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Philip R Christensen - One of the best experts on this subject based on the ideXlab platform.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998, when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15 m mC O 2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near Northern Hemisphere fall equinox, winter solstice, and spring equinox as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at northern midlatitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally, good qualitative agreement is found.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998 when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer (TES) has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15-micrometers CO2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near northern hemisphere fall equinox, winter solstice, and spring equinox, as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at mid-northern latitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally good qualitative agreement is found.

  • Global spectral classification of martian low albedo regions with Mars Global Surveyor thermal emission spectrometer mgs tes data
    Journal of Geophysical Research, 2007
    Co-Authors: Deanne A Rogers, Joshua L. Bandfield, Philip R Christensen
    Abstract:

    [1] Martian low-albedo surfaces (defined here as surfaces with Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) albedo values ≤0.15) were reexamined for regional variations in spectral response. Low-albedo regions exhibit spatially coherent variations in spectral character, which in this work are grouped into 11 representative spectral shapes. The use of these spectral shapes in modeling Global surface emissivity results in refined distributions of previously determined Global spectral unit types (Surface Types 1 and 2). Pure Type 2 surfaces are less extensive than previously thought, and are mostly confined to the northern lowlands. Regional-scale spectral variations are present within areas previously mapped as Surface Type 1 or as a mixture of the two surface types, suggesting variations in mineral abundance among basaltic units. For example, Syrtis Major, which was the Surface Type 1 type locality, is spectrally distinct from terrains that were also previously mapped as Type 1. A spectral difference also exists between southern and northern Acidalia Planitia, which may be due in part to a small amount of dust cover in southern Acidalia. Groups of these spectral shapes can be averaged to produce spectra that are similar to Surface Types 1 and 2, indicating that the originally derived surface types are representative of the average of all low-albedo regions.

  • Mars' “White Rock” feature lacks evidence of an aqueous origin: Results from Mars Global Surveyor
    Journal of Geophysical Research: Planets, 2001
    Co-Authors: Steven W. Ruff, Michael T Mellon, Hugh H Kieffer, Philip R Christensen, Bruce M. Jakosky, Joshua L. Bandfield, Roger N. Clark, Michael C. Malin, Melissa D. Lane, Marsha A. Presley
    Abstract:

    The “White Rock” feature on Mars has long been viewed as a type example for a Martian playa largely because of its apparent high albedo along with its location in a topographic basin (a crater). Data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) demonstrate that White Rock is not anomalously bright relative to other Martian bright regions, reducing the significance of its albedo and weakening the analogy to terrestrial playas. Its thermal inertia value indicates that it is not mantled by a layer of loose dust, nor is it bedrock. The thermal infrared spectrum of White Rock shows no obvious features of carbonates or sulfates and is, in fact, spectrally flat. Images from the Mars Orbiter Camera show that the White Rock massifs are consolidated enough to retain slopes and allow the passage of saltating grains over their surfaces. Material appears to be shed from the massifs and is concentrated at the crests of nearby bedforms. One explanation for these observations is that White Rock is an eroded accumulation of compacted or weakly cemented aeolian sediment.

  • analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the Mars Global Surveyor thermal emission spectrometer
    Journal of Geophysical Research, 2001
    Co-Authors: Victoria E. Hamilton, M B Wyatt, H Y Mcsween, Philip R Christensen
    Abstract:

    Atmospherically corrected thermal infrared spectra of large regions of the Martian surface from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) previously have been interpreted to represent two general spectral classes. One class represents a basalt to basaltic andesite composition, and the other class represents a basaltic andesite to andesite composition. We have performed new linear deconvolutions of the two Martian surface type spectra with an end-member set tailored to represent volcanic rock types. Our preparatory study of laboratory spectra of terrestrial volcanic rocks (acquired at 2 cm 21 sampling), convolved to TES spectral sampling (10 cm 21 ), shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data, indicating that the deconvolution technique is valid for analyzing data at TES resolution. Our spectral fits to the Martian data agree well with previous models and do not exhibit any notable deviations from the Martian spectra that would indicate the absence of any significant end-members in our model. Modal mineralogies obtained with these new spectral fits also compare favorably (within the previously stated uncertainties) to prior results. The newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks (introduced in a companion paper (Wyatt et al., this issue)) to classify the Martian compositions. Our results substantiate the previously proposed hypothesis that these two spectral classes on the Martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite.

Michael D. Smith - One of the best experts on this subject based on the ideXlab platform.

