bluuebunny/crossref_metadata_2025 huggingface dataset:
Shear‐wave splitting above the subducting Juan de Fuca Plate
Authors: Cassidy John F. , Bostock Michael G.
Published: February 2004

Shear‐wave splitting observed in three‐component broadband recordings of local earthquakes near southern Vancouver Island, British Columbia, provide the first constraints on shear‐wave anisotropy in the continental crust above the subducting Juan de Fuca plate. Waveforms of 22 “shallow” earthquakes (15–30 km depth) and 16 “deep” earthquakes (40–60 km depth) were examined for shear‐wave splitting. The fast‐polarization direction is well‐defined at 312±19° for the deep earthquakes, and 293±27° for the shallow earthquakes. These fast polarization directions are approximately parallel to the continental margin and coincide with the orientation of the pressure axes of small crustal earthquakes in this region. Interpreting this polarization pattern in terms of the extensive‐dilatancy anisotropy model indicates a margin‐parallel compressive stress regime. Comparing the average time delays between the fast and slow shear‐waves for the deep earthquakes (0.32 s) and the shallow earthquakes (0.20 s) suggests that the source of the seismic anisotropy is stronger in the upper 20 km of the continental crust. Here, the average differential shear‐wave anisotropy is estimated at 2.3%. These observations support the theory of weak coupling between the downgoing Juan de Fuca plate and the overlying North America plate, as the principal stress is perpendicular to the direction of subduction, and the S‐wave splitting above the subducting plate is nearly perpendicular to the SKS splitting direction in the upper mantle beneath the subducting plate.
A comparison of ozone measurements made by the ATMOS, MAS, and SSBUV instruments during ATLAS 1, 2, and 3
Authors: Kriebel D. L. , Bevilacqua R. M. , Hilsenrath E. , Gunson M. , Hartmann G. K. , Abrams M. , Daehler M. , Pauls T. A. , Newchurch M. , Aellig C. P. , Bories M. C.
Published: February 2004

Ozone profile measurements were made by three instruments, ATMOS, MAS, and SSBUV, using distinctly different observing techniques, as part of the ATLAS Space Shuttle missions in March 1992, April 1993, and November 1994. ATMOS makes solar‐occultation observations of infrared spectra using a Fourier transform interferometer. MAS uses a limb‐scanning antenna to measure emission spectra at millimeter wavelengths. SSBUV is a nadir‐viewing instrument measuring the transmission of scattered solar ultraviolet radiation modified by ozone absorption. A sample of zonal‐mean mixing ratio profiles indicates that these three ATLAS instruments generally agree to within 10%, although a few potential biases have been noted. There are significant differences in the character of the agreement between ATLAS 1 and ATLAS 2 which will require further study.
Airborne measurements of atmospheric methane over oil fields in western Siberia
Authors: Tohjima Y. , Maksyutov S. , Machida T. , Inoue G.
Published: February 2004

Airborne measurements of atmospheric methane (CH4) over oil fields in western Siberia were carried out on August 1, 1994. Extremely sharp CH4 peaks were observed in the horizontal distribution of CH4 at an altitude of 150 m above the ground surface; the half widths of the peaks were 3–4 km and the concentration of the largest peak exceeded 2.9 ppmv. Since the CH4 distribution was considered to reflect the distribution of CH4 emission strength on the surface, there was strong CH4 emission at the peak positions. All of the observed CH4 peak positions were located at or near oil production sites and/or oil pipelines, suggesting that natural gas was emitted from the facilities. Leakage or venting of natural gas are the probable CH4 sources.
Direct observations of the current structure east of the Bahamas
Authors: Hacker Peter , Firing Eric , Wilson W. Douglas , Molinari Robert
Published: February 2004

Quasisynoptic absolute velocity sections were obtained in the western North Atlantic to the east of the Bahamas on five cruises from 1992 to 1994, showing complex spatial and temporal variability of the currents throughout the water column. Lowered acoustic Doppler current profilers were used on all cruises; for comparison, an acoustically‐tracked free‐fall profiler was used on the August 1992 and June 1993 cruises. Where simultaneous profiles from both methods are available, depth‐averaged differences are less than 0.01 m s−1 in the ensemble mean and standard deviation. Though small, the mean difference appears to be statistically non‐zero for one of the two Doppler profilers used; no cause has been found. The individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth‐averaged components extending over the full sampling domain. Two sections show a picture of the southward‐flowing Deep Western Boundary Current (DWBC) differing from previous observations. During August 1992 and June 1993 the mean DWBC core was located more than 100 km offshore; in observations prior to 1990 it was usually near 50 km offshore. Net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 Sv with a mean of about 40 Sv (1 Sv = 1×106 m³ s−1). Our mean is consistent with previous estimates; our sections add new evidence that the transport is highly variable to at least 400 km offshore.
Time sequence and the recurrence models for large earthquakes along the Nankai Trough revisited
Authors: Kumagai Hiroyuki
Published: February 2004

It is suggested that time sequence of earthquakes can be explained by the time‐predictable recurrence model rather than the slip‐predictable recurrence model. However, the reliability of the model depends primarily on data accuracy; missing large events seriously affect the evaluation of the models. Although the time‐predictable model can explain the recent three large events along the Nankai trough back to A.D. 1707, there was serious discrepancy when the model was applied to older events. Recent archeological studies have discovered new events along the trough missed in historical documents. I found that with the addition of the archeologically discovered new events the recurrence models can be applied to older events, and that the time sequence including these new events suggests a time‐predictable recurrence pattern over a 1000‐year interval.
Field measurement evidence for an atmospheric chemical source of formic and acetic acids in the tropic
Authors: Sanhueza Eugenio , Santana Magaly , Trapp Dorothea , de Serves Claes , Figueroa Luis , Romero Rodrigo , Rondón Alberto , Donoso Loreto
Published: February 2004

