Presentation Slides for Chapter 8 of Fundamentals of Atmospheric Modeling 2nd Edition Mark Z. Jacobson Department of Civil & Environmental Engineering Stanford University Stanford, CA 94305-4020 [email protected] March 10, 2005
Download ReportTranscript Presentation Slides for Chapter 8 of Fundamentals of Atmospheric Modeling 2nd Edition Mark Z. Jacobson Department of Civil & Environmental Engineering Stanford University Stanford, CA 94305-4020 [email protected] March 10, 2005
Presentation Slides for Chapter 8 of Fundamentals of Atmospheric Modeling 2nd Edition Mark Z. Jacobson Department of Civil & Environmental Engineering Stanford University Stanford, CA 94305-4020 [email protected] March 10, 2005 Reynolds Stress Stress Force per unit area (e.g. N m-2 or kg m-1 s-2) Reynolds stress Stress that causes a parcel of air to deform during turbulent motion of air Fig. 8.1. Deformation by vertical momentum flux w u Stress from vertical transfer of turbulent u-momentum (8.1) zx a w u zx = stress acting in x-direction, along a plane (x-y) normal to the z-direction Momentum Fluxes Magnitude of Reynolds stress at ground surface (8.2) 2 1 2 z a w u w v 2 Kinematic vertical turbulent momentum flux (m2 s-2) (8.3) zx w u a w v zy a Friction wind speed (m s-1) (8.8) Scaling param. for surface-layer vert. flux of horiz. momentum 14 2 2 12 u* wu w v z a s s s Heat and Moisture Fluxes Vertical turbulent sensible-heat flux (W m-2) (8.4) H f ac p,d w v Kinematic vert. turbulent sensible-heat flux (m K s-1) Hf w v acp,d Vertical turbulent water vapor flux (kg m-2 s-1) (8.5) (8.6) E f a w q v Kinematic vert. turbulent moisture flux (m kg s-1 kg-1) (8.7) w q v Ef a Surf. Roughness Length for Momentum Height above surface at which mean wind extrapolates to zero • Longer roughness length --> greater turbulence • Exactly smooth surface, roughness length = 0 • Approximately 1/30 the height of the average roughness element protruding from the surface Surf. Roughness Length for Momentum ln z Method of calculating roughness length 1) Find wind speeds at many heights when wind is strong 2) Plot speeds on ln (height) vs. wind speed diagram 3) Extrapolate wind speed to altitude at which speed equals zero Fig. 6.5 Roughness Length for Momentum Over smooth ocean with slow wind (8.9) a a z0,m 0.11 0.11 u* au* Over rough ocean, fast wind (Charnock relation) (8.10) 2 u* z0,m c g Over urban areas containing structures ho So z0,m 0.5 Ao Over a vegetation canopy z0,m hc 1 0.91e 0.0075LT (8.11) (8.12) Roughness Length for Momentum Surface Type z0,m (m) 0.00001 0.0000150.0015 Ice 0.00001 Snow 0.00005-0.0001 Level desert 0.0003 Short grass 0.03-0.01 Long grass 0.04-0.1 Savannah 0.4 Agricultural crops 0.04-0.2 Orchard 0.5-1.0 Broadleaf evergreen forest 4.8 Broadleaf deciduous trees 2.7 Broad- and needleleaf trees 2.8 Needleleaf-evergreen trees 2.4 Needleleaf deciduous trees 2.4 Short vegetation/C4 grassland 0.12 Broadleaf shrubs w/ bare soil 0.06 Agriculture/C3 grassland 0.12 2500 m2 l ot w/ a b uilding 8-m 0.26 high and 160 m2 silhouette 25,000 m2 lot w/ a building 80-m 5.1 h c (m) d c (m) Smooth sea Rough sea high and 3200 m2 silhouette 0.02-0.1 0.25-1.0 8 0.4-2 5-10 35 20 20 17 17 1 0.5 1 8 80 4.8 0.27-1.3 3.3-6.7 26.3 15 15 12.8 12.8 0.75 0.38 0.75 Table 8.1 Roughness Length for Energy, Moisture Surface roughness length for energy (8.13) Dh z0,h ku* Surface roughness length