bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical density layer as obstacle at solar wind ‐ Exospheric ion interaction
Authors: Sauer K. , Roatsch T. , Baumgärtel K. , McKenzie J. F.
Published: February 2008

Recent spacecraft observations near Venus and Mars have shown that the position and shape of the planetary bow shock do not agree well with predictions of gas dynamic models in which the obstacle boundary is defined by ionopause/magnetopause pressure balance estimations. In order to simulate some aspects of this problem, we have considered plasma flow into a "heavy" ion cloud, whose maximum density is comparable to that of the inflowing protons. A simple bi‐ion fluid model is used which takes into account the electrostatic coupling between protons and (heavy) ions of exospheric origin; magnetic field effects are ignored. One‐dimensional studies show that for subsonic flows, representing the post‐shock solar wind, a critical cloud density exist at which the flow is accelerated up to the bi‐ion sound speed. Above this critical value no continuous solutions exist. The flow behaviour in three dimensions was studied in an axially‐symmetric model. For overcritical clouds the "critical density layer" appears as an "obstacle" forming an extended proton cavity. The planetopause at Mars may find an explanation within the present model.
Heterogeneous conversion of N2O5 TO HNO3 on background stratospheric aerosols: Comparisons of model results with data
Authors: Considine David B. , Douglass Anne R. , Stolarski Richard S.
Published: February 2008

A two dimensional photochemical model is used to examine the effects of heterogeneous processing by a parameterized lower stratospheric sulfate aerosol layer on model calculations. The single reaction considered is N2O5 + H2O → 2HNO3, at a rate consistent with recent laboratory measurements. The calculations are compared with data, to see if the heterogeneous chemistry improves the agreement between model calculations and data. The data used are Limb Infrared Monitor of the Stratosphere (LIMS) measurements of HNO3 and NO2, and in situ measurements of NO, NOy, and ClO taken by the NASA ER‐2 aircraft. A contradictory picture results. With heterogeneous processing, model HNO3 agrees better with LIMS HNO3; however, LIMS NO2, and NO2/HNO3 agree more closely with the results of a standard gas‐phase calculation. High‐latitude NO/NOy from in situ measurements in winter also favor standard chemistry, while the seasonal variation of NO and NO2 are better represented when the heterogeneous reaction is included. ClO is also better simulated when the heterogeneous reaction is included. These comparisons suggest that the assumptions made to parameterize the sulfate aerosol chemistry result in a rate of heterogeneous processing that is too vigorous. However, the lack of consistency in the different comparisons leaves the situation ambiguous, and a definite conclusion is unwarranted.
The effect of slip on the flow of fluid through a fracture
Authors: Olsson William A.
Published: February 2008

To measure the changes in fluid volume flow rates through an artificial fracture undergoing slip, silicone oil was pumped through a sawcut in welded tuff in the radial flow geometry during rotary shear. The flow rates at constant normal stress and constant fluid pressure gradient were measured at different amounts of fracture slip. The fluid volume flow rate for a smooth fracture increases at first then decreases with ongoing slip. For a rougher fracture the flow rate decreases over the whole range of slip. The results have implications for fluid withdrawal from reservoirs and underground waste disposal.
Large‐scale penetration of Gulf Stream water onto the Continental Shelf north of Cape Hatteras
Authors: Gawarkiewicz Glen , Church Thomas M. , Luther George W. , Ferdelman Timothy G. , Caruso Michael
Published: February 2008

A hydrographic cruise on the continental shelf between Chesapeake Bay and Cape Hatteras on the east coast of the United States during the summer of 1990 revealed the presence of a large volume of Gulf Stream water. Gulf Stream water was observed on the shelf between the depths of 10 m to 30 m, and penetrated the shelfbreak front which normally separates the shelf water from slope water and Gulf Stream water. The layer of Gulf Stream water on the shelf extended 60 km north of Cape Hatteras, and reached at least as far shoreward as the 25 m isobath. Velocities of Gulf Stream water in the upper 110 m of the water column along the 1000 m isobath indicated a flow of 18 to 25 cm/s directed toward the northwest. The Gulf Stream water on the shelf was associated with low values of fluorescence, transmissivity, and nutrient concentrations relative to adjacent shelf water. The presence of the seasonal stratification during the summer may allow for mid‐level penetration of Gulf Stream water onto the continental shelf north of Cape Hatteras.
Impact of recent total ozone changes on tropospheric ozone photodissociation, hydroxyl radicals, and methane trends
Authors: Madronich Sasha , Granier Claire
Published: February 2008

Trends in total atmospheric ozone from 1979–1989 were analyzed to derive the corresponding changes in the tropospheric photodissociation rate coefficient J1 for the reaction O3 + hv (λ < 330 nm) → O2 + O(1D). Zonally and annually integrated trends in J1 are +3.8±2.9 % per decade in the Northern hemisphere and +4.1±2.7 % per decade in the Southern hemisphere. Changes in [OH] due to the J1 trends may have contributed to the slowing of atmospheric methane increases observed in recent years.
Solar energetic and shock‐accelerated particles observed between 1 and 4 AU by the Kiel Electron Telescope (KET) on board Ulysses
Authors: Wibberenz G. , Kunow H. , Müller‐Mellin R. , Sierks H. , Heber B. , Kallenrode M.‐B. , Raviart A. , Ferrando P. , Ducros R.
Published: February 2008

