bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric convective plumes emanating from leads: 1. Thermodynamic structure
Authors: Pinto James O. , Curry Judith A. , McInnes Kathleen L.
Published: February 2004

A one‐dimensional model with detailed radiative transfer, a second‐order closure scheme for turbulence, and bulk cloud microphysics has been employed to simulate the convective atmosphere above a wide open lead. The development of a thermal internal boundary layer (TIBL) associated with the atmospheric convection above a wide open lead is modeled for several different temperature profiles characteristic of the Arctic winter. Large differences in the predicted top of the TIBL are observed between two simple diagnostic models and the time‐dependent model introduced here. The modeled thermodynamic processes (i.e., radiative transfer and condensation/evaporation) occurring within the TIBL above an open lead are shown to account for as much as 20% of the predicted TIBL top height. Radiative heating dominates the heat budget in the lowest model level while sensible and latent heating occur throughout the TIBL. The production of cloud water affects the modeled TIBL top height via enhanced radiative cooling near the top of the TIBL and by latent heat released during condensation and freezing. Under stable conditions the TIBL top height above an open lead increases with time as a decaying exponential. The initial temperature of a surface‐based isothermal layer can account for up to 50% of the variations in TIBL top height. The depth of the surface‐based inversion layer and the stability of the atmosphere above the inversion are both important controlling factors in TIBL development while the temperature difference across the inversion layer is slightly less important.
Orbital rotational motion and turbulence below laboratory wind water waves
Authors: Magnaudet Jacques , Thais Laurent
Published: February 2004

New experimental results describing the structure of both orbital and turbulent motions below laboratory wind water waves are presented. The data obtained by means of a submersible laser probe are processed through the triple decomposition method developed by the authors. This method allows one to distinguish three contributions in the fluctuating motion, namely the potential and rotational parts of the orbital motion, as well as the turbulent fluctuation. The results show that the orbital rotational motion has spectral properties very similar to those of its potential counterpart and represents a contribution of significant magnitude. The behavior of all three components of the turbulent motion is discussed. Their near‐surface level is comparable with that found near a wall, but their vertical decay is quite different The dissipation rate estimate confirms that under present conditions the turbulence is essentially unaffected by the orbital motion. In contrast, a study of the cross correlations between orbital rotational and potential motions shows that the rotational contribution plays a key role in energy transfers between the wave motion and the mean shear flow. Finally, the origin of the orbital rotational motion is addressed. Several theoretical mechanisms capable of contributing to the generation of a wave‐related component of the vorticity are examined. Comparison between theory and experiments supports the idea that in laboratory experiments an important part of the orbital rotational motion results from wave‐current interactions linked to the vertical variations of the mean shear.
A numerical simulation of the sea ice cover in the northern Greenland Sea
Authors: Holland David M. , Ingram R. Grant , Mysak Lawrence A. , Oberhuber Josef M.
Published: February 2004

A numerical simulation of the sea ice cover in the northern Greenland Sea (NGS) is presented. The simulation is carried out using the coupled sea ice ocean general circulation model of Oberhuber (1993). The coupled model is forced using monthly climatological atmospheric forcing. The model domain includes both the Arctic Ocean and the North Atlantic. The large‐scale characteristics of the observed sea ice cover in the NGS are reasonably well reproduced when compared with the limited observations available. Two notable aspects of the simulation are (1) a trough in the ice compactness across Fram Strait and (2) a polynya along the northeast coast of Greenland. Both of these features are evident in the observations during the spring‐summer period. A sensitivity experiment in which the ice internal stress term is removed from the ice model demonstrates that the inclusion of a realistic sea ice rheology is a key factor in simulating the detailed features noted above for the NGS.
Geophysical and oceanographic information in the marginal ice zone from ocean wave measurements
Authors: Squire Vernon A.
Published: February 2004

Consequent to recent experiments in marginal ice zones (MIZ), advances in remote sensing, and theoretical progress, studies have been published which invoke wave‐ice interactions to explain or predict certain geophysical phenomena. While admirable and desirable in principle, these works are based on a refutable surface boundary condition intended for a sheet or plate of solid ice, rather than a medium made up of individual ice floes. A case is argued for prudence, as derived results may originate entirely from the application of an inappropriate MIZ model.
Topographic enhancement of tidal motion in the western Barents Sea
Authors: Kowalik Z. , Proshutinsky A. Yu.
Published: February 2004

