bluuebunny/crossref_metadata_2025 huggingface dataset:
A modeling study of boundary layer processes associated with ozone layers observed during the 1993 North Atlantic regional experiment
Authors: Fast Jerome D. , Berkowitz Carl M.
Published: February 2004

Boundary layer processes associated with three pollution events during the North Atlantic Regional Experiment (NARE) 1993 field campaign are examined using airborne measurements and a Lagrangian particle dispersion model in conjunction with a mesoscale model employing four‐dimensional data assimilation. This nonphotochemical modeling system was able to qualitatively reproduce many of the observed features during a 15‐day period of the NARE field campaign. Simulated particle releases from urban regions within the daytime convective boundary layer were transported to heights up to 2 km above ground level. Particles located in the upper part of the residual layer in the early evening hours were quickly advected by higher wind speeds aloft to the sampling domain; however, particles released within the nocturnal stable boundary layer or the marine boundary layer remained within 200 m of the surface and often exhibited complex circulation patterns. As a consequence of the diurnal boundary layer characteristics, emissions released within a relatively close time interval were often found to have significantly different trajectories. Mixing of particles from various source regions results in a plume that does not have a unique age but is better characterized by a distribution of ages which vary with altitude. It is shown that much of the layering over Yarmouth is well established by convective boundary layer processes and vertical wind shears prior to the air masses leaving land. As expected, sea surface temperatures were found to play an important role in defining the vertical gradient of potential temperature and hence the amount of vertical mixing over the Gulf of Maine. Peak particle concentrations within 1 km of the ocean were often associated with a low‐level jet over the Gulf of Maine. A common feature during the analysis period is synoptic‐scale lifting in advance of low‐pressure systems which appears to be partially responsible for lifting particles to the heights observed over Yarmouth.
GAGE/AGAGE measurements indicating reductions in global emissions of CCl3F and CCl2F2 in 1992–1994
Authors: Cunnold D. M. , Weiss R. F. , Prinn R. G. , Hartley D. , Simmonds P. G. , Fraser P. J. , Miller B. , Alyea F. N. , Porter L.
Published: February 2004

Global Atmospheric Gases Experiment/Advanced GAGE (GAGE/AGAGE) observations of CCl3F indicate that global concentrations of this compound reached a maximum in 1993 and decayed slightly in 1994; CCl2F2 concentrations increased approximately 7 ppt in both 1993 and 1994. The observations suggest that world emissions in these two years were smaller than industry production figures would suggest and have decreased faster than expected under the Montreal Protocol and its amendments. An analysis of regional pollution events at the Mace Head site suggest that industry may be underestimating the decline of emissions in Europe. It is argued, however, that the decline in European emissions is not biasing the background Mace Head measurements (or the GAGE global averages). Combining the chlorofluorocarbon measurements, including CCl2FCClF2, with GAGE/AGAGE measured global decreases in CH3CCl3 and CCl4 after 1992 and with Cape Grim archived air measurements of CHClF2, the measurements suggest that anthropogenic atmospheric chlorine loading from these six gases maximized in 1992 at 2.95±0.04 ppb and that it had decreased by 0.02±0.01 ppb by the beginning of 1995.
Large‐scale distributions of tropospheric nitric, formic, and acetic acids over the western Pacific basin during wintertime
Authors: Talbot R. W. , Dibb J. E. , Lefer B. L. , Scheuer E. M. , Bradshaw J. D. , Sandholm S. T. , Smyth S. , Blake D. R. , Blake N. J. , Sachse G. W. , Collins J. E. , Gregory G. L.
Published: February 2004

We report here measurements of the acidic gases nitric (HNO3), formic (HCOOH), and acetic (CH3COOH) over the western Pacific basin during the February‐March 1994 Pacific Exploratory Mission‐West (PEM‐West B). These data were obtained aboard the NASA DC‐8 research aircraft as it flew missions in the altitude range of 0.3–12.5 km over equatorial regions near Guam and then further westward encompassing the entire Pacific Rim arc. Aged marine air over the equatorial Pacific generally exhibited mixing ratios of acidic gases <100 parts per trillion by volume (pptv). Near the Asian continent, discrete plumes encountered below 6 km altitude contained up to 8 parts per billion by volume (ppbv) HNO3 and 10 ppbv HCOOH and CH3COOH. Overall there was a general correlation between mixing ratios of acidic gases with those of CO, C2H2, and C2Cl4, indicative of emissions from combustion and industrial sources. The latitudinal distributions of HNO3 and CO showed that the largest mixing ratios were centered around 15°N, while HCOOH, CH3COOH, and C2Cl4 peaked at 25°N. The mixing ratios of HCOOH and CH3COOH were highly correlated (r2 = 0.87) below 6 km altitude, with a slope (0.89) characteristic of the nongrowing season at midlatitudes in the northern hemisphere. Above 6 km altitude, HCOOH and CH3COOH were marginally correlated (r2 = 0.50), and plumes well defined by CO, C2H2, and C2Cl4 were depleted in acidic gases, most likely due to scavenging during vertical transport of air masses through convective cloud systems over the Asian continent. In stratospheric air masses, HNO3 mixing ratios were several parts per billion by volume (ppbv), yielding relationships with O3 and N2O consistent with those previously reported for NOy.
Airborne infrared spectroscopy of 1994 western wildfires
Authors: Worden Helen , Beer Reinhard , Rinsland Curtis P.
Published: February 2004