The simultaneous measurements of atmospheric HCOOH, CH3COOH H2O2, organic peroxides, HCHO, CH3CHO and isoprene made in the Venezuelan savannah region, in the wet season (September, 1993) and during the period of high solar irradiation is reported. The average concentrations (in ppbv) between 10:00 and 16:00 were: HCOOH 0.75±0.32, CH3COOH 0.56±0.28, H2O21.37±0.48, the total peroxides 1.83±0.60, HCHO 1.38± .43, CH3CHO 0.35±0.15, and isoprene 2.18±0.78. A good correlation was observed between the concentrations (15 min averages) of both acids. The acids also correlate with isoprene (the most abundant olefin in the savannah atmosphere), H2O2and the total peroxides. HCOOH also correlates well with HCHO and CH3CHO. These results support the hypothesis that significant amount of formic and acetic acids are produced in the tropical atmosphere as a result of the oxidation of reactive hydrocarbons.
Global surface air temperature in 1995: Return to pre‐Pinatubo level
Authors: Hansen J. , Ruedy R. , Sato M. , Reynolds R.
Published: February 2004

Global surface air temperature has increased about 0.5°C from the minimum of mid‐1992, a year after the Mt. Pinatubo eruption. Both a land‐based surface air temperature record and a land‐marine temperature index place the meteorological year 1995 at approximately the same level as 1990, previously the warmest year in the period of instrumental data. As El Niño warming was small in 1995, the solar cycle near a minimum, and ozone depletion near record levels, the observed high temperature supports the contention of an underlying global warming trend. The pattern of Northern Hemisphere temperature change in recent decades appears to reflect a change of atmospheric dynamics.
Distinctive ozone structure in the high‐latitude stratosphere: Measurements by the Millimeter‐Wave Atmospheric Sounder
Authors: Olivero J. J. , Pauls T. A. , Bevilacqua R. M. , Kriebel D. , Daehler M. , Richards M. L. , Kämpfer N. , Berg A. , Stodden C.
Published: February 2004

MAS (Millimeter‐wave Atmospheric Sounder) observations from the shuttle ATLAS spacelab pallet have revealed some little known (and unexplained) structure in stratospheric ozone mixing ratio profiles at sub‐polar latitudes, of both hemispheres. Qualitatively similar features are observed by UARS instruments. Another possibly related feature has been observed by ground‐based remote sensing from the South Pole over an extended season. In all these cases, it seems likely that active photochemistry and highly structured horizontal and vertical transport play important roles. Some evidence of a similar feature is also present in a current 2‐D photochemical model. This high latitude phenomenon is both an intriguing challenge for current 3‐D models and potentially useful test for validating remote sensing experiments.
Isotopic signature of debris‐rich ice formed by regelation into a subglacial sediment bed
Authors: Iverson N. R. , Souchez R.
Published: February 2004

Among the processes that may entrain sediment in the bases of glaciers and ice sheets, basal ice may regelate downward into the pores of unlithified sediment. Laboratory studies suggest that this process leaves interstitial ice with a distribution of δ18O and δD that is distinct from that developed due to downward freezing of a semi‐closed water reservoir. Although as a result of both processes these isotopes lie on a freezing slope in a δD‐δ18O diagram, debris layers entrained by regelation past grains are both enriched in heavy isotopes with depth and display a downward decrease in deuterium excess, the converse of that due to downward freezing of a water reservoir. Moreover, the extent of enrichment can be significantly larger in the case of regelation into the bed. Reevaluated field data from West Greenland are consistent with regelation into the bed as an entrainment mechanism.
Ion heating within the ramp of quasi‐perpendicular subcritical collisionless shocks
Authors: Balikhin Michael A. , Wilkinson William P.
Published: February 2004

The heating of the bulk of the incident ions at low Mach number quasi‐perpendicular collisionless shocks is observed to take place very rapidly, within the shock ramp. In this paper we show that the trajectories of ions passing through the shock ramp lead to a dispersion in phase space resulting in an effective increase in ion temperature. The main heating is predicted to take place in the second half of the ramp. We present results of self‐consistent computer simulations which confirm this prediction.
Observations of the solar irradiance in the 200–350 nm interval during the ATLAS‐1 Mission: A comparison among three sets of measurements‐SSBUV, SOLSPEC, and SUSIM
Authors: Cebula R. P. , Thuillier G. O. , VanHoosier M. E. , Hilsenrath E. , Herse M. , Brueckner G. E. , Simon P. C.
Published: February 2004

The SOLSPEC, SSBUV, and SUSIM spectrometers simultaneously observed the solar spectral irradiance during the ATLAS‐1 mission flown on board the Space Shuttle Atlantis in March 1992. The three instruments use different methods and means of absolute calibration and were each calibrated preflight and postflight. The three data sets are reported from 200 to 350 nm at 1.1 nm resolution. The method of comparing the three independent data sets is discussed. The importance of a common, precise wavelength scale is shown when comparing the data in wavelength regions of strong Fraunhofer lines. The agreement among the solar irradiance measurements is better than ±5%. The fact that the calibrations of the three instruments were based on three independent standards provides confidence that the absolute solar spectral irradiance in the range 200–350 nm is now known with an accuracy better than ±5%. The mean ATLAS‐1 solar spectrum is compared with simultaneous solar observations from the UARS SOLSTICE and UARS SUSIM instruments. The two mean solar spectra agree to within ±3%.
Ozone change from 1992 to 1993 as observed from SSBUV on the ATLAS‐1 and Atlas‐2 missions
Authors: Hilsenrath E. , Newman P. A. , Cebula R. P. , DeCamp P. W. , Kelly T. J. , Coy L.
Published: February 2004