  • long term variability of Mars exosphere based on precise orbital analysis of Mars Global Surveyor and Mars odyssey
    Journal of Geophysical Research, 2014
    Co-Authors: Sean Bruinsma, J M Forbes, Jeancharles Marty, Xiaoli Zhang, Michael D. Smith
    Abstract:

    A long-term perspective on Mars' exosphere variability at 405 km is provided by merging together density data derived from precise orbit determination of the Mars Global Surveyor and Mars Odyssey (MO) satellites extending from 2001 to 2010. These data are heavily weighted toward afternoon local times at high latitudes in the Southern Hemisphere. Clear long-term solar and annual variations are well captured by empirical formulas. Residuals from the empirical fit show evidence for relative depletions in exosphere density around Mars' closest approach to Earth, which would be consistent with a scavenging mechanism that is dependent on solar wind dynamic pressure. Superimposed on this variation with Mars-Sun distance are positive density residuals during Mars year (MY)25, MY27, and MY29 that are apparently due to elevated dust levels in Mars' middle atmosphere. However, during MY24, MY26, and MY28 there are dust level increases without any corresponding increase in exosphere density. We suspect that this inconsistency is related to a variable ability to sense the response to dust-related effects, imposed by the high-latitude limitations of our measurements combined with interference between the mechanisms that translate middle atmosphere heating to an exosphere response. Evidence also supports the hypothesis that winter helium bulge effects contributed to the inferred interannual density variability during the 2007–2009 solar minimum period, when the O-He transition height likely resided near the ~405 km orbit of MO.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998, when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15 m mC O 2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near Northern Hemisphere fall equinox, winter solstice, and spring equinox as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at northern midlatitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally, good qualitative agreement is found.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998 when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer (TES) has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15-micrometers CO2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near northern hemisphere fall equinox, winter solstice, and spring equinox, as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at mid-northern latitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally good qualitative agreement is found.

  • Martian water ice clouds: A view from Mars Global Surveyor Thermal Emission Spectrometer
    Journal of Geophysical Research, 2011
    Co-Authors: A. Snyder Hale, L. K. Tamppari, Deborah Bass, Michael D. Smith
    Abstract:

    [1] We have used the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) data to map water ice clouds in the Martian atmosphere in the latitude range –60 to +60 over a period of three Martian years. We have used the same method we have previously used on Viking Infrared Thermal Mapper data in order to allow direct comparison of the cloud behavior in the Viking and MGS eras and confirmed the validity of this method by comparing it to MGS TES standard retrievals. We note that the large-scale behavior of water ice clouds is remarkably consistent, both between the Viking and the MGS eras as well as between years observed by MGS. We also compare our results to water ice absorption-only optical depths derived from TES data and show that correlation is best for type 2 water ice clouds.

  • Mars Global Surveyor thermal emission spectrometer tes observations of variations in atmospheric dust optical depth over cold surfaces
    Icarus, 2009
    Co-Authors: David Horne, Michael D. Smith
    Abstract:

    Abstract The Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument has returned over 200 million thermal infrared spectra of Mars taken between March 1999 and August 2004. This represents one of the most complete records of spatial and temporal changes of the martian atmosphere ever recorded by an orbiting spacecraft. Previous reports of the standard TES retrieval of aerosol optical depth have been limited to those observations taken over surfaces with temperatures above 210 K, limiting the spatiotemporal coverage of Polar Regions with TES. Here, we present an extension to the standard TES retrieval that better models the effects of cold surfaces below 200 K. This modification allows aerosol optical depth to be retrieved from TES spectra over a greater spatiotemporal range than was previously possible, specifically in Polar Regions. This new algorithm is applied to the Polar Regions to show the seasonal variability in dust and ice optical depth for the complete temporal range of the TES database (Mars Year 24, L s = 104 ° , 1 March 1999 to Mars Year 24, L s = 82 ° , 31 August 2004).

M H Acuna - One of the best experts on this subject based on the ideXlab platform.

