bluuebunny/crossref_metadata_2025 huggingface dataset:
The atmospheric correction for satellite infrared radiometer data in polar regions
Authors: Bamber J. L. , Harris A. R.
Published: February 2004

Mie scattering models suggest that the thermal infrared emissivity of snow is relatively insensitive to variations in its properties and is dependent, primarily, on viewing angle. This gives rise to the possibility of accurately measuring snow surface temperatures, over the polar ice sheets, using satellite infrared radiometers operating in the window region at 10–13 microns. These instruments were designed, primarily, to measure sea surface temperature and a substantial body of work has been undertaken on correcting for the effects of variable absorption by the atmosphere over oceans. The atmospheric conditions over the Antarctic and Greenland ice sheets are significantly different, however, and require special treatment. A three year dataset of radiosonde measurements, collected from six Antarctic stations, is used to investigate the behaviour of the “split‐window” algorithm. The same dataset has been used to test the performance of a dual‐view algorithm that can be used with the Along Track Scanning Radiometer onboard ERS‐1. It is shown that, given accurate emissivity estimates, the atmospheric correction has an rms error of 0.015 K using the dual‐view method. Combined with the excellent calibration and stability of the Along Track Scanning Radiometer and pixel averaging to reduce the detector noise it is possible to derive snow surface “skin” temperatures to an accuracy of about 0.1 K.
A singularity free approach to post glacial rebound calculations
Authors: Fang Ming , Hager Bradford H.
Published: February 2004

Calculating the post glacial response of a viscoelastic Earth model using the exponential decay normal mode technique leads to intrinsic singularities if viscosity varies continuously as a function of radius. We develop a numerical implementation of the Complex Real Fourier transform (CRFT) method as an accurate and stable procedure to avoid these singularities. Using CRFT, we investigate the response of a set of Maxwell Earth models to surface loading. We find that the effect of expanding a layered viscosity structure into a continuously varying structure is to destroy the modes associated with the boundary between layers. Horizontal motion is more sensitive than vertical motion to the viscosity structure just below the lithosphere. Horizontal motion is less sensitive to the viscosity of the lower mantle than the vertical motion is. When the viscosity increases at 670 km depth by a factor of about 60, the response of the lower mantle is close to its elastic limit. Any further increase of the viscosity contrast at 670 km depth or further increase of viscosity as a continuous function of depth starting from 670 km depth is unlikely to be resolved.
The role of specific humidity fields in the diagnosis of stratosphere troposphere exchange
Authors: Gray Lesley J. , Bithell Michael , Cox Barbara D.
Published: February 2004

METEOSAT 4 satellite observations of water vapour show evidence of a rich spectrum of fine scale structure that may be indicative of the transfer of dry, ozone‐rich air from the stratosphere deep into the troposphere [Appenzeller and Davies, 1992]. The extent to which air within stratospheric intrusions is irreversibly mixed and remains in the troposphere is of considerable current interest, particularly in respect of pollution effects of increasing numbers of subsonic and supersonic aircraft flights that traverse the lower stratosphere. Here, we diagnose potential vorticity and the corresponding distributions of specific humidity from a numerical weather forecast model and show that the latter field displays many of the characteristics of the Meteosat data. Specific humidity fields on both a pressure surface which corresponds approximately to the Meteosat data sampling and on an isentropic surface are compared. We show the presence of streamer‐like features in specific humidity that are not evident in the PV fields. We also note the prediliction for the streamers to break off, be advected by the flow and to subsequently become ‘attached’ to other features. Care is therefore required in the interpretation of the Meteosat data for stratosphere troposphere exchange studies. Nevertheless, we suggest that the importance of specific humidity as an indicator of the dynamical evolution of upper level atmospheric flow has previously been overlooked.
Spectra and magnitudes of T‐waves from the 1993 earthquake swarm on the Juan de Fuca Ridge
Authors: Schreiner Anthony E. , Fox Christopher G. , Dziak Robert P.
Published: February 2004

A swarm of earthquakes on the crest of the Juan de Fuca Ridge was detected in June and July 1993 by a network of hydrophones. The activity migrated 60 km along the crest, suggesting a lateral dike injection and the possibility of a volcanic eruption. Subsequent geologic and oceanographic investigations confirmed that an eruption had taken place. Examination of the individual acoustic arrivals shows changes in the character of the signal that are consistent with an injection of magma. A reduction in the rise time of the wave packet and a proportional increase in high frequency energy was observed and is interpreted to result from a shoaling of the earthquake source region. Second, the source magnitudes were largest at the onset of the swarm and became smaller over time, also consistent with shoaling of the dike. The appearance of the T‐wave arrivals changed significantly 5 days after the beginning of the swarm, potentially indicating the onset of a surface eruption.
Greenland precipitation estimates from the atmospheric moisture budget
Authors: Robasky Frank M. , Bromwich David H.
Published: February 2004

Eight radiosonde stations surrounding Greenland at an average separation of 750 km are used to compute the atmospheric moisture budget. Radiosonde data were available from 1963–89, but were not used for 1963–79 due to insufficient data coverage which likely resulted in a major underestimation of large moisture inflow events. There is a mean annual inflow of moisture to the atmospheric volume over Greenland through its southeast and southwest sectors, and outflow to the northeast. Moisture convergences, equivalent to precipitation minus evaporation, yield an areal average of 32 cm yr−1 of water equivalent; they also show high inter‐ and intra‐annual agreement with earlier modeled precipitation estimates found by the authors and serve as further confirmation of their modeling results. The time‐averaged eddy component accounts for 90% of the total moisture convergence, reflecting the dominant contribution of precipitation from synoptic‐scale cyclones.
Relocation analysis of earthquakes near Nanga Parbat‐Haramosh Massif, northwest Himalaya, Pakistan
Authors: Sverdrup Keith A. , Schurter Greg J. , Cronin Vincent S.
Published: February 2004

