Pressure
- Definition: Force exerted against a surface by the collision of gas molecules.
- Simply the weight of the air.
- Two important factors for Pressure:
- Temperature.
- Density (mass over volume).
- Highest pressures are recorded in winter when temperatures are lowest.
- Reason:
- Air pressure is proportional to both density and temperature.
- On cold days, air molecules are closer together (higher densities).
- Decrease in motion of molecules (because of lower temps) is offset by higher density.
- Lower temps--- greater density---greater pressure.
- Isobars - Lines of constant pressure:
- Isobars are drawn every 4mb.
- With Isobars, we can identify patterns of high and low pressure.
- Figure: Isobar.
- Pressure reported on a map, depicted on a Station Model:
- T---Temperature.
- P---pressure.
- Td---Dew point.
- Range of pressure: 950mb-1050mb.
- 2 Types of Pressure Variations:
- Vertical:
- Pressure Decreases with height.
- Horizontal:
- Reduction to Sea- Level pressure:
- Sea-Level Pressure = 1013.25(mb).
- Accounts for the vertical change in pressure.
- Equation of State (gas law):
- Describes the relationship between Pressure, Density, and Temperature.
- p = pressure.
- T = temperature.
- r = density.
- c = gas constant.
- Also shown as "R" (287 J/KgK) - dry air gas constant.
- Pressure and Wind
- Pressure
- Wind
- Upper-level winds
- Wind Measurement
- Lecture Notes
