bluuebunny/crossref_metadata_2025 huggingface dataset:
Frictional resistance of a fault zone with strong rotors
Authors: Brune James N. , Anooshehpoor A.
Published: February 2004

As a possible mechanism to explain the lack of a heat flow anomaly along the creeping section of the San Andreas Fault, we have determined the effect of placing hard rotors along a surface between two deformable media, in this case styrofoam balls between two blocks of foam rubber. The probable presence of Franciscan rocks at depth along the creeping section of the San Andreas Fault suggested this mechanism, since the Franciscan is characterized not only by basic serpentinous rocks which are weak, but also by embedded, more or less equidimensional, blocks of very strong rocks (knockers), e.g., high grade blueschists and eclogites, which might act as rotors. The results suggest that knocker rotation may be a viable mechanism for reduction of friction on the creeping section of the San Andreas fault, and thus be at least a partial explanation of the lack of any observed frictional heat flow anomaly there.
Lidar measurements of stratospheric aerosol over Mauna Loa Observatory
Authors: Barnes John E. , Hofmann David J.
Published: February 2004

Dual‐wavelength aerosol lidar backscatter measurements at Mauna Loa Observatory are used to monitor and characterize the 15–30 km stratospheric aerosol layer. The decay of aerosol loading following the El Chichón, Mexico (17°N) and Pinatubo, Philippine Islands (15°N) volcanic eruptions of 1982 and 1991, respectively, depends on the phase of the quasibiennial oscillation (QBO) in tropical stratospheric winds. Averaged over a 3‐year period, these effects are removed and an exponential decay with a characteristic (e−1) decay time of about 1 year is observed for both eruptions. By the end of 1996, about 5 ½ years after the Pinatubo eruption, stratospheric aerosol levels at Mauna Loa had decayed to pre‐eruption levels, approximately matching the lowest aerosol levels seen here in the past 17 years (about 6 × 10−5 sr−1 at 694 nm integrated between 15.8 and 33 km). However, this background stratospheric aerosol level at Mauna Loa may depend on the QBO, being slightly lower during the westerly phase. Analyses of aerosol backscatter, backscatter wavelength dependence, and trajectories provide evidence for a minor injection of aerosol from the Rabaul eruption in Papua, New Guinea (4°S) in September of 1994.
Water vapor dimers and atmospheric absorption of electromagnetic radiation
Authors: Chýlek Petr , Geldart D. J. W.
Published: February 2004

Using a simple model based on a quantum mechanical harmonic oscillator we estimate the average dimer absorption cross sections within six 3500 cm−1 wide bands. The cross section is of the order of 6 × 10−21 cm² in the first frequency band (1000 to 4500 cm−1) and it decreases by a factor of about 600 with increasing frequency from far infrared to visible portion of the spectrum. This relatively slow decrease is a result of anharmonic forces within a dimer, that weaken the selection rules of water monomer. Using numerical results of previous studies, we parameterize the concentration of dimers in the atmosphere and provide the formalism to calculate the absorption of solar radiation by water dimers as a function of total water vapor column amount and temperature. For water vapor column of 1 g/cm² and 80% relative humidity at 273 K, the dimers will absorb about 1.6% of the incident solar radiation. The absorbency increases with increasing temperature to about 4.6% at 298 K. Our estimates are accurate within a factor of about four. Most of the dimer absorption occurs at infrared wavelengths. Only about 5% of solar radiation absorbed by dimers is at wavelengths below 0.9 µm.
Modelling rough interfaces on seismic reflection profiles—The application of fractal concepts
Authors: Walia Rakesh K. , Bull Jonathan M.
Published: February 2004

The distortion of reflection continuity and amplitude by overburden structure in seismic reflection images of the subsurface is easily recognised and modelled when the wavelength of the shallower structure is relatively large. The effects of shorter wavelength structure although giving rise to little reflective response itself, cause significant distortion of the propagating wavefield, particularly when a moderate or strong acoustic impedance contrast is present in the shallow sub‐surface. Here we show how short as well as long spatial wavelengths of horizon roughness affect deeper reflection continuity, and develop a new method using fractal interpolation techniques to predict the total roughness of sub‐surface horizons from information contained in seismic reflection sections. Fractally complete depth‐velocity models are used in forward models, using the finite difference technique, to produce synthetic seismic profiles. The technique is illustrated with data from the Edoras Bank area of the Rockall Plateau, NE Atlantic, where apparently discontinuous reflectors underlying basalt flows are shown to be from continuous sedimentary horizons distorted by overlying rough horizons.
Interpreting shortwave albedo‐transmittance plots: True or apparent anomalous absorption?
Authors: Barker Howard W. , Li Zhanqing
Published: February 2004

The coefficients of linear regression lines fit to hourly observations of atmospheric transmittance and TOA albedo have been used previously to address the problem of anomalous cloud absorption (ACA). While these coefficients indicate, reasonably well, the impact of clouds on atmospheric absorptance for 1D model data, this is not necessarily the case for hourly data. This is because for nonuniform clouds, regression coefficients are reduced significantly relative to 1D model results due to the effects of horizontal transport of radiation and poor sampling of transmittance. These reductions are only illusions of ACA because domain‐averaged atmospheric absorptances are almost insensitive to cloud geometry. The ramifications of these effects can be seen in hourly data that were used in a previous study which claimed to support ACA. They are also demonstrated with a 3D Monte Carlo, broadband radiative transfer algorithm acting on data generated by a cloud‐resolving model.
Measurement of the isotopic ratio distribution of HD16O and H216O in the 20–38 km altitude range from far‐infrared spectra
Authors: Dinelli Bianca Maria , Lepri Gianmarco , Carlotti Massimo , Carli Bruno , Mencaraglia Francesco , Ridolfi Marco , Nolt Ira G. , Ade Peter A. R.
Published: February 2004