The Shuttle SBUV (SSBUV) conducted its fourth and fifth flights in late March 1992 and early April 1993 along with the ATLAS‐1 and ATLAS‐2 Shuttle missions, respectively. The two successive SSBUV flights yielded ozone data nearly one year apart. An analysis of the meteorological conditions, namely temperature and winds, during the two flight periods indicate that the conditions in the stratosphere were very similar. The temperatures had significantly warmed from winter throughout most of the stratosphere and the circulation was approaching normal summertime conditions for both periods. SSBUV‐4, flown in 1992, measured ozone from approximately 30S to 60N while SSBUV‐5, flown in 1993, measured ozone from approximately 55S to 60N. Zonal average column ozone amounts were derived from the two flights and compared to determine if a systematic change in ozone could be detected despite the fact that only a few days from each year were sampled. The comparison indicates that in the latitude range 30N to 60N total ozone was lower in 1993 than in 1992 by about 12%. This change is larger than the observational errors and the expected interannual variations. This result verifies similar data taken from ground and satellites.
Anomalous scaling of high cloud variability in the tropical Pacific
Authors: Pierrehumbert R. T.
Published: February 2004

We have analyzed a full month of daily and hourly satellite infrared data covering the Central Pacific, with an eye to identifying and characterizing self‐similar behavior of the cloud variability. It is found that the cloud outgoing longwave radiation field exhibits anomalous scaling, with parameters that are quite consistent across a broad range of synoptic situations. The presence of anomalous scaling means that, although the cloud field exhibits spatially self‐similar behavior, the power spectrum alone is not sufficient to characterize the spatial structure of cloud variability. The scaling laws do not conform to what would be expected from passive scalar advection/diffusion, but they do closely resemble the scaling laws for temperature fluctuations in a turbulent convecting layer.
The Sanriku‐Oki, Japan, Earthquake of December 28, 1994 (Mw 7.7): Rupture of a different asperity from a previous earthquake
Authors: Tanioka Yuichiro , Ruff Larry , Satake Kenji
Published: February 2004

Fault geometry, depth, and slip distribution of the Sanriku‐oki earthquake of December 28, 1994 (Ms 7.5) are estimated from seismic waveforms, geodetic measurements, and tsunami waveforms, and compared with those of the 1968 Tokachi‐oki earthquake (Mw 8.2), the most recent large earthquake in the epicentral region. Seismic wave inversions indicate a shallowly dipping thrust type mechanism and the focal depth of 22–28 km, representing an underthrust event at the subduction interface. The source time function has an initial stage of 20 s followed by a main pulse of 30 s duration, a shape similar to that of the 1968 Tokachi‐oki earthquake. Joint inversion of geodetic and tsunami data shows that the region of the largest slip, 1.7 m, corresponds to a region of relatively small slip for the 1968 Tokachi‐oki earthquake. Furthermore, the joint inversion shows that the region of the largest asperity of the 1968 earthquake had essentially zero slip during the 1994 Sanriku‐oki earthquake. These results indicate that the dominant asperities ruptured by the 1994 Sanriku and 1968 Tokachi‐oki earthquakes are different. The result of the joint inversion also shows that the aseismic zone near the Japan trench was not ruptured by the 1994 earthquake.
Formation of polar stratospheric clouds on preactivated background aerosols
Authors: Zhang Renyi , Leu Ming‐Taun , Molina Mario J.
Published: February 2004

Results of laboratory simulations of the growth of nitric acid trihydrate, HNO3;•3H2O, on sulfuric acid tetrahydrate, H2SO4•4H2O, are presented. The observations reveal that under typical stratospheric conditions uptake of HNO3 on a H2SO4•4H2O substrate results in a surface coverage of approximately one monolayer or less, and that initial HNO3•3H2O nucleation requires a large supersaturation. We also observe that a H2SO4•4H2O substrate, onto which a HNO3•3H2O film has been deposited and subsequently evaporated, exhibits a remarkable enhancement in its nucleation ability for this nitric acid hydrate. In the stratosphere, PSC particles may experience repeated cycles of evaporation and condensation of HNO3 on preexisting background frozen sulfate aerosols. Hence, growth of HNO3•3H2O on preactivated aerosols provides one important mechanism for polar stratospheric cloud formation and denitrification.
Simultaneous mesospheric wind measurements near South Pole by optical and meteor radar methods
Authors: Hernandez G. , Forbes J. M. , Smith R. W. , Portnyagin Y. , Booth J. F. , Makarov N.
Published: February 2004

