bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of initial potential gradient and particle charges in a Montana summer thunderstorm
Authors: Gardiner B. , Lamb D. , Pitter R. L. , Hallett J. , Saunders C. P. R.
Published: February 2008

An Aerocommander aircraft made three passes through a small isolated thunderstorm on July 19, 1981. These passes were made at a temperature of −5°C and were in conjunction with other aircraft at different altitudes. The Aerocommander was equipped to measure the vertical component of the ambient potential gradient, particle charge, particle size and character, cloud liquid water content, temperature, and vertical velocity. Evidence is presented for the association of charge with ice particles. The development of the potential gradient in relation to movement of these ice particles is discussed. In general, the highest charge densities, of order −0.5 C km−3, were coincident with regions of high graupel concentration and the highest potential gradients, of order −15 kV m−1, were measured below regions with the highest radar reflectivities. Only a small fraction (<10%) of ice particles were found to be charged significantly (>±5 pC), but these were found even at the earliest stages of electrification. The results are compared to concepts derived from recent laboratory experiments on the charge produced during ice particle collisions.
Comparisons of vertical winds measured with the Chatanika and Poker Flat radars
Authors: Watkins B. J. , Jayaweera K.
Published: February 2008

The Poker Flat, Alaska, MST radar and the Chatanika incoherent‐scatter radar (operated in an ST mode) were simultaneously operated to compare vertical air motions in the troposphere and lower stratosphere. The two nearby radars were operated with their antennas pointed vertically with 750‐m‐range resolutions. The radars have widely differing operating frequencies (50 MHz and 1290 MHz); for the long‐wavelength radar, returned signals are thought to result from combination of specular reflection and turbulence‐scattered signals, with either mechanism possibly being dominant at various heights. The short‐wavelength radar is expected to receive only turbulence‐scattered signals. Both radars were able to detect motions of a few centimeters per second and detect the presence of similar short‐period wave motions. However, when the data were averaged for an hour or more, significant differences in the averaged data were observed. We suggest that the differences are probably due to either experimental errors or apparent vertical motions observed with the Poker Flat radar as a result of off‐vertical specular echoes from horizontally moving tilted layers. An estimate of an apparent antenna pointing direction of 0.27° off vertical has been made for the Poker Flat radar. With the available data we are unable to determine if this is a true antenna pointing error or the result of horizontally moving tilted layers on the specular echoing mechanism. At heights where specular echoes are dominant, the physical pointing direction of the antenna is not critical. The effective pointing angle of the antenna is determined by the normal to the specular reflection layer. In this case a component of the horizontal wind may be interpreted as a vertical wind component because small tilts in the atmospheric layers control the effective antenna pointing direction. For the other heights where nonspecular scattering is dominant the physical pointing direction of the antenna is important; for vertically directed antennas, small pointing errors may cause a component of the horizontal wind to be interpreted as a vertical motion.
Nuclear winter: Three‐dimensional simulations including interactive transport, scavenging, and solar heating of smoke
Authors: Malone Robert C. , Auer Lawrence H. , Glatzmaier Gary A. , Wood Michael C. , Toon Owen B.
Published: February 2008

We reeaxmine the “nuclear winter” hypothesis with a three‐dimensional global model modified to allow for localized injection of smoke, its transport by the simulated winds, its absorption of sunlight, and its removal by model‐simulated precipitation. Smoke injected into the troposphere is driven upward by solar heating. The tropopause, initially above the smoke, reforms below the heated smoke layer and separates it from precipitation below. Although much smoke is scavenged while the thermal structure is being altered, the residence time of the remaining smoke is greatly increased. We find, particularly for July conditions, a longer‐lasting “nuclear winter” effect than was found in earlier modeling studies in which normal tropospheric residence times were assumed. In January the smaller solar flux in the northern hemisphere allows faster removal of smoke than in July. Significant cooling of the northern hemisphere continents is predicted; its dependence on season and injected smoke mass is described.
Saturation and the “universal” spectrum for vertical profiles of horizontal scalar winds in the atmosphere
Authors: Dewan E. M. , Good R. E.
Published: February 2008

A theory is presented which explains the universal nature of one‐dimensional vertical wave number, k, power spectral densities (PSDs) of horizontal winds as measured in the atmosphere and predicted by VanZandt. The theory is that the PSD amplitude at any given wave number (greater than a certain minimum, k*) is determined by its saturation value due either to shear instability (i.e., critical Richardson Number) or, more likely, to convective instability. This explains why the PSD amplitudes observed do not grow exponentially with increasing altitude. This saturation theory assumption plus other considerations leads to a PSD of the form N2/kn, where n is in the range of about 2.5 to 3 and N is the Brunt frequency. A simplified model involving superimposed narrow bands of gravity waves as well as a model based merely on dimensional arguments both lead to n = 3. The full model not only explains the observed spectral slopes but also predicts the PSD amplitude in the troposphere to be 3.5 times smaller than in the stratosphere. The derivation of the model is based on the saturation condition that ∫ k2PSD(k) dk = N2. The model may also apply to the ocean and explain the Garrett‐Munk vertical wave number spectrum.
Optimized retrievals of precipitable water fields from combinations of VAS satellite and conventional surface observations
Authors: Robinson Wayne D. , Chesters Dennis , Uccellini Louis W.
Published: February 2008