  • search for phobos and deimos gas dust tori using in situ observations from Mars Global Surveyor mag er
    Icarus, 2010
    Co-Authors: M Oieroset, D A Brain, Erin Simpson, David L Mitchell, T D Phan, J S Halekas, R P Lin, M H Acuna
    Abstract:

    Abstract More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible signatures of solar wind interaction with dust or gas escaping from the moons. A total of 1246 solar wind disturbance events were identified and their distribution was examined relative to Phobos, the Phobos orbit, and the Deimos orbit. We find that the spatial distribution of solar wind perturbations does not increase near or downstream of Phobos, Phobos’ orbit, or Deimos’ orbit, which would have been expected if there is significant outgassing or dust escape from the martian moons. Of the 1246 magnetic field perturbation events found in the MGS data set, 11 events were found within 2000 km of the Phobos orbit, while three events were found within 2000 km of the Deimos orbit. These events were analyzed in detail and found to likely have other causes than outgassing/dust escape from the martian moons. Thus we conclude that the amount of gas/dust escaping the martian moons is not significant enough to induce detectable magnetic field perturbations in the solar wind. In essence we have not found any clear evidence in the MGS magnetic field data for outgassing or dust escape from the martian moons.

  • interaction of the solar wind with Mars from Mars Global Surveyor mag er observations
    Journal of Atmospheric and Solar-Terrestrial Physics, 2005
    Co-Authors: C Bertucci, Christian Mazelle, M H Acuna
    Abstract:

    The observations of the magnetometer/electron reflectometer (MAG/ER) investigation onboard the Mars Global Surveyor (MGS) have greatly contributed to improve our understanding of the interaction of the solar wind with Mars. These observations established conclusively that a Global dynamo-generated magnetic field does not exist at Mars, and that the interaction with solar wind is of the atmospheric type. This article reviews the most important results obtained from MGS MAG/ER on the study of two major features in the Mars solar wind interaction. The first feature is the occurrence of large-amplitude, highly coherent waves at the proton cyclotron frequency in the region upstream from the Martian bow shock. The second feature is the magnetic pileup boundary (MPB), a well-defined plasma boundary inside of which the planetary exospheric ions outnumber the solar wind ions. The study of these two elements is crucial to characterize the properties of the Martian exosphere. In addition, the occurrence of an MPB at comets and Venus reveals common processes to all these unmagnetized atmospheric bodies in spite of their different physical nature and characteristic scales.

  • Mars Global Surveyor observations of the Halloween 2003 solar superstorm's encounter with Mars
    Journal of Geophysical Research: Space Physics, 2005
    Co-Authors: D H Crider, D. L. Mitchell, David Brain, Jared Espley, M H Acuna
    Abstract:

    [1] Like at Earth, disturbances from solar storms affect the space environment as they encounter Mars. The effects of the 28 October 2003 solar superstorm were among the greatest observed by the Mars Global Surveyor spacecraft at Mars to date. The disturbance, defined by an increase in incident solar wind pressure, encountered Mars on 30 October 2003 and persisted for 43 hours. We present the effects of the passage of this high-pressure disturbance and compare the modified Martian space environment to more quiescent times. We find that the horizontal component of magnetic field is increased on the dayside. In addition, the solar wind interaction region is compressed during the disturbance. The solar wind flow has access to lower altitudes than typical, which likely increases mass loss from the Martian atmosphere. Regions of opened magnetic field lines can be closed at 400 km due to the compression of minimagnetospheres, thus altering locations where ionospheric plasma is protected from solar wind scavenging at 400 km altitude.

  • martian shock and magnetic pile up boundary positions and shapes determined from the phobos 2 and Mars Global Surveyor data sets
    AGU Fall Meeting Abstracts, 2004
    Co-Authors: J G Trotignon, C Bertucci, Christian Mazelle, M H Acuna
    Abstract:

    Abstract A great many Martian bow shock and magnetic pile-up boundary crossings have been identified in the Phobos 2 and Mars Global Surveyor, MGS, data. From these observations the positions and shapes of the bow shock and magnetic pile-up boundary, MPB, have been derived and modelled, using curve-fitting techniques. The models thus derived separately from the Phobos 2 and MGS data sets do not differ drastically, despite the different time and space data coverages. The purpose of the paper is therefore to show the results obtained from the mixing of the Phobos 2 and MGS data bases and to compare the derived bow shock and MPB models with the ones obtained previously. The underlying objective was to see whether it was possible to determine improved bow shock and MPB models or not. The answer is definitely yes, and particularly for the MPB, thanks to the complementary nature of the observations. The boundaries crossed close to the subsolar direction or mostly far downstream by Phobos 2 indeed allow a better coverage of the Martian space environment to be considered. Nevertheless, in order to reduce the domination of the overabundant MGS data set and/or the crossings that are close to Mars (x>−4 RM, i.e. x>−13 562 km) weighting factors have been introduced.

