Download presentation
Presentation is loading. Please wait.
1
Mars Aerodynamic Roughness Maps and Their Effects on Boundary Layer Properties in A GCM Nicholas Heavens (with Mark Richardson and Anthony Toigo) 9 May 2007 Nicholas Heavens (with Mark Richardson and Anthony Toigo) 9 May 2007
2
The Roughness Parameter (z 0 ) Arises from the need to treat Heat and Momentum Transfer Between Atmosphere and Surface In a neutrally stratified near- surface layer: Arises from the need to treat Heat and Momentum Transfer Between Atmosphere and Surface In a neutrally stratified near- surface layer:
3
The influence of z 0 Z 0 primarily influence GCMs through u*, controlling: Surface Heat and Tracer Diffusion, Stress Partitioning to the Surface (dust/sand particle transport), often used in routines to simulate dry convection Z 0 primarily influence GCMs through u*, controlling: Surface Heat and Tracer Diffusion, Stress Partitioning to the Surface (dust/sand particle transport), often used in routines to simulate dry convection
4
Z 0 and Geometric Roughness (1-D) Z 0 =h triangle /30 Z 0 =h triangle /8 Z 0 =h triangle /30 |dh/dx|=low |dh/dx|=high |dh/dx|=low Idealized after Greeley and Iversen (1985)
5
Z 0 and geometric roughness (2.5-D) Imagine a Chessboard (nxn) with pieces of uniform height, H, distributed randomly with a Fractional occupation F Then the variance ( h 2 ) of the topography is equal to: H 2 (F-F 2 ) and h =H(F-F 2 ) 1/2 Imagine a Chessboard (nxn) with pieces of uniform height, H, distributed randomly with a Fractional occupation F Then the variance ( h 2 ) of the topography is equal to: H 2 (F-F 2 ) and h =H(F-F 2 ) 1/2
6
Theory + Observations (Dong et al. 2002) (2.5 D) H=12 mm. H=31 mm. H=43 mm. Z 0 =H 2n (F-F 2 ) n ?, 1>n>0.5?
7
Two Different Maps of z 0 One is Based on MOLA Pulse Width Roughness (How Laser Scattered by Surface) z 0max =15 cm. The Other is Based on Kreslavsky and Head’s (2001) Roughness Parameter C (relation with H 2? ), which we Extrapolate to C(10 m.~|L| in Vigorous Dry Convection) using self-affinity assumption: H 2 = AL 2J, 0<=J<=1 We calibrate using Pathfinder Estimate: z 0 =3 cm. One is Based on MOLA Pulse Width Roughness (How Laser Scattered by Surface) z 0max =15 cm. The Other is Based on Kreslavsky and Head’s (2001) Roughness Parameter C (relation with H 2? ), which we Extrapolate to C(10 m.~|L| in Vigorous Dry Convection) using self-affinity assumption: H 2 = AL 2J, 0<=J<=1 We calibrate using Pathfinder Estimate: z 0 =3 cm.
8
The Maps
9
MarsWRF Basics Uses 36x64 grid (heavy interpolation of much higher resolution maps) We compare here Year 8 of the Model forced by each model (Passive Dust Forcing makes interannual variability limited, only weather noise) Uses 36x64 grid (heavy interpolation of much higher resolution maps) We compare here Year 8 of the Model forced by each model (Passive Dust Forcing makes interannual variability limited, only weather noise)
10
370 Pa Daytime Comparison Smith, 2004 C(10 m.)Pulse width C(10 m.)-Pulse width
11
Vertical T Comparisons C-PW Daytime C-PW Nighttime C-PW (day) (10 m. above sfc.)C-PW (day) (3500 m. above sfc.)
12
Implications for Dust Devil Activity Kurgansky (2006) proposed that dust devil size distribution strong function of |l| Hess and Spillane (1990) proposed that Dust Devil Activity in General, a strong function of 1/|L|. Combination Could Result in High dust devil Density in High Lats, Large DDs at mid z 0 (Amazonis Planitia?) Alternate Explanations… Whelley et al. (2006)
13
Summary We present two different possible aerodynamic roughness maps (both with different controversial assumptions) Daytime summer temperatures in high latitudes very sensitive to z 0 change (reduced eddy diffusion wins over convection) Smoothness of high latitudes may explain high dust devil activity (provided tracks are a Good Metric) We present two different possible aerodynamic roughness maps (both with different controversial assumptions) Daytime summer temperatures in high latitudes very sensitive to z 0 change (reduced eddy diffusion wins over convection) Smoothness of high latitudes may explain high dust devil activity (provided tracks are a Good Metric)
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.