exam 4 Flashcards
Pressure Gradient Force
compels fluid to move from regions of high pressure to regions of low pressure; difference in pressure over distance
Coriolis Force
the invisible force that appears to deflect the wind; a direct result of the Earth’s rotation
Rotation Rate
of rotations / second
Number of rotations per second
Radial Velocity
rotation rate x radius
Velocity radial of the Earth
the radial velocity; purely a function of latitude
Velocity relative to Earth
possessed anytime an object moves from one location to another
Geostrophic Balance
When COR and PGF are equal (friction is negligible)
Anti-cyclones
Clockwise in NH, counterclockwise in SH
High pressure zones repel air
Diverge in the surfaces converge aloft
Cyclones
Counterclockwise in NH, clockwise in SH
Low pressure zones suck in air
Converge on the surface, diverge aloft
Vorticity
a measure of the spin of the air parcel
Positive vorticity
getting more counter clockwise
negative vorticity
getting more counterclockwise
Positive vorticity advection
horizontal transport of positive vorticity; associated with divergence
negative vorticity advection
horizontal transport of negative vorticity; associated with convergence
Occluded front
The faster cold front overtakes the warm front and pushes the warm front aloft, a signal that the cyclone has reached its peak intensity
Warm front
Cold air forces warm air to rise; warm air rises over a shallowly steep parcel of cold air
Cold fronts
Steeply sloped cold air forces the warm air to rise
A hockey puck is placed on a flat, infinite sheet of ice in the Southern Hemisphere. It is then given a slight push to the west. The sheet of ice is frictionless so that the speed of the puck after the push is constant. What horizontal force acts on the puck after the push? Describe (or draw) the path the puck takes after the push. Explain your description (or drawing).
The force that acts on the puck is the Coriolis force. After the push, the puck will deflect toward the south since it’s in the Southern Hemisphere. The frictionless surface is important because the only forces acting on it are the Coriolis and the push.
A friend of yours who is traveling the world reports that she recently experienced a day on which the surface wind blew from the southeast while simultaneously the clouds overhead were moving from east to west. Independently, she is made aware of the fact that on that day the PGF was the same at the surface and at the cloud height. What hemisphere was she in at the time? Explain your answer.
Because the clouds are moving from east to west, she is in the Southern Hemisphere. On the surface, she feels the wind blowing from the southeast because friction has changed the direction of the wind in order to keep the PGF balanced. For winds aloft, friction is negligible, so the wind is in geostrophic balance. Because they’re moving east to west, she is in the Southern Hemisphere.
A local forecaster predicts that strong surface winds (i.e. speeds in excess of 15 ms-1) will visit the Upper Midwest over the weekend. Which of the two statements below most likely motivated her forecast?
(a) Small differences in sea-level pressure will exist from station to station across the area.
(b) Large differences in sea-level pressure will exist from station to station across the area.
Give a scientific explanation of your choice.
Statement B will be most likely. The greater pressure differences from station to station will lead to a greater PGF meaning stronger winds because the wind strength is connected with the Coriolis which is dependent on the PGF.
What two forces are balanced in geostrophic flow? The winds well above the surface in the middle latitudes are nearly in geostrophic balance. How does this fact serve as proof that the Earth rotates on its axis?
The two balanced forces are pressure gradient force and the Coriolis force. The only forces involved in geostrophic balance are the Coriolis force and the PGF since friction is negligible. Without the COR, the wind would only flow from areas of high pressure to areas of low pressure, which it doesn’t. That means that the COR must be present in the middle latitudes and since COR is only dependent on the rotation of the earth, the earth must be rotating.
Thickness of the column
directly proportional to temperature
thermal wind/geostrophic wind shear
wind that comes as a result of the pole-to-equator temperature gradient
Jet stream
a core of very high-speed winds found very high in the atmosphere
air mass thunderstorms
remote from any organized fronts or cyclones
Cumulus stage: growth of the cumulus cloud; warm rising air from which liquid water condenses; no precipitation yet
Mature stage: particles are big enough to start falling, dragging dry air from outside the cloud into it; renders some of the in-cloud air negatively buoyant, helping to develop a significant down draft
Dissipating stage: precipitation ceases from the updraft, cumulus slowly evaporates
Severe thunderstorms
Long life span as the result of the tilted updrafts. Downdrafts are restricted to the western portion of the storm. Titled updrafts keep the precipitation from falling into the warm, moist airflow that feeds the storm
Tornadoes
In the presence of VWS, tubes of air are made to rotate. The updraft bends/distorts the rotating air sot he rotation becomes more and more vertical (mesocyclones). Air rushes into the mesocyclone, increasing the rotation. The southcentral U.S. is characterized by convective instability: the most potent instability in the atmosphere (dry air on top of moist air)