  • Mars Global Surveyor observations of solar wind magnetic field draping around Mars
    Space Science Reviews, 2004
    Co-Authors: D H Crider, D A Brain, M H Acuna, D Vignes, Christian Mazelle, C Bertucci
    Abstract:

    We examine the magnetic field in the martian magnetosheath due to solar wind draping. Mars Global Surveyor provided 3-D vector magnetic field measurements at a large range of altitudes, local times, and solar zenith angles as the spacecraft orbit evolved. We choose orbits with very clean signatures of draping to establish the nominal morphology of the magnetic field lines at local times of near-subsolar and near-terminator. Next, using a compilation of data from Mars Global Surveyor, we determine the average magnetic field morphology in the martian magnetosheath due to the solar wind interaction. The topology of the field is as expected from previous observations and predictions. The magnetic field magnitude peaks at low altitude and noon magnetic local time and decreases away from that point. The magnetic field has an inclination from the local horizontal of 5.6° on average in the dayside magnetosheath and 12.5° on the nightside. The inclination angle is closest to zero at noon magnetic local time and low altitude. It increases both upward and to later local times. The magnetic field in the induced magnetotail flares out from the Mars—Sun direction by 21°. Finally, we compare the observations to gasdynamic model predictions and find that the shocked solar wind flow in the martian magnetosheath can be treated as a gasdynamic flow with the magnetic pileup boundary as the inner boundary to the flow.

Paul Withers - One of the best experts on this subject based on the ideXlab platform.

  • the ionosphere of Mars from solar minimum to solar maximum dayside electron densities from maven and Mars Global Surveyor radio occultations
    Icarus, 2021
    Co-Authors: Paul Withers, Michael Mendillo, M Felici, K Hensley, E Barbinis, Daniel Kahan, K Oudrhiri, Z Girazian
    Abstract:

    Abstract Conditions in the ionosphere of Mars vary from solar minimum to solar maximum due to changes in the ionizing solar irradiance. Although changes in the main ionospheric layers, namely the M2 layer and the lower M1 layer, over the solar cycle have been well-characterized by previous work, corresponding changes in the upper regions of the photochemical ionosphere ( ∼ 140–200 km) have not. Here we investigate those changes using ionospheric electron density profiles acquired at solar zenith angles of 70°–90° under solar minimum conditions by the MAVEN Radio Occultation Science Experiment (ROSE) and under solar maximum conditions by a similar radio occultation experiment on Mars Global Surveyor. Due to the increase in ionizing irradiance from solar minimum to solar maximum, we expect that densities at all altitudes will increase from solar minimum to solar maximum. Due to the eccentricity of Mars’s orbit, observed electron density profiles must be adjusted to a common Mars–Sun distance to highlight solar cycle effects. This process involves increasing observed electron density values by a factor proportional to the Mars–Sun distance, which mitigates for variations in incident irradiance, and expressing altitude relative to the main ionospheric peak, which mitigates for variations in heating and expansion of the neutral thermosphere. We find that the scale height of the upper regions of the photochemical ionosphere is remarkably constant between solar minimum and solar maximum, whereas the corresponding neutral temperature increases by 50%. Yet these two quantities are thought to be proportional. Electron density values in the upper regions of the photochemical ionosphere and peak electron density values increase similarly from solar minimum to solar maximum.

  • modeling Mars ionosphere with constraints from same day observations by Mars Global Surveyor and Mars express
    Journal of Geophysical Research, 2011
    Co-Authors: Michael Mendillo, Paul Withers, A Lollo, Majd Matta, M Patzold, Silvia Tellmann
    Abstract:

    [1] We have analyzed a brief period of same-day observations of the Martian ionosphere using data obtained in December 2004 from the Mars Global Surveyor (MGS) and Mars Express (MEX) radio occultation experiments. These data were taken shortly after sunrise under solstice conditions in both hemispheres, with MGS in the summer (northern) hemisphere at high latitudes while MEX was in the winter (southern) hemisphere at midlatitudes. Such two-satellite, dual-hemisphere data sets are unique for the modern era of ionospheric observations at Mars and provide good test cases for constraints of key parameters commonly used in models of the Martian ionosphere. Several iterations of a 1-dimensional model are developed in attempts to simulate more successfully the altitudes, absolute magnitudes and shapes of the two photo-chemical layers (M1 and M2) obtained during the joint MGS-MEX observing period. Three basic processes are examined: (1) selection of the optimal model neutral atmospheres, (2) the effects due to departures from thermal equilibrium between electrons, ions and neutrals, (3) methods of handling secondary ionization. While general circulation models fully coupled to plasma transport codes are required for Global simulations of the full system, the computational complexity and computer resources needed often result in the use of parameterizations relating electron and ion temperatures to neutral temperatures and secondary ionization to primary photo-ionization profiles. Here we develop such schemes and test them within the framework of same day observations in both hemispheres. The occurrence of same day, separate hemisphere, radio occultation profiles is important because the solar irradiance has to be held constant for modeling both sites, and thus this is the first study of this kind to be done. The overall results stress the dominant influence of solar zenith angle effects on production for the M2-layer via primary solar ionization, its augmentation by ∼30% due to secondary ionization, and further enhancements due to reduced chemical loss when the electron temperature exceeds the neutral temperature. Secondary ionization is the most crucial process for the M1-layer. The influence of very different crustal magnetic field morphologies at the two observing locations did not seem to be a crucial source of differentiation for processes that control the average values of the peak electron densities of the two photo-chemical layers.

