Secondary Circulations in the Atmosphere

Weather systems comprising the secondary circulation of the atmosphereAtmosphere are steered by the primary circulation and include air masses and transitory cyclones and anticyclonesand anticyclones. Air masses are broad expanses of relatively homogeneous thermal and humidityand humidity properties that move within the general circulation to create weather patterns. In places whereHumidityand Africaand air masses air masses with greatly different properties interact, usually in the mid-latitudes, fronts form and are pushed along by the Rossby wavesHumidityand Africaand Rossby waves andFront (weather)polar polar frontJet streamAfrican easterlypolar front jet stream embedded within the mid-latitude westerliesWindmid-latitude westerlies. These fronts often trail from a counter-clockwise- and-inward-rotating (in the Northern HemisphereCounter-clockwise circulationcyclones in Northern Hemisphere), surface-based, low-pressure system known as a mid-latitude wave cycloneand cyclone, which can form for numerous reasons, including localized “hot spots,” vertical stretching of air as it descends a mountain slope, and position relative to Rossby wave ridges and troughs. Anomalous steering flow in the mid-latitudes can causecutoff low cutoff lows or blocking patterns that make weather patterns persist for days to weeks. In the tropics, an important secondary circulation system is the easterly wave, whichClockwise circulationcyclones in Southern Hemisphereeasterly wave trough axis in Southern Hemisphere is a kink in the trade windWindwesterlies, mid-latitude flow. The eastern side of theCounter-clockwise circulationeasterly wave trough axis in Northern Hemisphere easterly wave trough axisEasterly wavetrough axis supports storm intensification into tropicaltyphoons depressionshurricanes, tropical storms, and hurricanes/typhoonsHurricaneand Atlantic Multidecadal Oscillationas secondary circulations, but the western side suppresses storm intensification.