bluuebunny/crossref_metadata_2025 huggingface dataset:
Momentum and energy fluxes of monochromatic gravity waves observed by an OH imager at Starfire Optical Range, New Mexico
Authors: Swenson G. R. , Haque R. , Yang W. , Gardner C. S.
Published: September 2002

The intrinsic characteristics of acoustic gravity waves can be deduced when the wave parameters are measured simultaneously with the winds and temperatures so that Doppler effects can be compensated. During February and April, 1995, five nights of OH imager observations of structure were made at the Starfire Optical Range near Albuquerque, New Mexico, simultaneously with Na wind/temperature lidar. The observed (CO) and intrinsic (CI) phase speeds were deduced for 161 gravity waves from the movement of horizontal structure observed in the images (taken every 2 min) and lidar horizontal wind profiles. The mean of the horizontal wavelengths and horizontal phase speeds for the five nights are λh ∼ 28.8 km, CO = 33.4 m s−1, and CI = 61.4 m s−1. The mean vertical wavelength, intrinsic period, and vertical phase speed are λz ∼ 26.6 km, τI ∼ 7.7 min, and Cz ∼ 61.5 m s−1, respectively. Because of their large vertical phase velocities, these waves can propagate to almost 200‐km altitude before they are damped by molecular diffusion. The mean vertical flux of horizontal momentum (Fm) was 21.9 m2 s−2, and the mean zonal and meridional components were −5.3 and +6.1 m2 s−2, respectively. Monochromatic waves with τI > 1 hour and λz < 20 km were also characterized using the Na lidar wind and temperature profiles [Yang, 1998]. The waves measured simultaneously by the lidar in the same volume of atmosphere observed by the imager had a mean momentum flux of Fm = 13.3 m2 s−2. The mean zonal and meridional momentum fluxes of the combined data sets are −3.2 and +3.6 m2 s−2, respectively.
Detection of mineral dust over the North Atlantic Ocean and Africa with the Nimbus 7 TOMS
Authors: Chiapello I. , Prospero J. M. , Herman J. R. , Hsu N. C.
Published: September 2002

It has recently been found that the ultraviolet measurements obtained with the Nimbus 7 total ozone mapping spectrometer (TOMS) instrument can be used to retrieve information on the distribution of aerosols over oceanic and continental surfaces. Here we examine the use of the derived TOMS aerosol index (AI) for the detection of absorbing aerosol in terms of mineral dust aerosol over the North Atlantic Ocean and North Africa. Specifically, we compare the TOMS AI with the time series of daily aerosol measurements made in the boundary layer at Sal Island (Cape Verde), Barbados, and Miami and in the free troposphere on Tenerife (Canary Islands); these sites are frequently impacted by African dust events. At Tenerife, over the time period 1988–1992, TOMS detected 80% of the African dust events that yielded daily average dust concentrations greater than 20 μg m−3; at Barbados and Miami, TOMS detected 65% and 44% respectively of the events over the period 1979–1992. If we exclude events during which some of the TOMS data are missing and also short (1‐day) dust events, TOMS detected 99% of the events at Tenerife, 97% at Barbados, and 81% at Miami. TOMS was also successful in detecting the “low altitude” African dust events recorded at Sal during the winter season. Over Africa we compare the TOMS AI data with ground‐based measurements of aerosol optical thickness (AOT) obtained during field experiments in Senegal and Niger; these yield a nearly linear relationship between the TOMS AI and the AOT. Discrepancies between ground‐based measurements (in terms of dust concentrations or AOT) and TOMS AI can be attributed to a number of factors: variations in the physical properties of the aerosol; the sensitivity of the TOMS response to the altitude of the aerosol layer; or the coarse spatial resolution of the TOMS pixel. Nonetheless, our results clearly show that the TOMS AI provides a remarkably accurate picture of mineral dust distributions in the atmosphere over both continental and oceanic regions.
Characterization of the initial stage of negative rocket‐triggered lightning
Authors: Wang D. , Rakov V. A. , Uman M. A. , Fernandez M. I. , Rambo K. J. , Schnetzer G. H. , Fisher R. J.
Published: September 2002

