bluuebunny/crossref_metadata_2025 huggingface dataset:
Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model
Authors: Chandra S. , Ziemke J. R. , Martin R. V.
Published: May 2003

The tropospheric ozone residual method is used to derive zonal maps of tropospheric column ozone using concurrent measurements of total column ozone from Nimbus 7 and Earth Probe (EP) Total Ozone Mapping Spectrometer (TOMS) and stratospheric column ozone from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS). Our study shows that the zonal variability in TOMS total column ozone at tropical and subtropical latitudes is mostly of tropospheric origin. The seasonal and zonal variability in tropospheric column ozone (TCO), derived from the TOMS/MLS residual, is consistent with that derived from the convective cloud differential method and ozonesonde measurements in regions where these data overlap. A comparison of TCO derived from the TOMS/MLS residual and a global three‐dimensional model of tropospheric chemistry (GEOS‐CHEM) for 1996–1997 shows good agreement in the tropics south of the equator. Both the model and observations show similar zonal and seasonal characteristics including an enhancement of TCO in the Indonesian region associated with the 1997 El Niño. Both show the decline of the wave‐1 pattern from the tropics to the extratropics as lightning activity and the Walker circulation decline. Both show enhanced ozone in the downwelling branches of the Hadley Circulation near ±30o. Model and observational differences increase with latitude during winter and spring.
Tropospheric ozone over the tropical Atlantic: A satellite perspective
Authors: Edwards D. P. , Lamarque J.‐F. , Attié J.‐L. , Emmons L. K. , Richter A. , Cammas J.‐P. , Gille J. C. , Francis G. L. , Deeter M. N. , Warner J. , Ziskin D. C. , Lyjak L. V. , Drummond J. R. , Burrows J. P.
Published: May 2003

We use satellite sensor measurements to obtain a broad picture of the processes affecting tropical tropospheric O3 production over Africa and the Atlantic in the early part of the year. Terra/MOPITT CO retrievals correlate well with biomass burning fire counts observed by the TRMM/VIRS instrument in Northern Hemisphere savanna regions and allow investigation of the subsequent convection of the biomass burning plume at the intertropical convergence zone and interhemispheric transport. Measurements of NO2 from the ERS‐2/GOME instrument enable identification of two important tropical sources of this O3 precursor, biomass burning and lightning. Good correlation is seen between NO2 retrievals and TRMM/LIS lightning flash observations in southern African regions free of biomass burning, thus indicating a probable lightning source of NOx. The combination of MOPITT CO, GOME NO2, and TRMM fire and lightning flash counts provides a powerful tool for investigating the tropospheric production of O3 precursors. These data are used in conjunction with the MOZART‐2 chemical transport model to investigate the early year tropical Atlantic tropospheric O3 distribution using January 2001 as a case study. Inconsistencies between the various tropical tropospheric O3 column products obtained from EP/TOMS data, and between these products, in situ measurements, and modeling, have led to questions about how the Northern Hemisphere biomass burning is connected to the TOMS derived O3 maximum in the tropical southern Atlantic. We show that the early year tropical O3 distribution is actually characterized by two maxima. The first arises due to biomass burning emissions, is located near the Northern Hemisphere fires, and is most evident in the lower troposphere. The second is located in the southern tropical Atlantic midtroposphere, and results from NOx produced by lightning over southern Africa and South America.
Observations of new particle formation and size distributions at two different heights and surroundings in subarctic area in northern Finland
Authors: Komppula M. , Lihavainen H. , Hatakka J. , Paatero J. , Aalto P. , Kulmala M. , Viisanen Y.
Published: May 2003

Two years of continuous aerosol particle number size distribution measurements have been carried out in a subarctic area in northern Finland. Measurements have been made at two different heights (340 m and 560 m above sea level) and surroundings (inside a forest and at the top of a fjeld) to find out the effects of local‐scale conditions on new particle formation and growth as well as on the size distribution of aerosol particles. Measured aerosol particle size range was 7–500 nm. Average total number concentration in the year 2001 was 700 cm−3 at the higher and 870 cm−3 at the lower site. One‐day averages varied between 40 and 3500 cm−3. Seasonal variation of total concentration was observed to be similar at both stations, high values in spring and summer and low values in winter. Also, modal concentrations were compared. Diurnal variation of total particle concentration was similar at both sites. In total, 65 new particle formation events were recorded during the measuring period. The largest number of events occurred in April and May. Particle formation events started between 0825 and 1550 (UTC plus 2 hours), and the calculated starting times of 1 nm particle formation (nucleation) varied between 0450 and 1420. The particle growth rate was found to be 1.4–8.2 nm h−1, and the formation rate of 7 nm particles varied from 0.06 to 0.40 particles cm−3 s−1. Starting times of the formation events at the two stations had maximum difference of 30 min, and it could not be explained by wind direction and speed. One possible explanation for the time difference is vertical movement of air masses caused by turbulence. Solar radiation was observed to be one key factor needed for particle formation. Wind direction was mostly between west and north on formation days, indicating polar or arctic air masses.
Estimating photochemically produced ozone throughout a domain using flight data and a Lagrangian model
Authors: Methven J. , Arnold S. R. , O'Connor F. M. , Barjat H. , Dewey K. , Kent J. , Brough N.
Published: May 2003