Locations of earthquakes that have occurred between 1970 and 1988 in the northwest Himalaya of Pakistan, as computed by the ISC, were analyzed to improve knowledge of the spatial distribution of seismicity near the Nanga Parbat‐Haramosh Massif (NPHM). A set of 15 earthquakes were relocated using the multiple‐event relocation technique of Jordan and Sverdrup [1981]. Earthquakes located using records from at least 25 to 30 stations tend to be well‐located in the ISC database: smaller error ellipses and shorter distance of relocation. These analyses indicate that earthquakes with magnitudes mb > 4.0 have occurred since 1970 along the NPHM.
Practical modifications to improve the sledgehammer seismic source
Authors: Keiswetter Dean , Steeples Don
Published: February 2004

We have examined frequency and amplitude changes in high‐resolution seismic‐reflection data associated with practical modifications to the sledgehammer method. Our seismic data, acquired at three sites with different near‐surface geology, demonstrate the effects of seating the plate prior to recording, of centered versus noncentered impacts, of subsurface plate emplacement, of various plate‐surface covers, and of aluminum versus steel impact plates. Impacts on well‐seated plates produced as much as 4 dB higher seismic amplitude than data recorded using unseated plates, and increased the ratio of high‐to‐low frequencies. Sledgehammer impacts on the edge of the plate decreased seismic amplitude by 6 to 12 dB for frequencies above 100 Hz compared to centered impacts. Placement of the impact plate 1 meter below the ground surface produced a 12 dB amplitude increase for frequencies above 130 Hz at one test site. Plates made of either steel alloy or aluminum produced equivalent seismic signals. The site‐dependent nature of some of our results suggests that other investigators may benefit from conducting similar experiments prior to acquiring shallow seismic‐reflection data when using the sledgehammer source.
Fractional Lévy motion as a model for spatial variability in sedimentary rock
Authors: Painter Scott , Paterson Lincoln
Published: February 2004

A new approach to the modeling of spatial variability in sedimentary formations is introduced. This approach avoids the assumption of Gaussian behavior. Specifically, borehole measurements of physical properties of sedimentary rock from contrasting geological settings are shown to have a statistical character consistent with fractional Lévy motion. Successive increments in the measurement sequences are accurately modeled as having Lévy‐stable distributions. The Lévy parameters are similar for boreholes in the same sedimentary basin, but vary from basin to basin. Thinly bedded formations have smaller values for the Lévy index, suggesting that the Lévy index may be a useful measure of heterogeneity. The measurement sequences are also statistically self‐similar and have long‐range negative dependence among the increments (antipersistence). In addition to reproducing the statistical properties of well logs, the new model also mimics the most striking visual features of sedimentary formations.
Pn tomography beneath the Southern Great Basin
Authors: Hearn Thomas M. , Rosca Anca C. , Fehler Michael C.
Published: February 2004

P‐wave first arrival times recorded on the Southern Great Basin Seismic Network were used to tomographically image lateral variations in both crustal thickness and Pn velocity beneath the southern Great Basin. The tomographic image indicates that the southern Great Basin has a flat Moho at about 30 km depth. We attribute the flat Moho to both underplating by partial melt from the uppermost mantle and to ductile flow in the crust. Magmatic underplating probably dominates where Pn velocities are low (<7.8 km/s) and ductile flow should dominate where Pn velocities are high (>7.9 km/s). Low velocity regions occur predominantly beneath the east margin of the Walker Lane Belt and the Las Vegas Shear Zone suggesting that these shear zones overlie a zone of relatively weak mantle. A region of high Pn velocity northeast of Nevada Test Site (NTS) may correspond to old lithosphere or to a region that has experienced extensive basalt extraction.
Increase in levels of stratospheric chlorine and fluorine loading between 1985 and 1992
Authors: Gunson M. R. , Abrams M. C. , Lowes L. L. , Mahieu E. , Zander R. , Rinsland C. P. , Ko M. K. W. , Sze N. D. , Weisenstein D. K.
Published: February 2004

Mixing ratios of 3.44 ppbv (parts per billion by volume) and 1.23 ppbv for HCl and HF above 50 km, surrogates for total chlorine and fluorine, have been measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment on a March 1992 flight of the Space Shuttle. Compared to the measured values obtained on a 1985 flight, these correspond to a 37% and 62% increase for HCl and HF, respectively. The derived trend in HCl (∼0.13 ppbv per year) is in good agreement with the model‐predicted increase in chlorine loading of 0.13 ppbv per year [Prather and Watson, 1990], and with the measured trends in HCl total column abundance from reported ground‐based observations. The main source of this change can be attributed to the release of man‐made chlorofluorocarbons (CFCs) and hydrochloro‐fluorocarbons (HCFCs). This new value for HCl represents an upper limit to the inorganic chlorine concentration in the stratosphere available for participation in photochemical processes which destroy ozone.
Energetic atomic and molecular ions of ionospheric origin observed in distant magnetotail flow‐reversal events
Authors: Christon S. P. , Gloeckler G. , Williams D. J. , Mukai T. , McEntire R. W. , Jacquey C. , Angelopoulos V. , Lui A. T. Y. , Kokubun S. , Fairfield D. H. , Hirahara M. , Yamamoto T.
Published: February 2004