We present observations of solar energetic particles and shock‐accelerated particles observed by the Kiel Electron Telescope (KET) on board the Ulysses spacecraft in the time interval 26 October 1990 to mid November 1991. Prompt events with diffusive propagation were observed mainly at small radial distances while at larger distances shock‐related events became dominant. Particularly high intensities of high energy electrons and >30 MeV/n nuclei are observed at merged or double shocks. Slowly‐varying populations (SVP) with long time scales neither related to prompt events nor to local shock effects are a new feature at these intermediate distances.
ISEE 3 plasmoid and TCR observations during an extended interval of substorm activity
Authors: Slavin J. A. , Smith M. F. , Mazur E. L. , Baker D. N. , Iyemori T. , Singer H. J. , Greenstadt E. W.
Published: February 2008

On April 9–11, 1983, the ISEE 3 spacecraft was continuously located within the Earth's magnetotail for more than 36 hours at downstream distances of X= −76 to −80 Re. During this span of time, 12 major intervals of substorm activity were observed in the AL index with good ISEE 3 telemetry coverage for 11 of them. In addition, there were two small substorms outside of these intervals, both with complete observations in the distant tail. This unusual ISEE 3 data set provides a unique opportunity to test the predictions of the near‐Earth neutral line model. In particular, we examine the hypothesis that energy stored in the tail lobes during the growth phase is later dissipated, in part, through the release of one or more plasmoids following expansion phase onset. Clear growth phase enhancements in the lobe magnetic field intensity preceded the onsets of nine of the substorms. Plasmoids, or their lobe signatures, traveling compression regions (TCRs), were observed at ISEE 3 in association with all 11 of the major substorm intervals for which there were ISEE observations as well as for the two small substorms. No plasmoids or TCRs were observed in the absence of substorm activity. If these ISEE 3 observations are representative, then the release of plasmoids down the tail may be a feature common to all substorms.
Solar particle composition: Measurements in the March 1991 event at 2.5AU
Authors: Lanzerotti L. J. , Maclennan C. G. , Gold R. E. , Hawkins S. E. , Tappin S. J. , Forsyth R.
Published: February 2008

The time evolution of the very large solar particle event occurring on days 82–90 (March 23–31), 1991, as measured at 2.5 AU by the instrumentation on the Ulysses spacecraft was quite complex. Measurements by the HI‐SCALE instrument of the nuclear composition (emphasizing Z≥6) of the interplanetary particles at a time resolution of two hours provides information on the different interplanetary regions which swept over the spacecraft. The Fe/O abundance ratio is found to differ slightly in the regions before and after two tangential discontinuities. The Fe/O abundance ratio is also found to depend strongly on the energy/nucleon of the particle, with values of ∼0.7 for energies of ∼0.5–1.0 MeV/nucl. to values of∼0.2 for energies ∼8–16 MeV/nucl.
The uncertainty in earthquake conditional probabilities
Authors: Savage J. C.
Published: February 2008

The Working Group on California Earthquake Probabilities (WGCEP) questioned the relevance of uncertainty intervals assigned to earthquake conditional probabilities on the basis that the uncertainty in the probability estimate seemed to be greater the smaller the intrinsic breadth of the recurrence‐interval distribution. I show here that this paradox depends upon a faulty measure of uncertainty in the conditional probability and that with a proper measure of uncertainty no paradox exists. I also challenge the assertion that the WGCEP probability assessment in 1988 correctly forecast the 1989 Loma Prieta earthquake by showing that posterior probability of rupture inferred after the occurrence of the earthquake from the prior WGCEP probability distribution reverts to a nearly informationless distribution.
Gas exchange in a contaminated estuary inferred from chlorofluorocarbons
Authors: Clark Jordan F. , Simpson H. James , Smethie William M. , Toles Chris
Published: February 2008

A new method of quantifying mean rates of gas exchange for natural water systems using the distribution of pollutant chlorofluorocarbons (CFCs) is presented. Concentrations of dissolved CCl3F (F‐11), CCl2F2 (F‐12), and CC12FCC1F2 (F‐113) in the Hudson estuary are supersaturated with respect to the remote troposphere by as much as an order of magnitude. The most plausible source appears to be discharges from waste water treatment facilities. Loss of these compounds from the estuary water to the atmosphere occurs both upstream and downstream of the zone of input. Using a multi‐box model, gas exchange coefficients were calculated to be between 2 and 4 cm hr−1 based on the observed concentrations. This rate of gas exchange is similar to values determined in lakes and coastal bays and substantially lower than the mean value for the open ocean.
The interannual variability of trace gases in the stratosphere: A comparative study of the LIMS and UARS measurement periods
Authors: Gray L. J. , Ruth S.
Published: February 2008

The inter‐annual variability of trace gases in the equatorial lower stratosphere is examined in order to explore the usefulness of comparisons between measurements from LIMS and the UARS satellite instruments. The quasi biennial oscillation (QBO) is simulated in a two dimensional model by relaxing the modelled equatorial winds towards observed values. It is shown that during the LIMS data period the QBO was in the opposite phase to that expected during the first winter of the UARS measurements. The model predicts that LIMS measurements of ozone, NO2, and HNO3 may have been up to 30% less than the long‐term average in the equatorial lower stratosphere while the first few months of UARS measurements may observe abundances up to 30% more than the long‐term average. The importance of taking this variability into account and the desirability of several complete cycles of the QBO in the derivation of climatological values is noted.
Propagation velocity of shockwaves and pressure waves in soil and rock
Authors: Majtenyi Steven I. , Foster Eugene L.
Published: February 2008

