients in temperature and pressure. They bring abrupt changes in temperature and cause the air to rise to form clouds and cause precipitation.

Conditions required for Frontogenesis:

• Temperature difference: The two opposing air masses that converge to form a front must have a contrasting temperature. If one air mass is warm, moist, and light, a front can only be created when the other air mass is cold, dry, and dense.
  • Frontogenesis does not take place in the equatorial region as the two air masses converge at the equator (trade winds) but the temperature of both these air masses is uniform.
• Convergence of air masses: When two air masses having different temperatures converge, they try to invade the space of each other and this leads to the formation of the fronts.

Fronts and associated depressions tend to develop in a well-defined order.

The major regions of frontal development are as follows:

• East Asia and Eastern North America: Fronts are formed especially in winter, where there is a sharp temperature gradient between the snow-covered land and warm offshore currents.
  • Pacific Arctic fronts are formed along the Rockies-Great Lakes region.
  • Atlantic Polar fronts are formed when maritime tropical air masses meet continental polar air masses. Full development of this front takes place during winter.
  • Also, the frontal frequency is very high in the North Atlantic whereas it decreases eastward in the North Pacific because of less gradient of sea surface temperature. Frontal activity is also very common in the Central North Pacific.
• Mediterranean: Here the polar front commonly referred to as the Mediterranean front is located over the Mediterranean-Caspian Sea areas.
  • It is formed when the cold polar air masses of Europe meet the winter air masses of North African origin over the Mediterranean basin and initiate frontogenesis.
  • In the summer, because of the anticyclonic conditions, the frontal zone is absent. The Atlantic Arctic Front is formed when the maritime polar air masses meet the air masses developed along the boundary of the Arctic source- region. The associated weather phenomena are different in each type of front. The cold front brings lots of precipitation and cold weather whereas the warm front brings drizzly rain and warmer weather.