for moisture (8.13) Dv z0,v ku* Molecular thermal diffusion coefficient (8.14) a Dh ac p,m Molecular diffusion coefficient of water vapor (8.14) 1.94 1013.25 hP a T Dv 2.11 105 273.15 K p a Turbulence Description Turbulence Group of eddies of different size. Eddies range in size from a couple of millimeters to the size of the boundary layer. Turbulent kinetic energy (TKE) Mean kinetic energy per unit mass associated with eddies in turbulent flow Dissipation Conversio n of turbulence into heat by molecular viscosity Inertial cascade Decrease in eddy size from large eddy to small eddy to zero due to dissipation Turbulence Models Kolmogorov scale 14 3 k a d (8.15) Reynolds-averaged models Resolution greater than a few hundred meters Do not resolve large or small eddies Large-eddy simulation models Resolutio n between a few meters and a few hundred meters Resolve large eddies but not small ones Direct numerical simulation models Resolutio n on the order of the Kolmogorov scale Resolve all eddies Kinematic Vertical Momentum Flux Bulk aerodynamic formulae (8.16-7) Diffusion coefficient accounts for Skin drag: drag from molecular diffusion of air at surface Form drag: drag arising when wind hits large obstacles Wave drag: drag from momentum transfer due to gravity waves wu s CD v hzr u zr u z0,m wvs CD vh zr vzr vz0,m Kinematic Vertical Momentum Flux Bulk aerodynamic formulae (8.18) K-theory (8.18) wu s CD v hzr u zr u z0,m u wu Km,zx s z Wind speed gradient u u zr u z0,m z zr z0,m (8.19) Eddy diffusion coef. in terms of bulk aero. formulae Km,zx Km,zy CD v hzr zr z0,m (8.20) Kinematic Vertical Energy Flux Bulk aerodynamic formulae (8.21) K-theory (8.23) wv s CH vh zr v zr v z0,h v wv Kh,zz s z Potential virtual temperature gradient (8.24) v v zr v z0,h z zr z0,h Eddy diffusion coef. in terms of bulk aero. formulae Kh,zz CH v hzr zr z0,h (8.25) Vertical Turbulent Moisture Flux Bulk aero. kinematic vertical turbulent moisture flux (8.26) wq v s CE vhzr q v zr q v z0,v CE≈CH --> Kv,zz =Kh,zz Similarity Theory • Variables are first combined into a dimensionless group. • Experiment are conducted to obtain values for each variable in the group in relation to each other. • The dimensionless group, as a whole, is then fitted, as a function of some parameter, with an empirical equation. • The experiment is repeated. Usually, equations obtained from later experiments are similar to those from the first experiment. • The relationship between the dimensionless group and the empirical equation is a similarity relationship. • Similarity theory applied to the surface layer is Monin-Obukhov or surface-layer similarity theory. Similarity Relationship Dimensionless wind shear (8.28) m z vh k u* z Dimensionless wind shear from field data (8.29) 1 z m L z 1 4 m 1 m L 1 Integrate (8.28) from z0,m to zr z 0 L z 0 L z 0 L k v h zr u* z dz r m z 0,m z s tabl e uns table neutral (8.30) Integral of Dimensionless Wind Shear Integral of the dimensionless wind shear zr dz z0, m m z m zr zr z0,m ln z L 0,m 14 1 4 z zr 0,m 1 1 m 1 1 m L L ln ln 14 zr z0,m 1 4 1 m 1 1 m 1 L L 14 14 z z 2 tan1 1 m r 2 tan1 1 m 0,m L L ln zr z0,m (8.31) z 0 L z 0 L z 0 L s tabl e uns table neutral Monin-Obukhov Length Height proportional to the height above the surface at which buoyant production of turbulence first equals mechanical (shear) production of turbulence. (8.32) L u3* v kg wv s