bluuebunny/crossref_metadata_2025 huggingface dataset:
Chlorofluoromethanes in the northeast Pacific Ocean: Measured vertical distributions and application as transient tracers of upper ocean mixing
Authors: Gammon R. H. , Cline J. , Wisegarver D.
Published: February 2008

The vertical distributions of the man‐made chlorofluoromethanes CCl3F (F‐11) and CCl2F2(F‐12) have been measured at two locations in the eastern North Pacific Ocean to depths greater than 500 m. At both sites (46°N, 125°W off the Washington‐Oregon coast and 50°N, 140°W in the Gulf of Alaska) the halomethane concentrations were found to fall off exponentially with increasing depth below the mixed layer. For F‐11 at 50°N, the surface concentration (3.2×10−12 mol/l) was found to be in saturation equilibrium with the measured atmospheric concentration (190 pptv). The measured chlorofluoromethane profiles have been interpreted in terms of a one‐dimensional model for the vertical diffusion/advection of an exponentially driven, conservative tracer into a bottomless ocean. In the appropriate limit of ‘transient steady state’ the projected profiles are simple exponentials described by an advective‐diffusive scale depth H, which is a function of the vertical eddy diffusivity Kz, the upwelling velocity w, and the characteristic time τ for the exponential growth of the tracer concentration at the boundary. At the two ocean locations studied the freon thermocline depth scales were in the range H ≃ 120–140 m, with F‐12 generally 10–20% deeper than F‐11. At 50°N the F‐11 and F‐12 vertical profiles gave consistent values of vertical diffusivity (Kz ∼ 1.2–1.3 cm2 s−1) and upwelling velocity (w ≃ 12–14 m yr−1). The model also allows a simple scaling from one exponentially driven, transient tracer (freon) to another (fossil fuel CO2), leading to a predicted mean depth of penetration of fossil fuel CO2 of approximately 300 m in the eastern North Pacific.
On the use of laser profilometry for ocean wave studies
Authors: McClain Charles R. , Chen Davidson T. , Hart William D.
Published: February 2008

Airborne laser profilometer measurements of wave skewness and spectra are presented. The measurements were made during high wind and sea state conditions in the North Atlantic. The sea states ranged from 4.5 to 8.7 m and varied from swell to wind wave dominated situations. Skewness values for the five cases ranged from 0.08 to 0.28 and compare favorably with other existing measurements. Also, the Phillips and Wallops spectral models show excellent agreement with profilometer spectra of developing seas. For one case where the seas were fully developed, the Pierson‐Moskowitz spectrum provides the best representation.
The chemistry of western Atlantic precipitation at the mid‐Atlantic coast and on Bermuda
Authors: Church Thomas M. , Galloway James N. , Jickells Timothy D. , Knap Anthony H.
Published: February 2008

The major ion composition of western Atlantic precipitation falling at the coast of eastern United States (Lewes, Delaware) and at the Sargasso Sea (Bermuda Island) has been measured by event year round (May 1980 to April 1981) to assess the influence of the ocean on precipitation from storms that leave the North American continent and transit over the western Atlantic. Particular attention is paid to the oceanic influence on the sulfur and nitrogen precursors of ‘acid rains.’ While sea salt contributes over half (by weight) of the salt in precipitation at the coast and over three quarters at Bermuda, most of the sulfate (90% at the coast and 50% at Bermuda) is in excess to sea salt sodium. Since Bermuda precipitation is still acidified some factor of 8 relative to pure equilibrium with atmospheric carbon dioxide, this strong acidity has been attributed to the long‐range transport sulfur and nitrogen precursors in the marine troposphere during which the sulfuric acid component dominates. A sulfur budget for the western Atlantic troposphere shows that of the total amount of sulfur exported from the North American continent (>3.9 TgS/yr) less than 3% (0.1 TgS/yr) is from natural sources, the rest being from anthropogenic emissions. If Bermuda precipitation is taken as typical of wet fallout of sulfur over the western Atlantic, then no more than half (<2 TgS/yr) of north American excess (nonsea salt) sulfur export falls out to the western Atlantic and at least half undergoes potential transoceanic transport as acid rain precursors to the east of Bermuda.
Lipids in aerosols from the tropical North Pacific: Temporal variability
Authors: Gagosian Robert B. , Zafiriou Oliver C. , Peltzer Edward T. , Alford Jane B.
Published: February 2008

Lipid components in air masses were sampled during 1979 at Enewetak Atoll as part of the Sea‐Air Exchange Program (SEAREX). The investigation was designed to determine the terrestrial and marine sources and to search for atmospheric transformation processes of oceanic aerosols. Four particulate lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters, and salts) all unequivocally show a terrestrial vascular plant source. Their temporal trends correlate well with those of other continental source indicators, such as particulate Al and 210Pb. These particulate lipids originate from wind erosion of Eurasian soil and direct emission from vegetation rather than from biomass burning, anthropogenic sources, or evaporation/condensation processes. A series of apparently marine‐derived lower molecular weight alcohols and fatty acid salts and esters are also present. The more typically marine polyunsaturated acids are absent, probably due to their rapid rates of atmospheric degradation. A marine origin for the fatty acid salts <C20 would require marine aerosols to be enriched ca. 300‐fold over the levels found in surface seawater samples. Although particulate total organic carbon data imply major influences of atmospheric transformations on the atmospheric particulate material, these effects are not observed in the lipid class compound distributions.
Doppler sonar observation of tidal flow
Authors: Lhermitte Roger
Published: February 2008

