In addition to the wave patterns on upper-level charts, closed circulations (lows and highs) also exist. The vertical extent and slope of these systems were discussed in Unit 3, and at this time it might help if you quickly review that material. Basically, these highs and lows are classified according to the vertical variation in their temperature patterns.

l The semipermanent highs (warm core) and lows (cold core) maintain their closed circulations well into the upper troposphere. They are generally stationary with nearly vertical axes.

. Tropical cyclones and thermal lows are classified as warm-core systems, while the major high-pressure systems of Canada and Siberia are cold core. These warm-core systems are very shallow with the exception of mature tropical cyclones, and their closed circulations are con-fined to the lower half of the troposphere, disappearing with height.

. The dynamic migratory systems, like the semipermanent systems, also retain their closed circulations to appreciable altitudes. The lows slope upward toward the coldest tropospheric air (usually northwest of the surface low), and the highs slope toward the warmest tropospheric air (usually southwest of the surface high). In their final stages of development, those dynamic lows that fully occlude become cold-core with practically vertical axes. The intensification process of dynamic highs is similar to that of the lows, although we dont classify it as an occluding process. It results in a vertically stacked warm-core system.

These dynamic systems also have a relation-ship with the strongest belt of westerly winds. Dynamic lows are normally poleward of the strongest westerlies, while the dynamic highs are normally equatorward of these winds. Occasionally, this situation gets reversed and a dynamic low ends upon the equatorward side and a high on the poleward side. Highs and lows in this abnormal position are termed CUTOFF CENTERS.

Learning Objective: Define cutoff highs and lows, blocks, zonal and meridional flow, and the jet stream as they relate to upper-air charts.

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