bluuebunny/crossref_metadata_2025 huggingface dataset:
A fixed‐layer estimation of upper tropospheric specific humidity from the GOES water vapor channel: Parameterization and validation of the altered brightness temperature product
Authors: Wimmers A. J. , Moody J. L.
Published: February 2004

A derived‐product image (DPI) of specific humidity is determined at the pixel‐level using the GOES 6.7 μm water vapor channel and ancillary model temperature fields. By treating the brightness temperature, T6.7, as a composition of three effectively independent influences (specific humidity, temperature and zenith angle), the ancillary temperature fields allow an estimation of the sole effect of specific humidity on the variance of T6.7, primarily in the midlatitudes. This variance is approximately linear with the logarithm of a vertically weighted average of specific humidity. As an intermediate step, we have created a term called the altered brightness temperature product, Talt6.7, that represents the variance of T6.7 due to specific humidity plus an approximate mean of T6.7 in the midlatitudes. The domain of this derived product extends to zenith angles often greater than 70° within the GOES field of view. However, strong vertical gradients in specific humidity in the midtroposphere to upper troposphere were found to violate the linearity of the regression. In the validation, the slope of the first‐order regression is robust but the constant is inconclusive, rendering the product better for relative rather than absolute associations of specific humidity. Comparison to potential vorticity (PV) shows that the derived product corresponds best to PV at the 300 hPa pressure level at values of PV associated with the tropopause. The combined use of the DPI and model‐derived PV contours yields an effective tool for analyzing stratosphere‐troposphere exchange in the midlatitudes.
Updated radiative forcing estimates of 65 halocarbons and nonmethane hydrocarbons
Authors: Sihra Kamaljit , Hurley Michael D. , Shine Keith P. , Wallington Timothy J.
Published: February 2004

The direct radiative forcing of 65 chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, halons, iodoalkanes, chloroalkanes, bromoalkanes, perfluorocarbons and nonmethane hydrocarbons has been evaluated using a consistent set of infrared absorption cross sections. For the radiative transfer models, both line‐by‐line and random band model approaches were employed for each gas. The line‐by‐line model was first validated against measurements taken by the Airborne Research Interferometer Evaluation System (ARIES) of the U.K. Meteorological Office; the computed spectrally integrated radiance of agreed to within 2% with experimental measurements. Three model atmospheres, derived from a three‐dimensional climatology, were used in the radiative forcing calculations to more accurately represent hemispheric differences in water vapor, ozone concentrations, and cloud cover. Instantaneous, clear‐sky radiative forcing values calculated by the line‐by‐line and band models were in close agreement. The band model values were subsequently modified to ensure exact agreement with the line‐by‐line model values. Calibrated band model radiative forcing values, for atmospheric profiles with clouds and using stratospheric adjustment, are reported and compared with previous literature values. Fourteen of the 65 molecules have forcings that differ by more than 15% from those in the World Meteorological Organization [1999] compilation. Eleven of the molecules have not been reported previously. The 65‐molecule data set reported here is the most comprehensive and consistent database yet available to evaluate the relative impact of halocarbons and hydrocarbons on climate change.
Satellite estimation of spectral surface UV irradiance: 2. Effects of homogeneous clouds and snow
Authors: Krotkov N. A. , Herman J. R. , Bhartia P. K. , Fioletov V. , Ahmad Z.
Published: February 2004

This paper extends the theoretical analysis of the estimation of the surface UV irradiance from satellite ozone and reflectivity data from a clear‐sky case to a cloudy atmosphere and snow‐covered surface. Two methods are compared for the estimation of cloud‐transmission factor CT, the ratio of cloudy to clear‐sky surface irradiance: (1) the Lambert equivalent reflectivity (LER) method and (2) a method based on radiative transfer calculations for a homogeneous (plane parallel) cloud embedded into a molecular atmosphere with ozone absorption. The satellite‐derived CT from the NASA Total Ozone Mapping Spectrometer (TOMS) is compared with ground‐based CT estimations from the Canadian network of Brewer spectrometers for the period 1989–1998. For snow‐free conditions the TOMS derived CT at 324 nm approximately agrees with Brewer data with a correlation coefficient of ∼0.9 and a standard deviation of ∼0.1. The key source of uncertainty is the different size of the TOMS FOV (∼100 km field of view) and the much smaller ground instrument FOV. As expected, the standard deviations of weekly and monthly CT averages were smaller than for daily values. The plane‐parallel cloud method produces a systematic CT bias relative to the Brewer data (+7% at low solar zenith angles to −10% at large solar zenith angles). The TOMS algorithm can properly account for conservatively scattering clouds and snow/ice if the regional snow albedo RS is known from outside data. Since RS varies on a daily basis, using a climatology will result in additional error in the satellite‐estimated CT. The CT error has the same sign as the RS error and increases over highly reflecting surfaces. Finally, clouds polluted with absorbing aerosols transmit less radiation to the ground than conservative clouds for the same satellite reflectance and flatten spectral dependence of CT. Both effects reduce CT compared to that estimated assuming conservative cloud scattering. The error increases if polluted clouds are over snow.
Measurement of isoprene fluxes at the PROPHET site
Authors: Westberg H. , Lamb B. , Hafer R. , Hills A. , Shepson P. , Vogel C.
Published: February 2004

