bluuebunny/crossref_metadata_2025 huggingface dataset:
ALOHA‐93 measurements of intrinsic AGW characteristics using airborne airglow imager and groundbased Na wind/temperature lidar
Authors: Swenson G. R. , Taylor M. J. , Espy P. J. , Gardner C. , Tac X.
Published: February 2004

Monochromatic Acoustic Gravity Waves (AGWs) with periods < 1 hour are a prevalent feature in the mesospheric airglow layers. These waves are important dynamically and energetically to the region where their temporal and spatial morphology are not well established. The purpose of this study is establish the intrinsic AGW characteristics over an extended region (as flown by the NCAR Electra aircraft) and to present the data in terms of the predicted spectral domain defined by the Brunt‐Vaisala frequency and the diffusive filtering limit proposed by Gardner [1994]. On October 21, 1993, observations were made from the NCAR Electra aircraft during a 6 hour flight in a large triangle N and W of Maui, for a integral distance of ∼3000 km. The entire area observed [∼1 M km²] had a monochromatic AGW propagating toward the NW and the western half had a SW propagating wave superimposed. These waves were also observed with the Michelson interferometer on the aircraft and an airglow imager at the Haleakala location during this time. Intrinsic phase velocities were computed where the Na Wind/Temperature (W/T) lidar at Haleakala provided a measure of the mean wind to compensate phase velocities observed with the imager. The data were tabulated and plotted in an AGW spectral reference frame and compared to cutoff conditions predicted by diffusive filtering theory.
Long‐term variability in the solar diurnal tide observed by HRDI and simulated by the GSWM
Authors: Burrage M. D. , Hagan M. E. , Skinner W. R. , Wu D. L. , Hays P. B.
Published: February 2004

Observations of the mesosphere and lower thermosphere winds obtained by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) during 1991 to 1995 reveal a semiannual variation in the amplitude of the (1, 1) diurnal tide. The global‐scale wave model (GSWM) represents the first numerical modeling attempt at simulating this seasonal variability, and a preliminary comparison of the GSWM tidal results with HRDI measurements is presented. The results of the comparison and of numerical tests point to some vital and unresolved questions regarding tidal dissipation and tropospheric forcing. In addition to the seasonal variability, HRDI has revealed a strong interannual modulation of the diurnal tide with amplitudes observed to change by nearly a factor of 2 from 1992 to 1994.
Intensity variations of >70‐Mev cosmic rays measured by Pioneer 10, Voyager 1 & 2 and IMP in the heliosphere during the recovery period from 1992–1995
Authors: Webber W. R. , Lockwood J. A.
Published: February 2004

Using data from the >70‐MeV channel on the Pioneer 10 and Voyager 1 & 2 spacecraft we have examined the gradients and intensities of cosmic rays in the outer heliosphere between 1992 and 1995. During this time there is a slow increase of intensity towards the next maximum in ∼1997 and the radial gradient is small‐decreasing to ∼0.8%/AU at the end of this period. The latitude gradient has also decreased to only ∼0.1–0.2%/AU but remains negative as it was in the previous 11‐year cycle. These gradients are similar to those for >70‐MeV particles reported recently in the inner heliosphere but quite different from the positive gradients observed at this time throughout the heliosphere by the Ulysses and Voyager spacecraft for anomalous cosmic rays. Overall the cosmic ray intensity is almost uniform in radius, azimuth and latitude at this time in the outer heliosphere‐and far lower than the estimated interstellar intensity. The intensities are, in fact, much lower than would be expected based on data from the previous cycle. This, along with the very slow increase that is observed, suggests that, at the same radial distance, the intensity in 1977 will be much less than in the previous cycle in 1987‐resulting in a large 22‐year modulation wave. The data show some features which suggest that large scale drift patterns, which change when the solar magnetic polarity changes every 11 years, play a important role in the overall intensity distribution in the outer heliosphere‐but specific details, particularly in the present positive polarity cycle beginning in 1990 are not well predicted by current models.
Evidence for a winter sink of atmospheric carbonyl sulfide in the northeast Atlantic Ocean
Authors: Ulshöfer Veit S. , Uher Günther , Andreae Meinrat O.
Published: February 2004

Atmospheric and dissolved carbonyl sulfide (COS) concentrations were measured on 473 samples during three cruises into the northeast Atlantic Ocean. The cruises took place in April/May 1992, January 1994, and September 1994, covering three seasons. In January 1994, persistent undersaturation of COS in seawater with respect to the atmosphere was observed. This is the first data set to show a strong and persistent undersaturation with the mean saturation ratio (SR) being 46% and the standard deviation 13%. In April 1992, the seawater was slightly supersaturated, with a SR of 126±58 %. Only in September 1994, strong supersaturation of 214±86% was observed. The measured air concentrations were relatively uniform, averaging 410±67 pptv in January 1994, 466±42 pptv in April 1992, and 396±18 pptv in September 1994. Sea‐to‐air fluxes of COS were estimated using three different exchange models. We obtained moderate to low COS emissions in September (19 to 33 nmol m−2 d−1) and April/May (5 to 10 nmol m−2 d−1), in contrast to a significant flux from the atmosphere into the ocean in January (−76 to −31 nmol m−2 d−1). The strong seasonal variation of COS emissions with the possibility of reversed fluxes into the ocean during winter must be considered in future oceanic source estimates. The possible effect of an open ocean winter sink on global marine emissions of COS could be a reduction by some 10–15%.
Observations of a slow‐mode shock at the lobe‐plasma sheet boundary in Earth's distant magnetotail
Authors: Seon J. , Frank L. A. , Paterson W. R. , Scudder J. D. , Coroniti F. V. , Kokubun S. , Yamamoto T.
Published: February 2004