Simultaneous and co‐located measurements of mesospheric winds near South Pole, by high‐resolution optical and meteor radar methods, show that these two methods determine very similar motions at slightly different heights of observation. The measured atmospheric motions by the two techniques show that a) The mean wind during 12 days in June, 1995 was found to have a 7 m/s amplitude flowing towards the 5°E longitude direction. The latter direction is different from the 30E° direction found earlier during August 1991 and 1992. b) The observed dominant oscillations in the wind at both heights of observation are those of zonal wavenumber one character. Westward phase propagation was determined for the observed short‐period (∼0 hours) oscillations and eastward phase propagation for the longer‐period (∼3 days) oscillations, respectively. Because of the neighboring heights of observation by the optical and meteor radar methods, the in situ vertical wavelengths of propagation of the observed waves have been determined to be greater than 100 km for the 10‐hr oscillations and near 65 km for the longer period oscillations. With this new information we are able to independently establish the earlier assignment of the nearly 10‐hr oscillations as the different meridional modes of a zonal wavenumber one Lamb wave. The determined vertical wavelength and eastward phase progression of the longer periodicity waves indicate these oscillations are likely to be the gravest inertio‐gravity wave, which has the appropriate equivalent depths at these periods of oscillation. The simultaneous absence of statistically significant kinetic temperature and optical‐tracer emission rate oscillations at the frequencies corresponding to the wind motions, provides independent support to the earlier deductions on the ability of the atmosphere near the rotational poles to support only certain zonal character oscillations.
Maritime emission of selenium to the atmosphere in Eastern Mediterranean seas
Authors: Amouroux David , Donard Olivier F. X.
Published: February 2004

Results presented in this article report the first assessment of at least 3 volatile selenium species (MeSeH, DMSe, DMDSe) in marine water and air. Dimethyl selenide (DMSe) was the main compound encountered and the total concentration of the volatile selenides was found to be correlated with the marine plankton biomass as measured through chlorophyll a content. Estimation of a net selenium flux from the ocean to the marine atmosphere has been established. This gaseous flux corroborates previous hypotheses on selenium cycling and indicates that maritime emissions are a major source of selenium to the atmosphere in the Mediterranean basin.
Reflections from a distant subduction zone
Authors: Weber Michael , Wicks Charles W.
Published: February 2004

Accurate models of the distribution of heterogeneities in the Earth's mantle, especially of subduction zones, are crucial for our understanding of the composition and dynamics of the Earth. Here we present broad‐band (BB) seismograms with P‐waves reflected at the subduction zone under southern Japan at about 84° distance from German Regional Seismic Network. The earthquakes occurred in the Mariana Islands region at 100° to 105° distance. Array techniques allow the separation of this wave with an asymmetric path (P1P2) from reflections and conversions under the source, the receivers and the midpoint between the source and the receivers. Our observation demonstrates that subduction zones can act as strong seismic reflectors and can be mapped with a depth resolution of ±20km with BB arrays at teleseismic distances. The analysis of such data will help to derive a more detailed picture of the structure of the Earth's mantle.
Upstream ULF waves and energetic electrons associated with the lunar wake: Detection of precursor activity
Authors: Farrell W. M. , Fitzenreiter R. J. , Owen C. J. , Byrnes J. B. , Lepping R. P. , Ogilvie K. W. , Neubauer F.
Published: February 2004

We present observations of precursor ULF wave activity and energetic electron flows detected by the WIND spacecraft just prior to entry of the lunar wake on 27 December 1994. This activity occurs upstream of the wake on field lines directly connected to the wake penumbra region. The activity ceases near the penumbra entrance. The observations of upstream ULF wave activity and solar wind counterstreaming electron flows is similar to observations made upstream of collisionless bow shocks. Analogously, the wake precursor region is characterized by thermalization and information propagation ahead of the wake structure.
WIND observations of energetic ions far upstream of the Earth's bow‐shock
Authors: Sanderson T. R. , Henrion J. P. G. , Wenzel K.‐P. , Lin R. P. , Anderson K. A. , Ashford S. , Carlson C. W. , Curtis D. , Ergun R. E. , Larson D. , McFadden J. , Reme H. , Bosqued J. M. , Coutelier J. , Cotin F. , Lormant N. , d'Uston C. , Parks G. K. , McCarthy M. P. , Skoug R. M. , Winglee R. M.
Published: February 2004

During the first year of operation, the WIND spacecraft followed a complicated orbit which took it from the Earth to the upstream libration point and back again. During this time, a considerable number of upstream particle events were observed all the way out to the libration point. These events are typically of short duration (a few tens of minutes) and up until now have only been seen in the energetic protons (at energies of a few tens of keV, but extending up to several hundreds of keV). We present here new observations from the Three‐dimensional (3D) plasma and energetic particle experiment on the WIND spacecraft of these upstream events, with particular emphasis on the uniqueness of the observations from this instrument: energy spectra measured over the range from a few keV to several hundreds of keV, and complete three‐dimensional angular distributions covering the same range of energies. We present here for the first time a complete spectrum of these ions extending from a few eV to a few MeV. This spectrum, with a turnover at one or two keV, shows that the bulk of the energy density of the upstream ions is at around 1 keV. These are most likely the particles responsible for the low‐frequency waves which are usually seen accompanying upstream events.
Global mapping of the electrically conductive lower mantle
Authors: Petersons H. F. , Constable S.
Published: February 2004

