Wind Flashcards
What is wind?
A mystery.
I mean, wind is the horizontal movement of air caused by differences in pressure from one place to aother. Air moving from a high pressure area (heavy, sinking air) to a low pressure (less dense, rising air) creates wind.
What are isobars?
Lines that joint points of equal MSL pressure (4 millibar intervals)
**It is important to rememebr that all the pressure readings you see on a map have been reduced to sea level
In the picture, the wind is draw flowing in the direction it should in a perfect, inclosed system. It rarely follows such a clean path, especially when it is flowing from high to low pressure systems where it is also turning at the same time
What is a pressure gradient?
- The rate of change of pressure over distance
- Indicated by the pattern of isobars
- When the isobars are close together, the pressure gradient is steep and will produce strong wind
- The pressure gradient makes more difference in the weather than the value of the isobars
What direction are the winds blowing in the picture below and what altitude are they at?
Winds on a GFA are always at the surface
At altitudes above 3000ft AGL why does wind not perfectly move from high pressure to low pressure along the plotted gradient?
The coriolis force (the earth spins counter-clockwise, which drags the wind to the right) pulls the wind off course and causes it to more or less move parallel to the isobars with slight deflections.
What happens at 30 degrees North of the equator, in terms of the coriolis effect on winds aloft?
The warm, low pressure air rising from the equator starts to get dragged to the right in the same spot (about 30 degrees to the north).
This causes it to kind of pile up all in that one spot, which increases the pressure. This means some of the air is forced out and down and, once it hits the ground, spreads out to the north or south
This creates kind of a perma-high pressure area in a band around the earth at 30 degrees north. Which happens to lay accross desert areas of the USA.
What happens around 60 degrees north of the equator?
Air that got pushed out from aloft at 30 degrees north and hit the ground and chose to head north, collides with air coming down from the north and both get shoved back up aloft.
This creates a perma-low in a band around the earth at 60 degrees north
What are the three ‘cells’ created by the coriolis effect?
- Polar
- Ferrel
- Hadley
The coriolis effect will deflect winds on the surface. What direction do the winds generally go in each of the three cells and what are those winds called?
If the earth did not spin, then the winds would simply blow straight down from the north pole to the equator and straight up from the south pole to the equator.
Polar Easterlies
* Polar Cell: Winds blow down and to the right (if you had your back to the pole) and blow from east to west.
Westerlies
* Farrel Cell: Winds blow North (up) and to the left (If your back was to the pole) and blow from west to east.
Easterly Winds/ Trade Winds
* Hadley Cell (North of equator): Winds move south (down) and to the right (east to west) if you had your back to the pole
* Hadley Cell (South of equator): Winds move North (up) and to the left (still east to west) if you had your back to the pole
What is the resultant and geostrophic wind?
Resultant: The result of the pressure gradient and the coriolis force on winds at the surface
Geostrophic Wind: Is the resultant wind aloft. Around 2-3000AGL.
At heights around 2-3000 AGL, what direction does the wind flow in relation to the isobars?
Parrallel because it is out of the way of any friction from the ground.
At heights less than this, the resultant wind becomes modified. This ground friction causes the wind to:
- Slow down
- Makes the wind at the surface appear to be drifting to the left a bit in relation to the winds aloft from the coriolis force. This is why on GFAs winds are a little deflected off the isobars
- Causes winds to flow at a slight angle to the isobars near the surface
What is backing and veering?
Backing: Turning counter-clockwise (to the left/from left to right)
Veering: Turning clockwise (to the right/from right to left)
Example - Winds on the ground at 170@10 and at 3000ft they are 270@20
What is Buys Ballot?
If you stand with **your back to the wind* in the northern hemisphere, the low pressure system is always on your left. The high is always on your right.
During a climbout in a standard atmosphere, winds generally ____ and _____
During a climbout, winds veer and increase
During an approach in a standard atmosphere, winds generally ___ and ______
Back and decrease/slow down
In what direction does air flow to and from the ocean during the night and day?
Day: Land is hotter than the water during the day. Air over land rises, colder air from over water takes it’s place. Results in wind blowing from water to land.
Opposite during the night.
What are Rossby Waves and Jet Streams?
Rossby Waves: Very strong winds in upper troposphere. Result of temp variation and rotation of the earth (shown on upper level charts like the one below)
Embedded within these Rossby Waves are Jet Streams, which are parcels of air that can move up to 230/kmph