A lobe‐plasma sheet boundary observed within Earth's distant magnetotail (XGSM ≃ −135 RE) with the Geotail spacecraft is interpreted in terms of a slow‐mode shock. Measurements of the three‐dimensional velocity distributions of protons and electrons and of the magnetic fields allow a quantitative comparison with theoretical predictions for a steady‐state, one‐dimensional shock. The observed plasma moments and magnetic field upstream from the shock are successfully used to predict these parameters in the downstream region. The measured parameters for this example of a lobe‐plasma sheet boundary are in sufficient agreement with the theoretical predictions to provide considerable confidence that this boundary is a slow‐mode shock.
Height gradient of F region vertical drift in the evening equatorial ionosphere
Authors: Sastri J. Hanumath , Varma V. K. Meena , Nayar S. R. Prabhakaran
Published: February 2004

Simultaneous measurements of F‐region vertical drift are made in the evening hours (1700–2100 IST) at Trivandrum (dip 0.6°N) and Kodaikanal (dip 4°N) on fifteen days during December 1993–January 1994 using the HF phase path technique on two different probing frequencies. The data are used to study the height dependence of vertical plasma drift in the bottomside F‐region in the dusk sector after correcting the drifts (at Kodaikanal) for meridional wind effects and chemical loss. It is found that growth and decay of a positive height gradient in vertical drift occurs fairly regularly in the dusk period. On the average the vertical velocity gradient is positive in in the interval 1815–1925 IST and is preceded by negative values. The positive height gradient of vertical plasma drift below the F layer peak is interpreted in terms of altitude dependence of the relative contributions of E and F region dynamos to the electric fields responsible for plasma drifts (vertical and zonal) of the dusktime equatorial F‐region. These results are for winter solstice solar minimum conditions.
Response of equatorial‐low latitude ionosphere to sudden expansion of magnetosphere
Authors: Sastri J. Hanumath , Huang Y. N. , Shibata T. , Okuzawa T.
Published: February 2004

The response of the equatorial‐low latitude nightside ionosphere to the geomagnetic negative sudden impulse(si−) on March 15, 1993 is studied using recordings of Doppler velocity of ionospheric echoes at vertical incidence at Kodaikanal(10.2°N) and Doppler shift of standard HF signals on oblique paths at Lunping(25.0°N) and Kure(34.25°N). The si− at 1541 UT is characterised by a simple decrease of H‐field at low latitude stations widely distributed in longitude, and by a double‐pulse structure at mid and high latitude stations on the dayside. The usual downward drift of F region plasma during the premidnight hours over Kodaikanal near the dip equator abruptly increased for ≈ 2.5 min coincident with the first pulse of the si− and immediately reversed direction to upward. Recordings at Lunping and Kure also showed short‐lived Doppler frequency deviations simulataneous with those at Kodaikanal and of the same polarity and sequence. These observations constitute the first and direct experimental evidence for vertical plasma motions due to si− associated electric fields in the nighttime equatorial‐low latitude ionosphere. The case study supports the view that si− can be explained by the physical model of sc/si+ with a reversal in the direction of the global current systems responsible for the groundlevel magnetic field variations.
Further ozone decline during the northern hemisphere winter‐spring of 1994–1995 and the new record low ozone over Siberia
Authors: Bojkov Rumen D. , Fioletov Vitali E. , Balis Dimitrios S. , Zerefos Christos S. , Kadygrova Tatiana V. , Shalamjansky Arcady M.
Published: February 2004

Ground‐based total ozone observations show that during the second half of January 1995 through February, most of March, and the first week of April very low ozone values, again were observed in northern middle and high latitudes. Over Eastern and Southern Europe and North America the deficiency was 10–12% with a few periods down to 15–20%. Since mid January the ozone values fall 25% below the long‐term mean over Siberia and Yakutia. This anomaly lasted on the average for twelve consecutive weeks. For a number of days in early February and in the second half of March, the deficiency exceeded 35–40%. The monthly mean lower stratosphere temperatures over Siberia, where the polar vortex was displaced were 10°C below the normal for January and February falling down below −75°C to −80°C during the time of lowest ozone.
Sprite spectra; N2 1 PG band identification
Authors: Mende S. B. , Rairden R. L. , Swenson G. R. , Lyons W. A.
Published: February 2004

Imagery and spectra of high altitude luminous flashes, otherwise known as sprites, occurring in the stratosphere/mesosphere above electrically active cumulonimbus clouds were acquired on July 16, 1995 from an observation site near Ft. Collins, Colorado. The spectra, resolved from ∼4500–8000 Å included four spectral features in the 6000–7600 Å region which have been identified as N2 1PG system with Δv=2,3, and 4 from the v=2,4,5,6 vibrational levels of the B³πg state. The spectra were lacking in other features such as the N2+ Meinel or the N2+ 1st neg system indicating that the electron energy causing the excitation is quite low.
Oxfordian magnetostratigraphy in the Iberian Range
Authors: Juárez M. T. , Osete M. L. , Meléndez G. , Lowrie W.
Published: February 2004

