bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetosheath‐ionospheric plasma interactions in the cusp/cleft: 1, Observations of modulated injections and upwelling ion fluxes
Authors: Winglee R. M. , Menietti J. D. , Peterson W. K. , Burch J. L. , Waite J. H. , Giles B.
Published: February 2008

Insitu observations of the cusp/cleft are important as they allow a direct investigation of coupling solar wind energy to the ionosphere, plus they provide an opportunity for the remote sensing of the magnetopause. High time resolution observations from DE 1 are used to investigate these processes. It is shown that in the spacecraft frame the injection is modulated or pulsating with a period of approximately 18 ‐ 30 s with the injection duration possibly being as short as 6 s. This modulation indicates that there may be fast time scale and/or short scale length processes modulating the injection of the magnetosheath plasma across the magnetopause. In addition, the pulsating injection is seen to modulate the outflow of upwelling ionospheric ions to the magnetosphere. These upwelling ions are seen prior to the magnetosheath ion injection and therefore are not directly created by the injection. During the injection itself, the intensity of the upwelling ions is seen to dramatically decrease but their average energy increases. At end of the magnetosheath injections, the intensity of the upwelling ion flux is seen to increase to levels comparable to levels prior to the magnetosheath injection. On two occasions during the encounter, the particle fluxes are sufficiently high that enhanced downward flows of perpendicularly heated ions, of presumably ionospheric origin, are observed in association with a reduction in the intensity of the upwelling ions. These observations are probably the first detection of downward conics and suggest that there is momentum transfer between the magnetosheath and ionospheric ions. This momentum transfer eventually leads to an enhanced outflow of heated ionospheric plasma where their energy has been raised from a few tens of eV to a few hundred eV.
Magnetosheath‐ionospheric plasma interactions in the cusp/cleft: 2, Mesoscale particle simulations
Authors: Winglee R. M. , Menietti J. D. , Lin C. S.
Published: February 2008

Ionospheric plasma flowing out from the cusp can be an important source of plasma to the magnetosphere. One source of free energy that can drive this outflow is the injection of magnetosheath plasma into the cusp. Two‐dimensional (three velocity) mesoscale particle simulations are used to investigate the particle dynamics in the cusp during southward interplanetary magnetic field. This mesoscale model self‐consistently incorporates (1) global influences such as the convection of plasma across the cusp, the action of the mirror force, and the injection of the magnetosheath plasma, and (2) wave‐particle interactions which produce the actual coupling between the magnetosheath and ionospheric plasmas. It is shown that, because the thermal speed of the electrons is higher than the bulk motion of the magnetosheath plasma, an upward current is formed on the equator ward edge of the injection region with return currents on either side. However, the poleward return currents are the stronger due to the convection and mirroring of many of the magnetosheath electrons. The electron distribution in this latter region evolves from upward directed streams to single‐sided loss cones or possibly electron conics. The ion distribution also shows a variety of distinct features that are produced by spatial and/or temporal effects associated with varying convection patterns and wave‐particle interactions. On the equatorward edge the distribution has a downflowing magnetosheath component and an upflowing cold ionospheric component due to continuous convection of ionospheric plasma into the region. In the center of the magnetosheath region, heating from the development of an ion‐ion streaming instability causes the suppression of the cold ionospheric component and the formation of downward ionospheric streams. Further poleward there is velocity filtering of ions with low pitch angles, so that the magnetosheath ions develop a ring‐beam distribution and the ensuing wave instabilities generate downward ionospheric conics. These downward ionospheric components are eventually turned by the mirror force, leading to the production of upward conies at elevated energies throughout the region.
Experimental investigation of possible geomagnetic feedback from energetic (0.1 to 16 keV) terrestrial O+ ions in the magnetotail current sheet
Authors: Lennartsson O. W. , Klumpar D. M. , Shelley E. G. , Quinn J. M.
Published: February 2008

Data from energetic ion mass spectrometers on the ISEE 1 and AMPTE/CCE spacecraft are combined with geomagnetic and solar indices to investigate, in a statistical fashion, whether energized O+ ions of terrestrial origin constitute a source of feedback which triggers or amplifies geomagnetic activity, as has been suggested in the literature, by contributing a destabilizing mass increase in the magnetotail current sheet. The ISEE 1 data (0.1‐16 keV/e) provide in situ observations of the O+ concentration in the central plasma sheet, inside of 23 RE, during the rising and maximum phases of solar cycle 21, as well as inner magnetosphere data from same period. The CCE data (0.1‐17 keV/e), taken during the subsequent solar minimum, all within 9 RE, provide a reference for long‐term variations in the magnetosphere O+ content. Statistical correlations between the ion data and the indices, and between different indices, all point in the same direction: there is probably no feedback specific to the O+ ions, in spite of the fact that they often contribute most of the ion mass density in the tail current sheet.
Evaluation of interplanetary magnetic helicity effects on particle propagation at times of observed solar proton events
Authors: Valdés‐Galicia J. F. , Otaola J. A. , Saulés G.
Published: February 2008

