bluuebunny/crossref_metadata_2025 huggingface dataset:
A partial correlation analysis of the stratospheric ozone response to 27‐day solar UV variations with temperature effect removed
Authors: Zhou Shuntai , Miller Alvin J. , Hood Lon L.
Published: September 2002

Observational detection of upper stratospheric ozone responses to 27‐day solar ultraviolet (UV) variations is often inhibited by larger, dynamically induced ozone variations, which result mainly from the temperature dependence of reaction rates controlling the ozone balance. Here we show that partial correlation coefficients of solar UV and tropical upper stratospheric ozone (1–5 hPa) with the temperature effect removed are larger (07–0.8) than are total correlation coefficients of ozone and solar UV (0.4–0.6). The phase lag of ozone relative to solar UV is also increased, and the maximum ozone‐UV correlation is obtained at higher altitudes, as compared with correlation analyses using ozone and solar UV data alone. Assuming that temperature variations are not forced by solar UV variations, the ozone sensitivity to solar UV and temperature can be calculated using a linear multiple regression model. The ozone sensitivity to solar UV is generally independent of time periods used for the analysis. However, the magnitude of the ozone sensitivity to temperature at 1–2 hPa increased significantly from solar cycle 21 to solar cycle 22, possibly reflecting long‐term changes in the composition of the upper stratosphere.
Modeling the atmospheric distribution of mineral aerosol: Comparison with ground measurements and satellite observations for yearly and synoptic timescales over the North Atlantic
Authors: Guelle W. , Balkanski Y. J. , Schulz M. , Marticorena B. , Bergametti G. , Moulin C. , Arimoto R. , Perry K. D.
Published: September 2002

We present here a 3‐year simulation (1990 to 1992) of the atmospheric cycle of Saharan dust over the Atlantic with an off‐line three‐dimensional transport model. The results of the simulation have been compared with selected relevant measurements. Careful attention has been paid to the spatial and temporal consistency between the observations and the model results. Satellite observations of optical thickness and the model show a closely similar latitudinal shift and change of the aerosol plume extent from month to month over 3 years. This is explained by the dominant role of the large‐scale transport, well described by the European Centre for Medium‐Range Weather Forecasts winds, a sufficiently consistent description of aerosol physics along with a detailed prognostic source function. A feature not captured perfectly by the model is the winter maximum in observed optical depth, which is south of the satellite observation window. This underestimate in the very southern tropical region in winter suggests that additional aerosol sources become important, such as Sahelian dust and carbonaceous aerosols from biomass burning, not included in our simulation. However, spring and autumn simulated optical thickness is 50% less than that observed, while it is only 30% less in summer and winter. This is found for both the subtropical and the tropical Atlantic Ocean, which points to a general underestimate by the model, not just because of aerosol sources missing in the Sahel region. Another seasonal feature is discussed for Sal Island where measurements suggest that low‐level dust transport in winter is replaced by a pronounced high‐level Saharan dust layer in summer. The model reproduces this pattern except that there is also significant low level transport in summer, associated mainly with peculiar simulated dust transport events from the western Sahara. On a synoptic scale the frequency of dust outbreaks over the North Atlantic and of major dust deposition events in Spain and a dust vertical profile measured by a lidar over the Azores region are reproduced by the model.
Average statistical characteristics of long gravity waves observed with the middle and upper atmosphere radar in the mesosphere
Authors: Gavrilov N. M. , Fukao S. , Nakamura T.
Published: September 2002

Average statistical characteristics of internal gravity waves (IGWs) with horizontal wavelengths longer than 60 km are obtained at the altitudes 65–80 km from the observations with the middle and upper atmosphere radar at Shigaraki, Japan (35°N, 136°E) in 1986–1995. The numbers of signals selected with narrow frequency band filters attributed to IGW having periods 0.1–6 hours vary between 870 and 2300 for different seasons and altitudes. Long‐period IGWs have larger amplitudes and larger vertical wavelengths than short‐period IGWs. For waves with periods 0.1–6 hours the mean values of the horizontal and vertical wavelengths are 100–300 km and 6–10 km, respectively. IGW amplitudes and momentum fluxes have maxima in winter and summer and minima in spring and autumn. Distributions of the azimuths of IGW horizontal wave vectors and momentum fluxes are nearly isotropic with maxima in zonal directions in summer. The westward momentum flux is larger than the eastward flux in winter and is smaller than that in summer. The differences between eastward and westward wave momentum fluxes are larger for long‐period IGWs. The net zonal IGW momentum flux is mainly directed opposite to the mean wind in the mesosphere.
Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America
Authors: Schuster Paul F. , White David E. , Naftz David L. , Cecil L. DeWayne
Published: September 2002

The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid‐1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 m the refined age‐depth profile shows good agreement (1736±10 A.D.) with the 14C age date (1729±95 A.D.). The δ18O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for δ18O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of δ18O data alone. Other research has shown that changes in the δ18O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999‐point running average of the ECM data set and results from ƒ tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age‐depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are ±10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present‐day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale.
From model intercomparison toward benchmark UV spectra for six real atmospheric cases
Authors: van Weele M. , Martin T. J. , Blumthaler M. , Brogniez C. , den Outer P. N. , Engelsen O. , Lenoble J. , Mayer B. , Pfister G. , Ruggaber A. , Walravens B. , Weihs P. , Gardiner B. G. , Gillotay D. , Haferl D. , Kylling A. , Seckmeyer G. , Wauben W. M. F.
Published: September 2002

