Theoretical Principles and Conceptual Models for Jets and Fronts

Theoretical Principles and Conceptual Models for Jets and Fronts


An underlying premise of most conceptual models of jet circulation systems is that they obey quasi-geostrophic or semi-geostrophic dynamics. In these dynamical systems, the balanced (geostrophic) part of the flow creates a thermal wind imbalance, while the unbalanced (ageostrophic ) part of the flow acts to restore balance. In the process of restoring balance, patterns of ageostrophic acceleration are created. This naturally leads to patterns of divergence, and accordingly, vertical motions important to understanding the distribution of clouds and precipitation. The vertical motions are directly associated with the ageostrophic motions, and together form two-dimensional vertical circulations either transverse or parallel to the jet. These vertical circulations are responsible not only for maintaining thermal wind balance, but also for spinning up geostrophic vorticity and the creation/destruction of upper-level fronts and jets.

This discussion is organized along the following topics:

1. Review of the Primitive Equations

2. The Straight Jet Model: Four-Quadrants of Vertical Motion

3. The Highly Curved Jet Model: Two Cells of Vertical Motion

4. Combinations of Straight Jet, Curvature, and Thermal Advection Dynamics

5. Anafront and Katafront Models

6. Narrow Cold-Frontal Rainbands: The Anafront With a Low-Level Jet

7. Split Fronts and Cold Fronts Aloft

Note: Follow this link for excellent references on the topics of jet streak dynamics, ageostrophic circulation systems, and frontal conceptual models.