The paper presents and interprets results on observations of water velocity and turbulence obtained in a tidal channel by use of a high resolution Doppler sonar. The observations are presented in the form of vertical profiles of Doppler spectra expressed with a velocity resolution of 0.2 cm s−1 and obtained continuously through several days, thereby covering numerous tidal cycles. Vertical profiles of mean longitudinal water flow expressed with a water depth resolution of 3.5 cm are presented and discussed. The vertical profiles of spectral variance are also calculated and interpreted in terms of the presence of turbulence generation, dissipation and transport. The observed velocity variance involves contribution from scales extending from the scattering dimension (3 to 15 cm) to possibly less than 0.5 cm, depending on the concentration of the targets. There is a striking organization and repeatibility of the velocity structures during successive tidal cycles. An attempt to separate the contribution to spectral variance due to a possible covariance between horizontal and vertical velocity components, is presented.
An attempt to monitor the equatorial undercurrent
Authors: Wyrtki Klaus
Published: February 2008

The geostrophic balance is used to compare integrals of the observed density distribution with transports of the equatorial undercurrent measured directly during the Hawaii to Tahiti shuttle experiment. The scatter of the relationship is large, making the relation useless for monitoring purposes. The reason for the failure lies in the fast response of the density structure to anomalous up welling or downwelling.
Stratospheric sulfuric acid vapor: New and updated measurements
Authors: Viggiano A. A. , Arnold F.
Published: February 2008

The measurements of gas phase H2SO4 in the stratosphere have been continued. It has been realized that the measurements may include other sulfur‐containing species such as HSO3 and HSO5. The technique has been improved through the use of a mass spectrometer with a larger mass range and better measurements of the parameters involved in the derivation of the H2SO4 concentration. The results from the first two flights of this new instrument are reported, and the older data have been revised in accordance with the new measurements of the parameters. In addition, the lower height range has been extended to 15 km.
The sea state correction for GEOS 3 and SEASAT satellite altimeter data
Authors: Douglas B. C. , Agreen R. W.
Published: February 2008

Troughs of the ocean surface reflect more electromagnetic radiation to a satellite altimeter than crests, causing an apparent lengthening of the altimeter path. This effect, called the ‘EM bias’ has been estimated to be 2–10% of significant wave height (SWH) by various authors from GEOS 3 and aircraft experiments or theoretical analyses. For the case of the SEASAT altimeter, Born et al. (1982) at Jet Propulsion Laboratory (JPL) made an empirical estimate that gave the total correction to the altimeter path length as 7% of the SWH. A large value was expected for SEASAT because an instrumental effect in addition to the EM bias is known to exist. Waveform analyses performed at NASA Wallops flight center (Hayne and Hancock, 1982) give a correction for the instrument effect, but according to the authors their results cannot be compared with results obtained elsewhere for several reasons, including the large uncertainty (30%) of the JPL result. In this paper we resolve the situation for both GEOS and SEASAT altimeters by reinterpreting the results of Hayne and Hancock and making empirical studies using very large data sets to estimate the correction required for the effect of sea state. Empirical estimates of the correction were made by finding a value that minimized (in the sense of least squares) the differences of many (about 300) repeated pairs of altimetric profiles for each satellite. The total correction obtained is 1.9% of significant wave height for GEOS 3 and 6.4% for SEASAT, the latter result consistent with the analysis done at JPL of a smaller data set and our interpretation of the Hayne and Hancock waveform analysis.
L band radar backscatter dependence upon surface wind stress: A Summary of new SEASAT‐1 and aircraft observations
Authors: Thompson T. W. , Weissman D. E. , Gonzalez F. I.
Published: February 2008

Radar backscatter from the ocean depends on surface wind stress for a wide range of radar wavelengths. Here, we have reviewed the wind‐radar relationships for L band radar wavelengths near 25 cm and 20° angle of incidence and HH polarization using a number of aircraft and SEASAT‐I SAR observations. At this wavelength, the L band backscatter coefficient (σ°) from the ocean appears to depend upon surface wind speed (|U|) and direction (ϕ) in the following manner: σ° = K|Ū|a[1 + b cos (2ϕ)]. The wind‐speed coefficient a is 0.5±0.1 for a wide range of wind speeds. The wind‐direction coefficient b is near zero (i.e., b = 0.05 ± 0.05) for lower winds and stable marine boundary layers. However, one unusual aircraft observation suggests that b = 0.20 ± 0.05 for moderate wind speeds and an unstable marine boundary layer. We have examined a variety of aircraft and SEASAT‐I observations. SEASAT synthetic aperture radar (SAR) observations in conjunction with simultaneous SEASAT scatterometer measurements provide an excellent measurement of the wind‐speed coefficient a since a variety of wind speeds can be observed in a few minutes. Aircraft observations provide an excellent measurement of the wind‐direction coefficient b since a number of directions can be examined in about 1 hour with special flight patterns designed for multiple look directions. Thus, both aircraft and spacecraft observations were studied in this work. We have interpreted these aircraft and spacecraft results in terms of existing theoretical models for radar scattering from the ocean. We believe that modulation of echo power by the magnitude of the wind occurs through both large‐scale slope effects as well as through growth of the short gravity wave‐height spectrum. Our data is near an angle of incidence of 20° where a two scale scattering model must be used.
Melting characteristics of horizontal ice surfaces in cold saline water
Authors: Gebhart Benjamin , Sammakia Bahgat , Audunson Tore
Published: February 2008

