The Martian Planetary Boundary Layer Luis Vzquez Departamento

The Martian Planetary Boundary Layer Luis Vázquez (*) Departamento de Matemática Aplicada Facultad de Informática Universidad Complutense de Madrid / 28040 -Madrid and Real Academia de Ciencias Exactas, Físicas y Naturales lvazquez@fdi. ucm. es www. fdi. ucm. es/profesor/lvazquez www. meiga. metnet. org (*) G. Martínez and F. Valero THIRD MOSCOW SOLAR SYSTEM SYMPOSIUM (3 M-S 3) SPACE RESEARCH INSTITUTE (IKI) October 8 -12, 2012

References 1. Harri A. , Schmidt W. , Romero P. , Vazquez L. , Barderas G. , Kemppinen O. , Aguirre C. , Vazquez-Poletti J. , Llorente I. , Haukka H. , Paton M. , 2011, "Phobos eclipse detection on Mars: theory and practice" , Reports 2012: 2, Finnish Meteorological Institute. 2. A. Petrosyan, B. Galperin, S. E. Larsen, S. R. Lewis, A. Määttänen, P. L. Read, N. Renno, L. P. H. T. Rogberg, H. Savijärvi, T. Siili, A. Spiga, A. Toigo and L. Vázquez. “The Martian Atmospheric Boundary Layer”. Reviews of Geophysics 49, RG 3005, 1 -46, (2011). 3. G. M. Martínez, F. Valero and L. Vázquez. “TKE Budget in the Convective Martian PBL”. Quarterly Journal of the Royal Meteorological Society, DOI: 10 -1002/qj. 883. (2011). 4. G. M. Martínez, F. Valero and L. Vázquez. “Characterization of the Martian Convective Boundary Layer”. Journal of the Atmospheric Sciences 66, 2044 -2057 (2009). 5. G. M. Martínez, F. Valero and L. Vázquez. “Characterization of the Martian Surface 2 Layer”. Journal of the Atmospheric Sciences 66, 187 -198 (2009).

Outline 1) Definition and Importance of the PBL 1) Data 2) Methodology 3) Results 5) Comparison to Earth PBL 3

1. Definition Ø Planetary Boundary Layer Definition: the bottom part of the atmosphere directly influenced by the planet surface, and that responds to surface forcings with a timescale of about an hour or less. Studied by the Micrometeorology. Ø Main feature: Turbulent nature. Ø Above it, the free atmosphere. 4

1. Definition Parts of the PBL Under convective conditions (daytime), divided in: Ø Surface Layer (SL): Region at the bottom of the PBL where turbulent fluxes vary by less than 10% of their magnitude. The sharpest variations in meteorological magnitudes take place in this layer, and, consequently, the most significant exchanges of momentum, heat, and mass. Ø Mixed Layer (ML): It is characterized by an intense vertical mixing which tends to leave variables such as potential temperature and humidity nearly constant with height, even wind speed and direction. 5

1. Importance Ø The place where landers and rovers operate. Design of the sensors Ø Habitability (UV Radiation, Soil Water Content) Ø GCMs and Mesoscale models need to incorporate PBL phenomena. There exist feedbacks acting in both directions Climate Years Weather Micro Days Minutes 6

2. Data Set of Data used in this Work: Ø In situ Hourly Averaged Temperature Ø In situ Hourly Averaged Horizontal Wind Speed Ø Simulated Hourly Ground Temperature They correspond to some selected Sols (1 Sol is defined as one Martian day = 88775 s) belonging to: Ø Viking 1: Sols 27, 28, and 35 Measuring height 1. 6 m Ø Viking 2: Sols 20 and 25 Ø Pathfinder: Sol 25 Measuring height 1. 3 m 7

2. Data Viking Lander 1 Sol 27 Horizontal Velocity Temperature Ground Temperature 8

3. Methodology Given the nature of the in situ data available to research the Martian PBL, we have made an adaptation to Mars of: Ø Surface Layer Similarity Theory: Monin, A. S. , and A. M. Obukhov 1954, AN SSSR, 24, 163 -187 Ø Convective Mixed Layer (CML) Similarity Theory Deardorff, J. W. 1972, 29, JAS, 91 -115 All key thermodynamics variables both for the SL and CML can be derived from proper modifications of both theories 9

3. Methodology Limitations of the Methodology: The results are valid under the next topographical-environmental conditions: Ø Moderate Flat Terrains Ø No Synoptic Perturbations Ø Low Dust Load (radiative forcing < convective heating) To What Extent our Results are Representative? Ø Results expected to represent any Sol where the above three restrictions are met Ø Thus, results specially suitable for northern summertime Sols 10

