bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the atmospheric dust cycle: 2. Simulation of Saharan dust sources
Authors: Marticorena B. , Bergametti G. , Aumont B. , Callot Y. , N'Doumé C. , Legrand M.
Published: February 2004

A soil‐derived dust emission scheme has been designed in order to provide simulation of mineral dust sources for atmospheric transport models [Marticorena and Bergametti, 1995]. This physical scheme considers the influence of surface features to compute the erosion threshold and the intensity of the dust emissions. It has been validated by comparison with relevant experimental data. However, it was necessary to extend its applicability and to test its capability to reproduce dust emissions over large arid areas. Specific methods have been developed to determine the parameters required by the dust production model for large‐scale applications. The surface features (dimensions of the roughness elements and soil mineralogy) and the wind velocity allow the computation of the roughness lengths of the surface, the size distribution of the erodible soils, and the wind friction velocity. A map of these surface characteristics has been established for the western part of the Sahara. This map coupled to the Europan Center for Medium‐Range Weather Forecast (ECMWF) surface wind fields are used to simulate dust emissions in this desert region. The simulated emissions have been compared to the Infrared Difference Dust Index (IDDI), determined by means of the Meteosat thermal infrared imagery. The simulated dust event frequencies are in good agreement with those observed by satellite. The comparison between the simulated fluxes and the satellite observations for 3 months of the year 1991 has revealed a linear relationship between the logarithm of the simulated flux and the IDDI. The annual and monthly dust emissions for 1991 and 1992 have been estimated and compared to those established by d'Almeida [1986]. Both the frequencies and the intensities of the emissions are well reproduced by the model associated with the surface features map.
Meteorological factors affecting ozone profiles over the western North Atlantic
Authors: Doran J. C. , Zhong S. , Berkowitz C. M.
Published: February 2004

Ozone measurements taken with an aircraft over the western North Atlantic in the summer of 1992 revealed numerous profiles that consisted of two principal layers with different, nearly constant mixing ratios in each layer. The lower layer was characterized by relatively low mixing ratios (< 25–30 parts per billion by volume), while the upper layer had values a factor of 2 or more higher. The depths of the lower layer frequently corresponded to the depths of the mixed layer over the ocean as estimated from potential temperature observations. The upper ozone layer extended at least to the maximum sampling height of the aircraft on these flights, approximately 2.5 km. A mesoscale model is used to analyze the meteorology over the area for a representative case study day. Trajectory analysis shows that the air in the aircraft sampling region originated near Hudson Bay, followed a path that avoided major anthropogenic sources of ozone precursors over land, and eventually moved out over the ocean. Because of inhomogeneities in the sea surface temperatures in the observation area, the spatial and temporal evolution of the boundary layer over the ocean differed significantly over distances of only a few hundred kilometers. These differences, coupled with vertical mixing in the boundary layer and large‐scale vertical motions arising from synoptic and terrain influences, are identified as mechanisms responsible for the development of the characteristic shapes of the ozone and potential temperature profiles. This conclusion is supported by additional results obtained from using the mesoscale model to drive a Lagrangian particle dispersion model to simulate the transport and diffusion of a passive tracer; the major features of the ozone profiles are reproduced in the particle profiles. These findings indicate the critical role played by meteorological processes, irrespective of the details of the photochemical reactions. The results also imply that a failure to incorporate detailed descriptions of meteorology in photochemical models may lead to erroneous interpretations of the data.
Elemental characterization of particulate matter emitted from biomass burning: Wind tunnel derived source profiles for herbaceous and wood fuels
Authors: Turn S. Q. , Jenkins B. M. , Chow J. C. , Pritchett L. C. , Campbell D. , Cahill T. , Whalen S. A.
Published: February 2004

Particulate matter emitted from wind tunnel simulations of biomass burning for five herbaceous crop residues (rice, wheat and barley straws, corn stover, and sugar cane trash) and four wood fuels (walnut and almond prunings and ponderosa pine and Douglas fir slash) was collected and analyzed for major elements and water soluble species. Primary constituents of the particulate matter were C, K, Cl, and S. Carbon accounted for roughly 50% of the herbaceous fuel PM and about 70% for the wood fuels. For the herbaceous fuels, particulate matter from rice straw in the size range below 10 μm aerodynamic diameter (PM10) had the highest concentrations of both K (24%) and Cl, (17%) and barley straw PM10 contained the highest sulfur content (4%). K, Cl, and S were present in the PM of the wood fuels at reduced levels with maximum concentrations of 6.5% (almond prunings), 3% (walnut prunings), and 2% (almond prunings), respectively. Analysis of water soluble species indicated that ionic forms of K, Cl, and S made up the majority of these elements from all fuels. Element balances showed K, Cl, S, and N to have the highest recovery factors (fraction of fuel element found in the particulate matter) in the PM of the elements analyzed. In general, chlorine was the most efficiently recovered element for the herbaceous fuels (10 to 35%), whereas sulfur recovery was greatest for the wood fuels (25 to 45%). Unique potassium to elemental carbon ratios of 0.20 and 0.95 were computed for particulate matter (PM10 K/C(e)) from herbaceous and wood fuels, respectively. Similarly, in the size class below 2.5 μm, high‐temperature elemental carbon to bromine (PM2.5 C(eht)/Br) ratios of ∼7.5, 43, and 150 were found for the herbaceous fuels, orchard prunings, and forest slash, respectively. The molar ratios of particulate phase bromine to gas phase CO2(PM10 Br/CO2) are of the same order of magnitude as gas phase CH3Br/CO2reported by others.
Detection of cirrus overlapping low‐level clouds
Authors: Jin Yao , Rossow William B.
Published: February 2004