We performed a statistical study on the initial stage (IS) of negative rocket‐triggered lightning using 37 channel‐base current recordings obtained during the summer of 1994 at Fort McClellan, Alabama, and during the summers of 1996 and 1997 at Camp Blanding, Florida. The IS can be viewed as composed of an upward positive leader (UPL) followed by an initial continuous current ( ICC ). The IS has a geometric mean (GM) duration of 279 ms and lowers a GM charge of 27 C to the ground. The average IS current in an individual lightning discharge varies from a minimum of 27 A to a maximum of 316 A with a GM value of 96 A for the entire sample of 37 discharges. We examined the current variation at the beginning of the IS in 24 flashes. In 22 out of 24 cases this initial current variation (ICV) includes a current drop, probably associated with the disintegration of the copper triggering wire and the subsequent current reestablishment. The GM time interval between the onset of the initial stage and the abrupt decrease in current is 8.6 ms, and the GM current level just prior to the current decrease is 312 A, a value about 3 times the GM value of average current for the whole IS, 96 A. Before this abrupt current decrease, a GM charge of 0.8 C has been lowered to ground with a corresponding GM action integral of 110 A2 s. The abrupt current decrease takes typically several hundred microseconds and is followed, immediately or after a time interval up to several hundred microseconds, by a pulse with a typical peak of about 1 kA and a typical risetime of less than 100 μs. The ICC usually includes impulsive processes that resemble the M processes observed during the continuing currents that follow return strokes in both natural and triggered lightning. We present statistics for the following parameters of current pulses superimposed on the ICC: magnitude, risetime, half‐peak width, duration, charge transferred, preceding continuous current level, interpulse interval, and time interval between the onset of the IS and the first ICC pulse. The observed characteristics of ICC pulses varied significantly among the three data sets. For all data combined, the characteristics of the ICC pulses are similar to those of the M‐component current pulses studied by Thottappillil et al [1995]. This latter finding suggests that ICC impulsive processes are of the same nature as M processes.
Uncertainties in observationally based estimates of temperature change in the free atmosphere
Authors: Santer B. D. , Hnilo J. J. , Wigley T. M. L. , Boyle J. S. , Doutriaux C. , Fiorino M. , Parker D. E. , Taylor K. E.
Published: September 2002

Uncertainties are quantified in atmospheric temperature changes derived from satellites, radiosondes, and the reanalyses of the National Center for Environmental Prediction and European Centre for Medium‐Range Weather Forecasts (NCEP and ERA). To facilitate intercomparison, we compute from the reanalyses and radiosonde data deep layer temperatures equivalent to those estimated from the satellite‐based Microwave Sounding Unit (MSU). Equivalent MSU temperatures generated using global mean weighting functions and a radiative transfer code give similar results. NCEP's pre‐1979 global mean lower stratospheric temperature anomalies diverge markedly from radiosonde data. A smaller offset occurs in the midtroposphere. These differences are attributed to a likely warm bias in the tropical lower stratosphere in the temperature retrievals used by NCEP from November 1978 onward, and changes in the error characteristics of the assimilation model's simulation of the lower stratosphere. In the lower troposphere, ERA and NCEP show different global mean trends due to differences in assimilation strategy, input observational data, quality control procedures, and model physics. Over 1979–1993, ERA warms by 0.106°C/decade, while NCEP cools by 0.028°C/decade. Applying the HadRT1.1 (radiosonde) data availability mask to NCEP improves the agreement between these data sets. Neglecting coverage differences can yield misleading results in MSU‐radiosonde trend comparisons. Substantial trend uncertainties also arise from coverage differences between various radiosonde data sets. Version c of the MSU lower tropospheric temperature retrieval fails to adjust explicitly for orbital decay. If this were applied without any additional adjustments, it would resolve an important discrepancy: in MSUc the lower troposphere has cooled in relation to the midtroposphere, while the reverse is the case for both reanalyses and for the radiosonde data examined here.
Systematic variation of drop size and radar‐rainfall relations
Authors: Atlas David , Ulbrich Carlton W. , Marks Frank D. , Amitai Eyal , Williams Christopher R.
Published: September 2002

Time histories of the characteristics of the drop size distribution of surface disdrometer measurements collected at Kapingamarangi Atoll were partitioned for several storms using rain rate R, reflectivity factor Z, and median diameter of the distribution of water content D0. This partitioning produced physically based systematic variations of the drop size distribution (DSD) and Z‐R relations in accord with the precipitation types viewed simultaneously by a collocated radar wind profiler. These variations encompass the complete range of scatter around the mean Z‐R relations previously reported by Tokay and Short [1996] for convective and stratiform rain and demonstrate that the scatter is not random. The systematic time or space variations are also consistent with the structure of mesoscale convective complexes with a sequence of convective, transition, and stratiform rain described by various authors. There is a distinct inverse relation between the coefficient A and the exponent of the Z‐R relations which has been obscured in prior work because of the lack of proper discrimination of the rain types. Contrary to previous practice it is evident that there is also a distinct difference in the DSD and the Z‐R relations between the initial convective and the trailing transition zones. The previously reported Z‐R relation for convective rain is primarily representative of the transition rain that was included in the convective class. The failure of present algorithms to distinguish between the initial convective and the trailing transition rains causes an erroneous apportionment of the diabatic heating and cooling and defeats the primary intent of discriminating stratiform from convective rains.
Estimating biologically active UV irradiance from satellite radiance measurements: A sensitivity study
Authors: Soulen Peter F. , Frederick John E.
Published: September 2002

An algorithm for estimating biologically active UV irradiance from satellite measurements of ozone and reflectivity is presented. In contrast to previous work, this technique treats bulk radiative properties of clouds explicitly, assuming that clouds are reflecting surfaces. This work addresses the following issue: If clouds are characterized as simple reflecting surfaces of a specified albedo at a specified altitude covering a fraction of the sky, how precisely can surface UV irradiance be determined? To address this issue, an Eddington radiative transfer model is used to calculate not only ground level irradiance but also an estimate of the backscattered radiance in the nadir direction using the formal solution to the radiative transfer equation. While this model does not simulate detailed angular distributions of radiation scattered off clouds, it is found that this model retrieves average measured biologically active surface UV irradiance around solar noon quite well and that different combinations of parameters yield strikingly similar estimates of surface UV irradiance. The model is tested using four years of continuous‐scan SBUV data and Robertson‐Berger meter data for nine cities.
Combining afternoon and morning NOAA satellites for thermal inertia estimation: 1. Algorithm and its testing with Hydrologic Atmospheric Pilot Experiment‐Sahel data
Authors: Sobrino J. A. , El Kharraz M. H.
Published: September 2002

