Meteorology for modeling AP Marti Blad PhD PE

Meteorology Study of Earth’s atmosphere Weather science Climatology and study of weather patterns Study of different weather variables to make predictions Understand Planetary Boundary Layer

Planetary Boundary Layer thickness changes as function of wind and temperature.

4 Momentum, Heat & Mass Transport Advection – Movement by flow (wind) Convection – Movement by heat Heat island Radiation Diffusion – Movement from high to low concentration Dispersion – Tortuous path, spreading out because goes around obstacles

Why Air moves Vertical wind speeds typically much less than horizontal wind speed – Air pressure Measure of total force of collisions with air molecules Concentration = mass/volume=density – Molecule dance Translational Rotational Vibrational

Pressure related to density If air pressure different at two locations at same elevation, air will “blow” from higher pressure to lower pressure

Atmospheric Stability Key factor in determining severity of air pollution is stability of atmosphere

Atmospheric Stability Unstable atmosphere: vertical motion triggered by local heating- turbulence is enhanced Stable atmosphere: vertical air motion inhibited

Why Does Air Move? Localized solar heating causes air near ground to expand – Air is less dense than surrounding air – buoyant (“floats” upward & expands

Air pollution modeling Our goal: predict air pollution concentrations given knowledge of emission sources and meteorology Processes controlling air movement

12 Lapse Rate temperature change  altitude change – Can be positive or negative slope Ambient Lapse Rate – Recorded by weather stations Dry Adiabatic Lapse Rate (DALR)? – Theoretical line with constant slope Slopes are rates (per time) – How dry air rises and falls – Cools 1° C for each 100 meters rise – Warms 1° C for each 100 meters fall

Compare DALR to ambient data Inversion superadiabatic subadiabatic Dry adiabatic lapse rate = neutral DALR

14 Controlling process Dry adiabatic lapse rate – Air expands as pressure decreases Function of elevation – Rate at which dry air cools at it rises – Adiabatic = no heat exchange – Approx. 1° C for every 100 meters Speed pollution disperses & diffuses – “Air stability” class or PBL affects – Relationship between ambient slope & DALR

Air Pollution Dispersion (cont.) Pasquill Stability Categories Surface wind speed at 10 m (m/s) DayNight Incoming Solar radiationCloud Cover StrongModerateSlightThinly OvercastMostly Cloudy < 2AA-BB 2-3A-BBCEF 3-5BB-CCDE 5-6CC-DDDD >6CDDDD

How does stability affect what I see? Smoke plume behavior – a useful indicator Predict burning days Some Models use “stability class” How can pollutants concentrate? – Under an inversion – Maximum mixing height Mixing height: – Height plume will rise to given prevailing atmospheric conditions 16

Maximum Mixing Depth

Plume Behavior Compare slopes Compare the DALR with ambient lapse rate What height will plume rise-induced bouyancy

Maximum Mixing Depth (Height) Temperature inversion occurs when temperature increases with height Trapped air pollution by limiting maximum mixing depth (MMD) into which pollution can be dispersed

Coastal or Large Water Bodies

How is DALR determined? Launch radiosonde

Upper Air Data Soundings Radiosondes – Dropsoundes – Rocketsondes Isotherms Isobars Isohumes

NOAA data

Wrap up Air stability dictates movement of AP Understand basic phenomena – Heat, mass, momentum transport – Chemistry and reactions not discussed – Terrain & topography effects Complexity of weather data – More later with Glenn & Christina Different models = different assumptions – PBL, stability class, roughness length