A multispectral method is proposed to detect two‐layer cloud systems with an optically thin (τ<1.0) upper level (Pc<600 mbar) cloud layer over a lower (600 mbar < Pc ≤ 900 mbar) cloud layer of τ>1.0, with at least 100‐mbar separation. The method uses the results from different high‐resolution infrared radiometer sounder (HIRS) channel combinations assuming a single cloud layer in the CO2‐Slicing technique and is valid over both land and ocean. Two months of HIRS data (July 1989 and January 1990) have been analyzed with this method. Globally (excluding regions poleward of 60°) for HIRS field of view (FOV) (about 17 km at nadir) the fraction of such two‐layer cloudiness is 25.5% over land and 32.0% over ocean for July 1989 and is 17.8% over land and 25.6% over ocean for January 1990 (this is not the total fraction of two‐layer systems). The global distribution patterns of two‐layer cloudiness for these 2 months are also presented: the fraction of two‐layer cloudiness is larger over ocean than over land; it is larger in the tropics and midlatitude storm zones and smaller in the subtropical zones and marine stratiform cloud regions; over land it is larger in the summer than in the winter at all latitudes; over ocean it is larger in the summer for the northern hemispheric eastern Pacific region while is larger in the winter for all other regions. Qualitative comparisons to surface and upper air observations are also presented and are very encouraging.
Numerical study of the structure and evolution of a heated planetary boundary layer with a jet
Authors: Liou Yu‐Chieng , Lilly Douglas K.
Published: February 2004

The structure and evolution of a heated, sheared planetary boundary layer (PBL) similar to the one developed on July 11, 1987, during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) are investigated by a two‐ and a three‐dimensional large eddy simulation (LES) model. The simulated results are utilized to compare with the single Doppler lidar data whose validity, however, has never been thoroughly verified due to insufficient independent observations. In contrast to the traditional research on a buoyancy‐driven, windless convective boundary layer (CBL), the horizontal and vertical domains of this study are designed to be sufficiently large so that the principal physical processes involved in the development of this boundary layer can be successfully simulated. They include (1) large eddies generated by the surface sensible heat flux, (2) internal gravity waves excited in the stable layer due to the lifting mechanism exerted by the rising large eddies, (3) interaction between the waves and the background wind shear, and (4) wave breakdown caused by the convective instability when the flow speed exceeds the phase speed. The mean and statistical properties of this boundary layer turn out to be quite different from those of a CBL. Among them, the most unique feature is that in the stable layer the direction of the momentum flux (
), which is transported by the gravity waves, is countergradient. The occurrence of this phenomenon, derived by lidar and confirmed by the simulation, is associated with the existence of a critical layer where the Doppler‐shifted frequency vanishes. Under this critical layer the vertical profile of horizontal velocity variance (
) is found to exhibit a second maximum. The simulated results of potential temperature flux (
) as well as the potential temperature variance (
) also imply a second local absolute value maximum in the stable layer. The former is believed to be closely related to the formation of convective instability. Despite the model's ability in simulating the physical processes involved in the FIFE PBL, the large quantitative discrepancy discovered between the model‐generated and the lidar‐extracted statistical properties lead to a consistency check for the latter. It is shown that in the stable layer the magnitudes of the lidar‐observed momentum flux (
) and the vertical velocity variance (
) appear to be too strong. Several possible error sources which can contaminate the lidar observations are discussed.
Soot aerosol in the lower stratosphere: Pole‐to‐pole variability and contributions by aircraft
Authors: Pueschel R. F. , Boering K. A. , Verma S. , Howard S. D. , Ferry G. V. , Goodman J. , Allen D. A. , Hamill P.
Published: February 2004

A NASA ER‐2 high‐altitude research aircraft intercepted the exhaust wake of a supersonic Concorde aircraft in the stratosphere near New Zealand on October 8, 1994. Black carbon (soot) aerosol (BCA) was sampled by wire impactors during the first five of 12 short‐duration wake intercepts. BCA concentration in Concorde exhaust at 16.3 km altitude was 0.2 particles cm−3, the size distribution peaked at a geometric mean radius of 0.09 μm, and the mass loading was 2.0±1.4 ng m−3. With a plume dilution factor (DF) of 1.0×10−5, determined by the ratio of CO2 measured in the plume (above the ambient stratospheric background level) to CO2 in the engine exhaust plane, the Concorde BCA emission index was EI(BCA)=0.07±0.05 g BCA per kg fuel burned. Applying this EI to estimates of aircraft fuel burned by the current subsonic fleet in the stratosphere yields average stratospheric BCA loadings of 0.5 ng m−3, commensurate with observations in the northern stratosphere. Applying the Concorde EI to fuel consumption by a projected future fleet suggests a twofold‐threefold increase of stratospheric BCA by the year 2015. A strong gradient in BCA concentration exists between the northern and the southern hemispheres, indicating interhemispheric mixing times longer than stratospheric residence times.
Vertical profile measurements of ozone at Lauder, New Zealand, during ASHOE/MAESA
Authors: McGee Thomas J. , Gross Michael , Singh Upendra , Kimvilakani Patrick , Matthews Andrew , Bodeker Gregory , Connor Brian , Tsou J. J. , Proffitt Michael , Margitan James
Published: February 2004

