High-pressure systems form due to downward motion through the
troposphere, the
atmospheric layer where
weather occurs. Preferred areas within a
synoptic flow pattern in higher levels of the troposphere are beneath the western side of troughs. On weather maps, these areas show converging winds (isotachs), also known as
confluence, or converging height lines near or above the level of non-divergence, which is near the 500 hPa pressure surface about midway up through the troposphere. On weather maps, high-pressure centers are associated with the letter H placed within the
isobar with the highest pressure value. On constant pressure upper level charts, it is located within the highest height line contour. == See also ==