Power and helicity density spectra of the interplanetary magnetic field (IMF) are determined from data measured on board Helios spacecraft at times of three solar proton events (SPE) when they were at heliocentric distances ranging from 0.3 to 0.5 AU. The events were selected to represent different levels of perturbation in the IMF. The obtained spectra are also different in the three cases. These are used to calculate pitch angle scattering coefficients according to the classical quasi‐linear theory (QLT) treatment of particle propagation in fluctuating fields. Results reflect that in the three cases helicity effects are negligible and the energetic particle mean free paths deduced from the pitch angle diffusion coefficients are the same regardless of whether helicity effects are or are not included in the calculation. Note, however, that the mean free paths calculated here are markedly different in each case, and all of them are larger than those deduced by Jokipii and Coleman [1968], commonly referenced as the QLT result.
Relativistic solar proton database for the ground level enhancements during solar cycle 22
Authors: Gentile Louise C.
Published: February 2008

A new software application called GLEINFO has been established to enable scientists who have remote networking capability to examine the computerized database of relativistic solar proton data for the ground level enhancements during Solar Cycle 22. This database was compiled in cooperation with principal investigators of the international network of neutron monitors to provide a consistent data set for detailed analysis of the processes involved in solar proton acceleration and propagation.
Water group ion distributions in the midcometosheath of comet Halley
Authors: Huddleston D. E. , Neugebauer M. , Goldstein B. E.
Published: February 2008

In the midcometosheath of comet Halley (1 × 105−2 × 105 km from the nucleus) the center‐of‐mass plasma frame is approximately the bulk flow velocity of the cometary ions, and the Alfvén wave speed is an appreciable fraction of the flow speed. Here, the peaks of the water group ion distributions observed by the Giotto ion mass spectrometer are at velocities consistently below the expected pickup speed. It is shown that this effect is consistent with the scattering of the new pickup ions onto a bispherical shell distribution. The model does not fit the data inside ∼1.2×105 km, however, possibly as a result of the growing importance of collisions or the presence of other processes such as scattering on obliquely propagating magnetosonic waves.
Structured plasma sheet thinning observed by Galileo and 1984‐129
Authors: Reeves G. D. , Belian R. D. , Fritz T. A. , Kivelson M. G. , McEntire R. W. , Roelof E. C. , Wilken B. , Williams D. J.
Published: February 2008

On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that it crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984‐129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near‐Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near‐Earth tail during the growth phase of substorms. This period is unique in that Galileo provided a rapid radial profile of the near‐Earth plasma sheet while 1984‐129 provided an azimuthal profile. With measurements from these two spacecraft we can distinguish between spatial structures and temporal changes. Our observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft's magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours.
Analysis of water level changes induced by fault creep at Parkfield, California
Authors: Rudnicki J. W. , Yin J. , Roeloffs E. A.
Published: February 2008

This paper demonstrates that the recovery rates of water level changes due to fault creep can be used to infer the position of the slipping zone relative to the well. This technique is applied to five slip‐related water level changes observed in a well 460 m from the San Andreas fault near Parkfield, California during January 1989 to July 1990. The water level changes are all characterized by a rapid drop (in less than 8 hours) and a slow recovery of 15 to 30 days. The water level drop and the position of the well constrain right‐lateral slip to be predominantly to the southeast of the well. The recoveries are modeled by pore fluid diffusion due to a plane strain dislocation in a porous, fluid‐saturated elastic solid. Satisfactory agreement with the observations is obtained by assuming slip occurs instantaneously and extends indefinitely to the southeast of the well. The extent of the slip northwest of the well, which ranges from zero to 322 m, is determined by fitting the variations in recovery times among the five events. Calculations are carried out for the limiting cases of both an impermeable and a permeable fault. The permeability of the fault has little effect on inferences about the slip, but the inferred (horizontal) diffusivity differs for the two cases: 0.15 m2/s for the impermeable and 0.06 m2/s for the permeable. For two of the events the magnitude and distribution of slip inferred from the water level changes agree well with that measured on two nearby creepmeters. For a third event the agreement is moderately good. Discrepancies for the remaining two events suggest that the surface slip measured by the creepmeters may differ significantly from that near the 240 m depth of the well.
Melting of forsterite, Mg2SiO4, from 9.7 to 16.5 GPa
Authors: Presnall Dean C. , Walter Michael J.
Published: February 2008

