bluuebunny/crossref_metadata_2025 huggingface dataset:
Airborne measurements of stratospheric constituents over Antarctica in the Austral Spring 1987: 1. Method and ozone observations
Authors: Mankin William G. , Coffey M. T.
Published: February 2008

We have flown a Fourier transform spectrometer aboard a DC‐8 on 10 flights over Antarctica during August and September, 1987, as part of the Airborne Antarctic Ozone Experiment (AAOE). Observing the Sun at infrared wavelengths, we determined the integrated column amount above the flight altitude for ozone and a number of other chemical species that are believed to be important in the perturbed chemistry of the “ozone hole”. In this paper we describe the method, the observations, the data analysis procedure, and the ozone results. During the observation period, ozone developed a steep gradient near the edge of the polar vortex; deep within the vortex, the average ozone column decreased by about 1.6% per day during September.
Ozone destruction by chlorine radicals within the Antarctic vortex: The spatial and temporal evolution of ClO‐O3 anticorrelation based on in situ ER‐2 data
Authors: Anderson J. G. , Brune W. H. , Proffitt M. H.
Published: February 2008

In situ O3 and ClO data obtained from the ER‐2 aircraft are used to define the chemical evolution of the Antarctic vortex region from August 23 to September 22, 1987. Initial conditions are characterized at aircraft flight altitude (18 km) by highly amplified ClO mixing ratios (800 parts per trillion by volume (pptv)) within a well‐defined “chemically perturbed region” (CPR) poleward of the circumpolar jet, within which ozone exhibits limited erosion (∼15%) in middle to late August. Within this CPR, ozone decays consistently throughout the course of a 10‐flight series, such that by late September, 75% of the O3 has disappeared within the region of highly amplified ClO concentrations (which reached 500 times normal levels at ER‐2 cruise altitude). As this ozone depletion develops, O3 and ClO exhibit dramatic negative correlation on isentropic surfaces, obtained as the aircraft passed through the edge of the CPR. Taken in conjunction with an analysis of the mechanisms defining the rate of catalytic O3 destruction, it is concluded that ClO is an essential constituent in the catalytic destruction of ozone within the vortex. Therefore it is concluded that the observed disappearance of ozone within the Antarctic vortex would not have occurred in the absence of global chlorofluorocarbon release.
Ground‐based infrared measurements of tropospheric source gases over Antarctica during the 1986 Austral Spring
Authors: Toon G. C. , Farmer C. B. , Schaper P. W. , Blavier J.‐F. , Lowes L. L.
Published: February 2008

Simultaneous measurements of the atmospheric burdens of CH4, N2O, CO2, CF2Cl2, and CO above McMurdo Station, Antarctica, have been derived from solar absorption spectra obtained by the Jet Propulsion Laboratory high‐resolution Fourier transform spectrometer. In all cases the burdens are smaller than mid‐latitude values. Furthermore, retrievals of N2O and CH4, for which we have information on the vertical distribution not only from the zenith angle dependence of the strength of their absorption, but also from the shapes of their spectral lines, indicate that the tropospheric mixing ratios were normal and that the depletion of the burdens can best be accounted for by a downward shift of the volume mixing ratio profiles by some 6–8 km. This rules out the possibility of large‐scale upwelling of ozone‐poor tropospheric air into the stratosphere being the cause of the Antarctic springtime ozone depletion.
Synoptic and chemical evolution of the Antarctic vortex in late winter and early spring, 1987
Authors: Tuck A. F.
Published: February 2008

Evidence from the ER‐2 and DC‐8 aircraft flights is considered, together with analyses of temperature, winds, potential vorticity and trajectories, satellite data, and ozonesonde observations, to come to a view of whether the air in the lower stratosphere over Antarctica during winter and early spring of 1987 was a fixed slug of air, or if there was significant mass flow through the system. It is concluded that synoptic‐scale forcing, via “sudden coolings,” produced polar stratospheric clouds, which intervened to alter the homogeneous gas phase chemical balance. As a result, there was a source of the ClO molecule and sinks for H2O, NOy (equal to the sum of reactive gas phase nitrogen compounds), and O3 operating within the region of high potential vorticity gradients on isentropic surfaces, that is, inside the vortex. It is further concluded that as a result of horizontal mixing, downward diabatic motion, and, at potential temperatures below 400 K, advective transfer, that the effects of these polar sinks and chemical reactions can be transmitted to middle latitudes.
Effects on electrical parameters at Athens, Greece by radioactive fallout from a nuclear power plant accident
Authors: Retalis D. , Pitta A.
Published: February 2008

Some atmospheric electrical parameters, i.e., electric field, conductivity, and small ion concentration, measured at Athens, Greece, after the Chernobyl reactor accident, are analyzed and compared with their normal value and with measurements of radionuclide concentration and exposure rate in the air near the ground. The effects of the radioactive plume on the above electrical parameters, especially the conductivity, are very pronounced.
Climatology of polar mesospheric clouds: 2. Further analysis of solar mesosphere explorer data
Authors: Thomas G. E. , Olivero J. J.
Published: February 2008