In the summer of 1994 the 0.07 cm−1resolution infrared Airborne Emission Spectrometer (AES) acquired spectral data over two wildfires, one in central Oregon on August 3 and the other near San Luis Obispo, California, on August 15. The spectrometer was on board a NASA DC‐8 research aircraft, flying at an altitude of 12 km. The spectra from both fires clearly show features due to water vapor, carbon dioxide, carbon monoxide, ammonia, methanol, formic acid, and ethylene at significantly higher abundance and temperature than observed in downlooking spectra of normal atmospheric and ground conditions. Column densities are derived for several species, and molar ratios are compared with previous biomass fire measurements. We believe that this is the first time such data have been acquired by airborne spectral remote sensing.
A method to derive downwelling longwave fluxes at the Arctic surface from TIROS operational vertical sounder data
Authors: Francis Jennifer A.
Published: February 2004

The dominant component of the polar surface energy budget during half the year is the downwelling flux of longwave radiation (DLF), yet little is known about its spatial and temporal variability except on monthly timescales. As surface measurements will always be sparse, the most promising opportunity for diagnosing the DLF is provided by satellite data. Estimating this flux from space, however, presents challenges over all surface types and particularly in polar environments where cloud detection and cloud fraction estimation are less certain. A new method is presented to estimate DLF from measurements by the TIROS‐N operational vertical sounder (TOVS). Temperature profiles, humidity estimates, and cloud cover are retrieved from TOVS radiances using the improved initialization inversion algorithm, which has been modified to produce more accurate results over snow and sea ice. This information is combined with brightness temperature differences from pairs of infrared and near‐infrared TOVS channels. These differences are used to infer cloud phase and geometric thickness. Longwave fluxes are then calculated using a forward radiative transfer model. Results during winter 1988 and spring 1992 are compared with hourly radiation measurements from the Coordinated Eastern Arctic Experiment in the eastern Arctic basin and from the Lead Experiment in the Beaufort Sea. Error analyses yield a bias of approximately 3 W m−2, a standard deviation of 23 W m−2, and a correlation coefficient of about 0.75. These errors are comparable to results from similar studies over midlatitude land and ocean areas where clouds are more easily identified.
Is there an imbalance in the global budget of bomb‐produced radiocarbon?
Authors: Jain Atul K. , Kheshgi Haroon S. , Wuebbles Donald J.
Published: February 2004

Several recent studies of the global inventory of radiocarbon produced by above ground nuclear weapons testing have brought into question our understanding of the global cycle of bomb‐produced radiocarbon. Radiocarbon produced from these explosions has provided a unique test for global carbon cycle models used in the analysis of emission scenarios for carbon dioxide. We employ a globally aggregated model for the global cycles of carbon and its isotopes (13C and 14C) to examine these studies, and find several modeling approximations or assumptions which could be responsible for the differences between analyses. In light of the considerable uncertainty in both model‐based and data‐based estimates of global inventories, we conclude that the global budget of bomb‐produced radiocarbon cannot be shown to be out of balance. Uncertainties limit the utility of 14C as a tracer for determining the flow of carbon dioxide within the atmosphere‐ocean‐terrestrial‐biosphere system of carbon cycle. Our model‐based analyses suggest that improved analysis of past nuclear tests and their production of radiocarbon, as well as additional measurements of 14C in the biosphere and oceans, could reduce uncertainties in model studies of the evolution of 14C in the carbon cycle system.
An abrupt spring air temperature rise over the Greenland ice cap
Authors: Rogers Jeffrey C. , Hellstrom Robert A. , Mosley‐Thompson Ellen , Wang Chung‐Chieh
Published: February 2004

We report on an abrupt springtime temperature rise (ASTR) occurring over the Greenland ice cap. The abrupt 12°–15°C temperature rise typically occurs in May over a 24–36 hour period and is accompanied by a 16–22 hPa pressure rise that begins 2–3 days earlier. The Greenland ASTR is examined using composites of pressure and temperature data from Automatic Weather Stations at “Cathy” and “Kenton” for the years 1987 through 1990 and 1992 and 1993. Comparative analysis of the ASTR at coastal weather stations is made and contemporaneous atmospheric circulation variations are examined with gridded hemispheric sea level pressure and 500 hPa data. At the ice cap summit the ASTR is accompanied by an average 360 m rise in 500 hPa geopotential heights, strong surface winds, and high relative humidities. During an ASTR, concomitant air temperatures along the western coast of Greenland and on Baffin Island also rise, but with a magnitude only half that at the ice cap summit. The contemporaneous ASTR pressure rise at coastal stations is of equivalent magnitude to that at the summit and is most prominent at Greenland stations and on Iceland. Evidence is presented that the ASTR is linked to a seasonal readjustment in the regional Atlantic atmospheric circulation in which the westerlies become weakest in May and migrate northward into the Arctic. A meridional flow regime is established with southwesterly flow advecting mild air over Greenland. Blocking highs form over the Atlantic and the surface mean Icelandic low is weak, or replaced by mean high pressure. The nature and timing of the ASTR is important for planning field activities on the Greenland ice sheet. Further study of the ASTR should lead to a better understanding of boundary layer processes over the ice sheet.
Laboratory studies of ternary H2SO4/HNO3/H2O particles: Implications for polar stratospheric cloud formation
Authors: Anthony S. E. , Onasch T. B. , Tisdale R. T. , Disselkamp R. S. , Tolbert M. A. , Wilson J. C.
Published: February 2004