The altitude distribution of the isotopic ratio between HD16O and H216O in the stratosphere is derived by retrieving the mixing ratio profiles (from 20 km to 38 km of altitude) of the two isotopic species from far‐infrared emission spectra. The measurements were made with a balloon‐borne Fourier Transform Spectrometer capable of 0.0025 cm−1 spectral resolution during the IBEX 92 campaign. The retrievals were carried out using the global‐fit procedure on a statistically significant number of spectra for each isotope, in the 40–75 cm−1 spectral region. This measurement determines the D/H ratio in stratospheric water over an altitude range larger than that of previous measurements. The value of the HD16O/H216O ratio, normalized to the standard value, ranges from 0.4 to 0.5 (with a 10% random error) in the altitude range studied and is in good agreement with the values previously measured.
On the occurrence of ClO in cirrus clouds and volcanic aerosol in the tropopause region
Authors: Borrmann Stephan , Solomon Susan , Avallone Linnea , Toohey Darin , Baumgardner Darrel
Published: February 2004

Airborne observations during descents of the ER‐2 through layers of volcanic aerosol (Mount Pinatubo eruption of 1991) and a cirrus cloud are utilized to study the the abundance of ClO and its relation to aerosol surface area in the midlatitude tropopause region. During a cirrus event near the tropopause ClO mixing ratios up to 2.7 pptv were detected and near the tropopause ClO levels from a few to 70 pptv were found. These measurements are associated with large experimental uncertainties but demonstrate the possible presence of ClO inside cirrus clouds and near the tropopause. Model calculations show that possible enhancements of ClO by heterogeneous chemistry on cirrus cloud particles could considerably increase the ozone loss rates and could have implications for the ozone budget in this region. It is not possible to decide from the limited data base whether the observed ClO levels are due to transport or heterogeneous chemistry.
Can long‐wavelength dynamical signatures be compatible with layered mantle convection?
Authors: Čadek Ondřej , Čížková Hana , Yuen David A.
Published: February 2004

Analyses of the long‐wavelength geoid with seismic tomographic models have been providing for a long time important estimates of mantle viscosity. These estimates have nearly been derived under the assumption of whole mantle flow. It has been commonly held that a fully impermeable boundary at 660 km depth is incompatible with the long‐wavelength gravity signal. On the other hand, models with whole mantle circulation, which can explain a large portion of the geoid signal, usually produce excessive amplitudes of the dynamical topography, especially for long wavelengths. Using recent tomographic models together with genetic algorithm we have successfully demonstrated that the layered convection model can also produce a reasonable fit to the geoid, which is comparable in quality with that obtained for the whole mantle model. The layered model can simultaneously yield realistic amplitudes of the dynamical topographies of the surface and the 660‐km discontinuity.
West Coast tides during Cascadia Subduction Zone tsunamis
Authors: Mofjeld Harold O. , Foreman Michael G. G. , Ruffman Alan
Published: February 2004

Low, neap tides occurred along the West Coast of the United States and Canada around 0500 UT January 27, 1700, a time for the last major Cascadia earthquake/tsunami based on teletsunami arrival times in Japan [Satake et al., 1996]. However, high‐range perigean spring tides occurred only a week later, illustrating how accurately occurrence times must be known to constrain the region's background water levels during such events. The ranges of background water levels increase northward from 3 m at Monterey to 8.5 m at Queen Charlotte, as estimated from the amplitudes of perigean spring tides and subtidal winter fluctuations.
Deep upwelling and diffusivity in the southern central Indian Basin
Authors: McCarthy Mary C. , Talley Lynne D. , Baringer Molly O.
Published: February 2004

Transport of the deepest water westward through a gap at 28°S in the Ninetyeast Ridge between the Central Indian Basin and the West Australia Basin is calculated from hydrographic data collected as part of WOCE Hydrographic Program section I8N. Zero reference velocity levels at mid‐depth were chosen through consideration of water masses. The small transport of 1.0 Sv westward of water denser than σ4 = 45.92 kg m−3 through the gap must all upwell in the southern Central Indian Basin. Of this, 0.7 Sv upwells between the central and western sill sections, that is, close to the sill itself. Using the areas covered by the isopycnal, we calculate an average vertical velocity of 3.3 · 10−3 cm s−1 close to the sill and of 4.2 · 10−4 cm s−1 west of the sill. Associated average vertical diffusivities are 105 cm² s−1 close to the sill and 13 cm² s−1 west of the sill, in this bottom layer.
New aspects in the annual variation of the ionosphere observed by the MU Radar
Authors: Balan N. , Otsuka Y. , Fukao S.
Published: February 2004