A variable pressure wave propagation velocity is developed and analyzed in ground materials which may be characterized by an exponential density ‐ pressure relationship. The peak overpressure dependence is minor in the low pressure range and the propagation velocity of the pressure wave is essentially a constant, in fact, it is the seismic P‐wave propagation velocity. Pressure dependence becomes increasingly more significant at peak overpressures exceeding 1 kbar (108 Pa). At very high pressure levels encountered only in shockwaves at and above 10 kbar (109 Pa), the initial mechanical characteristics of the ground materials become less significant, and the propagation velocity depends primarily upon the peak overpressure.
Multi‐satellite observations of plasmoids: IMP 8 and ISEE 3
Authors: Moldwin Mark B. , Hughes W. Jeffrey
Published: February 2008

An examination of IMP 8 and ISEE 3 magnetotail data during the 1983 Geotail Mission yielded one plasmoid event which was observed by both satellites and two other possible cases. These are the first multi‐satellite observations of plasmoids. These observations provide a unique opportunity to examine how plasmoid characteristics change as plasmoids propagate downtail and they show that plasmoids are very stable structures.
Asymmetry of the mantle structure beneath the Mid‐Atlantic Ridge
Authors: Goslin Jean , Aslanian Daniel
Published: February 2008

Altimetry data from repetitive orbits of the GEOSAT satellite are interpreted together with sea‐floor depths over the Mid‐Atlantic Ridge, South of Iceland and South of the Azores. Geoid / Topography ratios indicate a strong asymmetry of the upper mantle structure in oceanic areas created since 35 My, extending several hundreds kilometers from Iceland to the Azores. A model including interaction between the MAR and two layers of mantle convection seems adequate to produce the observed asymmetry.
Atmospheric excitation of polar motion during the GIG '91 Measurement Campaign
Authors: Gross Richard S. , Lindqwister Ulf J.
Published: February 2008

Daily determinations of the Earth's pole position from Global Positioning System (GPS) observations acquired during the first GPS IERS and Geodynamics (GIG) experiment held during January 22, 1991 to February 13, 1991 are interpreted in terms of atmospheric wind and pressure fluctuations as parameterized by the atmospheric angular momentum (AAM) χ‐functions. All available AAM χ‐functions spanning the GIG '91 period have been collected and compared to the observations in the time and polar motion domains. The greatest level of agreement is obtained using the total (wind plus pressure) χ‐functions from the Japanese Meteorological Agency (JMA) where the pressure term is computed by assuming the inverted barometer approximation. In this case, the correlation coefficient between the observed and JMA‐induced polar motion series is 0.91 for the x‐component and 0.72 for the y‐component, the rms of the difference between the observed and JMA‐induced series is 0.71 mas for the x‐component and 0.69 mas for the y‐component, and the percentage of the variance of the observed series explained by the JMA‐induced series is 83% for the x‐component and 48% for the y‐component. Thus, it is demonstrated that atmospheric wind and pressure fluctuations are largely responsible for exciting the rapid polar motions observed during GIG '91.
Fractal structures as least energy patterns: The case of river networks
Authors: Rodriguez‐Iturbe Ignacio , Rinaldo Andrea , Rigon Riccardo , Bras Rafael L. , Ijjasz‐Vasquez Ede , Marani Alessandro
Published: February 2008

Natural drainage networks, like river basins, exhibit fractal and multifractal properties. This work shows that these properties evolve from arbitrary initial conditions by minimizing the local and global rates of energy expenditure in the system. This suggests that many fractal structures may arise as a natural consequence of least energy dissipation requirements.
Acoustic Doppler current profiling along the Pacific Equator from 95°W to 165°E
Authors: Eldin Gérard , Morlière Alain , Reverdin Gilles
Published: February 2008

Acoustic Doppler current profiler and CTD data were collected in the equatorial Pacific, from 95W to 165E, during the ALIZE2 cruise, in January–March 1991. These data provide a quasi‐synoptic picture of both currents and hydrology of this region. The Equatorial zonal and meridional current structures and associated density distribution are presented and compared with previous measurements. The Equatorial Undercurrent appears stronger and shallower than climatology in the eastern Pacific, but close to average in the west. Intense 20–30 day period oscillations are noticeable east of 140W. Wind measurements and dynamic height computations are used to estimate some terms of the zonal momentum balance along the Equator.
A model for the production of Jupiter's decametric modulation lanes
Authors: Imai K. , Wang L. , Carr T. D.
Published: February 2008

We present an interference‐screen model for the production of the modulation lanes often observed in Jupiter's decametric radiation. As radiation traverses a grid‐like screen composed of field‐aligned columns of enhanced plasma density downstream from Io, rays scattered on passing through the columns interfere constructively and destructively with those passing relatively unscattered between columns. Due to the geometrical relationship between the radio‐emitting flux tube and the interference screen, the resulting rotating lobe pattern received at Earth synthesizes modulation lanes that very closely match those actually observed.
Assessment of pollutant emission inventories by principal component analysis of ambient air measurements
Authors: Buhr M. P. , Trainer M. , Parrish D. D. , Sievers R. E. , Fehsenfeld F. C.
Published: February 2008

