bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic and acoustic signals detected at Lo'ihi Seamount by the Hawai'i Undersea Geo‐Observatory
Authors: Caplan‐Auerbach J. , Duennebier F.
Published: February 2004

The Hawai'i Undersea Geo‐Observatory (HUGO) is an ocean bottom observatory located on the summit of Lo'ihi seamount, Hawai'i. An electro‐optical cable connects the HUGO junction box to a shore station on the Big Island of Hawaii, thereby enabling the first real‐time monitoring of a submarine volcano. HUGO was active for 3 months in 1998, collecting nearly continuous, real‐time data on a high‐rate hydrophone. Signals detected during that time include local as well as teleseismic earthquakes, T phases from Pacific‐wide earthquakes, landslides on the submarine flank of Kilauea, and eruption sounds from the current Kilauea eruption. The data do not indicate a Lo'ihi eruption during the time that HUGO was active. The variety and quality of signals detected by the HUGO hydrophone confirms that a real‐time observatory can serve a valuable role in studies of oceanic acoustics, local and teleseismic earthquakes, and submarine eruption mechanics.
Subminute measurements of SO2 at low parts per trillion by volume mixing ratios in the atmosphere
Authors: Jr Dennis K. Nicks , Benner Richard L.
Published: February 2004

The continuous sulfur dioxide detector (CSD) is a sensitive instrument for reliable measurements at high time resolution in the atmosphere. This new instrument is based on a SO2 measurement technique utilizing the sulfur chemiluminescence detector, previously validated in a rigorously blind experiment sponsored by the National Science Foundation. Simplified sample handling, dénuder separation technology, and the intrinsic sensitivity and fast response of the detector permit measurement at levels below 100 parts per trillion by volume in tens of seconds with the CSD. The CSD provides a differential measurement where response from ambient SO2 is determined by the difference between air containing SO2 and air scrubbed of SO2, where both air samples contain other detectable sulfur species. Digital signal post processing with phase‐locked amplification of the detector signal enhances the precision and temporal resolution of the CSD. Oversampling of the detector signal at 10 Hz permits subsequent data retrieval to be adapted to changing ambient levels by either enhancing signal to noise when sulfur dioxide levels are low or by maximizing temporal resolution of derived data when levels are high. he instrument has advantages over existing instruments based on Chromatographie separation in that the CSD provides accurate and reliable measurements at low parts per trillion by volume sulfur dioxide with high time resolution. The CSD is compact and automated and does not require cryogenic materials, making this instrument suitable for remote field locations. The high temporal resolution, specificity for SO2, and sensitivity of the CSD make it a good candidate for installation on an aircraft. Airborne studies of SO2 with a sensitive, fast time response instrument may offer new insight into the understanding of phenomena such as gas‐to‐particle conversion, long‐range transport of pollutants, and the oxidation of biogenically produced sulfur gases.
NOAA/CSIRO Flask Air Intercomparison Experiment: A strategy for directly assessing consistency among atmospheric measurements made by independent laboratories
Authors: Masarie K. A. , Langenfelds R. L. , Allison C. E. , Conway T. J. , Dlugokencky E. J. , Francey R. J. , Novelli P. C. , Steele L. P. , Tans P. P. , Vaughn B. , White J. W. C.
Published: February 2004

Since 1992, the National Oceanic and Atmospheric Administration (NOAA), Climate Monitoring and Diagnostics Laboratory of the United States and the Commonwealth Scientific and Industrial Research Organization (CSIRO), Division of Atmospheric Research of Australia have routinely analyzed the same air sample collected biweekly at Cape Grim, Tasmania. Comparisons of measurements of atmospheric CO2, CH4, CO, H2, and the stable isotopes of CO2 (δ13C, δ18O) are used to assess the consistency of observations independently made by the two laboratories. Results demonstrate that conventional intercomparison strategies based on occasional exchange of high‐pressure cylinders are not sufficient to ensure adequate comparability between flask data records. The NOAA/CSIRO flask air intercomparison experiment has higher time resolution and captures artifacts that are specific to flask measurements. This ongoing experiment provides a stringent quality control test of individual laboratories' experimental methods and internal calibration schemes, and is a valuable tool in working toward reliable integration of atmospheric data from independent laboratories. Results from the first 7 years of this intercomparison show that NOAA and CSIRO Cape Grim measurement records of CH4 are consistent to within 1 nmol mol−1 (0.04%) and the CO2 records to ∼0.2 μmol mol−1 (0.06%). CH4 and CO2 observations from the two programs may be combined into more extensive data sets for specific purposes. Several causes of the observed differences in the measurements of δ13C and δ18O Of CO2 have been identified and independently corroborated; combined data sets of these isotopomers appear possible. Possible explanations are provided for the observed differences in measurements of CO and H2 from the same sample, which show significant variability with time.
Spectral analysis of QuikSCAT surface winds and two‐dimensional turbulence
Authors: Patoux Jérôme , Brown Robert A.
Published: February 2004