A high‐resolution numerical lattice is used to study a topographically trapped motion around islands and shallow banks of the western Barents Sea caused both by the semidiurnal and diurnal tidal waves. Observations and model computations in the vicinity of Bear Island show well‐developed trapped motion with distinctive tidal oscillatory motion. Numerical investigations demonstrate that one source of the trapped motion is tidal current rectification over shallow topography. Tidal motion supports residual currents of the order of 8 cm s−1 around Bear Island and shallow Spitsbergenbanken. The structures of enhanced tidal currents for the semidiurnal components are generated in the shallow areas due to topographic amplification. In the diurnal band of oscillations the maximum current is associated with the shelf wave occurrence. Residual currents due to diurnal tides occur at both the shallow areas and the shelf slope in regions of maximum topographic gradients. Surface manifestation of the diurnal current enhancement is the local maximum of tidal amplitude at the shelf break of the order of 5 to 10 cm. Tidal current enhancement and tidally generated residual currents in the Bear Island and Spitsbergenbanken regions cause an increased generation of ice leads, ridges and, trapped motion of the ice floes.
On a generating mechanism for Yanai waves and the 25‐day oscillation
Authors: Kelly Brian G. , Meyers Steven D. , O'Brien James J.
Published: February 2004

A spectral Chebyshev‐collocation method applied to the linear, 1.5 layer reduced‐gravity ocean model equations is used to study the dynamics of Yanai (or mixed Rossby‐gravity) wave packets. These are of interest because of the observations of equatorial instability waves (which have the characteristics of Yanai waves) and their role in the momentum and heat budgets in the tropics. A series of experiments is performed to investigate the generation of the waves by simple cross‐equatorial wind stress forcings in various configurations and the influence of a western boundary on the waves. They may be generated in the interior ocean as well as from a western boundary. The observations from all the oceans indicate that the waves have a preferential period and wavelength of around 25 days and 1000 km respectively. These properties are also seen in the model results and a plausible explanation is provided as being due to the dispersive properties of Yanai waves.
Bounds on the complex permittivity of sea ice
Authors: Golden K.
Published: February 2004

An analytic method for obtaining bounds on effective properties of composites is applied to the complex permittivity ∈* of sea ice. The sea ice is assumed to be a two‐component random medium consisting of pure ice of permittivity ∈1 and brine of permittivity ∈2. The method exploits the properties of ∈* as an analytic function of the ratio ∈1/∈2. Two types of bounds on ∈* are obtained. The first bound R1 is a region in the complex ∈* plane which assumes only that the relative volume fractions p1 and p2 = 1 ‐ p1 of the ice and brine are known. The region R1 is bounded by circular arcs and ∈* for any microgeometry with the given volume fractions must lie inside it. In addition to the volume fractions, the second bound R2 assumes that the sea ice is statistically isotropic within the horizontal plane. The region R2 is again bounded by circular arcs and lies inside R1. Built into the method is a systematic way of obtaining tighter bounds on ∈* by incorporating information about the correlation functions of the brine inclusions. The bounding method developed here, which does not assume any specific geometry for the brine inclusions, offers an alternative to the classical mixing formula approach adopted previously in the study of sea ice. In these mixing formulas, specific assumptions are made about the inclusion geometry, which are simply not satisfied by the sea ice under many conditions. The bounds R1 and R2 are compared with experimental data obtained from artificially grown sea ice at the frequencies 4.8 and 9.5 GHz. Excellent agreement with the data is achieved.
Vertical structure of the upper ocean during the Marine Light‐Mixed Layers experiment
Authors: Plueddemann Albert J. , Weller Robert A. , Stramska Malgorzata , Dickey Tommy D. , Marra John
Published: February 2004

The Marine Light‐Mixed Layers (MLML) experiments took place in the subarctic North Atlantic Ocean, approximately 275 miles south of Reykjavik, Iceland, during 1989 and 1991. The 1991 field program took place from April 30 to September 6 and included a central surface mooring to document the temporal evolution of physical, biological, and optical properties. In this paper we describe the physical variability observed at the 1991 mooring site, concentrating on the vertical structure of temperature and velocity in the upper 300 m of the water column and their changes in response to heat and momentum fluxes at the sea surface. The deployment period included the spring transition, when upper ocean re stratification was initiated after deep winter mixing, and the fall transition, when mixed layer deepening began again. The dominant signal in temperature was seasonal variation, with a 6°C increase observed at the sea surface from May to August. Prior to development of the seasonal stratification, a period dominated by near‐surface temperature variability was observed in association with a 15‐day mean flux of only 20 W m−2 into the ocean. Pronounced day/night oscillations of heat flux during this period resulted in alternating development and destruction of stratification and intense diurnal cycling of the mixed layer depth. A qualitative comparison of the observed temperature structure to the prediction of a one‐dimensional mixed layer model showed that local processes dominated during the initiation of restratification and during most of the summer warming period. Nonlocal processes were important after the fall transition.
The diurnal mixed layer and upper ocean heat budget in the western equatorial Pacific
Authors: Richards K. J. , Inall M. E. , Wells N. C.
Published: February 2004

