James E. Tillman

The Indirect Determination of Stability, Heat and Momentum Fluxes in the Atmospheric Boundary Layer from Simple Scalar Variables During Dry Unstable Conditions

Abstract Turbulence data from two sites have been analyzed to obtain an indirect relation between the Obukhov stability parameter, z/L, and temperature statistics during dry unstable conditions. The skewness of a single scalar variable, temperature, at a single height is used to obtain z/L, thereby demonstrating the value and importance of the no-Gaussian properties of the temperature statistics. A relation between σθ/T* and z/L has been obtained for the stability range −60< z/L≤0.5 Explicit forms for heat flux and shear stress have been obtained for the unstable portion of this range in terms of z/L,k, σθ, z, θ and constants. Combining the above techniques provides a method of obtaining z/L, H/pcp and u* from temperature statistics during dry unstable conditions. Within the limitations of the observational uncertainties, the functions appear to be consistent for one or more different sites.

Diurnal Variations of the Martian Surface Layer Meteorological Parameters During the First 45 Sols at Two Viking Lander Sites

Abstract Wind speed, ambient and surface temperatures from both Viking Landers have been used to compute bulk Richardson numbers and Monin-Obukhov lengths during the earliest phase of the Mars missions. These parameters are used to estimate drag and heat transfer coefficients, friction velocities and surface heat fluxes at the two sites. The principal uncertainty is in the specification of the roughness length. Maximum heat flux occur near local noon at both sites, and are estimated to be in the range 15–20 W m−2 at the Viking 1 site and 10–15 W m−2 at the Viking 2 site. Maximum values of friction velocity occur in late morning at Viking 1 and are estimated to be 0.4–0.6 m s−1. They occur shortly after dawn at the Viking 2 site where peak values are estimated to be in the range 0.25–0.35 m s−1. Extension of these calculations to later times during the mission will require allowance for dust opacity effects in the estimation of surface temperature and in the correction of radiation errors of the Viking 2 t...

The Martian annual atmospheric pressure cycle - Years without great dust storms

A model of the annual cycle of pressure on Mars has been developed for a 2-year period chosen to include 1 year at Lander 2 and to minimize the effect of great dust storms at the 22°N Lander 1 site. The model was developed by weighted least squares fitting of the Viking Lander pressure measurements to an annual mean, and fundamental and the first four harmonics of the annual cycle. The very close agreement between the two years suggests that an accurate representation of the annual CO2 condensation-sublimation cycle can be established for such years. The two annual mean pressures are identical to 0.006 mbar out of 7.9 mbar, and the differences in amplitudes for the first five periodic components between the two years range from 0.017 to 0.001 mbar. The phase angles, primarily dependent on solar insolation determined orbital dynamics, differ by −3.0° Ls for the second harmonic (year 1 minus year 2), and drop to ≤ 0.7° for the fundamental and fourth harmonic. Although the slight year-to-year differences appear to be real, this model is proposed as a “nominal” Martian annual pressure cycle and applications are suggested. By analogy, the corresponding first years representation at Lander 2 is also proposed as the “nominal” cycle, although it has not been verified by data from a subsequent year. These models provide a method of removing low frequencies from the annual pressure cycle for spectral analyses of baroclinic, tidal, and normal mode oscillations, and for comparisons of the interannual variability.

Three Mars years: Viking Lander 1 imaging observations

The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3:3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohesion of the undisturbed surface material.

The Three-Dimensional Structure of Convection in the Atmospheric Surface Layer

Abstract During April 1978, a field experiment was undertaken at the Boulder Atmospheric Observatory (BAO), near Boulder, Colorado, to investigate convective plumes in the atmospheric surface layer. The plume translational velocities are determined for a wide range of stabilities, using an array of 16 temperature sensors, spanning a 100 m × 40 m area at a height of 4 m, and a three-dimensional sonic anemometer. The translational velocities are calculated from the phase information of the temperature cross spectrum, and by measuring the transit times of the plumes between sensors aligned in a direction parallel to the wind. Velocities obtained by the two methods are shown to be in rough agreement. Individual plume velocities are found to vary in proportion to the plume height. The three-dimensional plume structure is investigated using both the horizontal array and the 300 m BAO tower. Under slightly unstable, high wind speed conditions, the majority of the plumes are distinctly elongated in the mean wind ...

