Met 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