Annual variations of the daytime ionosphere studied with the MU radar during a full solar cycle show equinoctial asymmetry in density, temperature, and plasma velocity. The electron density (Ne) in the bottomside ionosphere is slightly greater in September equinox compared to March equinox, which arises from the asymmetry in thermospheric composition. At higher altitudes, the asymmetry in Ne reverses and becomes strong; the values of Ne in March equinox exceed those in September equinox by up to 150%. The electron temperature (Te) shows an asymmetry, which is opposite to the asymmetry in Ne; the values of Te in the topside in March equinox are less than those in September equinox by up to 300K. The asymmetry in ion temperature (Ti) is weak (about 100K) and in phase with the asymmetry in Ne. The northward perpendicular plasma velocity (V⟂) is slightly greater in March equinox compared to September equinox. The meridional component of the thermospheric neutral wind velocity (Uθ), derived from the field‐parallel plasma velocity V∥, is up to 50% lower in March equinox compared to September equinox. The asymmetry in neutral winds accounts for the asymmetry in ionospheric density and temperature in the topside, with minor contribution from the asymmetry in plasma drifts.
Mid‐altitude modeling of cusp ion injection under steady and varying conditions
Authors: Xue S. , Reiff P. H. , Onsager T. G.
Published: February 2004

A cusp ion injection model incorporating mutually consistent electric and magnetic fields is developed. We have simulated cusp ion energy‐latitude spectrograms for paths similar to certain orbits of DE‐1 and Viking. Both the large‐scale energy‐latitude dispersion and the embedded small‐scale energy‐pitch‐angle V signatures are clearly evident in these simulated spectrograms. Our results show that a much narrower V microsignature is obtained when the ion injection source is restricted to a small region. However, the cutoff of the plasma injection at the magnetosheath sonic line alone also yields relatively narrow V‧s, without restricting the injection region. This effect is most noticeable in winter conditions. By introducing a time‐dependent magnetosheath plasma density variation along the magnetopause to our cusp model, we are also able to reproduce a well observed meso‐scale ion injection pattern which can appear to be the overlap of multiple injections, even with assuming steady interconnection.
Ganymede: A new radio source
Authors: Kurth W. S. , Gurnett D. A. , Roux A. , Bolton S. J.
Published: February 2004

Observations by the Galileo plasma wave receiver during the first two flybys of Ganymede revealed that this Jovian moon is the source of narrowband electromagnetic radio waves, making it the only satellite in the solar system known to generate non‐thermal radio emissions. The emissions are the result of mode‐coupling from electrostatic electron cyclotron emissions near the upper hybrid resonance frequency, similar to non‐thermal continuum radiation found at the known magnetized planets.
Determination of the translational temperature of the high altitude terrestrial thermosphere from the rotational distribution of the 5.3 µm emission from NO(v=1)
Authors: Sharma R. D. , Duff J. W.
Published: February 2004

The rotational distribution of vibrationally excited nitric oxide produced by impacts with atomic oxygen is investigated using a quasiclassical trajectory approach. The present study confirms the earlier result that the nascent rotational distribution may be described by a Maxwell‐Boltzmann (MB) distribution. It further shows that the temperature describing the nascent distribution is about 25% lower than the translational temperature and equals it after 3 to 5 collisions. Translational temperature as function of altitude is derived from the nighttime rotational distribution of the 5.3 µm emission observed by cryogenic infrared radiance for shuttle (CIRRIS 1A) and compared with the mass spectrometer incoherent scatter (MSIS) model temperature. Because of the strong 5.3 µm emission this method has larger signal than the N + O radiative recombination currently used to determine the nighttime thermospheric temperatures.
Response of the upper tropospheric humidity and moisture transport to changes of tropical convection. A comparison between observations and a GCM over an ENSO cycle
Authors: Fu Rong , Dickinson Robert E. , Newkirk Brett
Published: February 2004

Comparison of the upper tropospheric relative humidity (UTH) of CCM2 forced by observed sea surface temperatures (SSTs) with data from TOVS, MSU, and the GEOS‐1 assimilation shows that the model reproduces the observed large‐scale pattern of interannual changes of UTH in the tropics, but gives too much drying during the 1987 El Niño. How UTH responds to the changes of precipitation is well‐simulated in the areas of anomalous subsidence and drying in the subtropical Pacific. However, the exaggerated increase of precipitation in the model in the equatorial central Pacific leads to excessive amplitudes of vertical motion, which dries the subtropical upper troposphere. Since the uplift does not result in excessive moistening in the equatorial Pacific, the effect of the too vigorous hydrological cycle is an unrealistically large reduction of UTH in the tropics during an El Niño in CCM2.
Io's thermal anomalies: Clues to their origins from comparison of ground based observations between 1 and 20 µm
Authors: Blaney Diana L. , Veeder Glenn J. , Matson Dennis L. , Johnson Torrence V. , Goguen Jay D. , Spencer John R.
Published: February 2004