The validity of a radiative transfer model can be checked either by comparing its results with measurements or with solutions for artificial cases. Unfortunately, neither type of comparison can guarantee that the spectral UV surface irradiance is accurately calculated for real atmospheric cases. There is a need therefore for benchmarks, i.e., standard results that can be used as a validation tool for UV radiation models. In this paper we give such benchmarks for six cloud‐free situations. The chosen cases are characterized by different values of solar zenith angle, ozone column, aerosol loading, and surface albedo. Observations are also available for these cases to allow a further comparison between model results and measurements. An intercomparison of 12 numerical models is used to construct the benchmarks. Each model is supplied with identical input data, and a distinction is made between models that assume a planeparallel geometry and those that use a pseudospherical approximation. Differences remain between the model results, because of different treatments of the input data set. Calculations of direct and global transmission and direct and global irradiance are within 3% for wavelengths longer than 320 nm. For the low‐Sun cases the calculations are within 10% for wavelengths longer than 300 nm. On the basis of these calculations, six benchmark UV spectra (295–400 nm) are established with a standard deviation of 2%. Relative standard deviations are higher for the lowest absolute intensities at low Sun (5% at 300 nm). The variation between models is typically less than the variation seen between model and measurement. Differences between the benchmarks and the observed spectra are mainly due to the uncertainty in the input parameters. In four of the six cases the benchmarks agree with the observed spectra within 13% over the whole UV spectral region.
Chemical effects of UV fluctuations inferred from total ozone and tropospheric aerosol variations
Authors: Jonson J. E. , Kylling A. , Berntsen T. K. , Isaksen I. S. A. , Zerefos C. S. , Kourtidis K.
Published: September 2002

A regional‐scale photochemistry model with 50 km horizontal resolution and 20 layers in the vertical is described. The model's domain includes Europe and most of the North Atlantic and the Arctic region. Model results for the summer months April–September 1996 are presented and compared to measurements. Emphasis is on the Aegean Sea where extensive measurements were made as part of the European Union project Photochemical Activity and Solar Ultraviolet Radiation (PAUR). The model sensitivity with respect to changes in UV radiation, caused by moderate variations in the total ozone column (25 Dobson units), are explored and shown to be small. Aerosol optical depth was calculated from Mie scattering theory using the modeled total sulphate column and used to calculate perturbations of the photolysis rates due to sulphate aerosols. Only small effects on monthly averaged ozone are found with the inclusion of aerosols. For individual days, occasional large variations in calculated ozone levels are seen when the aerosol optical depth is fixed at a high value. The inclusion of aerosols result in a slight reduction of high ozone events over central parts of Europe.
Response of lower stratospheric HCl/Cly to volcanic aerosol: Observations from aircraft, balloon, space shuttle, and satellite instruments
Authors: Webster C. R. , Michelsen H. A. , Gunson M. R. , Margitan J. J. , Russell J. M. , Toon G. C. , Traub W. A.
Published: September 2002

Vertical profiles of HCl/Cly measured by space shuttle (Atmospheric Trace Molecule Spectroscopy (ATMOS)) and balloon (MkIV) instruments from 1985 through 1994 show that the increased volcanic aerosol from Mount Pinatubo had little effect on chlorine partitioning above 21 km. Below 21 km, however, large changes in HCl/Cly were observed. Aircraft (Aircraft Laser Infrared Absorption Spectrometer), balloon (MkIV, Far Infrared Spectrometer 2), space shuttle (ATMOS), and satellite (Halogen Occultation Experiment) measurements below 21 km reveal an increase in HCl/Cly between early 1993 and late 1997 of 31±9%. This growth rate is 2 to 3 times larger than model estimates of the effect of the change in aerosol surface area and volume over this time period. For 1993 the five independent direct measurements of HCl/Cly produce a mean value of 0.57±0.05, whereas by 1997 the mean value was 0.75±0.07, in excellent agreement with the pre‐Pinatubo mean of 0.74±0.11. Measurements made in 1992 at the peak of the post‐Pinatubo midlatitude aerosol loading demonstrate large variability, which is qualitatively consistent with model predictions. This variability appears to be attributable to the temperature sensitivity of the Cly partitioning when aerosol abundances are high.
Production of nitrogen oxides by a large spark generator
Authors: Cook D. R. , Liaw Y. P. , Sisterson D. L. , Miller N. L.
Published: September 2002