An analysis is presented of nine summer seasons of Solar Mesosphere Explorer (SME) satellite data used to study large‐scale geographical and temporal variability of polar mesospheric clouds (PMC). PMC are scattering layers occurring in the cold summertime polar cap atmosphere near 85 km. This region is often supersaturated with respect to water‐ice crystals in a narrow height domain where temperatures fall below 140 K. An earlier analysis showed that PMC appear to be a regular feature of the arctic and antarctic mesosphere during summer solstice. PMC grow in brightness with latitude frcm near their detection threshold at about 55° latitude toward the pole. In the current study we examine a larger set of SME data, from 1981 to 1985. In addition we have removed the Rayleigh‐scattering background from the cloud data. We find that this subtraction results in a better defined cloud activity index in the low latitude regions where clouds are infrequent. We find that the PMC season begins at the highest latitudes observed and propagates to lower latitudes within 10 to 20 days. This occurs at about 20 to 40 days before summer solstice. The season ends about 60 days after solstice, with the maximum occurrence frequency to be found at 1 to 3 weeks following solstice. The beginning and ending of the PMC season occur about 1 to 2 weeks later than published values of the noctilucent cloud season, as observed from the ground at northerly latitudes of 50°–65°. The northern PMC extend farther from the pole by about 5° than their southern counterparts. A comparison with rocket data for the seasonal variation of temperature at 70° latitude indicates similar time lags of about 3 weeks after solstice for minimum mesopause temperature and maximum cloud frequency. This suggests that variations of temperature and/or the accompanying upward advective water vapor flux are responsible for the seasonal variations of PMC. We present observational differences between PMC and noctilucent clouds as well as a possible unification of our understanding of the two phenomena. A study of the longitudinal variability of PMC indicates no significant large‐scale variations; variations of the scale of 40° are masked by the uneven sampling from year to year. There is significant interannual variability (of the order of 15%) of unknown cause, but no consistent year‐to‐year trends in activity. There is no indication of an influence of the location of the auroral oval on the geographical distribution of PMC; any possible causal connection between PMC and auroral activity remains unknown.
Solar variability influences on weather and climate: Possible connections through cosmic ray fluxes and storm intensification
Authors: Tinsley Brian A. , Brown Geoffrey M. , Scherrer Philip H.
Published: February 2008

The question of the mechanism for solar‐variability effects on weather and climate can be separated into (1) the identification of the carrier of the solar variability and (2) the identification of the physical link between the carrier and the meteorological response. The suggestion that galactic cosmic rays (GCR), as modulated by the solar wind, are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and considerable evidence for it has now accumulated. Variations of GCR occur with the 11‐year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasi‐biennial oscillation of equatorial stratospheric winds (QBO). Variations in GCR occur on the time scale of centuries with a well‐defined peak in the coldest decade of the little ice age. Here we present new evidence on the meteorological responses to variations on the time scale of a few days. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. The responses reported here include changes in the vertical temperature profile in the troposphere and lower stratosphere and in the northern hemisphere vorticity area index, associated with Forbush decreases in GCR. The meteorological responses to Forbush decreases are in the opposite sense but otherwise are quite similar to responses that immediately follow solar flares. This is to be expected, based on the hypothesis that particles with energy about 100–1000 MeV are the external forcing function for the tropospheric response, since large solar flares increase the particle flux and ionization and minor species production in the lower stratosphere, whereas Forbush decreases reduce them. The mechanism or mechanisms linking changes in low‐energy GCR and other particles in this energy range of 100–1000 MeV to tropospheric temperature and dynamic responses have not been identified. This can be attributed to current uncertainties regarding the microphysical and electrical properties of aerosols and clouds. One possibility is that changes in clouds lead to changes in cloud radiative forcing. The height distribution of the tropospheric response and the amount of energy involved and the rapidity of the time response suggest that the release of latent heat could also be involved. These could lead to the observed tropospheric responses which are understandable in terms of changes in the intensity of cyclonic disturbances. Theoretical considerations link such changes to the observed latitudinal movement of the jet stream.
Damping of acoustic gravity waves caused by the conductivity of the ionosphere
Authors: Miesen R. H. M. , de Jagher P. C. , Kamp L. P. J. , Sluijter F. W.
Published: February 2008

The influence of ionization and conduction on the dispersion of acoustic gravity waves in the upper atmosphere has been investigated by means of an analysis of the corresponding dispersion relation, when the geomagnetic field is directed horizontally. It is shown that we have to distinguish two situations, i.e., acoustic gravity waves propagating perpendicular or nearly perpendicular to the Earth's magnetic field and acoustic gravity waves propagating oblique or parallel to the Earth's magnetic field. This last situation is the one considered in a paper by Hines and Hooke (1970). In the present paper both situations are described analytically; the transition between the two is studied numerically. A consequence of the incorporation of ionospheric conductivity is a damping of acoustic gravity waves with a damping rate lying between a characteristic damping rate that scales with the Pedersen conductivity and zero, depending on the frequency of the wave and the direction of propagation. This angular and frequency dependence of the damping rate may be experimentally verifiable.
Observations of condensation nuclei in the Airborne Antarctic Ozone Experiment: Implications for new particle formation and polar stratospheric cloud formation
Authors: Wilson J. C. , Loewenstein M. , Fahey D. W. , Gary B. , Smith S. D. , Kelly K. K. , Ferry G. V. , Chan K. R.
Published: February 2008