This is the first in a series of two papers on the thermal inertia estimation from satellite data. In this paper we have evaluated the behavior of three algorithms to retrieve surface thermal inertia from NOAA‐advanced very high resolution radiometer (AVHRR) data. These are Price's [1977] algorithm, and two different algorithms based on the model of Xue and Cracknell [1995]; Xue and Cracknell's algorithm (XC), and a new approach which we have named FTA (four temperatures algorithm) since it uses four AVHRR measurements (XC plus two from NOAA morning satellites). The main advantage of the FTA is that it only uses satellite data. The algorithms were tested with a set of in situ measurements taken over a region of Niger in the frame of the Hydrologic Atmospheric Pilot Experiment‐Sahel. The analysis was done in two different ways: (1) by comparing the ST (surface temperature) predicted by the algorithms with the measured ones every 10 minutes, and (2) by comparing the predicted and measured maximum and minimum ST values as well as their respective times. Our results indicate that the FTA is the most appropriate algorithm for presenting the diurnal cycle of the ground ST with these experimental data. For 90% of the cases the absolute difference between predicted and measured STs is lower than 2 K, with a standard deviation of 1.5 K that improves to 1 K when predicting the maximum and minimum STs. The FTA also predicts their respective times with a standard deviation of less than 30 min. These results suggest that it is possible to predict the minimum ST and corresponding time from NOAA data, which might be useful to forecast frost during nights of radiative cooling (cloudless and calm wind).
Modeling CO2 sources, sinks, and fluxes within a forest canopy
Authors: Katul Gabriel G. , Albertson John D.
Published: September 2002

A practical method to infer CO2 sources, sinks, and fluxes from measured mean concentration profiles is proposed and field‐tested in a uniform pine forest using eddy covariance measurements. The proposed method computes the velocity statistics from a second‐order closure model and uses these statistics to infer profiles of scalar fluxes using a scalar‐flux budget. The model input requirements are leaf area density profile, mean shear stress at the canopy top, and measured concentration profiles within and just above the canopy. In contrast to the localized near‐field (LNF) theory the model does not assume zero vertical velocity skewness, negligible advective effects, and local vertical homogeneity in the near‐field concentration. The model results compared well with eddy covariance CO2 flux measurements inside the canopy and reproduced qualitatively much of the physiologically known daytime evolution of the CO2 source‐sink profile.
Effects of sea surface temperature and large‐scale dynamics on the thermodynamic equilibrium state and convection over the tropical western Pacific
Authors: Wu Xiaoqing , Moncrieff Mitchell W.
Published: September 2002

The effects of sea surface temperature (SST) variations and large‐scale dynamics on the cloud feedback and water vapor feedback are quantified using a fine‐scale numerical model, or cloud‐resolving model, in which the cloud‐scale dynamics is explicitly treated instead of being parameterized as is necessary in a general circulation model. The SST variation has large impacts on the water vapor feedback and small impacts on the cloud feedback, radiation budget, and surface energy budget under a given large‐scale dynamic state. As the SST gets warmer (increasing 2°), the warm and moist equilibrium state of temperature and water vapor mixing ratio is obtained; the upper tropospheric relative humidity is enhanced; and the cloud amount and convective intensity are slightly reduced. The cooling (about 10 W m−2) at the surface due to the increase of surface evaporation is almost compensated by the warming at the surface due to the increase of surface shortwave flux, which results in a small increase of net surface heat flux. However, the change of large‐scale dynamics has large effects on the cloud feedback, radiation budget, and surface energy budget and small effects on the water vapor feedback under a constant SST. An increased large‐scale forcing slightly affects the equilibrium states of temperature and water vapor mixing ratio; the relative humidity is decreased above 10 km and increased below; and the cloud amount and convective intensity are enhanced. Both the variations of SST and large‐scale dynamics are positively correlated with the surface precipitation.
Relationships between cloud droplet effective radius, liquid water content, and droplet concentration for warm clouds in Brazil embedded in biomass smoke
Authors: Reid Jeffrey S. , Hobbs Peter V. , Rangno Arthur L. , Hegg Dean A.
Published: September 2002