The magnetostratigraphy has been established in two sections of middle and late Oxfordian age from the Iberian Range (Spain). The polarity sequences correlate well with the magnetozones in sections at Aguilón and Tosos [Juárez et al., 1994]. A composite magnetostratigraphic sequence has been derived for all the sections in the Iberian Range. It correlates with the Handschumacher et al. [1988] extension of the geomagnetic polarity time scale, and ties the oceanic magnetic anomaly sequence to the Oxfordian sedimentary sections.
Measurements of HCFC‐142b and HCFC‐141b in the Cape Grim air Archive: 1978–1993
Authors: Oram D. E. , Reeves C. E. , Penkett S. A. , Fraser P. J.
Published: February 2004

Stored air samples collected at Cape Grim, Tasmania since 1978, have been analyzed by GC‐MS to investigate the change in the tropospheric concentration of HCFC‐142b and HCFC‐141b over the past 15 years. Between April 1978 and September 1993 the concentration of HCFC‐142b rose from 0.20±0.02 pptv to 3.0±0.3 pptv, with the majority of this increase occurring from 1989 onwards. By mid‐1993 the rate of increase had reached 0.9±0.1 pptv/yr. From 1982 to 1991 the average concentration of HCFC‐141b was 0.08±0.01 pptv. A very sharp increase in concentration began in 1992 however, such that it reached 0.46±0.05 pptv by September 1993. Using a 2‐D model of atmospheric chemistry, constrained by these observations, global emissions of these two compounds have been calculated and found to differ from other estimates. This is partly due to the background concentration levels which existed prior to the start of the other estimated emissions.
Large‐scale, persistent latitude structures in the mesospheric temperature during ANLC‐93
Authors: Espy Patrick J. , Huppi Ronald , Manson Alan
Published: February 2004

Michelson interferometer measurements of the hydroxyl (OH) Meinel night‐airglow emissions were made from the NCAR aircraft during the ANLC‐93 Campaign. The spectra have been analysed to give the OH band radiance and rotational temperature, which is taken to be the neutral temperature at the peak of the OH emissions near 87 km. On two occasions, once in the presence of Noctilucent Clouds (NLC), the research flights spanned ∼10° of latitude and reached as high as 66°N. The mean latitudinal structure of the measured mesospheric temperature field is in good agreement with the CIRA‐86 model. In addition, both measurements show large‐amplitude (∼15 K), large‐scale (2–4° of latitude), quasi‐periodic oscillations about the model mean. Finally, the data support the hypothesis that these oscillations are temporally stable, and that they, along with the air mass characterized by the mean temperature field, can be advected with the tidal winds, and play a role in NLC formation.
Observational studies of the role of polar regions in mid‐latitude ozone loss
Authors: Jones R. L. , MacKenzie A. R.
Published: February 2004

Recent analysis of global measurements of ozone distributions using satellites have revealed widespread declines in mid‐latitude ozone, with regional reductions approaching ∼1% per annum (Stolarksi et al., 1991). The existence of mid‐latitude ozone losses has prompted much debate over whether and how perturbations to the chemical composition at high latitudes within the polar vortex may contribute to the reduced ozone amounts observed at lower latitudes (e.g. Schoeberl et al., 1992; Proffitt et al. 1990, 1992, Tuck et al., 1992, 1993, 1994). The export of polar air to low latitudes during each winter can bring air that has undergone recent ozone depletion or air in which chlorine activation has occurred, both potentially contributing to mid‐latitude ozone loss. If this ‘vortex outflow’ is large enough, it may influence the relationship between atmospheric chlorine loading and ozone loss, and knowledge of this process is thus essential for prediction models.

In this paper in‐situ observations of nitrogen compounds from both hemispheres are used to quantify the transport of chemically perturbed polar air to lower latitudes, and show that the transport of air from the polar vortex, at least above the 400K potential temperature surface, appears small.
All‐sky measurements of short period waves imaged in the OI(557.7 nm), Na(589.2 nm) and near infrared OH and O2(0,1) nightglow emissions during the ALOHA‐93 Campaign
Authors: Taylor M. J. , Bishop M. B. , Taylor V.
Published: February 2004

As part of the ALOHA‐93 campaign a high performance all‐sky CCD imaging system was operated at Haleakala Crater, Maui, to obtain novel information on the properties and sources of short period gravity waves over an extended height range ∼80–100 km. Sequential observations of the near infrared OH and O2(0,1) bands and the visible wavelength OI(557.7 nm) and Na(589.2 nm) line emissions have enabled a unique comparison of the morphology and dynamics of the wave motions and their occurrence frequency at each emission altitude to be made. Two major findings are: (a) the detection of significantly higher amounts of wave structure at OI altitudes (∼96 km) compared with that in the OH emission (∼87 km) and (b) the discovery of an unusual morphology, small‐scale wave pattern that was most conspicuous in the OI emission and essentially absent at OH heights. These data provide strong evidence for the presence of ducted wave motions in the lower thermosphere.
Spectrometric and imaging measurements of a spectacular gravity wave event observed during the ALOHA‐93 Campaign
Authors: Taylor M. J. , Turnbull D. N. , Lowe R. P.
Published: February 2004