4. Results Thermodynamical Characterization of the PBL Key Values Friction Velocity Ø Height up to where shear dominates convection Ø By definition, negative under local static instability conditions Ø Around -20 m at noon Ø Similar values on Earth Ø It represents the shear at surface Surface Layer Monin-Obukhov Length Ø Values around 0. 5 m/s at noon Ø Important for the saltation of dust Ø Similar values on Earth 11

4. Results Thermodynamical Characterization of the PBL Key Values Surface Dynamic Heat Flux H 0 Surface Layer Scale Temperature Energy Budget at surface Ø Eddy temperature fluctuations Ø By definition, negative under local static instability conditions Ø Higher absolute values close to noon Ø Its values consistent with the fluctuation measured by PF and VK landers Daytime Nightime Ø Positive during the daytime (“Breathing”, Cooling) Ø Negative during the night (Soil Heated by H 0) Ø It does not counteract the net radiative heating (SW=120 W/m 2 vs H 0=7 W/m 2 ) during daytime Ø It does not counteract the LW radiative 12 cooling (LW=50 W/m 2 vs H 0=0. 5 W/m 2 ) at night

4. Results Thermodynamical Characterization of the PBL Key Values Convective Mixed Layer PBL Height Convective Velocity Ø The height up to where turbulence is always present Ø It represents the upward velocity of thermals Ø Up to 11 kms, due to the vigorous kinematic heat flux (though the dynamic heat flux is relative small due to the low density) Ø Values around 2 and 4. 5 m/s 13

4. Results Thermodynamical Characterization of the PBL Key Values Convective Mixed Layer Convective Temperature Scale Ø It represents how much warmer thermals are than the environment Ø Values mainly in the range (0. 1, 0. 3) K Mean Turbulent Temperature Standard Deviation Ø Typical turbulent temperature fluctuations promediated in the whole Convective ML Ø Values are representative of the whole CML 14

4. Results Definition of the TKE Ø Turbulent Kinetic Energy (TKE) is defined as: Ø Velocity variances are obtained averaging over periods falling in the spectral gap (Mesoscale ≈ 1 h), so the departure from the mean corresponds to the Turbulent Part of the spectrum 15

4. Results Ø The Equation ruling the evolution of the TKE is given by: Ø B: Buoyancy Ø S: Shear Ø Tr: Turbulent Transport Ø Diss: Dissipation Ø Err: Imbalance with the Im term given by: Im expected to be small Ø We next show values both in the SL and CML for each of the above terms

4. Results 1) SURFACE LAYER PATHFINDER SOL 25 (z = 1. 3 m) Vertical and Horizontal St. Deviations Turbulent Kinetic Energy (TKE) Ø During the most convective hours, we can consider steady state for the TKE, as shown encircled in yellow the in the figures above Ø Horizontal Turbulence higher than Vertical one (4 or 5 times). Turbulence not isotropic 17 Ø TKE of the order of 3 m 2 s-2

4. Results SURFACE LAYER TKE BUDGET PF SOL 25 Ø Shear main creator of TKE Ø Dissipation balances Shear Ø Buoyancy and Transport two orders of magnitude lower than Shear and Dissipation Ø Buoyancy and Transport balance each other Ø Buoyancy is positive (creation), due to upward kinematic heat flux Ø Transport sends TKE upwards, and thus is negative (it removes TKE) Ø Imbalance one order of magnitude lower than the main 18 mechanisms

4. Results CONVECTIVE MIXED LAYER PATHFINDER SOL 25 Averaged Vertical and Horizontal St. Deviations Turbulent Kinetic Energy (TKE) Ø During the most convective hours, we can consider steady state for the TKE, as shown encircled in yellow the in the figures above Ø Horizontal Turbulence equals Vertical one, at least handling with mean values. Turbulence isotropic 19 Ø TKE of the order of 8 m 2 s-2. This value matches other estimations

4. Results CONVECTIVE MIXED LAYER TKE BUDGET PF SOL 25 Ø Buoyancy the main mechanism creating TKE Ø Dissipation almost balances the Buoyancy, being the main TKE remover Ø Shear becomes negligible Ø Transport becomes now positive, since in the average TKE is being transported to the CML Ø Imbalance is lower than the main terms, which gives reliability to the results 20

5. Comparison to Earth PBL Surface Layer - Typical values of Monin-Obukhov lenght and friction velocity agree on both planets, while the scale temperature is one order of magnitude higher on Mars - TKE values are similar on both planets, and so is the TKE budget (qualitatively and quantitatively). Convective Mixed Layer - Convective mixed layer height is much higher on Mars (~8 Km vs ~1 km), and so are the velocity scale and the convective scale temperature (more than double wrt their terrestrial value) - TKE values more than 2 times higher than on Earth. TKE budget are similar qualitatively in both planets, with the exception that the transport term is comparable to the buoyancy term. Quantitavely, both TKE budget seem to show similar behavior 21

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