A multianvil apparatus has been used to determine the pressure‐temperature melting curve of forsterite from 9.7 to 16.5 GPa. At 10.1 GPa a singular point occurs that marks the change from congruent melting at lower pressures to incongruent melting (forsterite = periclase + liquid) at higher pressures. The melting curve also passes through two invariant points. At one (15.6 GPa, 2310°C), the phases forsterite, periclase, anhydrous B, and liquid coexist and the melting reaction changes from forsterite = periclase + liquid at lower pressures to forsterite = anhydrous B + liquid at higher pressures. At the other (16.7 GPa, 2315°C), the phases forsterite, modified spinel, anhydrous B, and liquid coexist, and the melting reaction changes from forsterite = anhydrous B + liquid at lower pressures to modified spinel = anhydrous B + liquid at higher pressures. The Simon equation, P(GPa) = 2.44[(T(°K)/2171)11.4 − 1], fits both our melting curve data and the lower pressure data of Davis and England (1964). At low pressures, the melting curve of forsterite lies at higher temperatures than that of enstatite, but the two curves cross at 13.3 GPa because of the lower dT/dP slope of the forsterite melting curve. This causes the forsterite‐enstatite eutectic to shift toward forsterite as pressure increases, but our data are consistent with earlier findings that the shift is not sufficient to support an origin for the mantle by eutectic‐like melting at high pressures.
The use of paleomagnetic analysis to assess nonbrittle deformation within the San Andreas Fault Zone
Authors: Nagy Elizabeth A. , Sieh Kerry E.
Published: February 2008

A recently developed paleomagnetic extraction technique successfully permits sample collection from unconsolidated sediments. Traditional measurement and demagnetization procedures can subsequently be performed, and several studies have already shown that soft‐sediment samples yield reliable magnetic polarity information. To test the robustness of the extraction technique, as well as the resolution limits of the resultant magnetic vector directions, a total of 238 paleomagnetic samples were taken from unconsolidated strata exposed in an excavation across the San Andreas fault zone in the Carrizo Plain, California. Variable fault offset values for the most recent earthquakes at this locality favored the likelihood of rotational, nonbrittle, deformation. Such deformation could possibly be recorded in the DRM (detrital remanent magnetization) of sediment deposited across the zone. Declination directions of sample groups taken from presumably unrotated strata show general agreement with the most recent secular variation curve constructed for southern California, supporting the assumption that the stratigraphic units sampled do record an accurate DRM. However, significant variations in declination directions are found between magnetically stable samples within sample groups (i.e., taken as close as 1 cm apart within the same stratigraphic horizon). Probable causes of such declination variations include postdepositional, physical disturbances associated with rupture events and errors generated by the sampling technique. Inadvertent sample rotation about the axis of the glass holders is one of the most evident sources of error found in this study, although only samples which underwent large rotations (> 60°) could be identified. Regardless of its origin, the variability of the magnetic declination directions found for the 29 magnetically stable groups forces us to conclude that paleomagnetic results calculated in this study are not precise enough to discern reasonable (< 20°) amounts of rotation. These results question a similar soft‐sediment study upon which this study was modeled which claims to have successfully detected less than 20° in rotational deformation using an identical sampling method. Additional studies are needed, preferably not within active fault zones, to better define sources of error for this relatively new soft‐sediment sampling technique and to determine its resolution limits for discerning small changes in paleomagnetic vector directions.
Dehydration and rehydration of a tuff vitrophyre
Authors: Vaniman D. , Bish D. , Chipera S.
Published: February 2008

The basal vitrophyre of the Topopah Spring Member of the Paintbrush Tuff at Yucca Mountain, Nevada, is a perlitic glass with 2.8 to 4.6% water. The dehydration of this vitrophyre was studied by thermogravimetric analysis (TGA) and by isothermal heating at 50°, 100°, 200°, and 400°C for 3.4 years followed by 1.1 years of rehydration at high controlled humidity (∼79% relative humidity). No crystallization of the glass was observed in long‐term dehydration or rehydration; the only observed chemical alteration was loss of up to 60% of original fluorine. TGA studies show a characteristic two‐stage dehydration of the vitrophyre, with two‐thirds to three‐fourths weight loss occurring most rapidly at temperatures ranging from 278° to 346°C in 10°C/min heating experiments. The remaining water, about 1% in all of the vitrophyre samples studied regardless of total water content, is lost only on second‐stage heating to temperatures above 650°C. Long‐term isothermal heating at ≤400°C releases only the first‐stage water. Loss of essentially all first‐stage water occurred in less than 1 hour at 400°C; proportionately lower losses were obtained at 200° and 100°C. Small (0.2%) water loss occurred in the 50°C experiment. A time‐temperature‐dehydration diagram generated from the isothermal heating data shows a clustering of dehydration contours that are the equilibrium equivalent of the rapid first‐stage water loss in dynamic TGA experiments. These dry‐heating experiments provide an end‐member characterization of glass transformations for comparison with water‐saturated heating experiments in which glass alteration is prominent.
A primitive equation ocean circulation model using a general vertical coordinate transformation: 2. Application to an overflow problem
Authors: Gerdes Rüdiger
Published: February 2008