This paper presents the results of an experiment in the western equatorial Pacific centered on the equator at 165°E which was designed to study the changes to the structure of the upper ocean on timescales of a few days and spatial scales of tens of kilometers. The results show that the response of the upper ocean to atmospheric forcing is very sensitive to the vertical structure of both the temperature and salinity. The diurnal response of the near‐surface temperature to daytime heating and nighttime cooling was found to have an amplitude of a few tenths of a degree Celsius, This compares with a horizontal variation of temperature on scales of a few tens of kilometers of a similar magnitude. Even away from the very fresh surface layers typical of the area, salinity is found to play an important role in limiting the depth of nighttime mixing. In this case a subsurface salinity maximum restricts the depth to around 40 m. The nighttime convection is severely limited by either a small change in the surface forcing or the horizontal advection of slightly cooler waters from the east; we are unable to determine which is the dominant mechanism in the present case. The reduced mixing leads to an increase of the diurnal variation of sea surface temperature to over 1°C. The estimated net surface heat flux from the atmosphere to the ocean was found to be not significantly different from zero at 10 W m−2, in agreement with recent measurements. The net surface heat flux during the period of the heat budget experiment, which took place on the equator, was substantially higher at 65 W m−2. Changes of in situ temperature are found to be dominated by advection. The vertical velocity is estimated to be of order 10 m d−1 and to be caused by advection along east‐west sloping density surfaces. Changes to the temperature structure of the upper ocean induced by motions with a timescale of a few days (possibly planetary waves) are found to be significantly greater than longer‐term wind‐induced upwelling or advection.
Seasonal heat storage in the North Pacific: 1976–1989
Authors: Yan X.‐H. , Niiler P. P. , Nadiga S. K. , Stewart R. H. , Cayan D. R.
Published: February 2004

Volunteer observing ship expendable bathythermograph data obtained during the period 1976–1989, from 30°N to 40°N in the North Pacific, were used to compute the rate of change of heat storage to a fixed upper ocean temperature surface. The variability of the storage rate in the seasonal timescale, computed on a 5° latitude by 5° longitude spatial scale, is compared to the net surface heat flux computed from available surface marine weather data to the same spatial and temporal resolution. Averaged across the entire basin, the difference between the average monthly heat storage rate and the average monthly heat flux is 3.76 Wm−1. The average basin‐wide absolute heat storage rate agrees to within 7.5% of the average absolute heat flux for the whole basin. An empirical orthogonal decomposition of the spatial patterns of the difference between the heat storage rate and the net heat flux reveals no obvious trends in the heat flux computation or possible physical processes responsible for the difference. Instead, the eddies shed by the warm boundary current, the Kuroshio, is probably responsible for the major part of the difference patterns in locations where the difference values are maximum. The most important results of this study are that the heat storage rate computed to a fixed isotherm matches the net heat flux extremely well at the chosen locations and across the whole basin; and the heat storage rate computation is sensitive to the isotherm choice and to the space scale involved.
Meteorological variability and air‐sea fluxes at a closely spaced array of surface moorings
Authors: Weller Robert A. , Rudnick Daniel L. , Brink Nancy J.
Published: February 2004

Data from an array of five surface moorings, deployed in a region of transient ocean fronts with separations of between 17 and 55 km, were used to document meteorological variability at an open ocean site and to look for evidence of links between the surface meteorology and air‐sea fluxes and the gradients in sea surface temperatures. Averages over the array were also compared to historical and model‐produced data. Spatial variability in surface meteorology was observed infrequently, and much ofthat was associated with atmospheric fronts and periods of low winds. Air‐sea fluxes computed using the bulk formulae included spatial variability linked to the ocean, but spatial gradients in ocean surface velocities introduced a larger signal in the bulk formulae fluxes than did the gradients in sea surface temperature. The greatest differences between the observations and climatological data were seen in relative humidity and sea surface temperature. The bulk estimate of net longwave radiation was the heat flux component most different from the climatology. Wind stress time series from numerical weather prediction models were in best agreement with the observations at periods of a few days and longer.
Results of a stratified snow emissivity model based on the wave approach: Application to the Antarctic ice sheet
Authors: Surdyk S. , Fily M.
Published: February 2004

The results from a snow emissivity model are used to help with the interpretation of the Scanning Multichannel Microwave Radiometer data (aboard the satellite Nimbus 7, 1978–1986) over Antarctica. The model is based on the solution of Maxwell's equations through strong fluctuation theory (Stogryn, 1986). The snow is considered isothermal with horizontal stratification, isotropic inside each stratum, and with smooth interfaces. To wipe out the interference pattern created by plane stratification and in order to take into account the spatial variability of the snow characteristics, the final result is a mean value of many computations done with many stratigraphies randomly distributed around a mean profile. The spatial distribution of the microwave signatures over Antarctica reveals three areas with typical spectral signatures. These areas are identified from the point of view of snow characteristics through a ground data set (Surdyk and FiIy, 1993). The model reproduces well the effect of the stratification on the polarization differences as observed. The strong gradient of emissivity versus frequency observed on one of the test sites is not completely understood. Depth hoar layers characterized by faceted and cup‐shaped, coarse snow grains seem to have a particular scattering behavior compared with that of the usual grains. When those coarse grains are replaced by fine grains, the model results are closer to the measured data. The presence of crusts, the roughness at the snow‐ice interfaces, and crystal orientation may also have significant effects.
Use of a coupled ice‐ocean model to investigate the sensitivity of the Arctic ice cover to doubling atmospheric CO2
Authors: Ramsden D. , Fleming G.
Published: February 2004