VISSR (visible and infrared spin‐scan radiometer) atmospheric sounder (VAS) radiances and conventional surface temperature and dewpoint data are used in several combinations within a regression approach to determine the optimum resolution and accuracy of precipitable water (PW) fields retrieved from satellite observations. Point retrievals at radiosonde stations are used to determine the numerical accuracy of each retrieval technique, and image sequences of the retrieved PW fields are used to determine the temporal stability and spatial coherence of mesoscale PW features. VAS channels 5, 6, 7, and 8 (at 13, 4.5, 12, and 11 μm) and the surface dewpoint contribute the most information to regression‐based retrievals of PW. The most accurate PW retrievals are obtained when radiances are averaged to a resolution of 15 to 60 km. A physical “split‐window” approach provides better PW estimates than regression when only the 11‐ and 12‐μm VAS channels are available (as when the satellite operates in a multispectral image mode) or when radiosonde‐based training is limited to only one time period.
Evidence for nonlocal thermodynamic equilibrium in the ν3 mode of mesospheric ozone
Authors: Solomon S. , Kiehl J. T. , Kerridge B. J. , Remsberg E. E. , Russell J. M.
Published: February 2008

Laboratory kinetic studies suggest that an appreciable fraction of the ozone produced by recombination of atomic oxygen is vibrationally excited in the ν3 mode. Further, laboratory data are available for the physical quenching of ν3, its radiative relaxation, and its radiative excitation by resonant absorption. It is shown that these chemical and physical processes are likely to result in substantial departures from local thermodynamic equilibrium for the ν3 mode of ozone in the mesosphere and therefore have important effects on infrared mesospheric ozone measurements by emission in the 9.6‐μm band. Implications of these effects upon the Limb Infrared Monitor of the Stratosphere data, particularly their night/day ratio, are discussed.
Atmospheric lifetime and annual release estimates for CFCl3 and CF2Cl2 from 5 years of ALE data
Authors: Cunnold D. M. , Prinn R. G. , Rasmussen R. A. , Simmonds P. G. , Alyea F. N. , Cardelino C. A. , Crawford A. J. , Fraser P. J. , Rosen R. D.
Published: February 2008

Atmospheric Lifetime Experiment measurements of CFCl3 and CF2Cl2 several times per day at five remote surface sites from July 1978 to June 1983 are reported. For January 1, 1981, the mean latitudinally averaged mixing ratios were 177.5 parts per trillion by volume (pptv) and 300.4 pptv for CFCl3 and CF2Cl2, respectively. The atmospheric content at that time is estimated to have been 3,960 million kg of CFCl3 and 6,000 million kg of CF2Cl2. The mixing ratios exhibited an annual rate of increase of 9.0 and 15.3 pptv/yr for CFCl3 and CF2Cl2, respectively. Trend lifetime estimates for January 1, 1981 from this 5‐year data set are 74−17+31 years for CFCl3 and 111−44+222 years for CF2Cl2. On the basis of a comparison of CFCl3 data on two different chromatographic columns, it is shown that the spectrum of measurement errors maximizes at low frequencies but may be relatively flat at periods longer than approximately 3 years. The uncertainties in the trend lifetime estimates are, however, dominated by release uncertainties. Inverting the analysis, assuming stratospheric photodissociation to be the only atmospheric sink of fluorocarbons, yields annual release estimates with an accuracy, based on the precision of the measurement system, of approximtely 8%. Excellent agreement with the Chemical Manufacturers Association release estimates is found for CFCl3; for CF2Cl2 the estimates, although exhibiting variability from year to year, suggest that the emissions in the USSR and Eastern Europe have remained roughly constant over the years 1979–1982.
Biological methanogenesis and the CO2 greenhouse effect
Authors: Guthrie Paul D.
Published: February 2008

It is well established that plants tend to increase net photosynthesis under increased carbon dioxide. It is also well established that a large fraction of atmospheric methane is produced by microbial metabolism of organic sediments in paddies and freshwater wetlands, where a major source of organic debris is local plant growth. As CO2 increases, it may lead to increased methane production and a resulting enhancement of the expected greenhouse warming. A rough estimate of the present rate of this biologically mediated feedback on the climate system indicates that it might account for as much as 30% of the observed methane increase and speed up the greenhouse forcing by as much as 15%.
Possible perturbations to atmospheric CO, CH4, and OH
Authors: Thompson Anne M. , Cicerone Ralph J.
Published: February 2008

