bluuebunny/crossref_metadata_2025 huggingface dataset:
Concurrent altimeter and infrared observations of Rossby wave propagation near 34°N in the northeast Atlantic
Authors: Cipollini Paolo , Cromwell David , Jones Matthew S. , Quartly Graham D. , Challenor Peter G.
Published: February 2004

We present observations of long‐wavelength baroclinic Rossby waves near 34° N in the Northeast Atlantic ocean (east of the Mid‐Atlantic Ridge) using both TOPEX/POSEIDON sea surface height (SSH) altimeter data and ERS‐1 Along‐Track Scanning Radiometer sea surface temperature (SST) measurements. Using the Fourier transforms of longitude‐time diagrams of the zonal gradients of SST and SSH we locate the spectral components corresponding to westward wave propagation and estimate wavelength, period and propagation speed. The energy associated with the propagating waves in that region is distinctly higher than in the surrounding areas. The similarities between the properties of the SST and SSH zonal gradients are remarkable with the same propagating signals clearly observed in both fields. It is believed that the interaction between the Rossby waves and the Azores current could play a major role in the amplification of the waves themselves.
Solar wind‐magnetosphere coupling during an isolated substorm event: A multispacecraft ISTP study
Authors: Pulkkinen T. I. , Baker D. N. , Turner N. E. , Singer H. J. , Frank L. A. , Sigwarth J. B. , Scudder J. , Anderson R. , Kokubun S. , Nakamura R. , Mukai T. , Blake J. B. , Russell C. T. , Kawano H. , Mozer F. , Slavin J. A.
Published: February 2004

Multispacecraft data from the upstream solar wind, polar cusp, and inner magnetotail are used to show that the polar ionosphere responds within a few minutes to a southward IMF turning, whereas the inner tail signatures are visible within ten min from the southward turning. Comparison of two subsequent substorm onsets, one during southward and the other during northward IMF, demonstrates the dependence of the expansion phase characteristics on the external driving conditions. Both onsets are shown to have initiated in the midtail, with signatures in the inner tail and auroral oval following a few minutes later.
The Brazil/Guará Equatorial Spread F Campaign: Results of the large scale measurements
Authors: LaBelle J. , Jahn J.‐M. , Pfaff R. F. , Swartz W. E. , Sobral J. H. A. , Abdu M. A. , Muralikrishna P. , dePaula E. R.
Published: February 2004

The Guará campaign equatorial spread F rocket was launched from Alcântara, Brazil, on 14 October 1994 at 1955 LT (2255 UT) into an active topside spread F event. Spread F plasma irregularities observed up to 822 km altitude correlate well with plumes observed simultaneously with a coherent backscatter radar. Matching 1–10 km features in the rocket and radar data over the altitude range 300–800 km implies an eastward drift speed of ∼ 110 m/s, versus 95 m/s at 400–500 km based on radar interferometry. Combining these two measurements implies an average upward drift of 30 m/s for the highest altitude structures. The amplitude difference between low‐ and high‐altitude 10‐km density structures, if attributed to temporal effects, implies an effective diffusion coefficient (decay time constant) of 500–1000 m²/s (2‐4×10−4 s−1), which agrees with previous estimates from other techniques and supports the idea that the decay of spread F turbulence occurs in a scale‐independent manner.
Impact of the tropopause on upward propagation of mountain waves
Authors: Worthington R. M. , Thomas L.
Published: February 2004

The vertical propagation of mountain waves into the stratosphere is investigated, with reference to the Scorer parameter profile in the troposphere, and the change in Brunt‐Väisälä frequency at the tropopause. VHF radar provides data on the vertical and horizontal wind velocities, and echo power, while radiosondes supply temperature profiles. In studies of four large‐amplitude mountain‐wave events, where the wave phase remains nearly constant throughout the troposphere, partial reflection at a sharp tropopause offers a better explanation than wave trapping below a minimum in the Scorer parameter.
The nighttime production of OH radicals in the continental troposphere
Authors: Bey Isabelle , Aumont Bernard , Toupance Gérard
Published: February 2004

Chemical pathways involved in the nocturnal production of hydroxyl radical (OH) and associated peroxy radicals (HO2 and RO2) are quantified for various environmental situations of the continental troposphere by means of numerical simulations. In the nocturnal stable layer, most of the OH radicals are directly produced by VOC+O3 reactions in rural and semipolluted environments while in urban environments, they result mainly from the radical chain propagation from RO2 and HO2. The radical propagation is mainly driven by NO: the nitrate radical (NO3) plays no role in such processes but is significantly involved in the direct formation of RO2 radicals. Above the nocturnal stable layer, whatever the environmental situation, OH radicals are mainly due to radical chain propagation in which NO3 plays a significant role. The nighttime simulated OH concentrations are 3 × 104 to 5 × 105 and 1 × 104 to 5 × 104 molec cm−3 for the nocturnal stable and residual layers respectively.
On the influence of electrostatic charging on coagulation of dust and ice particles in the upper mesosphere
Authors: Reid George C.
Published: February 2004