The Boundary Layer of Mars: Fluxes, Stability, Turbulent Spectra, and Growth of the Mixed Layer

Abstract Spectra of wind from high-frequency measurements in the Martian atmospheric surface layer, along with the diurnal variation of the height of the mixed surface layer, are calculated for the first time for Mars. Heat and momentum fluxes, stability, and z0, are estimated for early spring from a surface temperature model and from Viking Lander 2 temperatures and winds at 44°N, using Monin–Obukhov similarity theory. Flow distortion by the lander is also taken into account. Model spectra for two measuring heights and three surface roughnesses are calculated using the depth of the mixed layer and the surface-layer parameters. These experiments indicate that z0 probably lies between 1.0 and 3.0 cm, and most likely is closer to 1.0 cm. The spectra are adjusted to simulate aliasing and high-frequency rolloff, the latter caused by both the sensor response and the large Kolmogorov length on Mars. Since the spectral models depend on the surface parameters, including the estimated surface temperature, their ag...

atmospheric measurements on Mars: the Viking Meteorology Experiment

The Viking Meteorology Experiment is one of nine experiments to be carried out on the surface of Mars by each of two Viking Landers positioned at different latitudes and longitudes in the Northern Hemisphere. The meteorology experiment will measure pressure, temperature, wind speed, and wind direction at 1½ h intervals throughout the Martian day. The duration of each measurement period, the interval between data samples for a measurement period, and the time at which the measurement period is started will be varied throughout the mission. The scientific investigation and the sensors and electronics used for making the atmospheric measurement are discussed.

Preliminary meteorological results on Mars from the viking 1 lander.

The results from the meteorology instruments on the Viking 1 lander are presented for the first 4 sols of operation. The instruments are working satisfactorily. Temperatures fluctuated from a low of 188�K to an estimated maximum of 244�K. The mean pressure is 7.65 millibars with a diurnal variation of amplitude 0.1 millibar. Wind speeds averaged over several minutes have ranged from essentially calm to 9 meters per second. Wind directions have exhibited a remarkable regularity which may be associated with nocturnal downslope winds and gravitational oscillations, or to tidal effects of the diurnal pressure wave, or to both.

Network science landers for Mars

Abstract The NetLander Mission will deploy four landers to the Martian surface. Each lander includes a network science payload with instrumentation for studying the interior of Mars, the atmosphere and the subsurface, as well as the ionospheric structure and geodesy. The NetLander Mission is the first planetary mission focusing on investigations of the interior of the planet and the large-scale circulation of the atmosphere. A broad consortium of national space agencies and research laboratories will implement the mission. It is managed by CNES (the French Space Agency), with other major players being FMI (the Finnish Meteorological Institute), DLR (the German Space Agency), and other research institutes. According to current plans, the NetLander Mission will be launched in 2005 by means of an Ariane V launch, together with the Mars Sample Return mission. The landers will be separated from the spacecraft and targeted to their locations on the Martian surface several days prior to the spacecrafts arrival at Mars. The landing system employs parachutes and airbags. During the baseline mission of one Martian year, the network payloads will conduct simultaneous seismological, atmospheric, magnetic, ionospheric, geodetic measurements and ground penetrating radar mapping supported by panoramic images. The payloads also include entry phase measurements of the atmospheric vertical structure. The scientific data could be combined with simultaneous observations of the atmosphere and surface of Mars by the Mars Express Orbiter that is expected to be functional during the NetLander Missions operational phase. Communication between the landers and the Earth would take place via a data relay onboard the Mars Express Orbiter.

Aspects Of The Atmospheric Surface Layers On Mars And Earth

The structures of mean flow and turbulence in the atmospheric surface boundary layer have been extensively studied on Earth, and to a far less extent on Mars, where only the Viking missions and the Pathfinder mission have delivered in-situ data. Largely the behaviour of surface-layer turbulence and mean flow on Mars is found to obey the same scaling laws as on Earth. The largest micrometeorological differences between the two atmospheres are associated with the low air density of the Martian atmosphere. Together with the virtual absence of water vapour, it reduces the importance of the atmospheric heat flux in the surface energy budget. This increases the temperature variation of the surface forcing the near-surface temperature gradient and thereby the diabatic heat flux to higher values than are typical on the Earth, resulting in turn in a deeper daytime boundary layer. As wind speed is much like that of the Earth, this larger diabatic heat flux is carried mostly by larger maximal values of T*, the surface scale temperature. The higher kinematic viscosity yields a Kolmogorov scale of the order of ten times larger than on Earth, influencing the transition between rough and smooth flow for the same surface features.The scaling laws have been validated analysing the Martian surface-layer data for the relations between the power spectra of wind and temperature turbulence and the corresponding mean values of wind speed and temperature. Usual spectral formulations were used based on the scaling laws ruling the Earth atmospheric surface layer, whereby the Earths atmosphere is used as a standard for the Martian atmosphere.