Wednesday, January 22, 2014

  • Near the equator, from about 5° north and 5° south, the northeast trade winds and southeast trade winds converge in a low pressure zone known as the Intertropical Convergence Zone or ITCZ. 
    • Solar heating in the region forces air to rise through convection which results in a plethora of precipitation. The ITCZ is a key component of the global circulation system.
    • Weather stations in the equatorial region record precipitation up to 200 days each year, making the equatorial and ITC zones the wettest on the planet. The equatorial region lacks a dry season and is constantly hot and humid.
    • The location of the ITCZ varies throughout the year and while it remains near the equator, the ITCZ over land ventures farther north or south than the ITCZ over the oceans due to the variation in 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.
    • In Africa, the ITCZ is located just south of the Sahel at about 10°, dumping rain on the region to the south of the desert.
    • The Intertropical Convergence Zone has been called the doldrums by sailors due to the lack of horizontal air movement (the air simply rises with convection). The ITCZ is also known as the Equatorial Convergence Zone or Intertropical Front.
    • There's a diurnal cycle to the precipitation in the ITCZ. Clouds form in the late morning and early afternoon hours and then by 3 to 4 p.m., the hottest time of the day, convectional thunderstorms form and precipitation begins. These storms are generally short in duration.

    Why do Doldrums occur ?

    • In the Intertropical Convergence Zone, the northern and southern trade winds come together. 
    • Because of the rotation of the Earth, the winds cannot really cross the equator without losing energy. 
    • Instead of continuing over the Earth horizontally, the winds thus move vertically toward the upper atmosphere. 
    • The heating of the Earth's ocean currents by the sun assists in this process, making the air warmer and letting it rise. 
    • The result is that the Intertropical Convergence Zone has low air pressure near the Earth's surface. 
    • The lack of horizontal wind movement in the region caused sailors to nickname the Intertropical Convergence Zone, "the doldrums."

    Why do Thuderstorms occur in ITCZ ?

    • Rainfall in the Intertropical Convergence Zone typically is not gentle rainfall that lasts for long periods. 
    • Instead, the high amounts of energy from thermal and solar heating cause moisture to condense quickly into clouds in the hottest part of the day. 
    • Circular typhoons thus often form as the air currents move. Some of the strongest winds on the Earth have been recorded in these storms. 
    • Thunderstorms with heavy lightening also are common.

    Why do ITCZ do not have a consistent location ?

    • The Intertropical Convergence Zone is characterized by inconsistent location around the equator. 
    • As the Earth moves with the seasons, the area which receives the highest amount of heat energy from the sun varies. 
    • The thermal equator around which the Intertropical Convergence Zone forms thus moves, depending on the season. 
    • In some cases, this shift can result in the complete reversal of normal trade wind patterns, particularly in the Indian Ocean.


    Role of ITCZ  in monsoons ?

    • Inter Tropical Convergence Zone (ITCZ) The Inter Tropical Convergence Zone (ITCZ) is a low pressure zone located at the equator where trade winds converge, and so, it is a zone where air tends to ascend. 
    • In July, the ITCZ is located around 20ºN latitudes (over the Gangetic plain),  sometimes called the monsoon trough. 
    • This monsoon trough encourages the development of thermal low over north and northwest India. 
    • Due to the shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40ºE and 60ºE longitudes and start blowing from southwest to northeast due to the Coriolis force. It becomes southwest monsoon. 
    • In winter, the ITCZ moves southward, and so the reversal of winds from northeast to south and southwest, takes place. They are called northeast monsoons.


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