The upper mesosphere, at heights above about 80 km, is the region of the atmosphere in which most ablation of incoming meteoric material takes place, and is thought to contain tiny nanometer‐size smoke and dust particles with concentrations of several thousand per cubic centimeter. In the extremely cold summer conditions at high latitudes, these particles probably form the condensation nuclei on which ice particles grow, giving rise to a variety of unique phenomena, including noctilucent clouds and localized electron depletions (“biteouts”). Recent work has shown that the particles become electrically charged by scavenging free electrons and positive ions from the background ionosphere. Under normal daytime conditions, calculations of charge balance have shown that most of the particles will carry a single negative charge, and it has been pointed out that electrostatic repulsion will inhibit coagulation of the particles, which would otherwise be an important mechanism for their growth. It is shown here that the opposite is true when ionization rates are very low, for example at night in the absence of energetic‐particle precipitation. In this case, positively and negatively charged particles tend to exist in equal numbers, and coagulation is enhanced by charging, instead of being inhibited. Because of the major unknown factors other than charging that affect coagulation, only idealized semi‐quantitative estimates of coagulation rates can be made. Electrical charging, however, appears to be a much less serious barrier to coagulation than had been thought, and may actually be a powerful stimulant.
Diffusion and viscosity in silicate liquids: Percolation and effective medium theories
Authors: Sen Sabyasachi , Mukerji Tapan
Published: February 2004

The compositional variations of the diffusivity of network‐forming ions (Si, Al, O) and viscosity in silicate liquids have been modeled using percolation theory . The relative fraction of bridging oxygen (BO) and non‐bridging oxygen (NBO) in a silicate liquid serves the purpose of the simplest critical variable with respect to which diffusion and viscous flow show interesting cross‐over behaviors. The diffusion of network‐forming ions is found to be strongly coupled to one another and show a percolation transition at 16 vol% of NBO's. The viscosities of silicate liquids also show a rigidity percolation behavior at a similar volume fraction of NBO's. These observations indicate that microscopic diffusion events are probable precursors of viscous flow. Effective medium theories have also been used to model the compositional dependence of the viscosity of silicate liquids.
Diffraction of long period Rayleigh waves by a slab: effects of mode coupling
Authors: Lognonné Philippe , Clévédé Eric
Published: February 2004

We compute seismograms of the fundamental Rayleigh waves propagating through a slab structure, with either a lateral variation in seismic velocities, or in attenuation. At periods of 100 sec, we show that the phase delay is strongly reduced by the surface waves Fresnel zone, and that coupling must be considered far along the dispersion branch, up to at least ℓ±25. Limiting the coupling to fewer modes produces a signal associated to a ghost structure at the antipode of the slab. We also show that the amplitude perturbations produced by the diffraction and the attenuation of the slab are comparable in size.

Future waveform studies, especially those associated to global waveform inversions, must then carefully consider these effects.
Seasonal and interannual variability of mesospheric echoes observed with the Middle and Upper Atmosphere Radar during 1986–1995
Authors: Kubo Koji , Sugiyama Takuya , Nakamura Takuji , Fukao Shoichiro
Published: February 2004

To investigate long‐term variabilities of radar echo intensities from the mesosphere, we have analyzed a 10‐year data set obtained with the middle and upper atmosphere (MU) radar at Shigaraki, Japan (34°51′N, 136°6′E) during the period from 1986 to 1995. Two types of echoes have been identified: The echoes are primarily due to isotropic scattering from 70 to 85 km in altitude in summer, whereas they are mainly due to specular scattering from 60 to 70 km in other seasons. Clear annual variabilities have been observed in both occurrence frequency and intensity of the echoes. The upper end of summertime mesospheric echoes seems to be located just below the summer mesopause. An interannual variability of summertime mesopause height has also been suggested.
The potential effect of oceanic biological degradation on the lifetime of atmospheric CH3Br
Authors: Yvon‐Lewis Shari A. , Butler James H.
Published: February 2004

We use a global, coupled, ocean‐atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric CH3Br. The results of this study show that both the value of the oceanic degradation rate constant and its geographic distribution are important in determining the calculated atmospheric lifetime. The best estimate of the partial lifetime of atmospheric CH3Br with respect to oceanic loss now comes to 1.8–1.9 y with a full possible range of 1.1–3.9 y, which, together with other, non‐oceanic losses, yields a total atmospheric lifetime of 0.7 y (0.6–0.9 y). A subsequent revision of the budget for atmospheric CH3Br indicates that estimated sinks of CH3Br today exceed estimated sources by about 70 Gg y−1.
The latitudinal dependence of ion temperature in the Io plasma torus
Authors: Thomas Nicolas , Lichtenberg Günter
Published: February 2004

A set of ground‐based spectroscopic observations of the [SII] 6716 Å, 6731 Å emission from the Io plasma torus (IPT) is described. The Doppler‐resolved spectra show that the perpendicular ion temperature increases significantly with increasing distance from the plasma equator at 6.0 RJ. Using a simple model, a “Kappa”‐distribution of form similar to that used previously in an analysis of electron temperature dependence with magnetic latitude [Meyer‐Vernet et al., Icarus, 116, 202, 1995] provides a reasonable fit to our data. It is also shown that the ion temperature (Ti) measured by the Voyager 1 plasma sciences experiment (PLS) can be successfully modelled with the derived parameters, assuming an L−8/3 fall‐off of Ti with distance along the plasma equator which is consistent with previous ground‐based and spacecraft measurements. The results suggest that extrapolation of PLS measurements assuming two overlapping Maxwellian distributions with constant temperatures along magnetic field lines to construct 3‐D models of the IPT need to be re‐assessed.
Water vapour and ozone in the mesosphere as measured by UARS MLS
Authors: Pumphrey Hugh C. , Harwood Robert S.
Published: February 2004