It is known that the electrical conductivity of the Earth's mantle increases to about 1 S/m at depths between 500 and 1000 km. This increase could equally well be ascribed to thermally activated conduction or to enhanced conductivity in high pressure mineral phases. Thermal activation would produce a smooth conductivity profile while conductivity associated with abrupt phase changes would also vary abruptly. Unfortunately, geomagnetic data alone cannot distinguish between these two models. However, under the assumption that the variation is indeed abrupt, we seek the best estimate for the depth to a conductivity jump. A peak in the geomagnetic spectrum around a period of 27 days produces an electromagnetic response at this period with least uncertainty and least bias associated with breakdown of an assumed P10 source‐field geometry. Fitting such data using a simple two‐parameter model of a buried conducting sphere, we estimate a conductivity of 1.18±0.10 S/m at a depth of 65±20 km. The coincidence of this result with estimated depths to the 660 km seismic discontinuity provides independent support for the hypothesis that the observed abrupt change in the elasticity of the mantle is also accompanied by an equally abrupt change in the electrical conductivity. Both physical properties are presumably associated with a mineral transition from an olivine‐dominated upper mantle composition to perovskite/wüstite assemblage.
Reply to “Inaccuracies in seismicity and magnitude data used by Varotsos and Co‐workers,” by M. Wyss
Authors: Varotsos P. , Eftaxias K. , Lazaridou M. , Dologlou E. , Hadjicontis V.
Published: February 2004

A direct comparison of the predicted magnitude values (Mpred) to the actual magnitude values (MEQ) of the earthquakes (EQs) is allowed only when both values, i.e., Mpred and MEQ, refer to the same scale. In view of the fact that the Seismological Institute of the National Observatory of Athens (SI‐NOA) publicly announces as MEQ the ML+0.5 value (where ML the local magnitude), VAN made it clear long ago, that the predicted values Mpred (after a proper calibration) referred to ML+0.5. Therefore, a self‐consistent evaluation of VAN‐predictions should consist of a direct comparison of Mpred with the actual ML+0.5. Unfortunately, Wyss [1996] confuses the discussion by proceeding to a direct comparison of Mpred with Ms(PDE); this is not allowed because the values of ML+0.5 exceed, on the average, Ms(PDE) by 1.0 unit. An additional confusion arises from the fact that the relation suggested by Hamada [1993], i.e., ML+0.5=mb+0.3, is misinterpreted by Wyss as saying Ms(PDE)=mb+0.3. These two alterations by Wyss reveal that his Figures 1 and 2 are erroneous.

Wyss [1996] also criticizes VAN, because (in an early publication) Varotsos et al. [1981b] used the Preliminary Bulletin of SI‐NOA, instead of the final one. First of all, the final bulletin could not be used by VAN at that time, because it appeared (more than one year) after the publication of the paper by Varotsos et al. [1981b]. Secondly, the correlation between SESs and EQs is evident, when we use consistently, either the preliminary, or the final bulletin of SI‐NOA. On the other hand, Wyss [1996] claims that he could not find any correlation between EQs and SESs; we show that this is due to the fact that Wyss included, in his study, small EQs that occurred several hundreds km away from the measuring VAN station (i.e., in Albania, western Turkey, etc.), but he simultaneously deleted the small magnitude EQs that occurred very close to that station. Wyss's procedure is, of course, not acceptable and hence his Appendix B is wrong. Furthermore, Wyss's claim that VAN added 25% of events to the list, is shown to be untrue.

Beyond the unusual fact that Wyss quotes “VAN's statements” that have never been published by VAN, the following is also noted: although Wyss [1996] uses quotation marks (in order to indicate that he reproduced exactly what VAN said), he adds critical wording to VAN statements and hence their true meaning is drastically changed. For example, Wyss states: “Varotsos et al. [1981a] had first formulated that SESs “occurred a few minutes before each earthquake [related to that SES]” (Varotsos et al. [1981a]).” Thus, Wyss leads the reader to the wrong conclusion that VAN initially claimed that SES have a lead time of a few minutes, and that VAN changed it later. However, we show that this lead time (published by VAN) referred to another type of precursor, and not to SES, but the words in brackets (which are added by Wyss) alter the true meaning of our statement.
SCIFER‐Height measurements of the midmorning aurora
Authors: Sigernes F. , Moen J. , Lorentzen D. A. , Deehr C. S. , Smith R. , Øieroset M. , Lybekk B. , Holtet J.
Published: February 2004

Dual‐site ground‐based optical observations were performed January 25, 1995 in support of the SCIFER rocket campaign (Sounding of the Cleft Ion Foundation Energization Region). Two Meridian Scanning Photometers (MSPs) were operative simultaneously at Ny‐Ålesund (NYA) and Nordlysstasjonen in Adventdalen (LYR) 118 km apart in the geomagnetic meridian. The photometers at each station scanned approximately along the same geomagnetic meridian plane and measured the intensity of auroral wavelengths as a function of zenith angle and time. The principal wavelengths used in the present analysis were the green 5577 Å and the red 6300 Å emission lines of atomic oxygen. For the magnetospheric cleft auroral activity studied here at 10 hr magnetic local time (MLT), the luminosity maximum for the green line varied in altitude between 125 and 160 km. The red line maximum was in the range 200 to 220 km. The absolute intensity ratio and the height‐luminosity profiles obtained using this method were consistent with the near simultaneous rocket measurement of the field‐aligned electrons having a characteristic energy of 230 eV by the SCIFER experiment [Lorentzen, et al., 1996]. Geomagnetic disturbance data obtained during the flight included an example of a magnetic impulse event (MIE) coinciding with a bright, discrete arc. The altitude of this arc was >140 km, and it is doubtful that it produced an increase of conductivity in the E Region or developed a current system which could be associated with the MIE. It is proposed that the transient magnetic events were associated with the energetic pulsating aurora which was occurring equatorward of the zenith. In addition, the altitude of three poleward‐moving auroral forms (PMAFs) was measured. Within the error of the observations, the PMAFs do not seem to change in altitude with increasing latitude. The sample is too small for a definitive conclusion, but the method shows promise.
Modeling solar extreme ultraviolet irradiance variability using emission measure distributions
Authors: Warren H. P. , Mariska J. T. , Lean J. , Marquette W. , Johannesson A.
Published: February 2004