During the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) project, the microphysical properties of over 1000 warm, nonprecipitating, clouds were measured from the University of Washington research aircraft. The clouds were partially embedded in the continental‐scale, smoky haze that envelops much of Brazil during the biomass‐burning season. For the entire data set, the most universal parameterization for the effective cloud droplet radius (reff) is as a function of the ratio of cloud liquid water content (LWC) to droplet concentration (essentially the volume mean radius, rv); this agrees with previous studies under less polluted conditions. Comparisons of SCAR‐B data with data from the east coast of the United States and clean oceanic areas show that the reff‐rv relationship is similar in all three cases, suggesting that even the extreme case of clouds impacted by large biomass fires can be treated similarly to more typical clouds. Beyond a certain ambient concentration of accumulation‐mode particles (∼3000–4000 cm−3), cloud drop number concentrations for cumulus clouds in Brazil were almost constant, so that further increases in the ambient particle concentration did not change reff and reff correlates well with LWC alone. For example, a cumulus cloud, which capped a particularly large smoke plume with total particle concentrations >150,000 cm−3, had the same reff‐LWC relationship as other clouds in the region where the ambient particle concentrations were ∼3000 cm−3. In this study the values of reff for cumulus clouds in Brazil affected by smoke were between 3 and 8 μm, compared to 9 to 14 μm inferred from satellite measurements of cloud reflectivity at 3.7 μm by Kaufman and Fraser [1997].
A new method of retrieving surface bidirectional reflectance from ground measurements: Atmospheric sensitivity study
Authors: Lyapustin A. I. , Privette J. L.
Published: September 2002

Commonly, experimental data on surface directional reflectance are not properly corrected for atmospheric effects. In this paper, we describe a new method for rigorous retrieval of the bidirectional reflectance distribution function (BRDF) from ground‐based measurements. It obtains the pointwise BRDF in the view directions and the best fit parameters of the approximating analytical model. Unlike previously developed algorithms, it can perform a retrieval using directional observations made at a single solar angle. This improvement allows one to process experiments with incomplete sets of measurements, such as those contaminated by clouds. The paper describes the performance of the method and its sensitivity to atmospheric parameters. Using rigorous direct modeling of the reflected radiance and developed inversion algorithm, we performed an analysis of BRDF errors, typical for measurements. It shows that the BRDF shape distortions due to diffuse irradiance are considerable in the visible and near‐IR, even for low aerosol content in the atmosphere. This result confirms that an accurate atmospheric correction should be a required processing step in the experimental research of anisotropic surface reflectance.
Albedo bias and the horizontal variability of clouds in subtropical marine boundary layers: Observations from ships and satellites
Authors: Pincus Robert , McFarlane Sally A. , Klein Stephen A.
Published: September 2002

Cloud optical properties vary dramatically at spatial scales smaller than typical grid cells in large‐scale models, which can cause a significant overestimate of cloud albedo by the model. This plane parallel homogeneous (PPH) albedo bias exist may be reduced if the mean cloud optical thickness and the amount of variability are available, but little is known about how much variability exists in nature and to what factors it is sensitive. The authors combine 1331 observations made by volunteer surface observers with satellite imagery to assess the relationships between cloud fraction, cloud optical properties, and cloud type in marine boundary layer clouds off the coast of California during summer. Estimates of cloud fraction from the two datasets are in best agreement when a reflectance threshold between 0.09 and 0.10 is used. Satellite‐derived cloud fraction increases slowly with sensor resolution at spatial scales from 1 to 32 km. Cloud fraction in scenes dominated by cumulus is much more sensitive to the reflectance threshold used for cloud detection than are scenes containing stratiform clouds. The mean magnitude of the PPH bias found here, 0.025, is considerably smaller than those found in other recent studies. When fit to the observed distributions of optical thickness both log‐normal and gamma distributions substantially reduce the PPH bias. The mean and dispersion of log optical thickness are related to cloud type: optical thickness increases as cloud type changes from cumuliform to stratiform, while the relative amount of variability decreases. The authors suggest a basis for the parameterization of unresolved variability in large scale models.
Indirect forcing by anthropogenic aerosols: A global climate model calculation of the effective‐radius and cloud‐lifetime effects
Authors: Rotstayn Leon D.
Published: September 2002

A global climate model (GCM) that includes a physically based cloud scheme is used to calculate the indirect radiative forcing due to the modification of liquid‐water cloud properties by anthropogenic aerosols. The distribution of cloud‐droplet number concentration Nd required by the cloud scheme is estimated empirically from monthly mean fields of sulfate mass generated by a chemical transport model. The effects of anthropogenic changes in Nd are considered in the calculation of precipitation (the “cloud‐lifetime” effect) and of the droplet effective radius used in the shortwave and longwave radiation schemes (the “effective‐radius” effect). The modeled cloud‐droplet effective radii for present‐day conditions agree quite well with satellite‐retrieved values, although the land‐ocean and hemispheric contrasts are weaker in the model than in the observations. The total indirect forcing is −2.1 W m−2, including a small longwave forcing of +0.1 W m−2. The forcing results from a 1% increase in cloudiness, a 6% increase in liquid water path, and a 7% decrease in droplet effective radius. The breakdown of the total indirect forcing into the effective‐radius and cloud‐lifetime effects is estimated by performing separate GCM experiments in which each effect is included individually. The estimated forcings due to the effective‐radius and cloud‐lifetime effects are −1.2 and −1.0 W m−2, respectively. The calculated forcings show some sensitivity to the autoconversion threshold, the sulfate‐Nd relation, and the vertical distribution of sulfate, but in each case the cloud‐lifetime forcing is at least 25% of the total indirect forcing. These results suggest that the cloud‐lifetime effect should not be ignored in future calculations of the indirect forcing due to anthropogenic aerosols.
Exploring for a record of ancient Martian life
Authors: Farmer Jack D. , Des Marais David J.
Published: September 2002