Until recently, measurements of water vapour in the upper mesosphere were scarce. Instruments on the UARS platform have made the first global measurements of upper mesospheric H2O; the Microwave Limb Sounder is one of these instruments. It has also measured upper mesospheric ozone. So far, various random and systematic errors have prevented accurate retrievals of either species in the upper mesosphere but much can be learned from the raw radiance measurements. In this paper we present these measurements and show how they can provide information on the dynamics of the mesosphere.
Variability of UV‐B at four stations in Europe
Authors: Zerefos C. S. , Balis D. S. , Bais A. F. , Gillotay D. , Simon P. C. , Mayer B. , Seckmeyer G.
Published: February 2004

The variability of solar irradiance in the UV‐B spectral region is studied at four stations operating well‐calibrated spectroradiometers during the period 1991–96. It is confirmed that total ozone is the controlling factor in long‐term changes of solar irradianee below 320 nm received at the ground. This result is supported by the similar long‐term variability under clear sky and all sky conditions during the past five years. The study includes estimates of the amplitude of the annual cycle and estimates of long‐term changes. An important result of this note is, that calculated changes in solar irradiance depend on the length of the observational period and that any speculations on its future changes should be treated always with caution. It is estimated that a 2.7% change per year in solar irradiance at 305 nm at Thessaloniki is a rate that could possibly continue in view of the expected continuation of the ozone decline resulting to an increase of 27% per decade, which is comparable to the amplitude of the annual cycle at that station.
Solar wind polytropic index in the vicinity of stream interactions
Authors: Newbury J. A. , Russell C. T. , Lindsay G. M.
Published: February 2004

In an ideal, 3‐D, closed system that experiences compression and expansion, the temperature (T) and density (n) of a monatomic gas are related adiabatically through the polytropic law; i.e., T ∝ nα−1, where α is the polytropic index and equals 5/3. This relationship has been examined over a variety of scale sizes in the solar wind, and empirical measurements of α vary a great deal. As shown in this paper, blanket applications of the polytropic law to ambient solar wind can return misleading measurements of α, due to inhomogeneities in the solar wind originating at coronal source regions. However, on a smaller and more localized scale, adiabatic compression and expansion is observed. In this paper, we measure α by examining parcels of originally homogeneous material that have become compressed at stream interactions. A superposed epoch analysis of 73 isolated stream interactions observed by PVO illustrates this adiabatic behavior. Observations of individual stream interactions show clear intervals where α ∼ 5/3 and also a few cases where α ∼ 2, suggesting that the number of degrees of freedom may occasionally be restricted.
Helicon modes driven by ionospheric O+ ions in the plasma sheet region
Authors: Lakhina Gurbax S. , Tsurutani Bruce T.
Published: February 2004

The presence of ionospheric‐origin oxygen ions in the plasma sheet region results in only partial cancellation of the electron Hall current leading to the occurrence of the helicon mode rather than the Alfvén mode. It is shown that the presence of ionospheric‐origin oxygen ion beams with anisotropic pressure can excite helicon mode instability in the near‐Earth plasma sheet region provided their Alfvénic Mach numbers lie in a certain range. The helicon modes are easily excited under the conditions when the usual long wave‐lengths fire‐hose modes are stable. The typical real frequencies of the excited helicon modes are between 1 to 10 mHz, and the typical e‐folding time of the instability is about 3 to 15 minutes at wavelengths of 1 to 5 RE. Therefore these modes are likely to attain saturation during enhanced convection events lasting for a few hours. Large amplitude helicon modes would distort the ambient magnetic field and may be observable as flux ropes. Low‐frequency turbulence produced by these modes could scatter electrons and help excitation of the ion tearing modes leading to substorm onset.
Uptake of HNO3 on ice under upper tropospheric conditions
Authors: Zondlo Mark A. , Barone Stephen B. , Tolbert Margaret A.
Published: February 2004

The uptake of HNO3 on thin ice films was investigated under upper tropospheric temperature and pressure conditions using a Knudsen cell reactor and FTIR reflection‐absorption spectroscopy. Two different HNO3 uptake regimes were noted with the critical threshold being the supercooled H2O/HNO3 liquid isotherm at a specific temperature. For H2O/HNO3 partial pressures below the supercooled H2O/HNO3 liquid isotherm, a time‐dependent uptake of HNO3 was observed until the HNO3 surface coverage reached approximately one monolayer. The initial uptake coefficient of HNO3 on the ice film was γ ≥ 0.005 which became progressively smaller until a steady‐state uptake coefficient of γ=0.0002±0.0001 was obtained after monolayer coverage of HNO3. In contrast, when H2O and HNO3 partial pressures were greater than the supercooled H2O/HNO3 isotherm, unlimited uptake of HNO3 was observed with an uptake coefficient γ > 0.005. Under these conditions, the infrared spectra showed the formation and continual growth of a supercooled H2O/HNO3 liquid. By using the best estimates of HNO3 mixing ratios and ice surface area densities in the upper troposphere, two limiting cases of HNO3 uptake are discussed in the context of upper tropospheric chemistry.
Tracer transport in the tropical stratosphere due to vertical diffusion and horizontal mixing
Authors: Hall Timothy M. , Waugh Darryn
Published: February 2004

