bluuebunny/crossref_metadata_2025 huggingface dataset:
Note on estimating surface sensible heat fluxes using surface temperatures measured from a geostationary satellite during FIFE 1989
Authors: Diak George R. , Whipple Mark S.
Published: February 2004

Twelve‐hour daytime totals of surface sensible heat flux were estimated using geostationary satellite measured surface “skin” temperatures and models of the land surface and the planetary boundary layer for 4 days in August 1989 at the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment site. During this period in August a rapid “dry down” occurred in which daytime surface sensible heat flux totals, as estimated from the surface flux measurements, rose from approximately 2–4 MJ m−2 to 6–9 MJ m−2 within the span of a few days. In this period the daytime surface temperature range as measured from the geostationary satellite rose by several degrees Celsius. The standard errors of estimate comparing satellite‐derived sensible heating totals with surface measurements were 0.93 and 1.43 MJ m−2, respectively, using surface roughness length estimates of 1 and 5 cm in the planetary boundary layer model.
The chemical composition of ancient atmospheres: A model study constrained by ice core data
Authors: Martinerie Patricia , Brasseur Guy P. , Granier Claire
Published: February 2004

A coupled chemistry radiation transport two‐dimensional model of the lower and middle atmosphere was adapted to study the chemical composition of the atmosphere at preindustrial time and last glacial maximum (LGM). The model was constrained by trace gas concentrations (CO2, CH4, and N2O) inferred from polar ice core records. The formulation of tropospheric dynamics and chemistry was improved in order to more accurately simulate the transport and the oxidation processes below the tropopause. Our objectives are to infer the changes in middle‐atmosphere temperature, ozone layer, and oxidation capacity of the atmosphere (e.g., methane lifetime) over the last 18,000 years. A middle‐atmosphere cooling was obtained between LGM and preindustrial Holocene (PIH) as well as between PIH and present time. This is mainly due to changes in the CO2 and chlorofluorocarbon (CFC) concentrations, respectively. CFCs are also the main contributors to the middle‐atmosphere ozone decrease since PIH. Between LGM and PIH the compensating effects of CO2 and N2O lead to little variation in stratospheric ozone. A 17% decrease in tropospheric OH was obtained between LGM and PIH, whereas the model provides a 6% OH increase since PIH. The corresponding changes in the methane sink are too small to have played a dominant role in the past methane concentration changes. Our model derived methane emissions for LGM, PIH, and present time are in good agreement with methane sources evaluated during these three periods.
Three‐dimensional model studies of exchange processes of ozone in the troposphere over Europe
Authors: Flatøy Frode , Hov Øystein , Smit Herman
Published: February 2004

A three‐dimensional Mesoscale Chemistry Transport (MCT) model driven by meteorological data from a Numerical Weather Prediction (NWP) model is used to calculate ozone and other chemical species over Europe over a 10‐day period. The meteorological model uses cloud water as one of the prognostic variables and has an advanced treatment of stratiform and convective cloud and precipitation processes. In this way an improved resolution in time and space of cumulus cloud episodes is obtained with a better simulation of the convective transport as a consequence. It should also improve the computations of the photolysis rates which are highly dependent on cloud cover and cloud optical depth. The 10‐day period (July 1–10, 1991) is characterized by warm weather and frequent occurrence of cumulus convection. The model results are compared to ground‐based ozone measurements and ozone profiles. The results presented suggest that physical processes, especially convection, may dominate in the vertical distribution of ozone in the free troposphere, that sinking air which compensates for convective updrafts is important for the tropospheric ozone budget, and that transport of O3 precursors from the boundary layer into the free troposphere by convection enhances the rate of O3 production significantly. However, considerable uncertainty of the absolute magnitude of the convective mixing exists.
Inversion of a soil bidirectional reflectance model for use with vegetation reflectance models
Authors: Privette Jeffrey L. , Myneni Ranga B. , Emery William J. , Pinty Bernard
Published: February 2004

The need for anisotropic soil reflectance in canopy reflectance modeling is assessed for different sampling and canopy conditions. Based on the results for grasslands, a soil model is inverted with ground‐based radiometer data from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). A general solution applicable over different spectral bands, solar angles, and soil moisture levels is determined using a diverse data set. With this solution, the model can be used as a lower boundary condition in FIFE canopy modeling. Despite the previously reported independence of retrieved model parameters to data sampling conditions, solutions determined with more limited data sets vary significantly. Moreover, the semiphysically based model may not accurately predict reflectance in angular regions where data are absent in the inversion process. These findings are important for the Earth Observing System multiangle imaging spectroradiometer (MISR), which will gather data in essentially one azimuthal plane per pass like the instrument used in this study did.
Diagnostics of land surface spatial variability and water vapor flux
Authors: Chen Daoyi , Brutsaert Wilfried
Published: February 2004

