Atmospheric Flow

Question 1

What are the components of air flow?

Answer 1

1. Translation
2. Rotation (clockwise or anticlockwise)
3. Divergence
4. Convergence
5. Deformation

Question 2

Define translation

Answer 2

The movement of a parcel of air from A to B (in any direction) without rotating/altering its shape or volume.

Question 3

Define Divergence

Answer 3

Occurs when a body of air expands horizontally. More precisely, a fixed volume of air is divergent when horizontal outflow EXCEEDS the horizontal inflow.

Question 4

Define convergence

Answer 4

Occurs when a body of air contracts horizontally. More precisely, a fixed volume of air is convergent when horizontal inflow EXCEEDS the horizontal inflow.

Question 5

Define confluence and diffluence and describe how they work relative to conversion/diversion

Answer 5

Confluence: Wind streamlines coming together
Diffluence: Wind streamlines moving apart.
-Both can influence conversion/diversion generated, however, Confluence/Diffluence can exist without conversion/diversion.

Question 6

Generic rules for Divergence and Convergence (3)

Answer 6

1. The net inflow must equal the net outflow.
2. Divergence and convergence only work within the horizontal.
3. The horizontal deficit/excess is made up for by vertical inflow (DIV) or outflow (CON)

Question 7

Describe how conversion works in a parcel of air

Answer 7

1. Inflow of 20kts in horizontal
2. Outflow of 10kts in the horizontal
3. Therefore a loss of 10kts vertically.
   - Loss of 10kts in the vertical induces low pressure system at the SFC. Tropopause will sink.

Question 8

Describe how diversion works in a parcel of air

Answer 8

1. Inflow of 10kts in horizontal
2. Outflow of 20kts in horizontal
3. Therefore a gain of 10kts vertically
   - Gain of 10kts in the vertical induces high pressure system at the SFC. Tropopause will rise

Question 9

Why are conversion and diversion important?

Answer 9

Because they lead to vertical motions in the atmosphere, which in turn results in cloud and precip formation, as well as cloud suppression.

Question 10

What causes conversion and diversion?

Answer 10

Occur due to changes in absolute vorticity.

Question 11

Define curvature vorticity

Answer 11

Occurs in the bends of both anticyclones and cyclones and rotates in the direction of the wind around the pressure system.

Question 12

Define Shear vorticity

Answer 12

Occurs in straight isobars around both Low and High pressure systems, and occurs due to the difference in faster and slower moving air. (like a barrier jet).

Question 13

Define relative vorticity

Answer 13

The sum of the curvature and shear vorticities gives the relative vorticity. Which is relative to the SFC of the earth and can be cyclonic or anticyclonic in nature.

Question 14

Define the Earths vorticity

Answer 14

Arises from the shear produced by the earths rotation around its axis, and increases in strength with latitude (towards the poles).

Question 15

Define Absolute vorticity

(3) points about absolute vorticity

Answer 15

Is the sum of relative vorticity plus the earths vorticity.

1. Earths vorticity is much greater than Relative vorticity.
2. Earths vorticity is always cyclonic (in Southern Hemisphere)
3. Therefore Absolute vorticity is ALWAYS cyclonic in nature.

Question 16

What does change in Absolute vorticity cause?

Answer 16

1. Conversion/diversion are affected
2. Ascent or subsidence of the columns of air above these systems are affected (High/Low pressure systems)
3. Therefore the development or decay of cloud/precip is affected.

Question 17

General rule for Absolute vorticity

Answer 17

1. Increase in AV = Convergence (Low pressure at SFC)

2. Decrease in AV = Divergence (High pressure at SFC)

Question 18

Define Deformation

Answer 18

Occurs when a body of air changes its shape. When it happens, both confluence and diffluence are present. (think of CT4 diagrams)

Question 19

Why is deformation important

Answer 19

1. Important in production of fronts when confluence brings isotherms together, increasing temp gradient, producing front.
2. Therefore has a major role in shaping the cloud system in the atmosphere.