Atmospheric Composition
78% Nitrogen, 21% Oxygen, 1% Argon and greenhouse gases
Hydrological Cycle
Vapor ←→ liquid (condensation, evaporation)
Liquid ←→ solid (freezing, melting)
Vapor ←→ solid (deposition, sublimation)
Layers of the Atmosphere
Troposphere, Tropopause, Stratosphere, Stratopause, Ozone Layer, Mesosphere, Mesopause, Thermosphere, Ionosphere
Relationship between pressure, temperature, density, and altitude
Temperature inversions at each -pause
Density decreases with height
Pressure decreases with height
Wet Bulb Temperature
Lowest temperature that can be reached by evaporating water
Dew Point Temperature
Temperature saturation would occur if moist air cooled isobarically
1st Law of Thermodynamics
Change in internal energy of closed system will be equal to the energy added to the system minus the work done by the system on its surroundings
1st Law of Thermodynamics Equation
ΔU = Q + W
Entropy Equation
ΔS = Q/T
Isothermal Process
temperature is constant, changes in phase or state
Isobaric Process
pressure is constant, boiling water
Isochoric / Isovolumetric Process
volume is constant, otto cycle (how a car uses gasoline)
Adiabatic Process
a process where the parcel temperature changes due to an expansion or compression, no heat is added or taken away from the parcel, lightning strikes or thunderstorms
Wet Bulb Potential Temperature
Temperature an air parcel would have if cooled from its initial state to saturation and brought 1000 hPa in a moist adiabatic process
Potential Temperature
the temperature an air parcel of temperature T and pressure P would have if it were expanded or compressed under adiabatic conditions to some reference pressure
Lapse Rate
the rate at which temperature changes with height
Dry Adiabatic Lapse Rate
Unsaturated parcels cool at a rate of 10°C km-1
Moist Adiabatic Lapse Rate
For a saturated parcel of air, then it cools at the rate of 6°C km-1
Why the moist adiabatic lapse rate less than the dry adiabatic lapse rate
as vapor condenses into water (or water freezes into ice) for a saturated parcel, latent heat is released into the parcel, mitigating the adiabatic cooling
Vapor Pressure
the pressure of a vapor in contact with its liquid substance
Saturation Vapor Pressure
is the vapor pressure which is in equilibrium with an open liquid surface
Mixing Ratio
the abundance of one component of a mixture relative to the total mixture
Saturation Mixing Ratio
the ratio of the mass of water vapor to the mass of dry air in a parcel of air at saturation
Relative Humidity
ratio of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated
Absolute Humidity
a measure of the actual amount of water vapor in the air, regardless of the air's temperature
Specific Humidity
the weight of water vapor contained in a unit weight of air
Lifting Condensation Level
the level at which a parcel becomes saturated
Mixed Condensation Level
the lowest level at which condensation occurs (if at all) as a result of vertical mixing through a given layer
CAPE
Is the amount of energy available or required to develop a thunderstorm
Geopotential Height
work that must be done against the Earth’s gravitational field to raise a mass of 1 kg from sea level to a given point
Geopotential Height Equation
Φ(Z) = ∫ gdz or Z = Φ(Z)/g0 = (1/g0) ∫ gdz
Hydrostatic Equation Definition
balance between the gravity force and vertical component of the pressure gradient force
Hydrostatic Equation
dp/dz = -ρg
Geopotential Version of Hydrostatic Equation
gdz = dΦ = -RTdln(p)
Derivation of potential temperature equation from an adiabatic process
For adiabatic expansion potential temperature is conserved
Thus, θ = Ts=T(ps/p)^(R/Cp)
Substituting from ideal gas law, T = p/(ρR) gives: ps/ρs= (p/ρ)(ps/p)^(R/Cp)
Using Cv = Cp - R, we get ρ = ρs(p/ps)^(cv/cp)
Clausius-Clapeyron
Describes equilibrium condition for a thermo system w/ water and its vapor
Saturation Vapor Pressure Equation
e₂(r) = e₂(∞)exp[2σ/rRvρT]
Calculate sea level pressure from a station
Psl = P(293/(293-h*0.0065))
Atmospheric Instability Cases
Absolute stability: Γd > Γm > Γe
Absolute instability: Γe> Γd> Γm
Conditional instability: Γd> Γe> Γm
High Pressure Subsidence
High pressure promotes sinking air. As air sinks it warms adiabatically
Radiative Inversion
earth is cooled at night by longwave radiation emission to space
Frontal Inversion
when the air associated with the shallow air mass is colder than the air aloft, thus creating an inversion
Tropopause Inversion
created by the absorption of shortwave radiation by ozone
Richardson Number
used as a rough measure of expected turbulence
Relationship between CAPE and vertical velocity
Higher vertical velocities correlate with more severe thunderstorms thus higher velocities means more available energy to develop thunderstorms
Processes that affect atmospheric stability
Mixing - cooling the top layer and warming the bottom
Lifting due to surface heating - condensation due to rising thermals
Cold air flowing over warm body of water - creates increase in temperature with height
Radii of Cloud and Rain Droplets
Cloud drops: r<0.1mm
Drizzle drops: r ~ 0.1mm
Raindrops: r>0.1mm
Heterogeneous Nucleation
when water droplets form on nuclei from the vapor phase
Homogeneous Nucleation
when droplets form from the vapor phase in a pure environment (requires high supersaturations)
Haze Particles
tiny airborne particles (such as dust, smoke, or pollutants) that scatter light and reduce visibility in the atmosphere
Activated Droplet
a small water droplet that has grown to a size sufficient for cloud formation due to condensation or other processes
Homogeneous Freezing
the process by which a supercooled liquid drop freezes without the assistance of an ice nuclei; becomes statistically more likely as temperature decreases such that below -39°C all drops will freeze
Heterogeneous Freezing
the process by which a supercooled liquid drop freezes with the assistance of a solid aerosol particle which is able to act as an ice nuclei
Heterogeneous Deposition
the process by which water vapor is deposited onto an ice nuclei and takes on a crystalline form directly without first being in the liquid phase
Collision Efficiency
is equal to the fraction of those droplets with radius r in the path swept out by the collector drop that actually collide with it. Collision does not guarantee coalescence
Collection Efficiency
is the growth of a droplet by the collision-coalescence process. This is the product of collision efficiency and coalescence efficiency
Coalescence Efficiency
is the ratio of the number of coalescences to the number of collisions
Deposition Nucleation
a heterogeneous ice nucleation mechanism where water vapor molecules are deposited directly into the ice phase on an ice nucleating particle
Freezing Nucleation
the spontaneous freezing that occurs within supercooled liquid-water droplets as temperature decreases to near –40°C
Immersion Nucleation
induced by a particle immersed in the body of supercooled water
Contact Nucleation
occurs when an Ice Nucleating Particle comes into contact with the surface of a supercooled droplet and triggers the freezing
Two ways cloud particles can grow rapidly to precipitation
Collision and Coalescence
Liquid Water Content (LWC)
LWC = ρ
Critical Radius Equation