It has recently been suggested that type Ib polar stratospheric clouds are composed of supercooled ternary‐solutions of sulfuric acid (H2SO4), nitric acid (HNO3), and water (H2O). We have studied the low‐temperature behavior of ternary‐solution aerosols to determine if they will undergo homogeneous freezing nucleation under polar stratospheric conditions. Ternary‐solution aerosols were injected into a low‐temperature chamber and observed for periods of up to 3 hours. Fourier transform infrared spectroscopy was used to determine the aerosol composition and phase as a function of time. We found that ternary‐solution aerosols with compositions similar to those expected in the polar stratosphere remained supercooled for the duration of our experiments. Homogeneous freezing of the particles was never observed, even after warming from 190 to 204 K. However, heterogeneous freezing was occasionally observed for particles adhering to the infrared optics within the chamber.
The gravity wave Doppler spread theory applied in a numerical spectral model of the middle atmosphere: 2. Equatorial oscillations
Authors: Mayr H. G. , Mengel J. G. , Hines C. O. , Chan K. L. , Arnold N. F. , Reddy C. A. , Porter H. S.
Published: February 2004

Mayr et al. [this issue] discussed a two‐dimensional version of the numerical spectral model (NSM) of Chan et al. [1994a, b] that incorporates the Doppler spread parameterization (DSP) for momentum deposition by small‐scale gravity waves (GW) developed by Hines [1997a, b] and presented numerical results describing the global scale seasonal variations in the temperature and wind fields of the middle atmosphere. Even with the simplest assumptions for the GW flux emanating from the troposphere, to be isotropic and independent of latitude and season, this model also produces significant oscillations in the equatorial zonal circulation which are discussed here. Our model results lead to the following conclusions: (1) At altitudes above 40 km, a periodicity of 6 month dominates, resembling the observed semiannual oscillation (SAO). The peak amplitude of this oscillation is close to 18 m/s near 50 km (20–30 m/s observed). A secondary maximum is excited near 80 km with an amplitude of about 11 m/s (15–25 m/s observed), whose phase is opposite to that at 50 km. In this altitude range, the downward phase progression is about 9 km/month, in agreement with observations. The computed SAO is confined to equatorial latitudes, as observed. (2) At altitudes below 40 km, the period of the computed oscillation is almost 21 months, approaching that of the observed quasi‐biennial oscillation (QBO). The maximum wind amplitudes are close to 8 m/s (20 m/s observed), and the downward phase progression is about 1.6 km/month (1.3 km/month observed). The model also produces a QBO in the upper mesosphere, in qualitative agreement with recent UARS measurements [Burrage et al., 1996]. (3) When the eddy diffusivity is reduced by a factor of two, the QBO period increases to 30 months and the maximum wind amplitude approaches 13 m/s. Computer experiments are discussed for constant, equinoctial solar heating to elucidate the GW excitation mechanism for the equatorial oscillations in the zonal circulation.
Sun photometric measurements of atmospheric water vapor column abundance in the 940‐nm band
Authors: Halthore Rangasayi N. , Eck Thomas F. , Holben Brent N. , Markham Brian L.
Published: February 2004

Sun photometers operating in the strong water vapor absorption 940‐nm combination‐vibrational band have been used to determine water column abundance in the atmosphere when the path to the Sun is clear of clouds. We describe a procedure to perform a rapid determination of the water column abundance, using sun photometers with an accuracy that is easily comparable to that of the radiosondes. The effect of parameters, such as filter bandwidth, atmospheric lapse rate, and the water vapor amount, on the accuracy of the retrieved abundance is examined. It is seen that a narrow filter band of approximately 10‐nm bandwidth, positioned at the peak of absorption, is quite insensitive to the type of atmosphere present during calibration or measurement with less than 1% variability under extreme atmospheric conditions. A comparison of the retrieved water column abundance using sun photometers with contemporaneously measured values using radiosondes and microwave radiometers shows that the latest version of the radiative transfer algorithm used in this procedure, MODTRAN‐3, gives far superior results in comparison with earlier versions because of the use of improved absorption coefficients in the 940‐nm bands. Results from a network of sun photometers spread throughout the globe will be discussed.
Photochemistry of formaldehyde during the 1993 Tropospheric OH Photochemistry Experiment
Authors: Fried Alan , McKeen Stuart , Sewell Scott , Harder Jerry , Henry Bruce , Goldan Paul , Kuster William , Williams Eric , Baumann Karsten , Shetter Richard , Cantrell Chris
Published: February 2004