A spectral decomposition of QuikSCAT surface wind vectors reveals different levels of variance and different values of the spectral slope in various regions of the world ocean for the 12 months investigated. The traditional considerations on the factors affecting the shape of the spectra are reviewed and compared to the results. In particular, the influence of large‐scale synoptic systems is shown by comparing the steeper and more energetic spectra of the midlatitudes to the shallower spectra of the tropics. Similarly, the signature of convection is investigated by comparing spectra in the tropical convectively active and dry zones of the Pacific Ocean. Spectra of vorticity and divergence are calculated, along with spectral vorticity‐to‐divergence ratios. Their spatial and temporal variations are discussed. It is hypothesized that when convection is enhanced in the tropics, the spectral analysis captures the mesoscale/synoptic structures in which convection is embedded and that the spectra exhibit some of the characteristics of their midlatitude counterparts (i.e., steeper and more energetic).
Satellite observations of the southeast Pacific intertropical convergence zone during 1993–1998
Authors: Halpern David , Hung Chih‐Wen
Published: February 2004

An intertropical convergence zone in the southeast Pacific Ocean is described from monthly mean 1° × 1° ocean vector wind, rainfall, sea surface temperature, and integrated water vapor measurements recorded from satellites. Time interval of the investigation was January 1993 to December 1998, when ocean and atmosphere conditions during 1993–1996 were normal compared to the 1997–1998 El Niño. The southeast Pacific intertropical convergence zone (SITCZ) occurred in March‐April at 8°S–2°S, 130°W–90°W. During 1993–1996 the average March‐April values of SITCZ surface wind convergence, rain rate, sea surface temperature, and integrated water vapor were 3.3 × 10−6 s−1, 3.3 mm d−1, 27.3°C, and 45.3 mm, respectively. A statistical model of the monthly mean observations predicted rainfall greater than the 2 mm d−1 threshold when surface wind convergence was greater than the 1.5 × 10−6 s−1 threshold and sea surface temperature was above 27°C. During non‐El Niño conditions, SITCZ sea surface temperature was greater than sea surface temperature in the 2°S–2°N equatorial band, with maximum difference in March–April which would create a surface wind convergence larger in March‐April compared to other months. The Intertropical Convergence Zone (ITCZ), which occurred north of the equator throughout the year, and the SITCZ were separated by divergent wind, low (<2 mm d−1) rainfall, and cold (<27°C) surface water, except during the intense 1998 El Niño. The rain rate of the ITCZ was minimum in March‐April during 1993–1996 and comparable to the SITCZ rain rate.
Effects of glacial meltwater in the GISS coupled atmosphereocean model: 1. North Atlantic Deep Water response
Authors: Rind D. , deMenocal P. , Russell G. , Sheth S. , Collins D. , Schmidt G. , Teller J.
Published: February 2004

Varying magnitudes of freshwater input through the St. Lawrence are added to different versions of the GISS coupled atmosphere‐ocean model. The results show a generally linear response in percentage North Atlantic Deep Water (NADW) reduction to the volume of water added without any obvious threshold effects. When the estimated best guess freshwater input for the Allerod‐Younger Dryas interval is added, only small reductions in NADW production occur in less than a century, with complete cessation requiring more than 300 years. If the ocean circulation was weaker in the Allerod preceding the Younger Dryas, somewhat larger percentage reductions occur, and it would take 150–200 years for a complete shutdown. The freshening is aided by a positive feedback associated with the reduction in evaporation relative to precipitation in the North Atlantic, amounting to some 20–30% of the added freshwater runoff. When the freshwater input is stopped after complete NADW shutdown, NADW production does not resume. With complete NADW cessation, cooling eventually occurs throughout the Northern Hemisphere, including regions where it is not thought to have arisen during the Younger Dryas, and the globe cools by 1°C due primarily to the sea ice albedo feedback; while in many regions the observed cooling is reproduced, the cooling in Greenland is much less than is estimated. With only 50% NADW cessation, cooling is primarily around the North Atlantic. No rapid warming is seen in response to freshwater cessation. The sensitivity displayed here for NADW reduction due to freshwater input from the St. Lawrence is roughly similar to that associated with increased precipitation accompanying global warming in the next century, so a similar sensitivity may arise with Younger Dryas freshwater inputs from other suspected locations (Greenland, Europe).
Understanding trends in stratospheric NOy and NO2
Authors: McLinden C. A. , Olsen S. C. , Prather M. J. , Liley J. B.
Published: February 2004

Nitrous oxide (N2O), an important greenhouse gas, has been increasing since 1980 at a rate of about +3% per decade. Recently, a notably greater rate of increase of about +5% per decade since 1980 was reported for measurements of stratospheric nitrogen dioxide (NO2) over Lauder, New Zealand. Since N2O is the dominant source of odd‐nitrogen compounds in the stratosphere, including NO2, this presents an obvious conundrum. Analysis here shows that these apparently conflicting trends are generally consistent when viewed in a global‐change framework, specifically, when concurrent trends in stratospheric ozone and halogens are included. Using a combination of photochemical and three‐dimensional chemistry‐transport models, we predict a 1980–2000 trend in the NO2, as measured over Lauder, New Zealand, of +4.3%/decade when these concurrent trends are considered. Of this, only +2.4%/decade is attributed directly to the increase in N2O; the remainder includes +2.5%/decade due to the ozone change and −0.6%/decade to the increased halogens' impact on odd‐nitrogen partitioning. The slant column densities of NO2, as measured from the zenith scattered sunlight during twilight, are found to (1) overestimate the trend by +0.4%/decade as compared to the true vertical column densities and (2) display a diurnally varying trend with a maximum during the night and large gradients through sunrise and sunset in good agreement with measurement. Nonetheless, measurements such as these are essential for identifying global change and provide a lesson in understanding it: careful simulation of the time, location, and geometry of measurements must be combined with concurrent trends in related chemical species and climate parameters.
Onset, extent, and duration of dehydration in the southern hemisphere polar vortex
Authors: Stone Elizabeth M. , Tabazadeh Azadeh , Jensen Eric , Pumphrey Hugh C. , Santee Michelle L. , Mergenthaler John L.
Published: February 2004