The ER‐2 Condensation Nucleus Counter (ER‐2 CNC) was operated in the Airborne Antarctic Ozone Experiment in August, September, and October 1987. The ER‐2 CNC measures the mixing ratio of particles, CN, with diameters from approximately 0.02 μm to approximately 1 μm. Comparisons of CN and other aerosol measurements with N2O show that the vertical profile of the sulfate aerosol was probably displaced downward by the subsidence and mixing processes that determined the inclination of the N2O isopleths. At altitudes above the minimum in the CN mixing ratio profile, CN mixing ratios correlated negatively with that of N2O, demonstrating new particle production. The region of particle production was above and south of the 160 ppbv N2O isopleth. The relationship between CN and N2O did not change noticeably when moving from air containing normal levels of reactive nitrogen compounds (NOy) to air depleted in those compounds. This suggests that the removal of NOy was accompanied by the removal of a small minority of the CN. Concentrations of CN are compared with those of larger particles to study cloud formation mechanisms. In some cases condensation of water or nitric acid trihydrate following rapid cooling caused most of the CN to grow to diameters larger than 0.81 μm. Models published elsewhere predict that these conditions should result in a large fraction of particles growing to these sizes. Episodes of this type probably did not remove reactive nitrogen compounds through particle sedimentation from the chemically perturbed region. Small numbers of large particles were observed in other instances. The composition of the particles and their origins are unclear.
Time offsets and power spectra of the ER‐2 data set from the 1987 Airborne Antarctic Ozone Experiment
Authors: Murphy Daniel M.
Published: February 2008

The time offsets and power spectra of the data taken from the ER‐2 during the 1987 Airborne Antarctic Ozone Experiment (AAOE) are described. All of the ER‐2 data appear to be aligned in time to within ±5 s. Power spectra for most of the chemical species and meteorological conditions measured from the ER‐2 show clear transitions from white noise to atmospheric variability. All data except that from the ozone instruments showed noise at frequencies above 0.1 Hz, corresponding to length scales below 2 km. The pressure, temperature, and wind data reported by the meteorological measurement and navigation recorder systems are consistent with each other, with pressures generally within 2%, wind speeds within 15% and temperatures differing by <1 K.
Late Cenozoic uplift in southern Asia and the American West: Rationale for general circulation modeling experiments
Authors: Ruddiman W. F. , Prell W. L. , Raymo M. E.
Published: February 2008

Geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late Cenozoic, especially in the last 10 m.y. Regions of major uplift include the Tibetan Plateau and Himalayan Mountains of southern Asia; and the Sierra Nevada, Colorado Plateau, Basin and Range, Rocky Mountains, and High Plains of the American west. Uplift occurred at a scale large enough to affect regional and global climate in a number of ways, several of which we evaluate by General Circulation Model experiments in accompanying papers.
Wave number spectra from temperature‐humidity infrared radiometer 6.7‐μm water vapor data
Authors: Manney Gloria L. , Stanford John L.
Published: February 2008

Wave number spectra from Nimbus 7 temperature‐humidity infrared radiometer 6.7‐μm water vapor data are analyzed using series 4800 km long, in regions free of high clouds and frontal zones. In these regions, the brightness temperatures approximate temperatures on a water vapor isosteric (constant density) surface, rather than averages over a broad vertical layer. Power above the noise can be extracted down to wavelengths of about 60 km. Fitting the power spectrum versus horizontal wave number k to a k−n power law for wavelengths from 60 to a few hundred kilometers gives slopes of n = 2.7 to 3.0, depending on the exact wave numbers that are fitted. Thunderstorms and convective cloud systems may constitute an energy source for the reverse energy cascade which produces a −5/3 spectral slope. Our results suggest that when these features are not present, the enstrophy‐cascading process that gives a −3 slope may govern the motion at scales smaller than it has heretofore been observed.
Isoprene and its oxidation products: Methacrolein and methyl vinyl ketone
Authors: Pierotti David , Wofsy S. C. , Jacob D. , Rasmussen R. A.
Published: February 2008

The first measurements of methacrolein (MACR) and methyl vinyl ketone (MVK) in the atmosphere are reported. The compounds both show a strong seasonal variation, with a maximum in the summer. The concentrations of MACR and MVK are highly correlated with each other and with the concentration of isoprene, in accord with the expectation that they are the major initial products of isoprene oxidation. However, the observed MACR/MVK ratio does not agree with the model predictions over the range of conditions normally observed in the nonurban continental boudary layer. We suggest that this indicates a major gap in our understanding of the photochemistry of hydrocarbons in the nonurban troposphere.
Column atmospheric water vapor and vegetation liquid water retrievals from Airborne Imaging Spectrometer data
Authors: Gao Bo‐Cai , Goetz Alexander F. H.
Published: February 2008