A photochemical model is used to predict temporal trends in OH, CH4, and CO over the next 50 years and to assess possible past changes in these trace gases from 1860 to 1985. Various scenarios of perturbed CH4 and CO levels based on recently reported CH4 and CO data are simulated at several levels of background NOx. With low NOx conditions (NO + NO2 = 25 pptv (parts per trillion by volume)), typical of the nonpolluted troposphere, we compute a monotonic loss of tropospheric OH from 1860 to 2035, with the magnitude of the decrease dependent on CO and CH4 increases during the period. If current trends continue (ground‐level mixing ratios (mole fractions) of CH4 rising about 1% per year), by 2035 northern latitude CH4 will increase from 1.6 to 2.9 ppmv (parts per million by volume) and CO will double or triple its present day level (to about 250–350 ppbv (parts per billion by volume) in the nonpolluted northern hemisphere). The column abundance of OH in the background troposphere will decrease 25–35%, depending on the magnitude of CH4 and CO increases and assuming that global temperature increases do not raise water vapor levels during that time. Calculations with increased H2O show a 17–30% decrease in OH. Under higher‐NOx conditions (1 ppbv), OH shows a decline from 1860 to 2035, but it shows only half as much decline as with low‐NOx conditions. In the case of NOx in a transitional zone (i.e., NOx increasing from 20 pptv in 1860 to 0.5 ppbv in 2035), CO and CH4 increases accompany a rise in OH, followed by a small decline. The turning point in OH depends on the rate of change in NOx and O3. Recently observed upward trends in CO and CH4 are probably due to increasing emissions of both CH4 and CO. We always compute a temporal increase in tropospheric O3 when CH4 and CO increase. Typical 1860 values for surface O3 are 25 ppbv, compared to 30 ppbv (NOx = 25 pptv)and 40 ppbv (NOx = 1 ppbv) in 1985. In a transition NOx zone we find surface O3 increasing from 10 ppbv in 1860 to 27 ppbv in 1985.
The twilight sodium layer
Authors: Kirchhoff V. W. J. H. , Batista P. P. , Clemesha B. R. , Simonich D. M.
Published: February 2008

It is believed that sodium photochemistry is strongly influenced by mesospheric atomic oxygen and ozone, and one might thus expect sodium variations to occur during twilight. We have investigated this expectation by measuring the sodium density using a laser radar system. We report the results for 31 evening twilights and compare them with recent model calculations. The measurements show a rapid decrease in sodium density at the bottom of the layer, immediately after sunset, in agreement with theoretical predictions. Na variations are triggered by NaOH photolysis, while Na airglow variation occurs from O3 change.
Evidence for metastable ozone in the upper atmosphere?
Authors: Joens Jeffrey A.
Published: February 2008

Simultaneous measurements of atomic O, O2, N2, and O3 in the region 90–110 km obtained from a rocket‐borne mass spectrometer during the Aladdin 74 program indicate an ozone concentration as much as a factor of 50 times larger than predicted from the simple Chapman model. A possible explanation for the discrepancy is the formation of significant amounts of metastable ozone in this region of the atmosphere. The evidence for and the implications of such a metastable state of ozone are discussed.
Vertical profiles of ozone, carbon monoxide, and dew‐point temperature obtained during GTE/CITE 1, October‐November 1983
Authors: Fishman Jack , Gregory Gerald L. , Sachse Glen W. , Beck Sherwin M. , Hill Gerald F.
Published: February 2008

A set of 14 pairs of vertical profiles of ozone (O3) and carbon monoxide (CO), obtained with fast‐response instrumentation, is presented. Most of these profiles, which were measured in the remote troposphere, also have supporting fast‐response dew‐point temperature profiles. The data suggest that the continental boundary layer is a source of tropospheric ozone, even in October and November, when photochemical activity should be rather small. In general, the small‐scale vertical variability between CO and O3 is in phase. At low latitudes this relationship defines levels in the atmosphere where mid‐latitude air is being transported to lower latitudes, since lower dew‐point temperatures accompany these higher CO and O3 concentrations. A set of profiles which is suggestive of interhemispheric transport is also presented. Independent meteorological analyses support these interpretations.
Electrical potential measurements in the lower atmosphere
Authors: Woosley J. D. , Holzworth R. H.
Published: February 2008

Lower‐atmospheric potential measurements obtained in 1983 through 1985 using the Hy‐wire technique are summarized in this paper. Observed values of the potential were in the range of 50–100 kV in Fairbanks, Alaska, compared with 100–200 kV at Wallops Island, Virginia. While differences are seen in absolute potential for different sites, the daily variations are similar in character. When 1‐hour averages are formed from the entire data set the result is a unitary variation very reminiscent of both the Carnegie curve and more recent stratospheric electric field data. A comparison with an aircraft potential measurement in the same vicinity during April 1983 demonstrates that the two techniques yield roughly similar results, except that the Hy‐wire measurements were 20–30% lower in absolute value. For the Alaska data, no clear effect on the potential was seen during a 400‐nT auroral magnetic perturbation.
The electrostatic energy of a thunderstorm and its rate of change
Authors: Weinheimer Andrew J.
Published: February 2008

Two points are addressed: (1) As has been noted, the method most commonly used to assess the contribution of a single, charged precipitation particle to the rate of change of electrostatic energy of a thunderstorm is problematic. Equating the rate to the product of the net electrical force and a velocity leads to an arbitrary value of the contribution of a single particle. Here this arbitrariness is removed by viewing the contribution of a single particle as being due to its motions with respect to all the other individual charges. It is also shown that in spite of this arbitrariness of the usual method when applied to individual particles, it nonetheless yields a nonarbitrary value for the total rate of change of electrostatic energy for the whole collection of charges. (2) In the event that differences in sedimentation velocity are not adequate to account for the electrification of thunderstorms, this does not imply that all precipitation‐based mechanisms are ineffective, as is sometimes suggested. The possibility yet remains that convective processes may be effective in driving the large‐scale separation of precipitation particles from other charged particles.
Sensitivity studies and a simple ozone perturbation experiment with a truncated two‐dimensional model of the stratosphere
Authors: Stordal Frode , Garcia Rolando R.
Published: February 2008