A coupled ice‐ocean Arctic ocean model is forced with output from a Canadian Climate Center (CCC) model of the atmosphere. Two cases are considered, the first where the atmospheric CO2 is “normal” and the second where the atmospheric CO2 is “doubled.” The CCC normal forcing data are also compared with observed fields, It is found that the forcing fields from the CCC normal model run are quite similar to observed values of surface temperature and humidity. The wind stresses are, however, lower than observed geostrophic values and are hence scaled to more closely match observed values. Significant differences are found between the normal and doubled CO2 forcing fields in regard to temperature and humidity forcing fields. In particular, the surface air temperature is typically 10° Celsius warmer in the doubled case for the winter months, and the relative humidity is up to 50% higher in the summer months. The surface moisture flux from the CCC data is found to be relatively insensitive to doubling of CO2, with more precipitation less evaporation (P–E) in winter months. When the ice‐ocean model is run, less ice volume and increased areas of open ocean are observed with the doubled forcing, however, the decrease in ice volume is not as large as previous, simpler models have suggested and the model ice cover differs significantly from the ice cover from the atmospheric model. It is also found that there are differences in the oceanic temperature and salinity fields consistent with the forcing inputs, but these appear to be minimized by the insulating properties of the ice cover. On balance, the Arctic ice field appears to act as a regulator of climate change, rather than an accelerator.
An observational and numerical study of wind stress variations within marginal ice zones
Authors: Guest Peter S. , Glendening John W. , Davidson Kenneth L.
Published: February 2004

Published studies of ocean mesoscale processes in marginal ice zones (MIZs) using numerical coupled ice‐ocean models usually assume that the surface wind speed is constant over the model domain and that wind stress variations are simply proportional to surface roughness variations. We show that this assumption is not realistic in most situations because the surface wind stress is also significantly affected by mesoscale pressure variations, by changes in the surface wind vector, and by changes in surface layer stability. Two numerical case studies, utilizing detailed surface and atmospheric measurements, examine the factors affecting small‐scale (<5 km) variations in wind stress within MIZs. These case studies and surveyed observational and modeling results demonstrate that wind stress fields are qualitatively different from the surface roughness fields. A realistic wind stress scenario consists of a maximum just inside the ice edge and another maximum in the open ocean. Stress minima occur within the pack ice region away from the MIZ and over grease ice, if present. The effect of the rougher MIZ ice is counteracted when wind stresses over the open ocean are enhanced by large surface heat fluxes over the ocean, by a strong low level inversion over the ice, or by a sharp atmospheric front with surface winds paralleling the ice edge. Such situations are common in MIZ regions. Some simple methods for including first‐order atmospheric effects on wind stress variations, which could be incorporated into current ice‐ocean mesoscale models of MIZ regions, are suggested.
Variation of free tropospheric total nitrate at Mauna Loa Observatory, Hawaii
Authors: Lee Gangwoong , Merrill John T. , Huebert Barry J.
Published: February 2004

We measured total nitrate (TN) concentrations (defined as nitric acid vapor plus nitrate aerosol) nightly at the Mauna Loa Observatory (MLO) from September 1988 to September 1991. Using three meteorological criteria, (condensation nuclei, wind direction, and dew point) we selected samples that represented the free troposphere. The 3‐year mean and median of TN mixing ratios were 113 parts per trillion by volume (pptv) and 93 pptv, respectively. Each year the TN concentrations at MLO during the spring and summer were larger by more than a factor of 2 than those during the fall and winter. The springtime peak TN corresponded to incidents of increased Asian dust over the northern Pacific Ocean. Isentropic back trajectories confirmed that spring air masses with high TN originated over the Asian continent. Back trajectories also indicated that the North American continent was often the source of high TN during the summer. Air mass source regions and flow patterns to MLO were classified into five distinct groups of trajectories by cluster analysis.

Despite the different source regions for each of the clusters the distributions of TN were very similar. This suggests that the source region may be less important for determining TN at MLO than such factors as the degree of vertical mixing over source regions, stratospheric injection, and wet removal rates.
An improved model for estimating emissions of volatile organic compounds from forests in the eastern United States
Authors: Geron Christopher D. , Guenther Alex B. , Pierce Thomas E.
Published: February 2004