The Goddard Space Flight Center stratospheric ozone lidar was deployed at the National Institute for Water and Atmospheric Research (NIWA) facility at Lauder, New Zealand (45°S, 169°E), during all four of the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) flight periods. The site is about 500 km south of Christchurch. Efforts were made to acquire lidar data before dawn and after sunset on the days the ER‐2 was flown. A total of 79 measurements were made on 47 individual nights. Each measurement provided vertical profiles of aerosols, temperature, and ozone. Profiles begin at ∼8 km and extend to 35, 50–55, and 75 km for aerosols, ozone, and temperature, respectively. NIWA personnel launched electrochemical concentration cell ozonesondes on a number of these occasions. A summary of these data will be presented along with comparisons with data from ER‐2 instruments. Average profiles for each of the four ASHOE/MAESA deployments were constructed for use as a climatological profile for model initialization.
H2SO4 vapor pressure of sulfuric acid and ammonium sulfate solutions
Authors: Marti James J. , Jefferson Anne , Cai Xiao Ping , Richert Chad , McMurry Peter H. , Eisele Fred
Published: February 2004

Few measurements of H2SO4 vapor pressure have been made for sulfuric acid in the temperature and concentration ranges of atmospheric interest because of the very low pressures involved (below 10−4 Pa, or 10−6 torr); no such measurements appear to have been made for sulfuric acid solutions neutralized with ammonia. This work presents measurements of H2SO4 vapor pressure for aqueous sulfuric acid solutions between 55 and 77 wt% H2SO4 (corresponding to about 5–25% relative humidity), ammonium sulfate solids at low humidities, and partially neutralized sulfate solutions with [NH4+]: [SO4=] ratios between 0.13 and 1.0. The vapor pressure data collected over sulfuric acid solutions generally agree with the predictions of Ayers, et al. [1980], although positive deviation was observed for the more dilute solutions. The good agreement between this measurement and previous efforts by absolute techniques suggests that the evaporative coefficient for the H2SO4‐H2O system is near unity. H2SO4 vapor pressures over solid ammonium sulfate were measured between 27°C and 60°C; the data were fitted to In p = A/T + B, with A = −5928 and B = −3.77. The H2SO4 vapor pressures of mixed H2SO4‐H2O‐(NH4)2SO4 solutions dropped significantly as the [NH4+]:[SO4=] ratio exceeded 0.5. The results suggest that ammonia could very effectively stabilize molecular clusters of sulfuric acid and water in the atmosphere against evaporation, leading to rates of new particle formation higher than those predicted by binary H2SO4‐H2O theory.
Past, present, and future modeled ozone trends with comparisons to observed trends
Authors: Jackman Charles H. , Fleming Eric L. , Chandra Sushil , Considine David B. , Rosenfield Joan E.
Published: February 2004

The NASA Goddard Space Flight Center (GSFC) two‐dimensional (2‐D) model of stratospheric transport and photochemistry has been used to predict ozone changes that have occurred in the past 20 years from anthropogenic chlorine and bromine emissions, solar cycle ultraviolet flux variations, the changing sulfate aerosol abundance due to several volcanic eruptions including the major eruptions of El Chichón and Mount Pinatubo, solar proton events (SPEs), and galactic cosmic rays (GCRs). The same linear regression technique has been used to derive profile and total ozone trends from both measurements and the GSFC model. Derived 2‐D model ozone profile trends are similar in shape to the Solar Backscattered Ultraviolet (SBUV) and SBUV/2 trends with highest percentage decreases in the upper stratosphere at the highest latitudes. The general magnitude of the derived 2‐D model upper stratospheric negative ozone trend is larger than the trends derived from the observations, especially in the northern hemisphere. The derived 2‐D model negative trend in the lower stratosphere at middle northern latitudes is less than the measured trend. The derived 2‐D model total ozone trends are small in the tropics and larger at middle and high latitudes, a pattern that is very similar to the Total Ozone Mapping Spectrometer (TOMS) derived trends. The differences between the derived 2‐D model and TOMS trends are generally within 1–2% in the northern hemisphere and the tropics. The derived 2‐D model trends are generally more in southern middle and high latitudes by 2–4%. Our 2‐D model predictions are also compared with the temporal variations in total ozone averaged between 65°S and 65°N over the TOMS observing period (1979–1993). Inclusion of anthropogenic chlorine and bromine increases, solar cycle ultraviolet flux variations, and the changing sulfate aerosol area abundance into our model captures much of the observed TOMS global total ozone changes. The model simulations predict a decrease in ozone of about 4% from 1979 to 1995 due to the chlorine and bromine increases. The changing sulfate aerosol abundances were computed to significantly affect ozone and result in a maximum decrease of about 2.8% in 1992 in the annually averaged almost global total ozone (AAGTO) computed between 65°S and 65°N. Solar ultraviolet flux variations are calculated to provide a moderate perturbation to the AAGTO over the solar cycle by a maximum of ±0.6% (about 1.2% from solar maximum to minimum). Effects from SPEs are relatively small, with a predicted maximum AAGTO decrease of 0.22% in 1990 after the extremely large events of October 1989. GCRs are computed to cause relatively minuscule variations of a maximum of + 0.02% in AAGTO over a solar cycle.
Short‐period fluctuations of the diurnal tide observed with low‐latitude MF and meteor radars during CADRE: Evidence for gravity wave/tidal interactions
Authors: Nakamura T. , Fritts D. C. , Isler J. R. , Tsuda T. , Vincent R. A. , Reid I. M.
Published: February 2004