The emission ratios of [CO]/[NOx] and [SO2]/[NOx] in point and area type sources in the northeastern United States are estimated through a combination of principal component and bivariate regression analyses of concurrent measurements of [CO], [SO2], [NOx], and [NOy] made at a rural Pennsylvania field site during the summer of 1988. Principal component analysis is used to identify time periods when the covariation of [NOy] with either [CO] or [SO2] indicates that the air mass was dominated by emissions from either area or point type sources, respectively. A regression analysis is used to extrapolate the observed pollutant ratios to the emission ratios. The resulting emission ratios compare reasonably well with emission ratios derived from the 1985 NAPAP (National Acid Precipitation Assessment Program) emissions inventory, although this analysis indicates that the NAPAP inventory may underestimate the [CO]/[NOx] emission ratio for area sources by a factor of 1.0 to 2.2 (95% confidence limits).
Detection of polar stratospheric clouds from NOAA‐HIRS data: A case study
Authors: Meerkoetter R.
Published: February 2008

A bispectral approach for temperature determination of semitransparent clouds is taken to identify areas covered by Polar Stratospheric Clouds (PSCs). The method is based upon the information obtained from two satellite pixels and two spectral channels of the passive HIRS instrument onboard the NOAA satellites. Since PSCs form and emit in very cold stratospheric environments (<195 K) solutions of the bispectral method yield low temperatures in a range that clearly differs from those derived for a cold but cloudfree stratosphere. Application of the method to NOAA satellite data gained during the major PSC event on January 31 1989 demonstrates that large areas covered by dense PSCs are found with a horizontal distribution in very good agreement to independent airborne and satellite measurements.
Venus: Satellite orbital decay, ephemeral ring formation, and subsequent crater production
Authors: Bills Bruce G.
Published: February 2008

The remarkable state of preservation of Venus impact craters may reflect their recent origin from a circumplanetary source, rather than a recent decline in resurfacing efficiency. Many of the craters observed on Venus may have been produced by impacts of particles on tidally decaying, high inclination orbits about the planet, rather than asteroidal or cometary debris on heliocentric orbits. A single satellite with radius of 100–200 km, and initial orbital distance of 15–20 times the radius of Venus could have been the original source for all of the impacting material. Over a fairly wide range of initial conditions and tidal evolution models, the transfer of angular momentum from the satellite orbit to the planetary spin leads to a situation in which the satellite passes inside the Roche limit at high inclination to the equator of Venus. After the satellite is tidally disrupted, the fragments quickly spread out over the orbital path, and differential precession forms a partial shell of material. Subsequent collisional damping of relative inclinations collapses the particles into a flat ring, with one of three possible stable orientations; prograde equatorial, retrograde equatorial, or perpendicular to the equatorial plane. Rapid radial inflow accompanies collapse into either equatorial ring. Initial inclinations greater than 30° at the time of disruption will lead to impact onto the surface during ring formation. Fragmentation reaches a steady state when the largest remaining particles have radii of 10–20 km. Bilateral symmetry of ejecta patterns reflect grazing impacts.
The 1991 Antarctic Ozone Hole; TOMS observations
Authors: Krueger Arlin , Schoeberl Mark , Newman Paul , Stolarski Richard
Published: February 2008

The 1991 Antarctic springtime ozone decline, as measured by the Total Ozone Mapping Spectrometer (TOMS), was similar to those of earlier deep ozone hole years, 1987, 1989, and 1990. The minimum total ozone value was recorded on October 5, 1991 at 108 Dobson units near the South Pole. This was 8 DU lower than in any of the earlier years. Four of the last five years have exhibited an extensive, deep ozone hole. The area of the hole was about the same as in 1987, 1989, and 1990. The recovery of the low total ozone values occurred in mid‐November as the polar vortex broke up.
Thermal expansion of molten Fe2SiO4 at high pressure
Authors: Agee Carl B.
Published: February 2008

The density of molten Fe2SiO4 has been bracketed at 1573,1673,1773, and 1873K in the pressure range 1.1 to 1.6 GPa by observing sinking and floating ruby buoyancy markers in piston‐cylinder experiments. From these data a coefficient of thermal expansion
K−1 was calculated from the relationship:

where dρ/dP=0.09±0.01 g cm−3 GPa−1 [Agee, 1992]. The high pressure thermal expansion result for molten Fe2SiO4 reported here is in excellent agreement with the coefficient of thermal expansion (α=7.13×10−5 K−1) from Shiraishi et al. [1978] done at 105 Pa by the double‐bob Archimedean method using iron crucibles in a stream of argon, and the ultrasonically derived (∂α/∂P)T=− 1.8×10−5 K−1 GPa−1 from Rivers and Carmichael [1987].
strong Langmuir turbulence at Jupiter?
Authors: Cairns Iver H. , Robinson P. A.
Published: February 2008

Langmuir wave packets with short scale lengths l ≲ 100λe have been observed in Jupiter's foreshock. We assess whether the observations are consistent with the relatively new nucleation mechanism for nonlinear collapse of Langmuir waves. Theoretical constraints on the electric fields and scale sizes of collapsing wave packets are summarized, extended and placed in a form suitable for easy comparison with Voyager and Ulysses data. The published data are reviewed and possible instrumental underestimation of fields discussed. New upper limits for the fields of the published wave packets are estimated. Our results are: (1) Wave packets formed at the nucleation scale from the observed large‐scale fields cannot collapse because they are disrupted before collapse occurs. (2) The published wave packets are quantitatively inconsistent with strong turbulence collapse. (3) Strict constraints exist for more intense wave packets to be able to collapse: E ≳ 1 – 8 mV m−1 for scales l ≲ 1000λe. Means for testing these conclusions using Voyager and Ulysses data are suggested.
Continuous monitoring of ultrafine aerosol emissions at Mt. Etna
Authors: Ammann Markus , Scherrer Leo , Mueller Wolfgang , Burtscher Heinz , Siegmann Hans‐Christoph
Published: February 2008