As part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET), isoprene fluxes were measured in the surface layer immediately above the forest canopy by relaxed eddy accumulation (REA) and eddy covariance (EC). Isoprene profiles obtained from aircraft flights at higher altitudes allowed larger‐scale isoprene flux estimates based on a mixed layer gradient modeling technique. Emission results derived from the three methods have been compared and used to generate standard emission factors for use in biogenic emission modeling. A standard emission flux of 11.4 mg m−2 h−1 was determined for the canopy footprint region. The aspen and oak isoprene emitting biomass density in the footprint amounted to approximately 150 g m−2 which, when combined with the standard flux, gives a standard emission rate of 76 μg g−1 h−1 for this northern Michigan forest. We found good agreement between isoprene fluxes determined by REA and EC methods. The general emission pattern is the same for both methods, and in many cases, the REA and EC fluxes were nearly identical. The mixed layer modeling approach gave isoprene fluxes that were consistent with those made at the same time at the canopy scale. The continuous coverage of isoprene fluxes by eddy covariance has provided more detailed insight into emission variability during the daytime period. During the midday period, canopy fluxes often changed significantly from one 30 min period to the next.
Calibration of Meteosat water vapor channel observations with independent satellite observations
Authors: Tjemkes Stephen A. , König Marianne , Lutz Hans‐Joachim , van de Berg Leo , Schmetz Johannes
Published: February 2004

The objective of this study is to identify potential problems of and increase confidence in the operational calibration of the water vapor channel of the Meteosat Visible and Infrared Radiation Imager (MVIRI). First, the operational vicarious calibration method of the MVIRI water vapor channel is analyzed. This is done through a comparison of the operational calibration coefficient with a calibration coefficient derived from collocated satellite observations taken by water‐vapor‐sensitive channel 12 of the High Resolution Infrared Sounder (HIRS) on NOAA 14. The analysis suggests a relatively large difference between the two calibration coefficients, the operational calibration coefficient being 10–15% larger than the one from the intersatellite calibration. Second, no such difference is found to exist between the MVIRI operational calibration coefficient and an intersatellite calibration coefficient derived from collocated GOES 8 water‐vapor‐sensitive channel 3 observations. Third, it is shown that the operational calibration coefficient for the MVIRI water vapor channel on Meteosat 7 is consistent with its blackbody calibration. At the present stage of the research no definite conclusions can be made. The results support the previously documented accuracy of 5% for the operational calibration coefficient of the MVIRI water vapor channel.
Methyl bromide loss rates in surface waters of the North Atlantic Ocean, Caribbean Sea, and eastern Pacific Ocean (8°–45°N)
Authors: Tokarczyk Ryszard , Saltzman Eric S.
Published: February 2004

The first‐order loss rate constant of methyl bromide was measured in surface seawater samples from the North Atlantic Ocean, Caribbean Sea, and coastal eastern Pacific Ocean during May‐July 1998. A stable isotope incubation technique was used, which consisted of spiking seawater samples with 13CH3Br and following the loss rate of the isotopically labeled spike with gas chromatography and isotope dilution mass spectrometry. The analysis of both filtered and unfiltered aliquots of seawater provides insight into the relative importance of chemical and particle‐related (presumably biological) degradation pathways. Over the entire cruise, first‐order total degradation rate constants ranged from 0.03–0.40 day−1. On average, higher rate constants were observed during the last part of the cruise in the Caribbean Sea (mean 0.34 day−1) and coastal Pacific waters (0.31 day−1), than in the earlier passage through the North Atlantic Ocean (0.18 day−1, legs 1 and 3). In the warm waters of the Caribbean Sea and the Pacific, total degradation rate constants were controlled primarily by chemical losses (0.30 and 0.25 day−1, respectively). In the colder Atlantic waters the average chemical loss rate constant was lower (0.11 day−1), and biological losses constituted a significant fraction of the total loss rate constant (35%). Chemical loss rate constants varied strongly with water temperature, in good agreement with previous determinations of the rate constant for methyl bromide removal from seawater due to chloride substitution and hydrolysis. Biological losses were detected in most of the water samples analyzed, suggesting that the biological capability to degrade methyl bromide is ubiquitous in the oceans. Rate constants for biological removal exhibited no apparent relationship to seawater temperature, salinity, chlorophyll, or bacterial counts.
Introduction to special section: Modeling, measurement, and exploitation of anisotropy in the radiation field
Authors: Verstraete Michel M. , Pinty Bernard
Published: February 2004