Can airborne observations from infrequent flights be used to infer the budget of ozone in the upper troposphere with any degree of certainty or representativeness? Fluctuations in ozone mixing ratio observed along flights are dominated by flying between air masses with distinct origins, rather than the recent chemical transformation that has occurred within those air masses. Reverse domain filling trajectories arriving on a high‐resolution three‐dimensional grid (RDF3D) can simulate air mass structure accurately by coloring arrival grid points with specific humidity (q) from the origin of each trajectory. Typical displacement errors in tracer filaments are only about 30 km, but the associated phase errors greatly reduce the correlations between airborne observations of long‐lived chemicals and their model simulations. However, the comparison can be vastly improved if equivalent potential temperature (θe) and specific humidity are used as coordinates to label air masses. Both properties are approximately conserved following unsaturated air and serve as good markers of air masses even if the air is saturated or mixing takes place. Ozone simulations from a Lagrangian model are evaluated against observations in thermodynamic coordinates, factoring out many of the transport phase errors. The proportion of the atmosphere occupied by different chemical air masses is estimated by using RDF3D trajectories to simulate the distributions of q and θe and then assuming that chemical composition is homogeneous within air masses, each with characteristic (q, θe). Mass density in thermodynamic coordinates is used to weight the modeled ozone transformation and error in concentration (calculated along flight tracks) to estimate photochemically produced ozone throughout a volume encompassing the flights.
Note on the definition of clear sky in calculations of shortwave cloud forcing
Authors: Erlick Carynelisa , Ramaswamy V.
Published: May 2003

An important item to distinguish in estimations of cloud forcing is the characteristics of the “clear sky.” In this study we investigate the influence of the composition of the clear sky in calculations of shortwave cloud forcing based on two case studies from the Monterey Area Ship Track Experiment (MAST). The forcing is calculated with respect to a clear sky devoid of aerosol particles and with respect to a clear sky containing the aerosol particles present in and below the cloud layer at below‐cloud ambient humidity. It is found that in the case of a continentally influenced stratocumulus cloud containing a large concentration of dust and/or soot aerosols, the definition of clear sky makes an 8–10% difference in the upwelling solar irradiance and cloud forcing ratio.
Humidity‐dependent optical properties of fine particles during the Big Bend Regional Aerosol and Visibility Observational Study
Authors: Malm William C. , Day Derek E. , Kreidenweis Sonia M. , Collett Jeffrey L. , Lee Taehyoung
Published: May 2003

The Environmental Protection Agency (EPA) and National Park Service (NPS) initiated a comprehensive field experiment called The Big Bend Regional Aerosol and Visibility Observational Study (BRAVO) to investigate the source of visibility‐reducing aerosols at Big Bend National Park, Texas. The study was carried out over a period of 4 months starting in the first week of July 1999. One objective of the study was to gain insight into the atmospheric light‐scattering properties of ambient aerosols, especially as they relate to their hygroscopicity. This paper will report on comparisons between measured and modeled estimations of dry and ambient scattering and comparisons between measured and modeled ratios of wet and dry scattering, f(RH), as a function of relative humidity (RH). Two equilibrium models, exercised in combination with Mie scattering theory, were used to predict atmospheric aerosol water content and associated increase in atmospheric scattering. Modeled and measured deliquescence and crystallization points were also compared. Measured and modeled deliquescence were always within 10% RH while crystallization RHs were always within a few percentage points. The analysis suggests that on most days some water is retained by the aerosol at low RHs (20–30%) and in most cases the hygroscopic growth of only inorganic salts accounted for all the observed increase in scattering as a function of RH.
Time correlations and 1/f behavior in backscattering radar reflectivity measurements from cirrus cloud ice fluctuations
Authors: Ivanova K. , Ackerman T. P. , Clothiaux E. E. , Ivanov P. Ch. , Stanley H. E. , Ausloos M.
Published: May 2003

The state of the atmosphere is governed by the classical laws of fluid motion and exhibits correlations in various spatial and temporal scales. These correlations are crucial to understand the short‐ and long‐term trends in climate. Cirrus clouds are important ingredients of the atmospheric boundary layer. To improve future parameterization of cirrus clouds in climate models, it is important to understand the cloud properties and how they change within the cloud. We study correlations in the fluctuations of radar signals obtained at isodepths of winter and fall cirrus clouds. In particular, we focus on three quantities: (1) the backscattering cross‐section, (2) the Doppler velocity, and (3) the Doppler spectral width. They correspond to the physical coefficients used in Navier Stokes equations to describe flows, i.e., bulk modulus, viscosity, and thermal conductivity. In all cases we find that power law time correlations exist with a crossover between regimes at about 3 to 5 min. We also find that different type of correlations, including 1/f behavior, characterize the top and the bottom layers and the bulk of the clouds. The underlying mechanisms for such correlations are suggested to originate in ice nucleation and crystal growth processes.
Depositional characteristics of 7Be and 210Pb in southeastern Michigan
Authors: McNeary D. , Baskaran M.
Published: May 2003

