bluuebunny/crossref_metadata_2025 huggingface dataset:
Flux of anthropogenic carbon into the deep Greenland Sea
Authors: Anderson L. G. , Chierici M. , Fogelqvist E. , Johannessen T.
Published: September 2002

Measurements of the carbonate system and the transient tracers, CFC‐11 and carbon tetrachloride (CCl4), in the Greenland Sea and western Eurasian Basin are used to deduce the sources and magnitude of excess dissolved inorganic carbon in the deep Greenland Sea. The salinity in the deep Greenland Sea has increased during the past 20 years as a result of Arctic Ocean water advecting into the area. From salinity and temperature data the relative amount of advective water below 1500 m is estimated to ∼2% yr−1 between 1982 and 1994. Data from the western Eurasian Basin, collected during the Oden 91 cruise, are used as the advective source waters. A mixing box model is applied to estimate the evolution of CFCs and anthropogenic total dissolved inorganic carbon in the deep waters of the Greenland Sea since preindustrial times. The source functions are the surface water concentrations of CFC‐11, CCl4, and total dissolved inorganic carbon CT, which are the result of anthropogenic emission. In order to explain the measured CFC data in the Greenland Sea an annual percent renewal by deep water formation of between 0.5 and 1.2% is needed below 1500 m, corresponding to a mean ventilation of 0.17±0.05 Sv, considering realistic uncertainties in the calculations. This ventilation gives a sequestering of anthropogenic carbon dioxide, which in 1994 equaled 2.4±0.7×1012 g C yr−1.
Polynya activity in the Arctic Ocean from 1958 to 1997
Authors: Winsor Peter , Björk Göran
Published: September 2002

Arctic polynyas are investigated during 39 winter seasons from 1958 to 1997 by means of a polynya model forced by the National Centers for Environmental Prediction reanalysis data set of wind and air temperature. The model is able to reproduce polynya events (i.e., opening date, closing date, and size) at various locations around the Arctic Ocean. A mean ice production and corresponding salt flux from all Arctic polynyas of 300±30 km3 yr−1 and 6±0.6×l012 kg yr−1, respectively, is found. These values are ∼40% of the results in earlier satellite‐based investigations. The total annual ice production from polynyas shows a large interannual variability with a range between minimum and maximum values of 40% and with a distinct periodicy of 5 years. Single polynya events are shown to be important for the total ice production, with productions up to 5 m per event or some 50% of the seasonal mean in some areas. The mean salt flux from all polynyas can at maximum maintain a flow of 0.2 Sv with a salinity of 32.85 out from the shelves. This represents ∼30% of the estimated flux necessary to maintain the cold halocline layer of the Arctic Ocean. Areas contributing most to halocline water formation are the Barents, Kara, Chukchi, and Bering Seas, where the Chukchi Sea is the only area contributing actively to deep water formation. This investigation indicates that the cold and salty shelf waters formed in polynyas give a relatively small contribution to the intermediate and deep waters of the Arctic Ocean compared to other possible processes such as the modification of Atlantic water by cooling and ice melt.
Interaction of the Okhotsk Sea diurnal tides with the Kashevarov Bank polynya
Authors: Polyakov Igor , Martin Seelye
Published: September 2002

Satellite images show the existence of a recurrent polynya directly over and in the vicinity of Kashevarov Bank. Our modeling results using a coupled ice‐ocean model show that tides are important in the establishment and maintenance of this polynya. Ice appears and grows in areas surrounding the bank, while over the bank, tidal mixing transports heat to the sea surface, resulting in ice melt and polynya formation. The strong cooling of the upper sea layer forms a 100–200 m thick surface layer with negative temperatures. The large current amplitudes of the basic tidal waves K1 and O1 generate through nonlinear interactions a clockwise residual current and ice drift as well as secondary oscillations in the semidiurnal, fortnightly, and other tidal bands. In general, ice causes an amplification of the tidal currents and density‐driven components of the residual circulation over Kashevarov Bank while the barotropic component of the residual flow is weakened because of the underice boundary layer.
Surface fluxes and their influence on sea surface temperature in the western equatorial Pacific during the Coupled Ocean‐Atmosphere Response Experiment
Authors: Zhang Shuliang , Plueddemann Albert J. , Anderson Steven P. , Weller Robert A.
Published: September 2002

Surface fluxes in the western equatorial Pacific warm pool region and their influence on sea surface temperature (SST) variability were investigated for the period November 15, 1992, to February 15, 1993, during the Intensive Observing Period of the Coupled Ocean‐Atmosphere Response Experiment (COARE). A blended flux data set was developed using a “reanalysis” of surface meteorology from the European Centre for Medium‐Range Weather Forecasts (ECMWF), turbulent flux components from the COARE bulk flux algorithm, and shortwave radiation and precipitation estimates from satellite remote sensing. Comparison with in situ fluxes from the center of the warm pool showed that the blended fluxes captured variability associated with the intraseasonal oscillation (ISO) while the fluxes produced by ECMWF did not. The influence of surface forcing on SST was assessed by comparing the observed SST tendency to that produced by a one‐dimensional model forced by the blended fluxes. On the ISO timescale, SST changes in a substantial portion of the warm pool were found to be dominated by local surface forcing, although significant contributions from other processes (e.g., horizontal advection) were not ruled out. The results emphasize the fact that high‐quality surface fluxes are essential to developing accurate predictions of SST variability in the warm pool region.
Optical properties of the Kara Sea
Authors: Johnson Donald R. , Asper Vernon , McClimans Thomas , Weidemann Alan
Published: September 2002