During the ALOHA‐93 campaign coincident imaging and interferometric measurements of the near infrared and visible wavelength nightglow emissions were made from Haleakala Crater, Maui. On 10 October, 1993 a most unusual wave event was observed. This disturbance appeared as a sharp “front” followed by several conspicuous wave crests which progressed rapidly through the imager's field of view (180°). As the front passed overhead the interferometer detected a sudden jump in both the OH intensity (>50%) and its rotational temperature (∼20 K) with the temperature increase leading the intensity by almost 15 min. At the same time the imager registered a sharp decrease in the OI(557.7 nm) emission intensity. A description of this remarkable event follows.
Lidar observations of the temperature profile between 25 and 103 km: Evidence of strong tidal perturbation
Authors: Dao Phan D. , Farley Robert , Tao Xin , Gardner Chester S.
Published: February 2004

Simultaneous observations of the middle atmosphere and lower thermosphere by Na Wind/Temperature (W/T) and Rayleigh/Raman lidar and other ground‐based measurements were conducted the night of October 21, during the ALOHA‐93 campaign. Rayleigh/Raman lidar measurements provide density from 25 to 90 km and temperature from 25 to 85 km. From the same location, Na W/T lidar measurements were also obtained between ∼83 and 103 km. The combined data provides continuous temperature from 25 to 103 km. Strong perturbations which may be associated with the diurnal tide are observed in the temperature and wind profiles.
Potential distribution of methane hydrate beneath the European continental margins
Authors: Miles P. R.
Published: February 2004

Gridded datasets have been constructed for the physical parameters controlling the formation of gas hydrate. Simultaneous solutions to the gas hydrate phase and pressure‐temperature equations were obtained for each node of these grids. The results show sub‐bottom depths of potential methane hydrate BSRs. These are presented as colour contoured grids for the thickness of the hydrate stability zone for the European margins. The chart proposes that if gas hydrates exist over these areas, then this is the potential depth to the BSR. This depth is generally greater along the continental margins and also increases with increasing age of the margin. Shallowing of the BSR can be seen over areas of thinned continental crust and plateaus. The geological factors controlling gas hydrate formation determine areas of likely occurrence so the apparent paucity of identified hydrate layer BSRs off the European margins, particularly in the Mediterranean, is most notable
Observations of variations in airglow emissions during ALOHA‐93
Authors: Hecht James H. , Ramsay Howat Suzanne K. , Walterscheid Richard L. , Isler Joseph R.
Published: February 2004

Observations have been made of the OH Meinel and O2 Atmospheric intensity and temperature on 8 nights of ALOHA‐93. These data show the presence of diurnal and semidiurnal tides in the 85 to 95 km region whose amplitudes are much greater than were predicted. The signature of a 6 hour tide was also observed at least in the region above 90 km. The magnitudes of the gravity‐wave induced airglow fluctuations were at least as great or greater than were observed during ALOHA‐90. These fluctuations however were in general less than half the magnitude of the combined tidal amplitudes. One unusual observation was of airglow intensity increasing without an accompanying apparent increase in temperature. This is an indication of a non‐periodic change in atmospheric composition near the mesopause.
Large‐eddy simulation of aircraft exhaust plumes in the free atmosphere: Effective diffusivities and cross‐sections
Authors: Dürbeck Tilman , Gerz Thomas
Published: February 2004

The effective diffusion of aircraft emissions in the free stably stratified atmosphere is investigated by means of large‐eddy simulation in a domain of size 4.3 × 1.1 × 1.1 km³. On that scale, the atmosphere is represented by a weakly turbulent flow under uniformly stratified and shearless conditions. It is assumed that aircraft induced turbulence has ceased. The exhaust plumes of aircraft are represented by line sources with Gaussian cross‐sections. The stratification has been varied between 0.006 s−1 and 0.03 s−1. The computed effective horizontal diffusion coefficient lies between 11±2 m²s−1 and 21±4 m²s−1, depending on the level of stratification. Likewise the vertical diffusivity ranges from 2.3±0.6 m²s−1 to 0.37±0.04 m²s−1 in the beginning of the diffusion process, and amounts almost independently of the stratification to about 0.15±0.01 m²s−1 later on. The plume cross‐sections increase with time and stratification. The scattering of the results for a given stratification reflects the action of decaying, anisotropic, and homogeneous turbulence. The results confirm very well data from recent in‐situ flight measurements in the North‐Atlantic flight corridor in the tropopause region.
WINDII observation of a PMC breakup event during ANLC‐93
Authors: Wiens R. H. , Evans W. F. J. , Zalcik M. S. , Manson A. H. , Shepherd G. G.
Published: February 2004

WINDII, a limb‐viewing imaging interferometer aboard the UARS satellite, was employed to count occurrences of polar mesospheric clouds (PMC's) during the ANLC‐93 campaign in July, 1993. During this period large gaps formed in the PMC occurrence plots coincident with the southward extension of the visually observed NLC region. The strong southward radar winds measured on the night side at Saskatoon and a strong northward wind on the high‐latitude day side from WINDII the day before the breakup event suggest that meridional transport of the PMC source conditions or particles depleted the PMC region and enriched the NLC region to cause the event.
Size‐dependent stratospheric droplet composition in Lee wave temperature fluctuations and their potential role in PSC freezing
Authors: Meilinger S. K. , Koop T. , Luo B. P. , Huthwelker T. , Carslaw K. S. , Krieger U. , Crutzen P. J. , Peter Th.
Published: February 2004