Satellite observations of water vapor and aerosol extinction along with temperature trajectory calculations are analyzed for the Southern Hemisphere winter of 1992 in order to determine the onset, extent, and duration of dehydration within the polar vortex. Our investigation uses measurements of water vapor from the Microwave Limb Sounder (MLS) and aerosol extinction from the Cryogenic Limb Array Etalon Spectrometer (CLAES), both on board the Upper Atmosphere Research Satellite (UARS). Evidence of persistent ice cloud formation, supported by temperature statistics obtained from air parcel trajectories, suggests that the onset of the dehydration process occurs between late June and early July. By late August‐early September water vapor depleted areas within the vortex no longer coincide with high aerosol extinctions, indicating that severe dehydration has occurred with the irreversible removal of water vapor over vast areas. Areas with depleted levels of water vapor, below the prewinter values, persist well into November. Evidence for dehydration is found on potential temperature surfaces from 420 K (the lower limit of the MLS measurements) to 520 K (approximately 16 to 22 km). The horizontal extent of the dehydrated area at 465 K encompasses up to 35% of the total vortex area equatorward of 80°S. A comparison of CLAES aerosol extinction measurements and model calculations of aerosol extinction suggests an average ice particle number concentration and size of 10−2–10−3 cm−3 and 10–30 μm, respectively. We show that the difference between the timing of the onset of dehydration found here and that in a recent analysis of Polar Ozone and Aerosol Measurement III (POAM) observations can be explained by the latitudinal sampling pattern of the POAM instrument.
Eddy covariance measurements of oxygenated volatile organic compound fluxes from crop harvesting using a redesigned proton‐transfer‐reaction mass spectrometer
Authors: Karl Thomas , Guenther Alex , Lindinger Christian , Jordan Alfons , Fall Ray , Lindinger Werner
Published: February 2004

A redesigned proton‐transfer‐reaction mass spectrometer was deployed in the field to measure atmospheric fluxes of volatile organic compounds (VOCs) released following the cutting and drying of hay. The instrument has a fast response, around 0.1 s, allowing use of the eddy covariance technique. Measurements were done over a 3‐day period in a hay field in the eastern part of Tirol, Austria, in the early growing season and are compared to earlier results obtained using a slower‐response instrument in the late growing season [Karl et al., 2000]. Peak upward fluxes of the order of 9.9 × 10−6g m−2 s−1 for methanol, 1.5 × 10−6g m−2 s−1 for acetaldehyde, and 1.5 × 10−6g m−2 s−1 for the sum of hexenals, hexenols, hexanal, pentenols, 3‐methylbutanal, and butanone were observed during and after harvesting. Time‐integrated values for the first day were of the order of 65±20 mg m−2 (130±40 μg per gram dry weight(gdw)−1) for methanol and 13±4 mg m−2 (26±8 μg gdw−1) for acetaldehyde. VOC fluxes measured in this study were generally higher than in August 1999, which can be explained by higher temperatures and higher photosynthetic productivity. Good agreement with another means for estimating VOC fluxes, the surface gradient method, was achieved. This paper presents measurements of eddy covariance for a wide variety of oxygenated VOCs and shows that hay harvesting can influence the local air quality in many regions in the Alps on a short‐term basis.
On the performance of numerical solvers for a chemistry submodel in three‐dimensional air quality models: 1. Box model simulations
Authors: Huang Ho‐Chun , Chang Julius S.
Published: February 2004

The performance of numerical techniques in solving differential equations of the gas phase chemistry submodel (i.e., the chemical solver) is one of the most important factors in determining the overall computational cost for a three‐dimensional (3‐D) Air Quality Model (AQM). The estimated performance of a chemical solver in an AQM is often obtained by using simple box model analysis. In the present work some essential characteristics of the computational environment of any AQM, the operator splitting technique, have been identified and shown that different evaluation procedures will result in different conclusions for the relative performances of chemical solvers. A new box model evaluation procedure incorporating the impact of operator splitting has been designed to better mimic the true performances of various chemical solvers. Among the chemical solvers tested, the Hertel solver has the best overall performance and is the most robust in dealing with diverse computational environments.
Intercontinental transport of ozone and its precursors in a three‐dimensional global CTM
Authors: Wild Oliver , Akimoto Hajime
Published: February 2004

