bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Polar Ozone and Aerosol Measurement (POAM) II and Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol measurements from 1994 to 1996
Authors: Randall C. E. , Bevilacqua R. M. , Lumpe J. D. , Hoppel K. W. , Rusch D. W. , Shettle E. P.
Published: September 2002

We describe statistical comparisons between version 6.0 Polar Ozone and Aerosol Measurement (POAM) II and version 5.931 Stratospheric Aerosol and Gas Experiment (SAGE) II measurements of aerosol extinction and derived surface area and volume density between 1994 and 1996. Qualitatively, both instruments show similar decay of the aerosol extinction at visible and near‐IR wavelengths in the altitude range from 12 to 30 km, resulting from dissipation of the Mount Pinatubo aerosols. We present quantitative differences between the SAGE II and POAM II extinctions at 1 and 0.45 μm for temporally and spatially coincident measurements. On average, for the moderately elevated aerosol extinction levels encountered in 1994, differences in the extinction measurements at 1 μm are within ±10% between 12 and 27 km, increasing at higher and lower altitudes. Differences at 0.45 μm are within ±35% between 13 and 30 km, increasing at lower altitudes. For the lower aerosol extinction conditions of 1995 and 1996, the comparisons indicate that systematic errors contributed to larger relative differences between the instruments. These effects are manifested as “asymmetries” in the Northern Hemisphere versus Southern Hemisphere comparisons, and in the 1 μm versus 0.45 μm comparisons. We suggest that these systematic differences are partly due to altitude registration errors in one or both of the instruments. Average volume densities derived using a principal component analysis technique agreed within about 10% at high northern latitudes between 16 and 27 km, and within about 30% at high southern latitudes. In most cases, surface area density differences were somewhat larger. Although a dedicated validation campaign was not feasible for POAM II, overall the results presented here confirm the validity of the POAM II aerosol measurements for scientific studies.
A new analytical approach for size‐resolved speciation of organic compounds in atmospheric aerosol particles: Methods and first results
Authors: Neusüss Christian , Pelzing Matthias , Plewka Antje , Herrmann Hartmut
Published: September 2002

A new analytical approach for the characterization of organic compounds in size‐segregated atmospheric aerosol particles is described. Its potential is demonstrated for samples that were collected during the Second Aerosol Characterization Experiment in Sagres (Portugal) and at the Institut für Troposphärenforschung research station in Melpitz (Germany). Curie point pyrolysis gas chromatography/mass spectrometry is used to determine semivolatile compounds, capillary electrophoresis for organic acids. The main advantages are low sample amount and almost no sample preparation. Size distributions of alkanes, fatty acids, polycyclic aromatic hydrocarbons (PAHs), oxygenated polycyclic aromatic hydrocarbons (oxy‐PAHs), dicarboxylic acids, hydroxylated dicarboxylic acids, organic and elemental carbon, main water soluble ions, and gravimetric mass were determined by impactor measurements and are discussed. Compared to central Europe (hydroxylated) dicarboxylic acids show a higher concentration in marine air influenced by long‐range transport through European polluted air masses. Dicarboxylic acids show a maximum concentration in the coarse mode, whereas hydroxylated dicarboxylic acids are mostly found in submicrometer particles. Alkanes are found in higher concentrations and oxy‐PAHs are only found in central Europe. For the selected samples, 12–15% of the organic carbon could be assigned to individual species in the case of central Europe, and 20–40% could be assigned in the marine aerosol of Portugal. In all cases, semivolatile organic species such as alkanes and PAHs account for the major fraction of the speciated organic carbon.
Low‐ozone events and three‐dimensional transport at midlatitudes of South America during springs of 1996 and 1997
Authors: Pérez A. , Crino E. , Aguirre de Cárcer I. , Jaque F.
Published: September 2002

Sudden and transient decreases of ozone column values were detected over the midlatitudes of South America during the springs of 1996 and 1997 by a network of ground instruments. These low‐ozone events were accompanied by air temperature decreases in the lower stratosphere. The analysis of the events suggests a connection with the springtime Antarctic ozone hole. Three‐dimensional isentropic back trajectories showed that vertical motion also contributed to the decreases of total ozone observed at the midlatitudes of South America.
Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings
Authors: Naurzbaev M. M. , Vaganov E. A.
Published: September 2002