High spatial resolution column atmospheric water vapor amounts were derived from spectral data collected by the airborne visible‐infrared imaging spectrometer (AVIRIS), which covers the spectral region from 0.4 to 2.5 μm in 10‐nm bands and has a ground instantaneous field of view of 20×20 m from an altitude of 20 km. The quantitative derivation is made by curve fitting observed spectra with calculated spectra in the 1.14‐μm and 0.94‐μm water vapor band absorption regions using an atmospheric model, a narrowband spectral model, and a nonlinear least squares fitting technique. The derivation makes use of the facts that (1) the reflectances of many ground targets vary approximately linearly with wavelength in the 0.94‐ and 1.14‐μm water vapor band absorption regions, (2) the scattered radiation near 1 μm is small compared with the directly reflected radiation when the atmospheric aerosol concentrations are low, and (3) the scattered radiation in the lower part of the atmosphere is subjected to the water vapor absorption. The technique is directly applicable for retrieving column water vapor amounts from AVIRIS spectra measured on clear days with visibilities 20 km or greater. The precision of the retrieved column water vapor amounts from several data sets is 5% or better. Based on the analyses of an AVIRIS data set that was acquired within an hour of radiosonde launch, it appears that the accuracy approaches the precision. The derived column water vapor amounts are independent of the absolute surface reflectances. It now appears feasible to derive high spatial resolution column water vapor amounts over land areas from satellite altitude with the proposed high resolution imaging spectrometer (HIRIS). Curve fitting of spectra near 1 μm from areas covered with vegetation, using an atmospheric model and a simplified vegetation reflectance model, indicates that both the amount of atmospheric water vapor and the moisture content of vegetation can be retrieved simultaneously because the band centers of liquid water in vegetation and the atmospheric water vapor are offset by approximately 0.05 μm.
Geosat observations of the tropical Pacific cyclone pair of May 1986
Authors: Porter David L.
Published: February 2008

The radar altimeter aboard the U.S. Navy Geosat satellite was used to observe and track a cyclone pair which occurred during May 1986 in the equatorial Pacific. The data were binned into boxes 2° in latitude by 8° in longitude with a temporal resolution of 3 days. This smoothing in space and time lead to wind speed estimates substantially less than the instantaneous wind speeds. Nevertheless, the storm track derived from Geosat data was essentially the same as that obtained using imagery from a weather satellite, independent NOAA estimates of the storm tracks, and weather analyses by the Australian Royal Meteorological Service. This study demonstrates that Geosat wind speed data can be effectively used to investigate mesoscale storm features.
Analysis of the eight‐year trend in ozone depletion from empirical models of solar backscattered ultraviolet instrument degradation
Authors: Herman J. R. , Hudson R. D. , Serafino G.
Published: February 2008

Currently archived ozone data from the Solar Backscatter Ultraviolet (SBUV) spectrometer experiment on the Nimbus 7 satellite has been reported to show large global decreases in the amount of atmospheric ozone, both total content and as a function of altitude, for the period from 1978 to 1987. Analysis of atmospheric albedo data leading to these reported trends was based on empirical models of the SBUV spectrometer and diffuser plate degradation with time. Their combined degradation can be obtained from apparent decreases in measured solar irradiance at wavelengths where little or no long‐term intensity changes are expected. The central problem in analyzing SBUV data is to separately specify the diffuser plate degradation [Husdon et al., 1988]. Ratios of radiance to solar irradiance used to obtain ozone amounts are proportional only to diffuser reflectivity and independent of any spectrometer degradation. Even observations of relatively short‐term solar irradiance changes with time must be based on a model of diffuser plate degradation, since the SBUV data provide no internal means to uniquely specify diffuser plate reflectivity changes at ail wavelengths. A new class of explicitly empirical models have been developed that produce a better fit to all of the SBUV solar flux data. The models have a single free parameter to separately specify the diffuser plate and spectrometer degradation. This parameter must be within a narrow range to bring the calculated ozone trend into approximate agreement with data from the Dobson network, Solar Mesospheric Explorer (SME) and Stratospheric Aerosol Gas Experiment (SAGE) satellites, or with the different trends reported from the Umkehr ground stations. It is shown that outside sources of ozone data must be used to obtain a unique solution from SBUV radiance data within the precision necessary to determine the existence of a global annual ozone decrease. A correction factor is given as a function of time and altitude that brings the SBUV data into approximate agreement with SAGE, SME, and Dobson ozone trends. The total ozone results also agree with a recently developed wavelength pair justification method of internal calibration for the SBUV instrument. In our opinion, the currently archived SBUV ozone data should be used with caution for periods of analysis exceeding 1 year, since it is likely that the yearly decreases contained in the archived data are too large.
Seasonal variations in mesospheric sodium tidal activity
Authors: Batista P. P. , Clemesha B. R. , Simonich D. M.
Published: February 2008

