bluuebunny/crossref_metadata_2025 huggingface dataset:
Gaseous deposition to snow: 1. Experimental study of SO2 and NO2 deposition
Authors: Valdez Marc P. , Bales Roger C. , Stanley Deena A. , Dawson George A.
Published: February 2008

A series of 48 laboratory experiments has determined depth profiles of S(IV) and S(VI) accumulation in snow exposed to 20–140 ppb SO2 for 6–12 hours. Surface deposition velocity, calculated from the amount of sulfur taken up, divided by the gas‐phase concentration, averaged 0.06 cm s−1. Snow held near −2°C had an average deposition velocity of 0.04 cm s−1, with new snow having a value about double that for older, metamorphosed snow (0.05 versus 0.02 cm s−1). Snow held near 0°C had an average deposition velocity of 0.07 cm s−1, and snow held below zero, but with surface melting due to sunlight, had a value of 0.06 cm s−1. When sunlight and temperature allowed draining of meltwater, deposition velocities were much higher (0.14 cm s−1). Deposition velocities for snow at −2°C were as much as 60% higher for measurements over 6 hours versus 10–12 hours. Penetration of sulfur into the snow was generally about 7 cm for colder experiments and only 4 cm for snow with more liquid water present. Uptake of SO2 by snow is apparently determined largely by the liquid‐water‐to‐air ratio in the snowpack. SO2 and ozone concentrations had only small effects on deposition velocity. Most sulfur in the snow was found as S(VI), even in the absence of ozone, indicating that another oxidant is readily available, especially in new snow. Sunlight had no effect on uptake, other than increasing the liquid‐water‐to‐air ratio by surface melting of the snow. Four measurements of NO2 deposition to snow were also made; uptake was small, with deposition velocities averaging 0.005 cm s−1 in the dark and 0.012 cm s−1 in the sunlight.
Quasi‐Lagrangian measurements of density surface fluctuations and power spectra in the stratosphere
Authors: Quinn Elizabeth P. , Holzworth Robert H.
Published: February 2008

Pressure and temperature data from eight superpressure balloon flights at 26 km in the southern hemisphere stratosphere are analyzed. The balloons, which float on a constant density surface, travel steadily westward during summer and eastward during winter, as expected from local climatology. Two types of fluctuations are observed: neutral buoyancy oscillations (NBO) of around 4 min, and 0.1–to 1‐hour oscillations that are characterized as small‐amplitude density surface fluctuations. Lapse rates and densities are calculated and found to agree well with the expected values. Examples of wave damping and simultaneous fluctuation at two nearby balloons are presented. Spectral analysis is performed clearly showing the NBO and that the majority of the power is in the mesoscale range (3 hours > τ > 20 min). Spectral slopes of power versus frequency are measured to be on the average −2.18±0.24 for pressure and −1.72±0.24 for temperature. These slopes are compared to the predictions of turbulence theories and the theory of a universal gravity wave spectrum.
Air pressure waves from Mount St. Helens eruptions
Authors: Reed Jack W.
Published: February 2008

Weather station barograph records as well as infrasonic recordings of the pressure wave from the Mount St. Helens eruption of May 18, 1980, have been used to estimate an equivalent explosion airblast yield for this event. Pressure amplitude versus distance patterns in various directions compared with patterns from other large explosions, such as atmospheric nuclear tests, the Krakatoa eruption, and the Tunguska comet impact, indicate that the wave came from an explosion equivalent of a few megatons of TNT. The extent of tree blowdown is considerably greater than could be expected from such an explosion, and the observed forest damage is attributed to outflow of volcanic material. The pressure‐time signature obtained at Toledo, Washington, showed a long, 13‐min duration negative phase as well as a second, hour‐long compression phase, both probably caused by ejecta dynamics rather than standard explosion wave phenomenology. The peculiar audibility pattern, with the blast being heard only at ranges beyond about 100 km, is explicable by finite amplitude propagation effects. Near the source, compression was slow, taking more than a second but probably less than 5 s, so that it went unnoticed by human ears and susceptible buildings were not damaged. There was no damage at Toledo (54 km), where the recorded amplitude would have broken windows with a fast compression. An explanation is that wave emissions at high elevation angles traveled to the upper stratosphere, where low ambient air pressures caused this energetic pressure oscillation to form a shock wave with rapid, nearly instantaneous compression. Atmospheric refraction then returned part of this wave to ground level at long ranges, where the fast compressions were clearly audible.
Adjacency effect produced by the atmospheric scattering in thematic mapper data
Authors: Tanré D. , Deschamps P. Y. , Duhaut P. , Herman M.
Published: February 2008

Examination of thematic mapper (TM) data has shown that water spectral reflectances observed at the top of the scattering atmosphere are contaminated not only by an intrinsic atmospheric reflectance but also by the reflectance of the surrounding green vegetated land surface when the water surface has a small size. This last effect is called the adjacency (or background, or environment) effect. A theoretical formalism has been used to explain the effects and is validated by being able to simulate the TM observed spectral reflectances. Further consequences on land surface classification are discussed, as well as the impact of the adjacency effect on the method of using water surface for atmospheric correction.
Long‐term cluster growth modeling
Authors: Kyle Thomas G.
Published: February 2008