Regional tree ring chronology with extension 2209 years (from 212 B.C. till 1996 A.D.) was built for east Taymir and Putoran according to wood of living trees, well‐preserved remains of dead trees, and subfossil wood from alluvial bank deposits by the cross‐dating method. In addition, the “floating” tree ring width chronology for the period of Holocene optimum (3300–2600 B.C.) was built with extention 685 years and supported by several radiocarbon dates. High values of synchrony and correlation of individual tree ring series show a prevailing effect of one external factor on radial tree growth change in the studied region of the Siberian subarctic. It was established that the main factors of growth variability are the early summer and annual temperature, which explain up to 70% of tree growth rate variability. Cyclic components stable for two millennia were revealed at analysis of the tree ring chronology: double secular (∼180 years), secular (78–90 years), and intrasecular (44, 28, 11, and 6.7–6.9 years) variations. Models for reconstruction of the early summer and annual air temperature were obtained according to tree ring variability. Temperature dynamics in the eastern part of Taymir for the last two millenia agree well with temperature variations in the Northern Hemisphere obtained according to other indirect sources. The warming of the middle of the twentieth century is not extraordinary. The warming at the end of the first and beginning of the second millennia (“Medieval Warm Period”) was longer in time and closer in amplitude.
Heat transport and weakening of atmospheric stability induced by mesoscale flows
Authors: Dalu G. A. , Pielke R. A. , Vidale P. L. , Baldi M.
Published: September 2002

We present an analytical evaluation and interpretation on how diabatic heating of the convective boundary layer (CBL) is transported upward into the midtroposphere by mesoscale flows, and how the air mixes with the environment and therefore weakens the atmospheric static stability. The thermodynamic imprint on the free atmosphere due to the irreversible processes such as mixing, dissipation, and diffusion, associated with the mesoscale flow, is more clearly shown when the forcing is periodic in time. Convective mixing in the CBL accounts for a thermodynamic perturbation of the order of a few degrees, while mixing associated with the mesoscale activity accounts for a perturbation of the order of half a degree. To isolate this last effect, we prescribe a periodic forcing with a 1 day period, so over 24 hours, the net diabatic input averages to zero, and the contribution due to the advection cancels out. In this formulation the perturbation is solely due to irreversible processes associated with the mesoscale. These perturbations are relevant, since they are smaller, but of the same order of magnitude as perturbations associated with mesoscale advection and the CBL mixing. A more complete evaluation of the relative contribution to the atmospheric perturbations due to the mesoscale activity was completed using an initial value problem approach. In this case, there is a net transport of the diabatic heat induced by the mesoscale flow. As a consequence, when the mesoscale flow persists for several days, the static stability of the atmosphere is eroded by the combined action of the diabatic heat, CBL mixing, and transport and mixing due to the mesoscale activity. In this paper we first evaluate the contribution of the irreversible processes using a periodic in time forcing. Then we examine the atmospheric impact due to a sequence of several sea breeze days, starting from rest at time zero and letting the flow evolve as an initial value problem. Results suggest that perturbations associated with mesoscale flows generated by landscape variability are of climatological importance and need to be introduced in a parametric form in coarser large‐scale models, as presently is done with turbulent subgrid CBL processes.
Interannual variations of blockings in the southern hemisphere and their energetics
Authors: de Fátima Cruz Marques Rosa , Rao V. Brahmananda
Published: September 2002

Seasonal and interannual variations of blocking in the Southern Hemisphere (SH) are discussed using 25 years of NCEP and 14 years of ECMWF data sets. Both the data sets show that the highest blocking frequency occurs near New Zealand, but ECMWF data seem to show higher blocking frequency. There are large interannual variations in blocking frequency over east and west Pacific, the principal regions of blocking in the SH. Linear correlation coefficients (CC) between the frequency of blocking and the Southern Oscillation Index show mostly negative values, indicating that blocking increases during the El Niño events. A significant value (at 95% level) of CC is found only for the west Pacific in the austral autumn season. Two sets of three high and low blocking frequency years are selected to explore the possible causes for interannual variations. Mak's energy equations are used to examine the differences in energetics. To maximize the differences, two extreme years of blocking, a year of high blocking frequency, 1984, and a year of low blocking frequency, 1990, are considered. It is found that the generation of kinetic energy by barotropic processes on intraseasonal timescales is higher in 1984 than in 1990. This shows that the configuration of seasonal mean (deformation) field supports higher incidence of blocking in 1984 than in 1990.
Halogen Occultation Experiment confirmation of stratospheric chlorine decreases in accordance with the Montreal Protocol
Authors: Anderson J. , Russell J. M. , Solomon S. , Deaver L. E.
Published: September 2002

Near‐global time series of Halogen Occultation Experiment (HALOE) derived total Cl, F, and the Cl/F ratio were evaluated and compared with data from two ground‐based CFC measurement programs and United Nations Environment Programme (UNEP) best‐case scenarios for CFC emissions. The HALOE Cl profiles confirm that the chlorine burden near the stratopause is decreasing and this decrease is driven by tropospheric decreases of methyl chloroform. The HALOE F profiles show that the fluorine burden near the stratopause is primarily influenced by CFC‐12. The Cl/F ratio, which is insensitive to transport effects at 55 km, shows that the atmosphere near the stratopause is becoming more fluorinated since the inception of the HALOE mission and less chlorinated since the start of 1997. The temporal changes in the derived Cl, F, and Cl/F ratio at 55 km are in accord with UNEP projections and in situ observations. These combined results demonstrate that the Montreal Protocol and subsequent strengthening amendments are currently having the desired effect of reducing stratospheric chlorine.
Remote sensing of cloud properties using MODIS airborne simulator imagery during SUCCESS: 2. Cloud thermodynamic phase
Authors: Baum Bryan A. , Soulen Peter F. , Strabala Kathleen I. , King Michael D. , Ackerman Steven A. , Menzel W. Paul , Yang Ping
Published: September 2002