The present study examines in detail the photochemistry of the important hydrocarbon intermediate HCHO during the 1993 Fritz Peak/Idaho Hill OH Photochemistry Experiment. Measurement‐model relationships for HCHO were studied employing a box model with input measurements of hydrocarbons, photolysis frequencies, NOx, and HOx measured at the Idaho Hill sampling site during clean westerly flow. Tunable diode laser absorption and long‐path UV‐visible absorption spectroscopic techniques provided the high‐quality time‐resolved ambient HCHO database necessary for this study. For clear sky conditions during clean westerly flow, midday HCHO measurements and model calculations were in agreement to within 12% under various realistic model scenarios. This is significant since it places constraints on the OH concentrations as well as the characteristics of potential missing hydrocarbons necessary to balance measured and modeled OH. Measurement relationships between HCHO and CH3CHO were also investigated; polluted air from the Denver‐Boulder front range resulted in the following linear regression: [HCHO] = (0.62±0.20) ppbv + (1.83±0.15) CH3CHO. The slope reflects the large if not dominant influence of primary and biogenic emissions, and the intercept reflects the existence of HCHO sources which are not sources of CH3CHO. Clean westerly flow produced a significantly different relationship with no obvious correlation, and this is consistent with smaller biogenic sources of CH3CHO compared with the much larger known biogenic sources of HCHO.
Variations in NOy composition at Idaho Hill, Colorado
Authors: Williams E. J. , Roberts J. M. , Baumann K. , Bertman S. B. , Buhr S. , Norton R. B. , Fehsenfeld F. C.
Published: February 2004

Measurements of NOy, and the principal constituent NOy, species (NO, NO2, PAN, HNO3, PPN, NO3−) were taken during the fall of 1993 at a high‐elevation site in the Colorado mountains west of Boulder. The meteorology provided two principal flow regimes: strong westerly flow, bringing drier and cleaner air over the Continental Divide from the west where emission sources are sparse, and weaker easterly upslope flow which brought moist and more polluted air from the Denver‐Boulder urban corridor and perhaps from smaller more local sources such as the mountain town of Nederland. The upslope flow data generally indicate a balance between measured NOy, and the separately measured NOy, species with NOx, PAN, and HNO3 accounting for over 90%. Under these conditions, NOx was the dominant fraction of NOy, and occasionally fresh emissions were indicated as shown by NOx/NOy, close to unity. For downslope flow there was generally a shortfall in the NOy, balance where measured NOy, was higher than the constituent species by about 20%, on average. Known potential interferences in the measurements do not appear to account for the NOy deficit. Missing NOy correlated directly with NOx/NOy, O3, and aerosols and inversely with temperature. These relationships suggest the presence of one or more NOy species that were not measured by the individual techniques.
Seasonal trends in energy, water, and carbon dioxide fluxes at a northern boreal wetland
Authors: Lafleur Peter M. , McCaughey J. Harry , Joiner David W. , Bartlett Paul A. , Jelinski Dennis E.
Published: February 2004

Micrometeorological measurements were made over a northern boreal fen near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem‐Atmosphere Study. The measurement period extended from the start of snowmelt until the early fall, at which time senescence was widespread throughout the fen. Data analysis concentrated on identifying seasonal trends in energy, water, and carbon dioxide fluxes and linking them to observed surface cover changes. Albedos (solar and photosynthetically active radiation (PAR)) showed large decreases over the melt period, reaching seasonal lows at the end of melt. Solar albedo increased in the summer in response to vegetation growth on the fen, while PAR albedo remained constant. Incoming and outgoing longwave flux seasonal trends were similar, so seasonal changes in net radiation were driven by the net solar flux. During the spring thaw, the melting of snow and ground ice was equal to about 28% of the daily total net radiation, while the soil heat flux accounted for about 5%. Bowen ratios at this time were above unity. Mean Bowen ratio decreased to 0.70 during the period between spring thaw and leaf‐out. As the vascular vegetation cover developed, Bowen ratios decreased to seasonal lows of 0.10–0.20 near midsummer and then increased to above unity during senescence. The daily evaporative fraction (EF) was highest (≥0.80) during midsummer when the vascular vegetation was in full leaf and actively photosynthesizing, and EF decreased to a mean of 0.55 during senescence. Eddy correlation measurements of carbon dioxide flux showed the fen acting as a net sink for CO2 only while the vascular vegetation was actively photosynthesizing with a daily mean flux of −0.81 g CO2‐C m−2 d−1 (standard error = 0.16). Before leafing and during senescence the fen was a net source of CO2. Integrated over the study period of 124 days, the fen experienced a net loss of 30.4 g CO2 m−2 to the atmosphere.
Snow parameters derived from microwave measurements during the BOREAS winter field campaign
Authors: Chang A. T. C. , Foster J. L. , Hall D. K. , Goodison B. E. , Walker A. E. , Metcalfe J. R. , Harby A.
Published: February 2004