To assess the spatial variability of the water vapor (i.e., latent heat) flux LE, it is convenient to scale it with its equilibrium analog LEe. From an analysis of the data from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment, or FIFE, the spatial distribution of daily values of this dimensionless evaporation, α = LE/LEe, was found to be strongly related to the distributions of soil moisture and of the state of the vegetation. However, the relative strengths of these relationships depended on the soil moisture content and on its distribution. When the mean soil moisture content SM was high, in excess of about 27%, the distribution of evaporation was quite uniform regardless of the vegetation uniformity. In the intermediate range, with 20 < SM < 27%, both soil moisture and vegetation contributed to the spatial distribution of α. This distribution was controlled by the vegetation, when the soil moisture was uniform; under nonuniform soil moisture conditions, however, soil moisture exerted the major control. For SM < 20%, soil moisture normally was nonuniform, and it was found to hold the primary control of the spatial variation of α. The daily distribution of soil moisture content was largely independent from that of the state of the vegetation, due to the different timescales involved.
Microdischarges between ice particles
Authors: Coquillat Sylvain , Chauzy Serge , Médale Jean‐Claude
Published: February 2004

A laboratory experiment is performed in a cold chamber to produce microdischarges between frozen hydrometeors. A charged icicle is placed close to an uncharged one connected to a transient analyser. The electric current signature obtained during each event is then studied and characterized in function of both temperature and net charge. The existence of a transition temperature of about −15°C is detected, whereas net charge clearly governs the microdischarge characteristics. Furthermore, the radiated electric field is calculated and the spectral analysis, by means of fast Fourier transform, shows that this elementary phenomenon radiates within the VHF range. Comparisons are made with previous similar work by Chauzy and Kably (1989) on microdischarges between water drops.
Effect of background winds on vertical wavenumber spectra of atmospheric gravity waves
Authors: Eckermann Stephen D.
Published: February 2004

Observations of quasi‐invariant m−3 power spectra of various atmospheric perturbations at large vertical wavenumbers m have received considerable theoretical attention. Yet some other observations, most notably in the stratosphere, have revealed significant departures from this shape and much reduced spectral densities at large m. Here it is argued that these changes arise when a spectrum of gravity waves encounter mean wind changes which cause intrinsic horizontal phase speeds to increase. Concomitant changes in vertical wavenumbers, amplitudes, and shear variance can produce changes in spectral character qualitatively similar to observations. The two important dynamical processes governing the spectral response are refraction of vertical wavenumbers and conservation of Eliassen‐Palm flux for nondissipating waves, processes already encapsulated in both single‐wave and spectral parameterizations of gravity‐wave processes. Retrospective application of these ideas to various observations in the literature leads to successful “prediction” (based on the background wind profile) of either quasi‐invariant m−3 spectra or attenuated spectra at large m. However, while explaining their occurrence, the precise changes in spectral shape predicted by simple models of wind‐shifted spectra often differ from those observed.
Molecular nitrogen fluorescence lidar for remote sensing of the auroral ionosphere
Authors: Garner Richard C. , Dao Phan
Published: February 2004

We describe two types of molecular nitrogen fluorescence lidars which can be used to determine excited or ionized nitrogen density in the ionosphere during moderate or strong aurora. The lidars excite nitrogen already excited or ionized through impact with high‐energy auroral electrons. Several different configurations are considered for both types of lidar. The first type of lidar is a conventional fluorescence lidar which operates in the first postive system (N2(A3∑u+) → N2(B3Πg)) or the first negative system (N2+(X2∑g+) → N2+(B2∑u+)). Several different lasers are considered. The choice of laser determines the bands for excitation and fluorescence. The second type of lidar first pumps excited N2 to a higher energy state and then does conventional fluorescence lidar on that state. This lidar utilizes two lasers. The first laser, the pump, operates in the first positive system. The second laser, the probe, operates in the second positive system (N2(B3Πg)→N2(C3Πu)). Both lidars are described in detail and results of signal to noise calculations are performed using reasonable system parameters.
Reactive nitrogen and ozone over the western Pacific: Distribution, partitioning, and sources
Authors: Singh H. B. , Herlth D. , Kolyer R. , Salas L. , Bradshaw J. D. , Sandholm S. T. , Davis D. D. , Crawford J. , Kondo Y. , Koike M. , Talbot R. , Gregory G. L. , Sachse G. W. , Browell E. , Blake D. R. , Rowland F. S. , Newell R. , Merrill J. , Heikes B. , Liu S. C. , Crutzen P. J. , Kanakidou M.
Published: February 2004