A large spark generator was used outdoors to determine the production of nitrogen oxides (NOx) from sparks with characteristics similar to those of lightning strokes. The experiment was conducted at the Rocket Triggered Lightning Program facility at Cape Canaveral, Florida, in August 1991, during the Convection and Precipitation/Electrification field experiment. Plumes of NOx from spark generations were sensed by a NOx analyzer. The spark energy was 9.8±0.7×104 J, and the spark gap was 1.65 or 2.13 m. The plumes reached the analyzer inlet within 0.3–4.7 s after spark generation. The NOx concentrations varied, depending on the geometry of the plume. Laboratory studies of analyzer response permitted adjustment of the measured concentrations to corrected concentrations. Production of NOx, in terms of mass of nitrogen, averaged 22.5±2.9 mg per spark, 11.7±1.5 mg m−1 of spark length, and 1.1±0.2×1016 molecules J−1. The median ratio of nitric oxide (NO) to nitrogen dioxide (NO2) was 0.76, indicating substantial conversion within a few seconds. Scaling of NOx production to lightning energy levels and dimensions yielded an annual global NOx production of 9.7 Tg yr−1, similar to values estimated from recent thunderstorm measurements and modeling studies. Recent satellite measurements suggest that cloud‐to ground lightning flash frequency is an order of magnitude smaller than normally assumed; estimates of global NOx production by lightning might also need to be reduced by an order of magnitude.
Meridional distribution of hydroperoxides and formaldehyde in the marine boundary layer of the Atlantic (48°N‐35°S) measured during the Albatross campaign
Authors: Weller R. , Schrems O. , Boddenberg A. , Gäb S. , Gautrois M.
Published: September 2002

Gas phase H2O2, organic peroxides, and formaldehyde (HCHO) have been measured in situ during October/November 1996 on board RV Polarstern in surface air over the Atlantic from 48°N‐35°S with different analytical methods. The results indicate that recombination and self‐reactions of peroxy radicals largely dominate over scavenging by NO. The peroxy radical chemistry was governed by the photooxidation of CH4 and CO, as could be deduced from our failure to detect organic hydroperoxides other than CH3OOH (methyl hydroperoxide (MHP)). Hydroperoxide and formaldehyde mixing ratios were highest within the tropics with peak values of around 2000 parts per trillion by volume (pptv) (H2O2), 1500 pptv (MHP), and 1000 pptv (HCHO). In the case of H2O2 and MHP we observed diurnal variations of the mixing ratios in the tropical North Atlantic and derived deposition rates of around (1.8±0.6)×10−5 s−1 for H2O2 and (1.2±0.4)×10−5 s−1 for MHP. The measured MHP/(H2O2+MHP) and MHP/HCHO ratios corresponded to 0.32±0.12 and 0.87±0.4, respectively. HCHO mixing ratios observed during the expedition were significantly higher than predicted by current photochemical theory based on the photooxidation of CH4 and CO.
The modeling of tropospheric methane: How well can point measurements be reproduced by a global model?
Authors: Houweling Sander , Dentener Frank , Lelieveld Jos , Walter Bernadette , Dlugokencky Ed
Published: September 2002

Global model simulations of tropospheric methane are presented, using state of the art representations of its terrestrial sources. Parameters critical for its tropospheric sink and transport have been evaluated using CH3CCl3 and SF6. We assess how well available methane measurements can be reproduced by the model, and how model and measurements can most efficiently be compared. Using European Centre for Medium‐Range Weather Forecasts reanalyzed meteorological fields, direct comparisons between model results and flask or in situ measurements are presented, as opposed to comparing multiannual averaged seasonal cycles and trends as was done in previous studies. When comparing monthly means derived from weekly flask sampling and the model, the agreement at stations as Bermuda East and Mace Head is improved if, instead of sampling the model at each model time step, samples are taken at the same times as the measurements were taken. A method is presented to estimate the potential influence of subgrid variability using a marked tracer that is emitted in the vicinity of observational stations only. From the contribution of this tracer to the computed methane concentration at a particular station, the potential contribution of subgrid sources can be estimated. Radon 222 is used to select baseline conditions in the model to improve the comparability of model and measurements when a clean air sector is selected for sampling. Comparisons of model results and measurements, screened for local influences and artifacts of wind sector selection, indicate that the model has in particular difficulty reproducing seasonal cycles at higher latitude stations of the Northern Hemisphere. Sensitivity simulations show that the simulated annual variation at these stations is sensitive to the parameterization of wetland emissions. Also at the South China Sea, model simulations point to errors in the representation of methane sources. Marked tracer simulations indicate that this is most likely related to emissions from natural wetlands and rice paddies, in line with recent inverse modeling and up‐scaling estimates.
Diurnal ozone cycle in the tropical and subtropical marine boundary layer
Authors: de Laat A. T. J. , Lelieveld J.
Published: September 2002

A conceptual analysis of diurnal ozone (O3) changes in the marine boundary layer (MBL) is presented. Such changes are most pronounced downwind of O3 sources in tropical and subtropical latitudes and during summer at higher latitudes. Previously, it has been assumed that daytime photochemical O3 loss and nighttime replenishment through entrainment from the relatively O3‐rich free troposphere explain the diurnal O3 cycle. We show, however, that in a net O3 destruction environment (low NOx) this diurnal cycle can be explained by photochemistry and advection, which establish a horizontal O3 gradient that is typical for the MBL. We support this hypothesis first by calculations with a conceptual one‐dimensional (1‐D) advection‐diffusion model and second by simulations with an interactive 3‐D chemistry transport model. The results are in good agreement with observations, for example, in the Indian Ocean Experiment.
Spatial and temporal variability of atmospheric sulfur‐containing gases and particles during the Albatross campaign
Authors: Sciare J. , Baboukas E. , Kanakidou M. , Krischke U. , Belviso S. , Bardouki H. , Mihalopoulos N.
Published: September 2002