Passive microwave data have been used to infer the snow‐covered area and snow water equivalent (SWE) over forested areas, but the accuracy of these retrieved snow parameters cannot be easily validated for heterogeneous vegetated regions. The Boreal Ecosystem‐Atmosphere Study Winter Field Campaign provided the opportunity to study the effect of boreal forests on snow parameter retrieval in detail. Microwave radiometers (18, 37, and 92 GHz) were flown on board the Canadian National Aeronautical Establishment's Twin Otter. Flight lines covered both the southern study area near Prince Albert and the northern study area near Thompson, Canada. During the 1994 winter campaign, extensive ground‐based snow cover information, including depth, density, and grain size, was collected along most of the flight lines, jointly by U.S. and Canadian investigators. Satellite data collected by the special sensor microwave imager are also used for comparison. Preliminary results reconfirmed the relationship between microwave brightness temperature and SWE. However, the effect of forest cover observed by the aircraft sensors is different from that of the satellite observations. This is probably due to the difference in footprint averaging. There were also several flight lines flown over Candle Lake and Waskesiu Lake to assess lake ice signatures. Preliminary results show the thickness of the lake ice may be inferred from the airborne microwave observations. The microwave signature relationship between lake ice and snow matches the results from radiative transfer calculations.
Atmospheric circulation around the Greenland Crest
Authors: Stearns Charles R. , Weidner George A. , Keller Linda M.
Published: February 2004

The Greenland Ice Sheet Program 2 (GISP2) required meteorological support for the layout of the field camp, ice core site, landing strip, snow sampling sites, and air sampling sites. An automatic weather station installed in May 1987 provided the initial data for the support of several components of the program using the 2 year wind speed and direction distributions. The automatic weather station (AWS) network was expanded to six sites with four sites located approximately 100 km from the highest point in Greenland in the cardinal directions and sites located at GISP2 and at the air sampling site. The wind direction and speed wind roses for August and September 1994 show that there is considerable variation in the wind field around the Greenland Crest. The constancy (ratio of the vector wind speed to the scalar wind speed) of the monthly wind vectors was lowest at the southern site and increased as one moved clockwise around the crest to the eastern site. Vorticity and divergence were determined from triangles formed by three AWS sites. The mean horizontal divergence for August and September 1994 was 1.4×10−5 s−1, and the vorticity was −3.7×l0−5 s−1. Apparently, the flow around the Greenland Crest is most influenced by topography when the 500 hPa contours indicate a pressure ridge over central Greenland. The surface winds showed anticyclonic flow, positive horizontal divergence, and negative vertical vorticity. In the mean, this configuration indicates the presence of an inversion wind, especially at the sites located on the slopes to the west and east of the crest.
Seasonal trends and local influences on nonmethane hydrocarbon concentrations in the Canadian boreal forest
Authors: Young V. L. , Kieser B. N. , Chen S. P. , Niki H.
Published: February 2004

Mixing ratios of nonmethane hydrocarbons, both biogenic and anthropogenic, have been monitored year‐round at several sites in the boreal forests of Saskatchewan and Ontario. Seasonal patterns in hydrocarbon mixing ratios are explained by the wintertime effect of the Arctic air mass and the summertime increase in photochemical processing at all sites. Summer‐time differences in hydrocarbon distributions between sites are indicative of the density of anthropogenic sources and the oxidative capacity of the atmosphere in the region. Consideration of hydrocarbon mixing ratios and OH reaction rate constants suggests that the biogenic hydrocarbon isoprene may limit the oxidative capacity of the atmosphere in boreal regions. The observed temperature dependence of the isoprene mixing ratio suggests that the ambient isoprene concentration is strongly influenced by the emission rate.
A Lagrangian study of the Antarctic polar vortex
Authors: Paparella F. , Babiano A. , Basdevant C. , Provenzale A. , Tanga P.
Published: February 2004

We study the dynamics of passively advected tracers in the Antarctic polar vortex, using the wind fields provided by the European Centre for Medium‐Range Weather Forecasts' (ECMWF) analysis from August to October 1993. Advection on both isopycnal (0.0938 kg/m3) and isentropic surfaces (470°K) is considered. A new definition of the vortex edge, identified as the maximum of kinetic energy, is compared with the definition based on the maximum gradient of Ertel potential vorticity. Using the kinetic energy criterion, we study the permeability of the polar vortex in the framework of the launch strategy of the Stratospheric EoIe (Strateole) polar ozone experiment. We compare the dynamics of balloons launched from the latitudes corresponding to three different possible launching sites for the Strateole experiment, and we provide a quantitative estimate of the probability that a passive tracer may cross the vortex edge, confirming the strong impermeability of the polar vortex to inward and outward particle motions.
A modified linear‐mixing method for calculating atmospheric path radiances of aerosol mixtures
Authors: Abdou W. A. , Martonchik J. V. , Kahn R. A. , West R. A. , Diner D. J.
Published: February 2004

The top‐of‐atmosphere (TOA) path radiance generated by an aerosol mixture can be synthesized by linearly adding the contributions of the individual aerosol components, weighted by their fractional optical depths. The method, known as linear mixing, is exact in the single‐scattering limit. When multiple scattering is significant, the method reproduces the atmospheric path radiance of the mixture with <3% errors for weakly absorbing aerosols up to optical thickness of 0.5. However, when strongly absorbing aerosols are included in the mixture, the errors are much larger. This is due to neglecting the effect of multiple interactions between the aerosol components, especially when the values of the single‐scattering albedos of these components are so different that the parameter ε = ∑ fi | ϖi − ϖmix | / ϖi is larger than ∼0.1, where ϖi and ƒi are the single‐scattering albedo and the fractional abundance of the ith component, and ϖmix is the effective single‐scattering albedo of the mixture. We describe an empirical, modified linear‐mixing method which effectively accounts for the multiple interactions between aerosol components. The modified and standard methods are identical when ε=0.0 and give similar results when ε ≤ 0.05. For optical depths larger than ∼0.5, or when ε>0.05, only the modified method can reproduce the radiances within 5% error for common aerosol types up to optical thickness of 2.0. Because this method facilitates efficient and accurate atmospheric path radiance calculations for mixtures of a wide variety of aerosol types, it will be used as part of the aerosol retrieval methodology for the Earth Observing System (EOS) multiangle imaging spectroradiometer (MISR), scheduled for launch into polar orbit in 1998.
On the extraordinary katabatic winds of Adélie Land
Authors: Wendler Gerd , Stearns Charles , Weidner George , Dargaud Guillaume , Parish Thomas
Published: February 2004

