Hydrostatic Equation (dry air approximation)

The Change in Pressure in Dry Air calculator uses the hydrostatic equation, the density of dry air, the acceleration due to gravity and the change in height to estimate the change in pressure.

INSTRUCTIONS: Choose units and enter the following:

• (`Deltah`) Change in Height

Change in Pressure (Δp): The calculator returns the change in pressure in pascals.

The Math / Science

Hydrostatic Equation

  The hydrostatic equation is one of the most important and most basic equations in meteorology. Understanding the equation makes it easier to physically interpret  thickness charts (which display the difference in height between two atmospheric pressure levels). Pressure at any point in the atmosphere is equal to the weight of the air column above the point.  The equation can be generalized as:

`(dp)/(dh) = - "density" * "gravity"`

So, we can compute the change in pressure at an altitudes above the Earth's surface (sea level) to be:

   dp = - `rho` * g * dh, 

where:

• dp - change in pressure in dry air
• `rho` - the air density (assumed in this case to be the density of dry air)
• g - the gravitational acceleration constant at sea level
• dh - the change in height