The growth of particle clusters is modeled by allowing the particles to be moved by the atmospheric winds and a random velocity component. The dispersion of the cluster is followed for 432 hours. The results from many model runs using wind fields during a 2‐year period indicate that clusters grow with a time‐varying exponent. The growth between 40 and 150 hours is exponential in time. The rapid growth can be explained as resulting from horizontal wind shear.
Effect of E‐field mill location on accuracy of electric field measurements with instrumented airplane
Authors: Mazur Vladislav , Ruhnke Lothar H. , Rudolph Terence
Published: February 2008

Errors in ambient electric field measurements related to position of four shutter‐type sensors on an instrumented airplane are analyzed. It is shown that sensors' positions affect significantly the propagation of errors (1) in estimates of coefficients of the matrix equations that relate the ambient field to the local fields, and (2) in the signal processing into ambient electric field measurements. Positioning field mills on or near crossing points of the lines of the airplane's electrical symmetry minimizes the amplification of experimental errors. A computer‐simulated block model of the NASA F‐106B research airplane, placed in a uniform electric field, is used to calculate the matrix coefficients. The accuracy of this method is evaluated and compared with that of small‐scale model measurement and in‐flight calibration. A new calibration procedure to determine the net charge on the airplane is suggested.
Ozone over McMurdo Station, Antarctica, Austral Spring 1986: Altitude profiles for the middle and upper stratosphere
Authors: Connor Brian J. , Barrett J. W. , Parrish A. , Solomon P. M. , de Zafra R. L. , Jaramillo M.
Published: February 2008

The ozone altitude profile for 25 ≤ z ≤ 55 km was measured from McMurdo Station, Antarctica, by ground‐based millimeter‐wave spectrometry, on 34 days between September 12 and October 29, 1986. The mixing ratio peaked at altitudes ranging from 28 to 34 km, with peak values between 5 and 9 parts per million by volume (ppmv). The ozone mixing ratio at 25 km decreased by 15±5% (1σ uncertainty) during the period. No significant decrease was observed at higher altitudes; the upper limit on any secular trend at 33 or 40 km is ∼8%. Considerable variability was observed at all altitudes, on time scales of 1 to a few days. In the most dramatic case, ozone in a layer 25 ≤ z ≤ 40 km nearly doubled between September 20 and 23. This was accompanied by a significant warming and an increase in N2O at the same altitudes. We compare our results to concurrent balloonsonde ozone measurements, to a model prediction, and, by combining our results with the balloonsonde profiles, to satellite measurements of total ozone. The observation that ozone depletion was confined to the lower stratosphere is consistent with theories invoking heterogeneous chemistry associated with polar stratospheric clouds. It may be consistent with theories which predict upwelling of ozone‐poor air, if such upwelling is confined to the lower stratosphere. Our data do not support theories predicting depletion in the upper stratosphere, but the seasonal coverage of the measurements was too limited to be definitive.
Nitrogen and sulfur emissions from the burning of forest products near large urban areas
Authors: Hegg Dean A. , Radke Lawrence F. , Hobbs Peter V. , Brock Charles A. , Riggan Philip J.
Published: February 2008

Airborne measurements of trace gases and particles in the smoke from a prescribed burn of forest products in the Los Angeles basin show significantly higher emissions of NOx, SO2, and paniculate NO−3 than do measurements in smokes from the burning of biomass in rural areas. It is postulated that the high emissions are due to the revolatilization of previously deposited pollutants. Implications for pollutant source inventories and the nuclear winter hypothesis are briefly discussed.
Carbon disulfide in seawater and the marine atmosphere over the North Atlantic
Authors: Kim Ki‐Hyun , Andreae M. O.
Published: February 2008

Carbon disulfide (CS2) was determined in surface water and the overlying atmosphere during three cruises covering the coastal areas of the eastern United States, the temperate North Atlantic, and the Sargasso Sea (April/May, August, September 1986: 25°–44°N and 66°–81°W). The CS2 concentrations in surface waters were within the range of 2.5–510 pmol S(CS2) L−1 (picomol CS2‐sulfur per liter). The mean concentrations in open ocean waters and coastal waters were 16 ± 8 (n = 95) and 33 ± 19 pmol S(CS2) L−1 (n = 110), respectively. Comparison of the CS2 concentrations measured in April/May and in September suggests the possibility of seasonal variability in the production of CS2 in surface waters. The distribution patterns of CS2 in the atmospheric boundary layer were similar to those observed in surface waters, with higher concentrations near the coast and lower levels over the open ocean. The typical background mixing ratio of CS2 in the remote marine boundary layer is of the order of a few parts per trillion by volume. On the basis of our measurements of CS2 in surface seawater and the overlying atmosphere, the global sea‐to‐air CS2 flux is estimated to be 6.8 (3.4–14) Gmol S(CS2) yr−1, equivalent to 0.22 (0.11–0.44) Tg S yr−1.
A comparative study of mesospheric solar tides observed at Adelaide and Kyoto
Authors: Vincent R. A. , Tsuda T. , Kato S.
Published: February 2008

