Problem 8 EQ: What is air?

METEOROLOGY

What are the cookbook ingredients of weather?

What is air?

What is the atmosphere?

What is atmospheric pressure?

What is wind?

What are the four main “cooking ingredients” to cook up some weather?

Air

Water

Land

Heat (Solar)

WEATHER

Let’s talk about air first.

Air A mixture of gases: N2, O2, CO2, H20

Air Pressure demos toilet plunger on board note card supporting water in upside down jar can with boiling water crushes when placed upside

down in cold water water stays elevated in test tube when placed upside

down in beaker of water

Kinetic theory of matter: fast moving air molecules collide with surfaces creating a force

P = F / A

Last demo a type of barometer

mercury

aneroid

~30 in.

The Atmosphere

Structure

Atmosphere like “swimming pool” of air, P ~ 1 / alt

75% gases in troposphere

Stratosphere temp. increases due to O3 energy absorption

Tropopause “lid” on weather

Atmospheric Pressure

P = F / A (1 kg/cm2 or 14.7 lb/in2 at Earth surface = 10 meter column of water)

SI: 1 Pa = 1 N/m2

A standard atmosphere ( 1 atm), avg. at mid latitude location = 101,325 Pa at sea level.

National Weather Service unit is the millibar (mb). 1 mb = 100 Pa. Standard sea level pressure = 1013.25 mb.

Surface Atmospheric Pressure Surface pressure map = contour map of isobars

Isobars = lines of equal pressure

Pressure gradient = rate of pressure change

Pressure gradient force = force acting on air to accelerate it

1000 mb

950 mb

If the Earth did not rotate, which direction does the wind blow and what is its relative speed?

But the Earth does rotate and low and high pressure areas make isobars curve around them. As a result, winds tend

to move parallel to isobars due to a balance between pressure gradient force and Coriolis effect + inertia.

How does the temperature change in the troposphere?

Adiabatic lapse rate = ΔT / ∆Alt. Adiabatic means TE insulated air parcel (imaginary box of

air)

Air Parcel

P VolTE stays the sameT

DALR = Dry adiabatic lapse rate = cooling rate for air parcel <dew pt. Moist ALR = cooling rate for a.p. > dew pt. (latent heat release)

ELR = Environmental lapse rate = surrounding atm. lapse rate ΔDew pt. = change due to P change Lifting Condensation Level = (DALR-Δdew pt)-1x (TG-dew pt)

If ELR<DALR, then air is stable If ELR>DALR, then air is unstable, rising air will gain buoyancy

Altitude (m)

T(0C)

DALR ~3 -100C/kmUSE 100/km

ELR ~ 6.50/km

ΔDew Pt. ~ 20/km

Problem: Cumulus clouds are observed on a sunny afternoon. The temperature is 250C and the dew point is 70C. How high are the flat bottoms of the cumulus clouds?

Answer: 2.25 km or 7380 ft.

Wind

A convective response to temp/pressure difference.

Direct solar rays (concentrated energy) at Equator, and low angle rays (less concentrated light) at Poles makes temp differential.

Coriolis Effect (Earth rotation) on wind direction.

Model of global wind patterns.

Coriolis Effect, Hadley cell, ITCZ (doldrums), 00 latitude, Easterly trade wind, Horse latitudes, 300 latitude, Westerly trade winds, Subtropical jet stream, Polar front jet stream, 600 latitude. Polar Easterly trade winds