Mass Movement and Wind Flashcards
(28 cards)
What is “The Geostrophic Wind”
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
How does geostrophic wind work?
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.
When would actual wind equal geostrophic wind?
If there were no friction and isobars were perfectly straight
What is Centripetal acceleration?
For a body to follow a curved path there must be an inward acceleration towards the center of rotation.
When does air become Sub-geostrophic?
In a low pressure system When Gradient wind < Geostrophic wind
When does the air become Super-Geostrophic?
In a High pressure system Gradient wind > Geostrophic wind
What are the main kinds of air flow in terms of wind and pressure systems on a global scale?
Divergence / Convergence; Vertical Motion / Vorticity
Explain Divergence / Convergence
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.
What are confluence and diffluence associated with on terms of air velocity?
Confluence associated with an increase in air velocity and diffluence with a decrease in air velocity.
What would happen if all winds were geostrophic?
There could be no convergence or divergence and therefore no weather
Explain the importance of vertical motion
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.
Explain vorticity
Vorticity implies rotation or angular velocity of parcels of fluid.
What are the three components of vorticity?
Magnitude, direction and sense of rotation
What does cyclonic vorticity result from?
May result from the cyclonic curvature of the streamlines, from cyclonic shear (stronger winds on the left hand side of the current).
How does anticyclonic vorticity occur?
Anticyclonic curvature of the streamlines, from anticyclonic shear, (stronger winds on the right hand side of the current)
On a surface chart what might convergence (low pressure) and divergence, (high pressure), cause?
Convergence may result in clouds and rain; divergence may result in clearer skies
What is a shear flow in the context of wind?
The flow induced by a force gradient
What is positive and negative vorticity?
Positive = Cyclonic; Negative = Anticyclonic
What is the Jet Stream?
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.
What are the principal westerly jet streams?
Subtropical jet stream at about 150-200 mb and the main polar front associated jet stream at around 250-300 mb.
Where do the strongest jet cores tend to occur?
Over East Asia and Eastern North America in winter,
Name in order from 90N to 10S the Jet streams
Artic - Polar - Subtropical - Tropical easterly
What relationship does a jet stream have with temperature gradients?
Larger temperature gradient the stronger the flow.
What is a Rossby wave?
Large meanders in high altitude winds with major influence on the weather - they are associated with pressure systems and the jet stream.
