CONCEPT OF CONVEYER BELT IN FRONTS AND WAVES

1. CONCEPT OF CONVEYER BELT IN FRONTS AND WAVES

7. CONCEPTUAL MODEL • Vertical motion is responsible for layered clouds. • Not measured directly. • Indirectly measured from Horizontal winds NWP. • Normal charts only depict horizontal motion. • Clouds patterns reflect relative wind flow.

8. CONCEPTUAL MODEL • Relative streamlines are diff. • Near the trough the relative streamlines are anti cyclonically curved. • Depends on relative speeds. • Wind speed at the axis is same as trough speed.

9. CONCEPTUAL MODEL • If wind speed is greater some air will flow across axis --DCA‘ • Air moves in 3-D. • Actual streamline has to be visualized in 3-D. • A A‘ is rising air ahead of trough. • DD‘ is descending air behind trough. • These are conveyor belts.

10. CONCEPTUAL MODEL • Commonly 1-3 km deep. • 200-300 km wide. • Often 1000s of km long. • A A‘-coming from southern lat is called warm conveyor belt – main cloud producing airflow. • In saturated air moist isentropic surface is to be used.

11. Warm Conveyor Belt (WCB)

12. Warm Conveyor Belt (WCB) • Sharp western edge. • General rule – air does not cross sharp cloud boundary at the level of cloud. • Ragged edge indicates air flowing into and out of cloud. • Cloud band may be uniformly wide or broaden as conveyor belt air ascends.

13. Warm Conveyor Belt (WCB) • Detailed view with respect to trough ridge system of WCB as an isentropic surface. • SEly flow at X moving north curving to right. • Anti cyclonic curvature reflects Ci level winds. • Equator ward half represents veering of wind with ht. (warm advection).

14. Warm Conveyor Belt (WCB) • The surface is isentropic. • Not all rising air is cloudy-will depend on RH. • Within frontal cloud band clouds form at discrete layers depending on the history of AM

15. WARM CONVEYOR BELT (WCB) • Saturation at near S. • Thereafter rises along moist isentropic surface to U tropo. • Air moving along limiting streamline LL (nearest to cold air along axis of deformation) undergoes greatest overall ascent. • Precipitation is heaviest where trajectories rise rapidly post saturation. • Generally wind speed maxima exist near cloud edge in UTropo. • Middle level maxima may be found inside WCB cloud.

16. Warm Conveyor Belt (WCB) • (a) straight flow (an active cold front). • (b) Anti cyclonically curved flow (an active warm front). • (c) s-shaped flow after cyclogenesis (occluded system). • Prior to cyclogenesis WCB is normally curved Anti cyclonically. • Dev of s-shaped edge is due to cyclonic curvature in relative wind streamlines at the below cloud level.

17. Cold Conveyor Belt (CCB) • Advent of closed circulation in lower tropo results in easterly airflow pole ward of surface low. • Causing air ahead of the warm front to move beneath the limiting streamline. (CCB). • CC is CCB.

18. Cold Conveyor Belt (CCB) • CCB ascends towards west as it moves out from beneath the WCB. • This produces a separate cloud band west of WCB, forming a comma shape to overall cloud pattern. • CCB is moistened both by contact with ground of evaporation of pptn from WCB.

19. Cold Conveyor Belt (CCB) • Casual inspection of satellite image might suggest CCB cloud is part of cloud shield associated with WCB. • Careful analysis shows separate features. • Shadow at CC indicates this.

20. Thank You

21. 300 K Surface Pressure in mb Wind blowing from low pressure to high pressure- air descending Wind blowing from high pressure to low pressure- air ascending