MF and meteor radar data from four equatorial and subtropical sites (Hawaii, Christmas Island, Jakarta, and Adelaide) are used to examine diurnal tide amplitude and phase variability at mesosphere and lower thermosphere altitudes. All sites exhibit significant seasonal variability, with the largest amplitude fluctuations occurring at Hawaii and Adelaide. Shorter‐term variability is found to occur primarily on timescales of ∼5 to 30 days. Amplitude and phase fluctuations are well correlated among different sites on occasion, but in general, the amplitude and phase coherences are low and suggest significant local influences on the tidal structures. The temporal behavior of height variations of the diurnal tide amplitude and phase is also examined. Cross correlations and cross spectra of these tidal parameters, especially between the amplitude and phase, are examined closely. The tendency for phase maxima to lead amplitude maxima is consistent with tidal modulation of gravity wave propagation and momentum fluxes, with a corresponding feedback by the gravity wave momentum flux divergences on the observed tidal structures. These results substantially extend previous more limited studies of gravity wave/tidal interactions and provide a statistical basis for the possible importance of this interaction and its influences on the diurnal tidal structure.
Meteorological characteristics and spatial extent of upslope events during the 1993 Tropospheric OH Photochemistry Experiment
Authors: Baumann Karsten , Williams Eric J. , Olson Jane A. , Harder Jerald W. , Fehsenfeld Fred C.
Published: February 2004

A detailed study of mountain‐valley circulation at the Front Range, west of Boulder, Colorado, during the transition period from summer to fall has been conducted using an extensive chemical and meteorological data set. This set was collected during the Tropospheric OH Photochemistry Experiment (TOHPE) in August and September 1993. One major objective of TOHPE was to compare chemical trace gas concentrations measured simultaneously by a long‐path (10.3 km) absorption spectrometer and by various in situ methods that were located at the ends of the long‐path beam. Generally, the study area experienced clean westerly flow challenging the detection limits of the trace gas measurement techniques and limiting the dynamic range of the instrument comparison. Occasionally, however, the westerly flow was replaced by thermally driven upslope flow that brought in polluted air masses out of the Denver‐Boulder urban corridor from the east. The trace gas signatures of these upslope events are used to characterize the frequency and spatial extent of the specific flow mechanisms. Upslope flow reached regional scale at sunset, providing short instances of the best meteorological conditions for comparing the trace gas measurements at higher concentration levels. The concept of a generally easterly moving layer of regionally polluted air masses applies and agrees well with these observations. Two pollution events on September 28 and 29, 1993, are studied in detail and strongly support this concept. These complex upslope transport mechanisms may have the potential for mixing anthropogenic pollutants into the free troposphere.
Validation of atmospheric correction over the oceans
Authors: Clark D. K. , Gordon H. R. , Voss K. J. , Ge Y. , Broenkow W. , Trees C.
Published: February 2004

By validation of atmospheric correction, we mean quantification of the uncertainty expected to be associated with the retrieval of the water‐leaving radiance from the measurement of the total radiance exiting the ocean‐atmosphere system. This uncertainty includes that associated with the measurement or estimation of auxiliary data required for the retrieval process, for example, surface wind speed, surface atmospheric pressure, and total ozone concentration. For a definitive validation this quantification should be carried out over the full range of atmospheric types expected to be encountered. However, funding constraints require that the individual validation campaigns must be planned to address the individual components of the atmospheric correction algorithm believed to represent the greatest potential sources of error. In this paper we develop a strategy for validation of atmospheric correction over the oceans that is focused on EOS/MODIS. We also provide a description of the instrumentation and methods to be used in the implementation of the plan.
Synoptic climatology, and intrahemispheric associations, of cold air mesocyclones in the Australasian sector
Authors: Carleton Andrew M. , Song Yudong
Published: February 2004