Observations of winds in the upper mesosphere and lower thermosphere (∼80–110 km) measured at the geographically conjugate locations of Adelaide (35°S, 138°E) and Kyoto (35°N, 136°E) in the years 1983–1985 are used to study hemispheric differences in the behavior of the solar diurnal and semidiurnal tides. Comparisons of the tidal amplitude and phase parameters show that there are distinct hemispheric asymmetries. The diurnal tide is usually much larger in amplitude at Adelaide, and it exhibits a height structure which indicates a relatively larger contribution from the propagating (1, 1) mode at this location. Comparisons with recent theoretical work suggest that while some of these differences may be due to hemispheric differences in forcing and/or to interactions between the tide and the background winds in the middle atmosphere, it is also possible that they indicate weaker turbulent induced damping of the (1, 1) mode in the southern hemisphere. The characteristics of the semidiurnal tide agree well at the two locations. It is found that the zonal wind components are about 6 hours out of phase and the meridional components are in phase in all seasons. This behavior, taken together with the inferred vertical wavelengths, which are greater than 100 km in summer and ∼45–80 km in winter, indicates that there are strong contributions from the antisymmetric (2, 3) mode, probably forced by wind‐induced mode coupling from the symmetric (2, 2) mode. The phases near 90 km exhibit a “bimodal” or “two‐state” behavior with the phases being almost constant in one state near the June solstice and then making a rapid transition of between 4 and 6 hours to another phase‐stable state near the December solstice. The duration of the state near the June solstice (∼6–8 months) is longer than the duration of the state at the December solstice. Although the agreement between recent models and our observations is relatively good, better agreement may be expected when more realistic wind distributions, especially for the southern hemisphere, are used in the models.
Stable carbon isotopic composition of methane from some natural and anthropogenic sources
Authors: Stevens Charles M. , Engelkemeir Antoinette
Published: February 2008

The results of δ13C measurements of several types of major sources of atmospheric methane are as follows: rice paddies, −67‰; the peat bogs of the Lake Agassiz region of northern Minnesota, −67±5‰; swamps of the Florida Everglades, −55±3‰ and biomass burning, −24 to −32‰. In addition, results are presented of a study of the δ13C of CH4 released from a slough, compared to the CH4 in the bottom sediment. These isotopic values are used, together with previously published data, to make up a tentative budget of the fluxes of the major sources for atmospheric methane with an average isotopic composition matching the measured value for atmospheric CH4, taking into account the fractionation effect of the sink processes. This budget requires the existence of a significant flux from an anthropogenic source of heavy CH4, calculated to be 45±15 Tg yr−1 if attributed to CH4 from biomass burning, with δC = −25‰.
Tropospheric methane from an Amazonian floodplain lake
Authors: Crill Patrick M. , Bartlett Karen B. , Wilson John O. , Sebacher Daniel I. , Harriss Robert C. , Melack John M. , MacIntyre Sally , Lesack Lance , Smith‐Morrill Lesley
Published: February 2008

During July and August 1985, the sources of methane and its flux to the troposphere were measured from a houseboat laboratory anchored in Lago Calado, a stratified, dendritic lake of about 6 km2 area, located in the central Amazon basin. Methane concentrations in the mixed layer of the lake were varied (0.0001–0.0055 mM) and usually less than 0.004 mM CH4, with no consistant temporal trend. Methane concentrations increased with depth across the thermocline as oxygen dropped to less than 0.1 mg O2 L−1. Over 6 weeks, methane increased from less than 0.08 to greater than 0.21 mM in the anoxic hypolimnion below 6 m. Methane in the pore water approached saturation, with a pure methane atmosphere within 5 cm of the sediment/water interface. The gradient‐supported flux from the sediments to the overlying water could account for the methane increase in the bottom waters plus the surface flux. The measured methane flux from the surface of the open lake to the atmosphere averaged 27 mg CH4 m−2 d−1. This was consistent with the buildup in ambient methane in the nocturnal surface mixed layer of the troposphere. Ebullition contributed 70% to the average total flux. The diffusive flux measured with a static chamber ranged from 0 to 34 mg CH4 m−2 d−1, with an average of 8.3 mg m−2 d−1. From July 20 to September 2, 1985, average ambient air concentration was 1.89 (±0.16) ppm CH4, with a diurnal variation of 0.27 ppm.
Formic and acetic acid over the central Amazon region, Brazil: 1. Dry season
Authors: Andreae M. O. , Talbot R. W. , Andreae T. W. , Harriss R. C.
Published: February 2008

We have determined the atmospheric concentrations of formic and acetic acid in the gas phase, in aerosols, and in rain during the dry season (July–August 1985) in the Amazonia region of Brazil. At ground level the average concentrations of gas phase formic and acetic acid were 1.6±0.6 and 2.2±1.0 ppb, respectively. The diurnal behavior of both acids at ground level and their vertical distribution in the forest canopy point to the existence of vegetative sources as well as to production by chemical reactions in the atmosphere. Dry deposition of the gaseous acids appears to be a major sink. The concentrations of formic and acetic acid in the gas phase were about 2 orders of magnitude higher than concentrations of the corresponding species in the atmospheric aerosol. About 50–60% of the aerosol (total) formate and acetate were in the size fraction below 1.0 μm diameter. The highest levels of aerosol formate and acetate were found in haze layers derived from biomass burning. In precipitation, (total) formate and acetate represented about one half of the anion equivalents. This is in contrast to the atmospheric aerosol, where they contributed less than 10% of the soluble anionic equivalents. Furthermore, the precipitation contained considerable acidity (average 36 μeq L−1 during the study period), again in contrast to the aerosol, which was acid‐base neutral. The mean hydrogen ion concentration in rain was about 21–26 μeq L−1 (pH 4.6–4.7). Most of the precipitation acidity can be attributed to the organic acids, with sulfuric and nitric acids contributing only about 10–20% of the hydrogen ion concentration. Aerosol scavenging can explain only a small fraction of the observed amounts of formate and acetate in rain. The observed levels of these ions in rain are most likely the result of a combination of chemical reactions in hydrometeors and scavenging of the gaseous acids by cloud droplets.
Absolute infrared intensities for F‐113 and F‐114 and an assessment of their greenhouse warming potential relative to other chlorofluorocarbons
Authors: Rogers Jerry D. , Stephens Robert D.
Published: February 2008