Observations of linearly increasing (e.g., SF6) and periodically varying (e.g., H2O + 2CH4) long‐lived tracers in the lower stratosphere provide independent constraints on theories of transport in the region. Taken together, these data allow separation of the roles of diffusion (with coefficient Kθ) and advection (at rate Q) through isentropic surfaces, and mixing of extra‐tropical air into the tropics (with relaxation time τ). Using a one‐dimensional diffusive‐advective model of the tropical stratosphere, which allows relaxation of mixing ratios to extra‐tropical values, we obtain solutions for periodic and linear tracers. Fitting the solutions to observations yields Kθ ≈ 0.3 K²/day (Kz ≈ 0.01 m²/s), τ ≈ 1.3 years, and Q ≈ 0.5 K/day (
). These values produce profiles for CO2 in reasonable agreement with aircraft observations. However, a large range of Kθ results in equally good agreement, although τ and Q are more tightly constrained. In the lower tropical stratosphere, vertical diffusion appears to play little role in transporting tracer.
The Role of sea ice in 2×CO2 climate model sensitivity: Part II: Hemispheric dependencies
Authors: Rind D. , Healy R. , Parkinson C. , Martinson D.
Published: February 2004

How sensitive are doubled CO2 simulations to GCM control‐run sea ice thickness and extent? This issue is examined in a series of 10 control‐run simulations with different sea ice and corresponding doubled CO2 simulations. Results show that with increased control‐run sea ice coverage in the Southern Hemisphere, temperature sensitivity with climate change is enhanced, while there is little effect on temperature sensitivity of (reasonable) variations in control‐run sea ice thickness. In the Northern Hemisphere the situation is reversed: sea ice thickness is the key parameter, while (reasonable) variations in control‐run sea ice coverage are of less importance. In both cases, the quantity of sea ice that can be removed in the warmer climate is the determining factor. Overall, the Southern Hemisphere sea ice coverage change had a larger impact on global temperature, because Northern Hemisphere sea ice was sufficiently thick to limit its response to doubled CO2, and sea ice changes generally occurred at higher latitudes, reducing the sea ice‐albedo feedback. In both these experiments and earlier ones in which sea ice was not allowed to change, the model displayed a sensitivity of ∼0.02°C global warming per percent change in Southern Hemisphere sea ice coverage.
Long period geomagnetic field fluctuations at Terra Nova Bay (Antarctica)
Authors: Villante U. , Lepidi S. , Francia P. , Meloni A. , Palangio P.
Published: February 2004

A statistical analysis of the power spectra (0.7–5 mHz) of the geomagnetic field components H and D recorded at Terra Nova Bay (Antarctica) during three austral summers close to the maximum of solar activity reveals power enhancements in the H component at ≈ 3.3, 3.9 and 4.5 mHz, which become more evident during daytime intervals. During intervals characterized by higher solar wind speeds these spectral features more clearly emerge and are also accompanied by other enhancements at lower frequencies (≈ 1.2, 1.9 and 2.7 mHz). The observed frequencies are close to the ones detected both at auroral and low latitudes.
Stress fields generating ring faults in volcanoes
Authors: Gudmundsson Agust , Marti Joan , Turon Elisenda
Published: February 2004

Ring faults in volcanoes have been recognized for a long time, but their mechanics of formation is still poorly understood. While the subsidence on a ring fault during a large eruption from the associated chamber is easily understood, the initiation of the fault itself has been difficult to explain. For a ring fault to form, the tensile and shear stresses at the surface of the volcano must peak at a certain radial distance from the surface point above the center of the chamber. Empirical evidence, however, shows that during most periods of unrest in active volcanoes the stress field is not favorable for the initiation of ring faults. We made several tens of boundary‐element models of magma chambers of various geometries and subject to different loading conditions. The results indicate that overpressure or underpressure in the chamber as the only loading is unlikely to initiate ring faults. For a spherical chamber subject to horizontal extension or doming, and a sill‐like chamber subject to horizontal extension, the tensile and shear stresses at the surface of the volcano peak at a certain radial distance from the surface point above the center of the chamber. Then, however, the maximum stresses occur at the boundary of the chamber itself, which would normally lead to sheet injection rather than to ring‐fault formation. By contrast, a sill‐like magma chamber subject to doming gives rise to a stress field suitable for the initiation of a ring fault.
The modern atmospheric background dust load: Recognition in central Asian snowpack, and compositional constraints
Authors: Hinkley Todd , Pertsiger Felix , Zavjalova Liliya
Published: February 2004