u2* v kg* Kinematic vertical energy flux wv s u** (8.33) Potential Temperature Scale Dimensionless temperature gradient (8.34) h z v k * z Parameterization of * P r z t h L z 1 2 h P rt 1 h L P rt (8.35) z 0 L z 0 L z 0 L s tabl e uns table neutral Potential Temperature Scale Turbulent Prandtl number P rt Km,zx Kh,zz Integrate (8.23) from z0,m to zr h z v k * z (8.37) k v zr v z0,h * zr dz z0,h h z Integral of Dimensionless Temp. Grad. Integral of dimensionless temperature gradient (8.38) zr dz z0, h h z zr h zr z0,h P rt ln z L 0,h 12 z 1 h r 1 1 h L P rt ln ln 12 z 1 h r 1 1 h L zr P r ln t z 0,h 1 12 z0,h 1 L z 0 L s tabl e z 0 L uns table z 0 L neutral 12 z0,h L Equations to Solve Simultaneously Solution requires iteration k v h zr u* z dz r m z 0,m z L 3 u* v kg wv k v zr v z0,h * zr dz z0,h h z s 2 u* v kg* Noniterative Parameterization Friction wind speed u* k v h zr ln zr z0,m (8.40) Gm Potential temperature scale Gh 2 u* P rt ln zr z0,m k vh zr v z r v z0,h 2 * (8.40) Scale Parameterization Potential temperature scale (8.41) 9.4Rib Gm 1 1 70k 1 Gm ,Gh Rib 0 0.5 Rib 0 Rib zr z0,m ln 2 zr z0,m 2 9.4Rib Gh 1 0.5 50k 2 Rib zr z0,m ln2 zr z0,m 1 1 4.7Rib 2 Rib 0 Bulk Richardson Number Ratio of buoyancy to mechanical shear (8.39) zr z0,m Rib 2 2 v z0,h u zr v zr zr z0,h g v zr v z0,h 2 Gradient Richardson Number Ri g g v v z 2 (8.42) 2 u v z z Table 8.2. Vertical air flow characteristics for different Rib or Rig Value of Rib or Rig Type of Flow Level of Turbulence Due to Buoyancy Large, negative Small, negative Turbulent Turbulent Large Small Small positive Large positive Turbulent Laminar None (weak stable) None (strong stable) Level of Turbulence Due to Shear Small Large Large Small Gradient Richardson Number Ri g g v v z 2 (8.42) 2 u v z z Laminar flow becomes turbulent when Rig decreases to less than the critical Richardson number (Ric) = 0.25 Turbulent flow becomes laminar when Rig increase to greater than the termination Richardson number (RiT) = 1.0 Similarity Theory Turbulent Fluxes Friction wind speed 14 2 2 u* wu w v s s (8.8) Bulk aerodynamic kinematic momentum flux (8.16) wu s CD v hzr u zr u z0,m Friction wind speed (8.43) u* v hzr CD Rederive momentum flux in terms of similarity theory (8.43) 2 u* wu u zr s v h zr Eddy Diff. Coef. for Mom. Similarity K-theory kinematic turbulent momentum fluxes u wu Km,zx s z (8.18) v wv Km,zy s z Similarity theory kinematic turbulent fluxes 2 u* wu s v z u zr h r (8.44) 2 u* wvs v z v zr h r Combine the two Km,zx Km,zy (8.46) 2 u* zr z0,m z vh r Example Problem ---> vh zr ---> Gm ---> u* L ---> ---> Km,zx z0,m = 0.01 Prt = 0.95 z0,h = 0.0001 m k = 0.4 u(zr)=10 m s-1 v(zr)= 5 m s-1 v(zr)= 285 K v(z0,h)= 288 K = 11.18 m s-1 = 1.046 = 0.662 m s-1 = -169 m 2 u* ---> ---> Rib Gh ---> * zr z0,m z = -8.15 x 10-3 = 1.052 = -0.188 K = 0.39 m2 s-1 vh r u* * ---> K h,zz = 0.41 m2 s-1 ---> K m,zx K h,zz = 0.95 v z Eddy Diff. Coef. for Mom. Similarity Dimensionless wind shear (8.28) m z vh k u* z Wind shear Km,zx 2 u* (8.46) zr z0,m z vh r Combine expressions above (8.48) kzu* Km,zx Km,zy m kz = mixing length: average distance an eddy travels before exchanging momentum with surrounding eddies Energy Flux from Similarity Theory Vertical kinematic energy flux (8.49) wv s u** Surface vertical turbulent sensible heat flux H f acp,d wv acp,du* * s (8.53) Energy, Moisture Fluxes from Similarity Vertical