Climate: Tropical Humid

Causes of Tropical Humid Climate

Tropical humid climates experience warm temperatures throughout the year because of the high angles of incoming solar radiation and nearly continuous penetration of moist air masses over these regions. Tropical climate regions are broadly constrained by the Tropic of Cancer to the north and the Tropic of Capricorn to the south. Persistent high angles of incident solar radiation within the tropics cause consistently high temperatures throughout the year as the solar radiation received per square meter is high. In the higher latitudes, the persistent lower angles of incident solar radiation result in less radiation received per square meter. While the humid air masses release heat to the environment through the condensation of water vapor, the main causal factors for tropical climate are the following:

• 1.
  Consistent day length of about 12 hours throughout the year
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• 2.
  Persistent high angles of incident solar radiation
• 3.
  The passage of the intertropical convergence zone (ITCZ), which brings rain as it shifts seasonally following the location of the overhead sun
• 4.
  Unstable maritime air masses in the region (Although air masses of polar origin occasionally invade the tropical and equatorial zones, the tropical humid climate is almost wholly dominated by the tropical and equatorial air masses.)

Tropical humid regions are characterized by high rainfall totals in most months of the year. For rain to occur, there must be some mechanism for vertically lifting the humid air, referred to as “atmospheric lifting mechanisms,” so that the air is cooled and condensation occurs, forming clouds and rainfall. There are four types of atmospheric lifting mechanisms, the convergent, convectional, orographic, and air mass frontal processes. The convergent atmospheric lifting process occurs as air blown by southeast and northeast trade winds converges along the equatorial region, forming the ITCZ. As the rising air cools, clouds and rain develop. Areas under ITCZ have extensive air uplift, causing towering cumulonimbus cloud development and high annual precipitation. The convectional atmospheric lifting process occurs when air mass from a maritime source region passes over a warmer continental region. Such moist air is heated, becomes less dense and rises, condenses, and form clouds and precipitation. The orographic atmospheric lifting process occurs when the physical presence of a mountain acts as a topographic barrier to the migrating air mass or the incoming maritime air, which forces the air to rise upslope. Again, as air rises, it cools and condenses into clouds and precipitation. Frontal atmospheric lifting is not very dominant in the tropics but does occur in some areas. In the frontal atmospheric lifting process, the cold front (the leading edge of an advancing air mass) conflicts with the warm air mass front, forcing the warm, less dense air mass to rise and resulting in clouds and precipitation, similar to the orographic atmospheric lifting process.

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