The coupling of chemistry with atmospheric transport processes provides a mechanism for local and regional pollution from heavily populated continental regions to influence tropospheric composition at hemispheric and global scales. In this study we use the FRSGC/UCI 3‐D chemical transport model to quantify the impact of ozone precursors from anthropogenic sources in the United States, Europe, and East Asia on regional and global ozone budgets and to identify the key controlling processes. We find that the East Asian region has the greatest potential to affect tropospheric ozone due, principally, to efficient vertical transport but that Europe experiences the greatest intercontinental effects due to rapid, short‐distance transport from North America. In addition to significant boundary layer ozone production in each region, we find that 25–40% of the total net regional production occurs above 730 hPa in the free troposphere and that on a hemispheric scale, 70–85% of ozone from anthropogenic sources in the upper troposphere, above 400 hPa, is due to in situ chemistry rather than direct vertical transport. Increased surface ozone concentrations over remote continents are largest in spring and autumn at northern midlatitudes; while this seasonality is driven by horizontal transport in the free troposphere followed by subsidence, boundary layer and upper tropospheric chemical production make a substantial contribution. Although the effects are greatest in periodic episodes when meteorological conditions are favourable, there is significant enhancement in background ozone concentrations. We suggest that increasing emissions will significantly impact the oxidizing capacity of the troposphere by leading to greater polarization between ozone production and destruction environments.
Nitrous oxide emission from soil of the Mata Atlantica, Rio de Janeiro State, Brazil
Authors: Maddock John E. L. , dos Santos M. Bernadete P. , Prata Katia R.
Published: February 2004

Emissions of nitrous oxide by the soils of the Mata Atlantica subtropical forest were measured, on 21 days spread over one year, using a static chamber technique with natural flux calculation from nonlinear curves of chamber concentration versus time. The average of measured fluxes was 4.8 ng N Cm−2h−1 (n = 131). Emission rates increased by an order of magnitude during and after rainfall, and a mean flux from this environment, weighted for mean weather conditions, was estimated as 3.6 ng N cm−2h−1. These fluxes are comparable to others reported for humid tropical forests, among the highest for any environment.
Clear‐sky albedo measurements on a sloping glacier surface: A case study in the Bolivian Andes
Authors: Sicart Jean Emmanuel , Ribstein Pierre , Wagnon Patrick , Brunstein Daniel
Published: February 2004

An important potential source of error in snow albedo measurements under clear sky is the tilt of the surface when the sensors are placed parallel to the horizon. The error depends on the surface slope and aspect. A hemispherical radiation sensor receives its signal from within a surface area of several square meters, which generally is not a plane. Here we examined the influence of slope and aspect combinations related to surface irregularities on albedo measurements at two locations on the Zongo Glacier, Bolivia. The slope and aspect distributions determined through topographic measurements were used to correct the albedo measurements. The corrections were different between the two sites but resulted in similar albedo changes: the substantial albedo reductions observed from morning until evening were measurement artifacts. Even for slight slopes, an error of a few degrees on the slope estimation or an error of roughly 20° on the aspect estimation had an appreciable influence on the corrections. If the topography around the measurement site is not precisely known, the most reliable method for determining the daily albedo is to observe the measurements around solar noon. Corrected albedo diurnal variations were low and symmetrical, centered on a minimum at noon. During the dry season (the Southern Hemisphere winter), the diurnal fluctuations of the snow albedo on the Zongo Glacier seem to be controlled by the incidence angle cycle of solar radiation.
Imprint of large‐scale atmospheric transport patterns on sea‐salt records in northern Greenland ice cores
Authors: Fischer Hubertus
Published: February 2004

The decadal to interannual variability of sea‐salt aerosol concentrations in northern Greenland ice cores is investigated and contrasted to meteorological reanalysis data over the time span 1959–1993. Correlation analysis with average data on sea level pressure and geopotential height at the 500 mbar level identifies the eastern and northeastern Pacific region as the most important center of action responsible for variations in sea‐salt aerosol export onto the Greenland ice sheet which is related to the Pacific/North American teleconnection pattern. The Atlantic region, however, appears to be of secondary importance only. Correlation coefficients are highest during the first quarter of the year but also significant for annual pressure data, explaining ∼20% of the sea‐salt variance in the ice cores. Furthermore, higher storm activity in the Pacific center of action, as well as in the northern Atlantic, leads to higher sea‐salt concentrations in northern Greenland, explaining about 40% and 17% of the ice core variance. A 30% increase during the nineteenth century in a 600 year sea‐salt record from northeastern Greenland may be interpreted, at least in part, as an enhancement of sea‐salt export from the Pacific region during that time.
Evolution of the Arctic stratospheric aerosol mixing ratio measured with balloon‐borne aerosol backscatter sondes for years 1988–2000
Authors: Suortti T. , Karhu J. , Kivi R. , Kyrö E. , Rosen J. , Kjome N. , Larsen N. , Neuber R. , Khattatov V. , Rudakov V. , Yushkov V. , Nakane H.
Published: February 2004