The results of an experimental investigation of the buoyancy driven flow adjacent to and below a horizontal ice surface melting in cold water at near oceanic salinity are presented. This melting configuration is characteristic of circumstances encountered by sea ice, for example, by new ice and, also, on the bottom of tabular ice floes. Several ambient water temperatures t∞ are investigated, from t∞ = −1.75°C to t∞ = 3°C. Time exposure photographs of the flow field reveal that distinctively different flow regimes occur, across even that narrow range of ambient temperature. At all temperature levels, the flow immediately below the ice surface is found to be horizontally radially inward toward the center of the ice. Also, another outward moving horizontal layer appeared, parallel to and below the inward moving layer. The downward extent of penetration of this layer motion was seen to vary with t∞. The lower layer sinks lower into the ambient medium with increasing t∞. Measured water‐ice interface temperatures and ice melt rates are also presented. These results are compared with earlier similar measurements for vertical surfaces melting in cold saline water and found to vary in a similar way with ambient temperature t∞.
Edge waves as a cause of ice rideup onshore
Authors: Mollo‐Christensen Erik
Published: February 2008

Edge waves on ice‐covered water, generated elsewhere by wind, current, or wave impingement at the ice edge, can reach large amplitudes where bottom slope and current combine to give low group velocity. The amplitude of water velocity normal to shore can become large, and the resulting acceleration of the ice cover onto shore may be sufficient to cause ice rideup. Edge waves on an ice covered ocean with a mean current are analyzed to a linear approximation, and estimates are given of velocities and amplitudes.
The global distribution of atmospheric carbon dioxide: 1. Aspects of observations and modeling
Authors: Pearman G. I. , Hyson P. , Fraser P. J.
Published: February 2008

A two‐dimensional global atmospheric transport model is used to relate estimated air to surface exchanges of CO2 to spatial and temporal variations of atmospheric concentration of CO2. This serves to illustrate the gross features of the carbon cycle and the measurement precision required of the burgeoning global observational network if the latter is to contribute useful information to the quantitative description of the cycle. Calculations are based on the atmospheric model coupled to a fixed, or variable depth, oceanic mixed layer. Zonally averaged air‐sea fluxes of CO2 are estimated from a relationship between flux, partial pressure, temperature, and wind stress. The result is a time‐dependent (pre‐industrial to 1980) estimate of the meridional rates of net exchange of CO2 with the oceans. For example, it is estimated that, at present, the equatorial oceans release a net total of 1.3 Gt (Gt = 1012 kg) of carbon into the atmosphere annually, while high latitude oceans take up a net total of 4.4 Gt. Associated with the increasing release of fossil‐fuel derived CO2 into the northern hemisphere atmosphere, the model suggests that the interhemispheric difference in concentration of CO2 (high latitude north‐high latitude south) has changed from ∼‐1 ppmv preindustrially to ∼+1 ppmv in 1960 and to 4–5 ppmv at present. The 1960 distribution agrees with the limited observational data available for that time. Present day observations, although provisional, are in good agreement with model estimates of the annual mean global distribution of CO2. The influence of this changing interhemispheric distribution on the concept of the airborne fraction of CO2 is discussed. The sensitivity of the mean global distribution of CO2 to additional surface exchanges is demonstrated by modeling the hypothetical cases of a 1, 2, or 5 Gt yr−1 equatorial source (such as tropical deforestation) with a similar uptake by the temperate northern hemisphere forests. Such changes bring about a 20%, 40%, or 100% reduction, respectively, in the simulated interhemispheric concentration difference. Alternatively, the 1, 2, or 5 Gt yr−1 equatorial release is taken up by the global oceans. In this case, the south pole to equatorial concentration difference increases from 3 ppmv on average to 3.5, 4.0, and 5.5 ppmv, respectively. Taken in conjunction with presently available observations, which must be regarded as provisional, these results place constraints on the magnitude of any actual equatorial deforestation source. It is unlikely that such a source, combined with the sink, could amount to more than about 2 Gt yr−1. The difficulty of establishing more precisely the magnitude of such regional exchanges is discussed in light of the model limitations and required precision of the observational network.
Nonlinear response of stratospheric ozone column to chlorine injections
Authors: Cicerone Ralph J. , Walters Stacy , Liu S. C.
Published: February 2008