Measurements of important reactive nitrogen species (NO, NO2, HNO3, PAN, PPN, NO3−, NOy), C1 to C6 hydrocarbons, O3, chemical tracers (C2Cl4, CO), and meteorological parameters were made in the troposphere (0 to 12 km) over the western Pacific (0°–50°N) during the Pacific Exploratory Mission‐West A campaign (September–October 1991). Under clean conditions, mixing ratios of NO, NO2, NOy, and O3 increased with altitude and showed a distinct latitudinal gradient. PAN showed a midtropospheric maximum, while nitric acid mixing ratios were generally highest near the surface. Measured NOy concentrations were significantly greater than the sum of individually measured nitrogen species (mainly NOx, PAN, and HNO3), suggesting that a large fraction of reactive nitrogen present in the atmosphere is made up of hitherto unknown species. This shortfall was larger in the tropics (≈65%) compared to midlatitudes (≈40%) and was minimal in air masses with high HNO3 mixing ratios (>100 ppt). A global three‐dimensional photochemical model has been used to compare observations with predictions and to assess the significance of major sources. It is possible that the tropical lightning source is much greater than commonly assumed, and both lightning source and its distribution remain a major area of uncertainty in the budgets of NOy and NOx. A large disagreement between measurement and theory exists in the atmospheric distribution of HNO3. It appears that surface‐based anthropogenic emissions provide nearly 65% of the global atmospheric NOy reservoir. Relatively constant NOx/NOy ratios imply that NOy and NOx are in chemical equilibrium and the NOy reservoir may be an important in situ source of atmospheric NOx. Data are interpreted to suggest that only about 20% of the upper tropospheric (7–12 km) NOx is directly attributable to its surface NOx source, and free tropospheric sources are dominant. In situ release of NOx from the NOy reservoir, lightning, direct transport of surface NOx, aircraft emissions, and small stratospheric input collectively maintain the NOx balance in the atmosphere. It is shown that atmospheric ratios of reactive nitrogen and sulfur species, along with trajectory analysis, can be used to pinpoint the source of Asian continental outflow. Compared to rural atmospheres over North America, air masses over the Pacific are highly efficient in net O3 production. Sources of tropospheric NOx cannot yet be accurately defined due to shortcomings in measurements and theory.
Determination of the stratospheric organic chlorine budget in the spring arctic vortex from MIPAS B limb emission spectra and air sampling experiments
Authors: von Clarmann T. , Linden A. , Oelhaf H. , Fischer H. , Friedl‐Vallon F. , Piesch C. , Seefeldner M. , Völker W. , Bauer R. , Engel A. , Schmidt U.
Published: February 2004

Vertical profiles of halogenated source gases, CF2Cl2, CFCl3, CHF2Cl, Cl4, and CF4, were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS B) during a balloon flight launched from Esrange near Kiruna, northern Sweden (68°N) on March 14, 1992. This flight was a contribution to the balloon launch program of the European Arctic Stratospheric Ozone Experiment (EASOE) campaign. All problems encountered during the analysis of the recorded spectra are discussed in detail. These are primarily the lack of spectral data for HNO3 which interferes with the CF2Cl2 v6 band, and the strong effects attributed to the Pinatubo aerosol. As the air mass sounded by MIPAS was polar vortex air, these data supplement the results of in situ air sampling experiments, which investigated air masses outside or at the edge of the polar vortex at altitudes below 18 km during the last phase of EASOE. An analysis is made of the vertical profiles of the seven most abundant organic chlorine species (CF2Cl2, CFCl3, CHF2Cl, CCl4, CH3Cl, CH3CCl3, and C2F3Cl3) during that phase of the EASOE campaign. Mixing ratios of those organic chlorine compounds which had not been measured by MIPAS are inferred from profiles provided by air sampling experiments performed between November 30, 1991, and March 12, 1992. These profiles were adjusted to the dynamic conditions during the MIPAS observations, namely the effect of subsidence, using CF2Cl2 as a tracer. This allowed to derive the relative contributions of the organic chlorine species to the total chlorine budget of the air mass sounded by MIPAS. The results are consistent with the high ClONO2 mixing ratio of 2.6 parts per billion by volume (ppbv) observed at 18.9‐km altitude during this flight of MIPAS B.
Is the recently reported 65‐ to 70‐year surface‐temperature oscillation the result of climatic noise?
Authors: Schlesinger Michael E. , Ramankutty Navin
Published: February 2004

In a recent paper (Schlesinger and Ramankutty, 1994) we reported finding a 65‐ to 70‐year oscillation in each of the four records of observed global‐mean surface temperature. We also found that the oscillation does not exist everywhere over the earth, but rather only over the North Atlantic Ocean and its bordering continental regions of North America, Europe, and northern Africa. We proposed three possible causes for our finding: (1) random radiative forcing of the climate system, that is, climatic noise, (2) oscillatory forcing external to the climate system, such as by a variation in solar irradiance, and (3) an oscillation internal to the climate system, perhaps not unlike that of the El Niño‐Southern Oscillation, but with a longer timescale. In this paper we critically examine the first hypothesis. Our analysis shows that this hypothesis can be rejected at a very high level of statistical confidence.
Simulation of summer snowmelt on the Greenland ice sheet using a one‐dimensional model
Authors: Rowe Clinton M. , Kuivinen Karl C. , Jordan Rachel
Published: February 2004

A one‐dimensional heat and mass balance model of a snowpack over frozen soil was modified for use in glacial environments. The model solves a set of governing equations for the energy and mass balances of the snow, subject to observed meteorological conditions at the upper boundary and the assumption of a steady state at the lower boundary. The initial state of the snowpack is defined by the temperature, density and grain size profiles at the beginning of the simulation period. The data used to test the model on the Greenland ice sheet are a subset of the meteorological and surface data collected during the 1990 summer field season by the Swiss Federal Institute of Technology (ETH) Greenland Expedition. The site was located near the equilibrium line elevation on the west slope of the ice sheet. The relatively large amount of snowmelt experienced at this site during the summer of 1990 provides a robust test of the snowmelt model. Both the simulated height and mass of the snowpack agree well with the observations. The evolution of profiles of temperature, density and liquid water content also conform to our expectations of the physical changes taking place in the snowpack during melt. Results from the present model are also compared to those from a similar model and differences between the models are discussed.
Scene identification error probabilities for evaluating Earth radiation measurements
Authors: Smith G. Louis , Manalo‐Smith Natividad
Published: February 2004