Dusts in strata of snowpack in the Alai‐Pamir range, Kirghizstan, Central Asia, have chemical compositions that are in the same restricted range as those of the dusts found in snowpacks at three other locations: central south Greenland, the St. Elias range (Alaska), and coastal Antarctica, where special‐type local dust sources certainly cannot dominate. This similarity at the four widely separated sites appears to indicate that there is a modern atmospheric background dust that is the same on a regional, hemispheric, or global scale. The common compositional range is that of average crustal rock, or of moderately ferromagnesian volcanic rock. It is not that of carbonate, nor highly siliciceous rocks. Previously, the existence of an atmospheric background dust has been postulated only on the basis of its particle size distribution, and only from observations in polar regions. The present study partially determines the chemical composition of the background dust, and confirms its existence in snowpack at four localities worldwide, including the center of the earth's largest continent where dusts of local source have considerable influence.
The Guará Campaign: A series of rocket‐radar investigations of the Earth's upper atmosphere at the magnetic equator
Authors: Pfaff R. F. , Sobral J. H. A. , Abdu M. A. , Swartz W. E. , LaBelle J. W. , Larsen M. F. , Goldberg R. A. , Schmidlin F. J.
Published: February 2004

The Guará Campaign consisted of a series of sounding rockets that were launched from August‐October, 1994 at a new launch facility at Alcântara, Brazil, which is within one degree of the Earth's magnetic equator. The campaign consisted of focused scientific experiments designed to investigate the electrodynamics and irregularities in the equatorial ionosphere and mesosphere and to study their relationship with neutral upper atmosphere motions. In all, 13 large sounding rockets and 20 small meteorological rockets were launched as part of four different experiment groups designed to investigate: (1) the daytime equatorial electrojet, (2) very high altitude Spread‐F processes, (3) sunset electrodynamics, and (4) middle atmosphere‐thermosphere coupling at the equator. All of the experiments utilized ground‐based scientific instruments including a VHF backscatter radar interferometer, magnetometers, ionosondes, and scintillation receivers. The project was a joint undertaking of the National Aeronautics and Space Administration (NASA) of the United States and the Instituto Nacional de Pesquisas Espacias (INPE) of Brazil. The project was named the Guará Campaign after a beautiful species of bird that is native to the equatorial region of Brazil.
Mesospheric observations and modeling of the Zeeman split 233.9 GHz 18O16O Line
Authors: Sandor Brad J. , Clancy R. Todd
Published: February 2004

Observations made from Kitt Peak, AZ, of the 233.9 GHz emission line of 18O16O in the upper stratosphere and lower mesosphere are reported. A good model fit to the line is obtained by incorporation of pressure and temperature broadening effects, as well as a Zeeman splitting algorithm that uses a standard geomagnetic field model and a paramagnetic Hamiltonian description of the molecular energy states. These observations are used, along with the well known 18O16O mixing ratio, to establish absolute calibration for observations of other chemical species from Kitt Peak. Repeated measurements show no change in this absolute calibration between observation dates. The wide magnetic splitting (±1.8. MHz) exhibited by this line with only six Zeeman components provides a unique test of middle atmosphere Zeeman effect model calculations, supporting the use of O2 lines by microwave atmospheric sounders to measure pressure and temperature.
Middle Triassic paleomagnetic results from Central Hubei Province, China and their tectonic implications
Authors: Huang K. , Opdyke N. D.
Published: February 2004

Twenty one sites consisting of 4 to 7 samples per site were drilled from the redbeds of the Middle Triassic Badong Formation from central Hubei province, China. These samples were subjected to progressive thermal demagnetization which revealed two components of magnetization. The low temperature (A) component was probably acquired at a late stage of folding and is similar in direction to the late Mesozoic overprint widely observed in the eastern Yangtze Block. The high temperature (B) component is prefolding with dual polarity. Unlike the prefolding paleomagnetic directions observed in eastern Sichuan, western Hubei and northwestern Hunan, the B component resolved from central Hubei indicates no significant rotation with respect to other parts of the Yangtze Block. Since one of the two sampled sections is in the strongly deformed foreland fold‐thrust belt of the Qinling Fold Belt, this would seem to negate the possibility that the differential rotations observed in the border area between Sichuan, Hubei, Hunan and Guizhou are associated with the collision of the Yangtze Block with the North China Block.
SWICS/Ulysses observations: The three‐dimensional structure of the heliosphere in the declining/minimum phase of the solar cycle
Authors: Woch J. , Axford W. I. , Mall U. , Wilken B. , Livi S. , Geiss J. , Gloeckler G. , Forsyth R. J.
Published: February 2004

The ESA/NASA spacecraft Ulysses provides the first in‐situ observation of the solar wind at high solar latitudes. Data obtained with the Solar Wind Ion Composition Spectrometer (SWICS) during the first orbit of Ulysses around the Sun can be used to obtain a global view of the solar wind pattern within the heliosphere during the declining/minimum phase of the solar activity cycle. This provides information on the solar corona, specifically on any latitudinal variation of coronal parameters as far as they play a role in the solar wind acceleration process. The measurements show: The 3‐dim. distribution of the solar wind appears as a pattern of basically two states. The fast solar wind with speeds of about 750 km/s emanating from the polar coronal holes dominates the heliosphere. The slow solar wind from the streamer belts is restricted to a region of about +/−20° around the heliographic equator. The boundary between the two states of the solar wind is sharply defined. The coronal hole streams are remarkably stable and homogeneous on a larger scale. The two independent coronal holes are similar in terms of average speed and spatial extent. In both coronal holes a gradual increase (≤10%) of speed with solar latitude is observed.
Low‐energy electron measurements at Ganymede with the Galileo spacecraft: Probes of the magnetic topology
Authors: Frank L. A. , Paterson W. R. , Ackerson K. L. , Bolton S. J.
Published: February 2004