The immediate task facing exopaleontology is to define a strategy to explore Mars for a fossil record during the decade‐long exploration program that lies ahead. Consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability. The preservation of microbial fossils is strongly influenced by the physical, chemical, and biological factors of the environment which, acting together, determine the types of information that will be captured and retained in the rock record. In detrital sedimentary systems, preservation is favored by rapid burial in fine‐grained, clay‐rich sediments. In chemical sedimentary systems, preservation is enhanced by rapid entombment in fine‐grained chemical precipitates. For long‐term preservation, host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism. In this context, host rocks composed of highly ordered, chemically stable mineral phases, like silica (e.g., cherts) or phosphate (e.g., phosphorites), are especially favored. Such lithologies tend to have very long crustal residence times and, along with carbonates and shales, are the most common host rocks for the Precambrian microfossil record on Earth. Although we make the defensible assumption that Mars was more like the Earth early in its history, clearly, the geological and historical differences between the two planets are many. Such differences must be carefully considered when adapting an Earth‐based strategy to Mars.
Abiotic synthesis of polycyclic aromatic hydrocarbons on Mars
Authors: Zolotov Mikhail , Shock Everett
Published: September 2002

Thermochemical calculations of metastable equilibria are used to evaluate the stability of condensed polycyclic aromatic hydrocarbons (PAHs) in cooling thermal gases and hydrothermal fluids on ancient Mars, which are roughly similar to their terrestrial counterparts. The effects of temperature, pressure, the extent of PAH alkylation, and the relative stability of PAHs and alkanes are considered. Inhibition of methane and graphite formation favors synthesis of metastable mixtures of hydrocarbons from aqueous or gaseous CO, CO2, and H2below 200°–300°C. High‐temperature quenching of H2and CO in volcanic and impact gases and dynamic hydrothermal fluids also favor the synthesis of hydrocarbons. In addition, an excess of CO in cooling systems relative to equilibrium makes the synthesis from CO and H2more favorable energetically than from CO2and H2. Both the CO‐H2reactions through Fischer‐Tropsch (FT) type processes and the CO2‐H2reactions could be catalyzed by magnetite. Volcanic gases and hydrothermal fluids related to mafic and ultramafic magmas and rocks are more favorable for FT type synthesis than those associated with oxidized Fe2O3‐bearing rocks and regolith. We conclude that PAHs and aliphatic hydrocarbons on Mars and Earth could be formed without the contribution of biogenic carbon. Some PAHs could be formed because of pyrolysis of other hydrocarbons formed earlier by the FT type synthesis or other processes. If the PAHs found in the ALH 84001 martian meteorite formed together with other hydrocarbons through FT type synthesis, it may be possible to bracket the temperature of the synthesis. The approach presented here can be generalized to study the synthesis of hydrocarbons in terrestrial volcanic and hydrothermal processes.
On the role of solar EUV, photoelectrons, and auroral electrons in the chemistry of C(1D) and the production of C I 1931 Å in the cometary coma: A case for comet 1P/Halley
Authors: Bhardwaj Anil
Published: September 2002

The observations of C I 1931 Å emission in the ultraviolet spectra of comets show that a large fraction of carbon atoms in the cometary coma are produced in the metastable 1D excited state. A coupled‐chemistry transport model is employed to examine in detail the various processes of production and loss of the C(1D) atoms in the coma of comet 1P/Halley. Different mechanisms forming CI 1931 Å line are subsequently studied. The impacts of solar UV‐EUV photons, photoelectrons, and auroral electrons of solar wind origin, on the chemistry of C(1D) and the C I 1931 Å emission are evaluated. Dissociation of CO by solar photon and electron impact are the dominant mechanisms of the production of C(1D). Contrary to the findings of the earlier works, the dissociative e‐CO+ recombination is not a significant source of C(1D) in the inner (<104 km) coma. Quenching of C(1D) by H2O is the main loss mechanism of C(1D) in the inner most coma (<103 km), while radiative deexcitation dominates at larger radial distances. The density of C(1D) in the inner coma is found to be controlled predominantly by the CO and H2O density distribution. Deep in the coma (<300 km) the photodissociative excitation of CO is the major source of 1931 Å emission, while beyond 500 km the resonant scattering of solar radiation by C(1D) atoms dominates. The contribution of the solar resonance fluorescence to the 1931 Å IUE slit‐averaged intensity is about 80% in the normal and auroral conditions. Results of the model case studies performed to assess the impact of changing C(1D) + H2O quenching rate coefficient, C(1D) to C(3P) production ratio, neutral and electron temperatures, and extended CO source are discussed. The modeled intensity of carbon 1931 Å emission is found to be a factor of 3–6 smaller compared to the IUE‐observed intensity.
Processing and analysis of Mars Pathfinder science data at the Jet Propulsion Laboratory's Science Data Processing Systems Section
Authors: LaVoie Susan K. , Green William B. , Runkle Allan J. , Alexander Douglass A. , Andres Paul M. , DeJong Eric M. , Duxbury Elizabeth D. , Freda David J. , Gorjian Zareh , Hall Jeffrey R. , Hartman Frank R. , Levoe Steven R. , Lorre Jean J. , McAuley James M. , Suzuki Shigeru , Woncik Pamela J. , Wright John R.
Published: September 2002