For the first time, ultrafine volcanic aerosols are monitored continuously by Photoelectric Charging of Particles (PCP) at Mt.Etna, Sicily. The measured quantity, the photoelectric activity of the aerosols, ε, is a measure of the relative copper content in the nanometer sized particles and may be related to the release of chlorides from magma. A monitoring system was set up in the plume of Mt.Etna in 1991. The data show a connection to the volcanic activity. Events of magmatic activity on a short time scale of 45 sec as well as the general evolution over several months are apparent.
Cause of low velocity anomaly along the South Atlantic hotspots
Authors: Tanimoto Toshiro , Zhang Yu‐Shen
Published: February 2008

A recent upper‐mantle seismic velocity model shows a narrow strip of asthenospheric low velocity anomaly in the South Atlantic that connects four hotspots, Tristan da Cunha, St. Helena, Ascension and Cape Verde. This deep strip of slow velocity anomaly runs approximately along the seam where Africa and South America broke up, according to available plate reconstruction models. There is, thus, a possibility that the deep, slow velocity strip is preserving the shape of the boundary along which the break‐up occurred. If this is the case, it will be a useful constraint in the reconstruction of plates. A question arises, however, as to why there is a line of low velocity anomaly rather than localized low velocity anomalies near hotspots. We propose three possible causes for this observation, which are (1) upwelling along this line, (2) lithosphere‐controlled passive breakup and (3) plume controlled breakup with lateral channeled flow from plumes to the seam of breakup, when rifts were created between adjacent hotspots. We favor the last hypothesis since it naturally explains the local velocity minimums near hotspots as well as the connected low velocity anomaly and, furthermore, the same mechanism seems to be working under the Red Sea in the present Earth.
Periodic auroral events at the midday polar cap boundary: Implications for solar wind‐magnetosphere coupling
Authors: Sandholt P. E. , Moen J. , Opsvik D.
Published: February 2008

An interesting observed phenomenon of day‐side auroral activity is the periodic sequence of moving bright forms observed at the polar cap boundary during southward‐directed interplanetary magnetic field (IMF) conditions. The optical events reported here are elliptical‐shaped bright 630.0 nm forms of ∼ 200 km (N‐S) × 300–500 km (E‐W) spatial extent. They move eastward near the noon meridian with velocities of ∼ 1.5 km s−1 and repeat at intervals of 5–10 min. Coordinated ground and satellite observations show that these auroral forms slow down and fade out after ∼ 10 min., within the region of mantle precipitation. The present ground observations support the earlier indication that the direction of east‐west motion along the polar cap boundary at/near magnetic noon is determined by the IMF By polarity, consistent with models of field tension on magnetic flux tubes connected with the solar wind. The optical characteristics of the events documented here may have important implications for the nature of magnetic merging at the magnetopause and the associated transfer of energy and momentum to the ionosphere in the cusp/mantle region.
Mean electromotive force generated by asymmetric fluid flow near the surface of Earth's outer core
Authors: Bhattacharyya Archana
Published: February 2008

The ф‐component, ϵф, of the mean electromotive force
generated by asymmetric flow of fluid just beneath the core‐mantle boundary (CMB), is obtained using a geomagnetic field model. This analysis is based on the supposition that the axisymmetric part of fluid flow beneath the CMB is tangentially geostrophic and toroidal. For all the epochs studied, the computed ϵф is stronger in the southern hemisphere than that in the northern hemisphere. Assuming a linear relationship between
and the azimuthally averaged magnetic field
, the only non‐zero off‐diagonal components of the pseudotensor αijrelating
to
, are estimated as functions of colatitude θ and the physical implications of the results are discussed.
Raman lidar measurements of Pinatubo aerosols over southeastern Kansas during November‐December 1991
Authors: Ferrare R. A. , Melfi S. H. , Whiteman D. N. , Evans K. D.
Published: February 2008

Raman lidar measurements over southeastern Kansas of stratospheric aerosols produced by the June 1991 eruptions of Mt Pinatubo were made on 10 nights during November and December 1991. Both aerosol backscattering and extinction profiles were derived simultaneously from the lidar data since this system detects Raman scattering from nitrogen and oxygen as well as the backscattered light from aerosols and molecules. Aerosol scattering ratios greater than 3 (at 351 nm) were measured on several nights. Peak aerosol concentrations were located between 19‐22 km and varied significantly from night to night. Aerosol extinction/backscatter ratios computed from the lidar data and averaged over the altitude region of enhanced aerosol scattering between 15‐25 km varied between 18‐28 sr. Mie computations show these values to be consistent with scattering by aerosol particles with mode radii between 0.3 to 0.5 µm and that the ratios would increase to 40‐65 sr at 694 nm. Aerosol optical thicknesses derived from the lidar extinction measurements at 351 nm varied between 0.04 and 0.06.
First observation of mesopause temperatures lower than 100°K
Authors: Schmidlin F. J.
Published: February 2008