kinematic water vapor flux (8.49) wq v s u*q * Surface vertical turbulent water vapor flux (8.53) E f a wq v au*q* s Dimensionless specific humidity gradient (8.51) q z q v k q * z Specific humidity scale k q v zr q v z0,v q* z r dz z 0,v h z (8.52) Logarithmic Wind Profile Dimensionless wind shear (8.28) m z vh k u* z Rewrite (8.57) vh z u* u* m 1 1 m z kz kz Integrate --> surface layer vertical wind speed profile (8.59) u* vh z k z ln m z0,m Logarithmic Wind Profile Influence function for momentum (8.61,2) z dz m 1 m z 0,m z m L z z0,m 2 1 2 1 m z 1 m z ln 2 1 2 1 m z0,m 1 m z0,m 1 1 1 1 2 tan m z 2 tan m z0,m 0 z 0 L s tabl e z 0 L z 0 L uns table neutral Logarithmic Wind Profile Height above surface (m) Neutral conditions --> logarithmic wind profile (8.64) u* z vh z ln k z0,m Height above surface (m) Logarithmic wind profiles when u* = 1 m s-1. 10 8 6 z 4 0 ,m =1.0 m z 0 ,m =0.1 m 2 0 0 2 4 6 8 -1 Wind speed (m s ) 10 12 Fig. 8.3 Potential Virtual Temperature Profile Dimensionless potential temperature gradient (8.34) h z v k * z Rewrite (8.58) v * * h 1 1 h z kz kz Integrate --> potential virtual temperature profile * z v z v z0,h P rt ln h k z0,h (8.60) Potential Virtual Temperature Profile Influence function for energy (8.61,3) z dz h 1 h z0,h z 1 h P r L z z0,h t 1 h z1 2ln 1 1 h z0,h 0 z 0 L s tabl e z 0 L uns table z 0 L neutral Vertical Profiles in a Canopy ln z0,m Relationship among dc, hc, and z0,m Fig. 8.4 Vertical Profiles in a Canopy Momentum u* vh z k z d z d c c ln m z L 0,m Potential virtual temperature (8.66) (8.67) * z d c z dc v z v dc z0,h P rt ln h k L z0,h Specific humidity (8.68) q* q v z q v d c z0,v P rt k z d z d c c ln h L z0,v Local v. Nonlocal Closure Above Surface Local closure turbulence scheme Mixes momentum, energy, chemicals between adjacent layers. Hybrid E-l E-d Nonlocal closure turbulence scheme Mixes variables among all layers simultaneously Free-convective plume scheme Hybrid Scheme For momentum for stable/weakly unstable conditions (8.70) Captures small eddies but not large eddies due to free convection --> not valid when Rib is large and negative 2 2 Ri Ri u v c b Km,zx Km,zy l2e z z Ric Mixing Length For energy (8.71) kz le 1 kz lm K h,zz K m,zx Prt E (TKE)-l Scheme Prognostic equation for TKE (8.72) E E sqle 2E Ps Pb d t z z Prognositc equation for mixing length (8.73) 2 2El e 2El e le sl le 2E lee1 Ps Pb l e d 1 e2 t z z kz Production rate of shear u 2 v 2 Ps Km z z (8.74) E-l Scheme Production rate of buoyancy (8.75) g v Pb Kh v z Dissipation rate of TKE (8.76) d 2 E 3 2 B1l e Diffusion coefficients Km SM l e 2E (8.77) Kh Sh l e 2E E-d TKE Prognostic equation for dissipation rate d Km d d c 1 Ps Pb c 2 t z z E Eddy diffusion coefficient for momentum (8.88) 2d E (8.89) E2 K m c d Diagnostic equation for mixing length 32 34 E l e c d (8.90) Heat Conduction Equation Heat conduction equation Ts 1 Ts s t g cG z z (8.91) Thermal conductivity of soil-water-air mixture (8.92) log10 p 2.7 s max 418e , 0.172 Moisture potential Potential energy required to extract water from capillary and adhesive forces in the soil (8.93) wg,s b p p,s w g Heat Conduction Equation Density x specific heat of soil-water-air mixture (8.94) gcG 1 wg,s scS wgwcW Rate of change of soil water content (8.95) wg wg p 1 Dg Kg Kg t z z z z Hydraulic conductivity of soil Coefficient of permeability of liquid through soil wg 