The “1½−D” model of Holton (1986a), which is actually a highly truncated two‐dimensional model, describes latitudinal variations of tracer mixing ratios in terms of their projections onto second‐order Legendre polynomials. The present study extends the work of Holton by including tracers with photochemical production in the stratosphere (O3 and NOy). It also includes latitudinal variations in the photochemical sources and sinks, improving slightly the calculated global mean profiles for the long‐lived tracers studied by Holton and improving substantially the latitudinal behavior of ozone. Sensitivity tests of the dynamical parameters in the model are performed, showing that the response of the model to changes in vertical residual meridional winds and horizontal diffusion coefficients is similar to that of a full two‐dimensional model. A simple ozone perturbation experiment shows the model's ability to reproduce large‐scale latitudinal variations in total ozone column depletions as well as ozone changes in the chemically controlled upper stratosphere. Limitations of the model as a tool for perturbation studies are discussed, e.g., the fact that, as presently formulated, the model can only be used in a yearly averaged sense.
The reflection of solar radiation from bar cloud arrays
Authors: Joseph Joachim H. , Kagan Victor
Published: February 2008

An analytical solution for the albedo to solar radiation of a broken cloud field over a black, nonreflecting ocean surface is presented. The clouds are assumed to be infinitely long, nontransmitting bars, with any top and side albedos. Cloud‐cloud shading and reflections are fully and analytically taken into account in the assessment of the contribution of the cloud sides to the cloud field albedo, while assuming, for this latter purpose only, the bi‐directional reflectivity of the sides to be isotropic. The model is an explicit function of cloud thickness, width, and intercloud spacing for all solar zenith and azimuth angles. Results are presented in the form of an effective cloudiness in azimuthally averaged form and as a function of azimuth angle for different solar elevation angles, aspect ratios, amounts of cloudiness, optical depth, and albedo for single scattering. In order to show the dominant effect of the geometry over the radiative transfer in this case, we simulated the [Harshvardhan and Thomas, 1984] model, adding only the explicit solution for the cloud‐cloud interaction. We then compared our results to theirs as well as to their Monte Carlo calculations, achieving a much better fit to the latter. The present model is neither more difficult to use than previous ones nor is it in need of refitting to data when more features are added or when optical properties of the cloud are changed. Tabular values of some necessary coefficients are given for independent use of the model.
Antarctic springtime ozone depletion computed from temperature observations
Authors: Rosenfield Joan E. , Schoeberl Mark R. , Newman Paul A.
Published: February 2008

An observationally based, mechanistic dynamical model is used to simulate the decline of total ozone during September and October for the years 1979 through 1986. Vertical velocities derived from observed stratospheric temperature changes and computed radiative heating rates are used to advect an ozone mixing ratio profile during the Antarctic spring period. An early August 1982 Syowa balloonsonde ozone profile is used to initialize the computations. The model reasonably simulates the September and October changes in total ozone, considering the uncertainties in the observed data and the radiative heating. The simulated decline is found to be very sensitive to the choice of initial ozone profile and to small changes in the radiative heating. The results of this study suggest that the dynamical hypothesis of the Antarctic ozone depletion is both quantitatively credible and consistent with the observed temperature changes.
Thunder events and cloud‐to‐ground lightning frequencies
Authors: Changnon S. A. , Changnon D. , Pyle Richard B.
Published: February 2008

Data on thunder days, thunder events (discrete periods of nearly continuous thunder), and cloud‐to‐ground lightning flashes for portions of the United States were compared to discern how well the frequencies of thunder days, events, and lightning flashes related. Across the United States, thunder day frequencies related well to events with correlation coefficients of +0.97 to +0.84, being lowest in areas where multiple storm periods in a day occur most frequently. The number or duration of thunder events does not relate well to lightning flash frequencies; annual thunder events and durations explain less than 30% of the variance in lightning flashes. This poor relationship is caused by four factors: more than 50% of all thunder events had no cloud‐to‐ground lightning; many flashes (22–26% in the east and 31–40% in the west) occurred at times not in thunder periods, the frequency of lightning in thunder periods was extremely skewed, with 50% of all flashes occurring in 10% of the periods; and locational errors inherent in the detection system affect the preciseness of the relationships. The poor event‐lightning relationships indicate that historical values of thunder activity cannot be used to reconstruct historical lightning frequencies. The results also raise serious questions about the accuracy of the thunder event and thunder day records; clearly, they underestimate the actual storm activity at a weather station.
Dynamic variability of column ozone
Authors: Tung Ka Kit , Yang Hu
Published: February 2008

We give a first‐order, analytic estimate of the dynamical change in column ozone density as a function of temperature change in the lower stratosphere. It is found that for each 1% (∼2°C) cooling averaged over the lower stratosphere, the column ozone density can be expected to decrease by approximately 7%, if it can be assumed that such a temperature change is induced by changes in wave transports.
The Milankovitch theory and climate sensitivity: 2. Interaction between the northern hemisphere ice sheets and the climate system
Authors: Neeman Binyamin U. , Ohring George , Joseph Joachim H.
Published: February 2008