We introduce a new model of solar irradiance variability at extreme ultraviolet (EUV) wavelengths. The model combines a spectral emission line database, solar emission measure distributions, and estimates from ground‐based solar images of the fraction of the Sun covered by the various types of activity to synthesize the irradiance. Using Call K‐line images, the model can be used to estimate the irradiance from EUV line emission formed in the upper chromosphere and lower transition region. Comparisons of this new model with existing empirical models reveal both similarities and disagreements in the absolute magnitude, the amplitude of the rotational modulation, and the intermediate‐term solar cycle variability of the predicted fluxes.
SCIFER‐Cleft region thermal electron distribution functions
Authors: Pollock C. J. , Moore T. E. , Adrian M. L. , Kintner P. M. , Arnoldy R. L.
Published: February 2004

Differential directional ionospheric electron measurements at energies from <1 to 60 eV have been obtained in the Earth's geomagnetic cleft ionosphere on NASA's Sounding of the Cleft Region Ion Fountain Energization Region (SCIFER) rocket. We introduce the electron data set, present electron temperature measurements, and show examples of phase space distributions measured near and in the cleft ionosphere. Topside electron temperatures ranged from near 0.15 eV south of the high energy electron trapping boundary to near 1 eV within precipitation regions in the auroral cleft. Field‐aligned electron bursts extend down to thermal energies and merge with the core, yielding core heating and anisotropy in the derived electron temperature. One interval is identified where enhanced electron temperature is collocated with a deep density depletion, low frequency electrostatic waves, and transverse ion heating, consistent with operation of the current‐driven ion cyclotron instability. On the downleg, in what may be polar cap, the shape of the thermal electron energy distribution was observed to be quite uniform, with temperatures near 0.25 eV.
Magnetic properties of the stable fraction of remanence in large multidomain (MD) magnetite grains: Single‐domain or MD?
Authors: McClelland E. , Muxworthy A. R. , Thomas R. M.
Published: February 2004

It has been recognized since the early work of Verhoogen (1959) that a considerable proportion of remanence in multidomain (MD) magnetite grains is resistant to low‐field a.f. or low‐temperature demagnetization. The source of this high stability is still a matter of debate. A number of workers have suggested that MD grains of all sizes contain a remanence fraction with truly single domain (SD) character. We suggest that the critical diagnostic features which should be investigated to determine whether the high stability fraction is SD or MD in character are whether blocking (Tb) and unblocking (Tub) temperatures are equivalent, and whether the intensity of remanence is affected by the thermal pre‐history of the sample. We have carried out such experiments on samples containing crushed natural magnetites in 7 grain sizes from 5–10 µm, to 100–150 µm. We show that Tb and Tub are equivalent for pTRM40020 for grain sizes up to 15–20 µm, but that Tub extends up to the Curie temperature for larger grain sizes. We also show that the stable fraction of MD TRM and pTRM has the same dependence on pre‐history as the total TRM. Our experiments demonstrate that the stable fraction has magnetic properties which are truly MD in character for magnetite grains larger than 20 µm.
Space‐borne H2O observations in the Arctic stratosphere and mesosphere in the spring of 1992
Authors: Aellig C. P. , Bacmeister J. , Bevilacqua R. M. , Daehler M. , Kriebel D. , Pauls T. , Siskind D. , Kämpfer N. , Langen J. , Hartmann G. , Berg A. , Park J. H. , Russell J. M.
Published: February 2004

We report on stratospheric and mesospheric water vapor (H2O) observations obtained by the Millimeter wave Atmospheric Sounder (MAS) in the Arctic spring of 1992. In the lower stratosphere, the observations show enhanced H2O inside the vortex between 450 K and 625 K, in agreement with other H2O observations. In the upper stratosphere and lower mesosphere, at potential temperatures between 1850 K and 2200 K, we find regions of depressed H2O volume mixing ratio coincident with remnants of high potential vorticity. The depressed mesospheric H2O, as well as the enhanced lower stratospheric H2O, are consistent with wintertime descent. It also suggests effective containment of air up into the lower mesosphere.
An 1800‐year archeological experiment in remagnetization
Authors: Borradaile Graham John
Published: February 2004

Limestone masonry from monuments dating from 300AD to 1940, remagnetized partly and progressively with age, parallel to the present Earth's magnetic field. The remagnetization was probably due to viscous remanent magnetization (VRM). Néel's theory predicts that natural VRM acquired at low temperature (TA) over a long time (tA, disappears at a higher temperature (TD) in a short period (tD) in the laboratory. I calibrated TD for the postconstruction remagnetization against the ages (tD) of masonry used in well‐dated, historic buildings in Eastern England. Empirically, tA = m.(TD)b relates acquisition age (tAyears) to demagnetization temperature (TD °C). Lincoln limestone remagnetizes more quickly ( m = 1.298 × 10−6 and b = 3.598 over 1800 years) than Speeton Chalk ( m = 4298 × 10−6 and b = 1.973 over 350 years). Magnetite with an effective pseudo‐single domain or small multidomain size carries the remanence.
Voyager 2 fine‐scale velocity oscillations at 48 AU
Authors: Paularena K. I. , Belcher J. W. , Richardson J. D. , Gordon G. S. , Lazarus A. J.
Published: February 2004