Balloon‐borne aerosol backscatter measurements were made at 12 Arctic stations as part of a polar stratospheric cloud study. The record starts in 1988, which is well before the eruption of Mount Pinatubo in the beginning of June 1991, and continues to 2000. These measurements provide absolutely calibrated in situ detection of atmospheric aerosols with simultaneous measurements of pressure, temperature, relative humidity, and O3 partial pressure. The instrument is also capable of operating during cloudy conditions, which may be considered as an advantage compared with lidar measurements. Even though backscatter soundings represent the state of the atmosphere at the sounding time and site, we demonstrate here that with a limited, homogeneous set of measurements it is possible to effectively study the time development of atmospheric aerosol loading. The initial aim of the study has been to define the general features of aerosol distribution in the Arctic winter troposphere and stratosphere and then to document the perturbation in the lower stratospheric aerosols caused by the eruption of Mount Pinatubo and, in addition, to infer the background state of lower stratospheric aerosol loading during the pre‐ and post‐Pinatubo conditions. Our measurements suggest that the e‐folding time for the decaying volcanic aerosol intrusion was ∼0.7 year and the full recovery of the Arctic lower stratosphere from the Mount Pinatubo perturbation was roughly 5 years.
Radiance and Jacobian intercomparison of radiative transfer models applied to HIRS and AMSU channels
Authors: Garand L. , Turner D. S. , Larocque M. , Bates J. , Boukabara S. , Brunel P. , Chevallier F. , Deblonde G. , Engelen R. , Hollingshead M. , Jackson D. , Jedlovec G. , Joiner J. , Kleespies T. , McKague D. S. , McMillin L. , Moncet J.‐L. , Pardo J. R. , Rayer P. J. , Salathe E. , Saunders R. , Scott N. A. , Van Delst P. , Woolf H.
Published: February 2004

The goals of this study are the evaluation of current fast radiative transfer models (RTMs) and line‐by‐line (LBL) models. The intercomparison focuses on the modeling of 11 representative sounding channels routinely used at numerical weather prediction centers: 7 HIRS (High‐resolution Infrared Sounder) and 4 AMSU (advanced microwave sounding unit) channels. Interest in this topic was evident by the participation of 24 scientists from 16 institutions. An ensemble of 42 diverse atmospheres was used and results compiled for 19 infrared models and 10 microwave models, including several LBL RTMs. For the first time, not only radiances but also Jacobians (of temperature, water vapor, and ozone) were compared to various LBL models for many channels. In the infrared, LBL models typically agree to within 0.05–0.15 K (standard deviation) in terms of top‐of‐the‐atmosphere brightness temperature (BT). Individual differences up to 0.5 K still exist, systematic in some channels, and linked to the type of atmosphere in others. The best fast models emulate LBL BTs to within 0.25 K, but no model achieves this desirable level of success for all channels. The ozone modeling is particularly challenging. In the microwave, fast models generally do quite well against the LBL model to which they were tuned. However, significant differences were noted among LBL models. Extending the intercomparison to the Jacobians proved very useful in detecting subtle or more obvious modeling errors. In addition, total and single gas optical depths were calculated, which provided additional insight on the nature of differences.
Accounting for the effects of volcanoes and ENSO in comparisons of modeled and observed temperature trends
Authors: Santer B. D. , Wigley T. M. L. , Doutriaux C. , Boyle J. S. , Hansen J. E. , Jones P. D. , Meehl G. A. , Roeckner E. , Sengupta S. , Taylor K. E.
Published: February 2004

Several previous studies have attempted to remove the effects of explosive volcanic eruptions and El Niño‐Southern Oscillation (ENSO) variability from time series of globally averaged surface and tropospheric temperatures. Such work has largely ignored the nonzero correlation between volcanic signals and ENSO. Here we account for this collinearity using an iterative procedure. We remove estimated volcano and ENSO signals from the observed global mean temperature data, and then calculate trends over 1979–1999 in the residuals. Residual trends are sensitive to the choice of index used for removing ENSO effects and to uncertainties in key volcanic parameters. Despite these sensitivities, residual surface and lower tropospheric (2LT) trends are almost always larger than trends in the raw observational data. After removal of volcano and ENSO effects, the differential warming between the surface and lower troposphere is generally reduced. These results suggest that the net effect of volcanoes and ENSO over 1979–1999 was to reduce globally averaged surface and tropospheric temperatures and cool the troposphere by more than the surface. ENSO and incomplete volcanic forcing effects can hamper reliable assessment of the true correspondence between modeled and observed trends. In the second part of our study, we remove these effects from model data and compare simulated and observed residual trends. Residual temperature trends are not significantly different at the surface. In the lower troposphere the statistical significance of trend differences depends on the experiment considered, the choice of ENSO index, and the volcanic signal decay time. The simulated difference between surface and tropospheric warming rates is significantly smaller than observed in 51 out of 54 cases considered. We also examine multiple realizations of model experiments with relatively complete estimates of natural and anthropogenic forcing. ENSO and volcanic effects are not removed from these integrations. As in the case of residual trends, model and observed raw trends are in good agreement at the surface but differ significantly in terms of the trend differential between the surface and lower troposphere. Observed and simulated lower tropospheric trends are not significantly different in 17 out of 24 cases. Our study highlights the large uncertainties inherent in removing volcano and ENSO effects from atmospheric temperature data. It shows that statistical removal of these effects improves the correspondence between modeled and observed temperature trends over the satellite era. Accounting for volcanoes and ENSO cannot fully explain the observed warming of the surface relative to the lower troposphere, or why this differential warming is not reproduced in the model simulations considered here.
Spatial and temporal distribution of enhanced boundary layer BrO concentrations measured by the GOME instrument aboard ERS‐2
Authors: Wagner T. , Leue C. , Wenig M. , Pfeilsticker K. , Platt U.
Published: February 2004