The Mars Pathfinder mission required new capabilities and adaptation of existing capabilities in order to support science analysis and flight operations requirements imposed by the in situ nature of the mission. The Science Data Processing Systems Section of the Jet Propulsion Laboratory was responsible for the design, development, and application of the system required to perform telemetry processing, distribution, and archiving of data from the four primary science instruments, and support of flight operations through production of automatically generated stereo and color mosaics, terrain visualizations, and animations. The system developed for Mars Pathfinder incorporated new capabilities in producing computer‐generated color mosaics, for cataloging and distribution of science data, and utilized new display technology to support science analysis and flight operations requirements. This paper describes the data processing performed to support the science and operations payload on the Pathfinder lander and Sojourner rover.
General geology and geomorphology of the Mars Pathfinder landing site
Authors: Ward A. W. , Gaddis L. R. , Kirk R. L. , Soderblom L. A. , Tanaka K. L. , Golombek M. P. , Parker T. J. , Greeley Ronald , Kuzmin R. O.
Published: September 2002

The Mars Pathfinder (MPF) spacecraft landed on relatively young (late Hesperian‐early Amazonian; 3.1–0.7 Ga) plains in Chryse Planitia near the mouth of Ares Vallis. Images returned from the spacecraft reveal a complex landscape of ridges and troughs, large hills and crater rims, rocks and boulders of various sizes and shapes, and surficial deposits, indicating a complex, multistage geologic history of the landing site. After the deposition of one or more bedrock units, depositional and erosional fluvial processes shaped much of the present landscape. Multiple erosional events are inferred on the basis of observations of numerous channels, different orientations of many streamlined tails from their associated knobs and hills, and superposition of lineations and streamlines. Medium‐ and small‐scale features, interpreted to be related to late‐stage drainage of floodwaters, are recognized in several areas at the landing site. Streamlined knobs and hills seen in Viking orbiter images support this inference, as they seem to be complex forms, partly erosional and partly depositional, and may also indicate a series of scouring and depositional events that, in some cases, further eroded or partially buried these landforms. Although features such as these are cited as evidence for catastrophic flooding at Ares Vallis, some of these features may also be ascribed to alternative primary or secondary depositional processes, such as glacial or mass‐wasting processes. Close inspection of the landing site reveals rocks that are interpreted to be volcanic in origin and others that may be conglomeratic. If such sedimentary rocks are confirmed, fluvial processes have had a greater significance on Mars than previously thought. For the last several hundred million to few billion years, eolian processes have been dominant. Dunes and dune‐like features, ventifacts, and deflation and exhumation features around several rocks probably are the most recent landforms. The relatively pristine nature of the overall landscape at the MPF site suggests weathering and erosion processes on Mars are exceptionally slow.
Petrology of the Western Highland Province: Ancient crust formation at the Apollo 14 site
Authors: Shervais John W. , McGee James J.
Published: September 2002

Plutonic rocks found at the Apollo 14 site comprise four lithologic suites: the magnesian suite, the alkali suite, evolved lithologies, and the ferroan anorthosite suite (FAN). Rocks of the magnesian suite include troctolite, anorthosite, norite, dunite, and harzburgite; they are charaterized by plagioclase ≈An95 and mafic minerals with mg#s 82–92. Alkali suite rocks and evolved rocks generally have plagioclase ≈An90 to ≈An40 and mafic minerals with mg#s 82–40. Lithologies include anorthosite, norite, quartz monzodiorite, granite, and felsite. Ferroan anorthosites have plagioclase ≈An96 and mafic minerals with mg#s 45–70. Whole rock geochemical data show that most magnesian suite samples and all alkali anorthosites are cumulates with little or no trapped liquid component. Norites may contain significant trapped liquid component, and some alkali norites may represent cumulate‐enriched, near‐liquid compositions, similar to KREEP basalt 15386. Evolved lithologies include evolved partial cumulates related to alkali suite fractionation (quartz monzodiorite), immiscible melts derived from these evolved magmas (granites), and impact melts of preexisting granite (felsite). Plots of whole rock mg# versus whole rock Ca/(Ca + Na + K) show a distinct gap between rocks of the magnesian suite and rocks of the alkali suite, suggesting either distinct parent magmas or distinct physical processes of formation. Chondrite‐normalized rare earth element (REE) patterns show that rocks of both the magnesian suite and alkali suite have similar ranges, despite the large difference in major element chemistry. Current models for the origin of the magnesian suite call for a komatiitic parent magma derived from early magma ocean cumulates; these melts must assimilate plagiophile elements to form troctolites at low pressures and must assimilate a highly enriched KREEP component so that the resulting mixture has REE concentrations similar to high‐K KREEP. There are as yet no plausible scenarios that can explain these unusual requirements. We propose that partial melting of a primitive lunar interior and buffering of these melts by ultramagnesian early magma ocean cumulates provides a more reasonable pathway to form magnesian troctolites. Alkali anorthosites and norites formed by crystallization of a parent magma with major element compositions similar to KREEP basalt 15386. If the parent magma of the alkali suite and evolved rocks is related to the magnesian suite, then that magma must have evolved through combined assimilation‐fractional crystallization processes to form the alkali suite cumulates.
Introduction to the special section: Mars Pathfinder
Authors: Golombek Matthew
Published: September 2002