The depositional fluxes in the bulk and dry fallout as well as the concentrations of 7Be and 210Pb in aerosols were measured for a period of 17 months at Detroit, Michigan. The bulk depositional fluxes of 7Be and 210Pb varied between 3.11 and 63.0 dpm cm−2 yr−1 (mean of 11.4 dpm cm−2 yr−1) and 0.35 and 10.3 dpm cm−2 yr−1 (mean of 1.41 dpm cm−2 yr−1), respectively, and this variability in the depositional fluxes is attributed to the frequency and amount of precipitation and seasonal variations in the depositional fluxes. The dry depositional fluxes of 7Be and 210Pb contributed 2.1–19.8% and 3.6–48.6% of the bulk depositional fluxes, respectively. The higher precipitation‐normalized enrichment factor for 7Be during spring is attributed to the stratosphere‐troposphere exchange of air masses during spring and large‐scale atmospheric mixing during summer. We report that snow is more efficient than rain in removing 210Pb from the atmosphere, and this is likely due to higher surface area of snow flurries compared to the rain droplets. The volume‐weighted concentrations of 7Be and 210Pb are the highest reported in literature so far. The concentration of 7Be in the air showed a seasonal increase during the spring and summer months, and no seasonal variation was observed for 210Pb. The mean deposition velocities of aerosols calculated using concentrations of 7Be and 210Pb in air and precipitation are 1.6 and 1.1 cm s−1, respectively, and the corresponding washout ratios are 948 and 637. There is no significant correlation between the aerosol mass and depositional velocities of 7Be and 210Pb in the air masses. We propose that a relatively minor portion of the aerosols actively participate in the removal of these nuclides from the air masses.
Effect of petrochemical industrial emissions of reactive alkenes and NOx on tropospheric ozone formation in Houston, Texas
Authors: Ryerson T. B. , Trainer M. , Angevine W. M. , Brock C. A. , Dissly R. W. , Fehsenfeld F. C. , Frost G. J. , Goldan P. D. , Holloway J. S. , Hübler G. , Jakoubek R. O. , Kuster W. C. , Neuman J. A. , Nicks D. K. , Parrish D. D. , Roberts J. M. , Sueper D. T. , Atlas E. L. , Donnelly S. G. , Flocke F. , Fried A. , Potter W. T. , Schauffler S. , Stroud V. , Weinheimer A. J. , Wert B. P. , Wiedinmyer C. , Alvarez R. J. , Banta R. M. , Darby L. S. , Senff C. J.
Published: May 2003

Petrochemical industrial facilities can emit large amounts of highly reactive hydrocarbons and NOx to the atmosphere; in the summertime, such colocated emissions are shown to consistently result in rapid and efficient ozone (O3) formation downwind. Airborne measurements show initial hydrocarbon reactivity in petrochemical source plumes in the Houston, TX, metropolitan area is primarily due to routine emissions of the alkenes propene and ethene. Reported emissions of these highly reactive compounds are substantially lower than emissions inferred from measurements in the plumes from these sources. Net O3 formation rates and yields per NOx molecule oxidized in these petrochemical industrial source plumes are substantially higher than rates and yields observed in urban or rural power plant plumes. These observations suggest that reductions in reactive alkene emissions from petrochemical industrial sources are required to effectively address the most extreme O3 exceedences in the Houston metropolitan area.
Observations of a nonmigrating component of the semidiurnal tide over Antarctica
Authors: Murphy D. J. , Tsutsumi M. , Riggin D. M. , Jones G. O. L. , Vincent R. A. , Hagan M. E. , Avery S. K.
Published: May 2003

Data obtained from the MF radars situated at Davis, Syowa and Rothera in Antarctica are used to detect a nonmigrating component of the semidiurnal tide in the mesosphere and lower thermosphere. These radars are at similar latitudes and so share a common migrating tidal component. By fitting semidiurnal tide vectors to each stations data and performing subtractions of these vectors for pairs of stations, the migrating component can be removed and the difference between the nonmigrating components revealed. Non‐zero differences in the summer months (December to March) indicate the presence of a significant nonmigrating component. Modeling studies and observations at other sites suggest that it is most likely the westward propagating wavenumber 1 nonmigrating component that is contributing to the semidiurnal tide. The data presented here are found to be consistent with this hypothesis. A climatology of this nonmigrating component is presented and discussed. Comparisons with the Global Scale Wave Model suggest that latent heat release is not a significant forcing mechanism at these heights and latitudes.
Analysis of thermal inversions in the Khareef Salalah region in the Sultanate of Oman
Authors: Abdul‐Wahab Sabah A.
Published: May 2003