During the close flyby of Ganymede by the Galileo spacecraft on 6 September 1996 a plasma analyzer was used to obtain comprehensive measurements of the thermal electron plasmas in the vicinity of this moon. Our initial analyses are directed toward the character of energy influxes into Ganymede's polar caps and the pitch angle distributions for warm electrons in the energy range of 70 eV to 4.5 keV. The source of these electrons is Jupiter's plasma sheet within which Ganymede was embedded during the flyby. These electrons were present along the entire trajectory and provide the opportunity to use their pitch angle distributions with respect to the magnetic field in order to investigate the magnetic field topology at Ganymede. Observations of the loss cones for these pitch angle distributions are a simple means of determining whether or not a given magnetic field line intersects the moon's surface. It is found that the observed pitch angle distributions are inconsistent with the current magnetostatic model for the magnetic fields in the vicinity of Ganymede. Thus a major revision of this model is required that accounts for the contributions of the plasma dynamical interaction in order to achieve a more accurate assessment of an intrinsic magnetic moment in the interior of this moon. In addition, the electron energy fluxes into the polar cap at the time of flyby were measured to be about 1 erg/cm²‐s, or a total of approximately 5 × 1016 ergs/s over each polar cap available for excitation and ionization of any atmosphere near the moon's surface.
On the use of later teleseismic arrivals in ACH‐tomography with an application in SE‐Kenya
Authors: Kaspar Tilo , Ritter Joachim R. R.
Published: February 2004

The ACH‐tomography is used to image teleseismic travel‐time residuals into seismic velocity perturbations beneath a recording network. Commonly, these residuals are determined solely from first arrivals of body‐wave phases (e.g., P, PKP, or PKIKP). In this contribution we outline the benefit of adding later phases (e.g., PKKP, SKP, or PcP) to increase the amount of input data and to improve the ray sampling of the target volume. As a case study, a tomographic data set from the Chyulu Hills volcanic field in SE‐Kenya, East Africa, is taken. A model (M1) inverted from first arrival residuals is compared with one (M2) based on an extended data set, including 85 later arrival residuals. Model M2 has an improved statistical basis for evaluating the quality of the results. It confirms the principal features of M1, but shows a slightly larger low‐velocity anomaly beneath the volcanic field in the uppermost mantle, indicating active magmatic processes.
Uncertainties in reactive uptake coefficients for solid stratospheric particles‐1. Surface chemistry
Authors: Carslaw Kenneth S. , Peter Thomas
Published: February 2004

Laboratory data for reactions of ClONO2 or HOCl with HCl on nitric acid trihydrate and sulfuric acid tetrahydrate are compared using a surface reaction model. Data sets where both non‐reactive and reactive uptake were measured reveal that changes in the reactive uptake coefficients of ClONO2 and HOCl can be explained completely by the amount of HCl taken up by the hydrates. Large discrepancies are revealed between measurements from different laboratories which have important consequences for calculated ozone destruction (see companion paper II).
Gas exchange, dispersion, and biological productivity on the West Florida Shelf: Results from a Lagrangian Tracer Study
Authors: Wanninkhof Rik , Hitchcock Gary , Wiseman William J. , Vargo Gabe , Ortner Peter B. , Asher William , Ho David T. , Schlosser Peter , Dickson Mary‐Lynn , Masserini Robert , Fanning Kent , Zhang Jia‐Zhong
Published: February 2004

A Lagrangian tracer study was performed on the west Florida shelf in April 1996 using deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air‐sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium‐3 (³He). The second moment of the patch grew to 1.6 × 10³ km² over a period of 11 days. The gas transfer velocity, normalized to CO2 exchange at 20°C, was 8.4 cm hr−1 at an average wind speed, U10, of 4.4 m s−1 for the duration of the experiment, which is in good agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 µmol kg−1 day−1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO2.
Low‐frequency inertia‐gravity waves in the stratosphere revealed by three‐week continuous observation with the MU radar
Authors: Sato Kaoru , O'Sullivan Donal J. , Dunkerton Timothy J.
Published: February 2004

Continuous observations over three weeks were performed with the MU radar at Shigaraki, Japan (35N, 136E) in April of 1995. By integrating radar echo spectra over 30 min after removing severe interferences, winds were successfully estimated offline up to 24 km in the lower stratosphere. It was found that inertia‐gravity waves with a period of about 20 h and a vertical wavelength of 3.5 km are dominant near 22 km in a region of weak background winds. Four wave packets were fitted to plane waves by a least‐squares method and wave parameters were estimated theoretically. The inertia‐gravity waves propagate energy upward, and their horizontal phase velocity is westward in the range −10 to −20 m s−1. The waves have large momentum fluxes of about −0.002 Nm−2. This result suggests that inertia‐gravity wave drag may contribute to the formation of easterlies in the summer stratosphere.
PKP differential travel times: Implications for 3‐D lower mantle structure
Authors: Song Xiaodong , Helmberger Don V.
Published: February 2004

