What are the cookbook ingredients of weather?What is air?What is the atmosphere?What is atmospheric pressure?What is wind? METEOROLOGY
Air • Water • Land • Heat (Solar) What are the four main “cooking ingredients” to cook up some weather? WEATHER Let’s talk about air first.
~30 in. • 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 Air
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 The Atmosphere
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. Atmospheric Pressure
950 mb 1000 mb • 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 Surface Atmospheric Pressure 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.
DALR ~3 -100C/km USE 100/km ELR ~ 6.50/km T(0C) ΔDew Pt. ~ 20/km P Vol TE stays the same T Altitude (m) Air Parcel • Adiabatic lapse rate = ΔT / ∆Alt. • Adiabatic means TE insulated air parcel (imaginary box of air) How does the temperature change in the troposphere? • 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
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.
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 Wind