The version of the ocean general circulation model of the Geophysical Fluid Dynamics Laboratory with a generalized vertical coordinate transformation introduced in part 1 is used to study the overflow of a zonal ridge in a coarse‐resolution grid typical for climate applications. The configuration roughly resembles the Greenland‐Scotland Ridge with respect to scale, latitude, and height of the ridge. Reasonable qualitative agreement with observed conditions over the Iceland‐Faroe section has been achieved, especially when a deeper passage was included at the eastern end of the idealized model ridge. Upwelling of deep water occurs at the eastern boundary, where friction and, more importantly, diapycnal diffusion accomplish the necessary changes in potential vorticity. The overflow consists of intermediate water when the renewal time for the deep water is made much larger than that for intermediate water. The meridional mass transport is most sensitive to geometric factors like the height of the ridge. Frictional and diapycnal processes are crucial for the potential vorticity conversion at the ridge and have a strong effect on the water mass distribution. Bottom friction increases the near‐bottom flow across f/H lines, resulting in a large amount of northern basin deep water south of the ridge. This effect can be represented only when the frictional bottom boundary layer is adequately resolved by the numerical grid.
Ventilation of the Atlantic Ocean equatorial thermocline
Authors: Reverdin Gilles , Weiss Ray F. , Jenkins William J.
Published: February 2008

The ventilation of the lower equatorial Atlantic thermocline (100 m to 400 m) is investigated from the distributions of salinity, oxygen, the chlorofluoromethanes F‐11 and F‐12, tritium, and the excess helium 3; 1983 data suggest a correlation on isopycnal surfaces between oxygen, chlorofluoromethanes and to a lesser extent, with the apparent ages derived from F‐ll/F‐12 and helium 3/tritium. The apparent ages increase with depth from 10 years on σΘ=26.5 to over 15 years near 400 m. The tracers are largely undersaturated with respect to the surface concentrations corresponding to the apparent ages. We investigate the ventilation processes responsible for these distributions with simple circulation models, where water from the subtropical gyres reaches isopycnally the equatorial thermocline. The few model parameters are determined by fitting the simulations to the chlorofluoromethane distributions in 1983. The sensitivity of these parameters to expected errors on the past surface concentrations and to vertical mixing is comparable and can result in an error of more than 20% in the model parameters. In 1983, model [3H] and [3He]* are too large, in particular when no diapycnal mixing is modeled, but the differences could have arisen from errors on past surface concentrations. During the 1980s, the model overestimates the increase in chlorofluoromethanes, in particular F‐12. The fitted model inflow from the southern subtropical gyre between 110 m and 400 m is 14×106 m3 s−1, in the range of expected transports by the western boundary current near Brazil. The model oxygen utilization rate is on the order of 12 mmol kg−1 yr−1 at 100 m and 5 mmol kg−1 yr−1 at 400 m (below σΘ=27.1).
Wind field model‐based estimation of Seasat scatterometer winds
Authors: Long David G.
Published: February 2008

A model‐based approach to estimating near‐surface wind fields over the ocean from Seasat scatterometer (SASS) measurements is presented. The approach is a direct assimilation technique in which wind field model parameters are estimated directly from the scatterometer measurements of the radar backscatter of the ocean's surface using maximum likelihood principles. The wind field estimate is then computed from the estimated model parameters. The wind field model used in this approach is based on geostrophic approximation and on simplistic assumptions about the wind field vorticity and divergence but includes ageostrophic winds. Nine days of SASS data were processed to obtain unique wind estimates. Comparisons in performance to the traditional two‐step (point‐wise wind retrieval followed by ambiguity removal) wind estimate method and the model‐based method are provided using both simulated radar backscatter measurements and actual SASS measurements. In the latter case the results are compared to wind fields determined using subjective ambiguity removal. While the traditional approach results in missing measurements and reduced effective swath width due to fore/aft beam cell coregistration problems, the model‐based approach uses all available measurements to increase the effective swath width and to reduce data gaps. The results reveal that the model‐based wind estimates have accuracy comparable to traditionally estimated winds with less “noise” in the directional estimates, particularly at low wind speeds. In addition, wind fields generated using the model‐based procedure can be used to detect and correct ambiguity removal errors in ambiguity‐removed point‐wise wind fields. A separate procedure, based only on the wind field model, can also be used as a data quality check to detect errors in point‐wise ambiguity removal.
Fluorescence of dissolved organic matter: A comparison of north Pacific and north Atlantic oceans during April 1991
Authors: Hoge Frank E. , Swift Robert N. , Yungel James K. , Vodacek Anthony
Published: February 2008

Profiles of airborne‐laser‐induced fluorescence emission from dissolved organic matter in the upper ocean have been produced and compared for the Southern California Bight (SCB) and the Mid‐Atlantic Bight (MAB). Findings were as follows. (1) The fluorescent components of dissolved organic matter (FDOM) are present in easily measurable quantities from near shore to well over 300 km offshore in the SCB and are likewise easily measurable in the coastal, shelf, slope, and Gulf Stream waters of the MAB. (2) The range of FDOM in the MAB is considerably greater than that in the SCB. (3) The lowest FDOM levels observed in the SCB were higher than those found in the Gulf Stream. (4) The onshore‐to‐offshore spatial gradient of the FDOM was found to be considerably lower in the SCB than in the MAB, with the highest levels of FDOM being found immediately adjacent to the coast in the MAB. This suggests that the water adjacent to the SCB shoreline is not as strongly influenced by terrestrial and estuarine sources of FDOM as the MAB is. (5) The spatial distribution of the FDOM within both the SCB and the MAB is frequently coherent with the spatial distribution of chlorophyll determined from the concurrent airborne‐laser‐induced phytoplankton pigment fluorescence measurements. However, distinct noncoherency is sometimes observed, especially at water mass boundaries.
Ray theory and the scattering of topographic Rossby waves by an abrupt change of shelf width and coastline
Authors: Ripa P. , Carrasco Ana C.
Published: February 2008