Falling sphere measurements were part of a study to investigate the relationship between Noctilucent Clouds and Polar Mesospheric Summer Echoes within the context of interactions between the ionized and the neutral atmosphere. During this investigation there was one measurement of a very low mesopause temperature. This temperature is believed to be the lowest value ever observed in the terrestrial environment. The reasons why this cold mesopause measurement is considered to be valid are presented.
Chloro‐iodomethane in N. Atlantic waters: A potentially significant source of atmospheric iodine
Authors: Moore Robert M. , Tokarczyk Ryszard
Published: February 2008

Measurements have been made of chloroiodomethane (CH2ClI) in seawater samples collected in the N.W. Atlantic. Elevated concentrations (> 3 ng/ L) were found in surface waters at a number of locations in the pelagic zone. Background surface concentrations in the pelagic zone were 0.1–0.4 ng/L. Coastal/shelf regions averaged 0.1 ng/L off Labrador and Greenland, and 0.8 ng/L on the Grand Banks. We suggest that its distribution may be due to a phytoplankton source, either direct or indirect (i.e. via an intermediate compound). Using measurements of methyl iodide (CH3I) made on the same samples, we make a first order estimate of the comparative fluxes of the two compounds from ocean to atmosphere. This indicates that the iodine carried by CH2ClI may be comparable with that carried as CH3I. Refinement of the flux estimates requires measurements of atmospheric concentrations of CH2ClI, and determination of its Henry's Law constant.
Gaseous sulfuric acid and sulfur dioxide measurements in the Arctic troposphere and lower stratosphere: Implications for hydroxyl radical abundances
Authors: Möhler O. , Arnold F.
Published: February 2008

Measurements of gaseous sulfuric acid and sulfur dioxide were made in the winter arctic troposphere and lower stratosphere, using aircraft‐borne mass spectrometers. The measurements, covering altitudes between 3.5 and 11.4 km, took place on 14 and 18 February, 1987 in Northern Scandinavia. The abundance of H2SO4 was around 0.01 to 0.06 pptv (parts per trillion by volume) and the measured SO2 volume mixing ratios are around 50 to 400 pptv in the troposphere and decrease steeply above the tropopause to about 10 pptv. This decrease above the tropopause is in contrast to previous measurements showing constant or even increasing SO2 mixing ratios. The combined H2SO4 and SO2 measurements offer an interesting opportunity to infer hydroxyl radical concentrations. Inferred OH concentrations are around 0.1–1.0 × 105 cm−3 being roughly consistent with model predictions for winter time high latitudes.
Arctic ozone abundance and solar proton events
Authors: Shumilov O. I. , Henriksen K. , Raspopov O. M. , Kasatkina E. A.
Published: February 2008

In this study it is documented for the first time that the atmospheric ozone column density is decreased during solar proton events, GLEs (Ground Level Events), events with protons having energy exceeding 50 MeV and penetrating down to the ground. The ozone decrease was significant at the polar cap stations, Longyearbyen and Barentsburg at 78° N, whereas it was not detectable at the auroral zone stations Murmansk (69° N) and Tromsø (70° N). The duration of the depletion was limited to the days of the proton precipitation, and the depletion may be explained by the ability of energetic protons to produce nitric and hydrogen oxides in the stratosphere and their catalytic reactions with ozone. Similar events are identified in the Antarctic.
Observations of correlated behavior of stratospheric ozone and aerosol at Thule during winter 1991‐1992
Authors: di Sarra Alcide , Cacciani Marco , Di Girolamo Paolo , Fiocco Giorgio , Fuà Daniele , Knudsen Bjoern , Larsen Niels , Joergensen Torben S.
Published: February 2008

A lidar has been installed in Thule, Greenland, by the University of Rome in the fall of 1990. Intensive series of aerosol measurements have been carried out in the period early December 1991 – early March 1992, in the context of the European Arctic Stratospheric Ozone Experiment (EASOE). In the same period, several ozonesondes have been launched by the Danish Meteorological Institute. The arctic stratosphere appears loaded with aerosol following the Mt. Pinatubo eruption of June 1991. Scattering ratios as high as 5 have been observed. Both the aerosol and ozone profiles display a layered structure, with a large variability: the aerosol and ozone contents in the layers frequently appear to be negatively correlated, particularly in the height region around 16 km. Fluctuations of the ozone content as high as 50% of the average value have been observed in levels where aerosol layers are present. These results bear a relation to those obtained in past studies of the Mount Agung and El Chichón eruptions, and in observations of Polar Stratospheric Clouds obtained at South Pole.
Equatorial plasma bubbles/range spread F irregularities and the QBO
Authors: Chen Pei‐Ren
Published: February 2008

Investigation of the relationship between the percentage occurrence of equatorial plasma bubbles/range spread F irregularities (EPBRSI) and the Quasi‐Biennial Oscillation (QBO) of the lower‐stratospheric mean zonal wind in the equatorial zone reveals a QBO‐modulation effect on the percentage occurrence of the EPBRSI. A longitudinal dependence of this QBO‐modulation effect has also been found: the percentage occurrence of EPBRSI increases (decreases) in the easterly phase of the QBO in the Indian‐East African sector (in the American sector) and decreases (increases) in the westerly phase of the QBO in the Indian‐East African sector (in the American sector). It is suggested that this represents new evidence that the low‐latitude ionosphere is modulated by atmospheric planetary waves from below.
Nongyrotropy as a source of instability and mode coupling
Authors: Brinca A. L. , Borda de Água L. , Winske D.
Published: February 2008