Voyager 2 solar wind speeds show unusual variations beginning on day 40 of 1996. These variations are oscillations of approximately 30 km/s with periods of about two days and are unlike any variations heretofore detected in the outer heliosphere. Several possible sources of this behavior are examined. First, this speed feature may be due to a Kelvin‐Helmholtz instability on the boundary between the slow equatorial and fast high‐latitude flows, although this instability has not been observed at other radial distances and latitudes. A second possibility is that these waves are due to instabilities associated with interstellar pick‐up ions; at the ∼48 AU distance where these oscillations are observed, the pick‐up pressure far exceeds the pressure of the thermal solar wind proton population. A third possibility is that the waves are an upstream signature of the termination shock, similar to waves observed upstream of planetary bow shocks. Anomalous cosmic ray protons with 100 MeV energies satisfy the necessary cyclotron resonance conditions and carry sufficient energy density to produce the observed waves. This possibility would require magnetic connection to the shock and the presence of streaming anomalous cosmic ray ions. Plasma data alone cannot determine whether the necessary conditions for any of these possibilities exist. Further progress requires collaborative studies using all of the available particle and field data from Voyager 2.
The unsuitability of meteoritic and other nuclei for polar stratospheric cloud freezing
Authors: Biermann U. M. , Presper T. , Koop T. , Mößinger J. , Crutzen P. J. , Peter Th.
Published: February 2004

Bulk freezing experiments have been performed with binary and ternary HNO3/H2SO4/H2O solutions containing original micrometeorites, ground samples of representative larger meteorites and other freezing nuclei of potential stratospheric importance. The experiments enable us to determine upper bounds for the heterogeneous freezing rates of sulfuric and nitric acid hydrates. Based on an analysis of the meteoritic mass flux from space and of the modifications meteorites undergo when entering the atmosphere, the resulting morphology and surface area of extraterrestrial material in the stratosphere are estimated. From this micrometeorites gained from Antarctica are shown to be a good proxy for meteoritic surfaces in the stratosphere. In combination with this analysis the freezing experiments suggest that heterogeneous nucleation rates on micrometeorites are too low to enhance freezing of polar stratospheric clouds above the frost point.
Magnetic discrimination of pyrrhotite‐ and greigite‐bearing sediment samples
Authors: Torii M. , Fukuma K. , Horng C.‐S. , Lee T.‐Q.
Published: February 2004

By using bulk samples, rock magnetic measurements were performed to discriminate between pyrrhotite‐ and greigite‐bearing shallow marine sediments that are now uplifted above sea level in southwestern Taiwan. Thermal demagnetization of a composite isothermal remanent magnetization (IRM) was found to be effective in differentiating between the two types of sediments. To check the thermal instability and estimate the true unblocking temperature (TB) spectra of sediments containing these minerals, saturation IRMs (SIRMs) were imparted at each temperature step during demagnetization. While pyrrhotite‐bearing samples showed unambiguous TB temperature spectra, greigite‐bearing samples underwent considerable alteration which is responsible for most of the decrease in magnetization during thermal demagnetization. Such thermal instability of greigite is a practical and important clue for its identification. Zero‐field warming of IRM from 5 to 300 K sensitively indicates the presence of pyrrhotite and trace magnetite in bulk samples without any magnetic separation.
A comparison of measurements from ATMOS and instruments aboard the ER‐2 aircraft: Tracers of atmospheric transport
Authors: Chang A. Y. , Salawitch R. J. , Michelsen H. A. , Gunson M. R. , Abrams M. C. , Zander R. , Rinsland C. P. , Loewenstein M. , Podolske J. R. , Proffitt M. H. , Margitan J. J. , Fahey D. W. , Gao R.‐S. , Kelly K. K. , Elkins J. W. , Webster C. R. , May R. D. , Chan K. R. , Abbas M. M. , Goldman A. , Irion F. W. , Manney G. L. , Newchurch M. J. , Stiller G. P.
Published: February 2004

We compare volume mixing ratio profiles of N2O, O3, NOy, H2O, CH4, and CO in the mid‐latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS‐3 Space Shuttle Mission with in situ measurements acquired from the NASA ER‐2 aircraft during Nov 1994. ATMOS and ER‐2 observations of [N2O] show good agreement, as do measured correlations of [O3], [NOy], [H2O], and [CH4] with [N2O]. Thus a consistent measure of the hydrogen (H2O, CH4) content of the lower stratosphere is provided by the two platforms. The similarity of [NOy] determined by detection of individual species by ATMOS and the total [NOy] measurement on the ER‐2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric [CO] observed by ATMOS and the ER‐2 remains unexplained. Otherwise, the agreement for measurements of long‐lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.
A 2‐D model simulation of downward transport of NOy into the stratosphere: Effects on the 1994 austral spring O3and NOy
Authors: Callis Linwood B. , Baker Daniel N. , Natarajan Murali , Bernard J. Blake , Mewaldt Richard A. , Selesnick Richard S. , Cummings Jay R.
Published: February 2004

Simulations using SAMPEX and HALOE data suggest that NOy produced by thermospheric processes and by relativistic electron precipitation in the mesosphere and lower thermosphere have been important to stratospheric NOy and O3 during the austral spring in 1994. The relative importance of the two NOy sources is discussed. The results are supported by an analysis of HALOE NOx and CH4 data during October 1994 and are in agreement with ATMOS NOy observations made in November 1994.
Characteristics of Arctic Ocean climate based on COADS data, 1980–1993
Authors: Clark Martyn P. , Serreze Mark C. , Barry Roger G.
Published: February 2004