Diurnal and nocturnal laser radar measurements of mesospheric sodium density at São José dos Campos, Brazil (23°S, 46°W), show strong oscillations with 12 and 24 hour periods. Data obtained in 1981 showed that atmospheric tides, mainly the vertical wind field, are the major causes of the density variations at a fixed height, thus making it possible to infer vertical wind parameters over a limited height range. In this work, 1984 and 1985 data are added to the earlier 1981 data and the 12‐ and 24‐hour components are determined for different seasons in order to study the seasonal variations of the tides. It is shown that the amplitudes of the oscillations in sodium density and consequently the vertical wind amplitudes, in general, are larger in winter than in other seasons. Above 97 km, the semidiurnal amplitude is larger than the diurnal in winter, of the same order of magnitude at the equinoxes and smaller in summer. The phases of the inferred semidiurnal vertical wind component, above 97 km, show regular propagating characteristics with little differences between winter and equinoxes, but a confused pattern in summer. Below 93 km the wavelengths decrease from winter to summer. In all seasons, the phase of the inferred diurnal vertical wind component stays at around 19–23 h below 85 km and above 93 km. The behavior of the phase of the diurnal oscillation in sodium density between 85 and 90 km is quite different in the three seasons. This is explained by seasonal differences in the relative phases of the oscillations in vertical wind and density.
Interpretation of ground‐based radiometric observations in terms of a gravity wave model
Authors: Canavero F. G. , Einaudi F. , Westwater E. R. , Falls M. J. , Schroeder J. A. , Bedard A. J.
Published: February 2008

An analysis is presented of 2‐hour and 4‐hour segments of data taken at Denver, Colorado, on February 3, 1984, by a ground‐based radiometer designed and operated by the Wave Propagation Laboratory of the National Oceanic and Atmospheric Administration (NOAA). The zenith‐viewing instrument has two moisture‐sensing and four temperature‐sensing channels. It is demonstrated that a peak at a period of 10 min, present in the spectra of the measured brightness temperature and of the derived geopotential heights, thicknesses, and vertically integrated water vapor content, is due to an internal gravity wave generated by wind shear in the jet aloft. This analysis shows that the radiometer has the sensitivity to detect such disturbances and that the mathematical inversion technique used to retrieve the geopotential field and other integrated quantities retains the derived information as well. Finally, a linear expression is derived which relates the brightness temperature to the atmospheric temperature, density, humidity, and cloud liquid perturbation fields.
Discrete angle radiative transfer: 1. Scaling and similarity, universality and diffusion
Authors: Lovejoy Shaun , Davis Anthony , Gabriel Philip , Schertzer Daniel , Austin Geoffrey L.
Published: February 2008

In order to facilitate study of very inhomogeneous optical media such as clouds, the difficult angular part of radiative transfer calculations is simplified by considering systems in which scattering occurs only in certain directions. These directions are selected in such a way that the intensity field decouples into an infinite number of independent (e.g., orthogonal) families in direction space, each coupled only within its family. Further discretization, this time in space, lends itself readily to both analytical renormalization approaches (part 2) and to numerical calculations (part 2). We are particularly interested in scaling systems in which the optical density field has no characteristic size over a wide range of scales; these include internally homogeneous media of any shape but are more generally internally inhomogeneous and better described as fractals or multifractals. In this case, the albedo and transmission obey power laws in the thick cloud limit if scattering is conservative. By deriving powerful discrete angle (DA) similarity relations, we show that the scaling exponents that characterize these laws are “universal” in the sense that they are independent of the DA phase functions. We argue that these universality classes may be generally expected to extend beyond DA to include standard (continuous angle) phase functions and transfer equations. By comparing the DA equations with the diffusion equation, we show that in general the thick cloud limits of the two will be different: the thick cloud regime will only be “diffusive” in very homogeneous clouds, hence the term “universality class” is more appropriate. The DA similarity relations indicate that in scaling systems spatial variability is of primary importance, this suggests that far more research should be made to realistically model the spatial variability and to investigate its effect on radiative response, even if the angular aspect of the transfer process is made much less sophisticated than is possible in the classical plane‐parallel type medium.
Intercomparison of scanner and nonscanner measurements for the Earth Radiation Budget Experiment
Authors: Green Richard N. , House Frederick B. , Stackhouse Paul W. , Wu Xiangqian , Ackerman Steven A. , Smith William L. , Johnson Margaret J.
Published: February 2008

The Earth Radiation Budget Experiment nonscanner measurements are simulated with the scanner measurements. The error in simulating a single measurement is 1% for longwave and 3% for shortwave. Errors in simulating the average daily measurements are half these amounts. Four months of Earth Radiation Budget Satellite measurements were analyzed. The results show that changing sun geometry affects the accuracy of the nonscanner measurements. The medium field of view (MFOV) total channel and scanner agree to within 2% on average. The wide field of view (WFOV) total channel and scanner agree to within 1%. For the shortwave channels, the agreement with the scanner is 2% for the MFOV and 2.5% for the WFOV.
Dust devils at White Sands Missile Range, New Mexico: 1. Temporal and spatial distributions
Authors: Snow John T. , McClelland Thomas M.
Published: February 2008

