Tropical Regions

The tropical regions are the regions of the Earth near the equator and between the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere. This tropical region is also referred to as the tropical zone or the torrid zone. The word Tropical specifically means places near the equator. It is also sometimes used in a general sense for a tropical climate, a climate that is warm to hot and moist year-round. This article is on Tropical Regions

The three types of climate in tropical regions are classified as:

Tropical Rainforest or Equatorial (Af)
Tropical Monsoon (Am)
Tropical Wet and Dry or Savannah (Aw)

The map below shows the areas within the tropical regions which have all 12 months of the year with temperatures above 18°C.

As can be observed in the map these three tropical climates are confined to a global band known as the Tropics which falls between the northern latitude, Tropic of Cancer and the southern latitude, Tropic of Capricorn. The general pattern of the tropical climate is warm temperatures. Depending on the type of tropical climate, humidity is variable with Equatorial climates experiencing large quantities of precipitation all year round and Tropical Wet and Dry and Tropical Monsoon climates experiencing seasonal shifts in rain patterns.

THE TROPICAL CLIMATE CONTROL (Tropical Regions)

The most important climate control in regard to the tropical climate types relates to the position of the Inter Tropical Convergent Zone or ITCZ. The ITCZ is an area of low pressure and marks the point of trade wind convergence. These two roles make it an important ingredient in atmospheric circulation and give it a critical role in the formation of the Hadley cell.

The ITCZ’s location varies throughout the year and while it remains near the equator, the ITCZ over land drifts farther north or south than the ITCZ over oceans. This is due to greater variation of land temperatures.

The location of the ITCZ can vary as much as 40° to 45° of latitude north or south of the equator based on the pattern of land and ocean. Despite these variations the ITCZ relates closely to the altitude of the sun and marks the point where the sun is highest in the sky.

In temperate latitudes relative migration of the sun between the Tropic of Cancer and Tropic of Capricorn is responsible for creating the seasons but in tropical latitudes it is responsible for the migration of low pressure and the resulting shifts in seasonal tropical rains.

In addition to the ITCZ there are a number of other climate controls that influence the types of climate in the tropics. The influence of land and sea has a critical affect on the migration of the ITCZ. Due to the heat retention and stability of temperature within the ocean the ITCZ remains more anchored to one position over oceans. In contrast land temperature vary over the year and temperature is also influenced by altitude and relief. These factors create greater ITCZ migration and climatic variation north and south over continents. In Tropical Monsoon Climates the ITCZ can interact with other climatic patterns such as offshore winds that form as a result of deep lows over land. In combination with the ITCZ this helps produce enormous seasonal rains.

The second distinctive climate feature of tropical regions is the dry season. As you can see from the diagram, to the right of the Hadley circulation, air rises above the ITCZ to create a low pressure zone, characterized by high humidity and rainfall. Further north and south of this zone air begins to sink. As air sinks, it becomes warmer. Remember warm air can hold much more water vapour than cold air. As a result of its warming its relative humidity falls and moisture gets locked inside the warm air. The air continue to sink warming further. The resulting atmospheric conditions are hot, dry, calm and clear skies with high pressure, called Tropical Anticyclones.Theoretically there is more moisture in the air at these latitudes than above the British Isles but you just can’t see it. Over time the ITCZ migrates north and south and with it we see the migration of the warm dry highs.

1. Tropical Rainforest or Equatorial Climate

The Equatorial Climate is characterized by hot average temperature all year round and high monthly precipitation, typically no less than 60 mm a month with annual precipitation tending to be over 2000 mm. The diurnal temperature range is greater than the annual temperature range.
The reason for this regular climate is due to a feedback between low pressure convectional processes that result from the high altitude of the sun (ITCZ) and the high levels of soil moisture and interception of rainfall from the dense vegetation cover leading to transpiration. This feedback leads to a repetitive climate pattern of hot humid air, dry but misty mornings and late afternoon downpours and convectional storms.

The Equatorial Climate is easily recognizable in its climate graph. Singapore’s climate can be seen to have high flat temperature line (above 25°C) all year round and rainfall of no less than 150 mm in the month, reaching a maximum of 270 mm in December. It’s temperature range is just 2°C and its monthly rainfall minimum/maximum is 150mm/270mm.

2. Tropical Monsoon Climate

Tropical Monsoon Climates are relatively rare. They have a monthly mean temperature of above 18°C and feature wet and dry seasons as described above. Unlike Tropical Wet and Dry Climates however, a Tropical Monsoon Climate experiences greater than 1000 mm of rainfall in the year.
In addition a Tropical Monsoon Climate tends to see less variance in temperatures during the course of the year. This climate has a driest month which nearly always occurs at or soon after the “winter” solstice.
Tropical Monsoon Climate can come in two distinct forms. The first features wet and dry seasons, with less pronounced dry seasons. Regions with this form of Tropical Monsoon Climate typically see significant amounts of rain falling during the wet season, usually in the form of frequent thunderstorms with a less pronounced dry season. The second form of Tropical Monsoon Climate features wet and dry seasons, with extraordinarily rainy wet seasons and more pronounced dry seasons, similar to that of Dry and Wet Tropical Climates. However, the dry season is followed by a sustained period of extraordinary rainfall. In some instances, in excess of 1,000 mm of precipitation is observed per month for two or more consecutive months.

Areas which experience Tropical Monsoon Climate are affected by monsoon winds which blow in from the sea in summer and bring with them the seasonal rain. These can occur in both hot and cooler areas but are most commonly found in parts of Asia, the Indian Subcontinent and other areas around the Pacific Ocean. These seasonal winds are drawn into the continental interiors due to the intense heating of the land. In the wet monsoon season warm moist air is drawn into India from the Indian Ocean. The Monsoon dry season is caused by a reversal of winds due to the migration of the ITCZ south.

3. Tropical Wet and Dry Climate

Tropical Dry and Wet Climates with less than 60 mm in any single month and lower than 1000 mm annual rainfall. They are characterized by dry and wet seasons that relate to their situation in regard to the equator and the migration of the ITCZ.
Effectively as the ITCZ migrates away from the equator a zone of low pressure and converging air tracks it. At this zone of rising air seasonal rain occurs due to convectional forces. As you can see in the map the location of Tropical Dry and Wet Climates can be found north and south of the Equator within the tropical belt.

TROPICAL REVOLVING STORMS

Tropical revolving storms form over warm tropical waters towards the hot and humid season in close relationship with the migrating ITCZ. Central to the formation are converging trade winds and the development of low pressure troughs along the ITCZ.
This in turn creates strong divergence that feeds into the formation of tropical depressions. These tropical depressions can cluster around a low trough. As the convergence becomes stronger they become more organised and revolve around each other to form tropical cyclones.
Tropical Cyclones are known by different terms. Tropical cyclones in the Indian Ocean, Typhoons in the West Pacific and East Asia, Hurricanes in the Atlantic and East Pacific.

Hope you liked our article on Tropical Regions.