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Intertropical Convergence Zone

Intertropical Convergence Zone, ITCZ

The Intertropical Convergence Zone (ITCZ) is located in an area between 15 ° latitude N and S of the equator. It is a place where north-east and south-east tradewinds meet and together with incoming solar radiation they can create some serious convective weather. The ITCZ is part of the global circulation dividing the planets weather systems into the northern and southern hemisphere.

This area is characterized by strong convective weather consisting of Cumulus and Cumulonimbus clouds with turbulence and heavy rain at times. The exact location varies with the seasons throughout the year and follows more or less the sun's zenith point.

Aircraft crews passing through this area need to be fully aware of the meteorological effects of flying through the ITCZ and its related tradewinds.

ITCZ properties

The ITCZ is characterized by a number of properties: with low intensity tradewinds the resulting Cumulus (Cu) and Cumulonimbus (Cb) are readily isolated from each other. But with much stronger tradewinds, you will see lines of very active Cb's and other clouds at higher levels in the area.

Cloud tops

Cloud tops may reach FL550 or 55000 feet. Even airliners will have to fly around these massive Cb's. Pilots of lower flying aircraft will sometimes have to wait out the weather and avoid the periods the ITCZ is the most active. The ITCZ also sees some diurnal action so you will notice more activity during the afternoon from around 3 to 4 pm (15:00 - 16:00) local time.

Zone width

The width of the ITCZ varies from day to day and together with seasonal influences it can reach an area of 300 to 500 nm wide. Which will result in crossing the ITCZ being a good day of flying for a regular 100 kt general aviation aircraft.

ITCZ Genesis

Intertropical Convergence Zone GenesisEarth\'s Wind Patterns
Earth's Wind Patterns (source: WUWT)

The ITCZ find its origin in the tradewinds from the north- and south-east around the equator. These winds meet and combined with incoming solar radiation, forced rising of possibly unstable air and convective action is the result. With enough moisture, clouds and instability thunderstorms may eventually develop easily here.

Tradewinds

As already mentioned, these winds will come generally from the north-east in the northern hemisphere and from the south-east in the southern hemisphere. Land mass and orographic features will influence their final direction. The base of the clouds will be around 2500 to 3500 feet. When these winds blow over the ocean they pick up moisture and clouds will rise to higher altitudes than over land usually.

Location

The location where these tradewinds meet is called the Intertropical Convergence Zone and aircraft and crew flying through the area will need to be prepared for these convective situations. Sometimes with serious effects to the safety of the flight.

ITCZ Effects

The type of cloud development in the ITCZ consists basically of convective nature, one may expect the same hazards as with common Cumulus (Cu) and Cumulonimbus (Cb) clouds. You will experience turbulence (sometimes heavy), downbursts, heavy rain, icing and hail during short periods of time. With these Cb's, thunder and lightning may be on the menu too!
More information on Cb's and turbulence can be found in our article on flight hazards.

Intensity

convective breakthrough

Due to the high angle of incoming solar radiation combined with high moisture content as a result to higher temperatures, especially over large oceanic regions, you may expect the convective intensity to be much higher than at other higher latitudes (> 30° latitude north and south).

At certain times, convective breakthrough into the tropopause has been observed when the air is very unstable with lots of moisture. This can be important for air transport category aircraft as they usually tend to fly at or near these levels.

Tropopause

The altitude of the tropopause varies with latitude, it is lower at the poles (~20000 feet) and all the way up to 60000 feet at the equator. From the tropopause and higher up the outside air temperature is somewhat constant with rising altitude. This is where you also will find JET streams pushing the weather systems around the planet from west to east.
More information in our dedicated article on JET streams.

Conclusion

The ITCZ is a tropical weather phenomenon in an area around the equator with possible serious implications to aircraft flying through the area. Airline crews and general aviation pilots wishing to pass this region should properly prepare themselves by studying the phenomena, their aircraft and thoroughly inform passengers before crossing as to ensure the safety of the flight and the well being of the passengers.

Written by EAI.


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