From May 13, through August 21, 1986, and again from April 3, through May 28, 1987, a dust devil census was conducted at the Permanent High Explosive Test Site on White Sands Missile Range, New Mexico. In a 260‐km2 observation area, a total of 3134 dust devils were counted on 97 days (out of 112 observing days). Within the observation area, the dust devils were concentrated in a relatively small area and showed strong correlation with roadways and other cleared areas. However, from the summer of 1986 to the spring of 1987, the center of activity shifted from a relatively undisturbed region to an area whose surface had been recently modified. This shift is attributed to changes in soil moisture and surface thermal properties. It is suggested that the co‐location of the center of activity in 1987 with the modified surface is an example of inadvertent weather modification on a very local scale. The dust devils had a daily distribution very similar to that found by Sinclair (1969) in comparable terrain in the vicinity of Tucson, Arizona. The time of the first observed dust devil was very regular on days with dry surface conditions at sunrise and clear skies through the morning. The time of the first dust devil was delayed and the degree of activity reduced if precipitation had occurred on a previous day in the observation area. The production of dust devils often ended abruptly with the onset of an afternoon thundershower in the observation area.
Airborne sodium lidar observations of horizontal and vertical wave number spectra of mesopause density and wind perturbations
Authors: Kwon Kang H. , Senft Daniel C. , Gardner Chester S.
Published: February 2008

We present kinetic energy horizontal and vertical wave number spectra of wind and density perturbations at mid‐latitudes for the altitude range from approximately 80 to 100 km. The spectra are inferred from Na density profiles collected with an airborne lidar during two flights conducted in November 1986. The two flights included one round trip from Denver, Colorado, to Springfield, Illinois, and another round trip from Denver to the Pacific Coast. The horizontal wave number spectra exhibited an approximately kh−1.2 dependence at horizontal scales from 70 to 700 km, while the vertical wave number spectra exhibited an approximately kz−2.7 dependence at vertical scales from 2 to 10 km. These spectra are compared with spectra obtained from ground‐based lidar, radar, shuttle re‐entry, and Global Atmospheric Sampling Program observations. The rms horizontal wind velocity inferred from the airborne Na lidar data increased with time and with longitude from the Pacific Coast to the Great Plains. The inferred mean rms horizontal wind velocity was 32 m s−1, and the mean horizontal velocity variance was about 1100 m2 s−2. This horizontal velocity variance is comparable to horizontal velocity variances inferred from radar observations, but larger than horizontal velocity variances inferred from shuttle re‐entry observations. During the round trip flight from Denver, Colorado, to Springfield, Illinois, two quasi‐monochromatic waves were observed. The longer wavelength wave had an intrinsic zonal wavelength of 772 km, intrinsic zonal phase velocity of 35 m s−1 westward, and intrinsic period of 6.1 hours. This wave appears to be propagating almost due west. The shorter wavelength wave had an intrinsic zonal wavelength of 263 km, zonal phase velocity of 43 m s−1 westward, and period of 1.7 hours.
Natural hydrocarbons, urbanization, and urban ozone
Authors: Cardelino C. A. , Chameides W. L.
Published: February 2008

Using the Atlanta metropolitan area as a case study, we examine the effects of urbanization and its associated heat island on urban ozone concentrations. Air quality data from Atlanta suggest that urban ozone concentrations are enhanced by increases in ambient temperature. Model calculations suggest that this enhancement is caused by the effect of temperature on the atmospheric chemistry of peroxyacetyl nitrate (PAN), as well as the temperature dependence of natural and anthropogenic hydrocarbon emissions. A comparison of summertime temperatures in Atlanta and a nearby rural station, suggests that Atlanta's temperature over the past 15 years has increased by about 2°C due to urbanization and its concomitant intensification of the urban heat island. Numerical simulations using conditions of a typical summertime day in Atlanta suggest that this rise in temperature could have, (1.) resulted in a significant increase in the net emissions of natural hydrocarbons in the area in spite of the loss of about 20% of the area's forests over the same period, and (2.) negated the beneficial effects on summertime ozone concentrations that would have been obtained from a 50% reduction in anthropogenic hydrocarbon emissions. Because a NOx‐based ozone abatement strategy appears to be less sensitive to temperature increases than does a hydrocarbon‐based strategy, a NOx strategy may prove to be more effective in the future if temperatures continue to rise as a result of urbanization and the “greenhouse effect”.
Effects of nonstationarity on spectral analysis of mesoscale motions in the atmosphere
Authors: Eckermann Stephen D.
Published: February 2008