Satellite IR images for seven months in 1992 are interpreted for cold air mesoscale cyclones (mesocyclones) occurring in the Australasian sector (∼70°E–150°W) of the Southern Ocean. Time‐averaged (monthly, seasonal) distributions of mesocyclogenesis, mesocyclolysis, and tracks of movement, along with statistical summaries of mesocyclone attributes (e.g., cloud vortex size, speeds of movement), are presented and discussed in the context of the larger‐scale atmospheric circulation. Maximum frequencies of mesocyclones occurred in the transitional months of April and October 1992, with a secondary peak in July. Statistically significant differences in mesocyclone track length between months appear related dominantly to changes in speed of the background flow, associated with the semiannual oscillation (SAO) of tropospheric pressure/height. The associations of mesocyclone “outbreaks” with composite anomaly fields of pressure and height are identified for three subareas of the Australasian sector suggested by the analysis of mesocyclone spatial patterns. Outbreaks occur in the strong southerly geostrophic airflow located between pressure and height anomalies that are negative (positive) to the eastward (westward). When outbreaks occurred in the New Zealand subarea in 1992, a similarly strong couplet of pressure/height anomalies developed in the southern South America/Antarctic Peninsula sector but not when outbreaks occurred south of Australia. The mesocyclone remote association that is suggested is evaluated by using polar orbiter IR imagery for the southeastern Pacific region. Frequencies of mesocyclones increase (decrease) west of Chile but decrease (increase) through Drake Passage when mesocyclone outbreaks occur near New Zealand (south of Australia). These long distance associations of mesocyclone outbreaks are consistent with the connectivity of the baroclinic waves and might prove useful in the development of techniques to forecast mesocyclones over the Southern Ocean.
Aliased power of a stochastic temperature field on a sphere
Authors: Li Ta‐Hsin , North Gerald R. , Shen Samuel S.
Published: February 2004

A random climate field over the globe can be decomposed into a series of spherical harmonic functions. This paper shows that the mean square sampling error for a spherical harmonic coefficient is composed of aliased powers from other spherical harmonic components due to the spatial gaps in sampling networks. A general formula is given for calculating the aliased powers. On the basis of the spectra derived from a noise‐forced linear energy balance model (EBM) for the climate field the aliased powers are investigated in detail for the Gauss‐Legendre networks and the latitude‐longitude uniform networks. It is found that the Gauss‐Legendre networks outperform the uniform networks of the same size as long as the number of stations is sufficiently large.
Stratospheric CH4, N2O, H2O, NO2, N2O5, and ClONO2 profiles retrieved from Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A)/STS 39 measurements
Authors: Zhou D. K. , Bingham G. E. , Rezai B. K. , Anderson G. P. , Smith D. R. , Nadile R. M.
Published: February 2004

Atmospheric infrared spectral measurements were made by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) during the Space Transportation System 39 (STS 39) mission (April 28 to May 6, 1991). High quality Earth limb emissions were collected by an interference filter bandwidth limited cryogenic Michelson interferometer. Volume mixing ratios (VMRs) of the various gases were retrieved using an onion‐peeling technique with the Fast Atmospheric Signature Code 3 and the HITRAN92 database as a forward model and predetermined temperature‐pressure profiles from the National Meteorological Center as the auxiliary parameters. The high quality of the moderate‐resolution (∼1.0 cm−1) CIRRIS 1A (C‐1A) interferometer data and the accuracy of the forward model allowed VMR profiles of the prominent atmospheric gases (e.g., CFC‐11, CFC‐12, HNO3, O3, CH4, N2O, H2O, NO2, N2O5, and ClONO2) to be retrieved simultaneously through the stratosphere. Profiles were recorded near the northern arctic region (daytime) and in the southern midlatitude region (nighttime). VMR profiles from C‐1A measurements reported in this paper are compared with measurements collected by other investigators. While only a few atmospheric profiles are available from the C‐1A data set, the values are significant, as they are the last atmospheric profiles of these strategically important gases collected before the Mount Pinatubo eruption of June 12–15, 1991.
Modeling air movement and bubble trapping in firn
Authors: Trudinger C. M. , Enting I. G. , Etheridge D. M. , Francey R. J. , Levchenko V. A. , Steele L. P. , Raynaud D. , Arnaud L.
Published: February 2004

A finite difference model for gas diffusion and bubble trapping in firn is described. The model uses prescribed profiles of density, open and closed porosity, and diffusivity to determine the diffusion and trapping processes. The model is calibrated and tested by using measured air composition in the firn at the DE08‐2 site on Law Dome, Antarctica. In particular, we focus on carbon dioxide (CO2), methane (CH4), and sulfur hexafluoride (SF6), which have well‐determined atmospheric records (CO2 since 1958, CH4 since 1983, and SF6 since 1978). These trace gases are used to tune the diffusivity‐porosity relationship, which is the most uncertain of the model inputs. Modeled trace gas profiles in the DE08‐2 firn are improved if allowance is made for reduced diffusion through the most prominent DE08‐2 melt layer from the summer of 1989/1990. The relatively rapid growth rate of SF6 in the atmosphere permits good definition of the diffusion reduction due to the melt layer (about 80%). The model quantifies the smoothing effect of the firn diffusion and bubble trapping on atmospheric signals. Gravitational separation in the firn is investigated by comparison of modeled δ15N2 with observations. The model is used to calculate the isotopic diffusion correction for δ13C02 and δ13CH4. This corrects for the fractionating effects of the firn diffusion process on the different isotopes. The diffusion and gravitational corrections are critical at the measurement precision currently being obtained; for δ13CO2 the diffusion correction is up to about 10 times the current measurement precision. The diffusion correction is even more significant for δ13CH4; at over 1‰ at the bottom of the firn it is more than double the change over the last decade. The fully corrected δ13C02 record from the DE08‐2 firn is compared with the history of Cape Grim direct atmospheric measurements with excellent agreement.
A global three‐dimensional chemical transport model: 2. Nitrogen oxides and nonmethane hydrocarbon results
Authors: Jaffe Daniel A. , Berntsen Terje K. , Isaksen Ivar S. A.
Published: February 2004