Meteorology and topography (shape of the land) are two of the most important environmental factors that control the movement of pollutants in the atmosphere. A well‐known example of the importance of topography and meteorology is the so‐called monsoon season in Salalah (Khareef Salalah) in the Sultanate of Oman. The purpose of this paper is to investigate the role of the elevated stable layer, particularly during monsoon season in Salalah. The study addresses the statistical analysis of inversion parameters. It will also improve our common understanding of the monsoon and how it is dominated by inversions. In this work, the monthly characteristics of inversions are investigated using the daily radiosonde measurements to a height of 2 km over a period of 1 year. Both surface‐based and elevated inversions are investigated. Based on the analysis of data recovered from weather balloons, the study shows a strong monthly change in inversion frequency, depth, and strength. Overall, inversions are less common in summer (55.4% in May) than in winter (82.8% in January). The surface‐based inversion frequency is at a minimum in summer and at a maximum in winter. The surface‐based inversions reach a maximum depth in winter and are almost absent during summer. An opposite trend in elevated inversion is seen. Most summer inversions are elevated, and a maximum in their frequencies is found during May to September. The elevated inversions are generally deeper and stronger than the surface‐based inversions. The correlation coefficient for the relationships between the inversion depth and temperature difference across the inversion was determined for both the surface‐based and elevated inversions. It was 0.82 for the surface‐based inversion, whereas it was appreciably lower (0.39) for the elevated inversion. Moreover, the correlation coefficient between the log inversion depth and the log temperature difference across the elevated inversion was high (i.e., 0.75).
The Tropospheric Ozone Production about the Spring Equinox (TOPSE) Experiment: Introduction
Authors: Atlas Elliot L. , Ridley Brian A. , Cantrell Christopher A.
Published: May 2003

The Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment was conducted during February–March, 2000 to study the evolution of tropospheric chemistry at mid to high latitudes over North America. The experiment used airborne in situ and remote sensing measurements of trace gases, radiation, and aerosols, combined with model simulations, to describe the major processes that control evolution of ozone and oxidants during the winter‐spring transition. This paper introduces the major scientific questions of the TOPSE experiment, describes the conduct of the mission, and introduces the scientific results discussed in a series of companion papers in this special section. Among the significant findings of the experiment was that tropospheric ozone increases from winter to spring were dominated by in situ photochemical production in the troposphere, rather than by transport from the stratosphere. Also unique observations of widespread surface ozone depletion events, and of seasonal evolution of trace gases and aerosols as a function of latitude and altitude, were obtained over the course of the mission.
Remote sensing of smoke, land, and clouds from the NASA ER‐2 during SAFARI 2000
Authors: King Michael D. , Platnick Steven , Moeller Christopher C. , Revercomb Henry E. , Chu D. Allen
Published: May 2003

The NASA ER‐2 aircraft was deployed to southern Africa between 13 August and 25 September 2000 as part of the Southern African Regional Science Initiative (SAFARI) 2000. This aircraft carried a sophisticated array of multispectral scanners, multiangle spectroradiometers, a monostatic lidar, a gas correlation radiometer, upward and downward spectral flux radiometers, and two metric mapping cameras. These observations were obtained over a 3200 × 2800 km region of savanna, woody savanna, open shrubland, and grassland ecosystems throughout southern Africa and were quite often coordinated with overflights by NASA's Terra and Landsat 7 satellites. The primary purpose of this high‐altitude observing platform was to obtain independent observations of smoke, clouds, and land surfaces that could be used to check the validity of various remote sensing measurements derived by Earth‐orbiting satellites. These include such things as the accuracy of the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask for distinguishing clouds and heavy aerosol from land and ocean surfaces and Terra analyses of cloud optical and microphysical properties, aerosol properties, leaf area index, vegetation index, fire occurrence, carbon monoxide, and surface radiation budget. In addition to coordination with Terra and Landsat 7 satellites, numerous flights were conducted over surface AERONET sites, flux towers in South Africa, Botswana, and Zambia, and in situ aircraft from the University of Washington, South Africa, and the United Kingdom. As a result of this experiment, the MODIS cloud mask was shown to distinguish clouds, cloud shadows, and fires over land ecosystems of southern Africa with a high degree of accuracy. In addition, data acquired from the ER‐2 show the vertical distribution and stratification of aerosol layers over the subcontinent and make the first observations of a “blue spike” spectral emission signature associated with air heated by fire advecting over a cooler land surface.
Foreword: Layered phenomena in the mesopause region
Authors: Thayer Jeffrey P. , Thomas Gary E. , Lübken Franz‐Josef
Published: May 2003

Layered phenomena in the mesopause region is the subject of an international working group whose main focus concerns the physics and chemistry of the summertime mesosphere and the processes involved in forming polar mesospheric summertime echoes (PMSEs) and polar mesospheric clouds (PMCs)—the global equivalent to ground observer's noctilucent clouds (NLCs). PMCs are ice clouds that occur in the summer mesosphere at altitudes typically between 81 and 86 km, and poleward of 50 degrees latitude. PMSEs are strong backscattered signals from the summer mesosphere region, recorded largely, although not exclusively, by VHF radars, that occur most often poleward of 50 degrees latitude and at altitudes typically between 82 and 88 km. The major areas of research within this working group involve understanding and numerically modeling the dynamical, thermal, and chemical processes related to the summer mesosphere; microphysical modeling of MCs; determining the scattering, composition, and shape of mesospheric particles; resolving sources of condensation nuclei; performing laboratory experiments of relevant reactions and related constituents involved in PMC and PMSE behavior, and determining the properties and conditions of PMC, PMSE, and the summer mesosphere by making rocket, satellite, and ground‐based radar and lidar measurements.
Did the Alba Patera and Syria Planum regions of Mars lose their lithospheric roots in convective overturn events?
Authors: Scott Eve , Wilson Lionel
Published: May 2003

