Subtropical Ridge

The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during daylight hours caused by the stable atmosphere found near its location. Air flows out from its center toward the upper and lower latitudes of each hemisphere, creating both the trade winds and the westerlies. It moves poleward during the summer, reaching its most northern latitude in early fall, before moving equatorward during the cold season. The ENSO climate cycle can displace the subtropical ridge, with La Niñas allowing for a more northerly axis for the ridge, while El Niños show flatter, more southerly ridges. The change of the ridge position during ENSO cycles changes tracks of tropical cyclones that form around their southern and western peripheries. As the subtropical ridge varies in position and strength, it can enhance or depress monsoon regimes around their southern periphery.