The interaction of ice sheets with climate models possessing different sensitivities is tested with the aid of a vertically integrated ice sheet model with isostatic bedrock adjustment. The ice sheet model has two horizontal dimensions and a coarse geography/topography over a domain encompassing the area north of 40°N. Two coupled ice sheet‐climate model experiments are designed. The first experiment is started with today's surface conditions and continuous extreme low summer insolation orbital conditions are switched on. The second experiment is started with boundary conditions of the last glacial maximum (LGM) and a continuous extreme high summer insolation is applied. Control runs with current orbital conditions are compared. For each of the two experiments, coupled runs are performed twice: (1) with a climate component possessing a moderate sensitivity (β = 1.8°C) and (2) with a high sensitivity (β = 4.0°C) to 1% changes in solar constant, as developed in Part 1 of this study. The moderate‐sensitivity coupled run cannot explain the onset of ice age in the first experiment, while the high‐sensitivity coupled run utterly fails to reproduce the decay of the LGM ice sheet in the second experiment. A great significance is attached to the geographical distribution as resolved in two horizontal dimensions by our ice sheet model. The land portion susceptible to glaciation onset is extremely small, while the land portion crucial for deglaciation is much larger. The lower continentality of North America is found to be a promoting factor for glaciation but an impeding factor for deglaciation. The feedback between the ice sheets and climate component is well simulated when the coupled system is exposed to variations in the solar constant (−2.5%/+5% have simulated creation/destruction of a large ice sheet with the moderate‐sensitivity coupled run), resulting in a steady drift of climate and ice sheet extent for each successive run of the coupled components. Insolation changes of limited duration are found to have a durable effect, shifting the ice sheet‐climate system into a new mode. Evidence for the global synchronism of ice age terminations (with a slight lag of the northern, more massive ice) and for the existence of ∼ 100‐Kyr cycles in nonglacial eras leads us to suspect that there might be a missing mechanism for the translation of weak orbital forcing into global equivalent insolation changes, but we cannot rule out genuine solar constant variations or purely internal changes in the global radiation budget as the primary cause for the major glacial‐interglacial transitions.
A model relating laboratory measurements of rates of nitric oxide production and field measurements of nitric oxide emission from soils
Authors: Galbally I. E. , Johansson C.
Published: February 2008

An explanatory model that relates laboratory measurements of nitric oxide (NO) production in soil to field measurements of the diffusive flux of NO from the same soil to the atmosphere is presented. Microbial NO production in soils is represented by a production term independent of, and an uptake term with first‐order dependence on, NO concentration. These production and first‐order uptake terms can be measured in flow‐through soil columns. Within the model, representing a field soil, the divergence in vertical diffusive flux of NO is represented by the production minus uptake and so a flux to the atmosphere is calculated. At Kjettslinge, Sweden, a field flux of NO of 2 − 17 × 10−9 g N m−2 s−1 was observed under aerobic conditions, while laboratory measurements and the model give a calculated flux of NO for the same soil under the same environmental conditions of 3 − 11 × 10−9 g N m−2 s−1. Thus the results suggest that laboratory measurements on a specific soil may be used to determine the field flux from the same soil under certain well specified conditions.
SAGE II aerosol data validation based on retrieved aerosol model size distribution from SAGE II aerosol measurements
Authors: Wang Pi‐Huan , McCormick M. P. , McMaster L. R. , Chu W. P. , Swissler T. J. , Osborn M. T. , Russell P. B. , Oberbeck V. R. , Livingston J. , Rosen J. M. , Hofmann D. J. , Grams G. W. , Fuller W. H. , Yue G. K.
Published: February 2008

This paper describes an investigation of the comprehensive aerosol correlative measurement experiments conducted between November 1984 and July 1986 for the satellite measurement program of the Stratospheric Aerosol and Gas Experiment (SAGE II). The correlative sensors involved in the experiments consist of the NASA Ames Research Center impactor/laser probe, the University of Wyoming dustsonde, and the NASA Langley Research Center airborne 14‐inch (36 cm) lidar system. The approach of the analysis is to compare the primary aerosol quantities measured by the ground‐based instruments with the calculated ones based on the aerosol size distributions retrieved from the SAGE II aerosol extinction measurements. The analysis shows that the aerosol size distributions derived from the SAGE II observations agree qualitatively with the in situ measurements made by the impactor/laser probe. The SAGE II‐derived vertical distributions of the ratio N0.15/N0.25 (where Nr is the cumulative aerosol concentration for particle radii greater than r, in micrometers) and the aerosol backscatter profiles at 0.532‐ and 0.6943‐μm lidar wavelengths are shown to agree with the dustsonde and the 14‐inch (36 cm) lidar observations, with the differences being within the respective uncertainties of the SAGE II and the other instruments.
An observational study of the southern stratospheric spring wave features during 1979–1982, utilizing TOMS data
Authors: Sabutis Joseph L.
Published: February 2008

