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Friday, March 18, 2016

Physical Principles: The Hydrostatic Equation

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward AguadoJames E. Burt.





   Hydrostatic Balance = if the net upwards force is equal to the downward force
     For an atmosphere in hydrostatic balance, the balance of forces in the vertical requires that…
   Or, the Hydrostatic Equation:
     The negative sign ensures that the pressure decreases with increasing height
     Because
 we can rearrange the hydrostatic equation to give…

   Above a fixed point on Earth…
     That is, the pressure at height z is equal to the weight of the air in the vertical column of unit cross-sectional are lying about that level.

Hydrostatic Equilibrium
   Pressure gradient force causes wind to flow from high to low pressure
   Air pressure rapidly decreases with altitude
   Gravity pulls all mass, including the atmosphere, downward.
   Hydrostatic Equilibrium = vertical pressure gradient force and the force of gravity are normally of nearly equal value and operate in opposite directions
     When, gravitational force = vertical pressure gradient force in magnitude à no vertical acceleration occurs
     When, gravitational force > vertical pressure gradient force à downward motion
When, gravitational force < vertical pressure gradient force à updrafts can develop that are associated with powerful thunderstorms

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