The literature concerning the “greenhouse” warming potentials of Chlorofluorocarbons F‐11, F‐12, F‐22, F‐113, F‐114, F‐134a, and F‐142b is reviewed. Additionally, infrared intensities are reported for each of the fundamental absorption bands of F‐113 (CF2ClCFCl2) and F‐114 (CF2ClCF2Cl) in the region between 8 and 20 μm. The measurements were made with a Fourier transform infrared spectrometer operated at 0.04 cm−1 apodized resolution. The total intensities measured for this region were 4905 cm−2 atm−1 for F‐113 and 6064 cm−2 atm−1 for F‐114, compared to a total intensity of 3404 cm−2 atm−1 for F‐12 (CF2Cl2) in the same region. On the basis of these infrared intensities and the atmospheric lifetimes of F‐113 and of F‐114 relative to F‐12, and on a per unit mass basis, F‐113 and F‐114 are about 0.8 and 1.9 times as effective, respectively, as F‐12 in the “greenhouse” warming of the Earth.
A vertically integrated snow/ice model over land/sea for climate models: 1. Development
Authors: Neeman Binyamin U. , Joseph Joachim H. , Ohring George
Published: February 2008

Sea ice/snow and land snow models are developed using a vertically integrated formulation (VIF). The VIF model has the capability of simulating the nonlinear effects of heat storage and transfer through the layers of snow and ice, which are felt particularly in spring and fall, yet this is achieved without resorting to the addition of layers to the numerical scheme. For comparison, a stable multilayer model is developed and tested. It is demonstrated that the VIF shares the accuracy of the multilayer formulation, and at the same time benefits from computational flexibility typical of linear formulations. The validity of the VIF assumptions and their parameter dependence are analyzed using an analytically solvable example. It is suggested that the VIF model may be specifically suitable for the implementation in a variety of climate models and general circulation models. A simple parameterization is applied to include seasonal and latitudinal changes in the heat flux from the mixed layer to the ice layer. This flux, though small in magnitude on an annual and latitudinal average, has an important influence on the ice thickness and its seasonal cycle and was taken as a constant in previous sea ice modeling. Latitudinal dynamical sea ice transport is also included in a simple parameterized form.
Resonant and nonresonant wave‐wave interactions in an isothermal atmosphere
Authors: Dong Bao , Yeh K. C.
Published: February 2008

We consider the weakly nonlinear three‐wave interactions in an isothermal atmosphere. The mutual interactions among the three linear branches of dynamical‐thermodynamical atmospheric motions (gravity waves, acoustic waves, and vortical motions) are investigated. In addition to the resonant case, nonresonant interactions are also considered. On the basis of the analytical solution of the linearized wave‐amplitude equation with possible existence of a frequency mismatch, the resonance surface, the interaction domain, and growth time in three‐dimensional geometry in k‐space in various cases have been calculated and some numerical results are given. It is found that the nonresonant interaction can be very important, especially when a gravity wave and two vortical modes of motions interact as a nonresonant trio. The energy transfer from the gravity wave to vortical motions might limit the growth of the gravity wave amplitude and hence might provide a reasonable mechanism for gravity waves to saturate in the middle atmosphere.
Effects of dirty snow in nuclear winter simulations
Authors: Vogelmann A. M. , Robock A. , Ellingson R. G.
Published: February 2008

A large‐scale nuclear war would inject smoke into the atmosphere from burning forests, cities, and industries in targeted areas. This smoke could fall out onto snow and ice and would lower cryospheric albedos by as much as 50%. A global energy balance climate model is used to investigate the maximum effect these “dirty snow” albedos have on the surface temperature in nuclear winter simulations which span several years. These effects are investigated for different nuclear winter scenarios, snow precipitation rates, latitudinal distributions of smoke, and seasonal timings. We find that dirty snow, in general, would have a small temperature effect at mid‐ and low latitudes but could have a large temperature effect at polar latitudes, particularly if the soot is able to reappear significantly in later summers. Factors which limit the climatic importance of the dirty snow are (1) the dirty snow albedo is lowest when the atmosphere still contains a large amount of light‐absorbing smoke; (2) even with dirty snow, sea ice areas can still increase, which helps maintain colder temperatures through the sea ice thermal inertia feedback; (3) the snow and ice areas affected by the dirty snow albedos are largest when there is little seasonal solar insolation; and (4) the area affected by the dirty snow is relatively small under all circumstances.
The typical structure of tornado proximity soundings
Authors: Schaefer Joseph T. , Livingston Richard L.
Published: February 2008