Energetic atomic (O+1 and N+1) and molecular (O2+1, NO+1, and N2+1) ions of ionospheric origin were observed in Earth's magnetotail at X ∼ −146 RE during two plasma sheet sunward/tailward flow‐reversal events measured by instruments on the GEOTAIL spacecraft. These events were associated with concurrent ground‐measured geomagnetic disturbance intensification at auroral‐ and mid‐latitudes (Kp = 7−). Energetic ions in the sunward‐component and tailward flows were from both the solar wind and ionosphere. Plasma and energetic ions participated in the flows. During tailward flow, ionospheric origin ion abundance ratios at ∼200–900 km/s in the rest frame were N+1/O+1 = ∼25–30% and (O2+1, NO+1, and N2+1) /O+1 = ∼1–2%. We argue that tailward flow most likely initiated ∼80–100 RE tailward of Earth and molecular ions were in the plasma sheet prior to geomagnetic intensification onset.
An explanation for tailward flows with positive Bz in the distant tail neutral sheet during quiet times
Authors: Lyons L. R. , Pridmore‐Brown D. C.
Published: February 2004

ISEE‐3 and GEOTAIL observations have revealed that at x = −210 to −220 RE, the z‐component of magnetic field across the tail neutral sheet is positive, and the plasma flow is tailward during geomagnetically quiet times. Observations have also shown that the y‐ and z‐components of the interplanetary magnetic field (IMF) partially penetrate into the magnetotail for both positive and negative IMF Bz. We have evaluated the topology of the magnetospheric magnetic field expected from a partial penetration of the IMF when it has a positive z‐component. We find that, in addition to the closed and purely IMF field lines that are generally acknowledged to exist for a southward IMF Bz, there is a region at intermediate radial distances of open field lines that cross the tail neutral sheet before exiting the magnetosphere. This region lies between x ≈ −150 RE and x ≈ −325 RE for the representative IMF orientation and model that we have used. We suggest that the quiet‐time observations from ISEE‐3 and GEOTAIL of tailward flow and positive Bz across the distant tail neutral sheet were obtained during positive IMF Bz conditions and in the region of open field lines. Such an explanation would also account for the GEOTAIL observation that magnetosheath‐like plasma associated with positive Bz is common in the distant tail plasma sheet beyond 150 RE but not closer to the Earth.
GEOTAIL observation of ring‐shaped ion distribution functions in the plasma sheet‐lobe boundary
Authors: Saito Yoshifumi , Mukai Toshifumi , Hirahara Masafumi , Machida Shinobu , Nishida Atsuhiro , Terasawa Toshio , Kokubun Susumu , Yamamoto Tatsundo
Published: February 2004

The ring‐shaped velocity distribution of ions with energies of a few keV of the gyrating motion has at times been detected in the boundary region between the plasma sheet and the lobe in the distant tail at XGSM ∼ −70 and −170Re. The normal direction of the ring‐shaped distribution is almost parallel to the magnetic field, and the distribution moves tailward. In many cases the fast flowing ions of the Plasma Sheet Boundary Layer (PSBL) are observed simultaneously. The density of the ring is comparable to the density of the cold ion stream observed in the lobe. We discuss the possibility that these ring ions are generated from cold proton streams by the thermoelectric field that exists at the plasma sheet‐lobe boundary.
Acceleration of heavy ions in the magnetotail reconnection layer
Authors: Fujimoto M. , Nakamura M.
Published: February 2004

The acceleration process of minor heavy ions in the magnetotail reconnection layer is studied by 1D hybrid simulations. In the plasma sheet, different acceleration mechanisms are found to be operative according to the heavy ion mass, not only because of their different inertia but also because of the evolutions of different downstream states. Despite this difference, the ions, including the major protons, are accelerated up to the maximum velocity of twice the lobe Alfven velocity: the energy gain is proportional to the ion mass.
Survey of plasma parameters in Earth's distant magnetotail with the Geotail spacecraft
Authors: Paterson W. R. , Frank L. A.
Published: February 2004

The three‐dimensional velocity distributions for both electrons and positive ions as determined with plasma instrumentation on board the Geotail spacecraft are used to compute number densities, ion bulk velocities, and electron and ion temperatures. We present a statistical survey of these plasma parameters for the magnetotail at distances from Earth in the range of 10 to 210 RE for the period 19 October 1992 through 10 July 1993. The ion temperature is used to discriminate “hot” plasmas from “cold” plasmas. The hot ion plasmas are frequently found to stream either towards or away from Earth and we identify these with the plasma sheet, plasma sheet boundary layer, and regions of acceleration. The cold ion plasmas are typically streaming away from Earth. These cold plasmas appear to be associated with the plasma mantle, the magnetosheath, and boundary layers interior to the magnetosheath, although the contribution from the ionosphere has not yet been evaluated.
Wave form analysis of the continuum radiation observed by GEOTAIL
Authors: Nagano I. , Yagitani S. , Kojima H. , Kakehi Y. , Shiozaki T. , Matsumoto H. , Hashimoto K. , Okada T. , Kokubun S. , Yamamoto T.
Published: February 2004

