Transcript Document
Chapter 8: Air Masses, Fronts, and Middle-Latitude Cyclones Air masses Fronts Middle-latitude cyclones Air Mass Source Regions air mass: an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any altitude source regions: regions dominated by surface high pressure • Because air sinks in high pressure systems, air stays in contact with the surface and acquires its temperature and moisture characteristics. Classification: • Temperature and humidity • Naming conventions Table 8-1, p. 205 Fig. 8-2, p. 206 cP (Continental Polar) and cA (Continental Arctic) Air Masses Continental polar continental Arctic lake effect snows In the continental US, the coldest winter air is associated with cA air masses. mP (Maritime polar) Air Masses Pacific air • mP air often brings rain to the west coast of the US. mT (Maritime Tropical Air Masses) subtropical air Bermuda high • mT air brings hot, muggy air to the eastern US in summer. cT (Continental Tropical Air Masses) Northern Mexico and southwestern U.S. Summer Fronts A transition zone between two air masses of different temperature and/or humidity Stationary Fronts Has essentially no movement, and wind is usually parallel with the stationary front Light precipitation may or may not appear • This terminology was developed by Norwegian meteorologists shortly after World War I. Cold Fronts cold front: Temperature, humidity, clouds and precipitation vertical cross section: slope of 1:50 wind direction differences Warm Fronts overrunning: slope of 1:300 weather changes precipitation patterns vertical cross section Dryline Fig. 8-19, p. 220 Occluded Fronts cold occlusion warm occlusion • Occluded fronts have characteristics of both warm and cold fronts. Polar Front Theory wave cyclone frontal wave open wave warm sector mature cyclone Where Do Mid-Latitude Cyclones Tend to Form? cyclogenesis lee-side low Alberta Clipper • Mid-latitude cyclones specific to certain areas get interesting names: Panhandle hook, nor’easter, Hatteras Low. Northeasters (or nor’easters): develops or intensified off the eastern seaboard of North America then move northeastward along the coast Figure 4, p. 226 Developing Mid-Latitude Cyclones and Anticyclones convergence and divergence • convergence and divergence patterns aloft are extremely important to the development of mid-latitude cyclones Jet Streams and Developing Mid-Latitude Cyclones jet stream jet streak: jet stream core upper-air support • During World War II, the jet stream was used by the Japanese to carry balloon bombs across the Pacific Ocean to North America. Fig. 8-30, p. 231