What are large, semi-permanent high-pressure systems found at about 30 degrees latitude called?

Large, semi-permanent high-pressure systems located around 30 degrees latitude are known as subtropical highs. These systems are characterized by descending air, which results in clear skies and dry conditions typical of many desert regions.

The subtropical highs form as warm air rises near the equator, with the cooler, denser air then descending around 30 degrees latitude. This descending air creates a stable atmospheric condition that suppresses cloud formation and leads to high-pressure conditions. The subtropical highs play a crucial role in global wind patterns and climate, influencing the location of major deserts.

Trade winds, which originate from subtropical highs, blow from east to west in the tropics but do not themselves describe the high-pressure systems. Hadley cells refer to the large-scale atmospheric circulation pattern that includes the rising and sinking of air between the equator and the subtropics. The westerlies are prevailing winds found in the mid-latitudes that flow from west to east but are not specific to the high-pressure systems around 30 degrees latitude.