The winds observed in Adélie Land, eastern Antarctica, are the strongest observed anywhere on Earth close to sea level, e.g. Cape Denison measured a mean annual wind speed of about 20 m s−1. Some historic data from the area are available; however, such measurements were carried out at different places for different time periods. Hence in December 1992, we placed four automatic weather stations along the coast of Adélie Land, two in the maximum wind jet (Port Martin and Cape Denison) and one on each side of this jet (D 10 close to Dumont d'Urville and Penguin Point, respectively). We obtained about three months of good data, as on March 25, 1993, a strong storm destroyed three of the four wind sensors. Wind velocities are discussed as a function of other meteorological parameters. Further, the interrelationships between the stations are described. Some of the findings are (1) the very high wind speeds reported earlier this century are in agreement with our measurements; the wind directional constancy is high; (2) historic measurements reported Cape Denison to be the windiest station, not only for Antarctica, but also close to sea level for planet Earth; again our measurements are in agreement; (3) very strong wind speeds have a more down‐slope direction than weaker ones; (4) the general atmospheric pressure gradient enhanced or inhibited the gravity flow; this is especially well pronounced in summer; and (5) in summer, above normal pressure is correlated with above normal temperatures; in fall the opposite holds true.
Re‐formation of chlorine reservoirs in southern hemisphere polar spring
Authors: Grooss Jens‐Uwe , Pierce R. Bradley , Crutzen Paul J. , Grose William L. , Russell James M.
Published: February 2004

This paper focuses on the recovery of chlorine reservoir species in the lower stratosphere in late Antarctic spring. The investigations are based on measurements from the Halogen Occultation Experiment (HALOE) on board the Upper Atmosphere Research Satellite (UARS) and calculations by the Mainz photochemical box model and the NASA Langley Research Center trajectory model. During late Antarctic spring 1994, HALOE observed high HCl mixing ratios up to 2.7 ppbv at 20 km altitude in the ozone‐depleted air inside the polar vortex. These values correspond approximately to the sum of all available inorganic chlorine species. In the preceding period of chlorine activation on polar stratospheric clouds (PSCs), the observed HCl mixing ratios in some cases were below 0.3 ppbv. This indicates a fast conversion of active chlorine species into the form of HCl after PSCs disappear with increasing stratospheric temperatures. Box model calculations are presented that assess the rate of HCl increase in late spring when heterogeneous chemistry on polar stratospheric clouds becomes insignificant. The calculations were performed along Lagrangian trajectories starting from HALOE measurements in September 1994. Sensitivity calculations are presented regarding uncertainties in input parameters of the calculations. In the vortex edge region, calculated HCl increase rates are significantly lower compared with HALOE observations. Introducing additional HCl‐yielding branches of the reactions of ClO with OH and HO2 helps to reduce this discrepancy.
Microwave observations and modeling of O2(1Δg) and O3 diurnal variation in the mesosphere
Authors: Sandor Brad J. , Clancy R. Todd , Rusch David W. , Randall Cora E. , Eckman Richard S. , Siskind David S. , Muhleman Duane O.
Published: February 2004

The first microwave measurements of an electronically excited molecular species in the Earth's atmosphere are presented. Local thermodynamic equilibrium (LTE) rotational line emission from mesospheric O2(1Δg) was observed at a frequency of 255.01794 GHz (λ∼1.2 mm), employing the National Radio Astronomy Observatory (NRAO) millimeter facility at Kitt Peak, Arizona (32°N, 111°W). The pressure‐broadened line shapes of the O2(1Δg) spectra, which were obtained in January and April 1992 and in January and November 1993, are inverted to retrieve O2(1Δg) mixing profiles over the 50–70 km altitude region. The observed daytime abundances exceed ozone abundances in the lower mesosphere, which are separately retrieved with coincident O3 spectral line (249.7886 GHz) observations. The January and November 1993 observations are binned into 20–60 min time intervals to study O2(1Δg) diurnal behavior. Derived abundances of O2(1Δg) between 50 and 70 km for the four observation dates are 9%, 31%, 3%, and 26%, respectively, each ±10% higher than predicted, based on the simple photochemistry of lower mesospheric O2(1Δg). Modeled variation of [O2(1Δg)] with time of day agrees with observed variation in that the observed difference between model and data abundances is constant throughout the daylight hours of each observation date. Model underprediction of [O2(1Δg)] is consistent with similar model underprediction of mesospheric [O3]. A perturbation to the photochemical model that forces decreased ozone chemical loss brings brings both model [O3] and [O2(1Δg)] into agreement with the observations. O2(1Δg) abundances derived from these 1.2 mm observations agree with [O2(1Δg)] values derived from comparable SME observations of the 1.27 μm emission, with assumption of a 3880 s O2(1Δg) radiative lifetime [Badger et al., 1965]. The 6800 s O2(1Δg) radiative lifetime proposed by Mlynczak and Nesbitt [1995] is ruled out by the similar comparison.
Aerosol optical depths in a semiarid region
Authors: Pinker R. T. , Ferrare R. A. , Karnieli A. , Aro T. O. , Kaufman Y. J. , Zangvil A.
Published: February 2004