Rapid temperature fluctuations are shown to cause liquid H2SO4/HNO3/H2O stratospheric aerosols to depart considerably from thermodynamic equilibrium. While HNO3 uptake by larger droplets is diffusively hindered, small droplets can approach the composition of a pure binary HNO3/H2O solution with up to 52 wt% HNO3, 48 wt% H2O and very small amounts of H2SO4. The stoichiometry of these droplets is close to that of nitric acid trihydrate (NAT) and freezing experiments suggest that this could be a suitable pathway for the formation of frozen polar stratospheric clouds (PSCs) of type‐Ia.
The 22‐year variation of geomagnetic activity: Implications for the polar magnetic field of the Sun
Authors: Russell C. T. , Mulligan T.
Published: February 2004

We examine the average behavior of the aa index and its recent extension using proxy data over the period 1844 to the present. Over this period the daily average aa index fell from an average of about 18 in 1850 to a low of about 14.4 in 1900 to a high of 23 over the most recent solar cycles. Independently the amplitude of the 22‐year variation of geomagnetic activity has also changed. It was its largest in the years 1862 to 1908 when it reached 30% of the mean activity but has been close to 0 in other years except from 1949 to 1970 when it was about 15% of the mean level of activity. Because the 22‐year variation of geomagnetic activity is thought to be associated with the reversals of the polar magnetic field of the sun, these latter variations suggest that the strength of the polar magnetic field of the sun varies considerably over the long term.
Maps of the magnetic anomaly field at Earth's surface from scalar satellite data
Authors: Langel R. A. , Whaler K. A.
Published: February 2004

Satellite measurements of the magnetic anomaly field intensity have been used to estimate components of the vector field at the Earth's surface, using a linear approximation to relate satellite scalar measurements to downward‐continued vector components. The relation between data and model was inverted using a depleted harmonic spline basis to find an almost minimum norm solution, enabling the detail present in satellite data to be preserved over continental‐sized areas. In their development of the depleted basis method, Parker and Shure (1982) advocated using a subset of the original data as points in the depleted basis. Here, it is shown that a depleted basis formed from vertical component data kernels is much more satisfactory than a subset of measured intensity data kernels; however, we do form the depleted basis at the physical locations of actual data. The downward‐continued map over Africa agrees well with its counterpart produced from Magsat orthogonal component data.
Ulysses solar wind plasma observations from pole to pole
Authors: Phillips J. L. , Bame S. J. , Barnes A. , Barraclough B. L. , Feldman W. C. , Goldstein B. E. , Gosling J. T. , Hoogeveen G. W. , McComas D. J. , Neugebauer M. , Suess S. T.
Published: February 2004

We present Ulysses solar wind plasma data from the peak southerly latitude of −80.2° on 12 September 1994 through the corresponding northerly latitude on 31 July 1995. Ulysses encountered fast wind throughout this time except for a 43° band centered on the solar equator. Median mass flux was nearly constant with latitude, while speed and density had positive and negative poleward gradients, respectively. Solar wind momentum flux was highest at high latitudes, suggesting a latitudinal asymmetry in the heliopause cross section. Solar wind energy flux density was also highest at high latitudes.
Radial fluid flow and reaction during contact metamorphism
Authors: Dipple Gregory M.
Published: February 2004

Radial fluid flow in cylindrical and spherical contact metamorphic aureoles produces alteration patterns that are distinctly different from those predicted for cartesian one‐dimensional flow. The combined effects of flow focusing and decreasing reactive rock volume during inward flow result in more alteration and steeper alteration versus distance profiles. Applied to contact metamorphism, cartesian models overestimate, by as much as an order‐of‐magnitude, the time‐integrated fluid fluxes necessary to produce observed alteration by inward fluid flow. Outward radial flow is less efficient than cartesian flow because reactive rock volume increases and fluid flux is defocused; cartesian models tend to underestimate the quantity of magmatic fluid required to produce alteration by outward flow.
Large amplitude IMF fluctuations in corotating interaction regions: Ulysses at midlatitudes
Authors: Tsurutani Bruce T. , Ho Christian M. , Arballo John K. , Goldstein Bruce E. , Balogh Andre
Published: February 2004

Corotating Interaction Regions (CIRs), formed by high‐speed corotating streams interacting with slow speed streams, have been examined from −20° to −36° heliolatitudes. The high‐speed streams emanate from a polar coronal hole that Ulysses eventually becomes fully embedded in as it travels towards the south pole. We find that the trailing portion of the CIR, from the interface surface (IF) to the reverse shock (RS), contains both large amplitude transverse fluctuations and magnitude fluctuations. Similar fluctuations have been previously noted to exist within CIRs detected in the ecliptic plane, but their existence has not been explained. The normalized magnetic field component variances within this portion of the CIR and in the trailing high‐speed stream are approximately the same, indicating that the fluctuations in the CIR are compressed Alfvén waves. Mirror mode structures with lower intensities are also observed in the trailing portion of the CIR, presumably generated from a local instability driven by free energy associated with compression of the high‐speed solar wind plasma. The mixture of these two modes (compressed Alfvén waves and mirror modes) plus other modes generated by three wave processes (wave‐shock interactions) lead to a lower Alfvénicity within the trailing portion of the CIR than in the high‐speed stream proper. The results presented in this paper suggest a mechanism for generation of large amplitude Bz fluctuations within CIRs. Such phenomena have been noted to be responsible for the generation of moderate geomagnetic storms during the declining phase of the solar cycle.
Stratospheric ozone changes at 43°N And 36°N over Japan between 1991 and 1994
Authors: Kondo Y. , Zhao Y. , Uchino O. , Nagai T. , Fujimoto T. , Itabe T. , Mizutani K. , Shibata T.
Published: February 2004

