Lecture 6 Atmospheric Pressure

ATMOS 5130

Lecture 6

? Atmospheric Pressure

? Pressure Profiles for Idealized Atmosphere

Goal

? Understand how temperature, pressure and altitude are related in the atmosphere.

Recall from last lecture

Hypsometric Equation

= &( ln .

Allow for calculation of pressure at any height

Pressure Profiles for Idealized Atmosphere

? Constant Density Atmosphere

? Unrealistic ? Better representation of the ocean ? Atmosphere had the same mass as now, but had a constant density it

would be only 8.3 km deep

:1 - Hydrostatic Equation

:8

1(3)

8

/ = - /

15

9

= 9 -

Pressure decreases linearly with height

Pressure Profiles for Idealized Atmosphere

? Constant Density Atmosphere

? Pressure is decreasing with height

= 9 -

? Density is constant

? SO, Temperature must decease with height

= &

IDEAL GAS LAW

= &

Differentiate with respect to elevation

Substitute in Hydrostatic Equation

= -

:= = - > = -34.1 C/km

:8

?@

Constant Density Atmosphere

= 9 -

Autoconvective Lapse Rate

:= :8

=

-

> ?@

=

-34.1

C/km

=

BCDE

: > BCDE Density above greater than below! Density Inversion => Creates a mirage Above a very hot road, a layer of warm air whose density is lower than air above.

The denser air slows light very slightly more than the less dense layer. So, one sees sky where the road should be, we often interpret this as a reflection caused by water on the road

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