Nongyrotropic particle populations can bring about linear mode coupling in homogeneous media among the three eigen‐modes of parallel propagation in gyrotropic magnetoplasmas. These interactions stimulate, in general, wave activity that does not occur in corresponding (random gyrophase) gyrotropic ambients. Solutions of the dispersion equation illustrate that simple introduction of gyrophase organization can (i) excite electrostatic (and electromagnetic) perturbations in media whose free energy sources are solely electromagnetic, and (ii) drive hybrid (both electrostatic and electromagnetic) wave growth in thoroughly stable Maxwellian plasmas.
Volcanic aerosol and ozone depletion within the Antarctic polar vortex during the austral spring of 1991
Authors: Deshler T. , Adriani A. , Gobbi G. P. , Hofmann D. J. , Di Donfrancesco G. , Johnson B. J.
Published: February 2008

In the spring of 1991 the Antarctic lower stratosphere was characterized by a layer of volcanic aerosol from the Cerro Hudson eruption. This aerosol layer was observed from McMurdo Station, Antarctica, with both lidar and balloonborne particle counters beginning around 10 September. After 20 September the aerosol was observed daily between 9 and 13 km. In this layer homogeneous nucleation of new aerosol was observed with concentrations > 6000 cm−3. Comparisons of scattering ratio calculated from measured particle size distributions agree best with the lidar measurements when a real index of refraction near 1.5 is used. In the past 5 years of measurements, ozone below 13 km has been relatively unchanged during the annual Antarctic ozone depletion; however, in 1991 ozone below 13 km decreased at a rate of 4 – 8 ppb day−1 over 30 days. This change began shortly after the appearance of the volcanic aerosol, providing direct measurements correlating volcanic aerosol and ozone depletion.
Tropical cyclone frequencies inferred from Gray's yearly genesis parameter: Validation of GCM tropical climates
Authors: Ryan Brian F. , Watterson Ian G. , Evans Jenni L.
Published: February 2008

The Gray Yearly Genesis Parameter (YGP) is an empirical diagnostic tool used to infer regions in which necessary (but not sufficient) conditions exist for tropical cyclone development. This parameter is used here as a measure of the implied tropical cyclone frequency and area of occurrence in climate simulations generated by a General Circulation Model (GCM). In a simulation of the current climate, the CSIRO9 GCM shows reasonable agreement with the original Gray climatology. The YGP for a doubled CO2 simulation is presented.
N(2P) in the dayglow: Measurement and theory
Authors: Torr Marsha R. , Torr D. G. , Richards P. G.
Published: February 2008

During the ATLAS‐1 mission, the first dayglow altitude profiles were obtained of the N(2P) emission at 3466 Å. These observations were made in the sunlit thermosphere using the Imaging Spectrometric Observatory. As all previous work on this emission has been done under auroral conditions, this study represents the first examination of the photochemical sources and sinks of N(2P) in the normal daytime thermosphere, with comparison with measurements. We find that the observations are explained by a model in which the major source is photodissociation of N2, and quenching by O is the principal low‐altitude loss process, with radiative decay to N(2D) dominating above 200 km. As the dominant loss processes are likely to result in the production of N(2D), N(2P) could be a moderate source of N(2D) and may be a factor to be taken into consideration in modeling NO.
Heat flow anomaly in Lesotho: Implications for the southern boundary of the Kaapvaal Craton
Authors: Jones M Q W
Published: February 2008

Heat flow studies in southern Africa reveal a pattern of low heat flow in Archean cratons compared with Proterozoic mobile belts that provides grounds for modeling in which cratons have lower mantle heat flux and greater lithospheric thickness. There is little detailed information regarding thermal transitions across craton boundaries but new data from Lesotho provide insights into the nature of the boundary between the Kaapvaal craton and the Natal belt. Measurements at nine localities in a 90‐km‐long north‐south traverse show an increase of heat flow from typically cratonic values of about 45 mW m−2 in the north to about 80 mW m−2 where the craton abuts on the Natal belt in the south. The change occurs within 30 km, suggesting that the anomaly largely reflects an increase in radioactive heat from the upper crust in the orogenic front. The change in mantle heat flux across the boundary is probably considerably smaller. These and other results suggest that the surficial craton boundary is further north than usually depicted.
Moment spectra in a simple model of an earthquake fault
Authors: Shaw Bruce E.
Published: February 2008

The behavior of a simple one‐dimensional, homogeneous, deterministic model of an earthquake fault is examined on the timescale of the rupture process. The model generates a complex spatial and temporal distribution of events from a frictional instability. I measure the frequency spectra of the moment release rate for events of different sizes, and observe power laws for the spectra. A bend in the spectra of large events is also observed. The paper concludes with a discussion of how these results may be relevant to real earthquake faults.
Rayleigh waves guided by sea‐trench topography
Authors: Nakanishi Ichiro
Published: February 2008