With a reasonably complete and up‐to‐date photochemical model of the stratosphere, we find that the calculated stratospheric ozone‐column response to chlorine injections is highly nonlinear. The model calculations assume that the background inorganic (or odd) chlorine, ClX, is due to CH3Cl and CCl4. Additional ClX is added to the stratosphere by varying input fluxes of CCl2F2 and CCl3F. The sensitivity, ΔO3/ΔClX, of the stratospheric O3 column to added ClX is relatively small for ClX ≲3 ppb or ΔClX ≲2 ppb; slight ozone increases with ClX are possible over a limited range of ClX if the formation of chlorine nitrate proceeds rapidly. This may have important implications for total ozone‐column trend assessment. As ClX increases beyond 3 ppb, the stratospheric O3 column decreases with ClX increasingly rapidly. This marked departure from the linearity calculated in past years is largely due to presently accepted faster rates of reaction of OH with HNO3, HNO4, HO2, and H2O2. If stratospheric ClX increases to about 9 ppb due to continued usage of CCl2F2, CCl3F, and CH3CCl3, the stratospheric O3 column depletion is calculated to be 6.7–9.0%. Principal uncertainties in these calculations, including the rate of formation of chlorine nitrate, the products of its photolysis, and the present day mixing ratio of ClX are discussed. Calculated ozone decreases due to increased N2O concentrations are also presented.
Isotope geochemistry of the Amazon Basin: A reconnaissance
Authors: Longinelli A. , Edmond J. M.
Published: February 2008

On the transects of the Amazon River made by the Alpha Helix in 1976 and 1977, an extensive suite of samples was collected for isotopic analyses. The water isotopes (18O/16O, D/H) were determined in atmospheric water vapour and in river, rain, and leaf waters. 13C/12C ratios were measured in the dissolved and atmospheric CO2. Determinations were made of 34S/32S and oxygen isotopes in dissolved sulphate. The effect of ‘continentality’ on the water isotopes is minor reflecting the large scale recycling by evapotranspiration from the huge area of forest within the basin. Variations in the isotopic abundances between 1976 (June–July, dry season) and 1977 (May–June, end of wet season) are consistent with the changes in meteorological conditions. The isotopic composition of the CO2, both atmospheric and dissolved, is dominated by biological effects. In 1976 the dissolved CO2 showed downstream variations from −14‰ at Iquitos in Peru to −22‰ in the lower reaches. In 1977, no systematic trend was apparent, the data ranging around −19‰. The values for atmospheric CO2 decrease inland from marine values at the mouth to around −15‰ at Manaus. During the dry season (1976) the values in the interior, western basin were homogeneous at −20‰. In the wet season there were considerable variations reflecting atmospheric instabilities with the average value being about −13‰. The sulphur isotopic composition of the dissolved sulphate is remarkably uniform at around 7‰. In 1977 the 18O values in the sulphate decreased systematically downstream from 8‰ in Peru to 3‰ at the mouth, consistent with a progressive, redox‐mediated exchange with water and dissolved oxygen. In 1977 the values increased to over 11‰, apparently indicating exchange with a highly fractionated reservoir of dissolved oxygen perhaps in the semireducing environment of the flood plain lakes.
Measurement of stratospheric aerosol near Sanriku (39°N, 142°E) in Japan on May 31, 1979
Authors: Matsuzaki Akiyoshi , Nakamura Yoshiharu , Itoh Tomizo
Published: February 2008

The altitude profile of the scattering extinction of stratospheric aerosols was measured by using the balloon‐borne spectrometer with the solar occultation method near Sanriku (39°N, 142°E) in Japan on May 31, 1979. The result confirmed that the altitude profile of the scattering extinction turned out to be close to that of the SAM II measurement near Alaska during July 16–19, 1979.
Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill
Authors: Wand R. H. , Rastogi P. K. , Watkins B. J. , Loriot G. B.
Published: February 2008

The 440‐MHz radar at Millstone Hill (42.6°N, 71.5°W) was employed to examine the detailed evolution of turbulence structures in the tropostratosphere with a very fine Doppler resolution of 0.12 Hz, corresponding to 4 cm s−1 radial velocity resolution. The measurement technique involved directing the antenna downwind at a low elevation angle (15° or 20°) and processing the echos from a range where the background wind shear was high. Although no attempt was made to obtain good range resolution, a wide variety of turbulence structures were evident by virtue of their different Doppler shifts in the presence of a high wind shear. Using arguments based on the dominance of ‘shear broadening’ and the required velocity gradient to create instabilities, maximum layer thicknesses in the vicinity of 20–300 m were inferred. The implication of these observations to bulk transport of passive contaminants in the stratosphere is briefly discussed.
Observations of near‐surface currents and temperature in the central and western tropical Atlantic Ocean
Authors: Molinari Robert L.
Published: February 2008