The computation of radiant fluxes from radiance measurements by satellite radiometers requires the use of a bidirectional model. The bidirectional model, in turn, depends on the scene, so that a scene identification algorithm is required. The accuracy of scene identification varies with viewing zenith angle due mainly to geometric effects of the clouds and the measurements. This paper investigates the effects of viewing zenith angle on scene identification errors. Along‐track measurements from the Earth Radiation Budget Experiment (ERBE) have been analyzed to quantify the probabilities of identifying a given scene as to its level of cloudiness, as used by the ERBE data processing system. Scene identification probabilities were initially computed on the basis of a select set of pixels. These restricted scene identification probabilities were then used to compute scene identification probabilities for all pixels, including those of marginal scene type. These probabilities are found to be functions of viewing zenith angle, but are insensitive to other parameters such as solar zenith angle, relative azimuth, and latitude, except in the Sun glint region. For most cases, the scene identification probabilities change very slowly for viewing zenith angle less than 40°, but change rapidly for viewing zenith angle greater than 50°. With increasing viewing zenith angles, the probability increases for identifying, a scene as being more cloudy than its true cloud class. These results are useful for evaluation of flux errors due to scene identification errors in the data processing.
Effect of black carbon on the optical properties and climate forcing of sulfate aerosols
Authors: Chýlek Petr , Videen Gorden , Ngo Dat , Pinnick Ronald G. , Klett James D.
Published: February 2004

We study the optical properties of anthropogenic sulfate aerosols containing black carbon using a recently developed exact solution of the scattering problem for a spherical particle (sulfate aerosol) containing an eccentrically located spherical inclusion (black carbon). We present the expression for the change of planetary albedo due to addition of an absorbing, but optically thin aerosol layer and estimate the effect of the black carbon within the sulfate aerosol layer on the aerosol direct radiative forcing. The black carbon within the sulfate aerosol reduces the expected sulfate direct cooling effect by about 0.034 W/m2 for each 1% of the black carbon to sulfate mass mixing ratio. Thus the presence of black carbon within sulfate in the background aerosol does not significantly change the previous estimates of the global aerosol direct cooling effect. However, in regions where the black carbon in sulfate concentrations are of the order of 5% or more, the local and regional effects are significant.
On the calibration of the Meteosat water vapor channel
Authors: van de Berg L. C. J. , Schmetz J. , Whitlock J.
Published: February 2004

The calibration of the Meteosat water vapor channel image data is of prime importance for a quantitative use. The vicarious calibration technique employs the use of data from radiosonde ascents. A screening technique, removing spurious radiosonde information, has been improved and used operationally since February 4, 1994. It involves new quality control checks on satellite zenith angle and the upper tropospheric relative humidity measured by the radiosonde, leading to a lower (about 8%) and more stable calibration. The operational calibration technique uses averages for the clear‐sky (above 700 hPa) satellite observations over large areas and relates them to expected radiances at the top of the atmosphere, determined from radiosonde data. The approach, valid owing to the small gradients in the water vapor field in such areas, restricts the number of usable radiosonde observations severely. An alternative calibration method is outlined, which uses a smaller clear‐sky area, thus accepting more radiosonde ascents. This method further decreases the variability of the calibration coefficient by about 20%.
An approach to studying the effect of organic composition on atmospheric aerosol photochemistry
Authors: McDow Stephen R. , Jang Myoseon , Hong Yusen , Kamens Richard M.
Published: February 2004

Physical and chemical characteristics of atmospheric carbonaceous aerosol particles are reviewed, and their likely effects on the particulate matter as a reaction medium are discussed. An approach to studying the effects of organic components of atmospheric particulate matter on aerosol organic photochemistry based on this discussion is described. Available information suggests that atmospheric aerosols from common combustion sources, such as wood smoke or diesel soot, are almost entirely carbonaceous, consisting of a relatively thick, possibly liquid organic layer coating an elemental carbon core. This implies that organic compounds are fairly mobile and consequently that overall organic composition of an atmospheric aerosol could play an important role in the photochemical behavior of associated reactive organic substances. In accordance with this a photochemical turntable reactor was used to investigate the effects of organic aerosol constituents dissolved in an organic solvent, using benz[a]anthracene as a model photochemically reactive compound. Preliminary results showed that 4 out of 10 major organic compound classes found in atmospheric aerosols include compounds which accelerated benz[a]anthracene photodegradation. These were methoxyphenols, polycyclic aromatic ketones and quinones, substituted benzaldehydes, and substituted furans.
Reevaluation of the open ocean source of carbonyl sulfide to the atmosphere
Authors: Weiss Peter S. , Johnson James E. , Gammon Richard H. , Bates Timothy S.
Published: February 2004