Methods to infer cloud thermodynamic phase (ice or water) are investigated using multispectral imagery. An infrared (IR) trispectral algorithm using the 8.52‐, 11‐, and 12‐μm bands [Ackerman et al., 1990; Strabala et al., 1994] forms the basis of this work and will be applied to data from the Earth Observing System (EOS) Moderate‐Resolution Imaging Spectroradiometer (MODIS) instrument. Since the algorithm uses IR bands, it can be applied to either daytime or nighttime data and is not sensitive to the presence of cloud shadows. A case study analysis is performed with a MODIS airborne simulator (MAS) scene collected during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) on April 21, 1996, at 2000 UTC. The scene under scrutiny is quite complex, containing low‐level broken water clouds, cirrus cells, cloud shadows, sub visual cirrus, and contrails. The IR trispectral algorithm is found to be less accurate in (1) regions where more than one cloud phase type occurs and (2) regions of thin cirrus overlying a lower‐level cloud layer. To improve the phase retrieval accuracy in these areas of difficulty, additional bands located at 0.65, 1.63, and 1.90 μm are incorporated. Radiative transfer (RT) calculations are performed to simulate the MAS bands using the cirrus and water cloud models detailed by Baum et al. [this issue]. The RT calculations are performed for single‐layer cirrus‐ and water‐phase clouds as well as for the case of thin cirrus overlying a lower‐level water droplet cloud. Both modeled results and application of the theory to a case study suggest that the cloud thermodynamic phase retrieval accuracy can be improved by inclusion of the visible and near infrared bands.
Isotopic composition of sulfur in size‐resolved marine aerosols above the Atlantic Ocean
Authors: Patris Nicolas , Mihalopoulos Nikolaos , Baboukas Evangelos D. , Jouzel Jean
Published: September 2002

Sulfur isotope measurements were performed on size‐segregated aerosols collected during the Albatross oceanographic campaign from 61°N to 35°S above the Atlantic Ocean in October and November 1996. Results obviously showed the dependence of the sulfur isotope ratio upon particle size, the finest particles being depleted in 34S compared to coarse particles, suggesting a heavier continental influence in the fine mode. In the coarse mode, 50–90% of the excess sulfate in both hemispheres was found to be of biogenic origin. In the fine mode a different picture was obtained. In the Northern Hemisphere the contribution of biogenic sulfur was found to be less than 35% of the excess sulfur even in relatively clean air masses. On the other hand, in the Southern Hemisphere the participation of biogenic sulfur was about 60% of the excess sulfur in purely marine air. The contribution of continental sulfur to the fine fraction in the Southern Hemisphere was up to 40±25% even under pure oceanic conditions and far more in the Northern Hemisphere. These results attest to the possible importance of long‐range transport of fine sulfate particles or SO2, possibly through the free troposphere, or the importance of anthropogenic emissions due to shipping.
Litter decomposition as a potential natural source of methyl bromide
Authors: Lee‐Taylor J. M. , Holland E. A.
Published: September 2002

We assessed the potential significance of global litter decay as a new source of atmospheric methyl bromide. We combined information on the global distribution and quantity of litter decay, litter bromine content, and the halogen‐methylating ability of wood‐rotting fungi to produce a spatially explicit estimate of CH3Br emission from litter decay. The uncertainties are large and the potential methyl bromide source varies greatly in response to assumptions made, including those regarding the efficiency of bromine utilization and release. Our best estimate of the potential flux from woody litter, 0.5–5.2 kT yr−1, is unable to account for the entire “missing source.” Additional possible fluxes from regions of inadequate data and from nonwoody litter may raise this total. This proposed decomposition source is of potential interest to budget calculations and should be experimentally characterized and quantified.
Airborne spectral measurements of surface‐atmosphere anisotropy during the SCAR‐A, Kuwait oil fire, and TARFOX experiments
Authors: Soulen Peter F. , King Michael D. , Tsay Si‐Chee , Arnold G. Thomas , Li Jason Y.
Published: September 2002