An objective scheme based on empirical orthogonal function analysis to detect patterns in a single or multivariate data set is developed and applied to rawinsonde observations taken in the near‐tornado environment. If only temperature data are considered, two distinct categories, differentiated chiefly by the tropopause height, are found. When moisture observations are included with the temperatures, the separation between categories becomes less distinct. However, it is noted that within the near‐tornado environment there is an inverse relationship between the degree of observed convective and conditional instability. Analysis of only the winds shows that a low‐level veering with height is the rule. However, the strength of the veering can vary considerably. When the temperature, moisture, and winds are treated in concert, two categories again appear. One group occurs with strong winds and a low tropopause, while the other group features weak winds and a high tropopause. These groups correspond to “springtime” and “summertime” synoptic situations, respectively. Comparisons of the various analyses indicate that the near‐tornado environment typically features a balance between the strength of the veering of the winds and the amount of conditional instability present. Summer tornadoes feature strong conditional instability and weak winds, while springtime tornadoes occur with stronger veering and convective instability. The strongest tornadoes occur with springtime‐type conditions.
Polar stratospheric clouds and the Antarctic ozone hole
Authors: Poole Lamont R. , McCormick M. Patrick
Published: February 2008

A theoretical model is presented for the formation and growth of polar stratospheric clouds (PSCs). The process is assumed to occur in three stages: (1) a “precursor” stage of supercooled H2SO4‐H2O stratospheric aerosol droplets at temperatures well above the frost point; (2) an intermediate (type I) stage of PSC particle formation by codeposition of HNO3 · 3H2O at temperatures near, but above the frost point; (3) a final (type II) stage of deposition of pure water ice and HNO3 · 3H2O at temperatures below the frost point. The calculated temperature dependence of optical backscattering agrees well with values observed during two Arctic airborne lidar experiments except for small systematic errors at the 30‐mbar pressure level which may be due to poor characterization of the temperature field. Additional theoretical calculations address the issue of PSC formation in Antarctica. These results show that at the 70‐mbar level (near 17 km), about 80% and 30% of the respective HNO3 and H2O vapor available may be sequestered in relatively large (4‐μm radius) PSC particles at a temperature near 189 K, some 2 K below the estimated local frost point. Such large particles would fall at a rate of about 2 km wk−1, suggesting that PSCs may act to redistribute these trace gases in the stratosphere or perhaps remove them altogether by sedimentation to the troposphere.
Free and forced modes in the Martian atmosphere
Authors: Zurek Richard W.
Published: February 2008

Short‐period, apparently global oscillations are clearly present in the multiyear time series of surface pressure variations recorded at the two Viking Lander sites on Mars. Previous work has emphasized the contributions of solar‐driven thermal tides to the surface pressure field. Recent analyses of single‐station data on Earth and on Mars suggest that the planetary normal modes (i.e., free modes of planetary scale) may also contribute to the short‐term, seasonally modulated variability in surface pressure. In this paper the periods of free modes in the Martian atmosphere are computed, with due consideration to the short atmospheric radiative damping time and to the seasonal and interannual variation of globally representative temperatures, both of which differ by an order of magnitude from their terrestrial counterparts. The likelihood of atmospheric resonance (i.e., free modes) or of efficient excitation and possibly resonant amplification of forced modes is then discussed. In summary, a thermally forced diurnal Kelvin wave still seems the best explanation for the short‐period, transient mode which appears just prior to or during the episodic great dust storms on Mars. Resonant modes seem most likely to occur during northern spring and summer, as previously suggested by Tillman. However, the limited atmospheric temperature data appear to have the wrong seasonal trend for resonance alone to account for the transient surface pressure oscillations observed in mid to late northern summer at the Viking Landers. One possibility is that during this period, unobserved changes in the atmospheric static stability near the surface have temporarily amplified the resonant modes or have moved the resonant frequency through the frequencies of the solar thermotidal forcing.
Temperature dependence of cirrus extinction: Implications for climate feedback
Authors: Platt C. Martin R. , Harshvardhan
Published: February 2008

The measured temperature dependence of infrared absorption in cirrus cloud obtained from previous extensive lidar and radiometer (LIRAD) observations of cirrus is used to investigate the sensitivities of changes in cirrus optical properties to changes in global temperature. Values of infrared absorption and ice water content calculated previously from observations of cirrus cloud microphysics are also used to investigate climate sensitivities. The values of calculated mean infrared absorption give a very similar temperature dependence, and thus climate sensitivity, to the LIRAD results. Values of mean ice water content calculated from the observations of cloud microphysics are compared with the available ice water content calculated from moist adiabatic ascent through a vertical cloud depth of 300 m, and a similar temperature dependence is found in both cases. However, taking into account the observed cloud depths of cirrus, considerable dilution of ice water content below adiabatic values is obviously occurring. The temperature sensitivities of extinction (or absorption) coefficients (calculated from a combination of LIRAD and microphysics results) are found to be generally less than the temperature sensitivities of ice water contents, due to an increase in cloud particle mode radius with temperature. The temperature sensitivity of cirrus extinction is found to vary from 0.033°C−1 at −22.5°C to 0.200°C−1 at −72.5°C. Equivalent sensitivities for cirrus optical depth are influenced by observed changes in cirrus cloud depth with temperature and vary from 0.003°C−1 at −22.5°C to 0.241°C−1 at −72.5°C. As high cold cirrus clouds are considered to cause a positive feedback with global temperature change, such a feedback is seen to become particularly strong at the lowest temperatures. A simple method of parameterization of cirrus visible and infrared optical properties in terms of cloud temperature is presented, thus making it possible to introduce cirrus optical properties into a numerical model without requiring knowledge of the ice water content.
Intercomparison of total ozone measured by the Brewer and Dobson spectrophotometers at Toronto
Authors: Kerr J. B. , Asbridge I. A. , Evans W. F. J.
Published: February 2008