Convective removal of part of the thermal boundary layer and its replacement with hotter asthenosphere has been proposed to explain the unusual tectonic setting of the Tibetan plateau on Earth: a topographically highstanding plateau abutting an active region of continental collision and yet undergoing extensional tectonics. A similar model, adapted to take account of the probable absence of plate tectonic processes on Mars, can explain three of the distinctive morphological peculiarities of the shield volcano Alba Patera, namely, the extremely low angle of its flank slopes, the system of annular graben which surround the edifice, and the fact that the nature of volcanic activity apparently changed during the lifetime of the volcano from volatile rich to volatile poor. This change in eruptive style has previously been interpreted to be a consequence of the evolution of the Martian mantle, but we argue that the change is because late stage activity at Alba Patera is sourced from remelted underplated igneous material rather than juvenile melt from the mantle. Our model can also explain the tectonic geomorphology of the Syria Planum area and can relate the compressional regime which produced wrinkle ridges to the more abundante extensional tectonics. These two sets of features have previously been analyzed separately and taken as evidence for global heating or cooling, respectively. Our proposal removes the requirement to explain these features by diametrically opposed processes and on a global scale identifies the patera and large shield morphologies as the end‐members of a single evolutionary sequence.
Two Mars years of clouds detected by the Mars Orbiter Laser Altimeter
Authors: Neumann Gregory A. , Smith David E. , Zuber Maria T.
Published: May 2003

The Mars Orbiter Laser Altimeter (MOLA) instrument operated as an atmospheric lidar system as well as an altimeter, detecting absorptive clouds in northern latitudes shortly after orbit insertion in October 1997 and reflective clouds over the north polar cap at the start of the Science Phasing Orbits in March 1998. Global cloud measurements commenced with the primary mapping mission in March 1999, with nearly continuous coverage for 1.25 Mars years. MOLA tracked several dust storms, culminating with a major dust storm in June 2001. Reflective clouds, exhibiting distinctive patterns governed by insolation and the dynamics of the atmosphere, were detected at elevations up to 20 km above the surface, chiefly in the polar winter night. MOLA distinguishes cloud returns by pulse width and energy measurements. Unusually strong and brief reflections with minimal extinction suggest precipitation of CO2 snow under supercooled conditions. Weaker cloud reflections occurred at all latitudes. Some reflective daylight clouds at low latitudes suggested convective vortices or “dust devils.” Ground fogs composed of dust and H2O ice formed at night along the seasonal frost line. Absorptive clouds, while not resolved altimetrically, tracked the advancing and receding edges of the seasonal polar caps. The absorptive and reflective clouds provide a seasonal profile of atmospheric activity spanning two Martian years. Winter reflective cloud activity declined to background levels earlier in the second year at both poles, suggesting interannual warming.
Exploring for water on Mars: The case for mapping the low‐altitude magnetic field
Authors: Sprenke K. F. , Baker L. L.
Published: May 2003

Successful exploration for subsurface water on Mars is critical to future scientific endeavors on the planet. Although many sophisticated systems have been proposed for directly detecting water on Mars, it is worthwhile to look at the methods that are used in practice for water exploration in basaltic terrain on Earth. By far, the most commonly used instrument for this purpose, at least in the initial stages of exploration, is the magnetometer. The purpose of doing reconnaissance and detailed magnetic surveys for water exploration is not for direct detection but to find those subsurface geological environments in which water is most likely to reside. Magnetic surveys in the basalt‐covered Columbia Plateau are commonly used for such diverse tasks as locating buried valleys, delineating hidden faults, mapping contacts, and tracing dikes. This information leads to the discovery of groundwater, not directly but indirectly. On Mars, just as it is on Earth, the ultimate water supply problem will be a local one: exactly where to drill for water. The unpretentious magnetometer will prove to be a most useful geophysical instrument for making that decision. An important side benefit of using low‐altitude magnetic field measurements for groundwater exploration on Mars is the insight such near‐surface measurements will provide on the nature of the planet's ancient magnetic field.
Electrically conducting, Ca‐rich brines, rather than water, expected in the Martian subsurface
Authors: Burt D. M. , Knauth L. P.
Published: May 2003