Io's thermal emission for 1995 from eclipse photometry at 2.2 µm; broad band radiometry at 4.8 µm 8.7 µm and 20 µm; and in eclipse imaging between 1.7 and 5 µm are compared. The variability of thermal emission from Io at wavelengths between 1–5 µm (Silverstone et al., 1995; Spencer et al., 1997) is in agreement with the expected variability based on the 13 year record presented in Veeder et al. (1994) and Goguen et al. (1996). We conclude that 1995 was typical for Io, in terms of overall observed variability in the volcanic sources. Detailed comparison of data from Goguen et al. on Aug. 24 and Spencer et al. on Aug. 26 provides evidence of a high temperature eruption that produced a larger, cooler region over the course of two days. The observed frequency of occurrence of high temperature events, the linking of high and lower temperature thermal anomalies, and the observed stability of volcanic regions since Voyager suggests that high temperature silicate eruptions could support the entire observed population of cooler temperature anomalies. It may be more productive to consider sulfur flows on Io in the context of remobilization of existing sulfur deposits.
Low Mach number predictions in an extended axially symmetric MHD theory of the magnetosheath
Authors: Grabbe Crockett L.
Published: February 2004

A recent axisymmetric magnetohydrodynamic (MHD) model for the Earth's magnetosheath near the Sun‐Earth line, with boundary conditions given by Rankine‐Hugoniot (RH) equations at the bow shock and the Chapman‐Ferraro (CF) condition at the magnetopause, is extended by including smaller terms in the CF condition that become important at low Mach numbers. Three conclusions are predicted for the magnetosheath. (1) The magnetosheath thickness Δms decreases with decreasing Alfven Mach number MA for MA > M* (in which only the “gasdynamic” root of the RH equations for the bow shock boundary is physical), where M* ∼ 2 is the root‐transition value for the RH equations at which all 3 roots coalesce. When MA < M*switch‐on shock roots (purely MHD) are also physical, and Δms associated with those roots shows a rapid increase to a large value, followed by a rapid decrease back to a very small value as the decreasing MA approaches 1. Thus Δms associated with these switch‐on roots may give more distant bow shocks, and may rapidly vary with small MA changes. (2) Δms is very sensitive to the value for the CF constant kCF at the magnetopause. For larger MA and sonic Mach numbers Ms the ratio of Δms to the geocentric radial distance amp of the magnetopause varies from 0.44 for 90% coupling efficiency of the solar wind momentum density to the magnetopause down to 0.18 for 60% coupling efficiency. This suggests a balance between the solar wind coupling efficiency to the magnetopause and the thickness of the magnetosheath, in which an increase (decrease) in the coupling efficiency increases (decreases) the thickness of the magnetosheath to counter that efficiency by moving the bow shock further upstream (downstream), hence minimizing the variation in time of that coupling efficiency. (3) The linear relation between Δms and the density ratio ρsw/ρbs observed in simulations breaks down for MA or Ms ≲ 2. The slope steadily drops as Ms → 1, but increases as MA → 1.
Timing of the Antarctic cold reversal and the atmospheric CO2 increase with respect to the Younger Dryas Event
Authors: Blunier T. , Schwander J. , Stauffer B. , Stocker T. , Dällenbach A. , Indermühle A. , Tschumi J. , Chappellaz J. , Raynaud D. , Barnola J.‐M.
Published: February 2004

The transition from the Last Glacial to the Holocene is a key period for understanding the mechanisms of global climate change. Ice cores from the large polar ice sheets provide a wealth of information with good time resolution for this period. However, interactions between the two hemispheres can only be investigated if ice core records from Greenland and Antarctica can be synchronised accurately and reliably. The atmospheric methane concentration shows large and very fast changes during this period. These variations are well suited for a synchronisation of the age scales of ice cores from Greenland and Antarctica. Here we confirm the proposed lead of the Antarctic Cold Reversal on the Younger Dryas cold event. The Antarctic cooling precedes the Younger Dryas by at least 1.8 kyr. This suggests that northern and southern hemispheres were in anti‐phase during the Younger Dryas cold event. A further result of the synchronisation is that the long‐term glacial‐interglacial increase of atmospheric CO2 was not interrupted during the Younger Dryas event and that atmospheric CO2 changes are not necessarily dominated by changes in the North Atlantic circulation.
Direct observations of seasonal exchange through the Bab el Mandab Strait
Authors: Murray Stephen P. , Johns William
Published: February 2004

The exchange flow between the Red Sea and the Gulf of Aden‐Indian Ocean through the Bab el Mandab Strait was measured continuously for 10 months, June 1995–March 1996. ADCP and temperature‐salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the Gulf of Aden, and the high salinity outflow layer from the Red Sea. The timing, structure, and evolution of the summer season mid‐depth intrusion of cold, low salinity water into the Red Sea from the Gulf of Aden is measured for the complete intrusion cycle of 1995. We unexpectedly find the deep outflow still strong in June 1995, with speeds of 0.6 m/sec and transport of 0.4 Sv (1 Sv = 106 m³/sec). From July to mid–September, the deep outflow persists but is attenuated to speeds of 0.2 m/sec and transport of 0.05 Sv. The dominant summer feature, the cold low salinity intermediate layer intrusion, persists for 3 months, occupies 70% of the water column in the Strait and carries approximately 1.7 × 1012 m³ of cold nutrient‐rich water into the Red Sea. The winter regime begins in mid‐September, is fully developed by early November, and continues to the end of our first observation interval in March 1996. Speeds in the lower layer are 0.8–1.0 m/sec and 0.4–0.6 m/sec in the upper layer. At maximum exchange in mid‐February, outflow transport reaches 0.7 Sv. Ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along‐channel wind forcing and perhaps to coastally‐trapped waves.
Multiple receiver wind profiling techniques for the boundary layer in the presence of hydro‐meteors
Authors: Van Baelen Joel , Hirsch Lutz , Prada Claire
Published: February 2004

A UHF boundary layer wind profiler has been operated in a multiple receiver mode. The data sets collected are used to estimate the horizontal wind using different multiple receiver analysis techniques performed in the time and frequency domains. Those results are also compared with simultaneous Doppler beam swinging measurements.