During the SCAR‐A, Kuwait Oil Fire Smoke Experiment, and TARFOX deployments, angular distributions of spectral reflectance for various surfaces were measured using the scanning Cloud Absorption Radiometer (CAR) mounted on the nose of the University of Washington C‐131A research aircraft. The CAR contains 13 narrowband spectral channels between 0.47 and 2.3 μm with a 190° scan aperture (5° before zenith to 5° past nadir) and 1° instantaneous field of view. The bidirectional reflectance is obtained by flying a clockwise circular orbit above the surface, resulting in a ground track approximately 3 km in diameter within about 2 min. Spectral bidirectional reflectances of four surfaces are presented: the Great Dismal Swamp in Virginia with overlying haze layer, the Saudi Arabian Desert and the Persian Gulf in the Middle East, and the Atlantic Ocean measured east of Richmond, Virginia. Although the CAR measurements are contaminated by atmospheric effects, results show distinct spectral characteristics for various types of surface‐atmosphere systems, including hot spots, limb brightening and darkening, and Sun glint. In addition, the hemispherical albedo of each surface‐atmosphere system is calculated directly by integrating over all high angular‐resolution CAR measurements for each spectral channel. Comparing the nadir reflectance with the overall hemispherical albedo of each surface, we find that using nadir reflectances as a surrogate for hemispherical albedo can cause albedos to be underestimated by as much as 95% and overestimated by up to 160%, depending on the type of surface and solar zenith angle.
Effects of snow physical parameters on spectral albedo and bidirectional reflectance of snow surface
Authors: Aoki Teruo , Aoki Tadao , Fukabori Masashi , Hachikubo Akihiro , Tachibana Yoshihiro , Nishio Fumihiko
Published: September 2002

Observations of spectral albedo and bidirectional reflectance in the wavelength region of λ = 0.35–2.5 μm were made together with snow pit work on a flat snowfield in eastern Hokkaido, Japan. The effects of snow impurities, density, layer structure, and grain size attained by in situ and laboratory measurements were taken into account in snow models for which spectral albedos were calculated using a multiple‐scattering model for the atmosphere‐snow system. Comparisons of these theoretical albedos with measured ones suggest that the snow impurities were concentrated at the snow surface by dry fallout of atmospheric aerosols. The optically equivalent snow grain size was found to be of the order of a branch width of dendrites or of a dimension of narrower portion of broken crystals. This size was smaller than both the mean grain size and the effective grain size obtained from micrographs by image processing. The observational results for the bidirectional reflection distribution function (BRDF) normalized by the radiance at the nadir showed that the anisotropic reflection was very significant in the near‐infrared region, especially for λ > 1.4 μm, while the visible normalized BRDF (NBRDF) patterns were relatively flat. Comparison of this result with two kinds of theoretical NBRDFs, where one having been calculated using single‐scattering parameters by Mie theory and the other using the same parameters except for Henyey‐Greenstein (HG) phase function obtained from the same asymmetry factor as in the Mie theory, showed that the observed NBRDF agreed with the theoretical one using the HG phase function rather than with that using the Mie phase function, while the albedos calculated with both phase functions agreed well with each other.
Revision of the stratospheric bomb 14CO2 inventory
Authors: Hesshaimer Vago , Levin Ingeborg
Published: September 2002

About 4900 values of 14CO2 activity have been measured on stratospheric air samples collected between 1953 and 1975 when the major nuclear weapon tests injected large amounts of 14C into the atmosphere. However, the validity of these data published in Health and Safety Laboratory reports was repeatedly criticized and their relevance is thus usually denied in model studies tracing the global carbon cycle with bomb 14CO2. To oppose this criticism, we perform here a comprehensive analysis of the measurements and calculate stratospheric bomb 14CO2 inventories for the period in question. We find out that the recognized weaknesses of the survey do not justify a general discrimination against the 14CO2 observations. Our 14CO2 inventories determined using numerical methods to interpolate the observations widely confirm the more “hand‐made” results from a former study by Telegadas [1971] except in the northern poleward stratosphere. We are also able to clear away the reasons commonly advanced to call into question the stratospheric bomb 14CO2 inventories by up to 20%. These findings rehabilitate the most extensive data set of stratospheric 14CO2 observations and establish them, together with our corresponding bomb 14CO2 inventories, as a valuable observational constraint which should be seriously accounted for in global carbon cycle models and in other studies relying on an accurate simulation of air mass transport in the atmosphere.
Extended range forecasts over South America using the regional eta model
Authors: Chou S. C. , Nunes A. M. B. , Cavalcanti I. F. A.
Published: September 2002

An 80‐km National Centers for Environmental Prediction eta model was configured to run over the South America continent. This limited area model has 38 layers in the atmosphere, and its domain includes part of the adjacent Atlantic and Pacific Oceans. The model was setup to perform 1 month forecasts. The version used in these preliminary experiments uses a bucket model to describe water in the ground and a modified Betts‐Miller scheme for producing convective precipitation. The experiments used constant sea surface temperature field and initial soil moisture from climatology. Results obtained from a dry season month and a rainy season month over South America in 1997 show that the reinitialization of model at short range forecasts is not necessary as was done with the previous version of the model. These results show no obvious drying of the atmosphere or tendency with time of the domain average surface pressure. In both cases (dry and wet) the model seems to have reproduced the climatological signal of the forecast months. The monthly accumulated total precipitation agrees well with the observations. These runs showed that the current configuration of the eta model is stable and capable of producing continuous extended range runs over South America.
Effects of meteorological processes on aerosol particle size distribution in an urban background area
Authors: Väkevä M. , Hämeri K. , Puhakka T. , Nilsson E. D. , Hohti H. , Mäkelä J. M.
Published: September 2002