Mars Pathfinder successfully landed on the surface of Mars on July 4, 1997, ushering in a renewed phase of exploration of our neighboring world after a hiatus of over 20 years. In addition to successfully capturing the imagination of the public by landing a robust, low‐cost spacecraft and rover on the Red Planet, Pathfinder returned a significant volume of scientific data. Pathfinder was the first Mars mission to use a rover, which carried a chemical analysis instrument that characterized the rocks and soils in a landing area occupying hundreds of square meters. In 3 months of surface operations at Ares Vallis, Pathfinder's three science instruments, 10 technology experiments, and engineering subsystems aboard the rover and lander, addressed seven general areas of scientific investigations.
Optical properties of the Martian aerosols as derived from Imager for Mars Pathfinder midday sky brightness data
Authors: Markiewicz W. J. , Sablotny R. M. , Keller H. U. , Thomas N. , Titov D. , Smith P. H.
Published: September 2002

The Imager for Mars Pathfinder (IMP) obtained data on the midday sky brightness in filters centered at 443.6, 481.0, 670.8, 896.1 and 965.3 nm. Useful data sets were returned on sols 27, 40, 56, 65, 68, 74, and 82. Data from sol 56 were fitted with multiple scattering radiative transfer calculations, to extract the size distribution, optical properties and shape of the aerosols suspended in the atmosphere. The derived effective radius of the particles is about 1.71 + 0.29/ −0.26 μm with an effective variance of veff = 0.25 + 0.05/ − 0.1. The estimated values of the refractive index and shape parameters are close to those derived from Viking and Phobos data. This in turn implies that dust plays a significant and relatively constant role in the energy budget of the Martian atmosphere over the last two decades. Estimates of the optical depth agree well with those obtained independently from direct IMP imaging of the Sun. The derived single scattering phase function is more compatible with plate (clay) like particles rather than equal dimensional particles. The presented analysis assumes a simple single‐component dust atmosphere. The data‐model residuals exhibit, albeit weak, wavelength dependence. This dependence can be interpreted as an indication that during the time the analyzed images were taken, the dust particle distribution was bimodal or that the Martian atmosphere contained a second component, possibly submicron ice particles, in the aerosol's population.
A new data reduction approach for the Clementine NIR data set: Application to Aristillus, Aristarchus and Kepler
Authors: Le Mouélic Stéphane , Langevin Yves , Erard Stéphane
Published: September 2002

The Clementine spacecraft, launched in January 1994, has performed a nearly global surface mapping of the moon in eleven broad spectral bands at a resolution of ∼200 m. The UV‐visible (UV/VIS) camera performed observations in five bands ranging from 0.415 to 1.0 μm, while the near infrared camera (NIR) acquired data in six spectral bands ranging from 1.1 to 2.78 μm. UV/VIS images are calibrated to ∼4%. The calibrated NIR data set is yet to be finalized due to instrumental problems. Independently of the calibration effort for the full data set which is under the responsibility of the PI team, we present here the first results of a heuristic approach to extract mineralogical information from raw images in regions of particular interest. We processed images of craters Aristillus, Aristarchus, and Kepler. We computed band ratios using 0.75, 0.9, 0.95, 1.0, 1.1, 1.25, 1.5, and 2.0 μm images to map the compositional heterogeneity and to discriminate between pyroxene, olivine, or feldspar rich areas. Absolute reflectance spectra have been derived using telescopic spectra as ground truth. High orthopyroxene and clinopyroxene contents have been detected and spatially mapped on Aristillus. Our results are in good agreement with previous studies in the case of Aristarchus and show additional details due to the improved registration. Two regions exhibit spectra consistent with a high proportion of olivine with <25% pyroxene. The rim of Kepler exhibits a strong feature at 2 μm correlated with the 1 μm feature, suggesting either a high orthopyroxene content or a very immature soil. Our method could be of interest for further investigations of the lunar surface using Clementine NIR data.
General circulation model simulations of the Mars Pathfinder atmospheric structure investigation/meteorology data
Authors: Haberle Robert M. , Joshi Manoj M. , Murphy James R. , Barnes Jeffrey R. , Schofield John T. , Wilson Greg , Lopez‐Valverde Miguel , Hollingsworth Jeffery L. , Bridger Alison F. C. , Schaeffer James
Published: September 2002