The particularity of the data sets used for this inter‐comparison is that they were recorded while hydro‐meteors were present in the boundary layer. The large mean fall speed and the broad fall velocity distribution of rain drops causes a much more rapid decay of diffraction patterns than in the case of scattering by snow flakes or micro turbulence. Therefore, analysis methods which do not account for the effect of the decay of the diffraction patterns show an over‐estimation of the wind velocity, and do so in a different way whether snow or rain is present. To the contrary, algorithms that account for the effect of diffraction pattern decay appear to reasonably estimate the actual horizontal wind and compare well with the Doppler measurements.
Ground‐based measurements of tropospheric and stratospheric BrO at Arrival Heights, Antarctica
Authors: Kreher K. , Johnston P. V. , Wood S. W. , Nardi B. , Platt U.
Published: February 2004

Ground‐based measurements of BrO slant column densities (SCDs) were performed using zenith sky DOAS (Differential Optical Absorption Spectroscopy) during autumn (February to May) and spring (August to October) of 1995 at Arrival Heights (77.8°S, 166.7°E).

In both August and September, single episodes of sudden large BrO column enhancement (of magnitude 3.5 and 3.2 × 1014 molec. cm−2 respectively) were observed. The episode in August did not coincide with changes of other stratospheric parameters (OClO, NO2 and temperature). Furthermore, the diurnal variation in the SCD during these events was indicative of a tropospheric rather than a stratospheric absorber. The tropospheric BrO mixing ratios deduced from the data are similar to those observed by ground‐based measurements in the Arctic boundary layer (∼30 ppt).

Simultaneous balloon soundings, one during each of the two events, showed statistically significant (2 σ) tropospheric ozone depletion between 0.5 and 2 km in August and 1.5 and 2.8 km in September. Our results strongly suggest that halogen catalysed boundary layer ozone depletion not only occurs in the Arctic but also in Antarctica. This has the implication that Arctic Haze and anthropogenic influence is unlikely as a cause for this phenomenon.
Megahertz electron modulations during TSS 1R
Authors: Gough M. P. , Burke W. J. , Hardy D. A. , Huang C. Y. , Gentile L. C. , Rubin A. G. , Oberhardt M. R. , Drobot A. T. , Thompson D. C. , Raitt W. J.
Published: February 2004

Experiments were conducted during the Tethered Satellite System Reflight in which a 1 keV, 100 mA electron beam was emitted from the shuttle at pitch angles near 90°. Rapid plasma responses measured by the Shuttle Potential and Return Electron Experiment (SPREE) show time‐modulated electron fluxes within the beam flux tube. Megahertz modulations fall into two classes: (1) narrow‐bands close to harmonics of the electron gyrofrequency fce and (2) broad‐bands at interharmonic frequencies in which electrons of different energies had different modulation frequencies. When SPREE intercepted beam electrons after a single gyroturn they, too, were modulated at similar frequencies. Data suggest that beam electrons were modulated by strong plasma interactions near the emission aperture, generating time‐varying electric fields that modulated other electrons near the beam cylinder. This is analogous to the electron cyclotron maser responsible for auroral kilometric radiation.
Trapped electrons in Ganymede's magnetic field
Authors: Williams D. J. , Mauk B. , McEntire R. W.
Published: February 2004

The NASA Galileo satellite encountered the Jovian moon Ganymede on 7 May 1997. The Energetic Particles Detector (EPD) measured energetic electron pitch angle distributions characteristic of closed magnetic field lines. Significantly different from distributions observed during other encounters with Ganymede, they displayed loss cone features near both 0° and 180° pitch angles and an additional minimum near 90° pitch angle. These double loss cone, butterfly distributions are characteristic signatures of particles drifting in a distorted magnetic field configuration. Distortions due to the flow of Jovian plasma past Ganymede qualitatively could account for the observed distributions. Electron injection could then occur either through the equatorial downstream hemisphere or at low Ganymede altitudes on high‐latitude Ganymede‐Jovian field lines adjacent to the closed field line region. The data indicate maximum injection efficiences of 1–10%.
Excitation of oscillating two stream instability by upper hybrid pump waves in ionospheric heating experiments at Tromso
Authors: Kuo S. P. , Lee M. C. , Kossey Paul
Published: February 2004

It is shown that upper hybrid waves generated by the HF heater wave in the Tromso' heating experiments can excite oscillating two stream instability near the upper hybrid resonance layer of the heater wave. The sidebands of the investigated parametric instability are obliquely propagating Langmuir waves. These Langmuir waves can be excited in milliseconds and have a broad angular distribution. Thus, those waves propagating obliquely at small angles with respect to the geomagnetic field can contribute to the zero off‐set frequency component of the plasma line spectrum detected by a backscatter radar. The analyses also show that the wavelengths of the Langmuir waves have an upper bound and consequently, explain why the zero off‐set frequency plasma line has been detected by the EISCAT 933 MHz (UHF) radar, but not by the EISCAT 244 MHz (VHF) radar as reported in Stubbe et. al. [1992].
Effect of interannual meteorological variability on mid‐latitude O3
Authors: Hadjinicolaou P. , Pyle J. A. , Chipperfield M. P. , Kettleborough J. A.
Published: February 2004