Over the past four decades or so, advances in satellite remote sensing technology have resulted in the development of a wide variety of sensors and platforms of Earth observation. Flying at altitudes from a few hundred to a few thousand kilometers above the planet's surface, these sensors generate their data by absorbing the radiation reflected or emitted by the planet in their direction. Passive sensors rely on external sources of radiation (typically the Sun for visible and near‐infrared measurements, or the Earth itself for thermal emission), while active sensors (e.g., synthetic aperture radars) embark their own sources of electromagnetic radiation. The latter will not be discussed further in this paper.
Observations of reactive oxidized nitrogen and speciation of NOy during the PROPHET summer 1998 intensive
Authors: Thornberry Troy , Carroll Mary Anne , Keeler Gerald J. , Sillman Sanford , Bertman Steven B. , Pippin Margaret R. , Ostling Kristi , Grossenbacher John W. , Shepson Paul B. , Cooper Owen R. , Moody Jennie L. , Stockwell William R.
Published: February 2004

Measurements of NOy, NOx, PAN, PPN, MPAN, C3‐C5 alkyl nitrates, total isoprene nitrates, HNO3, HONO, and aerosol NO3− and NO2− were made during the summer 1998 intensive of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Mixing ratios of NOy, NOx, PAN, PPN, and alkyl nitrates were observed to have a strong dependence on the direction of transport to the site as was expected from the distribution of major urban and industrial sources. A peak in NOx and NOx/NOy during the morning in southerly flow provides evidence for the transport of relatively unprocessed emissions in layers above the nocturnal boundary layer. The difference in PAN and PPN levels between north and south flow directions indicates a net transport of reactive nitrogen to regions farther north. Isoprene nitrates were observed to typically comprise less than 1% of NOy in spite of the dominance of isoprene in local VOC chemistry, although due to the rapid losses of isoprene nitrates through reaction, vertical mixing, and deposition, their role in the processing of NOy may be significant. General agreement was observed between NOy and the sum of the individually measured constituents during ten 24 hour periods, although a linear regression indicates the potential for an interference in the individual measurements and a possible shortfall in NOy. Measurements indicate that HONO may play a larger role in the reactive nitrogen budget than previously expected for a rural site. HONO/NO2 for a 24 hour period was observed to be 0.09–0.25 and suggests the likelihood of a significant heterogeneous production pathway or pathways.
Numerical simulation of new particle formation over the northwest Atlantic using the MM5 mesoscale model coupled with sulfur chemistry
Authors: Liu Xiaohong , Hegg Dean A. , Stoelinga Mark T.
Published: February 2004

The production of sulfuric acid vapor and new particle formation are studied over the northwest Atlantic for two synoptic cases: a “wet” case in April with a large amount of cloud and precipitation in the simulation domain and a relatively “dry” one in March. The Fifth‐Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5) is utilized coupled on‐line with a simple sulfur chemistry mechanism. Our numerical simulations show that there are three regions where significant binary homogeneous nucleation occurs. One region is in convective outflow where high anthropogenic SO2 concentration transported upward and low air temperature in the free troposphere (FT) favor the binary homogeneous nucleation of sulfuric acid gas and water vapor. The second region is near the top of marine boundary layer (MBL) clouds. The third region is in the clear FT at 500–600 hPa. In the three regions, significant nucleation events are all connected with relative humidity (RH) higher than 60%. For the northwest Atlantic we found that homogeneous nucleation generally occurs from the late morning through the afternoon on the northwest side of our simulation domain where anthropogenic SO2 concentration is high enough to produce sufficient sulfuric acid gas through the oxidation by OH radical. Significant nucleation does not necessarily happen in regions with very low preexisting particle surface area in our simulated cases. Our simulated total aerosol number concentrations in regions with significant new particle formation are generally consistent with field measurements. Nucleation rates are enhanced by NH3 especially in the MBL. Sensitivity tests show that a grid of 10 km (and time step of 30 s) yielded significantly higher nucleation as compared with a grid size of 30 km (and time step of 90 s). The latter grid may be too coarse to resolve the concentration gradients, which likely strongly impact the highly nonlinear homogeneous nucleation system.
Source analysis of carbon monoxide pollution during INDOEX 1999
Authors: de Laat A. T. J. , Lelieveld J. , Roelofs G. J. , Dickerson R. R. , Lobert J. M.
Published: February 2004

A source analysis of carbon monoxide (CO) over the Indian Ocean is presented using marked tracers in a chemistry general circulation model. The model includes a nonmethane hydrocarbon chemistry scheme and has been used at two different resolutions (3.75° × 3.75° and 1.9° × 1.9°). European Centre for Medium‐Range Weather Forecasts meteorological analyses have been assimilated into the model to represent actual meteorology during February and March of 1999. A comparison with measurements indicates that the model simulates realistic CO distributions. In general, the model performance is more realistic at higher resolution. Discrepancies exist close to the Indian coasts, possibly related to a sea breeze circulation at the Indian west coast, not resolved by the model. Discrepancies are also found in the vicinity of convection at the Intertropical Convergence Zone (ITCZ). The marked tracer study suggests that biofuel use and agricultural waste burning in India are major CO sources for the Indian Ocean north of the ITCZ, with minor contributions from Middle East, China, and Southeast Asia. In the much cleaner boundary layer over the southern Indian Ocean, CO from hydrocarbon oxidation is a dominant source. There are no other regions around the globe where biofuel use and biomass burning contribute so much to the CO mixing ratios. In general, most of the Asian CO over the Indian Ocean remains north of the ITCZ, although some of the CO is transported to the southern hemisphere in the free troposphere near the African east coast.
Diurnal variation of ionic aerosol species and water‐soluble gas concentrations at a high‐elevation site in the Japanese Alps
Authors: Kido Mizuka , Osada Kazuo , Matsunaga Katsuji , Iwasaka Yasunobu
Published: February 2004