The scattering of topographic Rossby waves over a shelf that abruptly changes its width with a step‐shaped coast is studied by two methods: mode expansion (which in principle is exact) and ray theory. For the latter, we stress the importance of evaluating the phase field instead of limiting the results to the ray paths, as is often done. Ray theory is found to give a good approximation of the energy flux at low frequency and the correct location and strength of highs and lows of the transport function. However, ray theory predicts very sharp gradients of this field (which imply unrealistically high velocities) at the frontier of the region illuminated by a beam. These results suggest that ray theory may be an alternative, or complement, to numerical models for those scattering problems where a complicated topography and/or coastline prevents the use of the mode expansion method.
Lidar measurements of stratospheric aerosols during the SAGA 3 expedition
Authors: Kaufman Y. G. , Khmelevtsov S. S. , DeFoor Thomas E.
Published: February 2008

Backscatter lidar measurements of stratospheric aerosols were carried out over the tropical Pacific aboard the Akademik Korolev during SAGA 3 of February to March 1990. Measurements were made using a Maket 1 lidar system from the Institute of Experimental Meteorology. Regions of enhanced stratospheric backscatter, apparently from the February 10, 1991, eruption of Kelut (7.9°S, 112.3°E), were detected on several occasions. Integrated non‐Rayleigh backscatter at 532 nm between 16 km and 33 km ranged from a background value of 1.5 × 10−4 sr−1 to as high as 14.5 × 10−4 sr−1 in the volcanic plume. During the Akademik Korolev port of call at Hilo, Hawaii, at the start of SAGA 3, intercomparisons were attempted with the NOAA, ERL, CMDL Mauna Loa Observatory lidar located approximately 60 km SW at Mauna Loa Observatory (19.5°N, 155.6°W). The intercomparison results were encouraging but were inconclusive because of limited data and signal degradation resulting from poor observing conditions due to bad weather.
Fluxes of nitrogen oxides and ozone measured by eddy correlation over a shortgrass prairie
Authors: Stocker D. W. , Stedman D. H. , Zeller K. F. , Massman W. J. , Fox D. G.
Published: February 2008

The fluxes of NO2, NOy and ozone were measured by eddy correlation at a grassland field site from March 5 to August 2, 1988. The nitrogen oxide fluxes were generally small and upward during the day. Overnight, the fluxes were zero. The average daytime NO2 flux increased from 2.2 ng (N) m−2 s−1 during March and April (Julian days 65 to 121) to 5.7 ng (N) m−2 s−1 in June and July (Julian days 153 to 193). The average NOy flux for the period June 21 to August 2, 1988, was 7.6 ng (N) m−2 s−1 (Julian days 173 to 215). The largest fluxes were observed after rainstorms from drying surfaces, when the flux increased exponentially with soil temperature. Fluxes from dry soils were small and were not a strong function of soil temperature. The deposition of ozone, measured as oxidant to correct for homogeneous gas phase chemistry, showed a strong diurnal variation. The average daytime deposition velocity was 0.36 cm s−1 and 0.22 cm s−1 overnight. Surface resistance calculations show that under conditions of adequate soil moisture, approximately half of the ozone was deposited on the inner surfaces of the foliage, the remainder being deposited on the soil, outer leaf walls, and to the dead plant material. When soil moisture is low, less ozone is deposited on the foliage presumably because of water‐stress‐induced stomatal closure.
A point process model for tropical rainfall
Authors: Morrissey Mark L. , Krajewski Witold F.
Published: February 2008

Two recently developed point process models for temporal rainfall are tested using 7 years of hourly rain gauge data obtained from Majuro and Truk atolls in the northern equatorial Pacific. The models were fit to data from two seasons, winter (January ‐ March) and summer (June ‐ August). The results indicate that neither model can adequately reproduce the observed statistics for both seasons. A new model is proposed which characterizes the random nature of small convective events and the event like occurrences of large tropical convective cloud clusters. The model is shown to be superior to the previous models in reproducing the first‐ and second‐order moments of tropical rainfall as well as occurrence statistics such as the probability of rainfall and the expected rainfall conditional on rain.
Nitrous oxide emissions from motor vehicles in tunnels and their global extrapolation
Authors: Berges M. G. M. , Hofmann R. M. , Scharffe D. , Crutzen P. J.
Published: February 2008