We have used a three‐dimensional (3D) chemical transport model (CTM) to investigate the effect of interannual meteorological variability on ozone at middle latitudes. The CTM is forced by UK Meteorological Office analyses, includes a simple parameterization of ozone photochemistry and perturbed chlorine chemistry on polar stratospheric clouds (PSCs) and has been integrated for six years (1991–97). The modelled time series of the O3 column for the Northern Hemisphere middle latitudes shows a significant year‐to‐year variation which we attribute to transport processes, since the model's chemistry is effectively the same in each year. The model calculates its lowest ozone during 1993. This follows the Mt Pinatubo eruption but in this calculation cannot be due to chemistry on the enhanced aerosol surface area. The model indicates a contribution of the Arctic polar loss to mid‐latitude ozone depletion each year during springtime, its influence being seasonal and not accumulating through the years.
Shape and size of contrails ice particles
Authors: Goodman J. , Pueschel R. F. , Jensen E. J. , Verma S. , Ferry G. V. , Howard S. D. , Kinne S. A. , Baumgardner D.
Published: February 2004

A NASA DC‐8, equipped as an in‐situ sampling aircraft, flew in the exhaust wake of a Boeing 757 on May 4, 1996 over Kansas. Ice crystal samples were collected by impaction technique and replicated twice about 8 to 17 km behind the aircraft at an altitude of 11.8 km. The ice crystals in the contrail ( after about 1 minute of growing time ) had a unimodal size distribution, with an equivalent volume radius of less than 10 µm and an effective radius of about 2 µm. The crystal habits at the observed temperature of −61C were predominantly hexagonal plates (75%), columns (20%) and few triagonal plates (<5%). The habit was already well defined for crystals about 0.5 µm in radius.
Airborne in‐situ OH and HO2 observations in the cloud‐free troposphere and lower stratosphere during SUCCESS
Authors: Brune W. H. , Faloona I. C. , Tan D. , Weinheimer A. J. , Campos T. , Ridley B. A. , Vay S. A. , Collins J. E. , Sachse G. W. , Jaeglé L. , Jacob D. J.
Published: February 2004

The hydroxyl (OH) and hydroperoxyl (HO2) radicals were measured for the first time throughout the troposphere and in the lower stratosphere with a new instrument aboard the NASA DC‐8 aircraft during the 1996 SUCCESS mission. Typically midday OH was 0.1‐0.5 pptv and HO2 was 3‐15 pptv. Comparisons with a steady‐state model yield the following conclusions. First, even in the lower stratosphere OH was sensitive to the albedo of low clouds and distant high clouds. Second, although sometimes in agreement with models, observed OH and HO2 were more than 4 times larger at other times. Evidence suggests that for the California upper troposphere on 10 May this discrepancy was due to unmeasured HOx sources from Asia. Third, observed HO2/OH had the expected inverse dependence with NO, but was inexplicably higher than modeled HO2/OH by an average of 30%. Finally, small‐scale, midday OH and HO2 features were strongly linked to NO variations.
Plasma waves in the sheath of the TSS‐1R satellite
Authors: Iess L. , Harvey C. , Vannaroni G. , Lebreton J. P. , Dobrowolny M. , Manning R. , Cerulli‐Irelli P. , Onelli A. , De Venuto F.
Published: February 2004

The current flow in the Tethered Satellite System (TSS) induces a strong excitation of electric and magnetic fluctuations in the potential sheath surrounding the subsatellite. The wave sensors of the experiment RETE (Research on Electrodynamic Tether Effects) have measured power spectra of electromagnetic fields from 180 Hz to 12 MHz, providing information on the physical processes taking place around highly charged bodies in the ionosphere and, in particular, the role of wave‐particle interactions and anomalous collisionality. We report on the observations during three events of almost steady current flow at 50, 190 and 55 mA, taking place at positive satellite potentials of about 9, 200 and 2 V. The largest power spectral density occurs at frequencies between 2 and 4 kHz, close to the lower hybrid frequency, where electric field fluctuations up to 12 V/m have been observed. In this frequency band the fields are electrostatic and radially polarized, with a marked ram‐wake signature.
TSS‐1R electron currents: Magnetic limited collection from a heated presheath
Authors: Cooke David L. , Katz Ira
Published: February 2004

We show that currents collected by TSS‐1R are consistent with Parker‐Murphy magnetic limited collection from the ionosphere where the local electron temperatures are elevated as observed during the first TSS‐1 mission. An analytic development of the previous Katz et al. [1994] presheath model is presented. This model accounts for the heating that occurs as electrons fall through the potentials necessary to reflect the ram ions while satisfying the Bohm sheath stability criterion. This presheath model is coupled to a sheath sized to the Parker‐Murphy collection radius to predict the current collected by TSS‐1R. The resultant currents are 2 to 3 times larger than for the standard Parker‐Murphy collection model and are consistent with observations.
Kinetics of the heterogeneous reaction CO + O → CO2 on inorganic oxide and water ice surfaces: Implications for the Martian atmosphere
Authors: Choi Wonyong , Leu Ming‐Taun
Published: February 2004