Eleven satellite‐tracked drifting buoys were deployed in the central South Atlantic Ocean during two austral summer and two austral winter cruises. Between 7°S and 11°S and 23°W and 31°W during austral winter, net buoy drift was to the west. Surface geostrophic flow was to the east between 7°S and 9°S. It is proposed that strong southeast trade winds can induce directly driven surface flows to the west that are more intense than the eastward geostrophic flows associated with the South Equatorial Countercurrent (SECC). A sustained period of eastward drift within the SECC was observed during austral summer, when the trades are weaker. The trajectories indicate surface waters north of 8°S have a mean northward meridional component and those south of 8°S a southward component. The buoys which drifted north became entrained into the North Brazilian Coastal Current (NBCC) and those that drifted south into the Brazil Current. One buoy left the NBCC at about 5°N to drift northeastward in the North Equatorial Countercurrent (NECC). This trajectory and historical ship drift reports suggest that the NECC may extend only to 35°W to 40°W during boreal winter. Temperature data obtained as the buoys drifted westward and northward suggest that increases in upper layer heat content can be attributed to heat fluxes through the sea surface.
Sources, sinks, and seasonal cycles of atmospheric methane
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

It is shown that a long lifetime of about 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year (Tg = 1012 gm). On average there is 25–34 ppbv less methane in the atmosphere of the northern hemisphere during summer when compared with the rest of the year. Methane concentrations rise rapidly to their yearly maximums in fall. Seasonal cycles of CH4 concentration in the southern hemisphere include lowest concentrations during the late Australian summer and fall, being about 14 ppbv less than during the rest of the year. The repeating pattern of a rapid rise of CH4 concentrations during fall in the northern hemisphere suggests a large fall source at latitudes above 30°N. The remaining observed seasonal variations are consistent with the seasonal cycle of OH, which removes methane from the atmosphere. The extensive set of self consistent measurements of methane are reported and analyzed showing that methane has increased during the last 3–4 years at rates of 1–1.9% per year all over the world at sites ranging from inside the arctic circle to the south pole. Observational results are used to estimate the sources, sinks, seasonal cycles of CH4, and the effects of human activities on its atmospheric abundance.
The fine structure of the stratospheric flow revealed by differential sounding
Authors: Barat J.
Published: February 2008

Preliminary results concerning the fine vertical structure of the stratospheric flow in the middle stratosphere, above 18 km, are presented. By using a high‐resolution anemometer hung below slowly rising and descending balloons, the wind shear vector was measured over vertical distances as small as 50 m. Most of the soundings reveal an organized structure with a vertical wavelength of about 1 km. Shear instabilities are generally related to these structures. These observations, more detailed than those obtainable using radar‐balloon methods, suggest that long‐period inertio‐gravity waves are responsible for much of the variability.
Observation of stratospheric vertical ozone distribution by a XeCl lidar
Authors: Uchino O. , Maeda M. , Yamamura H. , Hirono M.
Published: February 2008

Based on the differential absorption method, stratospheric vertical ozone distributions have been continuously measured by XeCl lidar at Fukuoka (33°N, 130°E) since September 1979. Reliable data were obtained in an altitude range of 15–25 km. A high positive correlation was obtained between the XeCl lidar and the total ozone observed by the Dobson spectrophotometer at Tateno (36°N, 140°E). At a height of 17.25 km the ozone mixing ratio has a high positive correlation with the temperature. These results are in good agreement with those obtained by ozonesondes at Tateno in 1969–1970. According to these data, correlation between ozone and temperature is briefly discussed.
The 1980 eruptions of Mount St. Helens: Physical and chemical processes in the stratospheric clouds
Authors: Turco R. P. , Toon O. B. , Whitten R. C. , Hamill P. , Keesee R. G.
Published: February 2008

We investigate the physical and chemical properties of the stratospheric clouds produced by the recent eruptions of the Mount St. Helens volcano. The large and diverse set of observational data collected in the high‐altitude plumes of the May 18, May 25, and June 13, 1980, eruptions is organized and analyzed for evidence of the processes at work. The data are used to guide and constrain detailed model simulations of the volcanic clouds. For this purpose a comprehensive one‐dimensional model of stratospheric sulfate aerosols, sulfur precursor gases, and volcanic ash and dust is utilized. The model accounts for gas‐phase and condensed‐phase (heterogeneous) chemistry in the clouds, aerosol nucleation and growth, and cloud expansion. Computational results are given for the time histories of the gaseous species concentrations, aerosol size distributions, and ash burdens of the eruption clouds. The long‐term buildup of stratospheric aerosols in the Northern Hemisphere, and the persistent effects of injected chlorine and water vapor on stratospheric ozone, are also investigated. We conclude that SO2, water vapor, and ash were probably the most important substances injected into the stratosphere by the Mount St. Helens volcano, both with respect to their widespread effects on composition and their impact on climate. Despite the seemingly large magnitude of the Mt. St. Helens eruption, we also find that the volcano had little influence on the climate (≲0.05 K surface cooling in the Northern Hemisphere) or on stratospheric ozone (<0.2% maximum hemispherical depletion). The remaining problems in the field of volcanic cloud physics and chemistry, and the requirements for future experimental work, are also discussed.
Lightning and precipitation in a small multicellular thunderstorm
Authors: Proctor D. E.
Published: February 2008