In this paper, nitrogen oxide and total nonmethane hydrocarbons (NMHCs) from the University of Oslo global three‐dimensional chemical transport model (CTM) are presented and compared with data from both surface and free tropospheric observations. The model includes the most important processes, including photochemical and thermal reactions, wet and dry deposition, natural and anthropogenic emissions, stratospheric contributions of NOy, and daily variations in the meteorological fields generated from the NASA Goddard Institute for Space Studies general circulation model. The model exhibits daily and seasonal variations in NMHC and NOy species, consistent with our understanding of tropospheric photochemistry. Generally good agreement between modeled mixing ratios and observations is shown for NOy, PAN and total NMHCs over 3 orders of magnitude in both source and reote regions. For NOx, the model gives good agreement in rural and urban regions; however it tends to under predict clean free tropospheric concentrations by about 20 parts per trillion by volume (50–100%). This is most likely due to subgrid boundary layer exchange processes, too efficient removal of NOx and/or recent increases in NOx emissions which are not included in our 1980 emissions inventory (especially in east Asia). Seasonal cycles for NOx, PAN, NOy and NMHCs from a number of surface locations where these data are available are reproduced well. Speciation of NOy in the model is shown to be consistent with observations at three sites where such data are available; Scotia, Pennsylvania; Mauna Loa, Hawaii; and Alert, Northwest Territories where different NOy species dominate at each location (NOx, HNO3, and PAN respectively). Several uses of the CTM are demonstrated. Total tropospheric NOx, PAN5 HNO3, and NOy are calculated with the model and shown to vary seasonally. The seasonal variations are consistent with enhanced lifetimes during winter. The model is also used to determine the fractional contributions of NOy from the major anthropogenic source regions (Europe, Asia, and North America) at Mauna Loa. Future applications of the model will focus on the global ozone and nitrogen budgets and the sources of NOx to the remote free troposphere.
Aerosol size distribution models based on in situ measurements
Authors: Porter John N. , Clarke Antony D.
Published: February 2004

We present an aerosol size distribution model summarizing measurements of sulfate, sea salt, and dust aerosol obtained in the marine boundary layer and marine free troposphere. Stratospheric aerosol cases are not included here. Aerosols were sampled in both both clean background conditions and aged anthropogenic aerosol (>3 days) which had advected over the ocean. Model size distributions are developed for the sulfate accumulation mode, sea‐salt coarse mode, and dust coarse mode. The data demonstrate that both the accumulation and coarse mode aerosol gradually shift to larger diameters as the aerosol mass increases. Based on this relationship, it is possible to estimate the size distribution based on aerosol mass. Comparisons with other aerosol models show significant differences, which suggest further measuring and modeling efforts are needed.
Airborne lidar observations of tropospheric aerosols during the Global Backscatter Experiment (GLOBE) Pacific circumnavigation missions of 1989 and 1990
Authors: Menzies Robert T. , Tratt David M.
Published: February 2004

Tropospheric and lower stratospheric aerosol backscatter profiles were obtained with an airborne backscatter lidar at 9.25‐μm wavelength during the NASA Global Backscatter Experiment (GLOBE) airborne field campaigns in November 1989 and May/June 1990. The range of latitudes extended from 70°N to 62°S over the Pacific Ocean basin. The data provide evidence that the tropics are an effective sink for aerosol particles in the lidar‐active size range, most likely through efficient wet deposition processes. A reduction of planetary boundary layer (PBL) thickness and aerosol mass density was observed within the tropical regions of enhanced cumulus convection. PBL thickness maxima were consistently observed in the southern hemisphere at subtropical and high latitudes. The downward transport of volcanic aerosol from the February 1990 Kelut eruption into the upper troposphere was observed in the southern hemisphere during the May/June 1990 period. A springtime enhancement of aerosol in the middle troposphere, due to convection and transport of surface material, was observed in both hemispheres, although the seasonal enhancement was much more dramatic in the northern hemisphere due to the influence of the Asian continental source. Above the PBL the observed springtime enhancement was in the form of extensive layers, with the high‐altitude layers reaching the midlatitude tropopause near 140°E longitude.
Radiative forcing and climate response
Authors: Hansen J. , Sato M. , Ruedy R.
Published: February 2004