Carbonyl sulfide (COS) concentrations were measured in surface seawater samples and the overlying marine boundary layer of the Pacific Ocean by using gas chromatography (GC) and electron capture sulfur detection (ECD‐S). A wide latitudinal range was covered (55°N–70°S) on two cruises 9 months apart. COS saturation ratios (SRs) in seawater were found to be less than 1 (undersaturated) across wide regions of the open ocean, especially in the subtropical gyres and wintertime subpolar waters. SRs were highest in coastal/shelf regions and in spring/summertime temperate waters. Extensive undersaturation is attributed to a low COS photoproduction potential of the water, limited sunlight, and/or a rapid hydrolysis rate constant. Decreasing COS concentrations during diurnal cycles in tropical waters were fitted to first‐order exponentials, with resulting decay times agreeing with calculated hydrolysis lifetimes to within 15%. Air‐sea fluxes of COS from the open ocean were calculated by using two different expressions for the transfer velocity and averaged into six latitude bands and three seasons. On the basis of these data we report a global open ocean sea‐air flux of −0.032 (−0.010 to −0.054) Tg COS/yr, which is much lower than and of different sign from the current global estimate (0.14–0.58 Tg COS/yr). Atmospheric COS mixing ratios averaged 470 pptv on the first cruise and 442 pptv on the second cruise, with much of the difference possibly a result of a seasonal decrease in the northern hemisphere COS mixing ratio of up to 10%.
Seasonal variations of nonmethane hydrocarbons in rural New England: Constraints on OH concentrations in northern midlatitudes
Authors: Goldstein A. H. , Wofsy S. C. , Spivakovsky C. M.
Published: February 2004

Concentrations of C2–C6 hydrocarbons are reported at Harvard Forest in Central Massachusetts (42.54°N, 72.18°W; elevation, 340 m), measured at 45‐min intervals from August 1992 through July 1994. The seasonal cycle of background concentrations for anthropogenic alkanes (ethane, propane, butane, isobutane, pentane, and hexane) and acetylene could be cleanly extracted from the ∼900 measurements each month. Background concentrations exhibited seasonal maxima in winter and minima in summer. The phase of the seasonal cycle for each species reflected its rate of reaction with OH: The faster the reaction, the earlier the peak in winter, and the more rapid the decline in spring. Winter:summer ratios for hydrocarbons more reactive than propane were similar, implying a summer:winter ratio for OH of 9±2 at northern midlatitudes. The annual cycle for ethane provides a measure of the mass‐weighted annual mean OH concentration at northern midlatitudes, 7(±3.5)×105cm−3, as simulated by using a three‐dimensional chemical tracer model.
Carbonyl products of the ozone‐unsaturated alcohol reaction
Authors: Grosjean Daniel , Grosjean Eric
Published: February 2004

Carbonyl products of the gas phase reaction of ozone with four monosubstituted and three 1,2‐disubstituted unsaturated alcohols that are relevant to biogenic emissions have been identified in laboratory experiments involving unsaturated alcohol‐ozone mixtures in the dark. Cyclohexane was added to scavenge the hydroxyl radical, which forms as a product of the ozone‐unsaturated alcohol reaction. Major carbonyl products included formaldehyde and hydroxyacetaldehyde from allyl alcohol, acetaldehyde, and hydroxyacetaldehyde from 2‐buten‐1‐ol, propanal, and hydroxyacetaldehyde from cis‐2‐penten‐1‐ol, formaldehyde from 3‐buten‐2‐ol, 1‐penten‐3‐ol, and 2‐methyl‐3‐buten‐2‐ol, and hydroxyacetaldehyde from 2‐buten‐1, 4 diol. Yields of the primary carbonyls (ozone + unsaturated alcohol → 2 primary carbonyls + 2 biradicals) averaged 0.91±0.29, which compares to a theoretical value of 1.0. Yields of carbonyls that are not hydroxy substituted averaged 0.48±0.13, which compares to a theoretical value of 0.50 if one assumes that the alkyl‐substituted and the hydroxyalkyl‐substituted biradicals are formed in equal yields. The corresponding reaction mechanisms are outlined with focus on similarities between unsaturated alcohols and alkene structural homologues. Possible decomposition pathways for hydroxyalkyl‐substituted biradicals are examined. The atmospheric persistence and the fate of unsaturated alcohols from biogenic emissions and of their carbonyl products are briefly discussed.
Role of land surface in controlling daytime cloud amount: Two case studies in the GCIP‐SW area
Authors: Wetzel Peter J. , Argentini Stefania , Boone Aaron
Published: February 2004

Two summertime cases are studied, in which fields of low cumulus clouds develop out of an initially clear sky under quiescent synoptic scale conditions. Both sites fall within the southwest study area of the GEWEX (Global Energy and Water cycle Experiment) Continental‐Scale International Project (GCIP). The cases are modeled using a one‐dimensional soil‐vegetation‐boundary layer model known as the parameterization for land‐atmosphere‐cloud exchange (PLACE). PLACE accurately predicts cloud onset and amount in both cases, one from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) in Kansas and one from Oklahoma. Sensitivity tests with PLACE show further that in the Oklahoma case, morning cloud amount is highly sensitive to land surface characteristics, whereas in the FIFE case, much less sensitivity is found, primarily due to differences in the predawn atmospheric thermodynamic structure through which the boundary layer must grow. Analysis of observational data, including cloud amount inferred from GOES visible data and vegetation index from the advanced very high resolution radiometer (AVHRR) data confirm that the PLACE model predictions of sensitivities and of the sensitivity differences between cases are correct. In the Oklahoma case, atmospheric conditions and soil moisture are relatively uniform across the study area, but a significant gradient of satellite‐derived vegetation index is observed. Clouds form quickly due to a very shallow nocturnal inversion, with strong lapse conditions above. They form first over the hotter, more sparsely vegetated areas. Over areas covered with deciduous forest, clouds were observed to form 1 to 2 hours later due to the suppression of vertical mixing caused by increased latent heat release. In the FIFE case, because of a deep preexisting stable layer in the atmosphere the primary cause of spatial variations in morning cloud amount appears to be the amount of moisture in low levels of the atmosphere. In the afternoon, once the stable layer has been eroded, the FIFE study area begins to demonstrate more sensitivity of cloud amount to surface characteristics.
Relating chamber measurements to eddy correlation measurements of methane flux
Authors: Clement R. J. , Verma S. B. , Verry E. S.
Published: February 2004