The NASA Ames Mars General Circulation Model is used to interpret selected results from the Mars Pathfinder atmospheric structure instrument/meteorology (ASI/MET) experiment. The present version of the model has an improved soil thermal model, a new boundary layer scheme, and a correction for non‐local thermodynamic equilibrium effects at solar wavelengths. We find good agreement with the ASI/MET entry data if the dust observed at the Pathfinder site is assumed to be distributed throughout the lowest five to six scale heights. This implies that the dust is globally distributed as well. In the lower atmosphere the inversion between 10 and 16 km in Pathfinder's entry profile is likely due to thermal emission from a water ice cloud in that region. In the upper atmosphere (above 50 km), dynamical processes, tides in particular, appear to have a cooling effect and may play an important role in driving temperatures toward the CO2 condensation temperature near 80 km. Near‐surface air temperatures and wind directions are well simulated by the model by assuming a low surface albedo (0.16) and moderately high soil thermal inertia (336 SI). However, modeled tidal surface pressure amplitudes are about a factor of 2 smaller than observed. This may indicate that the model is not properly simulating interference effects between eastward and westward modes.
Results of the Mars Pathfinder atmospheric structure investigation
Authors: Magalhães Julio A. , Schofield John T. , Seiff Alvin
Published: September 2002

We report on a thorough analysis of the Mars Pathfinder atmospheric structure investigation (ASI) accelerometer data spanning the altitude range 161–8.9 km. Entry, descent, and landing occurred within 850 km of the Viking 1 lander and somewhat later in northern summer. The early morning entry (0300 hours) provided the first opportunity to study Mars' nighttime atmospheric structure; the close proximity to the Viking 1 site has permitted a search for changes in atmospheric structure during the 21 years between the landings. Our results confirm and refine the major features of the atmospheric structure discovered in the initial analysis of the ASI results reported by Schofield et al. [1997]. The current analysis has yielded a much better definition of the temperature structure above 90 km altitude. Pathfinder measured a thermospheric peak temperature of 153°K at 134 km, which is 30°K colder than the value found by Viking 1. Between 110 and 88 km, Pathfinder found a broad, nearly isothermal plateau at 127°K, which correlates very well with a similar structure evident in Viking 1 data at the same pressures, although the Pathfinder layer is 25°K colder. At levels above 88 km, wavelike oscillations with a wavelength ∼5 km and amplitudes of 2–3°K are evident, possibly reflecting gravity or planetary wave activity. Between 90 and 60 km the average temperature is 20–30°K cooler than Viking 1 values. Large‐amplitude (10–20°K) long‐wavelength (20–40 km) oscillations, which show a remarkable correspondence to equivalent structures found in the Viking 1 profile at the same pressures, occur in this region and are likely due to a diurnal tidal mode. Between 85 and 77 km a minimum of one oscillation results in temperatures up to 7°K below the saturation temperature of CO2, well outside the uncertainties in the measurements and the vapor pressure curve and comparable to observed supersaturations of water in Earth's mesosphere. Between 55 and 16 km, temperatures are close to or warmer than Viking 1 values; superposed long‐wavelength oscillations correspond well with similar structures observed by Viking 1. Between 16 and 9.9 km the temperature profile shows an unexpected strong thermal inversion, which may reflect radiative cooling due to a water cloud. At the base of the inversion, temperatures begin to increase abruptly until the last measurement at 8.9 km. The Viking‐like temperatures in the lower atmosphere are consistent with the Viking‐like dust optical depths observed by the Mars Pathfinder imager. The cool temperatures in the middle and upper atmosphere may be indicative of significant nighttime cooling at these levels, although other interpretations are possible.
Mixed hydrothermal fluids and the origin of the Martian soil
Authors: Newsom Horton E. , Hagerty Justin J. , Goff Fraser
Published: September 2002

The Martian soil consists mainly of weathered basaltic rock and a “salt” component enriched in volatile and mobile elements, primarily sulfur, chlorine, sodium, and potassium. Since the discovery of this mobile element component by the Viking X‐ray fluorescence spectrometer, volcanic aerosols have been considered a likely source for these enrichments. Alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism. We show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil. This model is constructed using terrestrial analogs constrained by the Viking and Pathfinder measurements of the Martian soil chemistry. The potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant. The two end‐member types of hydrothermal fluids considered in the model are the neutral‐chloride and the acid‐sulfate type. The neutral‐chloride fluids have high Cl and Na contents and a significant amount of K, but their S abundance relative to Cl (S/Cl ratio) is too low to match the Martian soil. However, acid‐sulfate hydrothermal systems characterized by substantial vapor transport and high S/Cl ratios are likely on Mars due to the low abundance of water. Indeed, as the availability of water declines in a hydrothermal system, the neutral‐chloride system can evolve to a vapor‐dominated acid‐sulfate system. A combination of the two types of fluids can quantitatively explain the S and Cl abundance in the soil and provide reasonable abundances of other mobile elements, including Na, K, and Br, without predicting an excess of any element measured in the soil. However, the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the Fe contents of the fluids are too low. Although the acid‐sulfate fluids have Fe concentrations a factor of 100 larger than the neutral‐chloride fluids, the acid‐sulfate fluids would contribute less than 1% of the total Fe in the soil. The volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable. Therefore, while volcanic aerosols can explain the mobile element component of the soil, significant contributions from other sources cannot be excluded. Determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the Martian soil of trace elements that provide signatures of the hydrothermal fluids, such as high lithium contents that are associated with neutral‐chloride fluids.