Mass Movement and Wind

Question 1

What is “The Geostrophic Wind”

Answer 1

In the free atmosphere (500 - 1000m above surface fricton affects), wind tends to blow at right angles to the pressure gradient. It is a balance between pressure gradient force and Coriolis. It is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force

Question 2

How does geostrophic wind work?

Answer 2

Air moves from high pressure to low pressure and turns to the right in the N.Hemisphere until Pgf = Co. True wind almost always differs from geostrophic wind due to other forces such as friction from the ground.

Question 3

When would actual wind equal geostrophic wind?

Answer 3

If there were no friction and isobars were perfectly straight

Question 4

What is Centripetal acceleration?

Answer 4

For a body to follow a curved path there must be an inward acceleration towards the center of rotation.

Question 5

When does air become Sub-geostrophic?

Answer 5

In a low pressure system When Gradient wind < Geostrophic wind

Question 6

When does the air become Super-Geostrophic?

Answer 6

In a High pressure system Gradient wind > Geostrophic wind

Question 7

What are the main kinds of air flow in terms of wind and pressure systems on a global scale?

Answer 7

Divergence / Convergence; Vertical Motion / Vorticity

Question 8

Explain Divergence / Convergence

Answer 8

Air may accelerate (or decelerate), leading to velocity divergence (or convergence). When streamlines of instantaneous air motion spread or squeeze together these are termed diffluence or confluence, respectively.

Question 9

What are confluence and diffluence associated with on terms of air velocity?

Answer 9

Confluence associated with an increase in air velocity and diffluence with a decrease in air velocity.

Question 10

What would happen if all winds were geostrophic?

Answer 10

There could be no convergence or divergence and therefore no weather

Question 11

Explain the importance of vertical motion

Answer 11

Horizontal inflow or outflow near the surface has to be compensated by vertical motion. Air rises above a low pressure cell and subsides over high pressure.

Question 12

Explain vorticity

Answer 12

Vorticity implies rotation or angular velocity of parcels of fluid.

Question 13

What are the three components of vorticity?

Answer 13

Magnitude, direction and sense of rotation

Question 14

What does cyclonic vorticity result from?

Answer 14

May result from the cyclonic curvature of the streamlines, from cyclonic shear (stronger winds on the left hand side of the current).

Question 15

How does anticyclonic vorticity occur?

Answer 15

Anticyclonic curvature of the streamlines, from anticyclonic shear, (stronger winds on the right hand side of the current)

Question 16

On a surface chart what might convergence (low pressure) and divergence, (high pressure), cause?

Answer 16

Convergence may result in clouds and rain; divergence may result in clearer skies

Question 17

What is a shear flow in the context of wind?

Answer 17

The flow induced by a force gradient

Question 18

What is positive and negative vorticity?

Answer 18

Positive = Cyclonic; Negative = Anticyclonic

Question 19

What is the Jet Stream?

Answer 19

A fast moving ribbon of air connected with the zone of maximum slope, folding or fragmentation of the tropopause; this in turn coincides with the latitude of maximum poleward temperature gradient or frontal zone.

Question 20

What are the principal westerly jet streams?

Answer 20

Subtropical jet stream at about 150-200 mb and the main polar front associated jet stream at around 250-300 mb.

Question 21

Where do the strongest jet cores tend to occur?

Answer 21

Over East Asia and Eastern North America in winter,

Question 22

Name in order from 90N to 10S the Jet streams

Answer 22

Artic - Polar - Subtropical - Tropical easterly

Question 23

What relationship does a jet stream have with temperature gradients?

Answer 23

Larger temperature gradient the stronger the flow.

Question 24

What is a Rossby wave?

Answer 24

Large meanders in high altitude winds with major influence on the weather - they are associated with pressure systems and the jet stream.

Question 25

How do atmospheric rossby waves emerge?

Answer 25

Due to shear in rotating fluids that the Coriolis force changes along the sheared coordinate.

Question 26

What can meanders in the jet stream give rise too?

Answer 26

Areas of strong convergence/divergence aloft, this has consequences for vertical flow and surface pressure patterns causing the development of depressions and anticyclones.

Question 27

What is the atmospheric effect of the Ekman spiral?

Answer 27

Frictional drag from the planetary boundary layer causes a clockwise motion of wind this effect becomes negligible when the wind attains geostrophic velocity at between 500 and 1000m in middle and higher latitudes.

Question 28

Why does wind blow - what does it depend on?

Answer 28

Depends on Coriolis force; angular velocity of the Earth; velocity of the moving body; position on the earths surface