The temporal and spatial distribution of enhanced boundary layer BrO concentrations in both hemispheres during 1997 is presented using observations of the Global Ozone Monitoring Experiment (GOME) on board the European research satellite ERS‐2. BrO concentrations (up to 50 ppt) are the major cause for catalytic boundary layer ozone destruction typically observed during polar spring in both hemispheres. While autocatalytic mechanisms are most probably responsible for the release of the observed high concentrations of reactive bromine compounds, uncertainties still remain with respect to the primary release mechanisms and whether the autocatalytic reactions are taking place on sea‐salt aerosol or the surface of sea ice. We find that enhanced boundary layer BrO concentrations correlate very well with ozone depletion events. Enhanced BrO concentrations are always found over or near to areas of frozen salt water (above sea ice or also above the frozen surface of the Caspian Sea) consistent with the assumption that such conditions are a prerequisite for the autocatalytic release of high BrO concentrations to the troposphere.
Retrieval of stratus cloud microphysical parameters using millimeter‐wave radar and visible optical depth in preparation for CloudSat: 1. Algorithm formulation
Authors: Austin Richard T. , Stephens Graeme L.
Published: February 2004

A new retrieval of stratus cloud microphysical parameters is developed based on measurements of millimeter‐wave radar reflectivity and visible optical depth. The retrieval assumes a lognormal distribution of cloud droplets with no significant amounts of drizzle. The retrieval is formulated in an estimation theory framework, allowing the inclusion of a priori information. This formulation provides quantitative measures of uncertainty in the retrieved quantities and the relative influence of the measurements and a priori data. A radar‐only version of the retrieval is described and compared with an analogous radar‐only retrieval that does not use an estimation theory approach. The retrievals are shown to agree in the limiting case of infinite a priori uncertainty and negligible measurement and forward model uncertainty. The estimation theory formulation is readily expanded to allow the inclusion of additional data streams. The planned formation flight of CloudSat, ESSP3 (formerly PICASSO‐CENA), and Aqua will provide numerous opportunities for the development of combined algorithms using this technique.
Analysis of 200 mbar zonal wind for the period 1958–1997
Authors: Pielke R. A. , Chase T. N. , Kittel T. G. F. , Knaff J. A. , Eastman J.
Published: February 2004

The value of the analyses of the 200 mbar zonal winds is proposed as a particularly effective tool to assess variability and trends in atmospheric circulation. Using the thermal wind relation, the 200 mbar zonal wind results from the vertically integrated north‐south temperature gradient between the Earth's surface and 200 mbar. We found a tendency for the 200 mbar winds to become somewhat stronger at higher latitudes since 1958.
On the formation of HNO3 in the Antarctic mid to upper stratosphere in winter
Authors: de Zafra Robert , Smyshlyaev Sergei P.
Published: February 2004

We address the previously unresolved puzzle of nitric acid formation in the polar winter mid to upper stratosphere, first indicated by Limb Infrared Monitor of the Stratosphere observations in the Arctic winter of 1978–1979. Several theoretical studies over the past 2 decades have tried to reproduce these observations with varying success. More recently, the onset, altitude range, and duration of the formation process have been clarified by the Cryogenic Limb Array Etalon Spectrometer onboard UARS and by a series of ground‐based observations taken at the South Pole during the Antarctic winters of 1993, 1995, and 1999. Using the Stony Brook‐SSt. Petersburg two‐dimensional photochemical model, we have reexplored HNO3 formation via both the ion cluster chemistry and heterogeneous chemistry on sulfate aerosols considered by earlier investigators. By including what we believe to be a realistic flux of NOy from the mesosphere, we find that the model can generate observed mixing ratios through a combination of ion‐clusterenhanced chemistry in the upper to mid stratosphere, augmented by heterogeneous chemistry on sulfate aerosol below ∼40 km. Results are presented which clarify the relative role of various processes and assumed NOy fluxes. These also point up the need to incorporate more accurate downward NOy fluxes in models being used to simulate the polar stratosphere. Finally, we emphasize the need to consider the influence of repartitioning of NOy or NOx into HNO3 before observed variations in amounts of the former reaching the mid to lower stratosphere in winter and early spring can properly be used as tracers to reflect variations in thermospheric‐mesospheric NOy production or transport.
Total ozone trends in the tropics
Authors: Sahai Y. , Kirchhoff V. W. J. H. , Lerne N. M. Paes , Casiccia C.
Published: February 2004

Measurements with Dobson spectrophotometers are used to study ozone trends at Cachoeira Paulista (22.7°S, 45.0°W) and Natal (5.8°S, 35.2°W) in Brazil. The time series are from 1974 to 1997 for Cachoeira Paulista and from 1978 to 1997 at Natal. Using a model that accounts for the quasi‐biennial oscillation, seasonal variation, and solar cycle, a trend in total ozone of −2.0±1.2% per decade was found at Cachoeira Paulista for the period 1974 to 1997. At Natal the trend was −0.8±0.8% per decade over the period 1978 to 1997. The annual values of column ozone reported at Cachoeira Paulista are lower in the 1990's than in the previous two decades: total ozone amounts are 12.5 Dobson units (DU), or 4.6%, lower in the 1990s than those observed during the 1970s. From a monthly analysis it is shown that these ozone decreases have occurred in all months of the year. There was no statistically significant change between the 1980s and 1990s at Natal.
Gas‐Phase Sulfur Intercomparison Experiment 2: Analysis and conclusions
Authors: Crosley David R. , Goldan Paul D. , Nicks Dennis K. , Benner Richard L. , Farwell Sherry O. , MacTaggart Douglas L. , Bamsberger W. Lee
Published: February 2004