Total ozone and ozonesonde profiles obtained from Sapporo (43°N) and Tsukuba (36°N), Japan showed significant ozone decreases in 1992 and 1993, coinciding with the large increase of aerosol loading from the Pinatubo eruption. The ozone anomaly in Sapporo was deeper and longer lasting than in Tsukuba, indicating a latitudinal variation. The ozone decrease occurred mainly below 24 km and was most pronounced in winter and spring. In addition, the altitude regions where significant ozone decreases occurred, descended between 1992 and 1994 coincident with the descent of the Pinatubo aerosol layer. Some increase in ozone was seen above 26 km at the two stations in the winter and spring of 1992. These ozone changes are indicative of heterogeneous chemical effects on ozone under perturbed aerosol loading.
Alfvén waves, alpha particles, and pickup ions in the solar wind
Authors: Goldstein B. E. , Neugebauer M. , Smith E. J.
Published: February 2004

Past studies of the properties of Alfvén waves in the solar wind have indicated that (1) the amplitude of the velocity fluctuations is almost always smaller than expected on the basis of the amplitude of the field fluctuations, even when the anisotropy of the plasma is taken into account, and (2) the alpha particles often do not participate in the wave motions because they “surf” on the waves carried by the proton fluid. Ulysses data are used to demonstrate that (1) the discrepancy between the velocity and field fluctuations is greater at high heliographic latitudes than in the ecliptic plane, and (2) the alphas do participate in the waves, being either in phase or out of phase with the proton motions depending on whether the differential flow speed between the alphas and protons is greater than or less than the “observed” wave speed, Vwave=δV Bo/δB, as determined from the ratio of amplitudes of velocity and magnetic fluctuations. The possibility that the modification of Alfvén wave propagation speed is due to pressure anisotropies resulting from pickup ion distributions is investigated.
Whistler‐mode wave generation around interplanetary shocks in and out of the ecliptic plane
Authors: Pierre F. , Solomon J. , Cornilleau‐Wehrlin N. , Canu P. , Scime E. E. , Phillips J. L. , Balogh A. , Forsyth R. J.
Published: February 2004

We present a study of whistler‐mode wave generation and wave particle interaction in the vicinity of interplanetary shocks in and out of the ecliptic plane, as observed by the Ulysses spacecraft. We focus here on one shock in the ecliptic plane as a reference and three shocks obtained at −30, −54 and −55.4 degrees of heliographic latitude respectively. Generally the whistler‐mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions in the energy range 1.6 to 862 eV, we compute the temperature anisotropy and the wave growth rate of the electromagnetic electron cyclotron instability for the case of parallel propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows only downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations. Broadening of the wave reduced frequency range of the instability and an increase of the temperature anisotropy with latitude are observed.
Signatures of impulsive convection in the magnetospheric lobes
Authors: Delcourt D. C. , Sauvaud J.‐A. , Vaisberg O. L. , Avanov L. A. , Burch J. L. , Waite J. H.
Published: February 2004

We analyze the injections of tailward flowing O+ ions measured by PROGNOZ‐8 in the magnetospheric lobes using three‐dimensional single‐particle codes. These injections are shaped as “inverted Vs” and unexpectedly well correlated with AE variations during a time interval of about 7 hours. Such a correlation leads us to consider the effect of transient intensification of the large‐scale magnetospheric convection. Using a simple model of time‐varying electric field, we show that the source of the O+ lies near the dayside cusp. This source extends over a narrow (a few degrees) latitudinal interval in the vicinity of the last closed field line, likely involving ions expelled into the magnetosphere after being transversely accelerated. We demonstrate that, downstream of the ejection site, impulsive convection leads to prominent structuring of the tailward streaming particles with abrupt energy variations on small length scales. A good agreement is obtained between the numerical results and the observations which supports our impulsive convection based interpretation framework.
Ulysses observations of Alfvén waves in the southern and northern solar hemispheres
Authors: Smith E. J. , Balogh A. , Neugebauer M. , McComas D.
Published: February 2004

Alfvén waves with periods from <1 to >10 hours are shown to be continuously present in the sun's south and north polar regions. Below ≈ 30° latitude, as revealed by the rapid traversal of the equatorial region by Ulysses, the wave power averaged over a solar rotation decreases abruptly. The correlations between magnetic field and solar wind velocity fluctuations, upon which the wave identification is based, indicate outward propagation in both hemispheres. The Ulysses observations are consistent with many of the properties of Alfvén waves seen in the ecliptic in association with high speed streams. Some implications of the waves in the polar regions are explored. Because of the long wavelengths, which reach ≈ 0.3AU, the waves resonate with 10–10³MeV/nucleon galactic cosmic rays and oppose their entry into the polar caps. The wave amplitudes imply a contribution to the acceleration of the high latitude wind due to momentum transfer of only a few percent.
Evidence of high velocity anomalies in the transition zone associated with Southern Kurile Subduction Zone
Authors: Tajima Fumiko , Grand Stephen P.
Published: February 2004