A 3 week measurement campaign was undertaken to study the effect of local weather parameters, transportation from an urban area, structure of boundary layer, and precipitation on submicron (8–450 nm in mobility diameter) aerosol particles in urban background area in Finland. Also, the concentrations of NOx, O3, and SO2 were monitored. The most important meteorological factor affecting aerosol particles was shown to be local wind direction. It was also seen that the diurnal behavior of boundary layer plays an important role for aerosol particle concentration and size distribution and gas phase chemistry at the ground level. Even the few occurrences of new particle formation that were observed seem to be connected with changes in the boundary layer. Clear indications of the possible effect of precipitation (rain or snow) on aerosol size distributions could not be detected in this study. The effect is obviously small compared to the influences of other meteorological processes.
Local mean state changes due to gravity wave breaking modulated by the diurnal tide
Authors: Liu Han‐Li , Hagan Maura E. , Roble Raymond G.
Published: September 2002

During gravity wave breaking, heating rates are determined by wave advection, turbulent diffusion, and turbulence dissipative heating. A series of numerical experiments show that the total heating rates can be larg (∼ ±10 Kh−1) and can cause large local temperature changes. The wave advection causes dynamical cooling in most of the wave breaking region, consistent with previous studies. Nonuniform vertical turbulent diffusion causes strong transient heating in the lower part of the wave breaking region and cooling above. The dissipative heating rate is relatively small compared with those due to the dynamical cooling and turbulent diffusion. In these numerical experiments, zonal wind and temperature perturbations of the diurnal tide and the zonal mean zonal wind and temperature compose the background state for the computation. This is used to examine the idea that temperature inversions, often observed in the mesosphere, are related to the gravity wave and tidal wave interactions. The simulation results show that the large temperature changes in this process can form temperature inversion layers that progress downward with a speed similar to that of a diurnal tide phase speed, which clearly suggests the tidal modulation of the gravity wave and mean flow interactions. Such a process is dependent on season and latitude, because the background state stability varies with season and latitude. The development of the temperature inversion is also affected by the gravity wave characteristics. It is also shown that the local mean wind, wind shear, and chemical species can undergo large changes accompanying the temperature inversion.
Quantifying the wave driving of the stratosphere
Authors: Newman Paul A. , Nash Eric R.
Published: September 2002

The zonal‐mean eddy heat flux is directly proportional to the wave activity that propagates from the troposphere into the stratosphere. This quantity is a simple eddy diagnostic which is calculated from conventional meteorological analyses. Because this “wave driving” of the stratosphere has a strong impact on the stratospheric temperature, it is necessary to compare the impact of the flux with respect to stratospheric radiative changes caused by greenhouse gas changes. Hence we must understand the precision and accuracy of the heat flux derived from our global meteorological analyses. Herein we quantify the stratospheric heat flux using five different meteorological analyses and show that there are 15% differences, on average, between these analyses during the disturbed conditions of the Northern Hemisphere winter. Such large differences result from the planetary differences in the stationary temperature and meridional wind fields. In contrast, planetary transient waves show excellent agreement among these five analyses, and this transient heat flux appears to have a long‐term downward trend.
LASE measurements of aerosol and water vapor profiles during TARFOX
Authors: Ismail Syed , Browell Edward V. , Ferrare Richard A. , Kooi Susan A. , Clayton Marian B. , Brackett Vincent G. , Russell Philip B.
Published: September 2002

The Lidar Atmospheric Sensing Experiment (LASE) was operated autonomously from the NASA high‐altitude ER‐2 aircraft on nine flights during July 10–26, 1996, as part of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). LASE measured high‐resolution profiles of water vapor and aerosols in regions of urban haze plumes over the U.S. eastern seaboard. Real‐time LASE aerosol measurements were used to guide the in situ aircraft to sample haze layers. In this paper the vertical and horizontal distributions of aerosol backscatter measured by LASE are presented along with the temporal evolution of the haze layers. The aerosol backscatter data also identify the presence of gradients in the aerosol plumes, the presence of low‐altitude clouds, and optically thin cirrus. This information is useful for many of the radiometeric observations made during TARFOX and can help explain observational differences among ground, airborne, and satellite observations. An iterative procedure is discussed which was used to invert lidar data to retrieve aerosol scattering ratios, extinction, and total optical depths from the LASE measurements. The sensitivity of these retrievals to assumed parameters is discussed and the results of retrievals are also compared to the well‐known Bernoulli method. LASE water vapor measurements were made across the entire troposphere using a three “line pair” method to cover the range of water vapor mixing ratio from < 0.01 g/kg near the tropopause to ∼ 20 g/kg near the surface in a single aircraft pass over the experiment region. These measurements also show two‐dimensional distributions of large spatial gradients in water vapor in the lower and upper troposphere. These observations are useful in the calculation of IR radiation fields and relative humidity fields, since relative humidity has a strong influence on the growth of aerosols and their scattering properties. Water vapor profiles, aerosol scattering ratios, aerosol extinction coefficients and aerosol optical depths were derived using the methodology presented in this paper from LASE measurements during TARFOX. These measurements are compared with other in situ and remote measurements during TARFOX in the companion papers [Ferrare et al., this issue (a, b)]
Validation of contour advection simulations with airborne lidar measurements of filaments during the Second European Stratospheric Arctic and Midlatitude Experiment (SESAME)
Authors: Flentje Harald , Renger Wolfgang , Wirth Martin , Lahoz William A.
Published: September 2002