The Plasma Wave Instrument (PWI) onboard the GEOTAIL spacecraft has frequently observed Continuum Radiation (CR) throughout the geomagnetic tail region, including the Magnetosheath (MS), the Lobe, the Plasma Sheet Boundary Layer (PSBL), and the Plasma Sheet (PS). In addition to the usual Escaping CR (from 10 kHz to 30 kHz) and the Trapped CR (from about 5 kHz to 10 kHz), CR with the frequency structure extending down to 1 kHz (the local plasma frequency) has often been observed in the Lobe region. Waveforms of the electric field in the frequency range less than 4 kHz, which is acquired by Wave Form Capture in the PWI, are used to analyze in detail the frequency‐time structure of such low‐frequency CR near the lower cutoff. Two distinct cutoff frequencies modulated by the antenna spinning indicates that the CR in the Lobe region propagates both in the O mode and in the X mode almost perpendicular to the earthward geomagnetic field line. The CR in the Lobe region, especially in the vicinity of the PSBL, is sometimes accompanied by intense electrostatic electron‐cyclotron‐harmonic (ECH) (n + 1/2) waves. These suggest that such a low‐frequency CR in the distant tail region is most likely to be generated from the ECH waves near the PSBL, and trapped within the Lobe between the PSBL and the MS.
Pc5 pulsations observed in the dayside magnetosphere by Geotail
Authors: Nakamura M. , Matsui H. , Kawano H. , Kokubun S. , Takahashi K. , Matsuoka A. , Yamamoto T. , Tsuruda K. , Hayakawa H. , Okada T.
Published: February 2004

The Geotail spacecraft remained close to the dayside magnetopause from October 17 to October 18, 1992. During the intervals of this very unique orbit when the spacecraft was within the magnetopause, Pc5 pulsations were observed almost continuously in the magnetic field and in the electric field. The signature of the pulsations agrees with the theory of field line standing oscillations with the mode being the fundamental. The observed Pc5 pulsations were regarded to be triggered by sudden compressions and expansions of the magnetic field. The resulted displacement of the field line reached a maximum of 2Re.
Relation between electrostatic solitary waves and hot plasma flow in the plasma sheet boundary layer: GEOTAIL observations
Authors: Kojima H. , Matsumoto H. , Miyatake T. , Nagano I. , Fujita A. , Frank L. A. , Mukai T. , Paterson W. R. , Saito Y. , Machida S. , Anderson R. R.
Published: February 2004

Most of the BEN wave forms observed by GEOTAIL in the Plasma Sheet Boundary Layer (PSBL) appear as a series of isolated spiky pulses which are termed “Electrostatic Solitary Waves (ESW).” Comparison between the BEN observations and plasma measurements shows that the uppermost frequency of the ESW is closely related to the temperature of the flowing ions in the PSBL. We also find that the observed spike width of the ESW and the inter‐pulse time‐span change very rapidly on time scales ranging from a few milliseconds to a few hundreds of milliseconds, suggesting that the speed of the ESW potential changes very rapidly.
Observations of geographically correlated orbit errors for TOPEX/Poseidon using the global positioning system
Authors: Christensen E. J. , Haines B. J. , McColl K. C. , Nerem R. S.
Published: February 2004

We have compared Global Positioning System (GPS)‐based dynamic and reduced‐dynamic TOPEX/Poseidon orbits over three 10‐day repeat cycles of the ground‐track. The results suggest that the prelaunch joint gravity model (JGM‐1) introduces geographically correlated errors (GCEs) which have a strong meridional dependence. The global distribution and magnitude of these GCEs are consistent with a prelaunch covariance analysis, with estimated and predicted global rms error statistics of 2.3 and 2.4 cm rms, respectively. Repeating the analysis with the post‐launch joint gravity model (JGM‐2) suggests that a portion of the meridional dependence observed in JGM‐1 still remains, with a global rms error of 1.2 cm.
Geotail observations of spiky electric fields and low‐frequency waves in the plasma sheet and plasma sheet boundary
Authors: Cattell C. , Mozer F. , Tsuruda K. , Hayakawa H. , Nakamura M. , Okada T. , Kokubun S. , Yamamoto T.
Published: February 2004

Electric field data from the Geotail spacecraft provide an opportunity to extend the observations of spiky fields made by ISEE‐1 to a region of the magnetosphere where quasistatic electric field measurements have not previously been made, to examine their possible importance in the dynamics of the middle and distant tail, and to test some hypotheses about their formation. In this paper, examples of large fields in the plasma sheet and its boundary at radial distances up to ∼90 RE are presented. It is shown that three different types of large electric fields can occur: (1) spiky fields; (2) “DC” fields; and (3) waves at frequencies comparable to the lower hybrid frequency. There is usually a gradation between (1) and (3), and often large electric field spikes are embedded in regions of lower amplitude waves. The waves tend to occur in short (few to 10's of seconds) packets whose start and stop times are not always correlated with changes in the magnetic field and/or density (as indicated by the spacecraft potential). The peak frequency is often less than but comparable to the lower hybrid frequency in agreement with theories of lower hybrid drift waves in the magnetotail. The largest spikes are not always associated with the largest changes in the spacecraft potential and/or magnetic field. It is suggested that the spiky fields may represent the nonlinear development of the waves.
GEOTAIL low energy particle and magnetic field observations of a plasmoid at XGSM = −142 RE
Authors: Machida S. , Mukai T. , Saito Y. , Obara T. , Yamamoto T. , Nishida A. , Hirahara M. , Terasawa T. , Kokubun S.
Published: February 2004