Both Brewer and Dobson Spectrophotometers have been taking routine simultaneous direct‐Sun total ozone measurements from the five stations in the Canadian ozone monitoring network. The longest record of intercomparison data is at Toronto, where the well‐maintained Canadian regional standard Dobson instrument 77 is stationed and where routine ozone measurements made by Brewer instrument 8 commenced in February 1983. Results of this intercomparison are presented, and the causes for minor differences are discussed. A suitable transfer function is developed to calculate simulated Dobson ozone data from the Brewer data in order to ensure that the ozone record remains continuous and uninterrupted by the transition from the Dobson to the Brewer instrument. With appropriate corrections applied, the Dobson ozone values are 3.8% greater than those of the Brewer, and the standard deviation between the daily mean values is 0.5%. The relative drift between the two instruments over the 5‐year period was found to be 0.05% per year, smaller than the 95% confidence estimate of 0.27% per year.
VHF radio pictures of lightning flashes to ground
Authors: Proctor David E. , Uytenbogaardt Richard , Meredith Bernice M.
Published: February 2008

We present information obtained from VHF radio pictures of 47 lightning flashes that struck ground 1430 m above mean sea level (msl) to the north of Johannesburg, over a period of 16 years. Radio pictures were obtained using a hyperbolic method, i.e., by taking differences between times at which radio noise from lightning arrived at five widely spaced stations. These data were supplemented by recordings of electric field change. We found that stepped leaders and intracloud streamers emitted pulses and progressed at speeds that averaged 1.6×105 ms−1. Stepped leaders ranged in length from 3 to 13 km. BIL (breakdown‐intermediate‐leader) waveforms of electric field change were caused by stepped leaders whose branched channels followed complicated paths. The electric field changes they recorded in an effective bandwidth of 3.5 kHz could be reproduced faithfully by calculations based on an assumption that the radio sources became charged at the expense of a region near the origin of each leader. Some return strokes radiated trains of noise, called Q noise, whose sources extended at speeds near 108 ms−1. Sources of this Q noise retraced leader channels before extending them at these high speeds. Interstroke processes radiated Q noise whose sources extended at speeds that averaged 8.7×107 ms−1. Most Q sources (98%) were directed vertically, but they pervaded regions that retrogressed at “speeds” that averaged 2.2×104 ms−1 in directions away from the starting points of the flashes. This retrogression was directed horizontally, but the vertical Q streamers caused J changes to have positive or negative slopes according to the relative positions of Q sources and the reversal cone. Sixty percent of our sample of ground flashes were endowed with portions that were cloud flashes or were themselves minor components of cloud flashes. A more detailed summary appears at the end of the paper.
An improved rocket ozonesonde (ROCOZ‐A): 3. Northern mid‐latitude ozone measurements from 1983 to 1985
Authors: Barnes Robert A. , Chamberlain Marcella A. , Parsons Chester L. , Holland Alfred C.
Published: February 2008

We report the results of a set of ozone measurements at the NASA Wallops Flight Facility (37.8°N, 75.5°W) from August 1983 to September 1985. Nineteen profiles were obtained during this period, using ROCOZ‐A and electrochemical concentration cell ozonesondes, standard U.S. meteorological radio‐sondes, and Super‐Loki datasondes. Complete profiles of ozone, pressure, and temperature were obtained from the ground to 52 km, and 18 of the profiles correspond to site overpasses by ozone instruments on NASA and National Oceanic and Atmospheric Administration (NOAA) satellites. The profiles from this data set show reasonable agreement with established ozone climatologies. The annual ozone variability from the data set is roughly two thirds of the variability from the ozone model for the U.S. Standard Atmosphere (1976). The agreement between total ozone measurements from this data set and concurrent Dobson direct‐Sun total ozone measurements is excellent. The precision of ROCOZ‐A ozone values has been measured at the 3% level (1σ), and the accuracy of the ozone values is estimated at 5–7%. Since the ROCOZ‐A radiometers are expendable, the long‐term repeatability of the ozone measurements is based on a calibration facility which uses standards that are traceable to the National Bureau of Standards (NBS). The assembly of ROCOZ‐A ozone, pressure, and temperature measurements presented here allows the use of this data set as a transfer standard between satellite instruments with different fundamental ozone measurements. In addition, this data set can be used for comparisons of modeled and measured ozone amounts in the stratosphere and lower mesosphere. Such comparisons should prove valuable, since model results are typically 30–50% lower than measured ozone concentrations at altitudes above 35 km.
VHF radar echoes observed in the summer and winter polar mesosphere over Andøya, Norway
Authors: Czechowsky Peter , Reid Iain M. , Rüster Rüdiger , Schmidt Gerhard
Published: February 2008