Radio images of 26 consecutive lightning flashes are described in relation to radar pictures of the storm. These flashes all started in two vertical turrets where reflectivity factors exceeded 25 dBZ. Five large cloud flashes pervaded an almost horizontal plume or low‐level anvil, and ground flashes occurred on the opposite side, in the propagating flank of this storm. Observers on the ground reported a light hailfall and copious rain. Most of the lightning occurred in a region that was 3–5 km above ground (AGL). Flashes originated at heights that ranged from 3.1 km (where the environmental air temperature was −5°C) to 5.1 km AGL (−16°C) and they began at a mean height of 3.94 km AGL (−10°C). The standard deviation of 26 heights at which flashes began was 440 m. Recorded electric field‐changes showed that the channels were charged negatively, and we inferred that negative charge had accumulated at these heights in the vertical turrets, and that the paths followed by cloud flashes were influenced by positive charge which had accumulated in a plume that was nearly horizontal and which had formed on the flank opposite to the propagating flank of the storm. The estimated total length of 18 consecutive lightning flashes that had occurred during a 3‐min interval was 486 km. Measurements of electric field‐change magnitudes were used to estimate totals of 440 C and 106 C that had been discharged in 180 s from two cells whose volumes (enclosed by 30 dBZ surfaces) were 260 and 80 km3, respectively. This paper also describes the geometries of stepped leaders that cause electric field‐changes of the BIL form. It discusses a continuing current which was carried by a cloud flash.
Air‐sea fluxes of transient atmospheric species
Authors: Thompson Anne M. , Zafiriou Oliver C.
Published: February 2008

The air‐to‐sea fluxes of the major reactive tropospheric gases and radicals have been estimated from the two‐layer stagnant film model by using concentrations appropriate for the unpolluted marine troposphere and by taking into account effects of species solubility and chemical reactivity on the exchange rate. Nearly all of the transfers appear to be limited by gas‐phase diffusion, in which case the exchange rate is equivalent to a conventional deposition velocity. The largest fluxes are associated with acids (HNO3, HCl) and the more abundant molecular and radical transients in the atmosphere (O3, H2O2, CH3OOH, HO2, CH3O2). For the acids and other soluble gases, e.g., H2O2, H2CO, addition of rainout and near‐surface particulate sinks reduces the calculated air‐sea (dry) fluxes up to a factor of 2. The atmospheric input to the ocean is smaller than estimated in situ water production for most species considered. Exceptions are NO3, CH3OOH, and CH3O2, for which the atmospheric source exceeds plausible oceanic sources. In contrast to the bulk aqueous and gas phases it appears that the chemistry of the interfacial layer at the sea surface is significantly influenced by the influx of radicals and reactive oxidants. Indeed, although a basic assumption of the two‐film model is that microlayer reactions affect only the exchange rate, they may be sufficiently intense to chemically modify the diffusing gases.
Atmospheric bromine in the Arctic
Authors: Berg Walter W. , Sperry Paul D. , Rahn Kenneth A. , Gladney Ernest S.
Published: February 2008

We report the first measurements of both particulate and gas phase bromine in the Arctic troposphere. Data from continuous sampling of the Arctic aerosol over a period of 4 years (1976–1980) indicate that the bromine content in the aerosol averages 6±4 ngBr/SCM (5±3 pptm Br) for 9 months of every year. During the 3‐month period between February 15 and May 15, however, we observed an annual sharp maximum in particulate bromine with levels exceeding 100 ngBr/SCM (82 pptm Br). The Arctic aerosol showed no bromine enrichment relative to seawater except for this 3 month peak period. During the bromine maximum, enrichment factors reached 40 with average values near 10. Calculations of the amount of excess bromine in the Arctic aerosol showed that over 90% of the peak bromine had an origin other than from direct bulk seawater injection. Total levels of gas phase bromine in the Arctic troposphere found during the peak aerosol period averaged 422±48 ngBr/SCM (118±14 pptv). Total bromine content during this period averaged 474±49 ngBr/SCM with gas‐to‐particle ratios ranging from 7 to 18. A measurement under nonpeak conditions showed total bromine levels at <25 ngBr/SCM. The possibility that local contamination contributed to the seasonal development of the 3‐month bromine peak was carefully considered and ruled out. Elevated particulate bromine levels, with peak values ranging from 22 to 30 ngBr/SCM, were also found at Ny‐Alesund, Spitsbergen (Norway). The apparent seasonal nature of this bromine peak suggests that the large bromine maximum observed at Barrow is not an isolated or unique phenomenon characteristic of that sampling location. The level of total bromine in the Arctic troposphere during the 3‐month maximum was found to exceed all measurements made in the natural troposphere by up to an order of magnitude. When compared to the natural background levels, the results presented in this paper indicate that the bromine concentrations in the Arctic troposphere are the highest found anywhere in the world.
Interannual variability of the equatorial Pacific—Revisited
Authors: Busalacchi Antonio J. , Takeuchi Kensuke , O'Brien James J.
Published: February 2008