The finding that catalytic converters enhance the N2O emissions from motor vehicles gave rise to the concern that they may represent a significant source of N2O. Measurements of N2O and CO2 emissions of a fleet of about 40,000 cars were conducted in two roadway tunnels in Stockholm, Sweden, and Hamburg, Germany, to estimate N2O emissions under normal driving conditions. To avoid any risk of artifact N2O formation, samples were analyzed within 1 min after collection. Median N2O to CO2 molar emission ratios of 1.4 × 10−4 and 0.6 × 10−4 were measured in Stockholm and Hamburg, respectively. The lower emission ratio in Hamburg may well reflect the smaller fraction of catalyst‐equipped cars in Germany (22%) compared to the Swedish vehicle fleet (33%) as well as low N2O emissions from trucks which were not allowed in the Stockholm tunnel. From our measurements we derive a N2O to CO2 molar emission ratio from cars equipped with catalysts in the median to interquartile range of 3.8 ± 2.2 × 10−4, from which present worldwide N2O emissions from cars are estimated to be 0.38 ± 0.22 Tg N2O (0.24 ± 0.14 Tg N) per year, corresponding to 3–16% of the atmospheric growth of 4.7 ± 0.9 Tg N2O/yr (3.0 ± 0.6 Tg N/yr). From the worldwide emission of 0.38 Tg N2O we derived an emission of about 170 mg N2O/km for catalyst‐equipped cars, significantly higher than those reported in earlier studies. If the entire present fleet of cars were to be equipped with current types of catalysts, the global N2O emission could double and reach 6–32% of the atmospheric growth rate.
Comment on “Annual and interannual variations of Earth‐emitted radiation based on a 10‐year data set” by T. D. Bess et al.
Authors: Hense Andreas
Published: February 2008

Bess et al. [1992] have stated that empirical orthogonal functions computed, from spherical harmonics amplitudes and transformed into grid point space are identical to empirical orthogonal functions (EOF) of grid point data derived from the transformed amplitudes if and only if an equal area grid is used. It will he shown that this does not hold in general and that there is always a one‐to‐one correspondence between EOF's in spherical harmonics or grid point representation. The equal area grid is only a special case of a more general approach. A simple example is given to illustrate the results of the mathematics.
CITE 3 meteorological highlights
Authors: Shipham Mark C. , Bachmeier A. Scott , Anderson Bruce E.
Published: February 2008

Meteorological highlights from the third NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 3) are presented. During August and September 1989, research flights were conducted from Wallops Island, Virginia, and Natal, Brazil, and included airborne sampling of air masses over adjacent regions of the Atlantic Ocean. Isentropic backward trajectory calculations, wind vector/streamline fields, rawinsonde data, and GOES and METEOSAT satellite imagery are utilized to examine the meteorological conditions for each flight and to determine the transport paths of the sampled air masses. Some aspects of the chemical signatures of the sampled air are also discussed. During the series of flights based at Wallops Island, Virginia, the flow into the experiment area was governed primarily by the position of the North Atlantic subtropical anticyclone. The large‐scale tropospheric circulation switched from primarily a marine flow during flights 1–4, to a predominantly offshore mid‐latitude continental flow during flights 5–10. During these later flights, the regional influences of large eastern U.S. cities along with vertical mixing by typical summertime convective activity strongly influenced the chemical characteristics of the sampled air. During the series of flights based at Natal, Brazil, the dominant synoptic feature was the South Atlantic subtropical anticyclone which generally transported air across the tropical Atlantic toward eastern Brazil. Pronounced subsidence and a well‐defined trade wind inversion often characterized the lower and middle troposphere over the Natal region. Some high‐altitude recirculation of air from South America was observed, as was cross‐equatorial transport which had come from northern Africa. Biomass burning plumes were observed on segments of all of the flights, the source region being the central and southern savannah regions of Africa.
The effect of atmospheric nitric acid vapor on cloud condensation nucleus activation
Authors: Kulmala M. , Laaksonen A. , Korhonen P. , Vesala T. , Ahonen T. , Barrett J. C.
Published: February 2008

Activation and growth of cloud condensation nuclei are investigated. A one‐dimensional cloud model including detailed microphysics is developed. The system studied consists of NaNO3 particles and condensing water and HNO3 vapors. According to numerical simulations, enhanced concentrations of atmospheric nitric acid vapor affect cloud formation by increasing the number of cloud droplets and decreasing their mean size compared to circumstances where no condensable vapors other than water are present. It is argued that the cloud albedo increases because of these effects.
Seasonal distribution of methane flux in a Minnesota peatland measured by eddy correlation
Authors: Shurpali N. J. , Verma S. B. , Clement R. J. , Billesbach D. P.
Published: February 2008