Data from the GEOTAIL Low Energy Particle (LEP) instrument and magnetometer (MGF) for a plasmoid event on October 8, 1993 when the spacecraft was located at XGMS ∼−142 RE were analyzed. The event started 16 minutes after a substorm onset with a tailward flow of electrons whose characteristic energy was several keV with an apparent energy dispersion. This was followed by the arrival of a beam of high energy ions, which also had a similar energy dispersion, and an enhancement of the magnetic field intensity. There was appreciably high flux of cold ions in the lobe region, and it was further enhanced at the front of the plasmoid. These cold ions were energized at the boundary of the plasmoid where a sharp decrease in the total magnetic field intensity was observed. It was found that the main part of the plasmoid had a significant dusk‐to‐dawn magnetic field, indicating the plasmoid had a flux rope, or a distorted closed‐loop magnetic field structure. After passing the main part of the plasmoid, the spacecraft entered a region characterized by high energy tailward flowing ions and coexisting cold ions. The level of low frequency magnetic field fluctuations was relatively high, and there were some time variations in both high‐energy and cold ion fluxes.

Synthesizing these features, we conclude that our observations are consistent with the creation of a plasmoid and surrounding energetic particle layers following a substorm as predicted by the near‐Earth neutral line model of a magnetospheric substorm.
Estimated SAGE II ozone mixing ratios in early 1993 and comparisons with stratospheric photochemistry, aerosols and dynamics expedition measurements
Authors: Yue G. K. , Veiga R. E. , Poole L. R. , Zawodny J. M. , Proffitt M. H.
Published: February 2004

An empirical time‐series model for estimating ozone mixing ratios based on Stratospheric Aerosol and Gas Experiment II monthly mean ozone data for the period October 1984 through June 1991 has been developed. The modeling results for ozone mixing ratios in the 10‐ to 30‐ km region in early months of 1993 are presented. In situ ozone profiles obtained by a dual‐beam UV‐absorption ozone photometer during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition campaign, May 1–14, 1993, are compared with the model results. With the exception of two profiles at altitudes below 16 km, ozone mixing ratios derived by the model and measured by the ozone photometer are in relatively good agreement within their individual uncertainties. The identified discrepancies in the two profiles are discussed.
Early trends in the global tropospheric abundance of hydrochlorofluorocarbon‐141b and 142b
Authors: Montzka S. A. , Myers R. C. , Butler J. H. , Elkins J. W.
Published: February 2004

Hydrochlorofluorocarbons (HCFCs) are rapidly replacing chlorofluorocarbons (CFCs) as foam‐blowing agents, solvents, and refrigerants. These substitutes, however, still contain chlorine and have the potential to deplete stratospheric ozone. Although the ozone destruction capacity of HCFCs is believed to be significantly less than that for CFCs, concern over unrestricted chlorine input to the atmosphere from HCFC use has prompted proposals for future limits on production. Here we report the first global time‐series for mixing ratios of HCFC‐141b (1,1‐dichloro‐1‐fluoroethane) and HCFC‐142b (1‐chloro‐1,1‐difluoroethane) in air collected at seven remote sampling stations. Global mean mixing ratios in mid‐1993 were 0.7 parts per 1012 (ppt) for HCFC‐141b and 4.3 ppt for HCFC‐142b. The global atmospheric abundance of HCFC‐141b increased by 0.9 ppt, or a factor of ∼3, in 1993. Global abundance of HCFC‐142b increased by 1.1 ppt yr−1 during 1992–1993. The results suggest that HCFCs are currently used extensively for replacing CFCs in selected applications. Furthermore, measured levels are significantly higher than expected based on available emission estimates and consumption predictions.
FTIR measurements of HF, N2O and CFCs during the Arctic polar night with the Moon as light source, subsidence during winter 1992/93
Authors: Notholt J.
Published: February 2004

Ground based FTIR absorption measurements have been performed to study the zenith column densities of HF, N2O, CFC‐12 and CFC‐22. The spectra were recorded in the Arctic (Ny‐Ålesund, Spitsbergen, 79°N, 12°E) during winter 1992/93 and spring/summer 1993. During the polar night the moon served as light source. The analysis of the spectra has been performed in the way to study vertical motions in the atmosphere. Compared to the summer observations a subsidence of −1.4 km at 12 km altitude and −4.9 km at about 15 km has been calculated for December 1992. For February 1993 the data yield a subsidence of −2.5 km at 12 km altitude and −6.3 km at about 15 km altitude.
The meridional wind component of the thermospheric tide observed by WINDII on UARS
Authors: McLandress C. , Rochon Y. , Shepherd G. G. , Solheim B. H. , Thuillier G. , Vial F.
Published: February 2004

Thermospheric meridional winds measured by the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) are analyzed for migrating solar tides for March/April 1993. Tidal signatures are extracted by zonally averaging and binning the data in equally spaced intervals of local time, latitude and altitude. An examination of the binned data reveals vertically propagating tides in the lower thermosphere with the diurnal tide dominating at low latitudes. Above 120 km evidence of vertical propagation ceases and the vertical gradients are significantly reduced. In regions where both daytime and nighttime data are available Fourier decomposition of the binned winds is used to extract the diurnal component of the tide. This analysis reveals that the propagating diurnal tide attains a maximum amplitude of 65 m/s at 20°N and 20°S at 95 km and exhibits a vertical wavelength of about 25 km.
Evolution of the plasmoid‐lobe interaction with downtail distance
Authors: Slavin J. A. , Owen C. J. , Hesse M.
Published: February 2004