Differential PKP AB‐DF travel‐time measurements are compared directly with predicted residuals for mantle tomographic models to investigate the heterogeneity of the lowermost mantle. Much of the AB‐DF time is accumulated in the lowermost portions of the mantle, resulting in heavy weighting of 3‐D lowermost mantle structure on the differential travel‐time perturbations. Comparisons of the observations with tomographic models show strong model dependence. The best variance reductions are achieved using the recent P‐wave model of van der Hilst et al. [1997] (up to 20%), but the heterogeneity in the lowermost mantle may be 8 times larger than what shown by the tomographic model. The predictions for present S‐wave tomographic models correlate poorly with the observations if we assume P‐velocity anomalies are proportional to S‐velocity anomalies. We argue that S‐velocity anomalies in the lowermost mantle do not always track P‐velocity anomalies. Our study shows no obvious evidence of slab effect on the observed AB‐DF anomalies and, thus, the use of PKP phases is likely to provide a powerful tool in mapping the P‐velocity structure in the lowermost mantle.
Darwin sea level pressure, 1876–1996: Evidence for climate change?
Authors: Harrison D. E. , Larkin N. K.
Published: February 2004

It has been argued that there was a period of prolonged ENSO conditions between 1990–95 so anomalous that it is “highly unlikely” to be due to “natural decadal‐timescale variation” [Trenberth and Hoar, 1996]. This conclusion follows from their study of the Darwin sea level pressure anomaly record, which found that the 1990–95 period would occur randomly about once every 1100–3000 yrs. Taking into account the uncertainty in number of degrees of freedom in the Darwin time series, we find that conditions like those of 1990–95 may be expected as often as every 150–200 yrs at the 95% confidence level. Student's‐t, ARMA, and Bootstrap/Monte Carlo tests of the time series all yield similar results. We therefore suggest that the 1990–95 period may plausibly be an aspect of the natural variability of the tropical Pacific.
Influence of DMS on the OX ‐ NOY partitioning and the NOX distribution in the marine background atmosphere
Authors: Platt U. , Le Bras G.
Published: February 2004

Recent investigations of the NO3‐DMS reaction showed that HNO3 is the dominant nitrogen product. It is argued that this finding can have implications on the NOX ‐ HNO3/nitrate partitioning, in particular lowering the NOX (= NO + NO2) concentrations in the remote marine boundary layer. Since there ozone formation is NOX limited, biogenic DMS sources may influence the ozone production on a global scale.
Transformation shear instability and the seismogenic zone for deep earthquakes
Authors: Marone Chris , Liu Ming
Published: February 2004

We use a numerical model for olivine‐spinel transformation to study deep earthquake nucleation and to delineate the seismogenic region within a subducting slab. The model includes laboratory‐derived flow laws, latent heat release, and phase transformation kinetics. We calculate deformation, transformation state, grain growth, and rheology for several paths within a subducting slab. Strain rate perturbations are imposed to define the necessary conditions for instability. Strain rate perturbations decay for ξ < a critical value ξc, and thus the coldest, interior portion of the metastable wedge deforms stably. For ξ≥ξc, strain rate perturbations grow, shear strength decreases with strain, and the system is potentially unstable. The instability condition is mapped to delineate the seismogenic zone within a subducting slab. The model seismogenic zone is bounded by ξc, and, at larger percent transformations, by coarsening of spinel grains and saturation of the transformation weakening effect. The model predicts a narrow seismogenic region along the outer edges of the metastable wedge and thus a “double seismic” zone, consistent with some seismic observations. Several simplifying assumptions are required due to lack of thermo‐kinetic data and incomplete knowledge of constituent mineralogy and rheology. However, the model provides a quantitative definition of the instability condition and a framework for testing the hypothesis of transformation‐induced instability.
Tracing the topology of the October 18–20, 1995, magnetic cloud with ∼0.1–10² keV electrons
Authors: Larson D. E. , Lin R. P. , McTiernan J. M. , McFadden J. P. , Ergun R. E. , McCarthy M. , Rème H. , Sanderson T. R. , Kaiser M. , Lepping R. P. , Mazur J.
Published: February 2004

Five solar impulsive ∼1–10² keV electron events were detected while the WIND spacecraft was inside the magnetic cloud observed upstream of the Earth on October 18–20, 1995. The solar type III radio bursts produced by these electrons can be directly traced from ∼1 AU back to X‐ray flares in solar active region AR 7912, implying that at least one leg of the cloud was magnetically connected to that region. Analysis of the electron arrival times shows that the lengths of magnetic field lines in that leg vary from ∼3 AU near the cloud exterior to ∼1.2 AU near the cloud center, consistent with a model force‐free helical flux rope. Although the cloud magnetic field exhibits the smooth, continuous rotation signature of a helical flux rope, the ∼0.1‐1 keV heat flux electrons and ∼1–10² keV energetic electrons show numerous simultaneous abrupt changes from bidirectional streaming to unidirectional streaming to complete flux dropouts. We interpret these as evidence for patchy disconnection of one end or both ends of cloud magnetic field lines from the Sun.
A new parameterization of H2SO4/H2O aerosol composition: Atmospheric implications
Authors: Tabazadeh Azadeh , Toon Owen B. , Clegg Simon L. , Hamill Patrick
Published: February 2004

