Atmos 5110/6110 Lab VI: PV Thinking

Objectives:

PV thinking is a powerful tool for examining the evolution of the large scale atmospheric flow and provides insight into the life cycle of baroclinic waves, tropopause folds, and tropical-extratropical interactions. In this lab we:
  • learn how to identify cyclonic and anticyclonic PV anomalies, PV walls, trough fractures and mergers, and tropopause folds,
  • begin to understand the relationship between PV, dynamic tropopause potential temperature, and dynamic tropopause pressure, and
  • use PV thinking to understand large-scale flow evolution.

Part 1

Select a recent GFS model forecast from the weather.utah.edu web page. Examine the 180 h forecast loop of 315 K potential vorticity over the Northern Hemisphere and identify examples of:
  • a cyclonic PV anomaly,
  • an anticyclonic PV anomaly,
  • trough fracture, and
  • trough merger
If necessary, use past model forecasts to find a good example. Save the appropriate images (you should only need 2 images to identify each of the above features) and print. Annotate the images to identify each example.

Part 2

Examine the 180 h forecast loop of DT potential temperature (theta) over the Northern Hemisphere. Determine the potential temperature of the DT in the regions of the cyclonic and anticyclonic PV anomalies identified above. Briefly explain the relationship between cyclonic and anticyclonic PV anomalies and dynamic tropopause potential temperature.

Part 3

Examine the 180 h forecast loop of Dynamic Tropopause Pressure over the Northern Hemisphere. Determine the dynamic tropopause pressure in the regions of the cyclonic and anticyclonic PV anomalies identified above. Briefly explain the relationship between cyclonic and anticyclonic PV anomalies and dynamic tropopause pressure.

Part 4:

Using IDV, plot a cross section through a cyclonic PV anomaly. Make sure that your cross section extends significantly on either side of the PV anomaly. Be sure to include PV, potential temperature, and wind analyses along the section. Clearly identify:
  • the PV wall,
  • the jet core, and
  • a tropopause fold.
Save the appropriate images (you may need to try several different times to find a cross-section with a tropopause fold). Summarize the relationship between cyclonic/anticyclonic PV anomalies and upper-level waves.