Synoptic meteorology and tropical weather systems, including the ITCZ and West African climatology
This domain tests synoptic analysis in the tropics, the ITCZ and ITD, easterly waves, monsoon flow and the West African seasonal cycle.
ITCZ and monsoon
The ITCZ is a belt of convergence, low pressure and deep convection near the thermal equator; its surface position is often analysed as the Intertropical Discontinuity (ITD) between dry Harmattan air to the north and moist monsoon air to the south. It migrates south in January and north in July–August. West Africa’s monsoon is driven by land–sea heating contrast and the subtropical ridge; moist south-westerly flow feeds convection. African easterly waves move westwards and often trigger squall lines and convection.
Synoptic features
Tropical weather includes scattered convection, mesoscale convective systems, squall lines, tropical cyclones and dust haze. Upper-air charts show the tropical easterly jet and subtropical ridge. Unlike mid-latitudes, temperature gradients are weak; moisture and convergence are better diagnostics.
Worked example
In January, Kano (about 12°N) is usually north of the ITD and experiences dry Harmattan dust haze; Lagos (about 6.5°N) is closer to the moist monsoon and can have humid haze or coastal cloud. In July, the ITD is farther north, so Kano receives monsoon rain and Lagos is in the wet season. The same country can therefore have two very different route weather patterns at the same time. Use ITD position, dew point and wind direction, not latitude alone.
Traps
The ITCZ is not a continuous line of thunderstorms. Monsoon is a seasonal wind reversal, not just rain. Easterly waves move east to west. Dust haze is not fog.