Computation of the power spectra of mesoscale atmospheric motions from experimental data has become a way of addressing a number of important dynamical questions. These include whether gravity waves or quasi two‐dimensional turbulence (also interpreted as vortical modes) are the more energetic mesoscale fluctuations, and whether the atmospheric gravity wave spectrum is convectively saturated. Yet the variance of these small‐scale atmospheric motions varies appreciably in space and time, and so spectra computed from such nonstationary data will generally differ from the stationary shape. A model of the vertical wave number spectrum of horizontal velocity fluctuations produced by saturated gravity wave motions has been developed, and it predicts that the spectral form varies considerably with altitude. The effects on spectral computations of this inherent nonstationarity are examined in depth. It is found that this altitude nonstationarity gives rise to computed spectra of the form m−t where t lies between the nominal unsaturated and saturated Values of 0 and 3 respectively. Many spectral measurements which do not compare favorably with the original model spectrum have this shape, and on inspection appear likely to suffer appreciably from nonstationarity, while other measurements which better compare with the model spectrum appear to do so because the nonstationarity was minimized in these measurements. Simulations involving observed examples of the temporal nonstationarity of time‐fluctuating motions reveal that computed frequency spectra are not significantly altered in shape. However, gravity wave and vortical mode theories both provide models of the ground‐based frequency spectrum, and both theories predict that these spectra are also nonstationary if the background wind speed varies with time, due to Doppler‐shifting effects. Representative simulations of the problem reveal that limited distortions to the gravity wave spectrum arise, but that the vortical mode spectrum can be modified significantly; on occasions its shape is altered to one more like that of the gravity wave model spectra. This may be a candidate for explaining why a number of studies comparing measured frequency spectra with model predictions, in order to ascertain whether gravity waves or vortical modes (or both) produce this fluctuating variance, have produced conflicting conclusions. Because of this possibility, a more stationary measure, termed the “polarization ratio”, is derived and presented as an additional independent means of evaluating whether gravity waves or vortical modes are responsible for the horizontal velocity fluctuations measured by ground‐based sensors.
Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season
Authors: Jacob Daniel J. , Wofsy Steven C.
Published: February 2008

The atmospheric composition over the Amazon forest during the wet season is simulated with a onedimensional photochemical model for the planetary boundary layer (PBL) extending from the ground to 2000‐m altitude. The model is constrained and evaluated using observations from the ABLE 2B field expedition. Results indicate that only ≈ 20% of NOx emitted by soils is exported to the atmosphere above the forest canopy. The balance is deposited to vegetation before leaving the canopy layer. The small NOx flux that escapes from the canopy is nevertheless sufficient to account for the low NO concentrations observed in the PBL. Decomposition of peroxyacetylnitrate (PAN) supplied from aloft provides only a minor source of NOx in the PBL, although it could provide the major source of NOx at higher altitudes. Soil emission can account for only a portion of NOy observed over the forest. Organic nitrates of nonbiogenic origin likely account for the balance of NOy. Enhancements of CO observed in the PBL cannot be explained by oxidation of biogenic hydrocarbons, and appear to reflect direct emission of CO by the forest ecosystem. Concentrations of O3 in the PBL are regulated largely by transport from aloft and deposition to the canopy, with little net influence from photochemistry. Ozone is photochemically produced immediately above the forest where NO concentrations are relatively high, but is photochemically consumed in the upper portion of the PBL.
Emission of nitric oxide (NO) from tropical forest soils and exchange of NO between the forest canopy and atmospheric boundary layers
Authors: Bakwin Peter S. , Wofsy Steven C. , Fan Song‐Miao , Keller Michael , Trumbore Susan E. , Da Costa Jose Maria
Published: February 2008

Emissions of NO from soils in the Amazon rain forest were measured at 66 locations (224 measurements) using an enclosure technique, and continuous vertical profiles of NO and O3 were measured between the ground and 41‐m altitude. Fluxes of NO averaged 8.9 (±1.5) × 109 molecules cm−2 s−1 from the dominant (yellow clay) soils of the region, with larger fluxes (33.7 (±6.5) × 109 molecules cm−2 s−1) observed from adjacent white sand soils. Fluxes from clay soils were lower by more than a factor of 5 than fluxes observed during the dry season at a nearby site. Low soil emission rates were reflected in lower concentrations of NO at the top of the forest canopy in the wet season, only 30–50 pptv (parts per trillion by volume) during the daytime. The measured fluxes are consistent with chemical mass balances for NO within the forest canopy, calculated from the NO and O3 profiles taken at night, and with observations of NO between 150 and 5000 m altitude (A. L. Torres and K. R. Hooks, unpublished manuscript, 1989). Measurements of NO emission rates from soil plots fertilized using NaNO3, NH4Cl or sucrose indicated that a reductive pathway (denitrification) may have been primarily responsible for production of the NO released by both clay and sand soils.
Atmosphere‐biosphere exchange of CO2 and O3 in the central Amazon Forest
Authors: Fan Song‐Miao , Wofsy Steven C. , Bakwin Peter S. , Jacob Daniel J. , Fitzjarrald David R.
Published: February 2008