This study was motivated by the need to understand dispersion processes which affect the redistribution of nuclear wastes in the Arctic from dump sites in the Kara Sea and in the rivers which flow into the Kara Sea. We focus on vertical profiles of light beam transmission and fluorometry made over the delta region fronting the Ob and Yenisey Rivers and over the East Novaya Zemlya Trough (ENZT). The delta region fronting the Ob River Estuary contains a large repository of particles in a dense bottom nepheloid layer with a maximum centered ∼100 km in front of the estuary entrance and covering an area of roughly 200 km diameter. This suspended particle mass repository appears to contain both sediments and detritus and lends credence to the Lisitsyn [1995] concept of the marginal filter zone. In the deep water of the ENZT we found a strong increase of beam attenuation with depth, indicating a relatively large increase of particle mass concentration from ∼50 m to the bottom (depths in excess of 300 m). The strongest concentration was adjacent to the southeast coast of Novaya Zemlya. We suggest that a type of hyperpycnical flow occurs from accumulation of sediments in the bottom waters of Novaya Zemlya fjords which then cascades down the steep slopes adjacent to the island, producing the particle mass distribution as observed by the transmissometer. The accumulation of these repositories of high particle mass concentrations in suspension would suggest that the residence time is high but that storm‐driven events could act to disperse the material.
Experiments on a plume with off‐source heating: Implications for cloud fluid dynamics
Authors: Venkatakrishnan L. , Bhat G. S. , Narasimha R.
Published: September 2002

We report here on a series of laboratory experiments on plumes, undertaken with the object of simulating the effect of the heat relase that occurs in clouds on condensation of water vapor. The experimental technique used for this purpose relies on ohmic heating generated in an electrically conducting plume fluid subjected to a suitable alternating voltage across specified axial stations in the plume flow [Bhat et al., 1989]. The present series of experiments achieves a value of the Richardson number that is toward the lower end of the range that characterizes cumulus clouds. It is found that the buoyancy enhancement due to heating disrupts the eddy structures in the flow and reduces the dilution owing to entrainment of ambient fluid that would otherwise have occurred in the central region of the plume. Heating also reduces the spread rate of the plume, but as it accelerates the flow as well, the overall specific mass flux in the plume does not show a very significant change at the heat input employed in the experiment. However, there is some indication that the entrainment rate (proportional to the streamwise derivative of the mass flux) is slightly higher immediately after heat injection and slightly lower farther downstream. The measurements support a previous proposal for a cloud scenario [Bhat and Narasimha, 1996] and demonstrate how fresh insights into certain aspects of the fluid dynamics of clouds may be derived from the experimental techniques employed here.
A numerical study of nonlinear propagation of a gravity‐wave packet in compressible atmosphere
Authors: Zhang Shao Dong , Yi Fan
Published: September 2002

By using a two‐dimentional full‐implicit‐continuous‐Eulerian scheme, numerical simulation for nonlinear propagation of Gaussian gravity‐wave packets in a compressible and isothermal atmosphere are carried out. The numerical analyses show that for an initially given upgoing gravity‐wave packet whose disturbance velocity is much less than ambient wind velocity, although there exists nonlinear interaction, during the propagation, the whole wave packet and the wave‐associated energy keep moving upward, while the wave front keeps moving downward. Wave‐associated perturbation velocity increases with the increasing height, and the mean flow shows obvious enhancement when the wave packet passes. After a long time propagation (several periods), wave‐associated perturbation and energy can still concentrate in a limited region that is comparable in size to that given initially. The propagation path of wave energy coincides well with the ray path predicted by the linear gravity wave theory, but the magnitude of wave energy propagation velocity is evidently smaller than the group velocity derived from the linear gravity wave theory. This indicates that once gravity waves are generated, they propagate almost freely along their rays, and the nonlinear effect will only lower the propagation velocity of the wave‐associated energy. While gravity‐wave packets propagate in a nonisothermal atmosphere, the nonlinear propagation paths of wave energy depart clearly from the ray paths derived from the linear gravity wave theory under the WKB approximation, which indicates that the linear gravity‐wave theory under the WKB approximation can not predict the nonlinear propagation of gravity‐wave packet in a nonisothermal atmosphere.
Sensitivity of a cloud parameterization package in the National Center for Atmospheric Research Community Climate Model
Authors: Kao C.‐Y. J. , Smith W. S.
Published: September 2002

