The Martian Planetary Boundary LayerLuis Vázquez Luis Vázquez (*)(*)

Departamento de Matemática Aplicada Departamento de Matemática Aplicada Facultad de InformáticaFacultad de Informática

Universidad Complutense de Madrid / Universidad Complutense de Madrid / 28040-Madrid 28040-Madrid

andandReal Academia de Ciencias Exactas, Físicas Real Academia de Ciencias Exactas, Físicas

y Naturales y Naturales lvazquez@fdi.ucm.es

www.fdi.ucm.es/profesor/lvazquezwww.meiga-metnet.org

(*) G. Martínez and F. Valero(*) G. Martínez and F. ValeroTHIRD MOSCOW SOLAR SYSTEM SYMPOSIUM (3M-S3)

SPACE RESEARCH INSTITUTE (IKI)October 8-12, 2012

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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, RG3005, 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 Layer”. Journal of the Atmospheric Sciences 66, 187-198 (2009).

Project: MEIGA METNET PRECURSOR: AYA2011- 29967-C05-02.

Outline

1) Definition and Importance of the PBL

1) Data

2) Methodology

3) Results

5) Comparison to Earth PBL

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1. Definition

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.

Main feature: Turbulent nature. Above it, the free atmosphere.

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Under convective conditions (daytime), divided in:

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.

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.

Parts of the PBL1. Definition

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1. Importance

The place where landers and rovers operate. Design of the sensors

Habitability (UV Radiation, Soil Water Content) GCMs and Mesoscale models need to incorporate PBL phenomena. There exist feedbacks acting in both directions

Climate Weather Micro

Years MinutesDays

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Set of Data used in this Work: In situ Hourly Averaged Temperature

In situ Hourly Averaged Horizontal Wind Speed

Simulated Hourly Ground Temperature

2. Data

They correspond to some selected Sols (1 Sol is defined asone Martian day = 88775 s) belonging to:

Viking 1: Sols 27, 28, and 35

Viking 2: Sols 20 and 25

Pathfinder: Sol 25

Measuring height 1.6 m

Measuring height 1.3 m

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Horizontal Velocity Temperature Ground Temperature

Viking Lander 1 Sol 27

2. Data

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3. Methodology

Given the nature of the in situ data available to research the Martian PBL, we have made an adaptation to Mars of:

Surface Layer Similarity Theory:

Convective Mixed Layer (CML) Similarity Theory

Monin, A. S., and A. M. Obukhov 1954, AN SSSR, 24, 163-187

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

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3. Methodology

Limitations of the Methodology:The results are valid under the next topographical-environmental conditions:

Moderate Flat Terrains

No Synoptic Perturbations

Low Dust Load (radiative forcing < convective heating)

To What Extent our Results are Representative? Results expected to represent any Sol where the above three restrictions are met Thus, results specially suitable for northern summertime Sols

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4. Results

Thermodynamical Characterization of the PBL Key Values

Su

rfac

e L

ayer

Height up to where shear dominates convection By definition, negative under local static instability conditions Around -20 m at noon Similar values on Earth

It represents the shear at surface

Values around 0.5 m/s at noon

Important for the saltation of dust

Similar values on Earth

Monin-Obukhov Length Friction Velocity

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4. Results S

urf

ace

Lay

er Thermodynamical Characterization of the PBL Key Values

Eddy temperature fluctuations By definition, negative under local static instability conditions Higher absolute values close to noon Its values consistent with the fluctuation measured by PF and VK landers

Positive during the daytime (“Breathing”, Cooling) Negative during the night (Soil Heated by H0) It does not counteract the net radiative heating (SW=120 W/m2 vs H0=7 W/m2 ) during daytime It does not counteract the LW radiative cooling (LW=50 W/m2 vs H0=0.5 W/m2 ) at night

Scale Temperature Surface Dynamic Heat Flux H0

DaytimeEnergy Budget at surface

Nightime

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4. Results

Thermodynamical Characterization of the PBL Key Values

PBL Height Convective Velocity

It represents the upward velocity of thermals

Values around 2 and 4.5 m/s

The height up to where turbulence is always present

Up to 11 kms, due to the vigorous kinematic heat flux (though the dynamic heat flux is relative small due to the low density)

Co

nve

ctiv

e M

ixed

Lay

er

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4. Results

Thermodynamical Characterization of the PBL Key Values

Co

nve

ctiv

e M

ixed

Lay

er

Convective Temperature ScaleMean Turbulent Temperature Standard Deviation

It represents how much warmer thermals are than the environment

Values mainly in the range (0.1,0.3) K

Typical turbulent temperature fluctuations promediated in the whole Convective ML

Values are representative of the whole CML

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Turbulent Kinetic Energy (TKE) is defined as:

Velocity variances are obtained averaging over periods falling in the spectral gap (Mesoscale ≈ 1h), so the departure from the mean corresponds to the Turbulent Part of the spectrum

Definition of the TKE4. Results

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The Equation ruling the evolution of the TKE is given by:

with the Im term given by:

We next show values both in the SL and CML for each of the above terms

B: Buoyancy S: Shear Tr: Turbulent Transport Diss: Dissipation Err: Imbalance

Im expected to be small

4. Results

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1) SURFACE LAYER PATHFINDER SOL 25 (z = 1.3 m)

Turbulent Kinetic Energy (TKE) Vertical and Horizontal St. Deviations

During the most convective hours, we can consider steady state for the TKE, as shown encircled in yellow the in the figures above

Horizontal Turbulence higher than Vertical one (4 or 5 times). Turbulence not isotropic

TKE of the order of 3 m2 s-2

4. Results

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SURFACE LAYER TKE BUDGET Shear main creator of TKE

Dissipation balances Shear

Buoyancy and Transport two orders of magnitude lower than Shear and Dissipation

Buoyancy and Transport balance each other

Buoyancy is positive (creation), due to upward kinematic heat flux

Transport sends TKE upwards, and thus is negative (it removes TKE)

Imbalance one order of magnitude lower than the main mechanisms

PF SOL 254. Results

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CONVECTIVE MIXED LAYER PATHFINDER SOL 25

Turbulent Kinetic Energy (TKE) Averaged Vertical and Horizontal

St. Deviations

During the most convective hours, we can consider steady state for the TKE, as shown encircled in yellow the in the figures above

Horizontal Turbulence equals Vertical one, at least handling with mean values. Turbulence isotropic

TKE of the order of 8 m2 s-2. This value matches other estimations

4. Results

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CONVECTIVE MIXED LAYER TKE BUDGET

Buoyancy the main mechanism creating TKE

Dissipation almost balances the Buoyancy, being the main TKE remover

Shear becomes negligible

Transport becomes now positive, since in the average TKE is being transported to the CML

Imbalance is lower than the main terms, which gives reliability to the results

PF SOL 254. Results

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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

Cпасибо!¡Muchas gracias! Thank you!...