To investigate the oxidation chemistry of dimethylsulfide (DMS) in the marine atmosphere, atmospheric DMS, SO2, as well as several DMS oxidation products in aerosol phase such as non‐sea‐salt sulfate (nss‐SO4), methanesulfonate (MSA), and dimethylsulfoxide (DMSOp) have been measured during the Albatross campaign in the Atlantic Ocean from October 9 to November 2, 1996. Long‐range transport, local sea‐to‐air flux of DMS (FDMS), marine boundary layer (MBL) height variation, and photochemistry were found to be the major factors controlling atmospheric DMS concentration which ranged from 29 to 396 parts per trillion by volume (pptv) (mean of 120±68 pptv) over the cruise. The spatial variability of MSA and DMSOp follows the latitudinal variations of FDMS. A 2‐day period of intensive photochemistry associated with quite stable atmospheric conditions south of the equator allowed the observation of anticorrelated diurnal variations between DMS and its main oxidation products. A chemical box model describing sulfur chemistry in the marine atmosphere was used to reproduce these variations and investigate coherence of experimentally calculated fluxes FDMS with observed DMS atmospheric concentrations. The model results reveal that the measured OH levels are not sufficient to explain the observed DMS daytime variation. Oxidizing species other than OH, probably BrO, must be involved in the oxidation of DMS to reproduce the observed data.
Stratospheric NO2 variations from a long time series at Lauder, New Zealand
Authors: Liley J. B. , Johnston P. V. , McKenzie R. L. , Thomas A. J. , Boyd I. S.
Published: September 2002

Eighteen years of NO2 measurements using zenith‐scattered sunlight are analyzed for seasonal, cyclic, and episodic variability and secular trends. The analysis shows a marked increase in stratospheric NO2 over the period, corresponding to a trend of 5% per decade, and the influences of both the El Chichón and Pinatubo eruptions are clearly evident. Smaller effects of the El Niño‐Southern Oscillation and quasi‐biennial oscillation are apparent, but correlation with the solar cycle is poor after correction for autocorrelation. All of these effects are similar for sunrise and sunset NO2.
A 25‐month database of stratus cloud properties generated from ground‐based measurements at the Atmospheric Radiation Measurement Southern Great Plains Site
Authors: Dong Xiquan , Minnis Patrick , Ackerman Thomas P. , Clothiaux Eugene E. , Mace Gerald G. , Long Charles N. , Liljegren James C.
Published: September 2002

A 25‐month database of the macrophysical, microphysical, and radiative properties of isolated and overcast low‐level stratus clouds has been generated using a newly developed parameterization and surface measurements from the Atmospheric Radiation Measurement central facility in Oklahoma. The database (5‐min resolution) includes two parts: measurements and retrievals. The former consist of cloud base and top heights, layer‐mean temperature, cloud liquid water path, and solar transmission ratio measured by a ground‐based lidar/ceilometer and radar pair, radiosondes, a microwave radiometer, and a standard Eppley precision spectral pyranometer, respectively. The retrievals include the cloud‐droplet effective radius and number concentration and broadband shortwave optical depth and cloud and top‐of‐atmosphere albedos. Stratus without any overlying mid or high‐level clouds occurred most frequently during winter and least often during summer. Mean cloud‐layer altitudes and geometric thicknesses were higher and greater, respectively, in summer than in winter. Both quantities are positively correlated with the cloud‐layer mean temperature. Mean cloud‐droplet effective radii range from 8.1 μm in winter to 9.7 μm during summer, while cloud‐droplet number concentrations during winter are nearly twice those in summer. Since cloud liquid water paths are almost the same in both seasons, cloud optical depth is higher during the winter, leading to greater cloud albedos and lower cloud transmittances.
Case studies of the SO2 + H2O2 reaction in clouds
Authors: Husain Liaquat , Rattigan O. V. , Dutkiewicz Vincent , Das Mita , Judd C. D. , Khan A. R. , Richter R. , Balasubramanian R. , Swami Kamal , Walcek C. J.
Published: September 2002