Methane flux was measured using the micrometeorological eddy correlation technique during 62 days in mid‐May through mid‐October 1991 in a peatland ecosystem in north central Minnesota. Application of this technique allows measurement of spatially integrated fluxes. The distribution of methane flux consisted of a gradual pattern with several episodic emissions superimposed. The gradual (nonepisodic) pattern of methane flux (daytime average) exhibited an increase from 30–120 mg m−2 d−1 in late May to early July to 125–160 mg m−2 d−1 in mid‐July to mid‐August and then a decline to 100–35 mg m−2 d−1 in early September to mid‐October. Peat temperature (at 0.1 m depth) and water table depth accounted for about 70% of the variance in the methane flux data. The episodic emissions were associated with drops in atmospheric pressure and a declining water table. Generally, the hourly values of daytime methane flux were fairly stable, perhaps with a slight depression during the midday. However, on days with episodic emissions, the daytime methane flux had a peak during the midafternoon, and its pattern appeared to be similar to those of the standard deviation of atmospheric pressure fluctuations and mean horizontal wind velocity. The ratio of soil CO2 to methane fluxes (during nonepisodic emission periods) increased with increasing water table depth in a manner similar to that observed in a laboratory study of peat columns from different wetland types in Quebec. The annual methane emission for this ecosystem was estimated to be about 16–19.5 g m−2 yr−1.
Use of stratospheric aerosol properties as diagnostics of Antarctic vortex processes
Authors: Thomason Larry W. , Poole Lamont R.
Published: February 2008

Physical properties of the stratospheric aerosol population are inferred from cloud‐free SAGE II multiwavelength extinction measurements in the Antarctic during late summer (February/March) and spring (September/October, November). Seasonal changes in these properties are used to infer physical processes occurring in the Antarctic stratosphere over the course of the winter. The analysis suggests that the apparent springtime cleansing of the Antarctic stratosphere is the result of aerosol redistribution through subsidence of the polar vortex air mass and sedimentation of large polar stratospheric cloud particles. The analysis also suggests that vortex processes are responsible for a significant downward transport of aerosol through the tropopause.
Central pit and dome craters: Exposing the interiors of Ganymede and Callisto
Authors: Schenk Paul M.
Published: February 2008

Central pit craters on the large icy satellites Ganymede and Callisto are an unusual crater class perhaps related to the unusual properties of water ice. The detailed morphology and dimensions of pit crater features differ from those of smaller, normal, complex craters on these two satellites. Pit crater depths appear to be constant regardless of diameter. Rim collapse is also restricted relative to that in lunar craters or smaller Ganymede craters. The floors of pits in craters larger than ∼60 km are occupied by smooth bright domes. Pit‐to‐crater and dome‐to‐crater diameter ratios increase linearly with crater diameter, and are indistinguishable on Ganymede and Callisto and with terrain type or surface longitude. The floors and central structures of young, bright‐rayed pit craters such as Osiris are covered by a thin uniformly bright impact melt or frost deposit. Thus, domes and pits form rapidly, on the time scale of the impact itself, rather than by long‐term, postimpact intrusion or extrusion. The bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice‐rich material from depths of ∼3.5 to 5 km during impact. This process is almost directly analogous to the uplift and exposure of anamolous deep‐seated material observed in terrestrial and lunar craters. The unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the Moon. Because crater morphology is strongly dependent on ice‐rock composition, the similarity of pit and dome dimensions on Ganymede and Callisto indicates that the structure and rheology of the crusts of these bodies (down to depths of ∼10 km) are very similar and have been for several b.y. Pit crater morphology indicates that the crusts of both satellites are probably ice‐rich and differentiated.
A new global‐scale emission event for Jupiter: tentative H2 dimer emission at 2.104 μm on February 15, 1992
Authors: Trafton L. M.
Published: February 2008

On February 15, 1992, from 0638 to 1023 UT, a single emission feature at 2.104 μm was observed over a wide area on Jupiter, covering much of the southern hemisphere. The emission was observed from the south limb to the equator along the central meridian at longitudes from 72° to 207° but appeared to be absent in the northern hemisphere. The emission was widespread in longitude, in that it was also visible at both the east and west limbs on a latitudinal chord 6 arc sec from the southern limb when the central meridian longitude was 189°–207°. The emission was not detected during the following two nights of the run. The wavelength is consistent with the l = 3 to l = 0 transition of the quasibound H2 dimer double transition Q1(1) + S0(1). No other emission features were detected.
A simple coastal ocean model for the Central California Basin during Late Miocene
Authors: Liu W. , Ghil M. , Neelin D. , Hall C. A.
Published: February 2008

A highly simplified coastal ocean model is constructed for central California during the middle to late Miocene (13–6 million years ago). Central California was a semienclosed shallow basin during that time, communicating with the open North Pacific Ocean. Surface temperatures for the basin have been derived using Tertiary fossil mollusks and siliceous deposits. The model provides qualitative information for reconstructing paleoclimatic and paleoceanic conditions. It is based on spatially two‐dimensional equations for the velocity and temperature in a single layer of shallow fluid. The model domain consists of a rectangular coastal basin partially connected to a portion of the Pacific Ocean. The wind stress is assumed to be spatially constant from a given direction. The flow in and out of the basin is driven by the bottom topography torque due to depth variation between basin and ocean. The temperature of the open ocean is prescribed. The temperature of the basin is governed by the relative influence of this oceanic temperature and the atmospheric reference temperature, to which vertical fluxes drive the basin in the absence of dynamical influences. Two different boundaries are used: fully open or semiopen, with a partial barrier between the basin and the ocean. We examine scenarios with different barrier extents, with openings to the ocean at one or both ends of the basin, and with different assumptions about the wind direction and currents. The effect of adding a second model layer is also investigated. We found that the results are quite insensitive to assumptions about the paleowind stress. The semiopen model appears closest to the paleocean data. This argues for the presence of a barrier during the late Miocene between the central California basin and the open ocean, at least in the basin's northern part.
Observations of time dependence in the relationship between rain attenuation and depolarization in the 18‐ to 21.2‐GHz region
Authors: Hendrix C. E. , Kulon G. , Russell T. A.
Published: February 2008

