Lecture 3Lecture 3

Vertical Structure of the Vertical Structure of the AtmosphereAtmosphere

Average Vertical Temperature profile

Atmospheric LayersAtmospheric Layers

TroposphereTroposphere On average, temperature decreases with On average, temperature decreases with

heightheight

StratosphereStratosphere On average, temperature increases with On average, temperature increases with

heightheight

MesosphereMesosphere

ThermosphereThermosphere

Lapse RateLapse Rate

Lapse rate is rate that temperature Lapse rate is rate that temperature decreases with heightdecreases with height

z

T

SoundingsSoundings

Actual vertical temperature profiles are Actual vertical temperature profiles are called called soundingssoundings

A sounding is obtained using an A sounding is obtained using an instrument package called a instrument package called a radiosonderadiosonde

Radiosondes are carried aloft using Radiosondes are carried aloft using balloons filled with hydrogen or heliumballoons filled with hydrogen or helium

Radiosonde

http://www.srh.noaa.gov/mob/balloon.shtml

Application: Reduction to Sea LevelApplication: Reduction to Sea Level(See Ahrens, Ch. 6)(See Ahrens, Ch. 6)

Surface pressure here

proportional to weight of this column of air

Surface pressure also called station pressure (if there is a weather station there!)

MathMath

sfcz

sfc dzgp

Obtained by integrating the hydrostatic equation from the surface to top of atmosphere.

Deficiencies of Surface PressureDeficiencies of Surface Pressure

Spatial variations in surface pressure Spatial variations in surface pressure mainly due to topography, not meteorologymainly due to topography, not meteorology

900

950

1000

1050

Height contours on topographic map

Units: m

It’s a mountain!

Put a bunch of barometers on the mountain.

Surface pressure (approximately)

885

890

895

900

Isobar pattern looks just like height-contour pattern!

Units: hPa

““Reduction to Sea Level”Reduction to Sea Level”

Sea Level

Surface pressure here

is proportional to weight of this column of air

Let T = sfc. temp. (12-hour avg.)

For sea level pressure

add weight of isothermal column of air

temp = T.

Pressure as Vertical CoordinatePressure as Vertical Coordinate

Pressure is a 1-1 function of heightPressure is a 1-1 function of height i.e., a given pressure occurs at a unique i.e., a given pressure occurs at a unique

heightheight

Thus, the pressure can be used to specify Thus, the pressure can be used to specify the vertical position of a pointthe vertical position of a point

Given p

At what height is the pressure equal to p?

Pressure SurfacesPressure Surfaces

Let the pressure, pLet the pressure, p11, be given., be given.

At a given instant, consider all points (x, y, z) At a given instant, consider all points (x, y, z) where p = pwhere p = p11

This set of points defines a This set of points defines a surfacesurface

x

z

p = p1

x1 x2

z(x1) z(x2)

Height ContoursHeight Contours

Heights indicated in dekameters (dam) 1dam = 10m

Two Pressure SurfacesTwo Pressure Surfacesz

p = p1

p = p2

z2

z1

z2 – z1

ThicknessThickness

zz22 – z – z11 is called the is called the thicknessthickness of the layer

Hypsometric equation thickness proportional to mean temperature of layer

Thickness GradientsThickness Gradientsz

p = p1

p = p2

Small thicknessLarge thickness

Coldwarm

ExerciseExerciseSuppose that the mean temperature Suppose that the mean temperature between 1000 hPa and 500 hPa is -10between 1000 hPa and 500 hPa is -10C.C.

Calculate the thickness (in dam)Calculate the thickness (in dam)

dammKKm

Ksm

Ksm

Ksm

K

Tg

Rzz

534534015.2633.20

15.26320.3

15.263693.081.9

kg287J

2ln

1

2

122

2

11-

12

Repeat, for T = -20Repeat, for T = -20CC

damm

KKmzz

5145140

15.2533.20 112

Thickness MapsThickness Maps