Regional estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for models of atmospheric chemistry and carbon budgets. Since forests are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rate. A new system is developed to estimate these emissions for specific tree genera at hourly and county level resolution. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis Eastwide Database is used to describe the areal extent, species composition, and tree diameter distributions of United States forests. Horizontal canopy occupancy by genera is then estimated as a function of diameter at breast height. Growing season peak foliar masses are derived from the empirical literature for canopies of deciduous and coniferous genera. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Leaf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera level estimates are then aggregated to regional levels for comparison with the regulatory model currently used and for input into air quality models. The proposed model yields isoprene emission rate estimates for specific countries that are 5 to 10 times higher (and total BVOC emission rates that are 3 to 5 times higher) than the Environmental Protection Agency BVOC emission rate model currently used. Emission estimates of isoprene and monoterpenes from the new system compare favorably with rates measured at various forested sites in the United States.
Influence of the vertical structure of the atmosphere on the seasonal variation of precipitable water and greenhouse effect
Authors: Bony Sandrine , Duvel Jean‐Philippe
Published: February 2004

By using satellite observations and European Centre for Medium Range Weather Forecasts analyses, we study the seasonal variations of the precipitable water and the greenhouse effect, defined as the normalized difference between the longwave flux emitted at the surface and that emergent at the top of the atmosphere. Results show a strong systematic influence of the vertical structure of the atmosphere on geographical and seasonal variations of both precipitable water and greenhouse effect. Over ocean, in middle and high latitudes, the seasonal variation of the mean temperature lapse rate in the troposphere leads to large seasonal phase lags between greenhouse effect and precipitable water. By contrast, the seasonal variation of the clear‐sky greenhouse effect over tropical oceans is mainly driven by the total atmospheric transmittance and thus by precipitable water variations. Over land, the seasonal variation of the tropospheric lapse rate acts to amplify the radiative impact of water vapor changes, giving a strong seasonal variation of the greenhouse effect. Over tropical land regions, monsoon activity generates a seasonal phase lag between surface temperature and relative humidity variations that gives a seasonal lag of about 2 months between the surface temperature and the clear‐sky greenhouse effect. Generally, the cloudiness amplifies clear‐sky tendencies. Finally, as an illustration, obtained results are used to evaluate the general circulation model of the Laboratoire de Météorologie Dynamique.
Errors in airborne flux measurements
Authors: Mann Jakob , Lenschow Donald H.
Published: February 2004

We present a general approach for estimating systematic and random errors in eddy correlation fluxes and flux gradients measured by aircraft in the convective boundary layer as a function of the length of the flight leg, or of the cutoff wavelength of a highpass filter. The estimates are obtained from empirical expressions for various length scales in the convective boundary layer and they are experimentally verified using data from the First ISLSCP (International Satellite Land Surface Climatology Experiment) Field Experiment (FIFE), the Air Mass Transformation Experiment (AMTEX), and the Electra Radome Experiment (ELDOME). We show that the systematic flux and flux gradient errors can be important if fluxes are calculated from a set of several short flight legs or if the vertical velocity and scalar time series are high‐pass filtered. While the systematic error of the flux is usually negative, that of the flux gradient can change sign. For example, for temperature flux divergence the systematic error changes from negative to positive about a quarter of the way up in the convective boundary layer.
O3 and NOy relationships at a rural site
Authors: Olszyna Kenneth J. , Bailey Elizabeth M. , Simonaitis Romualdas , Meagher James F.
Published: February 2004

Measurements of O3, NO, NO2, peroxyacetyl nitrate (PAN), HNO3, and NOy were made during a 6‐week period in the summer of 1991 in Giles County, Tennessee. These data were analyzed to determine the factors controlling the relationship between O3 and NOy at this rural site. A strong association was observed between the O3 and NOx oxidation product (NOz = NOy ‐ NOx) levels. The higher O3 levels were associated with air masses impacted by higher NOx emissions that had been photochemically processed. An analysis of the data indicates that the ultimate O3 production is about 10 molecules of O3 produced for each molecule of NOx emitted. The analysis results also suggest that O3 net production continues until about 70% of the NOx has been converted into NOz. The PAN/HNO3 ratios observed suggest that the air masses in Giles County are composed of higher volatile organic carbon/NOx ratios than the air masses observed at other rural sites in eastern North America. A comparison of the data analysis results to model simulations and smog chamber experiments suggests that most of the time, Giles County is in an NOx‐limited regime for O3 production.
Stratospheric ozone variations in the equatorial region as seen in Stratospheric Aerosol and Gas Experiment data
Authors: Shiotani Masato , Hasebe Fumio
Published: February 2004