A physically based cloud parameterization package, which includes the Arakawa‐Schubert (AS) scheme for subgrid‐scale convective clouds and the Sundqvist (SUN) scheme for nonconvective grid‐scale layered clouds (hereafter referred to as the SUNAS cloud package), is incorporated into the National Center for Atmospheric Research (NCAR) Community Climate Model, Version 2 (CCM2). The AS scheme is used for a more reasonable heating distribution due to convective clouds and their associated precipitation. The SUN scheme allows for the prognostic computation of cloud water so that the cloud optical properties are more physically determined for shortwave and longwave radiation calculations. In addition, the formation of anvil‐like clouds from deep convective systems is able to be simulated with the SUNAS package. A 10‐year simulation spanning the period from 1980 to 1989 is conducted, and the effect of the cloud package on the January climate is assessed by comparing it with various available data sets and the National Center for Environmental Protection/NCAR reanalysis. Strengths and deficiencies of both the SUN and AS methods are identified and discussed. The AS scheme improves some aspects of the model dynamics and precipitation, especially with respect to the Pacific North America (PNA) pattern. CCM2's tendency to produce a westward bias of the 500 mbar stationary wave (time‐averaged zonal anomalies) in the PNA sector is remedied apparently because of a less “locked‐in” heating pattern in the tropics. The additional degree of freedom added by the prognostic calculation of cloud water in the SUN scheme produces interesting results in the modeled cloud and radiation fields compared with data. In general, too little cloud water forms in the tropics, while excessive cloud cover and cloud liquid water are simulated in midlatitudes. This results in a somewhat degraded simulation of the radiation budget. The overall simulated precipitation by the SUNAS package is, however, substantially improved over the original CCM2.
The contribution of mixing in Lagrangian photochemical predictions of polar ozone loss over the Arctic in summer 1997
Authors: Fairlie T. Duncan , Pierce R. Bradley , Al‐Saadi Jassim. A. , Grose William L. , Russell James M. , Proffitt Michael H. , Webster Christopher R.
Published: September 2002

Measurements from the Halogen Occultation Experiment, together with assimilated winds, temperatures, and diabatic heating rates from the NASA Goddard data assimilation office, are used in the NASA Langley Research Center trajectory‐photochemical model to compute photochemistry along three‐dimensional air parcel trajectories for the Northern Hemisphere for the period March through September 1997. These calculations provide a global perspective for the interpretation of constituent measurements made from the ER‐2 platform during the Photochemistry of Ozone Loss in the Arctic Region in Summer aircraft campaign. An important component of the model is a parameterization of sub‐grid‐scale diffusive mixing. The parameterization uses an “n‐member mixing” approach which includes an efficiency factor that enhances the mixing in regions where strain dominates the large‐scale flow. Model predictions of O3 and CH4 are compared with in situ measurements made from the ER‐2. Comparison of the in situ data with model predictions, conducted with and without diffusive mixing, illustrates the contribution that irreversible mixing makes in establishing observed tracer‐tracer correlations. Comparisons made for an ER‐2 flight in late April 1997 show that irreversible mixing was important in establishing observed tracer‐tracer correlations during spring 1997. Comparisons made in late June 1997, when filaments of very low N2O and CH4 were observed, indicate that remnants of air from the polar vortex survived unmixed in the low stratosphere 6 weeks after the breakup of the polar vortex in May. The results demonstrate that the sub‐grid‐scale mixing parameterization used in the model is effective not only for strong mixing conditions in late winter and early spring, but also for relatively weak mixing conditions that prevail in summer.
A simple and efficient method for retrieving surface UV radiation dose rate from satellite
Authors: Li Zhanqing , Wang Pucai , Cihlar Josef
Published: September 2002

A continual trend of ozone depletion has drawn much attention to the biologically harmful UV‐B radiation from the Sun reaching the Earth's surface. Satellite remote sensing provides a sole means of monitoring the global distribution of surface UV‐B. At present, there are very few inversion algorithms with sufficient accuracy and robustness for operational application. A new algorithm is proposed here to infer surface UV‐B irradiance and UV erythemal dose rate from satellite observations. The method is based on a simple model that treats UV radiative transfer in three distinct layers: an absorbing layer of ozone, a scattering layer of molecules, cloud and aerosol particles, and a layer of the Earth's surface. UV‐B irradiance and dose rate at the surface are determined by the transmittance of the ozone layer, which can be derived from TOMS total ozone measurements, and the reflectance of the scattering layer, which can be determined from any UV or visible channel outside of ozone absorption bands. The inversion algorithm developed here is very simple (a couple of analytical expressions) and contains a few parameters that can be readily obtained from satellites (except for aerosol variables). The performance of the algorithm is validated against the results of comprehensive radiative transfer modeling using a DISORT‐based model. Under a wide range of conditions (clear, cloudy, and turbid atmospheres) the retrieved surface UV‐B irradiance and erythemal dose rate from the simple inversion algorithm are nearly as accurate as those calculated from the DISRORT‐based model but require much less computation and input data.
A new model for dust emission by saltation bombardment
Authors: Lu Hua , Shao Yaping
Published: September 2002

