AERMETEnergy Balance in PBLNet RadiationTransition between the CBL and SBLSurface Friction VelocitySlide 6Convective Velocity Scale (w*) in CBLConvective Mixing Height (zic)Surface Friction Velocity in SBLSlide 10Surface Heat Flux in SBLMechanical Mixing HeightSlide 13Meteorological InterfaceWind Speed ProfilingWind Speed ProfileWind Direction ProfilesPotential Temperature Gradient Profiles - SBLPotential Temperature ProfileVertical TurbulenceSlide 21Slide 22Lateral TurbulenceSlide 24Vertical Inhomogeneity in the BLSlide 26Slide 27Slide 28SummaryAERMET•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.01/14/2019 Aerosol & Particulate Research Lab 1Energy Balance in PBL•Surface sensible heat flux, H01/14/2019 Aerosol & Particulate Research Lab 2 00/119.0/1.0BRHEHBRGRGEHnnnB0: Bowen ratio – for available surface moisturelatent heat fluxSoil heat fluxnet radiationNet Radiation•If measured values for Rn not available, estimate from insolation and thermal radiation balance is used•Solar Radiation Corrected for Cloud Cover01/14/2019 Aerosol & Particulate Research Lab 3  3246111cncTTcRrRrefSBrefnC1=5.31×10-13 Wm-2K-6C2=60 Wm-2C3=0.12SB: Stefin Boltzman constant (5.67×10-8 Wm-2K-4)Tref: ambient air temperature at the reference height   o290' '15.0 1.0)exp()'1('rrrbabarrralbedo   2 30sin99075.0104.30ttRnRRp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, φcrit ~ 13o; for overcast conditions, φcrit ~ 23o.•If solar radiation measurements are available, determine φcrit from cloud cover. 01/14/2019 Aerosol & Particulate Research Lab 4Q: Does the transition occurs at sunset?     3075.0119901sin4.32461nrncTTcSBcrit4.3/1075.0/1RRneqSurface Friction Velocity01/14/2019 Aerosol & Particulate Research Lab 5•Stress (τ) 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 (τ/ρ) is stress per unit density (of air). •Surface friction velocity:/*uhttp://www.knowledgerush.com/kr/encyclopedia/Viscosity/ Monin-Obukhov LengthA parameter in the Monin–Obukhov similarity theory that relates surface friction velocity to potential temperatureSurface Friction Velocity (u*) and Monin-Obukhov Length (L) in CBL01/14/2019 Aerosol & Particulate Research Lab 6      HgkuTcLLzLzLzLzLzLzzzukurefprefmrefmmrefmrefref3*4/1004/10120001200*/161 and /161 2/tan221ln21ln2/ 2/tan221ln21ln2/ //)/ln(Initial guess for iteration: ψm = 0 (neutral) and u* = uref.k: von Karmon constant (=0.4)uref: wind speed at reference heightzref: reference measurement heightz0: roughness length•uref: typically 10 m can be chosen. However, for rough surface (e.g. urban areas), AERMOD accepts wind speed between 7z0 and 100 m. For temperature, the lower limit is 1z0.•Above 100 m, wind and temperature measurements are above the surface layer. 01/14/2019 Aerosol & Particulate Research Lab 7Convective Velocity Scale (w*) in CBL•Used to characterize the convective portion of the turbulence in the CBL. It is roughly the updraft speed. 3/1*refpicTczHgwConvective Mixing Height (zic)•Use measured heights, if available.•If not available, estimate from energy balance model:01/14/2019 Aerosol & Particulate Research Lab 8    ''4.100dtctHdzzzztpzicicicEarly morning temperature soundingTime varying surface heat fluxt: hour after sunrise.Surface Friction Velocity in SBL•Temperature scale•Wind speed profile in stable conditions01/14/2019 Aerosol & Particulate Research Lab 92****)/(ugkTLucHrefp DrefrefmcrrefDrefDmrefDrefrefmDCTgzuuuCuuCuzzkCuTgzCuu/4 21125 /ln/ 1*22/10*02***fordrag coefficient•For wind speed less than the critical value•θ* estimation–If cloud cover observation available–Bulk Richardson approachIteration of u*, θ* and L until convergence01/14/2019 Aerosol & Particulate Research Lab 10      crcrcrcruuuuuuuuuu//**** 2*5.0109.0 nn: fractional cloud cover  Lzzzzk121212*5lnrefrefmTgzu /*01,2 for two levels of temperature measurementSurface Heat Flux in SBL•AERMET limits loss to 64 W/m2.•In CBL: the larger of mechanical mixing height (zim) and convective mixing height (zic)•In SBL: equal to mechanical mixing height (zim)01/14/2019 Aerosol & Particulate Research Lab 11** ucHpMixing HeightQ: What processes affect the magnitude of mixing height?Mechanical Mixing Height•Use measured heights, if available.•If not available, first calculate equilibrium MH•In mid-latitudes•Time evolution of MMH01/14/2019 Aerosol & Particulate Research Lab 12fLuzie/4.0*f: Coriolis parameter2/3*2300uzieunsmoothed*/ uzzzdtdzimimieimτ: time scale to reach equilibriumβτ = 2Q: Is MMH a constant during the day? Why?Q: What would happen if zim < zie? When does it happen?•Smoothing–Discontinuity from night to day