Airborne lidar measurements of vertical sections of ozone and aerosol across the lower stratospheric vortex boundary during the Arctic winter 1994/1995 are used to study the permeability of this dynamical barrier. Both constituents exhibit strong gradients in the lower levels of the vortex edge and substantial structure at subsynoptic scales in the surrounding surf zone. These measurements provide validation of two‐dimensional (2‐D) Contour Advection (CA) calculations which use potential vorticity (PV) as a proxy tracer. The CA calculations are initialized from gridded U.K. Meteorological Office analyses and thus may smooth subgrid scale structures. Contour Advection reproduces most of the observed filaments with an accuracy of few tenths of a degree, but neglect of diabatic effects causes small errors. The CA calculations show that the arctic stratosphere was dynamically disturbed over extended periods by breaking planetary waves as indicated by numerous spiral‐like PV filaments which surrounded the polar vortex. The transport rate across the vortex boundary due to filamentation and subsequent detachment of the filaments off the vortex can be inferred from the model calculations. In winter 1994/1995, two wave breaking events eroded the area of the Arctic vortex by 8% and 40% at 450 K and by 22% and 60% at 600 K. A third event triggered off the final warming. Since the vortex air partly was chemically disturbed, this cross vortex boundary transport, together with effective catalytic ozone destruction cycles, has considerable potential for reducing ozone concentrations at midlatitudes.
Martian and terrestrial dust devils: Test of a scaling theory using Pathfinder data
Authors: Rennó Nilton O. , Nash Amelia Ann , Lunine Jonathan , Murphy James
Published: September 2002

The Mars Pathfinder meteorological station recorded wind, pressure, and temperature fluctuations that have been interpreted as dust devils: warm‐core vortices that form at the bottom of connective plumes. We apply a scaling theory [Rennó et al., 1998], developed to explain terrestrial dust devil observations, to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of Martian dust devils. The theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices. Our findings are as follows: For the best documented candidate event (sol 25), observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil. A number of other candidates, less well documented, however, also are consistent with passage of a dust devil over or near the lander. Temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package. The strongest dust devils predicted by our theory have a central pressure deficit of about 50 Pa and wind speed of about 60 m s−1. The strongest dust devils are capable of lofting dust and hence support the interpretation of selected Pathfinder images as showing the passage of dust devils within sight of the lander.
Wind‐driven surface waves on Titan
Authors: Ghafoor Nadeem A.‐L. , Zarnecki John C. , Challenor Peter , Srokosz Meric A.
Published: September 2002

The surface of Titan represents the largest surface area in the solar system essentially unexplored, although recent observations from Hubble Space Telescope and ground‐based telescopes using adaptive optics have given perhaps the first low‐resolution indications of its nature. Whilst early models citing global oceans have been all but abandoned, substantial bodies of liquid up to several hundred kilometers in extent are not precluded. If such reservoirs do exist then in the presence of any surface winds it is expected that wind‐driven surface waves will be generated. As on Earth, gravity remains the dominant controlling factor for such waves, with surface tension and viscous effects only becoming significant below wavelengths of several centimeters. Empirical models used for terrestrial wind‐driven sea waves are adapted to investigate the properties of such waves on Titan using predicted parameters for Titan's liquids. Significant wave height, peak period, wavelength, phase speed, and wave steepness are predicted as a function of wind speed and liquid body extent. It is found that waves will grow to a limiting height, limiting wavelength and limiting period which are all inversely proportional to gravity. The limiting significant wave height under the action of a 1 m s−1 Titan wind over 50 km, for example, is predicted to be 0.2 m compared to 0.02 m on Earth under similar circumstances. More interesting, however, is the wave growth prior to this limiting value. A useful visualization is that surface waves on a Titan sea arising from surface wind speeds of 0.3 and 1 m s−1 will resemble in scale waves on Earth generated by terrestrial winds of 1 and 3 m s−1 respectively. These particular Titan waves will have nearly 3 times the period and travel almost 3 times slower than the terrestrial waves, however. The wave parameters predicted in this work have potential surface mission implications for the European Space Agency's Huygens Probe which will land on Titan in 2004. Conversely, their measurement by instruments on board Huygens and NASA's Cassini spacecraft could yield important planetological information.
Deep Space 2: The Mars Microprobe Mission
Authors: Smrekar Suzanne , Catling David , Lorenz Ralph , Magalhães Julio , Moersch Jeffrey , Morgan Paul , Murray Bruce , Presley Marsha , Yen Albert , Zent Aaron , Blaney Diana
Published: September 2002