In this paper, we present an analysis on the mechanism of dust emission and describe a new model for the prediction of dust emission rate caused by saltation bombardment, based on the volume removal by impacting sand grains as they plough into the soil surface. The model predicts a relationship between the removed volume V and the particle impacting velocity U of the form V ∝ Un, with n = 2 ∼ 3. The dust emission rate is found to be proportional to u*n + 1, where u* is friction velocity. These model predictions are consistent with wind tunnel and field observations. The model offers a new interpretation of observed data and a simple scheme for the calculation of dust emission.
Aerosol backscatter fraction and single scattering albedo: Measured values and uncertainties at a coastal station in the Pacific Northwest
Authors: Anderson T. L. , Covert D. S. , Wheeler J. D. , Harris J. M. , Perry K. D. , Trost B. E. , Jaffe D. J. , Ogren J. A.
Published: September 2002

Light scattering, hemispheric backscattering, and absorption properties of submicrometer and supermicrometer aerosol particles at low relative humidity and 550 nm wavelength are investigated as a function of air mass category during a 2‐month campaign at a midlatitude Pacific coastal station at Cheeka Peak, Washington. The main source of uncertainty in single scattering albedo (ω) measurements, namely, the measurement of light absorption, is addressed by the deployment of three identical absorption photometers and by relying on a recent calibration of this device using direct optical measurements. The absorption photometer measurement is corrected for response to light scattering, and measurements of sea‐salt aerosol in this campaign provide a partial validation of this correction. Scattering measurements by nephelometry are also corrected for known instrumental nonidealities. Uncertainties stemming from instrumental noise, drift, calibration, and correction factors are propagated to allow comparisons among air mass categories and with other data sets and, ultimately, to constrain the values of ω and other optical properties used in climate models. Marine aerosol over the midlatitude eastern Pacific is found to be weakly absorbing for the sub‐μm component and virtually nonabsorbing for the super‐μm component (separated at 1 μm, low‐relative humidity, aerodynamic diameter). A distinct increase in sub‐μm light extinction (especially absorption) observed during 2 days of sustained marine flow appears to be Asian pollution transported across the Pacific. Low levels of gaseous NOx during this period rule out nearby combustion sources, and low levels of particulate Fe, Al, and Si rule out a significant contribution from mineral dust. Excluding this episode, both scattering and absorption properties for marine sampling conditions are similar to those observed in the clean midlatitude Southern Hemisphere (Cape Grim, Tasmania). In general, continental influence, as indicated by trends over the air mass categories, tends to raise the backscatter ratio and lower ω. Light absorption values compared to previous marine and coastal measurements confirm the range of values found by others and the highly variable nature of this quantity.
Three‐dimensional simulation of stratospheric trace gas distributions measured by CRISTA
Authors: Riese M. , Tie X. , Brasseur G. , Offermann D.
Published: September 2002

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment has been flown on two space shuttle missions (STS 66 and STS 85). During these missions, global trace gas distributions have been measured with high spatial resolution. The first flight was performed in early November 1994 during a period of disturbed dynamical conditions characterized by relatively large wave activity and associated exchange of tropical and extratropical air. As a result, numerous small‐ and medium‐scale structures were present in the trace gas distributions measured by CRISTA. The detailed structure of the constituent distributions has been modeled with the National Center for Atmospheric Research Research on Ozone in the Stratosphere and Its Evolution (ROSE) model, which is driven by assimilated winds and temperatures provided by the U.K. Meteorological Office. The modeled trace gas distributions capture much of the measured structures. Very good agreement is found in the lower stratosphere of the northern hemisphere, with the exception of unrealisticly high variability of the modeled trace gas fields at equatorial and subtropical latitudes. In this paper, model results of two specific tracers, CFC‐11 and N2O, are compared to respective CRISTA measurements. For quantitative comparisons of trace gas transport in the ROSE model and trace gas transport associated with the measurements, CRISTA version 1 (level 2) data have been assimilated into the model by using a simple sequential technique. The trace gas assimilation system interpolated the measured distributions of long‐lived tracers onto the model grid and yields synoptic fields that are consistent with the CRISTA measurements, at each time step of the model (20 min). Horizontal eddy fluxes of CFC‐11 (31.6 mbar) calculated from the assimilated trace gas concentrations are in reasonable agreement with respective fluxes calculated from modeled trace gas fields without data assimilation. Both data sets indicate a large degree of temporal cancellation of eddy transport during the time period of the CRISTA measurements. The assimilated trace gas distributions represent a value‐added level 3 product, which has been used for transport and budget studies of CFC‐11 (31.6 mbar) and CH4 (4.6 mbar). The study indicates that irreversible transport processes are rather important at the 4.6 mbar pressure level during the time period of the CRISTA measurements. Most interesting is a pronounced mixing event from midlatitudes into the tropics, which is also evident in measured and calculated zonal mean CH4 mixing ratio tendencies.
Global impact of fossil fuel combustion on atmospheric NOx
Authors: Horowitz Larry W. , Jacob Daniel J.
Published: September 2002

