• Previously, considered WCB airflow

• Now consider a second cloud band, the cold conveyor belt (CCB) can be created by a mature stage frontal cyclone

• first example: fig. 12.17 (highly schematic)
  1. fig. 12.17a shows parcels near low developing more cyclonic curvature as system intensifies
  2. fig 12.17b: air in CCB originates on cold air side of a warm front
  3. precip formed in the WCB falls into the CCB partly evaporates, elevating the moisture of the CCB air.
  4. CCB crosses under the WCB and (following the lower tropospheric winds) is wrapped around to the N and W of the surface low.
     Note that this motion is towards colder air, so surfaces must curve upwards. Hence, the air parcels are forced to rise.

• Relation to "occlusion" discussion earlier in course:
  • recall description that thickness ridge and surface trough come from warm sector air migrating around to NW of the junction between the warm and cold fronts at the surface. This is similar to the bending seen in the furthest right diagram in fig 12.17a.
  • the comma cloud seen on satellite imagery extends even further to the west: that is the CCB.
  • also note that part of the CCB could lie underneath the WCB that is associated with the occlusion

• Second example: figs 12.18 and 12.19
  • fig 12.18b satellite image:
    • WCB edge marked by letter C in three places -- much like seen in previous book section
    • CCB visible to the west, marked by CC -- note how NW edge of CCB becomes quite high (from cirrus cloud and from large shadow cast)
    • dry tongue (DT) behind cold front
  • fig 12.18a schematic to represent example in 12.18b
    • note motion accross P values of representative _W surfaces, a different one for each of the 3 regions: WCB (rising) , CCB (rising), and DT (sinking).
    • CCB motion clearly consistent with location of midlevel closed low to the south (L₅)
    • satellite analysis: note positions of:
      • 500 mb low center near southern tip (cloud cusp) of the CCB
      • surface low center near junction of south edge of CCB and west edge of the WCB
  • fig 12.19a is schematic of clouds in 12.18a, also shows the location of cross section in fig 12.19b
  • fig 12.19b is cross section along axis of CCB. Notice these items anticipated from fig 12.17:
    • deep cloud (WCB & CCB) to the right and below the jet (circled J)
    • CCB air rises even faster than the surfaces (arrows)
    • CCB clouds extend to higher elevations downstream (west edge)

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