The relationship between rain attenuation and depolarization over a 7‐km path was observed in about 30 separate rain events during the spring and summer of 1990. The experimental equipment was capable of measuring attenuation and cross‐polarization discrimination (XPD) directly at about one measurement per second. The relationship between these two variables was found to be of the nature of a deterministic relationship but with time‐varying parameters. Parameter variations appeared to be associated with rising and falling phases of rain attenuation. When successive measurements of XPD were plotted against the logarithm of attenuation, each rising or falling segment was found to follow a straight line relationship but a slightly different line for each segment. Further, in any given rain event, the slopes and intercepts of the extended straight lines were themselves highly correlated, indicating a tendency for all the lines to pass through a single point in the XPD‐log attenuation plane. A simple model in which the behavior is controlled by the parameters of rain density (attenuation) and the standard deviation of canting angle of the raindrops, varying independently, appears to be consistent with the observed data.
On the satisfaction of the reciprocity relationships in the context of the geometrical theory of diffraction
Authors: Bouche D. , Mittra R.
Published: February 2008

We examine the question of satisfaction of the reciprocity theorem in the context of geometrical theory of diffraction. To this end, we consider two sets of scattering problems involving a smooth, convex, perfectly conducting obstacle S, related by the reciprocity theorem. Initially, we find that the satisfaction of reciprocity conditions by the results derived from the use of the geometric theory of diffraction formulas is not obvious. We then proceed to show that they may be recast in forms that are indeed reciprocal in nature.
Theory of spatial solitons
Authors: Boardman A. D. , Xie K.
Published: February 2008

The basic theory of spatial solitons is presented with an emphasis upon analytical results. It is shown that both diffusive and saturated nonlinearities can be treated mathematically and that solitonlike solutions exist. Soliton interactions are investigated, and their properties are exposed with a variational method, leading to a particle representation. Examples concerning spatial solitons coupled by polarization or by being coupled in separate, identical, planar waveguides are discussed in detail. It is shown that an escape velocity exists and that below this velocity, spatial solitons engage in a periodic interaction, for which the period can be readily defined. The mathematical analysis is confirmed by a numerical simulation.
Characterization of power‐dependent high‐Tc superconducting microstrip line by modified spectral domain method
Authors: Liu Yaozhong , Itoh Tatsuo
Published: February 2008

Surface resistance of the high‐Tc superconducting thin film may depend upon the power level of the thin film surface. An iteration method using the spectral domain technique with an application of complex resistive boundary condition is adopted to analyze such a nonlinear problem. Numerical results for the phase and attenuation constants and current distributions are given for different structural and material parameters.
Modeling of high‐frequency oblique propagation and heating in the ionosphere
Authors: Hinkel‐Lipsker D. E. , Shoucri M. M. , Smith T. M. , Wagner T. M. , Hansen J. D. , Morales G. J.
Published: February 2008

An advanced ray‐tracing numerical method is coupled to an ionospheric plasma transport code to model the self‐consistent propagation of an obliquely incident high‐frequency (HF) beam in the ionosphere. An HF radar propagation scenario is presented as an application. During the daytime, a density increase in the lower ionosphere is predicted causing the defocusing of the incident HF beam.
Large and giant aerosols in the marine boundary layer during WATOX, January 4‐9, 1986
Authors: Bridgman Howard A. , Sievering Herman
Published: February 2008

Aircraft measurements of large and giant aerosols (1‐45 μm diameter) in the marine boundary layer over the western North Atlantic (32°‐40°N) under offshore flow conditions during the Western Atlantic Ocean Experiment on January 4, 6, and 9, 1986 (WATOX‐86), showed a domination by sea salt, with volume spectra peaks between 7 and 9 μm diameter. Aerosol mass increased rapidly when short‐term averaged wind speeds, ū, exceeded 17 m s−1. Aerosol mass also showed a qualitative dependence on relative humidity that was not as strong as the dependence on wind speed. Both wind speed and humidity variations can be used to explain the spatial variations in volume spectra along the flight track. Most models of sea salt mass or volume in the literature consider near‐surface aerosol sizes smaller than 2.0‐μm diameter and are not applicable to our data. At altitudes of 200‐600 m above the sea surface our WATOX data show a strong nonlinear dependence between coarse aerosol mass and volume, and short‐term wind speed. The best fit is a ū3 dependence (dry mass = 8.7 + 0.0065 ū3, R2 = 0.95; volume = 8.24 + 0.0065 ū3 R2 = 0.92). This dependence may have been enhanced by the offshore flow conditions that prevailed, and the location of the aircraft within 300 km of the coast.