Meteorology 1

Meteorology for Airborne Scientists Henry Fuelberg Department of Meteorology Florida State University

Atmospheric Structure and Thermodynamics Some Basics

Basic Atmospheric Variables • Pressure (p) • Temperature (T in oC or K) • Density (ρ) ( or specific volume (α = 1/density)) (kg m-3)

• Water vapor content • Three dimensional wind

Atmospheric Pressure Changes with Altitude Pressure = Force/Area 1 Pascal = 1 Newton m2

1 millibar (mb) = (hPa)

1 hectoPascal

Mean sea level pressure = 1013.25 mb

Thermal Structure of the Atmosphere Lapse rate = ∂T/∂z Troposphere has + lapse Stratosphere first isothermal, then – lapse Troposphere has

Height of the Tropopause Varies with Latitude

Thermodynamics Parcel = imaginary volume of air to study, like a balloon, separate from environment Atmosphere acts as an ideal gas—a mixture Equation of state (ideal gas law) Press = density x gas constant x temp

First Law of Thermodynamics • dq = cv dT + pdα heat change = internal energy change + work done to expand or contract vol. • dq= cp dT – α dp heat change = enthalpy change + …

Dry Adiabatic Process • • • • • • • • •

Consider an unsaturated parcel dq = 0 0 = cp dT – α dp Parcels still can change temperature due to expansion and contraction Example—parcel expands, expends energy, T becomes cooler Make substitutions and solve for dT/dz dT/dz = -g/cp = 9.8 oC/km = Γd (dry adiabatic lapse rate) Unsat. parcels always follow Γd Away from clouds and radiative processes, parcels ~ adiabatic for several days

Rising air

Potential Temperature (θ) Parcel at T and p Θis temp. parcel would have if taken dry adiabatically to p = 1000 mb If p = 1000 mb, Θ=T Θ = T (1000 mb/ p) R/cp R/cp = 0.286 Parcels conserve Θduring ascent, descent, etc. as long as conditions are adiabatic T is not conserved, it changes at Γd

Water Vapor • Vapor pressure = partial pressure of vapor (mb) • Mixing ratio = mass vapor/mass dry air (g/kg) • Concept of saturation • Dew point temperature = temp to which air must be cooled to become saturated (oC) • Relative humidity = mixing ratio / sat.

Saturated Adiabatic Process • Parcel is saturated • Lift parcel, condensation occurs, latent heat released, dq ≠ 0 • dq= cp dT – α dp • Let dq = latent heat release • Perform some magic • Γs = Γd [ ≤ 1] • Therefore……….. Γs ≤ Γd not a constant • Γs ≈ 5-6 oC/km

Radiosondes

Hydrostatic Stability Displace parcel upward (could go downward) Will displacement be Suppressed = Stable Layered clouds, steady precipitation Enhanced = Unstable Towering clouds, showers or

Absolute Stability Environmental Lapse Rate less than Wet Adiabatic Rate

Absolute Instability Environmental Lapse Rate greater than Dry Adiabatic Rate

Conditional Instability Environmental Lapse Rate between the Dry and Wet Adiabatic Rates

What Causes Wind to Blow ?? It is acted on by forces —most of which we can’t see

Surface Map Isobars = Lines of constant pressure

Straight Isobars

Flow Around Circular Low

Flow Around Circular High

Upper Level Charts Pressure is Vertical Coordinate

500 mb Chart

• • • • • • •

Planetary Boundary Layer Lowest layer of atmos—directly influenced (PBL)

by the surface PBL vs. Free Atmosphere What happens in PBL? Air is heated/cooled from below—radiation Inversions (stable) at night—suppress mixing Big lapse rate during day—less stable-lots of mixing Mechanical Turbulence—roughness (day or night)

• Wind Speed goes to zero at surface (no slip) • Speed increases with height according to Ekman Theory—direction also changes • The more mixing • the more θ is constant with height • the more mixing ratio constant with height • Height of PBL deep during day, shallow at night • Depth determined by

Transporting Air From Surface to Higher Levels Winds are stronger there Wind direction often changes with height

Jet Streams

Middle Latitude Wave Cyclones

Major Airstreams in Midlat Cyclone

Smaller Scale Circulations Also Provide Vertical Transport

Sea/Land Breezes

Mountain/Valley Breezes

Santa Ana Winds & Fires

Wires Fanned by Santa Ana Winds

Thunderstorms-Major Vertical Transporters

Lightning Creates NOx

FOG

Radiation Fog

Advection Fog

Yesterday’s Fog (4:46 PM)

This morning

Neat Picture Contrails Cover 0.1% of Earth’s

Eastern France

Trajectories Backward in time—where did air come from? What path did it take? Forward in time—where is air going to? What path will it take? Several possible procedures Isobaric—air keeps same pressure-move parcel by horizontal winds

• Kinematic method—move parcels by three-dimensional winds—most popular today Procedure for Forward Trajectories Start with 4-D grid of 3-D wind components—hope data every few hours Move parcel one time step by

• Take winds at new location and time and move parcel another time step • Repeat the process until you reach the ending time that you specify • Limit is usually 5-10 days • After that uncertainties are too great

Examples from ARCTAS-2008 10 days back from selected flight legs

Heading to N CA

Heading to S CA

Particle Dispersion Models •Establish locations of emissions and rates of emission •Release particles to simulate emission rate •Particles have specified mass and are released at specified rate •Three-dimensional winds move the particles •Can then watch the transport of the

WRF Nested Grid 45 km, 15 km, 5 km

Sprin g

Summer

Sources of Real Time Information Satellite, Radar, Surface Analyses, http://www.rap.ucar.edu/weat her/

Surface Plot 7 PM

Edward AFB Radar 8 PM

Enhanced IR Image 8 PM

Surface Plot 11 AM

Visible Images 10 AM

Edwards AFB Monday 5 AM

500 mb Analysis 5 AM Monday

Forecast Products NOAA National Center for Environmental Prediction http://www.nco.ncep.noaa.gov We look at 54 h progs valid 11 AM Wednesday

H

SFC Forecast

Clouds below 6000 ft

850 mb Forecast

700 mb Forecast

500 mb Forecast

500 mb

Zoom to CA Area

300 mb Forecast

Your Local NWS Office http://www.srh.noaa.gov

Other Interesting Sites Storm Prediction Center http://www.spc.noaa.gov National Hurricane Center http://www.nhc.noaa.gov