This study examines the interaction between plasmoids moving anti‐sunward at high speeds and the tail lobes which bound them to the north and south. Attention is focused on the influence of changing lobe conditions with downtail distance. It is shown using ISEE 3 measurements that the gradual filling of the lobes with mantle plasma and the decrease in magnetic field intensity reduces the average lobe MHD fast mode speed from 1200 km s−1 at X = −80 RE to 400 km s−1 at X = −220 RE. This results in the ratio of the plasmoid speed to the fast mode speed increasing with downtail distance, from 0.3 at X = −80 RE to ∼1 at X = −220 RE. It is argued that the “standard” traveling compression region (TCR) signature observed closer to the Earth will be distorted at large distances, where the fast mode transit time between the plasmoid and magnetopause becomes long compared to the time for the plasmoid to move past a given point in the tail. This change in the nature of the plasmoid‐lobe interaction with downtail distance is offered as an explanation for why the reported rate of TCR occurrence peaks at X = −60 to −130 RE and decreases in the more distant tail.
Subthermal nitric oxide spin‐orbit distributions in the thermosphere
Authors: Lipson S. J. , Armstrong P. S. , Dodd J. A. , Lowell J. R. , Blumberg W. A. M. , Nadile R. M.
Published: February 2004

The two NO(X²Π, υ=1, Ω=1/2,3/2) spin‐orbit populations in the Earth's thermosphere have been found to depart by more than a factor of 2 from the ratio expected from thermal equilibrium. The effective temperature describing the observed population distribution is as much as 700 K lower than the local kinetic temperature. Absolute NO(υ=1, J, Ω) column densities were derived from high‐resolution (1 cm−1) infrared earthlimb spectra for tangent altitudes up to 200 km, obtained in the CIRRIS 1A Space Shuttle experiment. Nonlinear least‐squares synthetic spectral fitting was used to analyze the NO Δυ=1 fundamental band emissions near 5.3 µm. The spin‐orbit distribution represents a third degree of freedom, along with vibration and rotation, that is not in equilibrium with the local kinetic temperature. These observations may significantly impact the interpretation of band‐integrated measurements of NO in the upper atmosphere, for which equilibrium sublevel distributions have been assumed. The subthermal distribution is most likely produced in the collisional uppumping of NO(υ=0) by O atoms, which is the major source of NO(υ=1) in the thermosphere. This inference suggests that the present effect is related to the subthermal spin‐orbit distributions observed in laboratory studies of NO2 photodissociation.
An observation of the atmospheric thermal emission spectrum of trichlorofluoromethane (CFC‐11)
Authors: Evans W. F. J. , Puckrin E.
Published: February 2004

Ground‐based measurements of the thermal emission from the clear zenith sky have been made which clearly show the ν4 band of CFC‐11 (or CCl3F). An atmospheric water spectrum has been derived from these measurements and used to subtract the water emission features from the thermal emission spectra. These observations have been compared to line‐by‐line atmospheric radiance calculations using the FASCD3P algorithm. The agreement of the atmospheric CFC‐11 emission band between the simulated result and the observed water‐subtracted result is good. From these measurements the total downward greenhouse flux from the CFC‐11 ν4 emission band has been found to be 0.25 W/m² ± 10%.
The tropospheric oxidation of dimethyl sulfide: A new source of carbonyl sulfide
Authors: Barnes I. , Becker K. H. , Patroescu I.
Published: February 2004

In laboratory investigations of the gas‐phase OH initiated oxidation of dimethyl sulfide (DMS: CH3SCH3) at room temperature the formation of SO2, dimethyl sulfoxide (DMSO: CH3SOCH3), and OCS have been observed. A yield of 0.7±0.2% S was measured for OCS. These new results represent a hitherto unknown and quite considerable in situ atmospheric source of OCS. Based on the global DMS source strength as given in the literature and provided that the results from the laboratory study are valid under atmospheric conditions we estimate a contribution in the range 0.10 to 0.28 Tg (OCS) yr−1 from the gas‐phase atmospheric photooxidation of DMS to the global OCS budget.
Wave‐modified mean exothermic heating in the mesopause region
Authors: Hickey Michael P. , Walterscheid Richard L.
Published: February 2004

We employ a model of wave‐driven OH nightglow fluctuations to calculate the effects of gravity waves on the chemical exothermic heating due to reactions involving odd hydrogen and odd oxygen species in the mesopause region. Using a model based on time means and deviations from those means, it is demonstrated that gravity waves contribute to the time‐average exothermic heating. The effect can be significant because the fractional fluctuations in minor species density can be substantially greater than the fractional fluctuation of the major gas density. Our calculations reveal that the waves mitigate the exothermic heating, demonstrating their potential importance in the heat budget of the mesopause region.
Tectonic fabric and lithospheric strength of northern Eurasia based on gravity data
Authors: Kogan Mikhail G. , Fairhead J. Derek , Balmino Georges , Makedonskii Efim L.
Published: February 2004