The in‐cloud reaction between SO2 and H2O2has been investigated using data from field campaigns of July 1995 and July–August 1997 at Whiteface Mountain, New York. Cloud water samples were collected at the mountain's summit (1.5 km, above mean sea level (amsl)), and aerosols in clear air at a site (Lodge) located at 0.6 km amsl and in cloud interstitial air at the summit. Cloud water and aerosol samples were analyzed for SO42− and selected trace elements. Gaseous SO2 and H2O2 were measured at both sampling sites. Criteria based on total sulfur and O3 concentrations were developed to decide when the two sites were coupled (i.e., air masses at the two sites had the same composition for the chemical species studied). Four case studies are presented that exhibit varying concentration levels and different meteorological conditions. In two cases the sites were coupled, and in two others they were decoupled. The clouds showed high pollutant concentrations with a mean pH of 3.5. A tracer technique was used to quantitatively determine the SO42− produced from in situ SO2 oxidation. In general, good agreement between the SO2 consumed and SO42− produced was observed. Similarly, H2O2 concentrations in precloud air showed stoichiometric mass balance with the sum of H2O2 observed in cloud interstitial air, in cloud water, and equimolar amounts needed to produce SO4in2− as determined by the tracer technique. Data from all 24 clouds showed that (1) ∼28% of the cloud water SO42− was due to in situ oxidation; (2) ∼75% of the SO2 in the precloud air was oxidized in situ at Whiteface Mountain; (3) the mean SO2 concentration in air masses associated with cloudy periods is approximately 1.4 ppb, significantly higher than the summer average of 0.5 ppb; (4) the mean H2O2 concentration in cloud‐free periods during summer is 1.1 ppb sufficient to oxidize SO2 present; (5) the frequent presence of H2O2 in cloud water indicated that the reaction had not often reached completion.
Variability of trace gases at the high‐Alpine site Jungfraujoch caused by meteorological transport processes
Authors: Forrer Jann , Rüttimann Ralph , Schneiter Daniel , Fischer Andrea , Buchmann Brigitte , Hofer Peter
Published: September 2002

The influence of meteorological transport processes on trace gas concentrations at the high‐Alpine site Jungfraujoch (3580 m above sea level) is investigated. These processes are subdivided into two categories: thermally driven transport, which takes place on a local scale, and transport on a regional (föhn) or synoptic scale (fronts). During thermally induced processes, which are mainly observed in summer and spring, the carbon monoxide (CO) mixing ratios show a diurnal variation with a maximum concentration at ≈ 1800 local time. Processes on the regional and synoptic scale which occur during the whole season induce large variability in the trace gas observations. The CO concentrations can be twice as large as the monthly median value during severe föhn episodes. The NOx values exhibit an even larger increase. Depending on the season, the O3 observations during these periods show an increase in summer and a pronounced decrease in winter. In addition, it is found that the calculated trajectories using the output of a mesoscale weather prediction model are a useful tool to detect and explain episodes with high NOx or CO concentrations. Altogether, the present results imply that meteorological transport processes on different spatial and timescales are important for the interpretation of the trace gas observations at the high‐Alpine site Jungfraujoch during the whole year.
Possible changes of δ18O in precipitation caused by a meltwater event in the North Atlantic
Authors: Werner Martin , Mikolajewicz Uwe , Hoffmann Georg , Heimann Martin
Published: September 2002

The Hamburg atmosphere general circulation model ECHAM‐4 is used to investigate how a meltwater event in the North Atlantic might alter the signal of stable water isotopes (H218O, HDO) in precipitation. Our results show that such a meltwater event will cause significant changes in the isotopic composition of the precipitation over many parts of the Northern Hemisphere, but also in the tropical Atlantic region. Model simulations suggest that for such a scenario isotope anomalies are not only related to temperature changes, but also to changes in the seasonality of precipitation or the precipitation amount. A changed isotopic composition of evaporating ocean surface waters (caused by a massive meltwater input into the North Atlantic) causes temperature‐independent isotope anomalies, too. Changes of the deuterium excess are even more affected by the imposed oceanic isotope anomaly due to the nonlinearity of the evaporation process.
Indirect effect of sulfate and carbonaceous aerosols: A mechanistic treatment
Authors: Lohmann Ulrike , Feichter Johann , Penner Joyce , Leaitch Richard
Published: September 2002

The indirect effect of anthropogenic aerosols, whereby aerosol particles change cloud optical properties, is the most uncertain component of climate forcing over the past 100 years. Here we use a mechanistic treatment of droplet nucleation and a prognostic treatment of the number of cloud droplets to study the indirect aerosol effect from changes in carbonaceous and sulfate aerosols. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and an activation parameter, which takes into account the mechanism of sulfate aerosol formation. Where previous studies focussed either on sulfate aerosols or carbonaceous aerosols only, here we estimate the combined effect. The combined indirect aerosol effect amounts to −1.1 W m−2 for an internally mixed aerosol and −1.5 W m−2 for an externally mixed aerosol compared to −1.4 W m−2, which we obtained by empirically relating sulfate mass to cloud droplet number. In the case of an internally mixed aerosol, the contribution from increasing carbonaceous and sulfate aerosols is close to being additive as the individual simulations yield an indirect effect of −0.4 W m−2 due to anthropogenic sulfate aerosols and −0.9 W m−2 due to anthropogenic carbonaceous aerosols. The contribution of anthropogenic sulfate to the indirect effect is close to zero if an externally mixed aerosol is assumed, while the contribution of carbonaceous aerosols increases to −1.3 W m−2. The effect of sulfate in the external mixture approach is much smaller than that of carbonaceous aerosols because its burden only increases by a third of that of carbonaceous aerosols and because the mode radius of sulfate is much larger than that of black and organic carbon.
Comparisons of LASE, aircraft, and satellite measurements of aerosol optical properties and water vapor during TARFOX
Authors: Ferrare R. , Ismail S. , Browell E. , Brackett V. , Kooi S. , Clayton M. , Hobbs P. V. , Hartley S. , Veefkind J. P. , Russell P. , Livingston J. , Tanré D. , Hignett P.
Published: September 2002

