Winds Flashcards
Define Wind
the horizontal movement of air
what are the two properties of wind?
speed and direction, reported from the direction that it originates
what causes wind?
differences in atmospheric pressure
Define Pressure
a measure of the force exerted by gas molecules, on all surfaces, per unit area
Pressure varies with ____ and over the entire earth
altitude
what is the average atmospheric pressure?
1013.2 millibar (mb) of pressure
how does pressure change horizontally compared to vertically?
horizontal pressure changes at a much smaller rate than the vertical pressure gradient.
- horizontal gradient 1mb/6km
- vertical gradient 1 mb/10m)
what is an isobar?
A line that connects points having the same pressure drawn at intervals of 4 MB on surface weather maps
What does the spacing of the isobars indicate? Isobar lines act like _____ lines on a topographic map.
the strength of the pressure gradient
contour lines
Wind speed and direction at the surface is affected by what four things??
- pressure gradients
- Coriolis effect
- Friction force
- Gravity
What is the most important factor when determining wind strengths?
pressure gradients (moving from high to low pressure)
Pressure decreases more rapidly in a ____ and ____ air column.
cold and dense
How are horizontal pressure gradients created at higher elevations?
The pressure decreases at higher elevations because of the cold temperature and dense area.
Upper-level maps are drawn for what four millibars of pressure? How often are they drawn?
- 300 mb
- 500 mb
- 700 mb
- 850 mb heights
drawn twice per day for forecasting
What is the Coriolis effect? How do winds curve in the northern hemisphere vs the southern hemisphere?
The apparent force caused by the rotation of the Earth that makes winds appear to curve to the right in the Northern Hemisphere and left in the Southern Hemisphere
Why does the Coriolis effect occur?
Because wind is measured relative to a moving surface (the earth)
How does the Coriolis effect differ at the equator vs the poles?
the effect equals zero at the equator and increases to a maximum at the poles
Does the Coriolis effect change the speed of a moving object?
no just the direction
The magnitude of the Coriolis effect increases with _____?
wind speed
Friction is important within the lowest ____km of the atmosphere
1.5 km
- air above 1.5 km experiences negligible friction
How does gravity play a role in the atmosphere?
it holds the atmosphere to the Earths surface
List the four upper atmospheric wind types
- Gradient flow (gradient wind)
- Geostrophic flow
- Supergeostrophic flow
- Subgeostrophic flow
What is gradient flow (gradient winds)?
- wind flowing parallel to the height contours, when frictional forces are negligible.
- when isobars are curved (from contours), there is a constant mismatch in the coriolis and pressure gradient force
What is geostrophic flow?
- a type of gradient wind that occurs when height contours are parallel and so Coriolis and pressure gradient force are equal