Total Ozone Mapping Spectrometer (TOMS) data during the southern hemisphere spring are analyzed to obtain time‐mean and transient wave amplitudes for zonal wave numbers 1–10. It is found that at latitudes south of 50°S, the October total ozone is dominated by the wave number 1 time‐mean component, with largest amplitudes occurring in 1979 and 1982. The November wave number 1 time‐mean amplitudes are reduced from their October values; the largest reductions occur in 1979 and 1982. In contrast, at 40°–45°S the transient amplitudes are dominant. Phases angles for time‐mean wave number 1 are also presented and little year‐to‐year variation is noted south of 50°S. Also obtained with these data are traveling wave power and coherence‐squared spectra. The spectra for eastward traveling features having zonal wave numbers 1–3 are presented. All of these wave numbers exhibit eastward traveling features at high latitudes, with no evidence of westward traveling features.
Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica: 5. Observations of the diurnal variations of BrO and OClO
Authors: Solomon S. , Sanders R. W. , Carroll M. A. , Schmeltekopf A. L.
Published: February 2008

Observations of the diurnal variations of OClO and BrO during austral spring, 1987, using long‐path visible and near‐ultraviolet absorption spectroscopy are presented and compared to simplified model calculations. It is shown that care must be taken to compare model calculations and measurements along the line of sight of the instrument. Evening twilight observations of OClO are found to be broadly consistent with current photochemical schemes, assuming ClO and BrO levels near 50 mbar of about 0.5 parts per billion by volume (ppbv) and 7 parts per trillion by volume (pptv), respectively, throughout the observing period from late August to mid‐October. Nighttime observations of OClO obtained using the Moon as a light source display evidence for growth after sunset in late August, but not in late September. Further, the observed morning twilight OClO abundances are in agreement with model calculations in late August, but they generally fall below calculations in late September and October. Observations of BrO in mid‐September show far greater evening than morning twilight abundances. It is shown that the diurnal variations of BrO and OClO in mid‐September and October can be explained by formation of the BrONO2 reservoir species at night, although other reservoir species with comparably long lifetimes could also explain the observations. If formation of BrONO2 is the correct explanation for these data, the observations suggest that NO2 levels in the Antarctic lower stratosphere are of the order of a few pptv or less in late August, a few tens of pptv in mid‐September, and a few hundred pptv in October.
Antarctic Ozone Hole: Possible implications for ozone trends in the southern hemisphere
Authors: Sze N. D. , Ko M. K. W. , Weisenstein D. K. , Rodriguez J. M. , Stolarski R. S. , Schoeberl M. R.
Published: February 2008

Satellite‐borne instruments (the Total Ozone Mapping Spectrometer and the Solar Backscattered Ultraviolet Instrument) show that, compared to 1979, total column ozone has a year‐round decrease of more than 5% in the neighborhood of 60°S. The meteorological conditions (warmer temperatures, the absence of polar stratospheric clouds) at these latitudes do not seem to favor heterogeneous chemistry as the direct cause for the observed year‐round ozone reduction. A mechanism involving the seasonal transport of ozone‐poor air from within the polar vortex to lower latitudes (the so‐called “dilution effect”) is proposed as a possible explanation for the observed year‐round ozone reduction in subpolar regions. A two‐dimensional model with an imposed springtime Antarctic ozone depletion is used to study the post‐ozone hole impact on the spatial and temporal distributions of column ozone at latitudes north of 60°S. It is found that the time constant associated with the dilution effect in the latitude region 40°–60°S is about 1 year, long enough to contribute to the observed year‐round decrease of total ozone in that region. Because of the relatively short ozone replacement time constant (∼1 month) at latitudes north of 30°S, the calculated dilution effect over these latitudes is small. Measurement strategies aimed at distinguishing various possible causes for the observed ozone reduction at middle to high latitudes in the southern hemisphere are proposed.
Maximum electric charge of a hydrometeor in the electric field of a thundercloud
Authors: Bourdeau Christine , Chauzy Serge
Published: February 2008

Computations have been made for the maximum electric charge that a hydrometeor can retain in the ambient field of a thundercloud. Two processes contribute to this limitation: water drop instability and corona discharge initiation. Solid hydrometeors are only affected by corona emission. Therefore, the numerical method presented here consists of computing the local electric field everywhere at the surface of the hydrometeor as a function of the ambient field and its net charge. When this surface field exceeds the corona onset at some point, as defined by Peek's law, the maximum charge is reached. For water drops the electric charge can be limited either by corona emission or by mechanical instability. The present model takes into account the influence of both drop rupture due to electrostatic pressure and corona emission. Dawson's experimental onset values are considered in this case. Since corona onset values are pressure dependent, so are the maximum charges of both kinds of hydrometeors. The computation results show that, at higher pressure, the maximum net charge of a solid, smooth hydrometeor is higher than that of a water drop of the same size located within the same ambient electric field. At lower pressures, this difference decreases. This preliminary work, in need of experimental confirmation, does not take into account temperature and purity of the particles but aims to reveal the relative parts played by the basic mechanisms in limiting net charge of the hydrometeors.
Greenhouse effect of chlorofluorocarbons and other trace gases
Authors: Hansen James , Lacis Andrew , Prather Michael
Published: February 2008