We address the use of regional broad‐band waveform data to better constrain the upper mantle transition zone structure. We then show evidence of high velocity anomalies in the transition zone associated with the southern Kurile subduction zone. Modeling of the triplicated regional waveforms supports that high velocity anomalies exist in the deeper part of the transition zone (over 500 km in depth), and the “660” discontinuity may be depressed to about 690 km depth. Our results suggest there is some degree of flattening of the slab in the southern Kuriles.
The shear wave velocity structure of the crust and uppermost mantle beneath Tagaytay, Philippines inferred from receiver function analysis
Authors: Besana G. M. , Shibutani T. , Hirano N. , Ando M. , Bautista B. , Narag I. , Punongbayan R. S.
Published: February 2004

Depths of the partially melted zone and the Moho discontinuity are probably at 18 kilometers and 34 kilometers, respectively beneath Tagaytay seismic station, Luzon, Philippines. This conclusion is based on the shear‐wave velocity structure determined in this study, which indicates the presence of a low‐velocity zone and high‐velocity zone at these depths. The shear wave velocity model was derived from the inversion of five receiver functions of teleseismic earthquakes recorded by the broadband seismometer at Tagaytay. However, due to the very limited information to constrain our initial model, other models with comparable waveform fit were also obtained but with deeper low velocity zone and shallower Moho.
The HW95 tidal potential catalogue
Authors: Hartmann Torsten , Wenzel Hans‐Georg
Published: February 2004

The catalogue named HW95 of the harmonic development of the Earth tide generating potential due to the Moon, the Sun and the planets Venus, Jupiter, Mars, Mercury and Saturn is presented here. This catalogue of the fully normalized potential coefficients contains 12935 waves, including 1483 waves due to the direct planetary effects (Hartmann and Wenzel 1994a,b). It is based on the DE200 numerical ephemerides of the planets and the Moon between the years 1850 and 2150. The error of gravity tides computed from the catalogue HW95 at mid‐latitude stations between the years 1850 and 2150 is estimated to about 1.4 (12.3) pm/s² rms (at maximum) in time domain and 0.002 (0.11) pm/s² rms (at maximum) in frequency domain (1 pm/s²=10−12 m/s²=0.1 ngal) using a new bench‐mark tidal gravity series (Wenzel 1996). An improvement in accuracy of a factor of 50 over the catalogues of Tamura (1987) and Xi (1989) has been achieved.
On noise reduction in vertical seismic records below 2 mHz using local barometric pressure
Authors: Zürn W. , Widmer R.
Published: February 2004

We propose a simple method for the reduction of noise in vertical seismic recordings at frequencies below 2 mHz. The method consists in subtracting the locally recorded, scaled, atmospheric pressure signal from the gravity record. The scale factor is frequency independent and can be linearly estimated from the data. While such a pressure correction was previously only used in the analysis of tidal records, it is equally efficient at the low‐frequency end of the normal mode band and we use gravity recordings of the big 1994 Shikotan and Bolivian quakes to demonstrate this point. Our examples also show that this correction permits to achieve noise levels well below the New Low Noise Model (NLNM) [Peterson, 1993]. The success of the correction also sheds some light on the physical processes responsible for the generation of low‐frequency seismic noise at quiet observatories.
High resolution global phase velocity distributions
Authors: Trampert J. , Woodhouse J. H.
Published: February 2004

We present global phase velocity distributions for fundamental mode Love and Rayleigh waves in the period range 40 to 150 seconds. The models, expressed in terms of spherical harmonic expansions up to degree and order 40, have beed derived from 28,479 Love wave and 33,662 Rayleigh wave measurements. The measurements were made using an automatic procedure based on non‐linear waveform inversion. We show that the results are characterized by lateral resolving radii between 500 and 850 km, a significant reduction from previous work. The improved global resolution is largely due to the inclusion of many more major arc measurements. The power spectra of the models are much whiter than has previously been found. The results show great similarity to the phase velocity distributions derived from the recent a priori model 3‐SMAC, in which the primary relevant features are the crustal thickness and crustal velocity distributions, the cooling oceanic lithosphere and the thick (300km) lithosphere of the continental cratons. The results thus confirm these features. Differences, for example, in the strengths of the crust, ridge and craton signatures should lead to refinement in the thermal and constitutive parameters upon which the a priori model depends.
Numerical simulations of large‐scale solar wind fluctuations observed by Ulysses at high heliographic latitudes
Authors: Goldstein M. L. , Roberts D. A. , Ghosh S.
Published: February 2004

An analysis of Ulysses plasma and magnetic field data from the high southern latitude pass revealed that at large spatial scales corresponding to wave frequencies below 10−5 Hz in the spacecraft frame, there is a transition from highly Alfvénic turbulence in all three spatial components of the fields to fluctuations which are Alfvénic only in field components transverse to the radial direction with uncorrelated radial magnetic and velocity fields. We find that the general properties of the turbulence can be simulated using a spectral method solution of the magnetohydrodynamic (MHD) equations only when certain types of initial conditions are employed. These simulations place constraints on conditions in the solar atmosphere that can generate the observed fluctuations.
VAN earthquake predictions‒An attempt at statistical evaluation
Authors: Kagan Y. Y.
Published: February 2004