A diffusion denuder, total sulfur chemiluminescence detector instrument for the measurement of SO2 was tested as the second part of the Gas‐Phase Sulfur Intercomparison Experiment (GASIE 2). The SO2 at mixing ratios between 27 and 182 parts per trillion by volume (pptv) was provided by a dynamic dilution apparatus. The data were kept blind from the other party and analyzed by two independent referees. The following was concluded: (1) The independent calibrations of each system are within a few percent. (2) The precision on any one day is better than day‐to‐day variability. (3) Runs in dry air show a small but significant nonzero intercept in correlation plots. (4) No effects of adding NO2 + O3 or CO2 + CH4 + CO + dimethylsulfide are distinguishable. (5) A small but significant effect due to added H2O is evident in both slope and intercept, but the source could not be discerned. (6) On any one day the systems can distinguish among 0, 20, and 40 pptv, but because of day‐to‐day variability, they can only distinguish among 0, 30, and 60 pptv on different days.
Correlation between continental air mass and ozone concentrations
Authors: Pont Véronique , Fontan Jacques
Published: February 2004

High ozone concentrations are observed in late spring and summer during anticyclonic situations. Much of the ozone is the result of a photochemical production on a large scale due to the presence of precursors NOx, CO and HC, while the air mass is moving over polluted areas. Daily concentration minima of radon, a radioactive gas emitted from the ground, can be considered as a good tracer of the continental character of the air mass. Correlation between daily maxima of ozone and daily minima of radon is analysed. Positive correlations are observed in summer, strengthening the hypothesis of ozone formation on a large scale (the half‐life of radon is 3.8 days). On the other hand, in winter, daily minima of radon and daily maxima of ozone are negatively correlated. During this season, deposition and chemical destruction of ozone seem to be more significant than production while the air mass is moving over the continent.
Nadir sensitivity of passive millimeter and submillimeter wave channels to clear air temperature and water vapor variations
Authors: Klein Marian , Gasiewski Albin J.
Published: February 2004

The upwelling microwave‐to‐submillimeter wave brightness temperature observed from above the Earth's atmosphere is sensitive to parameters such as pressure, temperature, water vapor, and hydrometeor content, and this sensitivity has been successfully used for passive vertical sounding of temperature and water vapor profiles. To determine optimal satellite observation strategies for future passive microwave instruments operating at frequencies above those now used, a study of the potential clear‐air vertical sounding capabilities of all significant microwave oxygen and water vapor absorption lines in the frequency range from approximately 10 to 1000 GHz has been performed. The study is based on a second‐order statistical climatological model covering four seasons, three latitudinal zones, and altitudes up to ∼70 km. The climatological model was developed by comparing data from three sources: the Upper Atmosphere Research Satellite Halogen Occultation Experiment (UARS HALOE) instrument, the TIROS Operational Vertical Sounder (TOVS) Initial Guess Retrieval radiosonde set, and the NOAA advanced microwave sounder unit (AMSU) radiosonde set. The Liebe MPM87 absorption model is used for water vapor and oxygen absorption and considers the effects of ozone and isotope absorption. Variations in the vertical sounding capabilities due to statistical variations of water vapor and temperature with latitude and season around each line are considered, and useful channel sets for geostationary microwave vertical sounding are suggested.
In situ studies on volatile jet exhaust particle emissions: Impact of fuel sulfur content and environmental conditions on nuclei mode aerosols
Authors: Schröder F. , Brock C. A. , Baumann R. , Petzold A. , Busen R. , Schulte P. , Fiebig M.
Published: February 2004

In situ measurements of ultrafine aerosol particle emissions were performed at cruise altitudes behind the Deutsches Zentrum für Luft‐und Raumfahrt ATTAS research jet (Rolls‐Royce/Snecma M45H M501 engines) and a B737‐300 aircraft (CFM International 56‐3B1 engines). Measurements were made 0.15–20 s after emission as the source aircraft burned fuel with sulfur contents (FSC) of 2.6, 56, or 118mg kg−1. Particle size distributions of from 3‐ to 60‐nm diameter were determined by using condensationnuclei‐counters with varying lower size detection limits. Volatile particle concentrations in the aircraft plumes strongly increased as diameter decreased toward the sizes of large molecular clusters, illustrating that apparent particle emissions are extremely sensitive to the smallest particle size detectable by the instrument used. Environmental conditions and plume age alone could influence the number of detected ultrafine (volatile) aerosols within an order of magnitude, as well. The observed volatile particle emissions decreased nonlinearly as FSC decreased to 60mg kg−1, reaching minimum values of about 2×1017kg−1 and 2×1016kg−1 for particles >3nm and >5nm, respectively. Volatile particle emissions did not change significantly as FSCs were further reduced below 60mg kg−1. Volatile particle emissions did not differ significantly between the two studied engine types. In contrast, soot particle emissions from the modern CFM56‐3B1 engines were 4–5 times less (4×1014kg−1) than from the older RR M45H M501 engines (1.8×1015kg−1). Contrail processing has been identified as an efficient sink/quenching parameter for ultrafine particles and reduces the remaining interstitial aerosol by factors of 2–10 depending on particle size. These and previously published data are consistent with volatile particle emissions of 2.4×1017kg−1 independent of environmental conditions, engine type and FSCs ranging between 2.6 and 2700mg kg−1. There are clear experimental indications that nonsulfate compounds (probably nonmethane hydrocarbons) begin to dominate the volatile particle composition as FSC decreases below ∼l00mg kg−1.
Surface albedo retrieval from Meteosat: 2. Applications
Authors: Pinty Bernard , Roveda Fausto , Verstraete Michel M. , Gobron Nadine , Govaerts Yves , Martonchik John V. , Diner David J. , Kahn Ralph A.
Published: February 2004

