1 Phoenix Large Eddy Simulation of Vertical Vortices in Highly Convective Martian Boundary Layer Babak Tavakoli-Gheynani and Peter A. Taylor 18th Symposium on Boundary Layers and Turbulence, 9-13 June 2008, Stockholm, Sweden Center for Research in Earth and Space Science (CRESS), York University

NASA/CSA Phoenix Lander 2007 Organizer: The NASA’s first scout program. Led by Dr. Peter Smith, University of Arizona. Duty: Measuring volatiles (water) and complex organic molecules in the arctic plains of Mars Launched: 4 Aug 2007, 5:25AM, Kennedy Space Center. Cruise: 10 months Land: 25 May 2008, near 68N deg. latitude, 127W deg. longitude Surface Operation: 3 months

Canadian Space Agency (CSA) contribution Phoenix Meteorological Station

4 As a part of phoenix Research on: The vertical size distribution of dust particles This study Considers: Local dust storm events in lifting dust from surface Focuses: Vertical vortices (dust devil) formation in highly convective Boundary Layers

5Approach Investigated: Planetary Boundary Layer (PBL) Employed: NCAR LES Sullivan et al. (1994) Theoretical scheme First-Order Closure scheme: Momentum SGSs: Two-part eddy viscosity Model Thermodynamic SGSs: S-L Model Boundary Conditions: No slip M-O (lower), Periodic (lateral), sponge layer (upper) Numerical scheme Third-order Runge-Kutta scheme Mixed pseudospectral (horizontal planes) Second order finite-difference (vertical direction) Computation Parallel Architecture MPI & OpenMP

6 Result comparison in convective boundary layer (a) Total heat flux, (b) Third-order resolved vertical velocity, (c) Third-order resolved virtual potential temperature, at t=2.8hr and zero geostrophic wind, (d) Total heat flux, (e) Third-order resolved vertical velocity, (f) Third-order resolved virtual potential temperature, at t=2.8hr and 20m/s geostrophic wind. A comparison exercise with Fedorovich et al. (2004)

7 Parameters Characterizing climate and atmosphere for Earth & Mars (Ryan & Henry 1979) Simulation Properties of Highly Convective Boundary Layers on Earth & Mars Heat flux: 0.9 Km/s, Simu. Time=4.5hr

8 Physical Characteristics of Vertical Vortices on Earth & Mars * Sinclair(1969) dust devil category.

9 Vorticity volume contour plot Simulation Results of Martian Highly Convective Boundary Layer at Phoenix lander site

10 Simulation Results of Martian Highly Convective Boundary Layer at Phoenix lander site Horizontal velocity vectors and vortices contour plot (back ground) at the first level (z=20m)

11 Horizontal temperature contour plot at the first level (z=20m) Simulation Results of Martian Highly Convective Boundary Layer at Phoenix lander site

12 Vertical velocity contour plot at vertical cross sections of the dust devil like vortex Simulation Results of Martian Highly Convective Boundary Layer at Phoenix lander site

13 Effect of geosrophic wind on vertical vortices formation on Mars Characteristic at 20m above surface014 8 Unit Simulated Time (~2700s) s Height (~) Helical m Rotation Sense0.47cw0.482cw0.55ccw0.7ccws -1 Horizontal Velocity (max/min) 6.5/-5.65/ /-7.215/-14.2ms -1 Vertical Velocity (max) ms -1 Diameter (~) m Temperature Increment (~) K Movement speed 0.4 xy 0.5 xy 2.5-x 6.4-xm/s Orientation (angle) Deg Ug = 0 m/s Ug = 4 m/s Ug = 8 m/s Location: Phoenix lander site, 70N, in a sunny summer day, heat flux=25wm.

14 How many vertical vortices form per ? a) Vorticity contour plot, b) Velocity vector field, at z=20m and t=2351s

15 Detection of 84 Vortices with no Ug at z=20m and t=2351s An algorithm have been performed based on Connecting regions of Opposite Velocity directions a) Vorticity contour plot and the locations of vortices, b) Velocity vector field and the locations of vortices

16 Physical characteristic of Martian Dust devil-like vortices Quiescent environment at 70deg N latitude

17 Physical characteristic of Martian Dust devil-like vortices Quiescent environment at 70deg N latitude Maximum PossibleMax.Avg.Min Vorticity (1/s) Diameter (m) Horizontal velocity (m/s) 92NA Vertical Velocity (m/s) <0.1 Temperature Increment (K) 167.5<

18 Conclusion and future works ■ Martian dust devils roughly are 6 times higher and 10 times wider than Earth’s dust devils. ■ Stronger winds cause vertical vortices spin faster, travel faster, curve sharper, and become shorter. ■ In windy condition, dust almost is lofted and migrates along wind direction. ■ The performed algorithm can provide the lifespan, diameter, max horizontal and vertical velocities of the vortices. ■ At Phoenix lander site, Majority of the vortices have 125m wide and horizontal velocity around 2 m/s. some detections are as intense as 600m wide and 10m/s horizontal velocity and as high as 2000m. ■ Further optimization will be applied to improve the algorithm results. ■ Recent performed algorithm will help us better to see if low ambient wind has any boost effect on dust devil formation. ■ Strive to use more relevant spacecrafts data for comparison and measurement.

19 Acknowledgment It is a great pleasure to acknowledge: Professor Peter Tayor, YU Dr. Peter Sullivan, NCAR Professor Allan Carswell, Optech Inc. CSA Sharcnet HPC