If Mars ever possessed a salty liquid hydrosphere, which later partly evaporated and froze down, then any aqueous fluids left near the surface could have evolved to become dense eutectic brines. Eutectic brines, by definition, are the last to freeze and the first to melt. If CaCl2‐rich, such brines can remain liquid until temperatures below 220°K, close to the average surface temperature of Mars. In the Martian subsurface, in intimate contact with the Ca‐rich basaltic regolith, NaCl‐rich early brines should have reacted to become Ca‐rich. Fractional crystallization (freezing) and partial melting would also drive brines toward CaCl2‐rich compositions. In other words, eutectic brine compositions could be present in the shallow subsurface of Mars, for the same reasons that eutectic magma compositions are common on Earth. Don Juan Pond, Antarctica, a CaCl2‐rich eutectic brine, provides a possible terrestrial analog, particularly because it is fed from a basaltic aquifer. Owing to their relative density and fluid nature, brines in the Martian regolith should eventually become sandwiched between ice above and salts beneath. A thawing “brine sandwich” provides one explanation (among many) for the “young gullies” recently attributed to seepage of liquid water on Mars. Whether or not brine seepage explains the gullies phenomenon, dense, CaCl2‐rich brines are to be expected in the deep subsurface of Mars, although they might be somewhat diluted (temperatures permitting) and of variable salt composition. In any case, they should be good conductors of electricity.
GPR, a ground‐penetrating radar for the Netlander mission
Authors: Berthelier J. J. , Ney R. , Ciarletti V. , Reineix A. , Martinat B. , Hamelin M. , Costard F. , Paillou P. , Duvanaud C. , Nevejans D. , Kofman W. , Trotignon J. G. , Grandjean G. , Zamora M. , Nagy A.
Published: May 2003

In the coming decade, several missions are planned that will land on the surface of Mars landers or instrumented geophysical stations. Among the scientific objectives of these projects, one of the most important will be to unravel the many unknowns in the geological and hydrological history of the planet. The Netlander mission offers a unique opportunity to explore the interior of Mars, its subsurface, its atmosphere, and its distant environment from four landing sites that will be selected to offer a variety of different geophysical conditions. We have thus proposed to fly on these four landers a ground‐penetrating radar (GPR) to explore the geological characteristics of the subsurface and search for water reservoirs down to a depth which may be sufficient to allow a possible detection of liquid water. We provide in this paper a short description of this radar which is based on a new concept to allow a 3‐D imaging of the subsurface by determining the range and direction of the underground reflectors. In order to access to deep layers, it will operate at a low frequency of 2 MHz. Some results obtained by a numerical modeling of the radar operation in an electromagnetic model of the Martian subsurface are presented in order to illustrate the main capabilities of the radar. In the last section, preliminary results from an initial field test are reported. In addition to its primary goal as a ground‐penetrating radar, the GPR will also be operated on Mars as an ionospheric sounder and, in a passive mode, as a HF receiver to measure the radio‐electric background.
Numerical simulation of the operation of the GPR experiment on NETLANDER
Authors: Ciarletti V. , Martinat B. , Reineix A. , Berthelier J. J. , Ney R.
Published: May 2003

The first objective of the Ground‐Penetrating Radar (GPR) experiment on NETLANDER is to investigate the geological structures of the Martian subsurface. The aim of this paper is to present initial results obtained in the first phase of a long‐term effort to build a numerical model of the GPR operation on Mars and test dedicated signal‐processing algorithms on the simulated data. The simulation is based on the use of a Finite Difference Time Domain method, and we have pointed out some of its advantages that allow us to take into account complex features of the underground. This model has given reliable estimates of the power budget of the radar for a simple but still representative model of the Martian subsurface. In addition, several detailed features such as gradients and roughness at the interfaces were introduced to appraise their possible influence on the GPR performances. In the frame of a simplified geometry of both the GPR antennas and the various underground interfaces, a simple and first‐order method was developed and tested on simulated data to show the ability of the GPR to retrieve a three‐dimensional distribution of the underground reflectors. Based on this model, and even with some rather crude hypothesis on the subsurface electromagnetic characteristics, information on the direction and distances of the reflectors has been retrieved with a satisfactory approximation.
Microwave remote sensing of physically buried objects in the Negev desert: Implications for subsurface Martian exploration
Authors: Daniels Julian , Blumberg Dan G. , Vulfson Leonid D. , Kotlyar Alex L. , Freiliker Valentin , Ronen Gefen , Ben‐Asher Jiftach
Published: May 2003

We report the remote detection of a physically buried specular reflecting object using microwave radar at Ashalim in the northern region of the Negev desert, Israel. Such detection provides an important terrestrial analogy for the potential detection of specularly reflecting subsurfaces under the desiccated regolith on Mars, such as ground‐ice and liquid water. At Ashalim, a scatterometer operating in the P‐band (441 MHz, 68 cm) was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors (forming a one meter square area reflector) buried down to a depth of 8 cm in dry sand. The decrease in measured backscattered power with increasing burial depth of the reflector is clearly evident. The experimental results compare well with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector. This experiment and the associated modeling approach is the first of a series of planned experiments, which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and VHF radar. We identify many potential subject areas for subsurface remote sensing in the Martian domain, particularly groundwater/ground‐ice.
Frequency and time domain permittivity measurements on solid CO2and solid CO2–soil mixtures as Martian soil simulants
Authors: Pettinelli Elena , Vannaroni Giuliano , Cereti Annamaria , Paolucci Francesca , Della Monica Giuseppe , Storini Marisa , Bella Francesco
Published: May 2003