The Mars Microprobe Mission will be the second of the New Millennium Program's technology development missions to planetary bodies. The mission consists of two penetrators that weigh 2.4 kg each and are being carried as a piggyback payload on the Mars Polar Lander cruise ring. The spacecraft arrive at Mars on December 3, 1999. The two identical penetrators will impact the surface at ∼190 m/s and penetrate up to 0.6 m. They will land within 1 to 10 km of each other and ∼50 km from the Polar Lander on the south polar layered terrain. The primary objective of the mission is to demonstrate technologies that will enable future science missions and, in particular, network science missions. A secondary goal is to acquire science data. A subsurface evolved water experiment and a thermal conductivity experiment will estimate the water content and thermal properties of the regolith. The atmospheric density, pressure, and temperature will be derived using descent deceleration data. Impact accelerometer data will be used to determine the depth of penetration, the hardness of the regolith, and the presence or absence of 10 cm scale layers.
Local and regional lunar regolith characteristics at Reiner Gamma Formation: Optical and spectroscopic properties from Clementine and Earth‐based data
Authors: Pinet Patrick C. , Shevchenko Vladislav V. , Chevrel Serge D. , Daydou Yves , Rosemberg Christine
Published: September 2002

A detailed remote sensing survey of the Reiner Gamma Formation (RGF) region by means of Earth‐based telescopic and Clementine multispectral imaging has been made in the UV‐visible‐near‐infrared domain. The spectral mixture analysis reveals the existence of three basic end‐members relevant for modeling the observed spectral variations in the RGF vicinity. These are MB (mare background), SWS (southwest swirl), and RGS (Reiner Gamma soil). The first two components exhibit spectral characteristics consistent with a prevailing contribution of mature mare soils for the surroundings (MB) and of immature mare crater‐like soils (RGS) at RGF. The third intermediate‐albedo component (SWS) has general characteristics of a mature mare soil, but with a redder continuum slope. The reported observation can be modeled by a mechanism which would remove the finest fraction in the soil (particle diameter <45 μm) at RGF and redistribute it in the vicinity with a laterally variable proportion and local accumulations such as at SWS site. According to the available set of in situ data documenting variations in the chemical composition, in the distribution of particle sizes, and in the degree of maturity with depth in the mare regolith, the characteristics depicted at RGF are those of a subsurface soil layer from a depth of the order of 0.3–0.8 m. In our view, the simplest way to account for the whole body of information available from the present work lies in the proposition that in the area of RGF the uppermost layer of the regolith has been optically and mechanically modified by a process involving the fall of fragments of a low‐density cometary nucleus previously disrupted by tidal interaction in the Earth‐Moon system. We recognize, however, that in the present state of knowledge, one cannot rule out the hypothesized existence of a zone of seismically modified terrain peripheral to the Imbrium or Orientale basins just beneath the mare surface that would be the actual source of the RGF magnetic anomaly.
Major lunar crustal terranes: Surface expressions and crust‐mantle origins
Authors: Jolliff Bradley L. , Gillis Jeffrey J. , Haskin Larry A. , Korotev Randy L. , Wieczorek Mark A.
Published: September 2002

In light of global remotely sensed data, the igneous crust of the Moon can no longer be viewed as a simple, globally stratified cumulus structure, composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual‐melt (KREEP) sandwich horizon near the base of the lower crust. Instead, global geochemical information derived from Clementine multispectral data and Lunar Prospector gamma‐ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique: (1) the Procellarum KREEP Terrane (PKT), (2) the Feldspathic High‐lands Terrane (FHT), and (3) the South Pole‐Aitken Terrane (SPAT). The PKT is a mafic province, coincident with the largely resurfaced area in the Procellarum‐Imbrium region whose petrogenesis relates to the early differentiation of the Moon. Here, some 40% of the Th in the Moon's crust is concentrated into a region that constitutes only about 10% of the crustal volume. This concentration of Th (average ∼5 ppm), and by implication the other heat producing elements, U and K, led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust. Lower‐crustal materials within the PKT likely interacted with underlying mantle materials to produce hybrid magmatism, leading to the magnesian suite of lunar rocks and possibly KREEP basalt. Although rare in the Apollo sample collection, widespread mare volcanic rocks having substantial Th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources. The FHT is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation. Basin impacts into this region do not excavate significantly more mafic material, suggesting a thickness of tens of kilometers of anorthositic crust. The feldspathic lunar meteorites may represent samples from the anorthositic central region of the FHT. Ejecta from deep‐penetrating basin impacts outside of the central anorthositic region, however, indicate an increasingly mafic composition with depth. The SPAT, a mafic anomaly of great magnitude, may include material of the upper mantle as well as lower crust; thus it is designated a separate terrane. Whether the SPA basin impact simply uncovered lower crust such as we infer for the FHT remains to be determined.
Separation of atmospheric and surface spectral features in Mars Global Surveyor Thermal Emission Spectrometer (TES) spectra
Authors: Smith Michael D. , Bandfield Joshua L. , Christensen Philip R.
Published: September 2002