A linear numerical model forced by monthly shipboard wind estimates used to study the interannual response of the tropical Pacific Ocean for 1961–1970 (Busalacchi and O'Brien, 1981) is extended through December 1978. The additional 8 years include the 1972 and 1976 Los Niños and the aborted event of 1975. Model pycnocline variations at several locations are compared with observed sea‐level fluctuations. El Niño events are depicted as periods when the pycnocline is persistently deep along the eastern boundary. Remotely forced equatorial Kelvin waves are responsible for this response. The character of each simulated El Niño is strongly dependent on the relation between zonal wind stress changes in the western and central equatorial Pacific. There are important differences in the location and timing of the wind changes associated with each El Niño. During the 1970's, the easterlies in the central equatorial Pacific had more of an active role in the evolution of El Niño than in the previous decade. In the western tropical Pacific a rapid shoaling of the pycnocline during each El Niño is caused by westward‐propagating Rossby waves. Interannual pycnocline displacements in the central equatorial Pacific are determined by the superposition of Kelvin waves excited to the west and first horizontal‐mode Rossby waves generated to the east.
Supercooling and energy exchange near the Arctic Ocean surface
Authors: Lewis E. L. , Perkin R. G.
Published: February 2008

Conductivity, temperature, and depth (CTD) measurements made north of Svalbard, centered around 83°N, 10°E, show regions in which the surface waters are supercooled to a depth of about 8 m. At other locations, warm Atlantic waters advected into the area by the West Spitzbergen current are melting the sea ice. The resulting large horizontal salinity gradients cause intrusive layering with layers at depth sometimes being below their surface freezing point. Supercooling is explained in terms of the pressure dependence of freezing temperature and the existence of ice keels well below the surface. It is noted that the potential heat sink for surface freezing provided by supercooling can be of the same order as that available from heat loss to the atmosphere. At the same time an equivalent amount of ice is being melted off the keels thus constituting an “ice pump.”
The persistence of air bubbles at a seawater surface
Authors: Burger Scott R. , Blanchard Duncan C.
Published: February 2008

The time an air bubble persists at a seawater surface is a function of many factors, including the relative humidity and speed of the air over the surface of the water. We find that bubble surface life increases in magnitude with decreasing humidity and increasing speed of the air. This appears to be caused by a salinity gradient along the bubble cap. This produces a surface tension gradient (Marangoni effect) that increases bubble surface life.
Long‐term changes in dynamic height
Authors: Barnett T. P.
Published: February 2008

Secular changes in the density structure of selected regions of the upper ocean are investigated to see if they can explain the apparent rise in sea level observed along the continental margins of the world's oceans. The time rate of change of dynamic height is estimated to be −0.8 dyn cm/century, a value that is indistinguishable statistically from 0. Further, the distribution of individual values entering the grand average are distributed normally to a high degree of approximation. Assuming the change in relative sea level is real, then it could be due to either melting of the polar caps or warming of the upper ocean. Warming, since the turn of the century, of the magnitude suggested in much of the literature would have been detectable in the density structure of the upper ocean. This signal was not seen in the current analysis. A more modest warming, allowing for instrumental biases over the last 50 years or melting of the polar caps by just enough to give the observed change in relative sea level, would have signatures in the upper ocean density field that would barely be detectable in the current study. A combination of warming and melting should have had a signal that was marginally detectable. This latter signal was not observed. A final possibility is that the ocean gyres have “spun up” causing increased sea level along the continental margins. The current analysis, while not designed to investigate this possibility, suggests further work is justified to test this idea. Explaining secular changes in the density field of the upper ocean will require long‐time series of hydrographic observations taken at key locations in the world's oceans. The temporal sampling must be particularly intense to filter the relatively small expected signal from the high background noise levels.
The modification of X and L band radar signals by monomolecular sea slicks
Authors: Hühnerfuss Heinrich , Alpers Werner , Cross Aubrey , Garrett William D. , Keller William C. , Lange Philipp A. , Plant William J. , Schlude Franz , Schuler Dale L.
Published: February 2008

One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind‐generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind‐generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at larger angles to the wind.
Measurement of breaking waves by a surface jump meter
Authors: Longuet‐Higgins M. S. , Smith N. D.
Published: February 2008

Quantitative information on the strength and size distribution of whitecaps in a given wave field is very scarce. During the MARSEN field experiments, observations of surface elevation were made with a capacitance wire wave recorder attached to a free floating spar buoy. Automatic analysis of the records with a differentiating circuit and counter allowed a histogram of jump‐heights to be constructed corresponding to any preset critical rise rate R of the surface elevation. Over a certain range of R the histogram was nearly independent of the precise value of R. This occurred usually when 0.6<R/c0<1.0 where c0 was the speed of the dominant waves. Records were obtained in wind speeds ranging from 1 to 14 m/s. At 14 m/s the number of “jumps” indicating either steep or breaking waves was of the order of 1 every 100 wave periods. It is shown that this number is consistent with previous theoretical estimates, and with visual observations of whitecap coverage. Because of the dispersive properties of waves, white‐capping in deep water is intermittent. Both theoretical calculation and laboratory experiments lead us to expect steep or breaking waves to induce separated flow, with a high local input of momentum to the wave field. It is concluded that such local events could contribute significantly to the total horizontal stress exerted by the wind.
Marine aerosol at southern mid‐latitudes
Authors: Gras J. L. , Ayers G. P.
Published: February 2008