Permittivity and conductivity measurements were performed to assess the dielectric behavior of solid CO2(i.e., CO2ice, snow, and powder) and solid CO2/soil mixtures. For comparison, some dielectric measurements were also conducted on H2O ice, dry glass beads, glass beads saturated with water, drained glass beads, and frozen drained glass beads. The measurements were performed in the frequency domain (20 Hz to 1 MHz) using a capacitive cell (Parallel Plate Capacitor) and in the time domain using a transmission line (Time Domain Reflectometry). The data obtained with both techniques have shown that solid CO2has a permittivity value that ranges between 1.4 and 2.1 as a function of density, values that distinguish it from H2O ice. In contrast, H2O ice, dry glass beads, frozen (drained) glass beads, and dry volcanic sand all have very similar permittivity values, and thus they cannot be clearly distinguished at higher frequencies. Data have also shown that a high volume fraction of solid CO2significantly reduces the permittivity value of a soil. Furthermore, almost all the samples tested in this work seem to behave like low loss materials, having a conductivity which is generally equal to or lower than 10−6Sm−1at the highest frequency (and smaller values at lower frequencies). Finally, TDR measurements and data from some dielectric models were compared in order to assess the capability of these models to predict the permittivity of a granular multiphase material.
Local geoelectrical models of the Martian subsurface for shallow groundwater detection using sounding radars
Authors: Heggy E. , Paillou P. , Costard F. , Mangold N. , Ruffie G. , Demontoux F. , Grandjean G. , Malézieux J. M.
Published: May 2003

Low‐frequency sounding radars should be able to probe the Martian subsurface layers down to varying depths, depending on the geoelectrical properties of the sounded sites. We present in this work four frequency‐dependent geoelectrical models of the Martian subsurface in the 1–20 MHz frequency band, based on laboratory electromagnetic characterization of Martian soil analogues. Those models correspond to local Martian sites that we considered to be of particular interest in the search for water using mainly the Ground‐Penetrating Radar (GPR) instrument of the Netlander mission. Results and discussion are also valid for both sounding experiments MARSIS and SHARAD. The four models of the Martian subsurface are designed to represent terrains where recent fluvial‐like features suggest the presence of near‐subsurface ground ice and probably liquid water. We performed measurements on volcanic and sedimentary materials that may be present on these sites under the appropriate geophysical conditions that may exist in those terrains. We then simulated the backscattered radar echo arising from each site in the 2 MHz frequency band, using the Finite Difference Time Domain (FDTD) algorithm, in order to evaluate the instrument performances to probe the subsurface stratigraphy of each site. Our results confirm that the near‐subsurface rich iron oxide mineralogy controls the instrument performances in terms of penetration depth and signal‐to‐noise ratio in the 2 MHz frequency band. We finally discuss the geophysical and geoelectrical sounding conditions that could lead to an ambiguous detection of shallow subsurface water on Mars for the Netlander GPR.
Redistribution of water in terrestrial soils at subfreezing temperatures: A review of processes and their potential relevance to Mars
Authors: Miller R. D. , Black P. B.
Published: May 2003

Any study of water behavior in the Martian regolith should begin with an examination of our current understanding of subsurface water in terrestrial cold regions. The terrestrial analog provides a wealth of readily available information to help formulate and test new ideas about possibilities on Mars. This paper discusses the major mechanisms driving the phenomenal ability of capillary media to redistribute moisture when freezing. It examines both thermally induced and freezing‐induced redistribution of moisture, the magnitude of which can vastly exceed the transport expected from Fickian diffusion alone. If the Martian crust is truly water‐rich, then these processes (in response to transient thermal disturbances caused by impacts, volcanic and magmatic activity, changes in climate, and potential future human activities) may induce substantial changes in the local distribution of subsurface ice.
Simulation of a surface‐penetrating radar for Mars exploration
Authors: Leuschen Carl , Clifford Stephen , Gogineni Prasad
Published: May 2003

In the near future, several exploratory missions to Mars are planned, which will include orbital radar sounders capable of characterizing the planet's subsurface structure to depths of up to a few kilometers. Due to the limited amount of resources concerning the properties of the Martian soils, in particular, those governing electromagnetic propagation and scattering, the ability of a radar system to detect and distinguish between subsurface interfaces is difficult to predict. Up to this time, most radar sounding simulations have been based on simplified models and do not accurately account for many of the factors that influence the response. To aid in the system evaluation and data interpretation for these missions, we developed a radar simulator to accurately model the response for various geological conditions. The simulator uses a frequency domain algorithm and is capable of modeling the effects of dielectric layering, volume debris, frequency dispersion, ohmic losses, and interface roughness. In this paper a geophysical model appropriate to the radar simulator is described, and the simulation algorithms are presented in detail. Factors influencing wave propagation and scattering are identified, including those that directly impact radar performance, specifically pertaining to expected penetration depths and unambiguous detection of water or ice. Finally, using a set of “standard” crustal models of different geological regions, simulation results are generated and presented.
Design and field experiments of a ground‐penetrating radar for Mars exploration
Authors: Leuschen Carl , Kanagaratnam Pannir , Yoshikawa Kenji , Arcone Steve , Gogineni Prasad
Published: May 2003