Arctic Ocean cloud cover, precipitation frequency and temperature are examined using COADS records for the period 1980–1993. Principal component analysis reveals two climatic regions, the ‘Northern Atlantic’ and ‘Central Arctic’, as well as a cold (November–April) and warm (June–September) season. For the Central Arctic, precipitation frequency and cloud cover peak during the warm season, with liquid precipitation comprising about 50% of all precipitation reports during July. For the Northern Atlantic, precipitation frequency and the frequency of moderate/heavy precipitation peak during the cold season, but with relatively constant cloud cover throughout the year. Liquid precipitation is common in all months, comprising the bulk of reports from June through September. Based on our analysis, the proposed location for the 1997–1998 Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment cannot be considered Central Arctic in character.
Aircraft‐generated aerosols and visible contrails
Authors: Kärcher B.
Published: February 2004

Model calculations for the formation of aerosols and the interaction between themselves and with exhaust gases in plumes of cruising airliners are presented. A subset of in situ‐nucleated H2SO4/H2O aerosols that stay liquid can transform into an almost pure HNO3/H2O mode because of enhanced uptake of HNO3. Soot embedded in a liquid coating containing H2SO4 and HNO3 triggers heterogeneous freezing of water ice and leads to visible contrails. At low temperatures and high fuel sulfur levels homogeneous freezing increases the ice mass. The ice particles may acquire a HNO3 · 3 H2O (NAT) coating upon evaporation of H2O, which can potentially lead to a lengthening of their lifetime. If future plume sampling experiments confirm these results, they would have important implications for ozone‐related heterogeneous plume chemistry.
Recent tropospheric growth rate and distribution of HFC‐134a (CF3CH2F)
Authors: Oram D. E. , Reeves C. E. , Sturges W. T. , Penkett S. A. , Fraser P. J. , Langenfelds R. L.
Published: February 2004

Air samples collected at Cape Grim, Tasmania (41°S) between 1978 and 1995, and at Mace Head, Ireland (53°N) between July 1994 and May 1995, have been analysed by GC‐MS to determine recent trends of HFC‐134a, an important CFC replacement, in the background atmosphere. Until 1990, the concentration of HFC‐134a at Cape Grim was below detection limits, the first quantifiable level (0.01 pptv) appearing in May 1990. Between 1992 and mid‐1995 the concentration grew exponentially at ∼200% yr¹, with the concentration at the end of 1994 reaching 0.43 pptv. At Mace Head, HFC‐134a grew at a rate of 1.24±0.11 pptv yr¹ between July 1994 and May 1995, with the concentration at the end of 1994 being 1.48 pptv. hi the absence of industrial production and release estimates for HFC‐134a, the observations have been used in conjunction with a 2‐D global model to estimate recent emissions. The model indicates that significant emissions (250 tonnes) began in 1991, increasing rapidly to a level of ∼8 ktonnes in 1994.
New Ultraviolet Spectroradiometer measurements at Mauna Loa Observatory
Authors: Bodhaine B. A. , McKenzie R. L. , Johnston P. V. , Hofmann D. J. , Dutton E. G. , Schnell R. C. , Barnes J. E. , Ryan S. C. , Kotkamp M.
Published: February 2004

A research‐grade scanning UV spectroradiometer was installed at Mauna Loa Observatory (MLO), Hawaii, in July 1995. This instrument, built around a commercially available double monochromator, is interfaced with a PC to provide automatic control and data acquisition. The spectral range sampled by the instrument is 290–450 nm, and the bandpass is about 1 nm. A complete scan requires about 200 seconds and is performed every 5 degrees of solar zenith angle (SZA) during daylight hours. Calibration is performed on site at 6‐month intervals using a 1000‐W standard quartz‐halogen FEL lamp with calibration traceable to NIST. The UV irradiances measured at MLO are much more intense than at low altitude mid‐latitude locations. For observations at a SZA of 45°, the erythemally weighted UV can exceed 18 μW cm−2, which is approximately 15‐20% greater than the maxima seen at Lauder, NeW Zealand, for similar ozone amounts. The difference is primarily due to the higher altitude at MLO. For overhead sun conditions at MLO, erythemal UV can exceed 45 μW cm−2, which to our knowledge is the highest recorded anywhere at the Earth's surface. UV irradiance is strongly correlated (inversely) with Dobson spectrophotometer total ozone measurements at MLO, with higher correlations at shorter wavelengths. The radiative amplification factor (RAF) for erythema at MLO is about 1.44±0.46 at SZA 45°. Using ozone retrievals from the UV spectra themselves, the deduced RAF for erythema is 1.26±0.38. The RAFs for erythema at SZA 60° are similar, and in agreement with other determinations within the limits of experimental uncertainty.
Implications of a new eddy parameterization for ocean models
Authors: McDougall T. J. , Hirst A. C. , England M. H. , McIntosh P. C.
Published: February 2004

A new parameterization of eddies in a coarse resolution ocean model yields deep ocean salinities and temperatures that are significantly closer to observations than with previous parameterizations. This is achieved because dense water is able to flow over sills and into the deep ocean without being diluted with the surrounding water. In addition, the depth to which surface‐induced tracers penetrate in the Southern Ocean is now realistic. This depth is overestimated by previous ocean models, including those used to estimate global warming. Adding this new eddy parameterization to coupled atmosphere‐ocean models is expected to yield greater global warming.