The mobile SOUSY VHF (53.5 MHz) Radar has been operated on a campaign basis on the island of Andøya in Northern Norway (69°17′N, 16°01′E), with the aim of investigating the backseattering structures and dynamics of the polar middle atmosphere, since November 1983. During winter the occurrence of mesospheric echoes at altitudes from 50 to 90 km is strongly correlated with radio wave absorption events measured with a riometer on 32.5 MHz. Individual structures are observed for up to 8 hours and, in general, appear as thin layers separated by 3–5 km, with typical maximum signal‐to‐noise ratios (SNRs) of 5–25 dB. Many of these are related to variations in the background wind produced by long‐period gravity waves and tidal period motions and, in as much, are similar to mesospheric layers at middle and low latitudes. In summer the echo region is largely restricted to a height interval from 75 to 95 km, with 80% of the echoes occurring in the 80‐ to 93‐km height range, and on average, it has a distinct maximum in SNR near 86 km. In the 83‐ to 91‐km height region, echoes are detected almost continuously, with a minimum occurrence rate of 85%. There is a low correlation (∼0.26) between echo strength and absorption. Many of the weaker echoing regions, those with SNRs up to 30 dB, are related to the background wind shear. Spectral analysis of time series of both SNR and zonal velocity for a period of 9 days reveals 54‐, 24‐, 12‐, and 8‐hour components, with the 12‐hour component dominating. Strong bursts in backscattered power tend to occur in the late afternoon and early morning hours, so they coincide with the time of maximum westward velocity of the semidiurnal tide. This suggests that the bursts are due to an increase in the turbulent intensity produced by dynamical instability of this mode. Layers consistent with dynamically unstable upward propagating inertio‐gravity waves are also often observed to move down through the 93‐ to 80‐km height range. Thus dynamical instability of the semidiurnal tide and long‐period gravity waves appears to play a major role in determining much of the structure observed in the backscatter region. However, the strongest summer polar mesopause echoes, those with peak SNRs greater than 30 dB, while showing modulation due to the background winds, often show no clear relation to the background wind shear. This supports the view that the production mechanism of the very strong SNRs associated with this layer is different in character from that of winter echoes observed in the polar mesosphere by VHF radars, and to those mesospheric layers observed at mid‐latitudes using the same technique.
Equilibrium size of atmospheric aerosol sulfates as a function of the relative humidity
Authors: Koutrakis Petros , Wolfson Jack M. , Spengler John D. , Stern Bonnie , Franklin Claire A.
Published: February 2008

Size‐fractionated acid aerosols were collected, using a microorifice cascade impactor, during the summer of 1986 in Dunnville, Ontario, as part of the Canadian Children Acute Respiratory Effects Study (CARES), sponsored by the Department of National Health and Welfare, Canada. Sulfate and hydrogen ions showed similar size distributions. The molar ratio of H+/SO42− varied little with particle size, but there was a considerable time‐dependent variation in aerosol acid content. It was also found that there is a distinct relationship between the geometric mean aerodynamic diameter of sulfate, da, and ambient relative humidity (RH). Atmospheric sulfate particle sizes observed in this study were slightly higher than those found in laboratory experiments at corresponding humidities. However, considering the uncertainties involved, the agreement between the field and laboratory data was remarkable.
Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements
Authors: Wang Pi‐Huan , McCormick M. P. , Swissler T. J. , Osborn M. T. , Fuller W. H. , Yue G. K.
Published: February 2008

In this paper the authors present a method that can be used to infer stratospheric aerosol composition and size distribution, based on the water vapor concentration and aerosol extinction measurements from the satellite instrument of the Stratospheric Aerosol and Gas Experiment (SAGE II) and the associated temperatures provided by the National Meteorological Center (NMC). To infer the chemical composition, the aerosols are assumed to be sulfuric acid‐water droplets. The equilibrium acid weight percentage and refractive index at the SAGE II aerosol wavelengths can then be estimated by using the SAGE II‐observed water vapor and the associated temperatures. To infer the aerosol size distribution, a modified Levenberg‐Marquardt algorithm is adopted for determining model size distribution parameters in the least squares sense, based on the SAGE II‐observed multiwavelength aerosol extinctions. Both single‐mode lognormal and modified gamma representations are employed in the analysis. One of the most significant conclusions from this analysis is a determination of the information content of the SAGE II multiwavelength aerosol extinctions with respect to stratospheric aerosol size distributions. It is concluded that the best aerosol size information is contained in the aerosol radius range between approximately 0.25 and 0.80 μm.
Comparison of model results transporting the odd nitrogen family with results transporting separate odd nitrogen species
Authors: Douglass Anne R. , Jackman Charles H. , Stolarski Richard S.
Published: February 2008

We have developed a fast two‐dimensional residual circulation stratospheric model. In order to calculate possible effects of long‐term changes for trace gases for a large number of scenarios and to examine the model sensitivities to dynamical and photochemical assumptions and inputs, the model is designed to minimize computer requirements. The species continuity equations are solved using process splitting, that is, by successively applying the operators associated with advective changes with photochemical and diffusive forcing. The first study undertaken with this model concerns family chemistry approximations, in which groups of species are related by photochemical equilibrium assumptions and transported as one species. These assumptions are tested by comparing results for the family transport model (FTM), in which odd nitrogen (NOy = N + NO + NO2 + NO3 + 2N2O5 + HO2NO2 + ClONO2 + HNO3) is transported as a family, with the results for a separate transport model (STM) in which HNO3, HO2NO2, ClONO2 and N2O5 are transported separately from NOx = N + NO + NO2 + NO3. Two cases are considered: (1) a current atmosphere annual cycle; and (2) a typical scenario for increased fluorocarbons, methane, and nitrous oxide. Although there are differences in odd nitrogen species partitioning, especially at high latitudes, the calculated O3 distributions are nearly identical. For the perturbation scenario the annual average column ozone change and its temporal and spatial characteristics are nearly the same for the FTM and the STM.
Condensed nitrate, sulfate, and chloride in Antarctic stratospheric aerosols
Authors: Pueschel R. F. , Snetsinger K. G. , Goodman J. K. , Toon O. B. , Ferry G. V. , Oberbeck V. R. , Livingston J. M. , Verma S. , Fong W. , Starr W. L. , Chan K. R.
Published: February 2008

