Pressure system minima in the pressure field. The minima are called low-pressure areas, and the maxima are called high-pressure areas. A "High" is often shown as H, and a "low" is shown as L. Elongated areas of low pressure, or troughs, are sometimes plotted as thick, brown dashed lines down the trough axis. Isobars are commonly used to place surface boundaries from the horse latitudes poleward, while streamline analyses are used in the tropics. A streamline analysis is a series of arrows oriented parallel to wind, showing wind motion within a certain geographic area. Cs depict cyclonic flow or likely areas of
High-pressure area that has been uplifted at the equator. As the hot air rises it cools, losing moisture; it is then transported poleward where it descends, creating the high-pressure area. This is part of the Hadley cell circulation and is known as the subtropical ridge or subtropical high, and is strongest in the summer. The subtropical ridge is a warm core high-pressure system, meaning it strengthens with height. Many of the world's deserts are caused by these climatological high-pressure systems. Some climatological high-pressure areas acquire regionally based names. The land-based Siberian High often remains quasi-stationary for more than a month during the