  • physical characteristics and occurrence rates of meteoric plasma layers detected in the martian ionosphere by the Mars Global Surveyor radio science experiment
    Journal of Geophysical Research, 2008
    Co-Authors: Paul Withers, D P Hinson, Michael Mendillo, Kerri Cahoy
    Abstract:

    [1] Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 ± 4.8 km. The mean peak electron density in the meteoric layer is (1.33 ± 0.25) × 1010 m−3. The mean width of the meteoric layer is 10.3 ± 5.2 km. The occurrence rate of meteoric layers varies with season, solar zenith angle, and latitude. Seasonal variations in occurrence rate are particularly strong, often exceeding an order of magnitude. Meteoric layer altitude, peak electron density, and width are all positively correlated, with correlation coefficients of 0.3–0.4. Other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties, such as scale height, solar zenith angle, and solar flux, have absolute values that are significantly smaller, indicating lack of correlation. The photochemical lifetime of plasma in meteoric layers is ∼12 days and depends on altitude.

  • Mars Global Surveyor and Mars Odyssey Accelerometer observations of the Martian upper atmosphere during aerobraking
    Geophysical Research Letters, 2006
    Co-Authors: Paul Withers
    Abstract:

    [1] Mars Global Surveyor and Mars Odyssey accelerometer measurements of martian upper atmospheric densities reveal the large-scale and small-scale structure of the thermosphere in unprecedented detail. Meridional density gradients, which are seasonally dependent, are greater on the dayside than the nightside, indicating stronger meridional winds on the dayside. Density scale heights do not vary greatly with latitude. Densities and density scale heights are lower on the nightside than on the dayside, but the day-night contrast is not as great as at Venus. Thus atmospheric circulation plays a greater role in determining the state of the thermosphere on Mars than on Venus. Oscillations in density along individual density profiles, probably due to gravity waves, are common and their amplitudes are tens of percent. Step-like changes in density are also observed, but their origin is less clear. Data coverage is extensive enough to permit studies of weather, not just climate.

B J Conrath - One of the best experts on this subject based on the ideXlab platform.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998, when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15 m mC O 2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near Northern Hemisphere fall equinox, winter solstice, and spring equinox as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at northern midlatitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally, good qualitative agreement is found.

  • Mars Global Surveyor thermal emission spectrometer tes observations atmospheric temperatures during aerobraking and science phasing
    2013
    Co-Authors: B J Conrath, Philip R Christensen, Michael D. Smith, J C Pearl, W C Maguire, Shymala Dason, Monte S Kaelberer
    Abstract:

    Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998 when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer (TES) has acquired an extensive data set spanning approximately half of a Martian year. Nadir-viewing spectral measurements from this data set within the 15-micrometers CO2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near northern hemisphere fall equinox, winter solstice, and spring equinox, as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near-equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at mid-northern latitudes suggests the presence of a strong cross-equatorial Hadley circulation. Although the Noachis dust storm did not become Global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally good qualitative agreement is found.