During the 1987 Airborne Antarctic Ozone Experiment we estimated the NO3, Cl, and SO4 contents of stratospheric aerosols by testing for the presence of condensed nitric, sulfuric, and hydrochloric acid. In various segments of the ER‐2 sample flights, aerosol particles were impacted on four 500‐mm‐diameter gold wires, strung across aluminum rings. The wires were pretreated to give results specific to certain physical and chemical aerosol properties. One wire was carbon coated and used for aerosol concentration and size analyses by scanning electron microscopy. Simultaneous X ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride, and silver nitrate to detect nitric, sulfuric, and hydrochloric acids, respectively, in the aerosols. Wires were exposed at a number of geographic locations at altitudes near 18 km. Immediately after collection, the acids were fixed as ammonium salts by exposing them in flight to NH3. Results show that condensed nitrate is found below a threshold temperature of 193.6±3.0 K, generally encountered at latitudes exceeding 64°S. A negative correlation exists between condensed nitrate and ozone concentration. This is consistent with theories that postulate removal of gas‐phase NOy as a necessary step in allowing active chlorine‐ozone reactions to occur. Condensed H2SO4 is present at concentrations between 0.2 and 0.9 parts per billion by mass. The mass of condensed HCl is estimated to be approximately 3% of the mass of sulfuric acid.
In situ measurements of total reactive nitrogen, total water, and aerosol in a polar stratospheric cloud in the Antarctic
Authors: Fahey D. W. , Kelly K. K. , Ferry G. V. , Poole L. R. , Wilson J. C. , Murphy D. M. , Loewenstein M. , Chan K. R.
Published: February 2008

Measurements of total reactive nitrogen (NOy), total water, and aerosol were made as part of the Airborne Antarctic Ozone Experiment during August and September 1987. The measurements were made using instruments located on board the NASA ER‐2 aircraft, which conducted 12 flights over the Antarctic continent, reaching pressure altitudes of 20 km at 72°S latitude. The data presented here focus on a flight during which a polar stratospheric cloud (PSC) was encountered, containing concentrations of 0.8‐ to 2.6‐μm diameter aerosol particles greater than 1 cm−3. The temperatures in the cloud ranged as low as 184 K near 65‐mbar pressure, but they remained above the frost point of water ice, except for short intervals. From knowledge of the vapor pressures over nitric acid condensates, the appearance of aerosol above the background level is consistent with the formation of the trihydrate phase, HNO3·3H2O. The anisokinetic feature of the NOy sample probe enhances the concentration of large aerosol particles in the inlet by a factor of ∼9. NOy levels above 20 parts per billion by volume (ppbv) observed in the PSC indicate that aerosol NOy species contribute substantially to the NOy signal. The amount of aerosol HNO3·3H2O necessary to enhance the NOy signal to observed levels is calculated from aerosol impaction theory and is found to be in satisfactory agreement with the observed aerosol volume. In addition, using the saturation vapor pressures and an estimate of available HNO3 in the cloud, the predicted volume of HNO3·3H2O also shows satisfactory agreement with the directly measured aerosol volume. These results indicate that substantial aerosol volume containing HNO3 and H2O is formed at temperatures above the frost point in the Antarctic stratosphere in the winter and spring months. Such aerosol formation is thought to be the prerequisite for the production of active chlorine in heterogeneous reactions and for the large‐scale removal of NOy through aerosol sedimentation.
New observations of a large concentration of ClO in the springtime lower stratosphere over Antarctica and its implications for ozone‐depleting chemistry
Authors: de Zafra R. L. , Jaramillo M. , Barrett J. , Emmons L. K. , Solomon P. M. , Parrish A.
Published: February 2008

We have made new measurements of stratospheric chlorine monoxide (ClO) at McMurdo Station, Antarctica, during the austral spring of 1987. Rotational emission line spectroscopy, employing a ground‐based detector, was used to determine mixing ratio profiles over the range ∼17–45 km. A spectral band pass double that was used for similar measurements in 1986 allowed an improvement to be made in the definition of the anomalous low‐altitude stratospheric ClO layer associated with springtime ozone depletion. A peak mixing ratio of 1.6±0.4 parts per billion by volume (ppbv) (95% confidence level) was found at 19.5±1 km at midday during the period September 20–24, 1987. The observed peak mixing ratio and diurnal behavior are discussed in relation to chemical depletion theories. Calculations indicate that the large observed ClO concentration provides an efficient closure for a catalytic Cl cycle through the ClO dimer mechanism, yielding good agreement with various observed features of O3 depletion.