We present two algorithms for the separation of spectral features caused by atmospheric and surface components in Thermal Emission Spectrometer (TES) data. One algorithm uses radiative transfer and successive least squares fitting to find spectral shapes first for atmospheric dust, then for water‐ice aerosols, and then, finally, for surface emissivity. A second independent algorithm uses a combination of factor analysis, target transformation, and deconvolution to simultaneously find dust, water ice, and surface emissivity spectral shapes. Both algorithms have been applied to TES spectra, and both find very similar atmospheric and surface spectral shapes. For TES spectra taken during aerobraking and science phasing periods in nadir‐geometry these two algorithms give meaningful and usable surface emissivity spectra that can be used for mineralogical identification.
Geology of the Smythii and Marginis region of the Moon: Using integrated remotely sensed data
Authors: Gillis Jeffrey J. , Spudis Paul D.
Published: September 2002

We characterized the diverse and complex geology of the eastern limb region of the Moon using a trio of remote‐sensing data sets: Clementine, Lunar Prospector, and Apollo. On the basis of Clementine‐derived iron and titanium maps we classify the highlands into low‐iron (3–6 wt% FeO) and high‐iron (6–9 wt% FeO) units. The association of the latter with basalt deposits west of Smythii basin suggests that the highland chemical variation is the result of mixing between basalt and highland lithologies. Mare Smythii and Mare Marginis soils are compositionally similar, containing moderate iron (15–18 wt% FeO) and titanium (2.5–3.5 wt% TiO2). Smythii basin, in addition to the basalt deposits, contains an older, moderate‐albedo plains unit. Our investigation reveals that the dark basin plains unit has a distinct albedo, chemistry, and surface texture and formed as a result of impact‐mixing between highland and mare lithologies in approximately equal proportions. Clementine iron and maturity maps show that swirls along the northern margin of Mare Marginis have the same iron composition as the surrounding nonswirl material and indicate that the swirl material is bright because of its low agglutinate content. Gravity data for the eastern limb show high, positive Bouguer gravity anomalies for areas of thin basalt cover (e.g., Smythii basin and complex craters Joliot, Lomonosov, and Neper). We deduce that the uplift of dense mantle material is the primary (and mare basaltic fill the secondary) source for generating the concentration of mass beneath large craters and basins.
Meteoric magnesium ions in the Martian atmosphere
Authors: Pesnell William Dean , Grebowsky Joseph
Published: September 2002

From a thorough modeling of the altitude profile of meteoric ionization in the Martian atmosphere we deduce that a persistent layer of magnesium ions should exist around an altitude of 70 km. On the basis of the estimated meteoroid mass flux density, a peak ion density of ∼104 ions cm−3 is predicted. Allowing for the uncertainties in all of the model parameters, this value is probably within an order of magnitude of the correct density. Of these parameters, the peak density is most sensitive to the meteoroid mass flux density which determines the source function for Mg from the ablating meteoroids. Unlike the terrestrial case, where the metallic ion production is dominated by charge‐exchange of the deposited neutral Mg with the ambient ions, Mg+ in the Martian atmosphere is produced predominantly by photoionization. The low ultraviolet absorption of the Martian atmosphere makes Mars an excellent laboratory in which to study meteoric ablation. Resonance lines in the ultraviolet that cannot be seen in the spectra of terrestrial meteors may be visible to a surface observatory in the Martian highlands.
Polar hydrogen deposits on the Moon
Authors: Feldman W. C. , Lawrence D. J. , Elphic R. C. , Barraclough B. L. , Maurice S. , Genetay I. , Binder A. B.
Published: September 2002

Neutron and gamma‐ray data measured using the Lunar Prospector spectrometers were analyzed to define the enhanced hydrogen deposits near both poles of the Moon. Combining the new low‐altitude neutron data (30±15 km) with previous high‐altitude (100±20 km) neutron data and the results of several recent radar investigations sharply constrains the characteristics of each of the polar deposits. The deposits at the north appear to be in the form of many small pockets or of generally distributed hydrogen that average to a 100 ppm weight fraction enhancement over that which exists in regolith at more equatorial latitudes. Those deposits in the permanently shaded craters near the south pole are consistent with a thick ferroan anorthosite regolith containing an enhancement of 1670±890 ppm hydrogen, which, if in the form of water ice, amounts to 1.5±0.8% weight fraction of H2O. Neutron data alone cannot discriminate between hydrogen implanted in lunar soil from the solar wind, hydrated minerals, or H2O. These craters appear to be surrounded by regolith that either contains small pockets of enhanced hydrogen or is soil that is uniformly impregnated with hydrogen enhanced on average by about 100 ppm above that contained in soils at more equatorial latitudes.