Complex sentence: The Harmattan blows during the dry season, which occurs during the lowest-sun months, when the subtropical ridge of high pressure stays over the central Sahara Desert and when the low-pressure Intertropical Convergence Zone (ITCZ) stays over the Gulf of Guinea.
Split into simpler sentences: The Harmattan blows during the dry season, which occurs during the lowest-sun months. In this season the subtropical ridge of high pressure stays over the central Sahara Desert and the low-pressure Intertropical Convergence Zone (ITCZ) stays over the Gulf of Guinea.