We compare the radiative (greenhouse) forcing of the climate system due to changes of atmospheric chlorofluorocarbons and other trace gases. We find that CFCs, defined to include chlorofluorocarbons, chlorocarbons, and fluorocarbons, now provide about one‐quarter of current annual increases in anthropogenic greenhouse climate forcing. If the growth rates of CFC production in the early 1970s had continued to the present, current annual growth of climate forcing due to CFCs would exceed that due to CO2.
In situ observations of BrO over Antarctica: ER‐2 aircraft results From 54°S to 72°S latitude
Authors: Brune W. H. , Anderson J. G. , Chan K. R.
Published: February 2008

Bromine monoxide was observed in situ during nine flights of the NASA ER‐2 aircraft from Punta Arenas, Chile (54°S latitude), to 72°S latitude over the Palmer Peninsula, Antarctica. The first flight for the BrO detection system was on August 28. The distribution of BrO inside the chemically perturbed region defined by greatly elevated ClO abundances was different from that found just outside. Inside, the BrO mixing ratio was 6.1±1.1 pptv above the 440 K potential temperature surface, 4.7±2.0 pptv between the 400 and 440 K surfaces, and less than 4 pptv below the 400 K surface. At high latitudes outside the chemically perturbed region, the BrO mixing ratio was 5.4±1.4 pptv near the 450 K surface, but decreased to 2.9±1.2 pptv at the 420 K surface. The abundance of BrO showed no discernible temporal trend during the course of the nine flights. Away from the south polar region, at latitudes between 47°S and 37°N and potential temperatures between 435 and 500 K (18.5‐ to 20.7‐km altitude), the BrO mixing ratio was 0.5–3.0 pptv.
Infrared emission measurements of morning stratospheric N2O5
Authors: Blatherwick R. D. , Murcray D. G. , Murcray F. H. , Murcray F. J. , Goldman A. , Vanasse G. A. , Massie S. T. , Cicerone R. J.
Published: February 2008

Infrared emission spectra obtained during a balloon flight of the Air Force Geophysics Laboratory SCRIBE system by the University of Denver are used to measure stratospheric N2O5 after sunrise over New Mexico (latitude 33°N). This is the first daytime measurement of N2O5. Comparisons with photochemical modeling show consistency between the observed and predicted decline of N2O5 during the morning hours.
A longwave radiation model for the nocturnal boundary layer
Authors: Tjemkes Stephen A. , Nieuwstadt Frans T. M.
Published: February 2008

A narrow band model is presented to simulate the transfer of infrared radiation through a cloudless nocturnal boundary layer. The absorption and emission by the rotational and vibrational lines of water vapor, carbon dioxide and ozone in the spectral region from 0–2800 cm−1 is modeled with the Goody band model, while the absorption of the water vapor continuum in the atmospheric window region is evaluated from the empirical formulas of Roberts et al. (1976). To approximate the integration of the absorption coefficient over the inhomogeneous path, the Curtis‐Godson method is used, and to approximate the integration over all zenith angles a diffusion factor of 5/3 independent of path length is adopted. It is shown that in the troposphere the results of the narrow band model diverge from cooling rate calculations performed by line by line models by about 0.2K d−1 (∼20%). Moreover, from a comparison with 44 observations of downward flux at the surface, it is shown that the simulated flux underestimates the observed flux by about 6 W m−2 (∼2%).
Multielemental composition of the Arctic aerosol
Authors: Landsberger S. , Vermette S. J. , Barrie L. A.
Published: February 2008

A series of 12 daily aerosol samples was collected during March 1985 at Alert, Canada. Trace elemental composition and ion analysis was performed on the samples employing the techniques of instrumental neutron activation analysis and ion chromatography. Current knowledge, enrichment factor calculations, and regression analysis suggest four main constituent sources for the Arctic aerosol in this period: crustal, oceanic, anthropogenic, and photochemical reactions of marine Br compounds. Elements derived mainly from crustal sources are Al, Ca, Ce, Co, Fe, K, La, Mn, Sc, Sm, Th, and Ti. Oceanic‐derived elements include Cl, I, and Na, while anthropogenic sources include As, In, NO3‐, NH4+, Sb, Se, SO4= and V. The source of zinc remains ambiguous. Elemental ratios give supporting evidence that anthropogenic sources have their origin in Eurasia. Calculations of excess bromine in the late winter confirm results of previous experiments done in the Arctic.
Comparison of stratospheric ozone profiles and their seasonal variations as measured by lidar and Stratospheric Aerosol and Gas Experiment during 1988
Authors: McDermid I. Stuart , Godin Sophie M. , Wang Pi‐Huan , McCormick M. Patrick
Published: February 2008

A ground‐based, high power, laser remote sensing system for measurements of stratospheric ozone concentration profiles has been in operation at the Jet Propulsion Laboratory Table Mountain Facility located in southern California, +34.4°N, −117.7°W, since January 1988. The seasonal variations observed in the ozone profiles, during 1988 and as a function of altitude, are described here. These profiles are compared with those from the Stratospheric Aerosol and Gas Experiment (SAGE II) satellite instrument made within a radius of 1000 km from the lidar and also with the zonal mean measurements made in the band 34.4°±5°. Comparison with the proposed new CIRA ozone reference model has also been carried out. The seasonal variations, between 25 km and 50 km, observed by the two instruments and indicated by the reference model are in good agreement.
Response of an interactive two‐dimensional model to ozone changes: An estimate of the radiative dynamical feedback effect
Authors: Schneider Hans R. , Ko Malcolm K. W.
Published: February 2008