An advanced algorithm to retrieve the radiative properties of terrestrial surfaces sampled by the Meteosat visible instrument was derived in a companion paper [Pinty et al., this issue]. Preliminary applications of this algorithm against a limited set of Meteosat data is performed and the required procedures to screen “clear‐sky” conditions only and to retrieve the “likely” solution of the inverse problem are presented and evaluated. The accumulation of results over two periods of 20 days each during the Northern Hemisphere summer and winter permits establishing sample geophysical maps of the algorithm products, including the surface albedo (i.e., directional hemispherical reflectance factors) over the entire African continent. The seasonal albedo changes occurring at a continental scale are interpreted on the basis of the most prominent environmental factors, namely the atmospheric circulation controlling the seasonal monsoon events and the biomass burning activities. The results of this study, supported by additional radiation transfer simulations, suggest that anthropogenic fire activities induce significant perturbations of the surface albedo values in the intertropical zones at the continental scale.
Dependence of in‐cloud scavenging of polar organic aerosol compounds on the water solubility
Authors: Limbeck Andreas , Puxbaum Hans
Published: February 2004

In spring 1997 at the Sonnblick Observatory, located at 3106m elevation in the Austrian Alps, interstitial aerosol and cloud water samples were simultaneously collected in supercooled convective clouds. These samples were analyzed for their polar organic composition using a newly developed analytical method that allows the simultaneous determination of dicarboxylic acids, monocarboxylic acids, and other polar organic constituents. Using the obtained data set, in‐cloud scavenging efficiencies (ε) for individual polar organic compounds were calculated. For the different organic substances, scavenging efficiencies ranged from 0.16 to 0.98, compared with sulfate, which exhibited an average scavenging efficiency of 0.94. For dicarboxylic acids, scavenging efficiencies (average of about 0.8) were of the same order as for sulfate. Distinctly lower values (average of about 0.6) were achieved for polar aromatic compounds like phthalic acid or diisobutylphenol. The lowest scavenging efficiencies (average about 0.4) were found for alcohols and monocarboxylic acids. Thus we found in the Sonnblick cloud experiment that more polar organic aerosol constituents are more efficiently scavenged into cloud droplets than less polar compounds. In addition, the scavenging efficiencies exhibited a dependence on the solubilities of the examined compounds. For highly water soluble compounds (1–1000 g L−1) a decrease of the water solubility for an individual compound leads to a decrease in the scavenging efficiency for this compound. For “poorly soluble” substances with water solubilities below l g L−1, a near‐constant value for the scavenging efficiency was found, indicating that their scavenging behavior is then dominated by the scavenging of the bulk noncarbonate carbon independent of the physical and chemical properties of the individual substances.
Seasonal variability of middle‐latitude ozone in the lowermost stratosphere derived from probability distribution functions
Authors: Rood Richard B. , Douglass Anne R. , Cerniglia Mark C. , Sparling Lynn C. , Nielsen J. Eric
Published: February 2004

We present a study of the distribution of ozone in the lowermost stratosphere with the goal of characterizing the observed variability. The air in the lowermost stratosphere is divided into two population groups based on Ertel's potential vorticity at 300 hPa. High (low) potential vorticity at 300 hPa indicates that the tropopause is low (high), and the identification of these two groups is made to account for the dynamic variability. Conditional probability distribution functions are used to define the statistics of the ozone distribution from both observations and a three‐dimensional model simulation using winds from the Goddard Earth Observing System Data Assimilation System for transport. Ozone data sets include ozonesonde observations from northern midlatitude stations (1991–1996) and midlatitude observations made by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) (1994–1998). The conditional probability distribution functions are calculated at a series of potential temperature surfaces spanning the domain from the midlatitude tropopause to surfaces higher than the mean tropical tropopause (∼380 K). The probability distribution functions are similar for the two data sources, despite differences in horizontal and vertical resolution and spatial and temporal sampling. Comparisons with the model demonstrate that the model maintains a mix of air in the lowermost stratosphere similar to the observations. The model also simulates a realistic annual cycle. Results show that during summer, much of the observed variability is explained by the height of the tropopause. During the winter and spring, when the tropopause fluctuations are larger, less of the variability is explained by tropopause height. This suggests that more mixing occurs during these seasons. During all seasons, there is a transition zone near the tropopause that contains air characteristic of both the troposphere and the stratosphere. The relevance of the results to the assessment of the environmental impact of aircraft effluence is also discussed.