An analysis is made of equatorial ozone variations for 5 years, 1984–1989, using the ozone profile data derived from the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument. Attention is focused on the annual cycle and also on interannual variability, particularly the quasi‐biennial oscillation (QBO) and El Niño‐Southern Oscillation (ENSO) variations in the lower stratosphere, where the largest contribution to total column ozone takes place. The annual variation in zonal mean total ozone around the equator is composed of symmetric and asymmetric modes with respect to the equator, with maximum contributions being around 19 km for the symmetric mode and around 25 km for the asymmetric mode. The persistent zonal wavenumber 1 structure observed by the total ozone mapping spectrometer over the equator is almost missing in the SAGE‐derived column amounts integrated in the stratosphere, suggesting a significant contribution from tropospheric ozone. Interannual variations in the equatorial ozone are dominated by the QBO above 20 km and the ENSO‐related variation below 20 km. The ozone QBO is characterized by zonally uniform phase changes in association with the zonal wind QBO in the equatorial lower stratosphere. The ENSO‐related ozone variation consists of both the east‐west vacillation and the zonally uniform phase variation. During the El Niño event, the east‐west contrast with positive (negative) deviations in the eastern (western) hemisphere is conspicuous, while the decreasing tendency of the zonal mean values is maximum at the same time.
Marine boundary layer measurements of new particle formation and the effects nonprecipitating clouds have on aerosol size distribution
Authors: Hoppel W. A. , Frick G. M. , Fitzgerald J. W. , Larson R. E.
Published: February 2004

Measurements of aerosol size distributions (0.005 < r < 20 μm), cloud droplet spectra, SO2, O3, CN, and other supporting quantities were made in the cloud‐topped and clear marine boundary layer (MBL) from an airship operating within about 50 km of the Oregon coast. Comparison of size distribution of interstitial aerosol within the cloud with the size distribution below the cloud clearly indicates that the processing of the aerosol through (nonprecipitating) stratus can lead to increased mass of the subset of particles which had served as cloud condensation nuclei (CCN). This increase in mass in the CCN results in a distinct “cloud residue” mode in the size distribution measured below the cloud. In all cases the aerosol mass in the cloud residue mode greatly exceeded the mass in the interstitial mode, even though the number concentration of interstitial particles sometimes exceeded the CCN concentration. Evidence of new particle formation in clear air was also found on numerous occasions. Analyses of the data indicate that the growth of newly formed particles into the observed size range is consistent with gas phase oxidation of SO2 to sulfate and subsequent condensation on the aerosol. However, the exact nucleation process, whether by homogeneous nucleation, ion‐assisted nucleation, or heterogeneous nucleation on precursor embryos, is still an open question.
Experimental demonstration of coupling of heat and matter fluxes at a gas‐water interface
Authors: Phillips Leon F.
Published: February 2004

Air‐water fluxes of oxygen and carbon dioxide have been calculated for a model which incorporates a turbulent air layer and takes into account the effects of the fluxes of sensible and latent heat on the temperature of the liquid surface. The calculated fluxes are compared with the experimental results of Liss et al (1981), Smith and Jones (1985), and Smith et al. (1991). The results of this comparison clearly demonstrate both the importance of coupling, in the sense of irreversible thermodynamics, of heat and matter fluxes at the gas‐water interface and the important role of the surface temperature of the liquid in controlling the magnitude and sometimes even the direction of the gas flux. The large carbon dioxide fluxes found by Smith and coworkers can be accounted for by assuming eddy diffusion, rather than molecular diffusion, on the seaside of the interface. This is consistent with an earlier suggestion that their measurements were affected by proximity to a surf zone. The present calculations might serve as the basis of a practical method of determining air‐sea fluxes of CO2 and other trace gases.
Relationship of ozone and carbon monoxide over North America
Authors: Chin Mian , Jacob Daniel J. , Munger J. William , Parrish David D. , Doddridge Bruce G.
Published: February 2004

Observations at sites in eastern North America show a strong correlation between O3 and CO concentrations in summer, with a consistent slope ΔO3/ΔCO ≈ 0.3. Observations in the aged Denver plume at Niwot Ridge, Colorado, also show a strong correlation but with ΔO3/ΔCO = 0.15. These data offer a sensitive test for evaluating the ability of photochemical models to simulate production of O3 over North America and its export to the global atmosphere. Application to the Harvard/Goddard Institute for Space Studies three‐dimensional, continental‐scale model shows that the model gives a good simulation of the observed O3‐CO correlations and of the associated ΔO3/ΔCO. This successful simulation lends support to model estimates of 6 Gmol d−1 for the net O3 production in the U.S. boundary layer in summer (corresponding to a net O3 production efficiency of 5.5, which is the number of O3 molecules produced per molecule of NOx consumed) and 70% for the fraction of the net production that is exported to the global atmosphere. Export of U.S. pollution appears to make a significant contribution to total tropospheric O3 over the northern hemisphere in summer. Simple interpretation of observed ΔO3/ΔCO as an O3/CO anthropogenic enhancement ratio is shown to underestimate substantially anthropogenic O3 production, because O3 and CO concentrations are negatively correlated in the absence of photochemistry. It is also shown that concurrent observations of ΔO3/ΔCO and ΔO3/Δ(NOy‐NOx) ratios can be used to impose lower and upper limits on the net O3 production efficiency.
Relating eddy correlation sensible heat flux to horizontal sensor separation in the unstable atmospheric surface layer
Authors: Lee Xuhui , Black T. Andrew
Published: February 2004