Size‐separated atmospheric aerosol particles, acidic gases, and ammonia were collected during the daytime and nighttime at Murododaira (36.6°N, 137.6°E, 2450 m above sea level), Mount Tateyama, Japan in early winter. Non‐sea‐salt (nss) SO42− in fine fractions (<2.1 μm in diameter) was the most dominant ionic constituent and occupied 44% on average of the ionic mass concentration other than H+. Concentration levels of aerosol ions and water‐soluble gases were higher during the day and lower at night. Concentrations of the nighttime aerosol particles and gases (except for SO2) were similar to free‐tropospheric background levels at various sites of northern midlatitudes in the literature, suggesting that nighttime data at Murododaira were representative of free‐tropospheric conditions. High concentration levels of SO2 at Murododaira were close to those over the northwest Pacific Rim region during the winter season. Molar ratios of nssSO42−/SO2 can be explained by the transport time from the Asian continent, suggesting that a significant source of fine nssSO42− aerosols at Murododaira in early winter could be due to the oxidation of anthropogenic SO2 derived from the Asian continent. The equivalent ratios of nssSO42− to NH4+ in fine particles were close to 0.5 under westerly wind conditions, suggesting the existence of half‐neutralized sulfate on average.
In situ chloroform measurements at Advanced Global Atmospheric Gases Experiment atmospheric research stations from 1994 to 1998
Authors: O'Doherty S. , Simmonds P. G. , Cunnold D. M. , Wang H. J. , Sturrock G. A. , Fraser P. J. , Ryall D. , Derwent R. G. , Weiss R. F. , Salameh P. , Miller B. R. , Prinn R. G.
Published: February 2004

Measurements of atmospheric chloroform (CHCl3) by in situ gas chromatography using electron capture detection are reported from the Advanced Global Atmospheric Gases Experiment (AGAGE) network of atmospheric research stations. They are some of the most comprehensive in situ, high‐frequency measurements to be reported for CHCl3 and provide valuable information not only on clean “baseline” mixing ratios but also on local and regional sources. Emissions from these sources cause substantial periodic increases in CHCl3 concentrations above their baseline levels, which can be used to identify source strengths. This is particularly the case for measurements made at Mace Head, Ireland. Furthermore, these local sources of CHCl3 emissions are significant in relation to current estimates of global emissions and illustrate that the understanding of competing sources and sinks of CHCl3 is still fragmentary. These observations also show that CHCl3 has a very pronounced seasonal cycle with a summer minimum and winter maximum presumably resulting from enhanced destruction by OH in the summer. The amplitude of the cycle is dependent on sampling location. Over the 57 months of in situ measurements a global average baseline concentration of 8.9±0.1 ppt was determined with no appreciable trend in the baseline detected.
A hemispheric dust storm affecting the Atlantic and Mediterranean in April 1994: Analyses, modeling, ground‐based measurements and satellite observations
Authors: Özsoy Emin , Kubilay Nilgün , Nickovic Slobodan , Moulin Cyril
Published: February 2004

One of the largest recorded dust transport events originating from the great Sahara desert during April 1994 affected the entire region extending from the Caribbean to the Eurasian continent. This hemispherical transport of airborne dust took place during a series of storms that developed during the first three weeks of April in a background of low‐index circulation. These repeated events are studied through the combined analyses and interpretation of atmospheric data, ground‐based aerosol measurements, visibility observations, AVHRR and Meteosat visible band satellite data, and the results of Eta model simulations, including an aerosol transport component. The observations produce a consistent picture of the temporal and spatial development of the dust events, whose main features are used in parts to verify the model results. The rate of dust suspension from some areas of the western Sahara desert exceeded 1.5 mg m−2 h−1 and the maximum column integrated dust load reached 2 g m−2 during April 3–5 1994, when the first major suspension event produced two simultaneous pulses of dust moving in opposite directions across the subtropical Atlantic Ocean and the eastern Mediterranean Sea. These dust suspensions were created by surface winds resulting from subsidence on the northeastern side of a blocking anticyclone in the Atlantic region and subsequent winds of an intense developing cyclone in the Mediterranean‐African region. In the following period, maximum dust loads of 4.5 and 2.5 g m−2 occurred on April 12 and 17, respectively, when new cyclones transported dust across the Mediterranean from Africa to Europe. The generation of the two dust pulses during the first even and the recurrent cyclone transport in the following period is shown to be the result of a large‐scale, anomalous atmospheric circulation connected with blocking in the Atlantic Ocean and the interactions of upper air jets downstream of the blocking. The particular state of the hemispheric circulation during the studied period corresponded to the positive phase of the North Atlantic Oscillation (NAO). While previous statistical evidence has consistently linked dust transport in the region with the NAO signatures, we show the same connection on the basis of this case study.
Atmospheric water vapor sensitivity and compensation requirement for Earth‐looking imaging spectrometers in the solar‐reflected spectrum
Authors: Green Robert O.
Published: February 2004

