AERMET - 9/13/11 Aerosol & Particulate AERMET...

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Unformatted text preview: 9/13/11 Aerosol & Particulate AERMET Meteorological Preprocessor for AERMOD Purpose - Use meteorological measurements to computer terrain boundary layer parameters to estimate profiles of wind, turbulence and temperature: Monin-Obukhov length ( L ), surface friction velocity ( u* ), surface roughness length ( zo ), surface heat flux ( H ), convective velocity scale ( w* ), convective and mechanical mixing layer heights ( zic and zim ) Defines stability of the PBL by the sign of H (convective for H > 0 and stable for H < 0) Passes all measurements of wind, turbulence and temperature in a form AERMOD needs. 9/13/11 Aerosol & Particulate 11 9/13/11 Aerosol & Particulate Energy Balance in PBL Surface sensible heat flux, H 9/13/11 Aerosol & Particulate 22 ( 29 / 1 1 9 . / 1 . B R H E H B R G R G E H n n n + = = = = + + B0 : Bowen ratio for available surface moisture latent heat flux Soil heat flux net radiation 9/13/11 Aerosol & Particulate Net Radiation If measured values for Rn not available, estimate from insolation and thermal radiation balance is used Solar Radiation Corrected for Cloud Cover 9/13/11 Aerosol & Particulate 33 { } ( 29 3 2 4 6 1 1 1 c n c T T c R r R ref SB ref n + +- +- = C1 =5.3110-13 Wm- 2K-6 C2 =60 Wm-2 C3 =0.12 9 SB : Stefin Boltzman constant (5.6710-8 Wm- 2K-4) Tref : ambient air temperature at the reference height { } ( 29 { } o 2 90 ' ' 1 5 . 1 . ) exp( ) ' 1 ( ' = =-- =- = +- + = r r r b a b a r r r albedo ( 29 { } {} 2 30 sin 990 75 . 1 4 . 3 t t R n R R p + =- =- = 9/13/11 Aerosol & Particulate Transition between the CBL and SBL When the PBL transitions from convective to stable, the heat flux changes sign from positive to negative Critical solar elevation angle For clear and partly cloudy conditions, crit ~ 13o; for overcast conditions, crit ~ 23o. If solar radiation measurements are available, determine crit from cloud cover. 9/13/11 Aerosol & Particulate 44 Q: Does the transition occurs at sunset? { } ( 29 ( 29 +--- +- = 30 75 . 1 1 990 1 sin 4 . 3 2 4 6 1 n r n c T T c SB crit 4 . 3 / 1 75 . / 1 - = R R n eq 9/13/11 Aerosol & Particulate Surface Friction Velocity 9/13/11 Aerosol & Particulate 55 Stress () is the vertical transfer of horizontal momentum, per unit area, though the air-land/water interface. It is not a function of height, and does not require adjustment dependent on atmospheric stability class. Kinematic stress (/) is stress per unit density (of air). Surface friction velocity: / * = u http://www.knowledgerush .com/kr/encyclopedia/Visc osity/ Monin-Obukhov Length A parameter in the MoninObukhov similarity theory that relates surface friction velocity to potential temperature 9/13/11 Aerosol & Particulate Surface Friction Velocity ( u* ) and Monin-Obukhov Length ( L ) in CBL 9/13/11 Aerosol & Particulate 66 Initial guess for iteration:...
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AERMET - 9/13/11 Aerosol & Particulate AERMET...

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