  • assimilation of thermal emission spectrometer atmospheric data during the Mars Global Surveyor aerobraking period
    Icarus, 2007
    Co-Authors: S R Lewis, B J Conrath, J C Pearl, P L Read, Michael D. Smith
    Abstract:

    Abstract The Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft has produced an extensive atmospheric data set, beginning during aerobraking and continuing throughout the extended scientific mapping phase. Temperature profiles for the atmosphere below about 40 km, surface temperatures and total dust and water ice opacities, can be retrieved from infrared spectra in nadir viewing mode. This paper describes assimilation of nadir retrievals from the spacecraft aerobraking period, L S = 190 ° – 260 ° , northern hemisphere autumn to winter, into a Mars general circulation model. The assimilation scheme is able to combine information from temperature and dust optical depth retrievals, making use of a model forecast containing information from the assimilation of earlier observations, to obtain a Global, time-dependent analysis. Given sufficient temperature retrievals, the assimilation procedure indicates errors in the a priori dust distribution assumptions even when lacking dust observations; in this case there are relatively cold regions above the poles compared to a model which assumes a horizontally-uniform dust distribution. One major reason for using assimilation techniques is in order to investigate the transient wave behavior on Mars. Whilst the data from the 2-h spacecraft mapping orbit phase is much more suitable for assimilation, even the longer (45–24 h) period aerobraking orbit data contain useful information about the three-dimensional synoptic-scale martian circulation which the assimilation procedure can reconstruct in a consistent way. Assimilations from the period of the Noachis regional dust storm demonstrate that the combined assimilation of temperature and dust retrievals has a beneficial impact on the atmospheric analysis.

  • comparison of atmospheric temperatures obtained through infrared sounding and radio occultation by Mars Global Surveyor
    Journal of Geophysical Research, 2004
    Co-Authors: D P Hinson, Michael D. Smith, B J Conrath
    Abstract:

    [1] Mars Global Surveyor monitors temperatures in the Martian atmosphere through infrared sounding by the Thermal Emission Spectrometer (TES) as well as Radio Science (RS) occultation experiments. We report results from extensive comparisons of TES nadir and RS temperature profiles, focusing on data obtained under conditions that allow nearly simultaneous measurements at the same location and local time. We analyzed data from 13 intervals with durations of 7–19 sols that sample latitudes of 62°–85°N during midspring through early autumn. Our results generally confirm the accuracy and reliability of both sets of observations. We find particularly good agreement between the zonal variations of temperature observed by the two instruments. Zonally averaged temperature profiles agree to within ∼2 K at pressures <400 Pa. Results are less satisfactory at 610 Pa, where the TES retrievals are persistently warmer by a margin of 2–8 K. These discrepancies arise primarily from a wide disparity in vertical resolution. The RS measurements reveal subtle but significant vertical variations of temperature, particularly at low altitudes, that the TES is unable to resolve. For the range of latitudes and seasons considered here, the most serious consequence is that vertical gradients of temperature deduced from TES profiles are unreliable in the lowest scale height above the surface. Our analysis also shows that the RS profiles from selected intervals might contain a low-altitude bias due to the unmodeled effect of water vapor. These results should contribute to a more confident characterization of Martian climate.

  • observations of martian ice clouds by the Mars Global Surveyor thermal emission spectrometer the first martian year
    Journal of Geophysical Research, 2001
    Co-Authors: J C Pearl, Joshua L. Bandfield, Michael D. Smith, B J Conrath, Philip R Christensen
    Abstract:

    Successful operation of the Mars Global Surveyor spacecraft, beginning in September 1997 (Ls = 184°), has permitted extensive observations over more than a Martian year. Initially, thin (normal optical depth <0.06 at 825 cm−1) ice clouds and hazes were widespread, showing a distinct latitudinal gradient. With the onset of a regional dust storm at Ls = 224°, ice clouds vanished in the southern hemisphere, to reappear gradually after the decay of the storm. The zonally averaged cloud opacities show little difference between the beginning and end of the first Martian year. A broad low-latitude cloud belt with considerable longitudinal structure was present in early northern summer. Apparently characteristic of the northern summer season, it vanished between Ls = 140° and 150°. The latitudinal extent of this feature is apparently controlled by the ascending branch of the Hadley circulation. The most opaque clouds (optical depth ∼0.6) were found above the summits of major volcanic features; these showed spatial structure possibly associated with wave activity. Variety among low-lying late morning clouds suggests localized differences in circulation and microclimates. Limb observations showed extensive optically thin (optical depth <0.04) stratiform clouds at altitudes up to 55 km. Considerable latitude and altitude variations were evident in ice clouds in early northern spring (Ls = 25°); near 30 km, thin clouds extended from just north of the equator to ∼45°N, nearly to the north polar vortex. A water ice haze was present in the north polar night (Ls = 30°) at altitudes up to 40 km. Because little dust was present this probably provided heterogeneous nucleation sites for the formation of CO2 clouds and snowfall at altitudes below ∼20 km, where atmospheric temperatures dropped to the CO2 condensation point. The relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 μm.