An increasing number of Earth‐looking imaging spectrometers are being developed to derive properties of the surface from measured upwelling spectral radiance that has passed through the atmosphere. However, the measurements are influenced by the amount of atmospheric water vapor. Water vapor is present in every spectrum and is highly variable through space and time. This research assesses the sensitivity to the accurate knowledge of atmospheric water vapor of imaging spectrometers with surface measurement objectives. This sensitivity is explored for a range of imaging spectrometer spectral resolutions from 5 to 20 nm as well as for a range of atmospheric water vapor from normal to dry conditions. The effect of atmospheric water vapor errors of 50, 25, 10, 5, and 1% is analyzed. In all cases the derived surface reflectance is shown to be strongly sensitive to the accurate knowledge of water vapor in the imaging spectrometer measurement. This result leads to a general requirement of 1% or better knowledge of atmospheric water vapor in order to derive surface reflectance that is largely free of water‐vapor‐induced errors, distortions, and spectral artifacts.
Inventory of methane emissions from U.S. cattle
Authors: Westberg H. , Lamb B. , Johnson K. A. , Huyler M.
Published: February 2004

Many countries, including the United States, are in the process of inventorying greenhouse gas emissions as a prerequisite for designing control strategies. We have developed a measurement‐based inventory of methane emissions from cattle in the United States. Methane emission factors were established for the major livestock groups using an internal tracer method. The groups studied included cows, replacement heifers, slaughter cattle, calves, and bulls in the beef sector and cows plus replacement heifers in the dairy industry. Since methane emission is dependent on the quality and quantity of feed, diets were chosen that are representative of the feed regimes utilized by producers in the United States. Regional cattle populations, obtained from U.S. Department of Agriculture statistics, were combined with the methane emission factors to yield regional emission estimates. The methane totals from the five regions were then summed to give a U.S. inventory of cattle emissions for 1990, 1992, 1994, 1996, and 1998. Annual releases ranged from 6.50 Tg in 1990 to a high of 6.98 Tg in 1996. On a regional scale the North Central region of the United States had the largest methane emissions from livestock followed by the South Central and the West. The beef cow group released the most methane (∼2.5 Tg yr−1) followed by slaughter cattle (∼1.7 Tg yr−1) and dairy cows at about 1.5 Tg yr−1. Methane released by cattle in the United States contributes about 11% of the global cattle source.
Assessment of Saharan dust absorption in the visible from SeaWiFS imagery
Authors: Moulin Cyril , Gordon Howard R. , Banzon Viva F. , Evans Robert H.
Published: February 2004

We have examined forty SeaWiFS images acquired during 1997 and 1998 off the west coast of Africa to develop theoretical models of Saharan dust radiative properties that could be used for atmospheric correction in this region, i.e., to predict the dust contribution to the measured reflectance in the visible from that measured in the near infrared (NIR). In contrast to nonabsorptive or weakly absorbing aerosols, the dust reflectance significantly decreases from the NIR to the blue because of the absorption of mineral particles in the visible. We chose simple but realistic vertical structures for the dust layer and examined the applicability of a set of aerosol size distributions and refractive indices with radiative properties computed from Mie theory. We found that 18 models (six aerosol size‐refractive index distributions times three aerosol vertical distributions) were general enough to estimate the dust reflectance in the visible with an absolute RMS error of the order of 5%. We show that these dust models can be used within a “spectral matching algorithm” [Gordon et al., 1997] to effect atmospheric correction of ocean color imagery in dust‐contaminated regions. We also found that our models all produce very similar top‐of‐atmosphere outgoing visible flux but that this flux may be significantly different from that predicted by other conventional dust models.
Wavelet analysis of stratospheric gravity wave packets over Macquarie Island: 1. Wave parameters
Authors: Zink Florian , Vincent Robert A.
Published: February 2004

We describe a technique to detect gravity wave packets in high‐resolution radiosonde soundings of horizontal wind and temperature. The vertical profiles of meridional and zonal wind speeds are transformed using the Morlet wavelet, and regions of high wind variance in height‐wavenumber space are identified as gravity wave packets. Application of the Stokes parameter analysis to horizontal wind and temperature profiles of the reconstructed wave packets yields the wave parameters. The technique was applied to twice‐daily radiosonde launches at Macquarie Island (55°S, 159°E) between 1993 and 1995. A strong seasonal cycle in the total wave variance was found, with a maximum in winter. The amount of wave energy propagating downward from the upper stratosphere also maximized in winter. Waves propagated predominately toward the southwest in winter, but in summer propagation directions were approximately isotropic. The intrinsic frequencies were close to the inertial frequency, and the waves had inferred horizontal wavelengths of several hundred kilometers.
Mapping of Mars O2(1Δ) dayglow
Authors: Krasnopolsky Vladimir A. , Bjoraker Gordon L.
Published: February 2004

