meteorology 1
DESCRIPTION
SARP MeteorologyTRANSCRIPT
Meteorology forAirborne Scientists
Henry FuelbergDepartment of Meteorology
Florida State University
Atmospheric Structureand 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 m-2
1 millibar (mb) =
1 hectoPascal (hPa)
Mean sea level pressure =
1013.25 mb
Mean sea level density =
1.25 kg m-3
Thermal Structureof the Atmosphere
Lapse rate = - ∂T/∂z
Troposphere has + lapse
Stratosphere first isothermal, then – lapse
Troposphere has small scale inversions that vary daily
Height of the TropopauseVaries with Latitude
ThermodynamicsParcel = imaginary volume of air to study, like a balloon, separate from environmentAtmosphere acts as an ideal gas—a mixtureEquation of state (ideal gas law)
Press = density x gas constant x temp
gas const = weighted by composition and molecular weight
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 cools
Potential Temperature (θ)Parcel at T and pΘ is temp. parcel would have if taken dry adiabatically to p = 1000 mbIf p = 1000 mb, Θ = TΘ = T (1000 mb/ p) R/cp R/cp = 0.286 Parcels conserve Θ during ascent, descent, etc. as
long as conditions are adiabatic T is not conserved, it changes at ΓdHow does θ vary in previous figure?Therefore, Θ can serve as a tracer for parcels
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. mixing ratio
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 StabilityDisplace parcel upward (could go downward)Will displacement be
Suppressed = Stable Layered clouds, steady precipitation Enhanced = Unstable Towering clouds, showers or Tstorms Neither = Neutral Parcel moves only to where pushed
Absolute StabilityEnvironmental Lapse Rate less than Wet Adiabatic Rate
Absolute InstabilityEnvironmental Lapse Rate greater than Dry Adiabatic Rate
Conditional InstabilityEnvironmental 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 ChartsPressure is Vertical Coordinate
500 mb Chart
Planetary Boundary Layer (PBL)• Lowest layer of atmos—directly influenced 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)• Thermal Turbulence—thermals (day)• You can bounce around a lot!!
• 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– Temperature– Wind Speed– Others
Transporting Air From Surface to Higher Levels
Winds are stronger thereWind direction often changes with height
Jet Streams
Middle Latitude Wave Cyclones
Major Airstreams in Midlat Cyclone
Smaller Scale CirculationsAlso 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 PictureContrails Cover 0.1% of Earth’s Surface
Eastern France
TrajectoriesBackward 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
Isentropic—air follows θ surface—move air by winds on the θ surface
• Kinematic method—move parcels by three-dimensional winds—most popular today
Procedure for Forward TrajectoriesStart with 4-D grid of 3-D wind
components—hope data every few hoursMove parcel one time step by these windsNow at a new location and a new time
• Take winds at new location and time and move parcel another time step
• Repeat the process until you reach theending time that you specify
• Limit is usually 5-10 days• After that uncertainties are too great
• If backward trajectories, process goes in reverse
Examples from ARCTAS-200810 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 emissions
WRF Nested Grid 45 km, 15 km, 5 km
Spring
Summer
Sources of Real Time Information
Satellite, Radar, Surface Analyses,Upper Air Analyses, Forecasts
http://www.rap.ucar.edu/weather/
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 valid11 AM Wednesday
SFC Forecast
H
Clouds below 6000 ft
850 mb Forecast
700 mb Forecast
500 mb Forecast500 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