The heterogeneous reaction CO + O → CO2 on water ice and various inorganic oxide (SiO2, Al2O3, Fe2O3, Fe3O4, CaO, MgO, and TiO2) surfaces has been investigated in order to evaluate the proposition that this heterogeneous reaction may contribute to the CO2 stability in the Martian atmosphere. The reaction probabilities were measured at both 196 K and 294 K by using a fast flow‐tube reactor coupled to an electron‐impact ionization mass spectrometer. The atomic oxygen was generated by passing a mixture of O2 and He through a microwave discharge at a side‐arm inlet and then allowed to react with CO over these substrates in the reactor. The reaction product, CO2, was monitored as a function of time at the downstream end of the flow‐tube reactor. The measured reaction probabilities were determined from the growth rates of CO2 signal and were found to range from 1.6 × 10−7 to 1.0 × 10−5 on the basis of the geometric area of the reactor. If we adopt a typical reaction probability of 5 × 10−7 for the heterogeneous CO + O reaction on Martian aerosols at 196 K, a simple calculation suggests that this mechanism plays a negligible role in CO2 recycling as compared to that of the homogeneous CO + OH reaction.
The polarization of auroral radio emissions
Authors: Shepherd S. G. , LaBelle J. , Trimpi M. L.
Published: February 2004

Ground level observations using two vertical loop antennas oriented at 90° to each other reveal the sense of polarization of several types of auroral radio emissions in the frequency range 30–5000 kHz. Auroral hiss is observed to be right elliptically polarized (RP) with respect to the local magnetic field, consistent with theoretical expectation for the whistler mode and with earlier measurements. Two less well‐understood auroral emissions, are found to be left elliptically polarized (LP). This polarization is inconsistent with their generation in the X‐mode as suggested by some theories.
Rapid N‐S extension in the Mygdonian Graben (northern Greece) deduced from repeated geodetic surveys
Authors: Martinod Joseph , Hatzfeld Denis , Savvaidis Paris , Katsambalos Kostas
Published: February 2004

In November 1994, a geodetic network situated on the Mygdonian graben, 30 km NE of Thessaloniki, Greece, was remeasured using the GPS technique. This network was established in 1979, in the epicentral area of the 1978 earthquake (Ms=6.5), and was measured using triangulation techniques seven times between 1979 and 1989. The comparison between 1979 and 1994 data shows that this part of the Mygdonian graben experienced about 8 cm of N‐S horizontal extension. Most of the extension is concentrated in a narrow (one or two kilometers) E‐W zone, located on the southern boundary of the graben. Furthermore, the analysis of repeated triangulation surveys suggests a rate of extension of 5.7±1.3 mm/y, that remained constant with time between 1979 and 1994. This extension could result from long‐term postseismic relaxation processes, or from continous aseismic slip within the graben.
Shuttle charging by tether controlled electron beam
Authors: Burke W. J. , Bonifazi C. , Hardy D. A. , Machuzak J. S. , Gentile L. C. , Olson D. G. , Huang C. Y. , Gilchrist B. E. , Lebreton J.‐P. , Gurgiolo C. A.
Published: February 2004

During the reflight of the tethered satellite system, the electron generator assembly (EGA) emitted steady electron beams six times with the satellite deployed between 6.2 and 16.1 km. Maximum beam energies and currents were 1.65 keV and 0.4 A, respectively. Data presented here show that: (1) emissions create local electron clouds that can charge the shuttle, (2) ionization of thruster gas by beam electrons in the sheath did not reduce the shuttle potential, (3) the EGA utilizes more than half the induced potential, and (4) ionospheric density gradients and magnetic field orientations affect the circuit's potential distribution.
Effect of statistics of small numbers on the chemistry of trace species in atmospheric particles
Authors: Mozurkewich Michael
Published: February 2004

In models of reactions occurring in atmospheric aerosol particles, calculated concentrations of some trace species often imply fractions of a molecule per particle. When this occurs, averaging rate or equilibrium expressions over a large number of particles gives results that differ from bulk solution. Two different effects are demonstrated here. In the first, the confinement of ions in submicrometer drops suppresses the dissociation of weak acids and bases relative to bulk solution. For free radicals, there is an isolation effect that suppresses radical chain termination reactions when radical concentrations are low. Under extreme non‐equilibrium conditions, half the drops contain one radical, even when bulk solution calculations indicate a concentration orders of magnitude smaller. This can greatly enhance the rates of radical chain reactions in drops relative to bulk solution. This latter effect has the potential to dramatically alter modelled rates of reactions in atmospheric particles.
Observations of cirrus clouds with airborne MIR, CLS, and MAS during SUCCESS
Authors: Wang J. R. , Racette P. , Spinhirne J. D. , Evans K. F. , Hart W. D.
Published: February 2004