Results of an investigation of aerosol particles at Cape Grim (41°S, 145°E) for the period February 1978 to May 1980 are presented. Size distributions were obtained for radii of ∼0.003 to ∼5 μm. These distributions typically are bimodal in dN/d log r versus log r with modes at ∼0.025 and 0.5 μm radius. No evidence was observed for a nucleus mode previously reported for this site. The aerosol consisted of three distinct fractions, a small particle fraction of ammonium sulfate, a sea‐salt fraction, and a small fraction (<1%) of insoluble noncrystalline but otherwise unidentified particles.
An investigation of sulfate production in clouds using a flow‐through chemical reactor model approach
Authors: Hong Min Sun , Carmichael Gregory R.
Published: February 2008

A flow‐through chemical reactor model is developed to describe the mass transfer and chemical processes that atmospheric gases undergo in clouds. The model includes the simultaneous absorption of SO2, NH3, O3, NOx, HNO3, CO2 and H2O2, the accompanying dissociation and oxidation reactions in cloud water, considers solution electral‐neutrality, and includes qualitative parameterization of cloud microphysics. The model is used to assess the importance of the oxidation reactions H2O2‐S(IV), O3 ‐ S(IV), and S(IV) ‐ Mn++ catalysis, and the effects of cloud parameters such as drop size, rain intensity, liquid water content, and updraft velocity. Both precipitating and nonprecipitating clouds are studied. Model results predict sulfate production rates varying from 3%/hr to 230%/hr (expressed in terms of gaseous SO2 conversion rate). The actual rate is highly dependent on the chemical composition of the uptake air and the physical conditions of the cloud. Model results also show that both the H2O2 and the O3 oxidation reactions can be significant.
Urban exports to the nonurban troposphere: Results from Project MISTT
Authors: White Warren H. , Patterson David E. , Wilson William E.
Published: February 2008

An identifiable plume of contaminated air forms downwind of metropolitan St. Louis under certain conditions. The contribution of this urban plume to tropospheric ozone and aerosol loadings is calculated from concentration and wind fields measured during Project MISTT. On all three summer days selected for study, net ozone exports reached 2–3×106 g mol/h, or about 3/2 mole per mole of emitted nitrogen, within hours of emission. Conversion of sulfur dioxide to sulfate aerosol was incomplete at the distances sampled; it is estimated that haze exports ultimately reached 500–600 km2/h, or 8–9 m2 per gram of emitted sulfur. Simple extrapolation of the yields observed at St. Louis indicates that anthropogenic inputs overwhelm natural contributions to ozone and aerosols over eastern North America.
Aerosol measurements at four background sites
Authors: Bodhaine Barry A.
Published: February 2008

Atmospheric monitoring stations are operated at Barrow, Alaska; Mauna Loa, Hawaii; American Samoa; and South Pole by the Geophysical Monitoring for Climatic Change program to measure the characteristics of gaseous and aerosol species under background conditions. A nearly continuous record of light‐scattering coefficient and condensation nuclei concentration measurements is available for Barrow since 1971, Mauna Loa since 1974, Samoa since 1977, and South Pole since 1974. The Barrow light‐scattering data exhibit a strong annual cycle with a maximum in winter and spring (the Arctic haze) and a minimum in summer. The Barrow condensation nuclei data exhibit a strong semiannual cycle with a maximum coinciding with that of light scattering and an additional maximum about August. The Mauna Loa light‐scattering data show a strong annual cycle with a maximum in April or May caused by long‐range transport of Asian desert dust. The Mauna Loa condensation nuclei data show no significant annual cycle. The Samoa light‐scattering and condensation nuclei data are representative of a clean marine atmosphere and exhibit no significant annual or diurnal cycle. The South Pole light‐scattering data show a complicated annual cycle with a maximum in the austral summer and a minimum about April. The austral winter is dominated by events most likely caused by the transport of sea salt in the troposphere from the coastal regions to the interior of the Antarctic continent. The South Pole condensation nuclei data show a repeatable annual cycle with a maximum in the austral summer and a minimum in the austral winter. Linear least squares trend analyses show no significant trend compared to the standard error about the regression line at any station.
Modification of stratospheric circulation by trace constituent changes?
Authors: Dunkerton Timothy J.
Published: February 2008

The effect on the quasi‐biennial oscillation of diabatic heating due to volcanic aerosols is investigated. A diabatic vertical velocity of the order of 0.2 km month−1, corresponding to a localized tropical heating rate of the order of 0.1°C/day, has an effect on the QBO similar to that observed in 1963–1965. Easterly shear zones are relatively cold at the equator; their descent is retarded by the diabatic circulation. When all other factors are assumed constant, the dynamical link between Agung and the QBO requires tropical confinement of the aerosol cloud and a radiative heating rate of the correct order of magnitude. There is evidence that these requirements may have been met at least in the first 2 years following the Agung eruption. In this case, the effect of the Agung aerosol cloud in 1963–1965 is seen to be dynamical as well as thermodynamical, resulting in an anomalously long QBO period.