We developed a wideband, low‐power, lightweight, prototype ground‐penetrating radar (GPR) for subsurface exploration for Mars. The transmitter and receiver subsystems were constructed using a commercially available radio frequency (RF) and digital integrated circuits, connectorized components, and evaluation boards. The transmit/receive system, antennas, laptop controller, and batteries are all accommodated on a 2.5‐m sled. Field experiments were conducted in Kansas and Alaska. The experiments in Kansas tested the operation of the system. The primary objective of the Alaska experiments was to investigate the ability of a GPR to detect and distinguish between subsurface deposits of ice and ice‐cemented soils. The investigation depths of these experiments ranged from 1 m to 30 m, and the subsurface geology included near‐surface thaw, discontinuous permafrost, water‐saturated soils, and lenses of pure ice. Dielectric contrasts within the ground were detected with near‐meter resolution; however, identifying the geologic context of an interface was difficult due to ambiguities associated with reflection data. These investigations demonstrate some of the difficulties associated with inverting reflection data to obtain dielectric properties of the subsurface. Fortunately, previous geophysical investigations such as drilled cores and seismic surveys helped to constrain the geology, and numerical simulations provided an additional resource for the interpretations. On Mars, additional geological context will be limited and numerical simulations will become extremely important for data interpretation. Due to these difficulties, we demonstrate in one experiment how dielectric information can be obtained directly from bistatic measurements with a fixed transmitter and mobile receiver. Finally, a comparison with a commercially available Geophysical Survey Systems, Inc. (GSSI) radar system is presented, and we discuss how the system can be modified and improved for future exploration on Mars.
On the role of widespread subsurface convection in bringing liquid water close to Mars' surface
Authors: Travis Bryan J. , Rosenberg Nina D. , Cuzzi Jeffrey N.
Published: May 2003

We report on the results of three‐dimensional calculations of thermohydrologic behavior on a planet with a frozen surface heated from below for ranges of model parameters relevant to Mars. Our results indicate that adopting a more realistic model (i.e., three‐dimensional convective view in contrast to a one‐dimensional static view) of the Martian subsurface significantly changes the possibilities with respect to the depth at which liquid water might exist on Mars. These calculations suggest that hydrothermal convection may occur in the Martian regolith, driven solely by background geothermal heating, and that the sustained upwelling of warm convecting fluids may significantly thin the permafrost ice layer on Mars at some locations, to as thin as 300 m for certain parameter choices.
Glaciers of the McMurdo dry valleys: Terrestrial analog for Martian polar sublimation
Authors: MacClune Karen Lewis , Fountain Andrew G. , Kargel Jeffery S. , MacAyeal Douglas R.
Published: May 2003

The surfaces of the Martian north and south polar residual caps are marked by unusual ice features: Dark spiralesque troughs up to 1 km deep, 10 km wide, and 300 km long appear on both ice caps, and circular pits that make up the “Swiss cheese” terrain appear on the south polar cap. Both types of features are of interest to researchers as a potential means of understanding ice composition and flow rates. Some glaciers of the McMurdo dry valleys have surface features unknown elsewhere on terrestrial glaciers, including canyons over 6 km long, 100 m wide, and tens of meters deep and basins up to 100 m across. High sublimation, dust accumulation, and very little melting is key to their origin. These processes and ice landforms are suggested as terrestrial analogs for the sublimation behavior of Martian ice caps, where dust accumulation and sublimation are significant but surface melting is absent. We have developed a solar radiation model of canyon formation and have applied it to the Martian polar caps. The modeled processes do well to describe direct and reflected radiation within V grooves, a process that may be significant in the development of the spiral troughs and Swiss cheese terrain. The model fails to reproduce the low observed slopes of the Martian troughs. The grooves are too shallow, with opening angles of ∼165° compared with model predictions of ∼90°. The reason for the failure may be that we have not included creep closure, which should flatten their slopes.
Radio wave borehole measurements to determine the in situ electric property distribution in a massif
Authors: Istratov Vyacheslav A. , Frolov Anatoly D.
Published: May 2003

The investigation of the Martian cryosphere, by ground‐penetrating radar and other electromagnetic techniques, requires accurate knowledge of the electrical properties of the planet's regolith and crust. In similar investigations of frozen ground in Siberia, this problem has been addressed by a technique called Radio Wave Geo‐Introscopy (RWGI), which is implemented by examining electromagnetic wave propagation between neighboring boreholes. In this way, temporal and spatial variations in the effective electrical resistivity and dielectric permittivity of the intervening frozen ground can be measured. This paper discusses the main principles of RWGI; the procedures, equipment and measurements needed to implement it; how the data is interpreted; and some applications of this technique to investigations of the terrestrial cryolithozone.
A review of the nature and geophysical studies of the thick permafrost in Siberia: Relevance to exploration on Mars
Authors: Frolov Anatoly D.
Published: May 2003

In this paper we discuss the best Siberian permafrost analog of the Martian cryosphere in connection with the design of deep‐sounding geophysical methods for the detection of liquid water beneath frozen formations on Mars. The peculiarities of the terrestrial cryolithozone and its unique thickness (up to 1.5 km) in the region under consideration (Western Yakutia) are described. The Russian experience in detecting the lower boundary of permafrost, by various geophysical methods, and suggestions regarding the most effective methods for the deep sounding of the Martian cryosphere are also briefly discussed.