We examine aerosol extinction and optical thickness from the Lidar Atmospheric Sensing Experiment (LASE), the in situ nephelometer and absorption photometer on the University of Washington C‐131A aircraft, and the NASA Ames Airborne Tracking Sun Photometer (AATS‐6) on the C‐131 A measured during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) over the east coast of the United States in July 1996. On July 17 and 24 the LASE profiles of aerosol extinction and aerosol optical thickness (AOT) had a bias difference of 0.0055 km−1 (10%) and a root‐mean‐square difference of 0.026 km−1 (42%) when compared to corresponding profiles derived from the airborne in situ data when the nephelometer measurements are adjusted to ambient relative humidities. Larger differences for two other days were associated with much smaller aerosol optical thicknesses (July 20) and differences in the locations sampled by the two aircraft (July 26). LASE profiles of AOT are about 10% higher than those derived from the airborne Sun photometer, which in turn are about 10–15% higher than those derived from the airborne in situ measurements. These differences are generally within the error estimates of the various measurements. The LASE measurements of AOT generally agree with AOT derived from both the Along‐Track and Scanning Radiometer 2 (ATSR 2) sensor flown on the European Remote Sensing Satellite 2 (ERS‐2) and from the Moderate‐Resolution Imaging Spectroradiometer (MODIS) airborne simulator (MAS) which flew with LASE on the NASA ER‐2 aircraft. Effective particle sizes derived from the MAS data indicate that the LASE retrievals of AOT are valid for effective particle radii less than 0.4 μm. Variations in the relative humidity derived from the LASE water vapor measurements on July 26 are found to be highly correlated with variations in the effective particle size derived from the MAS.
Brightness temperatures of the lunar surface: Calibration and global analysis of the Clementine long‐wave infrared camera data
Authors: Lawson Stefanie L. , Jakosky Bruce M. , Park Hye‐Sook , Mellon Michael T.
Published: September 2002

The scientific payload on the Clementine spacecraft included a long‐wave infrared (LWIR) camera with a single passband centered at a wavelength of 8.75 μm. The Clementine orbit deviated by ±30° from Sun synchronous, and for two lunar months, dayside nadir‐looking images were obtained near local noon. During the systematic mapping phase of the Clementine mission, approximately 220,000 thermal‐infrared images of the lunar surface were obtained. We have completed the calibration of the LWIR camera. Here we present the various steps involved in the calibration routine and the associated uncertainty analysis. The LWIR calibration routine can be outlined as follows: convert measured data number values to radiance via a calibration equation; subtract a zero‐flux background image from each lunar image; divide by a flatfield frame; identify bad pixels; smooth over only bad pixels; adjust radiances to reflect the absolute calibration; and convert radiances to brightness temperatures via the Planck function. Observed LWIR radiances can be converted to brightness temperatures, which provide information on various physical properties of the lunar surface. We also present here the LWIR global data set. The LWIR data from noontime orbits demonstrate that the Lambertian temperature model of cos1/4(i) is a fair approximation for nadir‐looking temperatures, rather than the cos1/6(i) behavior observed for ground‐based measurements of the full Moon. Deviations from the Lambertian model are likely due to surface roughness effects and variations in infrared emissivity. In addition, the LWIR global data set reveals the dayside lunar thermal emission to be largely governed by albedo and by the solar incidence angle.
Jupiter's visible aurora and Io footprint
Authors: Vasavada Ashwin R. , Bouchez Antonin H. , Ingersoll Andrew P. , Little Blane , Anger Clifford D.
Published: September 2002

Images obtained by the Galileo spacecraft's solid‐state imaging (SSI) system represent the first survey of Jupiter's northern auroral emissions at visible wavelengths and on the nightside of the planet. These images captured the emissions with unprecedented spatial resolutions down to ∼26 km pixel−1. Four classes of emission were observed: (1) a continuous, primary arc associated with the middle/outer magnetosphere, (2) a variable secondary arc associated with the region just beyond Io's torus, (3) diffuse “polar cap” emission, and (4) a patch and tail associated with the magnetic footprint of Io. The primary arc emission occurs at an altitude 245±30 km above the 1‐bar pressure level. Its horizontal width is typically a few hundred kilometers, and its total optical power output varied between ∼1010 and ∼1011 W in observations taken months apart. The location of the primary arc in planetary coordinates is similar to that on dayside images at other wavelengths and does not vary with local time. The morphology of the primary arc is not constant, changing from a multiply branched, latitudinally distributed pattern after dusk to a single, narrow arc before dawn. Emission from Io's ionospheric footprint is distinct from both the primary and secondary arcs. Measurements of its optical power output ranged from 2 to 7×108 W.
Raman spectroscopic characterization of a highly weathered basalt: Igneous mineralogy, alteration products, and a microorganism
Authors: Wang Alian , Jolliff Bradley L. , Haskin Larry A.
Published: September 2002