Recent results from a thermodynamic model of aqueous sulfuric acid are used to derive a new parameterization for the variation of sulfuric acid aerosol composition with temperature and relative humidity. This formulation is valid for relative humidities above 1% in the temperature range of 185 to 260 K. An expression for calculating the vapor pressure of supercooled liquid water, consistent with the sulfuric acid model, is also presented. We show that the Steele and Hamill [1981] formulation underestimates the water partial pressure over aqueous H2SO4 solutions by up to 12% at low temperatures. This difference results in a corresponding underestimate of the H2SO4 concentration in the aerosol by about 6% of the weight percent at approximately 190 K. In addition, the relation commonly used for estimating the vapor pressure of H2O over supercooled liquid water differs by up to 10% from our derived expression. The combined error can result in a 20% underestimation of water activity over a H2SO4 solution droplet in the stratosphere, which has implications for the parameterization of heterogeneous reaction rates in stratospheric sulfuric acid aerosols. The influence of aerosol composition on the rate of homogeneous ice nucleation from a H2SO4 solution droplet is also discussed. This parameterization can also be used for homogeneous gas phase nucleation calculations of H2SO4 solution droplets under various environmental conditions such as in aircraft exhaust or in volcanic plumes.
The climate response to CO2 of the Hadley Centre coupled AOGCM with and without flux adjustment
Authors: Gregory J. M. , Mitchell J. F. B.
Published: February 2004

Coupled atmosphere‐ocean general circulation models have a tendency to drift away from a realistic climatology. The modelled climate response to an increase of CO2 concentration may be incorrect if the simulation of the current climate has significant errors, so in many models, including ours, the drift is counteracted by applying prescribed fluxes of heat and fresh water at the ocean‐atmosphere interface in addition to the calculated surface exchanges. Since the additional fluxes do not have a physical basis, the use of this technique of “flux adjustment” itself introduces some uncertainty in the simulated response to increased CO2. We find that the global‐average temperature response of our model to CO2 increasing at 1% per year is about 30% less without flux adjustment than with flux adjustment. The geographical patterns of the response are similar, indicating that flux adjustment is not causing any gross distortion. The reduced size of the response is due to more effective vertical transport of heat into the ocean, and a somewhat smaller climate sensitivity. Although the response in both cases lies within the generally accepted range for the climate sensitivity, systematic uncertainties of this size are clearly undesirable, and the best strategy for future development is to improve the climate model in order to reduce the need for flux adjustment.
Energetic particle signatures at Ganymede: Implications for Ganymede's magnetic field
Authors: Williams D. J. , Mauk B. H. , McEntire R. W. , Roelof E. C. , Armstrong T. P. , Wilken B. , Roederer J. G. , Krimigis S. M. , Fritz T. A. , Lanzerotti L. J. , Murphy N.
Published: February 2004

The second encounter of the Galileo satellite with the Galilean moon Ganymede provided energetic particle measurements showing effects due to the presence of that moon. Jovian corotation signatures, present on approach to and departure from the Ganymede system, suddenly become much smaller when Galileo enters what has been termed Ganymede's magnetosphere. The location of these transitions agrees with magnetopause crossings identified by the magnetometer and plasma wave instruments. In Ganymede's magnetosphere, energetic ion and electron distributions display loss cone signatures whenever the Energetic Particles Detector (EPD) views along the magnetic field line. The loss cone measurements are used to estimate Ganymede's surface magnetic field along the satellite track. The results agree with model projections to Ganymede's polar cap and support the existence of a Ganymede‐intrinsic magnetic field. An evolution from single to double loss cone also occurs with increasing electron energy.
A preliminary estimate of the size of the coming solar cycle 23, based on Ohl's Precursor Method
Authors: Kane R. P.
Published: February 2004

Solar Cycle 22 seems to be nearing its end. The 12‐month moving averages of sunspot number and aa index seem to have levelled near 8.1 and 17.9. If these are confirmed as the minimum values, a prediction for Cycle 23 by the precursor method indicates a maximum amplitude of 170±13 (by the single variable regression analysis) and 177±21 (by the bivariate analysis), suggesting that cycle 23, potentially, will be one of the largest sunspot cycles on record (i.e., Rmax > 160).
High‐resolution seismic reflection profiling of the Santa Monica Fault Zone, west Los Angeles, California
Authors: Dolan James F. , Pratt Thomas L.
Published: February 2004

High‐resolution seismic reflection data obtained across the Santa Monica fault in west Los Angeles reveal the near‐surface geometry of this active, oblique‐reverse‐left‐lateral fault. Although near‐surface fault dips as great as 55° cannot be ruled out, we interpret the fault to dip northward at 30° to 35° in the upper few hundred meters, steepening to ≥65° at 1 to 2 km depth. A total of ∼180 m of near‐field thrust separation (fault slip plus drag folding) has occurred on the fault since the development of a prominent erosional surface atop ∼1.2 Ma strata. In the upper 20 to 40 m strain is partitioned between the north‐dipping main thrust strand and several closely spaced, near‐vertical strike‐slip faults observed in paleoseismologic trenches. The main thrust strand can be traced to within 20 m of the ground surface, suggesting that it breaks through to the surface in large earthquakes. Uplift of a ∼50,000‐year‐old alluvial fan surface indicates a short‐term, dip‐slip rate of ∼0.5 mm/yr, similar to the ∼0.6 mm/yr dip‐slip rate derived from vertical separation of the oxygen isotope stage 5e marine terrace 3 km west of the study site. If the 0.6 mm/yr minimum, dip‐slip‐only rate characterizes the entire history of the fault, then the currently active strand of the Santa Monica fault probably began moving within the past ∼300,000 years.