To monitor changes in surface conditions from space requires information on the state of the atmosphere to correct for atmospheric effects in the remotely sensed signal. The least observed and most variable atmospheric parameters are aerosols. Of particular interest are changes of surface conditions in areas where desert encroachment is of concern. An effort was initiated at one of such locations to monitor atmospheric conditions from the ground and surface conditions from space. In this paper we present results only on the ground observations of the aerosol optical depths, in particular their annual and diurnal variations, in the context of prevailing synoptic conditions.
Analysis of long‐term behavior of ultraviolet radiation measured by Robertson‐Berger meters at 14 sites in the United States
Authors: Weatherhead Elizabeth C. , Tiao George C. , Reinsel Gregory C. , Frederick John E. , DeLuisi John J. , Choi Dongseok , Tam Wing‐kuen
Published: February 2004

Surface ultraviolet (UV) radiation measurements from the Robertson‐Berger (RB) meter network and existing documentation of these data were examined to determine long‐term variations of UV. RB meter data from 14 sites in the United States were analyzed for trends over the period 1974–1991. A more in‐depth analysis of the RB meter data, including the use of supporting geophysical data, was carried out for four of the locations. Results based on analysis of data from the 14 sites show a significant negative trend of the order of −6% per decade overall, reasonably consistent with annual trends obtained by Scotto et al. [1988] using similar data for the period 1974–1985. However, when allowance is made for mean level shifts in the data for several of the stations around 1979, which may be due to calibration and other instrument‐related problems, the resulting overall trend is found to be of the order of +2% per decade and not statistically significant. An additional trend analysis using only RB meter data since 1979 at the 14 sites is also performed and leads to overall trend results similar to those from the analysis which allows for mean level shifts in the data. The more detailed analysis of data from four of the stations for the period 1979–1991 is performed to investigate the extent to which the trend behavior in the RB meter measurements can be explained by the behavior of other geophysical quantities such as cloudiness and total ozone. In particular, radiative transfer model‐based calculations of ultraviolet irradiance based on satellite data from the total ozone mapping spectrometer are compared with the RB meter measurements to help explain their behavior. Generally, inconsistencies are found between the trend behavior in RB meter measurements and radiative transfer calculations, with the RB data showing substantial downward movement relative to the calculations for three of the four sites. Significant evidence exists to indicate that problems with the network render the existing RB meter measurements unreliable for long‐term trend detection. Different reasonable treatments of the data result in dramatically different trend results. Without further information, the data, by themselves, do not allow for definitive trend analysis results.
Measurement of tropospheric trace gases by long‐path differential absorption spectroscopy during the 1993 OH Photochemistry Experiment
Authors: Harder J. W. , Jakoubek R. O. , Mount G. H.
Published: February 2004

In August and September 1993 a comparative study of tropospheric long‐path absorption techniques with in situ methods was performed for both the hydroxyl radical and the other important trace species. Long‐path measurements were made over the 10.3 km path between Fritz Peak Observatory and Caribou Mine in the mountains 17 km west of Boulder, Colorado. At Caribou Mine, a 121 element, 1 m2 retroreflector array folds the optical path to give a total path of 20.6 km. The in situ instruments were located at Idaho Hill 0.5 km northwest of Caribou Mine. The optical design and analysis techniques used to obtain the path‐integrated concentrations of O3, CH2O, SO2, and NO2 will be presented. The spectrograph used in this study is a 1/4 m double, crossed Czerny‐Turner that employs a diode array detector allowing the acquisition of 40 nm spectral bands in the near UV and visible spectral regions. This system also utilizes automatic alignment and self‐adjusting time integration so the system will acquire data in an unattended mode. The spectral bands selected for this study permit the simultaneous measurement of O3, NO2, CH2O, and SO2; NO2 and H2O; and NO3 and H2O. The data analysis uses a nonlinear least squares regression procedure to deduce the concentration of each of the species present in the atmosphere and also provides an effective method for removing the influence of scattered solar light for daytime measurements. An estimate of the measurement precision can be found by comparing atmospheric spectra analyzed with two different IO spectra; one measured through the atmosphere and the other a direct arc lamp spectrum.
Diurnal migrating tide as seen by the high‐resolution Doppler imager/UARS: 2. Monthly mean global zonal and vertical velocities, pressure, temperature, and inferred dissipation
Authors: Khattatov B. V. , Geller M. A. , Yubin V. A. , Hays P. B.
Published: February 2004