Methane fluxes were measured using eddy correlation and chamber techniques during 1991 and 1992 at a peatland in north central Minnesota. Comparisons of the two techniques were made using averages of methane flux data available during 1‐week periods. The seasonal patterns of fluxes measured by the two techniques compared well. Chamber flux, in 1991, was about 1.8 mg m−2 hr−1 greater than the flux obtained by the eddy correlation technique. In 1992, the chamber flux was about 1.5 mg m−2 hr−1 higher than the eddy correlation flux prior to midseason and 1.0 mg m−2 hr−1 lower than the eddy correlation flux after midseason. Chamber data from individual hummock and hollow pairs were used to calculate the averaged dF/dZ (rate of change of methane flux with surface height). During midseason in 1991, the magnitude of dF/dZ ranged between 10 and 100 (mg m−2 hr−1)m−1. We speculate that high water table conditions caused a decrease in the magnitude of dF/dZ after midseason of 1992. As compared to 1991, greater variability of dF/dZ in 1992 probably resulted from less frequent sampling. To obtain a more valid comparison of the results from the two measurement techniques, chamber data were adjusted to account for the spatial variation in methane flux. Accordingly, the chamber flux values were “scaled up” using the dF/dZ values and distributions of surface heights representative of the footprint of the eddy correlation sensors. The scaling procedure reduced the chamber fluxes by an average of 1.8 mg m−2 hr−1 in 1991 and 1.0 mg m−2 hr−1 in 1992. The comparison of eddy correlation and chamber fluxes was improved both before and after midseason in 1991. The slope of the linear regression between eddy correlation and chamber fluxes decreased from 1.49 to 1.14 (r2 increased from 0.53 to 0.75). During 1992, the scaling of chamber fluxes slightly improved their comparison with eddy correlation fluxes only prior to midseason. The lack of improvement after midseason in 1992 is likely the result of scaling assumptions when the water table was above the hollow surface. Results suggest that the adjustment of chamber flux data for spatial variations on microtopographical scales does provide fluxes more representative of a larger area. However, more information is needed on factors controlling spatial variation of methane flux to help refine the assumptions involved in the scaling procedure.
Photostationary state analysis of the NO2‐NO system based on airborne observations from the western and central North Pacific
Authors: Crawford J. , Davis D. , Chen G. , Bradshaw J. , Sandholm S. , Gregory G. , Sachse G. , Anderson B. , Collins J. , Blake D. , Singh H. , Heikes B. , Talbot R. , Rodriguez J.
Published: February 2004

On the basis of measurements taken during the NASA Global Tropospheric Experiment (GTE) Pacific Exploratory Mission‐West A (PEM‐West A), photostationary state model calculations were carried out for approximately 1300 three‐minute sample runs. The objective of this study was to look at a subset of this processed data to assess the level of agreement between observed ratios of NO2 to NO and those estimated using current photochemical theory. This filtered data subset consisted of 562 NO2‐NO data pairs. The comparison between observations and predictions was based on the use of the photochemical test ratio (NO2)expt/(NO2)calc, designated here as Re/ Rc. Although the expected median value for this test ratio was unity, for the PEM‐West A data set it was found to be 3.36. The value of the ratio Re/Rc showed a general trend of increasing magnitude with increasing altitude and decreasing latitude. Attempts to understand the sizable discrepancy between observation and prediction (especially for the high‐altitude and low‐latitude data) were explored in the context of two hypotheses: (1) incomplete model chemistry and (2) interferences in the measurement of NO2. Efforts to quantify the levels of HO2, CH3O2, RO2, and/or ClOx needed to correct the Re/Rc discrepancy led to major inconsistencies in the predicted levels of other chemical species. Bromine and iodine chemistries were also investigated with results requiring Brx and Ix radical levels well in excess of what would seem reasonable given our current understanding of the source strengths for these elements. This suggests that incompleteness in the model's chemistry was unlikely the major cause of the discrepancy. The second hypothesis, involving interference in the measurement of NO2, now appears to be the most likely explanation for the largest component of the deviation in Re/Rc from unity. For example, the disagreement between (NO2)expt and (NO2)calc was found to be a strong function of the NOx/NOy ratio. Also, the magnitude of the discrepancy between (NO2)expt and (NO2)calc fell within the possible limits defined by other reactive nitrogen species (e.g., ΔNOy) available to generate the interference. These results suggest that the further development of a new direct measurement technique for NO2, involving a wall collision‐free inlet system, should be considered a high priority. We should also continue, however, to examine the chemical basis of current photochemical models to assess whether yet untested mechanisms might not provide an explanation for these observations.
Fine particle size distributions at the Mauna Loa Observatory, Hawaii
Authors: Weber Rodney J. , McMurry Peter H.
Published: February 2004