A later phase of large‐amplitude is observed at a station in Hokkaido from several events of the December 1991 off‐Urup earthquake swarm in the Kurile Islands region. The phase is characterized by a narrow frequency‐band with a dominant period of about 15 s and retrograde particle motion in a vertical plane with a strike very different from the great‐circle direction between the station and the epicenter. The phase is observed from only the earthquakes that are located at shallow depths beneath the inner wall of the Kurile trench where sea depth is greater than 4 km. These characteristics indicate that the phase is a packet of Rayleigh waves that arrive at the station from an azimuth considerably different from the great‐circle direction. Rayleigh waves with periods around 15–20 s are well excited by the shallow earthquakes beneath the inner wall of the trench. This is supported by the dominance of a spectral peak at 15–20 s in the spectra of the direct Rayleigh‐waves and the later phase. Rayleigh waves that propagate in an oceanic region are strongly influenced by the thickness of the water layer at periods shorter than about 25 s. The group velocity decreases by 80% at 15 s with the increase of the sea depth from 4 km to 6 km. The sea‐trench topography therefore forms a strong low‐velocity zone. The observed later phase can be interpreted as a Rayleigh‐wave packet guided by this velocity complexity.
MF radar interferometry measurements of fluxes and Coriolis accelerations over Saskatoon (52° N, 107° W)
Authors: Hall G. E. , Meek C. E. , Manson A. H.
Published: February 2008

A new interferometry analysis of MF mesospheric radar scatter has been attempted. The experiment was run during local noon times for 17 days during the summer of 1989. The analysis yielded consistent values for the amplitude and direction of gravity wave fluxes. Also, the flux magnitudes found are in general agreement with that found in other studies. It is concluded that this interferometry analysis is very promising for gravity wave flux measurements.
Anisotropic ion heating and parallel O+ acceleration in regions of rapid E × B convection
Authors: Kőrösmezey Á. , Rasmussen C. E. , Gombosi T. I. , Khazanov G. V.
Published: February 2008

A numerical solution to the 20‐moment set of transport equations has been found in order to study subauroral ionospheric outflows during periods of enhanced perpendicular ion drifts. The numerical model solves the time‐dependent O+ density, momentum, and both the parallel and perpendicular energy and heat flow equations in the 200–6000 km altitude range. Assuming perpendicular drifts of 3 km/s relative to the neutral atmosphere, we have found that anisotropic heating of O+ (a result of ion‐neutral collisions) leads to a temperature anisotropy, with perpendicular temperatures exceeding 8000 K and parallel temperatures greater than 5000 K (near 200 km altitude). Above approximately 2000 km, transport processes dominate the effects of collisions and wavelike oscillations in O+ velocity, temperature and heat flux were noted.
The effect of stratospheric water vapor on the heterogeneous reaction rate of ClONO2 and H2O for sulfuric acid aerosol
Authors: Hofmann D. J. , Oltmans S. J.
Published: February 2008

Although it is well known that temperature affects the heterogeneous reaction probability (γ) of ClONO2 and H2O on suite acid aerosol surfaces by determining the amount of water which will co‐condense with H2SO4 vapor, the effect of the ambient water‐vapor concentration, which also affects the aerosol composition, has not been investigated in detail. A nearly constant stratospheric water vapor mixing ratio dictates that the water vapor partial pressure vary proportional to atmospheric pressure and thus increase rapidly in the lower stratosphere. In addition, the water vapor mixing ratio increases dramatically in the lower stratosphere following tropospheric‐stratospheric exchange. The increase in water vapor partial pressure results in a large increase in γ and may be a factor contributing to ozone destruction in the lower stratosphere. Comparison of the lifetime of ClONO2 to heterogeneous reactions with that expected from gas phase photochemistry is used to estimate the relative importance of these processes and indicates that winter and spring polar regions are the most likely to be affected.
Formation of the stable auroral arc that intensifies at substorm onset
Authors: Lyons L. R. , Samson J. C.
Published: February 2008

In a companion paper, we present observational evidence that the stable, growth‐phase auroral arc that intensifies at substorm expansion phase onset often forms on magnetic field lines that map to within ∼1 to 2 Re of synchronous. The equatorial plasma pressure is 1 to 10 nPa in this region, which can give a cross‐tail current > 0.1 A/m. In this paper, we propose that the arc is formed by a perpendicular magnetospheric‐current divergence that results from a strong dawn‐to‐dusk directed pressure gradient in the vicinity of magnetic midnight. We estimate that the current divergence is sufficiently strong that a > 1 kV field‐aligned potential drop is required to maintain ionospheric‐current continuity. We suggest that the azimuthal pressure gradient results from proton drifts in the vicinity of synchronous orbit that are directed nearly parallel to the cross‐tail electric field
Long path ftir spectroscopic study of the reactions of CF3O radicals with ethane and propane
Authors: Chen J. , Zhu T. , Niki H. , Mains G. J.
Published: February 2008

A long path FTIR‐based product study was carried out by the visible (λ > 400 nm) photolysis of mixtures containing CF3NO, NO and ethane or propane (in mtorr range) in 700 torr of synthetic air at 297 ± 2 K. Kinetic and spectroscopic evidence has been obtained for the reaction (1), CF3O + RH → CF3OH + R (RH = C2H6 or C3H8). Using the reaction (2), CF3O + NO → CF2O + FNO as the reference reaction, values for the relative rate constants k2/k1 were determined to be 50 ± 15(σ) and 20 ± 5(σ) for C2H6 and C3H8, respectively. These results suggest that the hydrocarbon reactions may provide a significant pathway for the tropospheric degradation of HFCs and HCFCs containing a CF3 group.