Meridional diurnal tidal winds derived as described by Khattatov et al. [this issue] from the high‐resolution Doppler imager (HRDI) data are used in the linearized tidal equations to solve for the diurnal tidal oscillations in the zonal and vertical velocity, pressure, temperature, and dissipation in the mesosphere and lower thermosphere. The resulting monthly mean latitude‐altitude cross sections of the amplitudes of the tidal zonal, meridional, and vertical velocity, pressure, temperature, and Rayleigh friction and vertical diffusivity are presented for 12 months of the combined 1992/1993 year. The results show profound seasonal changes and interhemispherical differences in the calculated tidal amplitudes and dissipation. The derived monthly mean vertical diffusion coefficients are compared with the results of Garcia and Solomon [1985]. The Rayleigh friction coefficients and vertical diffusivities derived from HRDI measurements can potentially have important impact on modeling of the chemistry and composition of the mesosphere and lower thermosphere, in particular, on numerical modeling of atmospheric thermal tides.
Analytic solutions of reaction diffusion equations and implications for the concept of an air parcel
Authors: McKenna D. S.
Published: February 2004

In the atmosphere, hydroxyl radical concentrations can be estimated by considering the relative change in the concentration of two hydrocarbons of differing reactivity. This approach is based on three assumptions: (1) that background concentrations of the two hydrocarbon are zero; (2) that transport processes will influence all hydrocarbon concentrations equally; that is, hydrocarbon changes can be separated into the product of a chemical term and a transport term; and (3) that hydrocarbons have the same spatial and temporal emission pattern. In this paper, analytical solutions to a steady state reaction diffusion equation are derived. The general solutions to this problem are nonseparable, with the degree of nonseparability defined by a single parameter that is a simple function of the system's intrinsic timescales. When this parameter is evaluated for diffusivities typical of the boundary layer (∼102 m2/s) and hydrocarbon reactivities that are sufficiently slow to be practically useful, it can be readily shown that for all practical purposes, separability can be assumed. This separability influences the spatial distribution of loss but not the net global loss. Thus even under nonseparable conditions, although the apparent local loss rate may be considerably less than the actual kinetic loss rate implied by hydrocarbon reactivity, when the apparent local loss rates are integrated to deduce a global loss rate, there will be no underestimate in the global loss rate, since the chemical loss rate is a linear function of hydrocarbon concentrations. It is conjectured that when much higher dispersion rates common in photochemical transport models (∼105–106 m2/s) are invoked, local photochemical balances may be perturbed when chemical loss rates are either spatially inhomogeneous or influenced by reactant concentrations. Thus in highly diffusive models the influence of highly reactive chemical species may be extended further from the source regions than is realistic, even though the globally averaged loss rates would still be consistent with the magnitude of the globally averaged sink.
A soil‐canopy‐atmosphere model for use in satellite microwave remote sensing
Authors: Lakshmi Venkataraman , Wood Eric F. , Choudhury Bhaskar J.
Published: February 2004

Regional and global scale studies of land‐surface‐atmosphere interactions require the use of observations for calibration and validation. In situ field observations are not representative of the distributed nature of land surface characteristics, and large‐scale field experiments are expensive undertakings. In light of these requirements and shortcomings, satellite observations serve our purposes adequately. The use of satellite data in land surface modeling requires developing a hydrological model with a thin upper layer to be compatible with the nature of the satellite observations and that would evaluate the soil moisture and soil temperature of a thin layer close to the surface. This paper outlines the formulation of a thin layer hydrological model for use in simulating the soil moistures and soil temperatures. This thin layer hydrological model is the first step in our attempt to use microwave brightness temperature data for regional soil moisture estimation. The hydrological model presented here has been calibrated using five years (1980–1984) of daily streamflow data for the Kings Creek catchment. The calibrated parameters are used to validate the daily streamflows for the next 5 year period (1985–1989). The comparison of surface soil moistures and surface temperatures for the period of the Intensive Field Campaigns (IFCs) during the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) in 1987 is carried out and yields good results. The thin layer hydrological model is coupled with a canopy radiative transfer model and an atmospheric attenuation model to create a coupled soil‐canopy‐atmosphere model in order to study the effect of the vegetation and the soil characteristics on the Special Sensor Microwave Imager (SSM/I) brightness temperatures. The sensitivities of the brightness temperatures to the soil and vegetation is examined in detail. The studies show that increasing leaf area index masks the polarization difference signal originating at the soil surface.
Photoinduced oxidation of H2S species: A sink for sulfide in seawater
Authors: Pos Willer H. , Milne Peter J. , Riemer Daniel D. , Zika Rod G.
Published: February 2004

Photokinetic studies demonstrate that sulfide is consumed in seawater upon light exposure. The half‐life (t1/2) of sulfide (10 μM) added to Biscayne Bay water and Gulf Stream water are 49(±15) and 147(±10) min, respectively. Both UV and visible radiation were shown to accelerate the photodecomposition of sulfide. However, due to a higher amount of radiation in the visible range reaching the sea surface, we predict that this portion of the light spectrum will be most important in inducing photoreaction of sufide in seawater. This as yet unaccounted sink of sulfide in seawater could be responsible for the sulfide daytime low and nighttime high concentration values observed by several investigators. This finding further unbalances the sulfide budget and reinforces the need for systematic research on the role of photochemical processes on sulfur species in seawater.