2b3 Kg Kg,s w g,s (8.96) Heat Conduction Equation Diffusion coefficient of water in soil (8.97) b 3 bKg,s p,s wg bKg,s p,s Dg Kg wg wg wg,s wg,s p wg b2 w g,s Heat Conduction Equation Rate of change of ground surface temperature (8.98) Ts 1 Ts s Fn,g H f Le E f t g cG z z Rate of change of moisture content at the surface w g t z (8.99) E f Pg w g Dg z K g w Surface energy balance equation Ts s,1 Fn,g H f L eE f 0 z (8.103) Temp and Moisture in Vegetated Soil Surface energy balance equation (8.103) Ts s,1 Fn,g H f L eE f 0 z Surface irradiance (8.104) F n,g fsFs Fi s BTg4 Vertical turbulent sensible heat flux a c p,d H f fs p zr Ra (8.105) Tg a c p,d Taf Tg fv Pg R f Pg Pf Temp and Moisture in Vegetated Soil Vertical turbulent latent heat flux (8.106) a a Le E f fs Le g q v zr qv,s Tg fv Le g q af q v,s Tg Ra Rf Temperature of air in foliage (8.109) Taf 0.3Ta zr 0.6Tf 0.1Tg Specific humidity of air in foliage q af 0.3q v zr 0.6q f 0.1q g (8.110) Foliage Temperature Iterative equation for foliage temperature (8.115) v s 4 F F T v i B g s v s v s fv v 2 s v s T 4 v B f v s v s Hv Le Ed Le Et Sensible heat flux Hv 1.1LT (8.116) a c p,d RfPf Taf T f Foliage Temperature Direct evaporation ad Ed LT q af q v,s T f Rf Transpiration (8.117) (8.118) a 1 d Et LT q af q v,s T f R f Rst Evaporation function 23 W c d Wc,m ax 1 (8.119) q af q v,s T f q af q v,s T f Foliage Temperature v s 4 F F T v i B g,t h s v s v s f v v 2 s v s 4 3 T v B f,t,n v s v s a c p,d d a t Taf Le LT a 1.1LT Rf P f R f R f Rst dqv,s T f ,t,n q af q v,s T f ,t,n T f ,t,n dT T f ,t,n1 a c p,d v 2 s v s 3 4 T 1.1L v B f ,t,n T R P v s v s f f dq T d a 1 d v,s f ,t,n L L e T a R R R dT f f st (8.122) Temperature of Vegetated Soil a c p,d Tg,t,n1 f p zr (8.125) s R P a g a c p,d Taf,t Tg,t,n1 fv R P P f f g L a e fs g qv zr q v,s Tg,t,n1 Ra L fv a e g q af q v,s Tg,t,n1 Rf 4 fs Fs Fi B s Tg,t,n1 s,1 D T1,t Tg,t,n1 1 Tg,t,n Tg,t,n1 a c p,d a c p,d s,1 3 fs R P fv R P 4 s B Tg,t,n1 D a g f g 1 Modeled/Measured Temperatures Fig. 8.5 Modeled/Measured Temperatures Fig. 8.5 C) 50 o Temperature ( Modeled/Measured Temperatures Predicted Measured 40 Lodi (LOD) 30 20 10 0 0 24 48 72 Hour after first midnight 96 Fig. 8.5 Road Temperature (8.128) a c p,d Tg,t,n1 p zr Pg Ra a Le d q v zr q v,s Tg,t,n1 Ra 4 F F T s i B as g,t,n1 as T 1,c,t Tg,t,n1 D1 Tg,t,n Tg,t,n1 a c p,d as 3 4 as B Tg,t,n1 Ra Pg D1 Temperatures of Soils and Surfaces Fig. 8.5 C) o Temperature ( Modeled/Measured Temperatures 50 Predicted Measured 40 Fremont (FRE) 30 20 10 0 0 24 48 72 Hour after first midnight 96 Fig. 8.5 Snow Depth (8.129) Ds,t Ds,t h hPs qv zr q v,s min Tg,t , Ts,m fs Ra a h sn q af q v,s min Tg,t , Ts,m fv Rf a c p,d Ts,m p zr fs R P a g a c p,d Taf ,t Ts,m fv R f P P f g a Ls f q z q T s v r v,s s,m R a a Ls q af q v,s Ts,m fv R f sn 4 fs Fs Fi B sn Ts,m T1,t Ts,m D 1 h sn Lm Water Temperature (8.130) a c p,d Tg,t h p zr Pg Ra a Le q v zr q v,s Tg,t h Ra F F T 4 i B w g,t h s Tg,t Tg,t h h sw c p,sw Dl Sea Ice Temperature (8.131) a c p,d Tg,t,n1 p zr Pg Ra a L s q z q T v r v,s g,t,n1 R a 4 Fs Fi B i Tg,t,n1 i Ti, f Tg,t,n1 Di,t h Tg,t,n Tg,t,n1 c i a p,d 3 4 i Tg,t,n1 Ra Pg Di,t h Temperature of Snow Over Sea Ice Tg,t,n Tg,t,n1 (8.134) a c p,d Tg,t,n1 p zr Pg Ra a Ls q z q v r v,s Tg,t,n 1 R a 4 Fs Fi B sn Tg,t,n 1 sn i Ti, f Tg,t,n1 sn Di,t h i Ds,t h a c p,d sn i 3 4 sn Tg,t,n1 Ra Pg sn Di,t h i Ds,t h