Fossil fuel combustion is the largest global source of NOx to the troposphere. This source is concentrated in polluted continental boundary layers, and the extent to which it impacts tropospheric chemistry on a global scale is uncertain. We use a global three‐dimensional model of tropospheric chemistry and transport to study the impact of fossil fuel combustion on the global distribution of NOx during nothern hemisphere summer. In the model, we tag fossil fuel NOx and its reservoir NOy species in order to determine the relative contribution of fossil fuel combustion to NOx concentrations in different regions of the world. Our model includes a detailed representation of NOx‐O3‐nonmethane hydrocarbon (NMHC) chemistry, which is necessary to properly simulate the export of reactive nitrogen, including organic nitrates such as peroxyacyl nitrates (PANs), from the continental boundary layer. We find that fossil fuel combustion accounts for over 40% of NOx. concentrations in the lower and middle troposphere throughout the extratropical northern hemisphere. PANs are shown to provide an important mechanism for transporting NOx from source regions to the remote troposphere, accounting for over 80% of the fossil fuel NOx in the lower troposphere over most of the ocean. Sources in the United States are found to contribute about half of the fossil fuel NOx over the North Atlantic Ocean. Emissions from China, which are expected to increase rapidly in the coming decades, currently account for about half of the fossil fuel NOx over the western North Pacific Ocean; the influence of these emissions extends into the tropics. Because of this tropical influence, emissions from China have more potential than emissions in the United States to perturb the global oxidizing power of the atmosphere.
Implications for water monomer and dimer solar absorption from observations at Boulder, Colorado
Authors: Daniel J. S. , Solomon S. , Sanders R. W. , Portmann R. W. , Miller D. C. , Madsen W.
Published: September 2002

We present ground‐based spectral measurements of downward direct and diffuse solar intensities between 624 and 686 nm. Using the rising Sun as a light source, it is shown that the water dimer does not absorb significantly in this wavelength region. Over Boulder, Colorado, on July 10, 1998, the upper limit to the dimer vertical optical depth at these wavelengths is approximately 0.001, with an implied upper limit for instantaneous clear‐sky absorption of solar radiation of about 0.8 W/m2for an overhead Sun. The direct Sun measurements also show that in the observed wavelength region no other unknown structured absorber can account for more than 0.6 W/m2absorption of the instantaneous downward direct solar flux for an overhead Sun. Observations of light scattered through a thick cloud reveal that when the atmosphere is saturated with respect to water vapor, no observable dimer absorption occurs and there is no significant spectral shape change in water monomer absorption at our spectral resolution.
Observations of precipitable water vapor fluctuations in convective boundary layer via microwave interferometry
Authors: Shao X. M. , Carlos R. C. , Kirkland M. W. , Kao C.‐Y. J. , Jacobson A. R.
Published: September 2002

At microwave frequencies, each centimeter of precipitable water vapor (PWV) causes about 6.45 cm of extra electrical path length relative to the “dry” air. The fluctuations of the water vapor dominate the changes of the effective path length through the atmosphere in a relatively short time period of a few hours. In this paper we describe a microwave interferometer developed for water vapor investigations and present the observation results. The interferometer consists of 10 antennas along two orthogonal 400‐m arms that form many baselines (antenna pairs) ranging from 100 to 400 m. All the antennas receive a common CW signal (11.7 GHz) from a geostationary television satellite, and phase differences between pairs of antennas are measured. The phase differences reflect the column‐integrated water vapor differences from the top of the atmosphere to the spatially separated antennas at the ground. The interferometric, baseline‐differential measurements allow us to study the statistical properties of the PWV fluctuations, as well as the turbulent activity of the convective boundary layer (CBL). Structure function analysis of the interferometer measurements shows good agreement with results obtained from the Very Large Array (VLA) and with a theoretical model developed for radio astronomical very long baseline interferometry (VLBI), reported previously by other investigators. The diurnally varying structure constant correlates remarkably well with the combination of the latent and sensible heat fluxes measured simultaneously from a 10‐m meteorological tower. The average drift velocity of the PWV over the interferometer was also derived from the measurements. The derived velocity agrees well during the morning hours with the wind measured by an anemometer at the center of the interferometer.
The coupling of ClONO2, ClO, and NO2 in the lower stratosphere from in situ observations using the NASA ER‐2 aircraft
Authors: Stimpfle R. M. , Cohen R. C. , Bonne G. P. , Voss P. B. , Perkins K. K. , Koch L. C. , Anderson J. G. , Salawitch R. J. , Lloyd S. A. , Gao R. S. , Del Negro L. A. , Keim E. R. , Bui T. P.
Published: September 2002