We examine the sensitivity of a climate model to a wide range of radiative forcings, including changes of solar irradiance, atmospheric CO2, O3, CFCs, clouds, aerosols, surface albedo, and a “ghost” forcing introduced at arbitrary heights, latitudes, longitudes, seasons, and times of day. We show that, in general, the climate response, specifically the global mean temperature change, is sensitive to the altitude, latitude, and nature of the forcing; that is, the response to a given forcing can vary by 50% or more depending upon characteristics of the forcing other than its magnitude measured in watts per square meter. The consistency of the response among different forcings is higher, within 20% or better, for most of the globally distributed forcings suspected of influencing global mean temperature in the past century, but exceptions occur for certain changes of ozone or absorbing aerosols, for which the climate response is less well behaved. In all cases the physical basis for the variations of the response can be understood. The principal mechanisms involve alterations of lapse rate and decrease (increase) of large‐scale cloud cover in layers that are preferentially heated (cooled). Although the magnitude of these effects must be model‐dependent, the existence and sense of the mechanisms appear to be reasonable. Overall, we reaffirm the value of the radiative forcing concept for predicting climate response and for comparative studies of different forcings; indeed, the present results can help improve the accuracy of such analyses and define error estimates. Our results also emphasize the need for measurements having the specificity and precision needed to define poorly known forcings such as absorbing aerosols and ozone change. Available data on aerosol single scatter albedo imply that anthropogenic aerosols cause less cooling than has commonly been assumed. However, negative forcing due to the net ozone change since 1979 appears to have counterbalanced 30–50% of the positive forcing due to the increase of well‐mixed greenhouse gases in the same period. As the net ozone change includes halogen‐driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen‐driven ozone depletion has counterbalanced more than half of the radiative forcing due to well‐mixed greenhouse gases since 1979.
Lagrangian forecasting during ASHOE/MAESA: Analysis of predictive skill for analyzed and reverse‐domain‐filled potential vorticity
Authors: Fairlie T. Duncan , Pierce R. Bradley , Grose William L. , Lingenfelser Gretchen , Loewenstein Max , Podolske James R.
Published: February 2004

A statistical analysis is conducted to determine to what extent analyzed and 5‐day reverse‐domain‐filled (RDF) potential vorticity (PV) obtained from meteorological analyses can predict ATLAS nitrous oxide (N2O) tracer structure encountered along the ER‐2 flight track during the Airborne Southern Hemisphere Ozone Experiment / Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign. The results indicate that RDF PV shows no statistically significant improvement in forecast skill over analyzed PV in predicting tracer structure along the ER‐2 flight track. In fact, RDF generally shows a degradation in predictive skill. RDF does show some success in refining large‐scale gradients and small‐scale structures, present in the analyzed PV fields. In at least one case, RDF PV captured a filament encountered by the ER‐2, but in general, such structure is marked by low confidence in the RDF PV analyses.
Image measurements of short‐period gravity waves at equatorial latitudes
Authors: Taylor M. J. , Pendleton W. R. , Clark S. , Takahashi H. , Gobbi D. , Goldberg R. A.
Published: February 2004

A high‐performance, all‐sky imaging system has been used to obtain novel data on the morphology and dynamics of short‐period (<1 hour) gravity waves at equatorial latitudes. Gravity waves imaged in the upper mesosphere and lower thermosphere were recorded in three nightglow emissions, the near‐infrared OH emission, and the visible wavelength OI (557.7 nm) and Na (589.2 nm) emissions spanning the altitude range ∼80–100 km. The measurements were made from Alcantara, Brazil (2.3°S, 44.5°W), during the period August‐October 1994 as part of the NASA/Instituto Nacional de Pesquisas Espaciais “Guara campaign”. Over 50 wave events were imaged from which a statistical study of the characteristics of equatorial gravity waves has been performed. The data were found to divide naturally into two groups. The first group corresponded to extensive, freely propagating (or ducted) gravity waves with observed periods ranging from 3.7 to 36.6 min, while the second group consisted of waves of a much smaller scale and transient nature. The later group exhibited a bimodal distribution for the observed periods at 5.18±0.26 min and 4.32±0.15 min, close to the local Brunt‐Vaisala period and the acoustic cutoff period, respectively. In comparison, the larger‐scale waves exhibited a clear tendency for their horizontal wavelengths to increase almost linearly with observed period. This trend was particularly well defined around the equinox and can be represented by a power‐law relationship of the form λh=(3.1±0.5)τob1.06±0.10, where λh is measured in kilometers and τob in minutes. This result is in very good agreement with previous radar and passive optical measurements but differs significantly from the relationship λh ∝ τ1.5ob inferred from recent lidar studies. The larger‐scale waves were also found to exhibit strong anisotropy in their propagation headings with the dominant direction of motion toward the‐NE‐ENE suggesting a preponderance for wave generation over the South American continent.
Interaction of the quasi‐biennial oscillation and stratopause semiannual oscillation
Authors: Dunkerton Timothy J. , Delisi Donald P.
Published: February 2004

Analysis of rawinsonde and rocketsonde data at Ascension Island (7.6°S, 14.4°W) and Kwajalein (8.7°N, 167°E) in 1962–1991 suggests that the quasi‐biennial oscillation (QBO) in the middle stratosphere is synchronized with the seasonal cycle and that descending westerly phases of the stratopause semiannual oscillation (SAO) are strongly influenced by the underlying QBO. The effect of the seasonal cycle on the QBO in the middle stratosphere is revealed in two, perhaps unrelated, observations: first, a tendency for deseasonalized QBO westerly maxima to occur in local winter (or to avoid local summer); second, a smooth, uninterrupted connection between descending SAO westerly shear zones and the formation of a new QBO westerly shear zone aloft. The timing of deseasonalized QBO westerly maxima in the middle stratosphere allows a simple composite of 2‐ and 3‐year cycles to be constructed from the data, illustrating the effect of the QBO on descending westerly phases of the stratopause SAO.
Global distribution of UV‐absorbing aerosols from Nimbus 7/TOMS data
Authors: Herman J. R. , Bhartia P. K. , Torres O. , Hsu C. , Seftor C. , Celarier E.
Published: February 2004