On‐surface identification of minerals on Mars is likely to depend mainly on observations of rocks and soils as found, without access to fresh surfaces or other sample preparation. Both the original mineralogy of rocks and their alteration mineralogy will be important. To determine the capability of Raman spectroscopy to provide good mineralogical characterization of an altered igneous rock such as might be encountered on Mars, we have analyzed the heavily weathered, exterior surface of a cobble of Keweenawan basalt and compared the results with those from a roughly cut, unpolished interior surface, using a Raman point‐counting method. Despite ubiquitous hematite, a strong Raman scatterer, and despite considerable alteration, original igneous plagioclase and pyroxene were identified and their approximate proportions determined from point‐counting traverses on the original surface of the rock. Saponite, an alteration product, was easily identified on the freshly cut surface but could only occasionally be identified on the weathered surface, where saponite‐rich areas were highly photoluminescent. Amygdular fill gave strong spectra of calcite and thomsonite (a zeolite). Tiny, sparse crustose lichen gave clear spectra of their waxy organic coating. On the basis of the surface Raman spectra alone, the rock could be identified as a mafic rock, probably basaltic, that was hydrothermally altered in an oxidizing environment at a temperature between ∼250 and ∼350°C.
A revised control network for Mercury
Authors: Robinson Mark S. , Davies Merton E. , Colvin Tim R. , Edwards Kathleen
Published: September 2002

An improved control net for Mercury has been completed by utilizing images acquired during the three Mariner 10 flybys in 1974–1975. Relative positional errors within the net are ∼1 km on average, and absolute locations are estimated to be better than 25 km. The analytical triangulation resulted in new values for focal lengths (Camera A: 1493.6 mm; Camera B: 1500.1 mm), W0 (329.548°), and camera orientation angles for 811 images acquired during all three flybys of Mercury.
Surface properties of Mars' polar layered deposits and polar landing sites
Authors: Vasavada Ashwin R. , Williams Jean‐Pierre , Paige David A. , Herkenhoff Ken E. , Bridges Nathan T. , Greeley Ronald , Murray Bruce C. , Bass Deborah S. , McBride Karen S.
Published: September 2002

On December 3, 1999, the Mars Polar Lander and Mars Microprobes will land on the planet's south polar layered deposits near (76°S, 195°W) and conduct the first in situ studies of the planet's polar regions. The scientific goals of these missions address several poorly understood and globally significant issues, such as polar meteorology, the composition and volatile content of the layered deposits, the erosional state and mass balance of their surface, their possible relationship to climate cycles, and the nature of bright and dark aeolian material. Derived thermal inertias of the southern layered deposits are very low (50–100 J m−2 s−1/2 K−1), suggesting that the surface down to a depth of a few centimeters is generally fine grained or porous and free of an appreciable amount of rock or ice. The landing site region is smoother than typical cratered terrain on ∼1 km pixel−1 Viking Orbiter images but contains low‐relief texture on ∼5 to 100 m pixel−1 Mariner 9 and Mars Global Surveyor images. The surface of the southern deposits is older than that of the northern deposits and appears to be modified by aeolian erosion or ablation of ground ice.
Thermal tides and stationary waves on Mars as revealed by Mars Global Surveyor thermal emission spectrometer
Authors: Banfield Don , Conrath Barney , Pearl John C. , Smith Michael D. , Christensen Phil
Published: September 2002

Atmospheric temperature retrievals from thermal emission spectrometer (TES) observed radiances make possible the most complete separation of the constituent wave modes evident in Mars atmosphere to date. We use all of the data from the first aerobraking period as well as the science phasing orbits, which affords good sampling of the diurnal tides and stationary waves. TES retrievals of atmospheric temperature on a grid of pressure levels are the fundamental data set in this study. We then fit this data to selected Fourier modes in longitude and time for altitude, latitude, and Ls bins. From this we have identified the amplitudes and phases of the diurnal and semidiurnal tides, the first few (gravest) stationary waves, and a few modes which arise because of couplings between sun‐fixed tides and topography. We also retrieve estimates of the zonal and time of day mean temperature meridional cross sections and their rates of change. The zonal and time of day mean temperature meridional cross sections agree with those of Conrath et al. [this issue] to within 1 K where we can reliably retrieve this mode (90°S to ∼20°S). Heating rates of up to 2.4 K/sol were observed around three scale heights above 60°S‐90°S during the Ls = 310°–320° dust storm. Diurnal tide amplitudes of greater than 8 K were observed during the Noachis and Ls = 310°–320° dust storms. From Ls = 255°–285° an unexplained phase reversal at two scale heights was observed in the diurnal tide from 60°S‐80°S. Convective penetration above the unstable boundary layer may explain anomalous (180° out of phase with the sun) diurnal tide phases between 0.5 and one scale height above the subsolar point. Semidiurnal tides are of order 2 K throughout the southern extratropics. A stationary mode of wavenumber one was observed with amplitude 1–4 K in the southern extratropics. Topographically coupled tidal modes were also quantified.
Direct measurements of rate coefficients for the reaction of ethynyl radical (C2H) with C2H2 at 90 and 120 K using a pulsed Laval nozzle apparatus
Authors: Lee Seonkyung , Samuels David A. , Hoobler Ray J. , Leone Stephen R.
Published: September 2002