The first in situ measurements of ClONO2 in the lower stratosphere, acquired using the NASA ER‐2 aircraft during the Polar Ozone Loss in the Arctic Region in Summer (POLARIS) mission, are combined with simultaneous measurements of ClO, NO2, temperature, pressure, and the calculated photolysis rate coefficient (JClONO2) to examine the balance between production and loss of ClONO2. The observations demonstrate that the ClONO2 photochemical steady state approximation, [ClONO2]PSS = k × [ClO] × [NO2] / JClONO2, is in good agreement with the direct measurement, [ClONO2]MEAS. For the bulk of the data (80%), where T>220 K and latitudes >45°N, [ClONO2]PSS = 1.15±0.36 (1σ) × [ClONO2]MEAS, while for T<220 K and latitudes <45°N the result is somewhat less at 1.01±0.30. The cause of the temperature and/or latitude trend is unidentified. These results are independent of solar zenith angle and air density, thus there is no evidence in support of a pressure‐dependent quantum yield for photodissociation of ClONO2 at wavelengths >300 nm. These measurements confirm the mechanism by which active nitrogen (NOx = NO + NO2) controls the abundance of active chlorine (Clx = ClO + Cl) in the stratosphere.
A method to generate surface UV radiation maps over Europe using GOME, Meteosat, and ancillary geophysical data
Authors: Verdebout Jean
Published: September 2002

This paper presents a method for generating surface ultraviolet (UV) radiation maps over Europe, with a spatial resolution of 0.05°, and potentially on a half‐hour basis. The UV irradiance is obtained by interpolation in a look‐up table (LUT), the entries of which are solar zenith angle, total column ozone amount, cloud liquid water thickness, near‐surface horizontal visibility, surface elevation, and UV albedo. Both satellite (Meteosat, GOME) and nonsatellite (synoptic observations, meteorological model results, digital elevation model) data are exploited to assign values to the influencing factors. With the help of another LUT simulating the visible signal, Meteosat data are processed to retrieve the cloud liquid water thickness. The radiative transfer calculations are performed with the UVspec code. A preliminary step consists in generating an effective surface Meteosat albedo map from a series of 10 consecutive days. In this process the well‐known difficulty of distinguishing clouds from snow‐covered surfaces is encountered. An attempt is made to partially resolve the ambiguity by using the Meteosat infrared channel and modeled snow cover data. After additional empirical cloud filtering, the effective albedo map is used as a baseline to estimate the cloud liquid water thickness. The UV surface albedo is assigned uniform values for land and sea/ocean, except in the presence of snow. In this case it is given a value proportional to the Meteosat effective albedo. The total column ozone is extracted from the level 3 GOME products. The aerosol optical thickness is mapped by gridding the daily measurements performed by ∼1000 ground stations. The digital elevation model is the GTOPO30 data set from the U.S. Geological Survey. European wide UV dose rate maps are presented for one day in April 1997, and the influence of the various factors is illustrated. A daily integrated dose map was also generated using 27 Meteosat acquisitions at half‐hour intervals on the same day. The dose map produced in this way takes into account the evolution of the cloud field and is thought to be more accurate than if it were estimated from one data take, in particular at the relatively high spatial resolution of the product. Finally, a preliminary comparison of modeled dose rate and daily dose with measurements performed with a ground instrument is discussed.
On the representativeness of carbon dioxide measurements
Authors: Haszpra László
Published: September 2002

On the basis of the measurements at two monitoring sites located close to each other (220 km) in plain regions in Hungary, the representativeness of low‐elevation continental CO2 measurements is estimated. It is shown that under such conditions only the measurements carried out in the early afternoon hours can be considered as regionally representative for the CO2 content of the planetary boundary layer (PBL). Filtering the data in this way, it is calculated that the characteristic CO2 mixing ratio in the PBL may be about 2.5 ppm higher over this part of Europe than at the Mauna Loa Observatory (National Oceanic and Atmospheric Administration), Hawaii.
Transport into the northern hemisphere lowermost stratosphere revealed by in situ tracer measurements
Authors: Ray Eric A. , Moore Fred L. , Elkins James W. , Dutton Geoffrey S. , Fahey David W. , Vömel Holger , Oltmans Samuel J. , Rosenlof Karen H.
Published: September 2002