Global distributions of UV‐absorbing aerosols are obtained using measured differences between the 340 and the 380 nm radiances from the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) for the years 1979–1993. Time series are shown for major sources of biomass burning and desert dust giving the frequency of occurrence and areal coverage over land and oceans. Minor sources of UV‐absorbing aerosols in the atmosphere are also discussed (volcanic ash and oil fires). Relative values of year‐to‐year variability of UV‐absorbing aerosol amounts are shown for major aerosol source regions: (1) central South America (Brazil) near 10°S latitude; (2) Africa near 0°–20°S and 0° to 10°N latitude; (3) Saharan Desert and sub‐Saharan region (Sahel), Arabian Peninsula, and the northern border region of India; (4) agricultural burning in Indonesia, Eastern China, and Indochina, and near the mouth of the Amazon River; and (5) coal burning and dust in northeastern China. The first three of these regions dominate the injection of UV‐absorbing aerosols into the atmosphere each year and cover areas far outside of their source regions from advection of UV‐absorbing particulates by atmospheric wind systems. During the peak months, smoke and dust from these sources are transported at altitudes above 1 km with an optical depth of at least 0.1 and can cover about 10% of the Earth's surface. Boundary layer absorbing aerosols are not readily seen by TOMS because the small amount of underlying Rayleigh scattering leads to a small signal. Significant portions of the observed dust originate from agricultural regions frequently within arid areas, such as in the Sahel region of Africa, especially from the dry lake‐bed near Lake Chad (13.5°N, 14°E), and intermittently dry drainage areas and streams. In addition to drought cycle effects, this suggests there may be an anthropogenic component to the amount of dust injected into the atmosphere each year. Detection of absorbing aerosols and calculation of optical depths are affected by the presence of large‐scale and subpixel clouds in the TOMS field of view.
High‐resolution estimates of total solar and PAR surface fluxes over large‐scale BOREAS study area from GOES measurements
Authors: Gu Jiujing , Smith Eric A.
Published: February 2004

A published physical algorithm designed for estimating total solar and photosynthetically active radiation (PAR) fluxes at the Earth's surface from GOES visible imagery has been modified for the Boreal Ecosystem‐Atmosphere Study (BOREAS) applications at high space and time resolutions (1 km/half‐hourly). Substantive changes to the algorithm are described, along with descriptions of various additional features needed to apply the algorithm over the boreal forest. Because of the propensity of forest fire smoke to impact the BOREAS study area during the summer period, particular attention has been given to the treatment of aerosol effects. To validate the algorithm, instantaneous estimates of downwelling total solar and PAR fluxes at half‐hourly time steps obtained from a GOES 7 data set are compared with 15‐min averaged in situ radiometer measurements obtained during the second summer intensive field campaign of 1994 from the array of BOREAS automatic meteorological stations. The validation results have been stratified according to sky conditions to help understand the detailed nature of algorithm performance and to identify weaknesses in the current algorithm design. A variety of sensitivity tests have also been conducted to help evaluate the algorithm's strengths and weaknesses. In addition, a large‐scale analysis of the retrievals over the five 1994 field campaigns has been carried out to provide background information for modelers on the nature of the solar component of the surface radiation budget across the boreal forest zone. The overall accuracies of the algorithm are 1.6% and 6.5% for total solar and PAR fluxes, with relative precisions of ∼20% considering all days, including those with extensive cloud cover and/or high concentrations of forest fire smoke. Such precisions are consistent with current published expectations at an hourly timescale. Better precisions of around 7% are found for clear, relatively aerosol‐free days, which represents noteworthy algorithm performance in terms of expectations at these timescales.
Solar spectral weight at low cloud tops
Authors: Li J. , Freidenreich S. M. , Ramaswamy V.
Published: February 2004

The spectral distribution of the incoming solar irradiance varies substantially from the top of the atmosphere to the surface. This occurs because of the selective spectral attenuation by the various atmospheric constituents. Using a line‐by‐line and doubling‐adding solar radiative transfer model, we formulate a prescription that accounts for this variation in the spectral solar irradiance and thereby determine the appropriate spectral weights for low clouds. The results are sufficiently general with respect to cloud top heights ranging from 680 to 860 mbar, while the range of applicability in terms of the solar zenith position extends to sun angles less than 75°. On the basis of the results here we suggest a reference cloud top height of 760 mbar and a reference zenith angle of 53°. The error in the radiative quantities relative to the “benchmark” calculations is generally less than 5% in most of the spectral bands. As a simple application, it is found that the enhancement of cloud absorption in a two band cloud optical properties parameterization can be largely avoided by using this simple modification of the solar spectral irradiance incident at the top of low‐lying clouds.