Forcing for Upward Motion

1. Synoptic Scale: QG-Omega Equation

Vertical Motion at Given Level (say, in the mid-troposphere)

Prop

 To

Vorticity Advection *

*(Really, differential vorticity advection centered at the level)

and/or

Temperature Advection at that Level

and/or

Sensible Temperature Change at that Level

and/or

Friction*

*(Really, differential friction centered at the level)

 

 

Term A

 

Term B

 

Term C

 

Term D

  Description

 

 

Vertical motion

Related to Divergence/Convergence

aloft associated with instantaneous geometry of the pattern (e.g., troughs/ ridges)

 

 

Vertical motion

Related to Divergence/Convergence

aloft associated with thermal (temperature advection) development of the pattern (e.g., pressure rises/falls)

 

  

Vertical motion

Related to Divergence/Convergence

aloft associated with thermal (sensible heating/cooling) development of the pattern (e.g., pressure rises/falls)

 

 

 

Visualization

 

Vertical Motion Associated With

"Dynamic*" Surface Pressure Systems
(Terms A and B)

*Generally connected to the stronger flow patterns associated with jet streams/low level jets etc. of baroclinic systems. However, Term C can modify the effects of Terms and B.

 

Vertical Motion Associated With "Thermal*" Surface Pressure Systems

(Term C)

*Seen uniquely only when Terms A and B are small or negligible. Generally connected to the usually weaker flow patterns (with no temperature advection) of barotropic systems.

 

The magnitude of the vertical velocity at a given level is directly proportional to (Term A + Term B + Term C + Term D). Note that meteorologists tend to look at each of these terms in isolation from one another. In the real atmosphere, Term C accounts alone for vertical velocity fields (and pressure patterns) only if the other terms are small/negligible, for example, during the summer over the middle latitude continents.

2. Non-synoptic Scale (Not what forecasters refer to as "Dynamics")

1.     Fronts (Solenoidally-direct): Upward in warm air, downward in cold air

2.     Thermodynamics: Spontaneous Upward Motion for Rising Air Parcels Above LFC