Rate coefficients for the reaction C2H + C2H2 → C4H2 + H are measured at 90 and 120 K by using a new pulsed Laval nozzle apparatus equipped with laser ionization, time‐of‐flight mass spectrometric detection. The C2H radicals are generated by 193 nm laser photolysis of C2H2, and the reaction product, C4H2, is directly detected by single‐photon ionization at 118 nm (10.5 eV). Rate coefficients of (2.7±0.5) × 10−10 and (2.5±0.4) × 10−10 cm3 molecule−1 s−1 are obtained at 90 and 120 K, compared to the room temperature value of 1.3×10−10 cm3 molecule−1 s−1. The results show a significant negative temperature dependence of the reaction rate coefficient below room temperature. The implications for models of planetary atmospheres, such as for Titan, are discussed.
Variations of terrestrial input and marine productivity in the Southern Ocean (48°S) during the last two deglaciations
Authors: Ikehara Minoru , Kawamura Kimitaka , Ohkouchi Naohiko , Murayama Masafumi , Nakamura Toshio , Taira Asahiko
Published: September 2002

Various biomarkers (n‐alkanes, n‐alcohols, and sterols) have been studied in a piston core TSP‐2PC taken from the Southern Ocean to reconstruct the paleoenvironmental changes in the subantarctic region for the last two deglaciations. Mass accumulation rates of terrestrial (higher molecular weight n‐alkanes and n‐alcohols) and marine (dinosterol and brassicasterol) biomarkers increased significantly at the last two glacials and stayed low during interglacial peaks (early Holocene and the Eemian). These records indicate that the enhanced atmospheric transport of continental materials and the increased marine biological productivity were synchronously linked in the Southern Ocean at the last two glacials. This suggests that increased glacial dust inputs have relieved iron limitation in the subantarctic Southern Ocean. These two processes, however, were not linked at the cooling phase from the Eemian to marine isotope stage (MIS) 5d. During this period, paleoproductivity may have been influenced by the latitudinal migration of the high‐production zone associated with the Antarctic Polar Front.
Foraminiferal responses to major Pleistocene paleoceanographic changes in the southern South China Sea
Authors: Jian Zhimin , Wang Pinxian , Chen Min‐Pen , Li Baohua , Zhao Quanhong , Bühring Christian , Laj Carlo , Lin Hui‐Ling , Pflaumann Uwe , Bian Yunhua , Wang Rujian , Cheng Xinrong
Published: September 2002

A detailed age model for core 17957‐2 of the southern South China Sea was developed based on δ18O, coarse fraction, magnetostratigraphy, and biostratigraphy for the last 1500 kyr. The δ18O record has clear ∼100‐kyr cycles after the Mid‐Pleistocene Revolution (MPR) at the entrance of marine isotopic stage (MIS) 22. Planktonic foraminifera responded to the MPR immediately, showing the increased sea surface temperature (SST) and dissolution after the MPR. Benthic foraminifera did not respond to it until the Brunhes/Matuyama boundary. Since the MPR, the depth of thermocline gradually became shallower until MISs 6–5. This major change within MISs 6–5 was also reflected in the decreased SSTs and increased productivity and Deep Water Mass. Thus two major Pleistocene paleoceanographic changes were found: One was around the MPR; the other occurred within MISs 6–5, which speculatively might be ascribed to the reorganization of surface and deep circulation, possibly induced by tectonic forces.
Last glacial and meltwater interbasin water exchanges and sedimentation in the World Ocean
Authors: Seidov Dan , Haupt Bernd J.
Published: September 2002

Modeling the global ocean thermohaline conveyor at present, at the Last Glacial Maximum, and at a subsequent meltwater event is revisited using a combination of an ocean global circulation model and a sediment transport model. The modeled changes of sediment deposition rates, linked to the changes of the global deep‐ocean thermohaline circulation, provide a better understanding of the glacial‐to‐interglacial variability of thermohaline currents, and help to identify the regions of the world ocean that are most sensitive to the glacial and meltwater impacts. In addition to the well‐known local changes of the conveyor in the Atlantic Ocean during the last glaciation and subsequent meltwater events, the simulations show the global character of these impacts, detected as far from the North Atlantic as the Indian and the southwestern Pacific Oceans. However, the numerical experiments challenge the idea of a global conveyor‐like deep flow strongly connecting the surface waters of northern parts of the North Atlantic and North Pacific Oceans at either glacial or meltwater intervals.
Rigorous analysis of frequency selective surfaces of finite extent using a hybrid finite difference time domain–boundary integral equation technique
Authors: Rogier Hendrik , De Zutter Daniël , Olyslager Frank
Published: September 2002

A hybrid finite difference time domain–boundary integral equation approach is used to model frequency selective surfaces of finite extent. Using the finite difference time domain technique, a system matrix is constructed for a box enclosing all relevant features within a unit cell. The open character of the finite frequency selective surface is modeled by coupling a boundary integral equation formulation to the system matrix found with the finite difference time domain approach. A number of relevant examples are studied, and a comparison is made between our new technique and the more classical finite difference time domain technique or the hybrid finite element–boundary integral equation method.