Observations of cirrus clouds were made with a host of instruments on board the NASA ER‐2 aircraft on April 16, 1996. These instruments provide radiometric measurements covering the visible, infrared, and millimeter‐wave regions of the electromagnetic wave spectrum, as well as profiles of lidar backscatter at 1.064 µm. The cirrus clouds are classified into two groups: the modest cirrus clouds with lidar backscatter from the surface and the intense cirrus clouds without lidar surface returns. For the modest clouds, the magnitudes of brightness depressions are typically less than 5 K and are comparable at 150 GHz and 220 GHz. The depressions for the water vapor channels (e.g. 183.3±7 GHz) are smaller. We interpret the microwave brightness depressions for the modest cirrus cases as due to reduced skin temperature from the cloud shadow, rather than ice scattering. For the intense cirrus cases, the magnitude of brightness depression at 220 GHz reach 35 K and are far greater than those at 150 GHz. After correcting for the skin temperature effect, a regression between the observed brightness depressions at 150 and 220 GHz frequencies results in a slope of 2.75. Comparison with radiative transfer modeling for solid spherical ice particles, indicates a median equivalent mass diameter of about 350 µm, and ice water path ranging up to 300 g/m². The results illustrate the potential utility of millimeter and sub‐millimeter wave radiometry for characterizing microphysical properties of thick cirrus.
3‐D time‐dependent simulations of the tethered satellite‐ionosphere interaction
Authors: Ma T. Z. , Schunk R. W.
Published: February 2004

A three‐dimensional time‐dependent fluid model was used to study the interaction of the TSS‐1R satellite with the ionosphere. The model was configured to take account of the correct satellite size (1.6m) and velocity (8 km/s), a realistic O+/electron mass ratio (29,150), the geomagnetic field, and the length of time the satellite stays on specific field lines. The simulation boundary was also moved far from the satellite (∼20m) in an effort to minimize boundary condition effects. The emphasis was on positive satellite potentials just above (10 v) and below (4 v) the O+ ram energy of 5 eV. The simulations indicated the following: (1) A very long, field‐aligned, cylindrical potential structure forms, which has a radius slightly larger than the satellite radius; (2) A sheath forms around the satellite in a toroidal region in the equatorial plane, but does not form in the cylindrical volume where the B‐field intersects the satellite. The sheath E‐field is mapped along B and exists in a thin cylindrical shell with radii that extend from the satellite surface (Rs) to about 1.3 Rs; (3) The sheath is asymmetric due to the satellite motion across B, but this makes a negligible contribution to the collected current because of the large satellite size; (4) For a 10‐volt satellite, the sheath reflects O+ ions in the ram direction, which results in a slight density buildup in front of the satellite; and (5) The bulk of the current flows along B, but Hall and E‐field components also exist. Their magnitudes vary markedly with position, but representative values can be given at locations where the currents are the largest. In terms of the thermal current, the parallel to B component is 4.2 along the polar axis one Rs away from the satellite. Close to the satellite, and in the equatorial plane and ram direction, the E × B component is 8.8 and the component parallel to E is 2.0. The collected current is much larger than that predicted by the simple Parker‐Murphy theory.
Gravity wave modulated airglow observation from spacecraft
Authors: Mende S. B. , Frey H. , Geller S. P. , Swenson G. R.
Published: February 2004

During the STS‐75 shuttle mission a special purpose electronic imager viewed the atmosphere below the shuttle orbiter in the wake direction with the objective of imaging gravity wave induced airglow modulation. A continuous sequence of images was taken with a picture repetition rate of 4 per second. A narrow band (3nm) filter was used to select the O2 atmospheric 0,0 band at 762 nm. The effectiveness of the filter was demonstrated by comparing images of tropospheric clouds with and without filter under full moon conditions. The test showed that the atmospheric O2 absorption combined with the filter was effective in suppressing intensity variations of the bright full moon illuminated clouds and any other earth albedo. Therefore under conditions of low moonlight the filtered images truly represented the modulation of the airglow intensity uncontaminated by earthshine. Longer sequences of airglow data were processed to compensate for spacecraft motion and to dynamically integrate the signal into a latitude and longitude map of airglow modulations. Because of the intrinsic low pass filtering of the slant view observation geometry preferential enhancement of the higher frequencies was needed to bring out waves in the wavelength range of <200 km. Although the shuttle based limited operation of the imager did not permit to make large area global surveys, the results demonstrated that spacecraft based imaging of the airglow on a long duration flight would produce a global data set much needed for the understanding of Mesosphere Lower Thermosphere dynamics.
Impact of inert organic nitrate formation on ground‐level ozone in a regional air quality model using the Carbon Bond Mechanism 4
Authors: Kasibhatla P. , Chameides W. L. , Duncan B. , Houyoux M. , Jang C. , Mathur R. , Odman T. , Xiu A.
Published: February 2004

A regional air quality model is used to assess the impact of inert organic nitrate formation on ground‐level ozone in the eastern United States during summer. The chemical mechanism used is the Carbon Bond Mechanism 4 (CBM4), which is widely used by regulatory agencies in the United States in air quality modeling applications. Recently, modifications were made to the reaction mechanism involving the organic peroxy radicals which form inert organic nitrates without a critical scientific review of the effects of these changes. In this study, we demonstrate for the first time that the simulated large‐scale distribution of ground‐level ozone is extremely sensitive to these mechanism changes. Inclusion of radical‐radical reactions involving the organic peroxy radicals suppresses inert organic nitrate formation, and leads to significant increases in nitrogen oxide levels over large parts of the model domain. As a consequence of increased rates of ozone photochemical production, ozone mixing ratios are enhanced by as much 10–25 ppbv when these additional radical termination pathways are considered in the model.