The
subtropical ridge, also known as the
subtropical high or
horse latitudes, is a significant belt of atmospheric
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. The subtropical ridge 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 northern hemisphere 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 equatorward and western peripheries. As the subtropical ridge varies in position and strength, it can enhance or depress
monsoon regimes around their low-latitude periphery. The term "
horse latitudes" refers to and is synonymous with the subtropical ridge or subtropical high.