The Lightweight Airborne Chromatograph Experiment (LACE) has made in situ measurements of several long‐lived trace gases in the upper troposphere and lower to middle stratosphere as part of the Observations of the Middle Stratosphere (OMS) balloon program. The tracers measured by LACE include several photolytic species (CFC‐11, CFC‐12, and halon‐1211) as well as SF6. LACE measurements of these long‐lived tracers as well as nearly simultaneous measurements of water vapor and CO2 are used to investigate transport into the lowermost stratosphere, a region where few in situ measurements exist. The measured photolytic species and water vapor are used in a simple mass balance calculation to estimate the mixture of tropospheric and overworld (θ>380 K) air in the lowermost stratosphere. In the northern midlatitudes during September 1996, most of the air in the lowermost stratosphere sampled at the flight location (34.5°N) was transported quasi‐isentropically from the troposphere. Measurements from both a May 1998 midlatitude flight and a June 1997 high‐latitude flight (64.5°N) revealed the air sampled in the lowermost stratosphere to be dominated by downward advection from the overworld. Atmospheric SF6 and CO2 can uniquely reveal timescales and spatial scales of transport due to these species' large growth rates and subsequent latitudinal surface and free tropospheric gradients. Measurements in the lowermost stratosphere from the September northern midlatitude flight coupled with surface measurements of these species revealed a transport timescale of no more than 1.5 months from the surface to the lowermost stratosphere. The SF6 and CO2 mixing ratios were also consistent with mostly Northern Hemisphere tropospheric air in the lowermost stratosphere. These results point out the usefulness of high‐resolution in situ measurements of long‐lived tracers to help determine timescales and spatial scales of transport in the region of the upper troposphere and lowermost stratosphere.
High spectral resolution atmospheric radiative transfer: Application of the equivalence theorem
Authors: Partain Philip T. , Heidinger Andrew K. , Stephens Graeme L.
Published: September 2002

This paper introduces several new variations of the equivalence theorem of Irvine [1964] which may increase the speed and accuracy of spectral radiative transfer models that calculate spectral radiance or flux. Using this theory, spectral gaseous, cloud, and surface absorptions are accommodated by integrating or summing over photon path length and scattering probability density functions (pdfs) after the completion of the multiple‐scattering calculation. This procedure can be performed for absorption coefficients at any spectral resolution within a wavelength interval in which scattering properties of the atmosphere can be considered constant. This technique eliminates the need to run the multiple‐scattering portion of a model more than once for each interval in lieu of integration and/or summation. If this procedure can be performed efficiently, dramatic increases in model speed may be realized. Also, because absorption coefficient spectral resolution can be extremely fine, the need for approximations or parameterizations is eliminated, increasing model accuracy. Unlike the original derivation, the new version of the gaseous absorption equation allows the use of complex model scattering atmospheres. An approximation is introduced which allows the use of gas profiles which vary in the vertical. Because employment of the complete theory requires a relatively large amount of computer memory, a pdf approximation is introduced to make it tractable. Validation of each relation is presented using a Monte Carlo model simulating shortwave flux. An example of shortwave flux transmitted through a three‐dimensional model atmosphere obtained from the Monte Carlo/equivalence theorem (MC/ET) model is shown along with an analysis of the effect of constant scattering property wavelength interval size on the resulting broadband flux.
Inverse modeling of annual atmospheric CO2 sources and sinks: 2. Sensitivity study
Authors: Bousquet P. , Peylin P. , Ciais P. , Ramonet M. , Monfray P.
Published: September 2002

Atmospheric transport models can be used to infer surface fluxes of atmospheric CO2 from observed concentrations using inverse methods. One of the main problem of these methods is the question of their sensivity to all the parameters involved in the calculation. In this paper we study precisely the influence of the main parameters on the net CO2 fluxes inferred by an annual Bayesian three‐dimensional (3‐D) inversion of atmospheric CO2 monthly concentrations. This inversion is described as the control inversion (S0) of Bousquet et al. [this issue]. Successively, at regional to global spatial scales we analyze the numerical stability of the solution to initial fluxes and errors, the influence of a priori flux scenario, the sensitivity to the atmospheric transport model used, the influence of δ13C measurements, and the influence of the atmospheric network. We find that the atmospheric transport model introduces a large uncertainty to the inferred budget, which overcomes our control run uncertainties. The effects of vertical transport on CO2 concentrations appear to be a critical point that has to be investigated further. Spatial patterns of fluxes also have significant influence on a regional basis. We notice that accounting for the Baltic Sea station (BAL) deeply modifies the Europe versus Asia partition of the land uptake at mid and high latitudes of the Northern Hemisphere. We also analyze the weak influence of using δ13C measurements as additional constraints. In the tropics we find that the low level of constraints imposed by the atmospheric network limits the analysis of fluxes to zonal means. Finally, we calculate overall estimates of CO2 net sources and sinks at continental scale, accounting for all sensivity tests. Concerning the controversial partition of CO2 sink at mid and high latitudes of the Northern Hemisphere, we find (on average, for the 1985–1995 period) an overall partition of the sink of 0.7±0.7 Gt C yr1 for North America, 0.2±0.3 Gt C yr−1 for the North Pacific Ocean, 0.5±0.8 Gt C yr−1 for Europe, 0.7±0.3 Gt C yr−1 for the North Atlantic Ocean, and 1.2±0.8 Gt C yr−1 for north Asia. This overall partition tends to place an important land uptake over north Asia. However, uncertainties remain large when we account for all the sensitivity tests.
A numerical simulation of the stratospheric ozone quasi‐biennial oscillation using a comprehensive general circulation model
Authors: Bruhwiler Lori Perliski , Hamilton Kevin
Published: September 2002