Statistical verification of the VAN or SES (seismic electric signals) predictions from 1987–1989 is considered. The test is carried out with the updated rules proposed by Varotsos et al. [1996]. Although for the Greek (SI‐NOA) earthquake catalog the VAN method formally is successful, this high rate of success is due either to the retroactive adjustment of prediction rules or to the non‐randomness of seismicity. A simple prediction algorithm accounting for earthquake clustering (foreshock‐mainshock‐aftershock sequences), yields similar or even better forecast results. If we remove dependent events from the catalog, the ‘prediction effect’ becomes statistically insignificant. For the PDE (NOAA) catalog the test shows that the VAN predictions' rate of success can be attributed to chance.
Numerical properties of staggered finite‐difference solutions of Maxwell's equations for ground‐penetrating radar modeling
Authors: Bergmann Tim , Robertsson Johan O. A. , Holliger Klaus
Published: February 2004

Accurate modeling of electromagnetic wave propagation in conducting media is important for the further development of ground‐penetrating radar technologies. Numerical stability and dispersion criteria are derived here for two common 1‐D finite‐difference solutions of Maxwell's equations. In one finite‐difference scheme one‐sided differences are used to approximate the conducting term and in the other centered differences are employed. Stability is governed by the well‐known Courant criterion. In addition there is a stability condition controlling the diffusive aspects of wave propagation for the one‐sided difference scheme. It is found that the centered difference approximation has significantly better stability and dispersion characteristics. For the centered scheme, the well‐known spatial sampling criteria for the non‐conducting case are found to be valid for conducting media. The results are tested and illustrated using 1‐D synthetic radargrams.
The propagation of sub‐MeV solar electrons to heliolatitudes above 50°S
Authors: Pick M. , Lanzerotti L. J. , Buttighoffer A. , Sarris E. T. , Armstrong T. P. , Simnett G. M. , Roelof E. C. , Kerdraon A.
Published: February 2004

On 27 February 1994 when the Ulysses spacecraft was at an heliolatitude of 54°S low energy electrons (∼50–400 keV) and high energy protons (14–31 MeV) were measured following a solar flare beyond the west limb. These measurements show that under favorable conditions energetic particles can be transported very rapidly across 60 degrees in heliocentric latitudes to radial distances beyond 35 AU. The interplanetary transport occurs inside a structure that was identified as a CME in interplanetary space by Gosling et al. [1994] and that was produced on 20 February. The flare associated with the interplanetary electron event was well documented by the Nancay radio heliograph and was located at 09°N 95°W in the same active region that can be associated with the earlier origin of the Gosling et al. event. This particle event presents many similarities with the June '93 interplanetary particle event observed at 32°S [Armstrong et al., 1994].
Optical spectral characteristics of sprites
Authors: Hampton D. L. , Heavner M. J. , Wescott E. M. , Sentman D. D.
Published: February 2004

A TV slit spectrograph was used to obtain the first optical spectra of sprites. Twenty‐five events were observed over a thunderstorm on the border of Nebraska and Colorado on the night of 22 June, 1995 between 0700 and 0900 UT. For 10 of these events optical spectra were measured in the wavelength range from 540 to 840 nm. After correcting for the spectrograph response function, digitized spectrograph video images are used to measure the wavelengths of and ratios between the emissions. All emissions are found to be of the first positive bands of N2. There is no evidence of the Meinel bands of N2+ indicating that the mechanism responsible for sprites produces little or no ionization at 70 km altitude.
Bursts of cloud condensation nuclei (CCN) by dissipating clouds at Palmer Station, Antarctica
Authors: Saxena V. K.
Published: February 2004

We present here a case study of cloud‐mediated production of cloud condensation nuclei (CCN) recorded at Palmer Station (64°46′S, 64°05′W), Antarctica on 20 Jan 1994. Four instances of CCN bursts occurred on Jan 17, 19, 20 and Feb 7, 1994 when cloud base descended to the surface and dissipated under prevailing meteorological conditions. The most spectacular event occurred on Jan 20 when the CCN concentration was enhanced by a factor of four at 0.25% supersaturation (with respect to water) compared to the pre‐event concentration. At 1.25% supersaturation, the corresponding enhancement was by a factor of seven. This indicated a larger production of aerosol particles in smaller size ranges. The elevated CCN concentrations were measured for over fifteen hours. The CCN activity spectrum during the event resembled the ones that are typical of previous measurements in the urban plumes of St. Louis and Denver.
Arctic ozone depletion observed by UARS MLS during the 1994–95 winter
Authors: Manney G. L. , Froidevaux L. , Waters J. W. , Santee M. L. , Read W. G. , Flower D. A. , Jarnot R. F. , Zurek R. W.
Published: February 2004

During the unusually cold 1994–95 Arctic winter, the Microwave Limb Sounder observed enhanced chlorine monoxide (ClO) in late Dec and throughout Feb and early Mar. Late Dec ClO was higher than during any of the previous 3 years, consistent with the colder early winter. Between late Dec 1994 and early Feb 1995, 465 K (∼50 hPa) vortex‐averaged ozone (O3) decreased by ∼15%, with local decreases of ∼30%; additional local decreases of ∼5% were seen between early Feb and early Mar. Transport calculations indicate that vortex‐averaged chemical loss between late Dec and early Feb was ∼20% at 465 K, with ∼1/4 of that masked by downward transport of O3. This Arctic chemical O3 loss is not readily detectable in MLS column O3 data.