The response of an interactive two‐dimensional model of the stratosphere to increased chemical removal of ozone is studied. A simplified ozone chemistry model was used. The radiative dynamical feedback in the model leads to a recovery of about one third of the calculated ozone decrease at high altitudes, and to about one sixth of the predicted losses in the column densities at high latitudes when compared with predictions by a model with fixed temperature and circulation. The model response is analyzed with the aid of stationary linear models for the diabatic circulation. A simple interpretation of the adjustment of dynamical quantities is obtained by comparing the global mean and the differential solar heating rates derived from perturbed and unperturbed ozone distributions. The feedback effect can be qualitatively described as (1) an adjustment of the global mean temperature in response to global mean solar heating changes and (2) an approximately linear response in all other dynamical variables, proportional to the change in the differential heating. The exact magnitude of the feedback effect on ozone in our model is a function of the simplified treatment of the photochemistry; however, we believe that the structure of the ozone changes and the interpretation of the dynamical response is independent of the details of the chemistry. Our model results further show an increase in the predicted high‐latitude ozone depletion with decreasing eddy diffusion in the model stratosphere. This effect can be explained by the reduction of advective and diffusive horizontal transport from the tropics to the polar region in the lower stratosphere with decreasing eddy diffusion.
A comparison of middle atmospheric dynamics at Saskatoon (52°N, 107°W) as measured by a medium‐frequency radar and a Fabry‐Perot interferometer
Authors: Lloyd N. , Manson A. H. , McEwen D. J. , Meek C. E.
Published: February 2008

The Saskatoon medium‐frequency radar and a recently installed Fabry‐Perot interferometer were operated together on a continuous basis during the autumn and early winter of 1987. Observations of the atomic oxygen OI 557.7‐nm emission provide Doppler winds from the airglow layer near 97 km. Radar winds are available from 60 to 110 km during daylight hours and from 80 to 110 km at night. A comparison of the two instruments is hampered, as radar data are few in number when auroral contamination of the airglow is minimal. Hence two types of comparisons are made: first, individual radar days and radar 4‐day means are compared with optical winds, and second, extrapolation of the radar's diurnal and semidiurnal tides, which dominate the wind flow of this region, are used to predict the observed nighttime wind field. Generally, the winds are very similar between systems, but differences emerge, stressing the need to avoid auroral contamination of airglow data at relatively high latitudes.
A cautionary note on the use of some mass flow controllers
Authors: Weinheimer Andrew J. , Ridley Brian A.
Published: February 2008

Commercial mass flow controllers are widely used in atmospheric research where precise and constant gas flows are required. We have determined, however, that some commonly used controllers are far more sensitive to ambient pressure than is acknowledged in the literature of the manufacturers. Since a flow error can lead directly to a measurement error of the same magnitude, this is a matter of great concern. Indeed, in our particular application, were we not aware of this problem, our measurements would be subject to a systematic error that increased with altitude (i.e., a drift), up to a factor of 2 at the highest altitudes (∼37 km). In this note we present laboratory measurements of the errors of two brands of flow controllers when operated at pressures down to a few millibars. The errors are as large as a factor of 2 to 3 and depend not simply on the ambient pressure at a given time, but also on the pressure history. In addition there is a large dependence on flow setting. In light of these flow errors, some past measurements of chemical species in the stratosphere will need to be revised.
Dry deposition of Asian mineral dust over the central North Pacific
Authors: Schneider B. , Tindale N. W. , Duce R. A.
Published: February 2008

Dry deposition of mineral particles was investigated on the windward coast of Oahu (Hawaii) using a surrogate surface technique. The collected particles were analyzed microscopically for the number of particles in different size classes. These data were used to estimate deposition rates to the deposition plate. Relating these fluxes to the corresponding concentrations of mineral particles in air, mean dry deposition velocities were determined. For the size classes 2–4, 4–8, and 8–15 μm these were 0.3, 1.2, and 2.6 cm s−1, respectively. Additionally, the dry deposition velocity curve in the range between 2 and 15 μm was determined on the assumption that the mineral particle mass size distributions in the air and in dry deposition were lognormal. This curve was compared with theoretical data calculated by a model for the deposition of particles to the sea surface. The discrepancies, in particular for smaller particles, are probably due to the different deposition conditions at the sea surface and the deposition plate. Also, the aggregates that were found in some samples and which consist of sea salt and mineral particles will affect the experimentally derived dry deposition curve.
An instability of acoustic waves caused by radiation and the influence of chemical reactions on it
Authors: De Jagher P. C.
Published: February 2008

In a gas which absorbs radiation an acoustic wave can be unstable. This instability is caused by the fact that the irradiant energy is absorbed preferentially in the high density region of the wave. If in the gas the chemical equilibrium AB ⇄ A + B is maintained by photo dissociation balancing the reactions due to collisions, the instability increases. This is due to the density dependence of the reaction rate of the reverse reaction. It is argued that this process may explain the excitation or amplification of disturbances in the upper atmosphere.