We observed the O2(1Δ) dayglow at 1.27 μm near northern midsummer (LS = 112°) with a long‐slit cryogenic echelle spectrograph (CSHELL at the NASA Infrared Telescope Facility) having a resolving power of 4×104. The observations resulted in a map of the O2 dayglow which extends from 1000 to 1645 in local time and from 45°S to 75°N. The O2 dayglow is formed by photolysis of high‐altitude ozone, and this dayglow is the best tracer of seasonal variations in photochemistry at low and middle latitudes, Our observations show that O2 dayglow can be mapped with existing ground‐based instruments. The measured dayglow intensities display a gradual increase from 1.5 MR at 75°N to 2.5 MR at 20°N, a weak minimum of 2.3 MR at the equator, and a steep increase to 5 MR at 35°–40°S. The dayglow in a low‐latitude belt from 5°S to 25°N (which is centered between the equator and the subsolar latitude) is maximum at 2.5 MR near 1300 and decreases to 1.5 MR at 1000 and 1645 LT. The observed dayglow intensities are smaller than those calculated using the model of Clancy and Nair [1996] by a factor of ≈3. The observation confirms the anticorrelation between ozone and water vapor observed from the Viking orbiters at midsummer. Coupled with the Thermal Emission Spectrometer (TES) observations of temperature, dust, and water vapor, the O2 dayglow measurements comprise a good database to study Mars' photochemistry and dynamics.
Tharsis dome, Mars: New evidence for Noachian‐Hesperian thick‐skin and Amazonian thin‐skin tectonics
Authors: Anguita Francisco , Farelo Agustín‐Felipe , López Valle , Mas Cristina , Muñoz‐Espadas María‐Jesús , Márquez Álvaro , Ruiz Javier
Published: February 2004

A photogeological reconnaissance of Viking mosaics and images of the Tharsis dome has been carried out. Fifteen new areas of transcurrent faulting have been located which, together with other structures previously detected, support a model in which the Thaumasia Plateau, the southeastern part of the Tharsis dome, is proposed to be an independent lithospheric block that experienced buckling and thrust faulting in Late Noachian or Early Hesperian times as a result of an E‐W directed compression. Evidence is presented that this stress field, rather than the Tharsis uplift, was decisive in the inception of Valles Marineris, which we consider a transtensive, dextral accident. The buckling spacing permits us, moreover, to tentatively reconstruct a Martian Hesperian lithosphere similar in elastic thickness to the mean present terrestrial oceanic lithosphere, thus supporting the possibility of a restricted lithospheric mobility in that period. Tharsis lithosphere was again subjected to shear stresses in Amazonian times, a period in which important accidents, such as strike‐slip faults, wrinkle ridges, and straight and sigmoidal graben, were formed under a thin‐skin tectonic regime, while the lithosphere as a mechanical unit had become too thick and strong to buckle. The possible causes of those stresses, and especially their relationships to a putative period of plate tectonics, are discussed.
Mars: The cloud effect on the blue clearing in the Syrtis Major region
Authors: Nakakushi T. , Akabane T. , Iwasaki K. , Larson Stephen M.
Published: February 2004

We conducted imaging observations of Mars in March 1997 and April 1999; these apparitions were around its northern summer oppositions. Mars showed highly developed clouds that formed the aphelion cloud belt. Comparing the diurnal variations of the apparent contrasts of Syrtis Major to the adjacent bright areas with those of the optical depths of the aphelion clouds over those regions, we conclude that the time when those regions are subject to the morning clouds is around 0900 Martian Local Time (MLT) and that the diurnal variation of the degree of blue clearing strongly depends on the difference between the optical depth of H2O ice clouds over Syrtis Major and that over the adjacent bright area. Moreover, our simple linear regression analyses of the degree of blue clearing to the optical depths of H2O ice clouds suggest that the key region in which the H2O ice cloud optical depth determines the degree of blue clearing is Syrtis Major.
TES premapping data: Slab ice and snow flurries in the Martian north polar night
Authors: Titus Timothy N. , Kieffer Hugh H. , Mullins Kevin F. , Christensen Phillip R.
Published: February 2004

In the 1970s, Mariner and Viking spacecraft observations of the north polar region of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO2 sublimation. For the past few decades, the scientific community has speculated as to the nature of these Martian polar cold spots. Thermal Emission Spectrometer (TES) thermal spectral data have shown these cold spots to result largely from fine‐grained CO2 and have constrained most of these cold spots to the surface (or near‐surface). Cold spot formation is strongly dependent on topography, forming preferentially near craters and on polar slopes. TES data, combined with Mars Orbiter Laser Altimeter (MOLA) cloud data, suggest atmospheric condensates form a small fraction of the observed cold spots. TES observations of spectra close to a blackbody indicate that another major component of the polar cap is slab CO2 ice; these spectrally bland regions commonly have a low albedo. The cause is uncertain but may result from most of the light being reflected toward the specular direction, from the slab ice being intrinsically dark, or from it being transparent. Regions of the cap where the difference between the brightness temperatures at 18 μm (T18) and 25 μm (T25) is less than 5° are taken to indicate deposits of slab ice. Slab ice is the dominant component of the polar cap at latitudes outside of the polar night.
Gravity field of Mars: A 75th Degree and Order Model
Authors: Yuan Dah‐Ning , Sjogren William L. , Konopliv Alex S. , Kucinskas Algis B.
Published: February 2004