The isostatic gravity anomalies over the whole former USSR (FSU) from land gravimetry are presented here for the first time at a spatial resolution adequate to study the tectonic fabric and the lithospheric rigidity. The short wavelength gravity anomalies improve the delineation of the regional tectonic units of the FSU, originally identified from the geological and aeromagnetic data. A study of the coherence between the Bouguer gravity anomaly and topography of East European and Siberian Cratons allowed us to estimate the elastic plate thickness Te of 78 to 109 km. Relying on the current knowledge of the thermal state of Archean lithosphere, we inferred from Te the thermal plate thickness Tp of 200–250 km.
Tectonic rotation about the termination of a major strike‐slip fault, Marlborough Fault System, New Zealand
Authors: Roberts Andrew P.
Published: February 2004

The Marlborough fault system comprises a series of major right‐lateral strike‐slip faults that link the Alpine fault to the Hikurangi subduction zone in the Pacific/Australia plate boundary zone in New Zealand. All of the major active faults of the Marlborough fault system have continuous traces except for the Clarence fault which terminates abruptly near the Ward syncline. Paleomagnetic data from upper Miocene and lower Pliocene sedimentary rocks between the Marlborough faults indicate a consistent post‐early Pliocene regional clockwise rotation of about 20°. An additional rotation of about 10° is evident at many localities near the termination of the Clarence fault. It is proposed that the additional rotation, relative to the rest of the region, is caused by a velocity gradient that likely exists between the active Awatere fault and the termination of the Clarence fault. The existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one‐third of the displacement in the Marlborough fault system occurs between the Awatere and Clarence faults. The kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the Clarence fault. The block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data.
Anisotropy at the Lacq hydrocarbon field (France) from shear‐wave splitting
Authors: Herquel Georges , Wittlinger Gérard
Published: February 2004

Three‐component seismograms from local earthquakes located beneath the reservoir of the Lacq hydrocarbon field have been analysed for shear‐wave splitting. Shear‐waves recorded at the station USI located on top of the hydrocarbon reservoir show a clear splitting in an average polarization direction N30°–40°E which is different from the present‐day local and regional stress direction. This direction seems approximately parallel to the Tertiary period stress field in this area which corresponds to the measured main crack directions in the gas reservoir. At station LDB, located outside of the anticlinal structure, no splitting was detected but due to a poor signal‐to‐noise ratio, only nine events were available and anisotropy could be absent or obscured. For a 250 m thick oil or gas field the velocity anisotropy is estimated at about 6–10%, which is in the same range as values obtained from VSPs in other hydrocarbon fields. Monitoring induced‐seismicity by three component stations could be a useful tool to characterize hydrocarbon fields in term of the rock's average properties in a large volume.
Ozone‐related trends in solar UV‐B series
Authors: Basher Reid E. , Zheng Xiaogu , Nichol Sylvia
Published: February 2004

It is now well established that stratospheric ozone has become depleted on a global scale, with downward trends of several percent per decade in populated mid‐latitude regions, but evidence of the expected parallel increases in solar UV‐B radiation has remained elusive to date; if anything, past studies have actually reported decreases. The broken, ten‐year record of Robertson‐Berger meter UV‐B measurements for a clean‐atmosphere, mid‐latitude site in the Southern Hemisphere that we analyse here is incapable of independently confirming a long‐term upward trend, but it does provide specific evidence in support of the trend hypothesis. In particular, there is a very strong relationship between daily clear‐sky UV‐B and parallel ozone measurements, with correlation coefficients in the range of 0.84 to 0.95, and the trends and variations in ozone are very well matched by corresponding opposite trends and variations in UV‐B.
Anthropogenic lead isotopes in Antarctica
Authors: Rosman K. J. R. , Chisholm W. , Boutron C. F. , Candelone J.‐P. , Patterson C. C.
Published: February 2004

We report the first measurements of Pb isotopes in Antarctic snow, which show that even recent snow containing 2.3 pg/g is highly polluted with anthropogenic Pb. This follows from a comparison of isotope abundances of Pb in surface snow and terrestrial dust extracted from ancient Antarctic ice (Dome C, depth 308 m, approximate age 7,500 a BP), the latter being distinctly more radiogenic. This result is independent of geochemical arguments based on measurements of Al, Na and SO4. South America is suggested as a likely source of this anthropogenic Pb. The presence of significantly less radiogenic Pb in the snow adjacent to two Antarctic base stations indicates that there is contamination from station emissions, although emission from Australia is an alternative explanation for a site 33 km from Dumont d'Urville.
Changes in cloud properties due to NOx emissions
Authors: Kulmala Markku , Korhonen Pekka , Laaksonen Ari , Vesala Timo
Published: February 2004

Climate forcing by anthropogenic aerosols has recently excited growing interest [Charlson et al., 1987; Charlson et al., 1990; Wigley, 1991; Charlson et al., 1992]. It has earlier been shown that increased cloud droplet concentrations can increase cloud albedos [e.g. Twomey et al., 1984]. Wigley [1991] and Charlson et al. [1990] have pointed out that the Northern Hemisphere may be warming more slowly than the Southern Hemisphere. According to them this is mainly due to the direct and indirect effects of sulphate aerosols. In this report we discuss an alternative mechanism which could enhance indirect climate forcing by aerosols. Increased concentrations of condensable vapours (such as HNO3 and HCl) in the atmosphere could activate an increased number of pre‐existing aerosol particles to act as cloud condensation nuclei [Kulmala et al., 1993]. This would cause similar effects on optical properties of clouds as an increase of aerosol particles in the atmosphere.
The characteristics of the magnetopause reconnection X‐line deduced from low‐altitude satellite observations of cusp ions
Authors: Lockwood M. , Onsager T. G. , Davis C. J. , Smith M. F. , Denig W. F.
Published: February 2004