Measurements at the Mauna Loa Observatory (MLO) of particle size distributions between 15 nm and 0.5 μm illustrated many of the mechanisms that influence the concentrations of these aerosols. The time variation of the size distribution suggested that homogeneous nucleation and growth by sulfuric acid vapor condensation dramatically increased the concentrations of particles in the Aitken mode (diameters between ∼15 nm and 80 nm). Bimodal distributions, similar in shape to those commonly observed in marine environments, were frequently measured at midday to late afternoon, in upslope air when the aerosol was likely to have passed through clouds. When bimodal distributions were recorded, there was always an associated local maximum in the measured aerosol surface area concentration. Removal of the accumulation mode (diameters between ∼80 nm and 1 μm) was observed during periods of fog and light rain. In one episode the atmosphere was cleansed of nearly all fine particles.
Dimethyl sulfide in the Arctic atmosphere
Authors: Ferek Ronald J. , Hobbs Peter V. , Radke Lawrence F. , Herring John A. , Sturges William T. , Cota Glenn F.
Published: February 2004

Dimethyl sulfide (DMS), sulfur dioxide, non‐sea‐salt sulfate, and various aerosol properties were measured during three field programs (two airborne and one ground‐based) near Barrow and Deadhorse (Prudhoe Bay), Alaska. The two airborne sampling programs took place in spring and early summer, and the ground‐based measurements spanned an entire summer. DMS concentrations in the Arctic atmosphere ranged from a few parts per trillion by volume (pptv) in spring and fall to higher values in summer (generally a few tens of pptv with occasional peaks of 100 to 300 pptv). In addition, DMS concentrations were measured during the spring near Resolute in seawater below the ice and in ice‐algae and kelp cultures. The seawater samples taken from below the ice in spring had DMS concentrations comparable to those in other oceanic regions. Taken together, these measurements show that the Arctic Ocean is potentially a substantial source of DMS, which likely becomes important as sea ice melts in the early summer. Local atmospheric concentrations increased throughout the summer, peaking in August. In regions where accumulation mode aerosols have been scavenged (e.g., by low‐level stratus clouds, which are common during the Arctic summer), evidence of rapid new particle production was observed. The seasonal cycle of atmospheric DMS closely resembles that of fine particles observed at Barrow, Alaska, and Alert, Northwest Territories, Canada. This finding indicates that DMS is likely an important precursor to the types of particles that dominate the background arctic aerosol in summertime. These results, together with those from several recently published studies of arctic aerosol, are combined to yield a consistent picture of the role of locally emitted DMS in the production of atmospheric aerosols in the Arctic in summer.
Land surface temperature and radiative fluxes response of the NCAR CCM2/Biosphere‐Atmosphere Transfer Scheme to modifications in the optical properties of clouds
Authors: Hahmann Andrea N. , Ward Dale M. , Dickinson Robert E.
Published: February 2004

Climate simulations of the National Center for Atmospheric Research (NCAR) community climate model version 2 (CCM2) are compared with several data sets. These data sets are a multiyear climatology of the Earth Radiation Budget Experiment (ERBE) top‐of‐the‐atmosphere (TOA) radiative fluxes, the International Satellite Cloud Climatology Project (ISCCP) cloudiness, and the Surface Radiation Budget (SRB) Project surface insolation. The comparison focuses on global and regional spatial scales and the seasonal timescale. In the control simulation, the overall pattern appears reasonable, but some serious discrepancies are found. In particular, in the midlatitude summer, the model reflects too little solar radiation according to ERBE data (by as much as 50–100 W m−2), has surface solar fluxes that are too large according to SRB data (by as much as 40–80 W m−2), and is low in fractional cloudiness according to ISCCP data (by as much as 10%). These biases are evidenced at the land surface through too warm (by up to 15°C) summer hemisphere continents. A revised computational scheme of the cloud optical properties is introduced in the solar and longwave radiative transfer parameterizations of CCM2. A new simulation with these revisions is in much closer agreement with the ERBE and ISCCP data and with midlatitude summer surface temperatures. This study demonstrates a large sensitivity of summer surface temperatures to cloud optical properties.
Passive tracer transport relevant to the TRACE A experiment
Authors: Krishnamurti T. N. , Sinha M. C. , Kanamitsu M. , Oosterhof D. , Fuelberg H. , Chatfield R. , Jacob D. J. , Logan J.
Published: February 2004