Radiometric tracking data collected by NASA's Deep Space Network (DSN) for Mariner 9, Viking 1 and 2 orbiters, and Mars Global Surveyor (MGS) have been analyzed to determine the gravity field of Mars. The gravity solution (MGS75D) is a complete spherical harmonics model to degree and order 75. Also parts of the solution are the gravitational constants of Mars, Phobos, and Deimos. The significant improvement in the MGS75D Mars gravity model is mainly a consequence of globally distributed data set collected from the MGS mapping orbits, the use of optimal weighting and constrained least squares solution techniques, and improved force and measurement models in the orbit determination process. The gravity anomaly map reveals significantly more detail and larger amplitudes than any previous Mars gravity map over the major impact and volcanic areas on Mars. Olympus Mons remains the largest known gravity anomaly in our solar system and Isidis Planitia, the highest‐amplitude mascon. There are mascons in the Hellas, Argyre, and Utopia basins. Valles Marineris has distinctive negative anomalies, and all volcanic features are positive. Gravity anomalies over several craters have also been resolved. The overall correlation of the MGS75D gravity anomaly map with topography derived from the Mars Orbiter Laser Altimeter (MOLA) is very high, while the polar regions display relatively poor correlation.
High‐resolution thermal inertia mapping of Mars: Sites of exobiological interest
Authors: Jakosky Bruce M. , Mellon Michael T.
Published: February 2004

We have mapped thermal inertia at high resolution for selected regions of Mars that are of potential biological relevance, using observations made by the Mars Global Surveyor Thermal Emission Spectrometer. Thermal inertia is a direct indicator of physical properties of the surface at the decimeter‐to‐meter scale. Our goal is to understand the geological processes by which the sites formed and their subsequent evolution, their current state, and their safety and science potential as landing sites for future lander, rover, and sample‐return spacecraft missions. The thermal inertia values at ∼3‐km scale for the sites considered span the entire range of values measured at Mars; thermal inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock, exposed rocks or blocks, or well‐indurated crusts. The highest thermal inertias correlate strongly with local morphology, while areas with intermediate and low thermal inertias generally show no such correlation. This suggests that selection of future landing sites will be plagued by a choice of a well‐mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe.
Space weathering from Mercury to the asteroid belt
Authors: Hapke Bruce
Published: February 2004

The variety of evidence bearing on the nature of space weathering is reviewed. The effects of space weathering include spectral darkening, reddening and subdued absorption bands, and the distinctive magnetic electron spin resonance caused by single‐domain metallic iron particles. Ever since the Apollo missions, two paradigms have dominated the thinking of the planetary science community concerning space weathering: (1) the optical effects are caused by impact‐vitrified glass in agglutinates, and (2) the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind. However, studies carried out since the Apollo program showed that both of these paradigms are invalid. A hypothesis first suggested by the author and his colleagues 26 years ago, but not generally accepted at that time, now appears to be essentially correct: Both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor‐deposited coatings on soil particle surfaces and inside agglutinates. The vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith. The iron is reduced by a physical process, the selective loss of oxygen that occurs during deposition of the vapor, and does not require heating, melting, or a reducing environment. A mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the Moon, Mercury and an S asteroid.
Mars Orbiter Camera geodesy campaign
Authors: Caplinger M. A. , Malin M. C.
Published: February 2004

During the “geodesy campaign” in May and June 1999 the wide‐angle system of the Mars Global Surveyor Mars Orbiter Camera imaged the visible surface of Mars from latitudes 70°S to 90°N. Over 90% of this portion of the planet was covered at two viewing angles to obtain side‐looking stereo at a resolution of ∼250 m/pixel and convergence angles of 21°–27°. Continuous radiometric spacecraft tracking during this period provided precise orbit determination of spacecraft location. This data set will become the basis of a new image mosaic of Mars, with the potential to exceed the geodetic precision and image quality of those presently available.
Tectonics of mascon loading: Resolution of the strike‐slip faulting paradox
Authors: Freed Andrew M. , Melosh H. Jay , Solomon Sean C.
Published: February 2004