We present an analysis of a “quasi‐steady” cusp ion dispersion signature observed at low altitudes. We reconstruct the field‐parallel part of the Cowley‐D ion distribution function, injected into the open LLBL in the vicinity of the reconnection X‐line. From this we find the field‐parallel magnetosheath flow at the X‐line was only 20 ± 60 km s−1, placing the reconnection site close to the flow streamline which is perpendicular to the magnetosheath field. Using interplanetary data and assuming the subsolar magnetopause is in pressure balance, we derive a wealth of information about the X‐line, including: the density, flow, magnetic field and Alfvén speed of the magnetosheath; the magnetic shear across the X‐line; the de‐Hoffman Teller speed with which field lines emerge from the X‐line; the magnetospheric field; and the ion transmission factor across the magnetopause. The results indicate that some heating takes place near the X‐line as the ions cross the magnetopause, and that sheath densities may be reduced in a plasma depletion layer. We also compute the reconnection rate. Despite its quasi‐steady appearance on an ion spectrogram, this cusp is found to reveal a large pulse of enhanced reconnection rate.
TOMS total ozone trends in potential vorticity coordinates
Authors: Randel William J. , Wu Fei
Published: February 2004

Global total ozone measurements from the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) are analyzed using potential vorticity (PV) as an approximate vortex‐following coordinate. We analyze the time period November 1978–May 1991, prior to the volcanic eruption of Mt. Pinatubo. The TOMS data are remapped into PV coordinates and trends are calculated, thereby characterizing ozone losses inside and outside the winter polar vortices. These analyses show large regions of ozone loss outside of the vortex in both hemispheres. Furthermore, these data suggest that midlatitude losses in the NH during winter‐spring do not result solely from the transport of ozone depleted air from inside to outside the vortex.
A shear failure strength law of rock in the brittle‐plastic transition regime
Authors: Ohnaka Mitiyasu
Published: February 2004

As a first step to establish the law governing shear failure of typical crustal materials in the brittle‐plastic transition regime under lithospheric conditions, and thereby to properly estimate a depth profile of lithospheric strength in quantitative terms, the effects of the normal stress σn across the fault surfaces and ambient temperature T on the shear failure strength of dry Westerly granite in the brittle to brittle‐plastic transition regimes are evaluated quantitatively, using experimental data published by earlier authors. The empirical law proposed can predict the shear failure strength at strain rates of 10−4‐10−5/S under any (σn, T) conditions in the brittle to brittle‐plastic transition regimes.
Present‐day Antarctic ice mass changes and crustal motion
Authors: James Thomas S. , Ivins Erik R.
Published: February 2004

The peak vertical velocities predicted by three realistic, but contrasting, present‐day scenarios of Antarctic ice sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak Antarctic vertical velocities of the ICE‐3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene Antarctic deglaciation history portrayed in ICE‐3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 1021 Pa·s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present‐day scenarios predict small vertical crustal velocities, their overall continent‐ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion

and time‐varying zonal gravity field
.
The 1993 Klamath Falls, Oregon, earthquake sequence: Source mechanisms from regional data
Authors: Braunmiller Jochen , Nábělek John , Leitner Beate , Qamar Anthony
Published: February 2004

We use regional broadband seismograms to obtain seismic moment‐tensor solutions of the two September 20, 1993, Mw=6, Klamath Falls, Oregon earthquakes, their foreshock and largest aftershocks (MD>3.5). Several sub‐groups with internally consistent solutions indicate activity on several fault segments and faults. From the estimated moment‐tensors and depths of the main shocks and from the aftershock distribution we deduce that both main shocks occurred on an east‐dipping normal fault, possibly related to the Lake of the Woods fault system. Rotation of T‐axes between the two main shocks is consistent with the two dominant trends of the aftershocks and mapped faults. We propose that a change in fault strike acted as temporary barrier separating the rupture of the main shocks. Empirical Green's function analysis shows that the first main event had a longer rupture duration (half‐duration 1.7 s) than the second (1.2 s). In December, vigorous shallow activity commenced near Klamath Lake's western shore, 5–10 km east of the primary aftershock zone. It appears a Mw=5.5 aftershock occurring the day before, though within the primary aftershock zone, triggered the activity.
Crustal thickness estimation using high frequency Rayleigh waves
Authors: Das Triparna , Nolet Guust
Published: February 2004

The method of nonlinear waveform‐fitting was extended to include changes in the depth of the Moho. Studies performed on synthetic data at 10° epicentral distance showed that it is theoretically possible to determine Moho‐depth with an accuracy of less than a kilometer if the frequency range extends to 0.12 Hz. We applied this method on several broadband records from two earthquakes in Western United States to invert for crustal thickness. Waveform‐fitting of Rayleigh waves for epicentral distances between 3° and 10° for individual paths in this region show that the average Moho‐depth can be resolved to 1–2 km. It was possible to obtain good waveform fits for frequencies between 0.02–0.08 Hz. We conclude that broadband seismic data from local events allow us to determine Moho‐depth independently from crustal shear‐wave velocity.