In these areas, the air is gently sinking from high altitudes toward the earth's surface. The sinking of the air results in areas of high barometric pressure and weak winds. These high-pressure areas shift farther north when it is summer in the Northern Hemisphere. They shift farther south when it is summer in the Southern Hemisphere. The horse latitudes coincide with the subtropical maritime anticyclones, or subtropical highs.
Subtropical highs are large areas of high pressure that occur over the oceans.
Changes in their size, shape, position, or direction influence weather conditions in many parts of the world. The general circulation of air causes cold air over the North and South poles to sink, forming high-pressure areas known as the polar anticyclones. But since this cold region has frequent storms, periods of calms are not so persistent as in warmer regions of calms. The doldrums are ocean regions centered slightly north of the equator. One area of doldrums lies in the Pacific Ocean extending westward from Central America and South America to the Philippines.