Subsidence of lunar mascon maria, impact basins partly filled with mare basalt and sites of prominent positive gravity anomalies, typically led to the formation of concentric graben (arcuate rilles) around the flanks of the basin, while compressive features (mare ridges) formed in interior regions. Although previous numerical models of the response of the lunar lithosphere to mascon loading predict that an annulus of strike‐slip faulting should also have formed around mascon maria, no such faults have been observed. This “strike‐slip faulting paradox,” however, arises from an oversimplification of the earlier models. Viscoelastic finite element models of lunar mascon basins that include the effects of lunar curvature, heterogeneous crustal strength, initial stress conditions, and multistage load histories show that the width of a predicted annulus of strike‐slip faulting may be small. The use of Anderson's criterion for predicting fault styles may also overpredict the width of strike‐slip faulting. A faulting‐style criterion that takes into account transitional faulting, in which both strike‐slip and dip‐slip components are present, predicts zones of pure strike‐slip faulting that are about half of the width predicted by the Anderson criterion. Furthermore, strike‐slip faulting should be observed only in regions in which flexural stresses are sufficient to induce rock failure. However, since stress patterns consistent with strike‐slip faulting around mascon loads represent a transition between compressional and extensional provinces, differential stresses tend to be low in these regions and for at least part of this region are not sufficient to induce rock failure. A mix of concentric and radial thrust faulting is observed in some mascon maria, at odds with previous models that predict only radial orientations away from the basin center. This apparent discrepancy may be partly explained by the multistage emplacement of mare basalt units, a scenario that leads to a stress pattern where concentric and radial orientations of thrust faults are equally preferred. Detailed models of the Serenitatis basin indicate a 25‐km‐thick lunar lithosphere at the time of rille formation and a 75‐km‐thick lithosphere at the time of late‐stage mare ridge formation. The extent of observed mare ridges and the inferred cessation of rille formation around Serenitatis prior to the time of emplacement of the youngest mare basalt units is consistent with the superposition of a global horizontal compressive stress field generated by the cooling and contraction of the lunar interior with the local stresses associated with lithospheric loading.
Energetic and thermal processing of interstellar ices
Authors: Ehrenfreund P. , d'Hendecourt L. , Charnley S. , Ruiterkamp R.
Published: February 2004

Our current knowledge on the chemical composition of interstellar ices is summarized with respect to the possible contribution of energetic photons and particles to their observed state. We describe the inventory of astronomical ices as determined by infrared observations from the Infrared Space Observatory (ISO) and laboratory spectroscopy. Sources of radiolysis, UV photolysis, and ice heating are then discussed in the context of the chemical state of material in dense molecular clouds and in protostellar cores. Through specific examples we show how energetic processing can explain the observed solid‐state characteristics of several key molecules: CH3OH, CO2, and OCN−. We also discuss the gaseous and solid‐state photochemistry of the first organic acid detected in interstellar ices, HCOOH.
Analysis of terrestrial and Martian volcanic compositions using thermal emission spectroscopy: 1. Determination of mineralogy, chemistry, and classification strategies
Authors: Wyatt Michael B. , Hamilton Victoria E. , McSween Harry Y. , Christensen Philip R. , Taylor Lawrence A.
Published: February 2004

We have examined and applied existing classification schemes for volcanic rocks and developed new schemes using thermal emission spectra of terrestrial volcanic rocks. Laboratory thermal infrared spectra (5–25 μm, at 2 cm−1 spectral sampling), deconvolved modal mineralogies, and derived mineral and bulk rock chemistries were used to distinguish basalt, basaltic andesite, andesite, and dacite. Modal mineralogies derived from linear deconvolution of terrestrial volcanic rocks were compared to modes measured by an electron microprobe phase mapping technique to determine the accuracy of linear deconvolution in modeling specific mineral abundances. One σ standard deviations of the absolute differences between modeled and measured mineral abundances range from 2.4 to 12.2 vol %, with an average standard deviation of 4.8 vol % being in agreement with average uncertainties calculated in previous studies. Weighted average compositions of feldspars in the deconvolution generally overlap the measured ranges of plagioclase compositions and the presence of low‐calcium and high‐calcium pyroxenes was correctly identified. Bulk chemistries of volcanic rocks were derived with a relatively high degree of accuracy (1σ standard deviations ranging from 0.4 to 2.6 vol %) by combining the compositions of spectrally modeled phases in proportion to their relative abundances in a particular sample. These data were collectively used to examine existing and develop new volcanic rock classification schemes. However, no single classification scheme was effective in accurately classifying all samples. Multiple steps of classification were required to distinguish volcanic rocks, reflecting the mineralogic diversity and continuum of compositions that exists in volcanic rock types. In a companion paper [Hamilton et al., this issue] these schemes are applied to the classification of Martian surface compositions.
Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars
Authors: Smith David E. , Zuber Maria T. , Frey Herbert V. , Garvin James B. , Head James W. , Muhleman Duane O. , Pettengill Gordon H. , Phillips Roger J. , Solomon Sean C. , Zwally H. Jay , Banerdt W. Bruce , Duxbury Thomas C. , Golombek Matthew P. , Lemoine Frank G. , Neumann Gregory A. , Rowlands David D. , Aharonson Oded , Ford Peter G. , Ivanov Anton B. , Johnson Catherine L. , McGovern Patrick J. , Abshire James B. , Afzal Robert S. , Sun Xiaoli
Published: February 2004

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064‐μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ∼1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1×2 km2at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100‐m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100‐m‐scale surface roughness and 1.064‐μm reflectivity with an accuracy of 5% have also been obtained.