This paper explores some of the mechanisms governing the accumulation of passive tracers over the tropical southern Atlantic Ocean during the northern hemisphere fall season. There has been a pioneering observation regarding ozone maxima over the South Atlantic during austral spring. The understanding of the formation of this maxima has been the prime motivation for this study. Using a global model as a frame of reference, we have carried out three kinds of experiments during the period of the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) project of 1992. The first of these is a simple advection of total ozone (a passive tracer) in time using the Florida State University global spectral model. Integration over the period of roughly 1 week showed that the model quite closely replicates the behavior of the observed total ozone from the total ozone mapping spectrometer (TOMS). This includes many of the changes in the features of total ozone over the tropical and subtropical region of the southern Atlantic Ocean. These studies suggest a correlation of 0.8 between the observed ozone over this region and ozone modeled from “dynamics alone,” i.e., without recourse to any photochemistry. The second series of experiments invoke sustained sources of a tracer over the biomass burn region of Africa and Brazil. Furthermore, sustained sources were also introduced in the active frontal “descending air” region of the southern hemisphere and over the Asian monsoon's east‐west circulation. These experiments strongly suggest that air motions help to accumulate tracer elements over the tropical southern Atlantic Ocean. A third series of experiments address what may be required to improve the deficiencies of the vertical stratification of ozone predicted by the model over the flight region of the tropical southern Atlantic during TRACE A. Here we use the global model to optimally derive plausible accumulation of burn elements over the fire count regions of Brazil and Africa to provide passive tracer advections to closely match what was observed from reconnaissance aircraft‐based measurements of ozone over the tropical southern Atlantic Ocean.
Volcanic perturbation of the atmosphere in both polar regions: 1991–1994
Authors: Herber A. , Thomason L. W. , Dethloff K. , Viterbo P. , Radionov V. F. , Leiterer U.
Published: February 2004

Long‐term measurements by sunphotometers of the spectral dependence of aerosol optical depth are reported for several sites in the Arctic and Antarctic for the period January 1991 through December 1994. In the Antarctic a pronounced increase of atmospheric turbidity was observed at the end of September 1991. The observed wavelength dependence in aerosol optical depth indicated that the increase was due to the presence of fresh and therefore small stratospheric aerosol particles associated with the eruption of Cerro Hudson in August 1991. After the breakdown of the polar vortex in mid‐November 1991 we measured a second significant increase of the aerosol optical depth. At this time the 1.0‐μm aerosol optical depth was approximately 0.12 or about 10 times background levels. This second increase is shown to be the result of the influx of Mount Pinatubo aerosols. A similar perturbation of the aerosol optical depth was observed in the Arctic with the return of sunlight in March 1992. However, the increased loading of the Arctic stratosphere by the Pinatubo aerosols was already evident at high northern latitudes in satellite measurements at the end of 1991. Stratospheric Aerosol and Gas Experiment II stratospheric 1.0‐μm optical depth measurements show that meridional transport of Pinatubo aerosol from equatorial to middle and higher latitudes is greatest in the winter/spring hemisphere. This observation explains the observed seasonal trend of aerosol optical depth during the posteruption. A significant decrease of the perturbation by Mount Pinatubo aerosol was observed in both polar regions by the end of 1994. The measured 1.0μm aerosol optical depths at this time were only ≈0.04; these values exceed the background level by about 0.01–0.02. Therefore the aerosol optical depth values are still slightly higher than during undisturbed conditions. In addition, we show that the occurrence of volcanic aerosols caused changes in the spectral dependence of the aerosol optical depth in the Arctic and the Antarctic. These variations, including the changes in the aerosol size distribution, derived from the aerosol optical depth, are discussed in comparison to undisturbed conditions.
Stratosphere‐troposphere exchange in a midlatitude mesoscale convective complex: 2. Numerical simulations
Authors: Stenchikov G. , Dickerson R. , Pickering K. , Ellis W. , Doddridge B. , Kondragunta S. , Poulida O. , Scala J. , Tao W.‐K.
Published: February 2004

Mixing across the tropopause due to intense convective events may significantly influence the atmospheric chemical balance. Stratosphere‐troposphere exchange acts as an important natural source of O3 in the troposphere, and a source of H2O, HCs, CFCs, HCFCs, and reactive nitrogen in the stratosphere. The redistribution of atmospheric trace gases produces secondary radiative, dynamical and climate effects, influencing lower stratospheric temperatures and the tropopause height. During the 1989 North Dakota Thunderstorm Project, a severe storm which evolved into a mesoscale convective complex (MCC) on June 28–29 showed the unusual feature of an anvil formed well within the stratosphere and produced strong vertical mixing of atmospheric trace gases including H2O, CO, O3 and NOy as discussed by Poulida et al. [this issue] in Part 1 of this paper. In this paper the two‐dimensional NASA Goddard Cumulus Ensemble (GCE) model was employed to simulate this convective storm using observed initial and boundary conditions. The sensitivity to the domain size, initial and boundary conditions, stability, and time resolution are evaluated. Synoptic‐scale moisture convergence, simulated by moist boundary inflow, influences significantly the storm intensity, spatial structure, and trace gas transport, and produces a storm that reintensifies after the initial decay, mimicking the observed behavior of the MCC. The deformation of the tropopause documented with aircraft observations was qualitatively reproduced along with transport of stratospheric ozone downward into the troposphere, and the transport of trace species from the boundary layer upward into the stratosphere. If the chemistry and dynamics of this storm are typical of the roughly 100 MCCs occurring annually over midlatitudes, then this mechanism plays an important role in CO, NOy, and O3 budgets and could be the dominant source of H2O in the lower stratosphere and upper troposphere over midlatitudes.