Measurements of a scalar flux from an extended surface are frequently made with the eddy correlation technique consisting of a vertical velocity sensor and a sensor for the scalar of interest. In many cases the two sensors have to be mounted with a significant horizontal separation to avoid flow interference. Consequently, the technique will underestimate the scalar flux. This paper addresses the issue of flux underestimation due to this separation. A model is developed in the framework of Monin‐Obukhov similarity for the spatial covariance of vertical velocity and air temperature in the unstable surface layer. It allows the underestimation of sensible heat flux to be assessed using information on separation orientation relative to wind direction, atmospheric stability, measurement height, and separation distance. The coefficient in the model is evaluated with observations made over a potato field and a clover field. The principles established here should also be applicable to fluxes of scalars other than sensible heat.
Dissolved input of manganese to the ocean: Aerosol source
Authors: Guieu Cécile , Duce Robert , Arimoto Richard
Published: February 2004

Aerosol particle samples representative of polluted air, dust‐laden air, and clean marine air were collected in marine regions and used in a series of dissolution studies. These samples were exposed to seawater for varying lengths of time and to deionized (Milli‐Q®) water at various values of pH. The percentage of aerosol Mn dissolved in Milli‐Q® water increased from 55 to 80% between pH 8 and pH 2 for pollution aerosols. Less dissolution occurred with the mineral aerosol particles, for which the dissolved Mn increased from 25 to 50% between pH 8 and pH 2. As similar behavior is found for particles collected in clean marine air, we conclude that the dissolution process for aerosol particles from a remote marine area, where crustal Mn dominates pollution Mn, is controlled by the background mineral content. The kinetics of Mn dissolution in seawater are rapid for all the samples: a concentration plateau is reached after 10 min or less of exposure. Release of dissolved Mn from polluted aerosols in seawater was approximately twice the value obtained with mineral particles (55 and 30%, respectively). Apparently, no additional Mn dissolution beyond that which has clearly taken place in rain occurs when rainwater enters the ocean. A positive relationship evidently exists between the total Mn concentration of the aerosol and the dissolved concentration after exposure in seawater. Extrapolating the relationship from the available data suggests that the dissolved saturation value is approximately 60 nmol L−1. Considering the different behavior found for the different types of particles, at least two cases must be considered when assessing mass balances or calculating atmospheric fluxes of Mn to the ocean. Based on the results of our dissolution studies, the resulting dissolved fluxes of Mn of atmospheric origin during a pulse of Saharan dust range from 0.16 to 0.33 μmol m−2d−1 over the duration of the pulse. The total dissolved Mn flux from anthropogenic sources in western North Europe is estimated to be 0.3 μmol m−2d−1. Fluxes of dissolved Mn of mineral and anthropogenic origin resulting from this calculation in the two examples selected are of the same order of magnitude. The spatial and temporal patterns of these different sources and the dynamics of the upper water column have to be taken into account to estimate quantitatively the impact of atmospheric input on Mn concentrations in the water column.
Microsecond‐scale electric field pulses in cloud lightning discharges
Authors: Villanueva Y. , Rakov V. A. , Uman M. A. , Brook M.
Published: February 2004

From wideband electric field records acquired using a 12‐bit digitizing system with a 500‐ns sampling interval, microsecond‐scale pulses in different stages of cloud flashes in Florida and New Mexico are analyzed. Pulse occurrence statistics and waveshape characteristics are presented. The larger pulses tend to occur early in the flash, confirming the results of Bils et al. (1988) and in contrast with the three‐stage representation of cloud‐discharge electric fields suggested by Kitagawa and Brook (1960). Possible explanations for the discrepancy are discussed. The tendency for the larger pulses to occur early in the cloud flash suggests that they are related to the initial in‐cloud channel formation processes and contradicts the common view found in the atmospheric radio‐noise literature that the main sources of VLF/LF electromagnetic radiation in cloud flashes are the K processes which occur in the final, or J type, part of the cloud discharge.
Convective transport over the central United States and its role in regional CO and ozone budgets
Authors: Thompson Anne M. , Pickering Kenneth E. , Dickerson Russell R. , Ellis William G. , Jacob Daniel J. , Scala John R. , Tao Wei‐Kuo , McNamara Donna P. , Simpson Joanne
Published: February 2004

