Intertropical Convergence Zone

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Two hemispheres trawind's form the floorboard of the convergence zone of airflow, convergence is also called the equator, English abbreviation for the ITCZ. As a result of this zone region near the pressure ratio is low, has called the equatorial trough. It is one of the important large tropical weather systems, the life, strong or weak, move, change, to the tropics has enormous influence on the long, medium and short-term changes in the weather.

Intertropical convergence zone (see photo), can be divided into two types: in the northern hemisphere summer, northeast trawind's position by north, southern hemisphere after the southeast trade winds across the equator is influenced by the coriolis force, steering and southwest, the southwest and northeast trawind meet and form the intertropical convergence zone, as a result of the activities in the Arabian sea and the west Pacific monsoon region, often called monsoon convergence. Region in the eastern Pacific and Atlantic ocean and the southern hemisphere trade trade winds in the northern hemisphere meet directly, and at this time of convergence, often referred to as trade wind convergence. Accordingly, the equatorial trough are often divided into monsoon trough and the trade wind trough. In intertropical convergence zone of generation and development of convective clouds are common, so it often correspond to the convective clouds belt on satellite cloud pictures.

Formation mechanism of intertropical convergence zone is the world's major heat source area, its formation mechanism, is one of the important issues of tropical meteorology. There are three main kinds of forming mechanism of: (1) SST. Intertropical convergence zone there are trend to move to a warm SST. (2) the second category of conditions (sexual) instability mechanism. Such as like mechanism of occurrence and development of typhoon, as long as the south area of the southwest low-level convergence to strengthen, form the convergence and the cyclonic vorticity zone, relying on the boundary layer friction convergence and the release of water vapor latent heat, can make a wide range of convective clouds constantly stimulate the development of itself up. (3) critical latitude boundary layer mechanism. Before the two mechanisms in zonal symmetry, no wave function can be generated, but the actual state is intertropical convergence bring fluctuate often overlay. Actual fluctuation theory to prove: the angular frequency if at a particular latitude and the frequency of the coriolis parameter is the same, within the boundary layer of the latitude will produce very big upward movement, the formation of convergence, the latitude is called critical latitude, north latitude in the actual calculation about 10 °.

Seasonal change of seasonal change of intertropical convergence zone position, mainly is the change of the monsoon convergence, trade wind convergence location change is not obvious. Monsoon convergence in winter in the southern hemisphere; Summer in the northern hemisphere, from Africa to the western Pacific east longitude 150 °. Especially in October, a monsoon convergence in the north and south hemisphere. According to the meteorological satellite cloud image analysis: west longitude 130 ° until America's shores of the east Pacific Ocean, east of late winter and spring also can appear double convergence cloud band; In the western Pacific Ocean, west of west longitude 160 °, has dual convergence cloud with all the year round. Don't spend the winter hemisphere cloud always weaker than summer hemisphere, so cloud belt of the western Pacific region, mainly in the southern hemisphere winter and summer in the northern hemisphere. In the northern hemisphere summer, Asia, Africa, the continental monsoon convergence, position the north; In winter, the south of equator 20 °. Monsoon convergence of seasonal change with sea and land distribution and terrain characteristics have close relationship.

Monsoon convergence in the monsoon convergence not only caused by PianBeiFeng north and south side PianNaFeng convergence, and in the southwest of the south and the strong wind speed convergence. So in the south of surface wind direction convergence, there is a wide range of convective activity, by water vapor condensation latent heat release in the troposphere, upper warmer. Summer intertropical convergence zone in the western Pacific south side of the mean monthly precipitation of 300 ~ 400 mm, and the bay of Bengal area monsoon convergence can reach more than 600 mm. Due to the release of a large latent heat, so the monsoon convergence is one of the main atmospheric heat source. Monsoon convergence after being heated, stimulate the production of the tropical system in this area, such as typhoon, monsoon convergence of convective clouds, etc., here often have hundreds of convective clouds gather into a cloud (see tropical clouds, the weather changes, the average daily rainfall of up to 20 mm. On the satellite cloud image, monsoon convergence is often shown as a thousands of kilometers, huge cloud band made up of many clouds.

Strong updraft in the monsoon convergence to reach high altitude, divided into two, one to the north, sinking in the subtropical region, composition, circulation; The other is moved to the southern hemisphere. South of the equator sinking 10 ° ~ 20 °, and then flow to the northern hemisphere, in the form of low-level cross-equatorial flow of monsoon region characteristic of the monsoon meridian circulation (see atmospheric circulation).

Trawind's convergence due to the trade wind convergence is only composed of southeast and northeast wind flow convergence, the coupling strength is far less than the monsoon convergence, and therefore have relatively narrow cloud with weaker, convective clouds are also less, its strong tropical weather systems such as the typhoon is less. In July the east Pacific Ocean trade winds convergence month average rainfall of about 200 mm, the eastern Atlantic, 300 millimeters. In the tropical Atlantic, besides can produce easterly wave on the northeast trade wind, also can produce tropical disturbance in convergence belt, the former average occurred in 12 ° north latitude, the latter in 7 ° north latitude. Intertropical convergence with disturbance, sometimes known as the intertropical convergence zone. While in the western Pacific, in addition to the east on the northeast trade wind storm, only in the northeast, south trade winds and convergence damaged only around 10 ° north latitude of easterly wave, sometimes called it the equatorial wave.

Due to the tropical area meteorological observatory (and shipping) few and far between, based on the analysis of the field wind field of the location of the intertropical convergence zone and its change with the satellite cloud image analysis result is not completely consistent, therefore, about the structure of the intertropical convergence zone and the weather, the formation and change and other issues remain to be further accumulated data in-depth study.