ATMO 10/21 - Wind Speed, Direction, Surface Maps

Pressure Gradient (PG):
- Change in pressure/change in distance
- Stronger the PG, stronger the winds
- PG points from higher to lower pressure
- PGF (F = Force) pushed air from high to low pressure
- No PG, no wind (calm conditions)

Weather Maps:

Surface (or sea level) maps:
- Plot "equivalent" sea level pressure
- Contours are iso bars (constant pressure lines)
- Use iso bars to estimate/visualize pressure gradients and winds

Upper air maps:
- Plot height of pressure surfaces
- Use height contours to estimate/visualize pressure gradients and winds

Surface Maps:
- Station pressure: measured (actual) air pressure mad using a barometer at a weather station
- Sea Level Pressure: estimate of air pressure if the station were at sea level (must make an altitude correction to the measured station pressure)

Corriolis Force:
- Effect on winds due to Earth rotating and air not being fixed to the surface

Friction Force:
- Near surface, winds are slowed by friction between the air and ground

Net Effect of Forces:
- Considering PG, CF, FF, the wind direction near ground (on sea level maps) is ~60 degrees to the right of the PG (or 30 degrees toward lower pressure).

Surface Low Pressure Area:
- Wind direction is generally counter-clockwise and slightly inward (resulting in surface convergence and rising air motions, possibly leading to clouds and precipitation).

Surface High Pressure Area:
- Wind direction is generally clockwise and slightly outward (resulting in surface divergence and sinking air motions, leading to fair weather)