We have constructed a regional budget for boundary layer carbon monoxide over the central United States (32.5°–50°N, 90°–105°W), emphasizing a detailed evaluation of deep convective vertical fluxes appropriate for the month of June. Deep convective venting of the boundary layer (upward) dominates other components of the CO budget, e.g., downward convective transport, loss of CO by oxidation, anthropogenic emissions, and CO produced from oxidation of methane, isoprene, and anthropogenic nonmethane hydrocarbons (NMHCs). Calculations of deep convective venting are based on the method of Pickering et al. [1992a] which uses a satellite‐derived deep convective cloud climatology along with transport statistics from convective cloud model simulations of observed prototype squall line events. This study uses analyses of convective episodes in 1985 and 1989 and CO measurements taken during several midwestern field campaigns. Deep convective venting of the boundary layer over this moderately polluted region provides a net (upward minus downward) flux of 18.1×108kg CO month−1 to the free troposphere during early summer, assuming the June statistics are typical. Shallow cumulus and synoptic‐scale weather systems together make a comparable contribution (total net flux 16.2×108 kg CO month−1). Boundary layer venting of CO with other O3 precursors leads to efficient free tropospheric O3 formation. We estimate that deep convective transport of CO and other precursors over the central United States in early summer leads to a gross production of 0.66–1.1 Gmol O3 d−1 in good agreement with estimates of O3 production from boundary layer venting in a continental‐scale model [Jacob et al., 1993a, b]. In this respect the central U.S. region acts as a “chimney” for the country, and presumably this O3 contributes to high background levels of O3 in the eastern United States and O3 export to the North Atlantic.
Total fluxes of sulfur dioxide from the Italian volcanoes Etna, Stromboli, and Vulcano measured by differential absorption lidar and passive differential optical absorption spectroscopy
Authors: Edner H. , Ragnarson P. , Svanberg S. , Wallinder E. , Ferrara R. , Cioni R. , Raco B. , Taddeucci G.
Published: February 2004

The total flux of sulfur dioxide from the Italian volcanoes Etna, Stromboli, and Vulcano was determined using the differential absorption lidar technique. The measurements were performed from an oceanographic research ship making traverses under the volcanic plumes with the lidar system sounding vertically. By combining the integrated gas concentration over the plume cross section with wind velocity data, it was possible to determine the total fluxes of SO2 from the three volcanoes, all measured within a 3‐day period in September 1992. We found total fluxes of about 25, 180, and 1300 t/d for Vulcano, Stromboli, and Etna, respectively. These data, collected with an active remote‐sensing technique, were compared with simultaneous recording with passive differential optical absorption spectroscopy (DOAS) using the sky radiation as the light source. Since the geometry of the light paths crossing the volcanic plume is not well defined in the passive measurements, a correction to the DOAS data is required. The SO2 results are also compared with previously available data from correlation spectroscopy measurements. Lidar measurements on atomic mercury were also made for the plumes from Stromboli and Vulcano, but the system sensitivity and range only allowed estimates of upper limits for the Hg fluxes.
Sulfur dioxide oxidation in winter orographic clouds
Authors: Snider Jefferson R. , Vali Gabor
Published: February 2004

The production of sulfate in cloud droplets, and the attendant depletion of sulfur dioxide (SO2) oxidants were studied in wintertime orographic clouds over southeastern Wyoming. By periodic (5–20 min) releases of SO2 into the cloud the mixing ratio of SO2 was raised to about double its background value of 0.7 parts per billion by volume (ppbv). Average values of the in‐cloud reaction time, pseudo‐first‐order SO2 reaction rate, and hydrogen peroxide (H2O2) depletion were 400 s, 2.3×10−4 s−1, and 0.04 ppbv, respectively. The measured sulfate yields and H2O2 depletions show that H2O2 is the dominant oxidant for SO2 in this situation; this finding is consistent with model results. Model simulations reveal that the O2/SO2 reaction pathway (catalyzed by Mn(II) and Fe(III)) was competitive with the H2O2/SO2 reaction pathway on one out of the nine observation days. Organohydroperoxides were not depleted and other modeled reaction pathways (O3/SO2 and HCHO/SO2) were inferred to be inhibited due to either the chemical (pH < 4.7) or physical (temperature below −5°C, cloud water content less than 0.3 cm3 m−3) properties of the cloud. The agreement found in this work between observed and predicted properties of the H2O2/SO2/H2O system contrasts with the work of Chandler et al. (1988a, b, 1989) and Gallagher et al. (1990) who observe a factor of 3 or larger discrepancy between laboratory and field measurements of the H2O2/SO2 reaction rate.
Accuracy of total ozone retrieval from NOAA SBUV/2 measurements: Impact of instrument performance
Authors: Ahmad Z. , DeLand M. T. , Cebula R. P. , Weiss H. , Wellemeyer C. G. , Planet W. G. , Lienesch J. H. , Bowman H. D. , Miller A. J. , Nagatani R. M.
Published: February 2004

The National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) has been collecting and evaluating the solar backscattered ultraviolet (SBUV/2) instrument data from NOAA 9 and NOAA 11 spacecraft since March 1985. Over 5 years (March 1985 to October 1990) of NOAA 9 (version 5.0) and over 4 years (January 1989 to June 1993) of NOAA 11 (version 6.0) reprocessed data are now available to the scientific community to study geophysical phenomena involving ozone. This paper examines the impact of the instrument performance on total ozone retrieval from the two instruments. We estimate that at the end of October 1990 the total postlaunch error for NOAA 9 due to instrument alone is −2.2%. A significant fraction of this error (−1.9%) is due to diffuser degradation which is not accounted for in the version 5 reprocessing. The estimate for NOAA 11 total postlaunch instrument error, at the end of June 1993, is −0.4%.