Measurements of vertical fluxes for CO2 and O3 were made at a level 10 m above the canopy of the Amazon forest during the wet season, using eddy correlation techniques. Vertical profiles of CO2 and O3 were recorded continuously from above the canopy to the soil surface, and forest floor respiration was measured using soil enclosures. Nocturnal respiration of CO2 by the forest ecosystem averaged 2.57 kgC/ha/h, with about 85% from the forest floor. During the daytime, CO2 was taken up at a mean rate of 4.4 kgC/ha/h. Net ecosystem uptake of carbon dioxide increased with solar flux by 0.015 (kgC/ha/h)/(W m−2), corresponding to fixation of 0.0076 moles CO2 per mole photons (about 0.017 moles CO2 per mole of absorbed photons at photosynthetically active wavelengths). The relationship between net ecosystem exchange and solar flux was virtually the same in the Amazon forest as in forests in Canada (Desjardins et al., 1982, 1985) and Tennessee (Baldocchi et al., 1987a,b). The relatively high efficiency for utilization of light (about 30% of the theoretical maximum) and the strong dependence of net CO2 uptake on solar flux suggest that light may significantly regulate net ecosystem exchange and carbon storage in the tropical forest. Changes in the distribution of cloud cover, associated for example with climatic shifts, might induce globally significant changes in carbon storage. Rates for uptake of O3 averaged 2.3×1011 molecules cm−2s−1 in the daytime (10 hours, 700–1700 hours), dropping by roughly a factor of 10 during the 14 hours from dusk to dawn. The mean O3 deposition velocity at 40 m was 0.26 cm s−1 in the night and 1.8 cm s−1 in the day. Diurnal variation of O3 deposition was regulated both by stratification of the atmospheric boundary layer and by stomatal response to light and water deficit. The total flux of O3 to the forest was limited largely by supply from the free troposphere above. Deposition of O3 to the forest canopy appears to be a regionally, and perhaps globally, important sink for tropospheric O3.
Use of a limited‐area model nested in a general circulation model for regional climate simulation over Europe
Authors: Giorgi Filippo , Marinucci Maria Rosaria , Visconti Guido
Published: February 2008

A limited‐area model (LAM) nested in a general circulation model (GCM) is applied to the simulation of wintertime (January) climate over Europe. The output of a coarse scale GCM is used to drive a high‐resolution LAM over an area including central and western Europe, the British Isles with adjacent oceans and the western Mediterranean. The models used are the Community Climate Model (CCM1) of the National Center for Atmospheric Research (NCAR) and the Pennsylvania State University /NCAR mesoscale model (MM4). The January climatology of a 10‐year simulation with the standard CCM1 at a 7.5°×4.5° (R15) longitude‐latitude resolution is first analyzed. The model simulates realistic average large‐scale circulations, major storm tracks, and large scale precipitation patterns over the region, although cyclogenesis over the Mediterranean is not captured due to the coarseness of the model topography. Using the output of the R15 simulation to provide driving lateral boundary conditions, 10 Januaries are simulated with the nested MM4 at 70 km grid point spacing, a spacing sufficient to resolve the main topographical features and coastlines of western Europe. Two storm cases simulated with the nested MM4 are discussed in detail, which show how the model captures cyclogenetic processes over the Mediterranean and in the lee of the Alps, and simulates realistic development of synoptic systems. Owing to its better representation of topography and coastlines, the nested MM4 produces a regional distribution of climatic variables such as precipitation, surface air temperature, cloudiness, and snow cover which is much more realistic than that of the driving CCM1 alone and compares well with high resolution observations.
Absorption measurements of oxygen between 330 and 1140 nm
Authors: Greenblatt Gary D. , Orlando John J. , Burkholder James B. , Ravishankara A. R.
Published: February 2008

The absorption spectrum of O2 and O2‐O2 collision pairs were measured over the wavelength range from 330 to 1140 nm using pressures of O2 from 1 to 55 atm at 298 K. Absorption cross sections, pressure dependences, band centers, and full widths at half maximum of the observed absorption bands centered at 343.4, 360.5, 380.2, 446.7, 477.3, 532.2, 577.2, 630.0, 688, 762, and 1065.2 nm are reported. The absorption bands centered at 360.5, 380.2, and 477.3 nm were also measured at 196 K and their temperature dependences were characterized.
Kelvin wave‐induced trace constituent oscillations in the equatorial stratosphere
Authors: Randel William J.
Published: February 2008

Kelvin wave induced oscillations in ozone (O3), water vapor (H2O), nitric acid (HNO3) and nitrogen dioxide (NO2) in the equatorial stratosphere are analyzed using Limb Infrared Monitor of the Stratosphere (LIMS) data. Power and cross‐spectrum analyses reveal coherent eastward propagating zonal wave 1 and 2 constituent fluctuations, due to the influence of Kelvin waves previously documented in the LIMS data. Comparison is made between a preliminary and the archival versions of the LIMS data (denoted V4 and V5, respectively); significant differences are found, demonstrating the sensitivity of constituent retrievals to derived temperature profiles. Because Kelvin waves have vanishing meridional velocity, analysis of tracer transport in the meridional plane is substantially simplified. Kelvin wave vertical advection is demonstrated by coherent, in‐phase temperature‐tracer oscillations, co‐located near regions of strong background vertical gradients. Regions of out‐of‐phase coherency between temperature and trace species are also observed which suggest temperature dependent photochemistry. The temperature‐ozone signatures in LIMS data are compared with a simple analytical model incorporating transport and photochemistry, and overall good agreement is found. These analyses provide a good cross‐check on the quality of satellite constituent retrievals in the tropics, and also allow simple testing of chemical model parameterization schemes.