The Geophysical Fluid Dynamics Laboratory's SKYHI general circulation model (GCM) including a new detailed stratospheric photochemistry module has been integrated for over 14 years with an imposed zonally symmetric momentum source designed to force a realistic quasi‐biennial oscillation (QBO) in the tropical stratosphere. The GCM features an internally consistent calculation of the annual stratospheric circulation cycle and exhibits realistic extratropical stratospheric interannual variability, making it appropriate for the detailed investigation of QBO/annual cycle interactions. The simulated ozone QBO is generally realistic in the tropics and subtropics, and, in particular, the QBO in total column ozone agrees quite well with that derived from satellite observations. A detailed analysis of the QBO modulation of the zonal‐mean ozone budget has been performed. The advective effects of the QBO‐induced residual mean circulation are found to be strongly dependent on season, in accord with recent results from some two‐dimensional model studies [Jones et al., 1998; Kinnersley and Tung, 1998]. In addition, the QBO modulation of explicitly resolved eddy transport in the GCM is found to make a significant contribution to the ozone budget, and this helps account for the strong seasonal synchronization of the ozone QBO.
Intercomparison of lamp and detector‐based UV‐irradiance scales for solar UV radiometry
Authors: Jokela Kari , Ylianttila Lasse , Visuri Reijo , Leszczynski Kirsti , Kärhä Petri , Ikonen Erkki
Published: September 2002

The high uncertainty of calibration is the most serious factor limiting accurate measurements of the solar UV, needed for the assessment of global UV trends. In this study, the calibration of FEL‐type standard lamps traceable to three primary standard laboratories were compared with a transfer uncertainty of ±1.4% (2σ). In comparison with the reference lamp, the spectral UV irradiance scales agreed within 1.5%. However, the difference between a new lamp and the present reference was 2%, which is close to the limits of total uncertainty. It was interesting to observe that one of the scales, based on a cryogenic absolute radiometer, was in good agreement with the scales based on blackbody radiation sources. Examination of the long‐term stability of the lamp‐based UV scale in Finland showed a significant decrease of 6% in the scale when the standard lamp was changed to a lamp directly traceable to the primary standard of the National Institute of Standards and Technology (NIST). Previously, the lamp was traceable to the NIST through the secondary standard of Optronic Laboratories Inc. The main obstacle in improving the global conformity of UV scales is the instability of halogen standard lamps. On the basis of the present study, it is strongly recommended to use detector stabilization of the standard lamps and to investigate the use of portable detector standards in the intercomparisons between primary standards laboratories.
Shortwave radiation budget of the northern hemisphere using International Satellite Cloud Climatology Project and NCEP/NCAR climatological data
Authors: Hatzianastassiou N. , Vardavas I.
Published: September 2002

A deterministic model for atmospheric shortwave (SW) radiation transfer was used with climatological data to predict the mean monthly zonal (10° latitudinal zones) SW radiation budget at the Earth's surface and at the top of atmosphere (TOA) for the Northern Hemisphere. The climatological data were obtained from the International Satellite Cloud Climatology Project (ISCCP, 1983–1990), and from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project (1979–1995). Aerosol particles are accounted for in the study. The model's outgoing fluxes agree within 4 W m−2on average with the corresponding values determined from the Earth Radiation Budget Experiment (ERBE, 1985–1989) satellite data. The model is able to predict the seasonal and latitudinal variation of SW TOA fluxes. Owing to the lack of a complete global climatology, the SW surface radiative fluxes predicted by our model were validated through intercomparison with other model results. Seasonal variations of mean hemispherical and latitudinal variations of mean annual fluxes are also estimated. Mean annual hemispherical values for the Northern Hemisphere were calculated for SW fluxes and for cloud radiative forcing. The model gives a mean planetary albedo for the Northern Hemisphere of 0.295, which is in agreement with 0.297±0.007 from the 5 years of ERBE data. The mean annual cloud radiative forcing for the Northern Hemisphere was found to be equal to −40 W m−2.
Lamps as means to homogenize solar ultraviolet irradiance measurements performed with different spectroradiometers
Authors: Kjeldstad Berit , Johnsen Bjørn , Koskela Tapani
Published: September 2002

Portable lamp irradiance calibration units of different size were used to transfer a relative calibration in a group of spectroradiometers operating at the same site. Every unit was used as normally in the field or at a home laboratory, i.e., including any errors related to the method itself. The calibration obtained for each instrument was used to reprocess their synchronous solar measurements. Solar measurements deviating by typically ±10% got a standard deviation as low as 3–4% when corrections derived from a common lamp measurement were applied. Because instrumental features remained the same in the original and in the reprocessed solar data, the improvement of the agreement in the solar measurements was considered as an indication of a more homogeneous irradiance scale. The remaining disagreement must be a sum of the uncertainty related to the use of each calibration unit and any instrumental peculiarities. Each of the lamp units could bring the scales of the specific instrument group closer. This was especially true for distinct outliers in the group. Even the smallest units performed almost as well as more sophisticated equipment, and an agreement of about 5% in the sky measurements could be reached, which is better than that seen in most recent intercomparisons.