bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical X ray auroral emissions – PIXIE observations
Authors: Petrinec S. M. , Chenette D. L. , Mobilia J. , Rinaldi M. A. , Imhof W. L.
Published: September 2002

The Polar Ionospheric X ray Imaging Experiment (PIXIE) on board the NASA/GGS POLAR spacecraft has been making observations of X rays emitted simultaneously over the entire auroral zone since March, 1996. PIXIE remotely senses the bremsstrahlung produced by the loss of multi‐keV electrons from the magnetosphere into the ionosphere. In this study we examine twenty‐six months (April 1996 – July 1998) of X ray observations of the northern auroral region from the PIXIE instrument. X ray flux is obtained from the PIXIE observations, which allows us to produce for the first time synoptic auroral maps representing the precipitation of energetic electrons, as a function of geomagnetic activity.
Cosmic ray anomaly: The Saros cycle and a lunar perturbation
Authors: Sonett Charles P. , Smith Leonard A.
Published: September 2002

The power spectral density (frequency dependence of the variance) of the annual Stuiver radiocarbon record (Δ14C) contains a major line with a 17.5 ± 0.5 (2σ) year period which is proposed to result from a hitherto unexpected forcing of the cosmic ray (CR) flux at the top of the atmosphere. The only known natural period with a corresponding value is the synodic Saros cycle, the retrograde period of rotation of the Moon's nodal plane; 18.5 years is the sidereal nodal regression period. It is proposed that the intersection of the Moon's downstream diamagnetic solar wind cavity with the Earth at the Saros period is the source of the apparent cosmic ray anomaly leading to this periodic change of Δ14C; arguably, eclipsing and/or a low energy acceleration of the GCR could take place, though the evidence from the Fourier spectrum appears to favor acceleration.
The rotating shadowband spectroradiometer (RSS) at SGP
Authors: Harrison Lee , Beauharnois Mark , Berndt Jerry , Kiedron Peter , Michalsky Joseph , Min Qilong
Published: September 2002

The RSS provides continuous spectral measurements of total‐horizontal, diffuse‐horizontal, and direct‐normal irradiance from 360 to 1100 nm using the automated shadowband technique. We show instrument performance, calibration method and accuracies, case data from the first‐generation instrument operated at the Southern Great Plains (SGP) site, and comparisons with the improved design now starting operation.
Typhoon and ENSO simulation using a high‐resolution coupled GCM
Authors: Matsuura T. , Yumoto M. , Iizuka S. , Kawamura R.
Published: September 2002

The relationship between the character of tropical storm (TS) activity in the northwestern equatorial Pacific (NWEP) and the El Niño‐Southern Oscillation (ENSO) is investigated from the viewpoint of how TS behavior varies interannually. A high‐resolution coupled general circulation model (CGCM) capable of simultaneously reproducing both TSs and ENSOs has been developed to study the role of air‐sea interaction in linking TS activity with ENSO. Analysis of 15 years simulation and observations shows that TS frequency decreases slightly off the Philippine Islands (120°E‐150°E, 5°N‐20°N) and that the location of their generation shifts toward the east during El Niño years. This results in inactive convection in the NWEP during El Niño years due to an increase in sea level pressure over ocean areas.
Ice particle formation and sedimentation in the tropopause region: A case study based on in situ measurements of total water during POLSTAR 1997
Authors: Schiller C. , Afchine A. , Eicke N. , Feigl C. , Fischer H. , Giez A. , Konopka P. , Schlager H. , Tuitjer F. , Wienhold F. G. , Zöger M.
Published: September 2002

During the Polar Stratospheric Aerosol Experiment, total water was measured using an airborne Lyman‐α fluorescence hygrometer. The inlet is designed for anisokinetic sampling, thus large ice particles are detected sensitively. During the flight on January 24, 1997, temperatures of 200 K occurred close to the tropopause. Within this cold area, the existence of large particles with radii ≥ 4 µm containing large amounts of water is observed. At the edge of this cloud, total water mixing ratios of 5–6 ppmv and close to saturation were measured at and below the tropopause. This observation together with analysis of the correlation of the H2O mixing ratio with other long‐lived tracers indicates that the air masses had been dried by sedimentation of large ice particles.
Ion‐cyclotron wave dissipation channel for Alfvén waves
Authors: Kaghashvili Edisher Kh.
Published: September 2002

The effect of inhomogeneous velocity flow on Alfvén wave dynamics in the solar wind is investigated. Unlike existing studies in this field that model energy deposition from high‐frequency waves to solar wind particles, we consider here the possibility of obtaining high‐frequency waves (in this case fast magnetosonic waves) from the ordinary Alfvén wave spectrum. It is shown that the spatial inhomogeneity of the velocity field can lead to dissipation of Alfvén waves through ion‐cyclotron resonance. Recent Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) observations indicate that preferential heating and acceleration of heavy ions occurs close to the Sun. The process described here provides a possible interpretation of such solar wind observations.
Intercomparison of measured and modelled BrO slant column amounts for the Arctic winter and spring 1994/95
Authors: Frieß U. , Chipperfield M. P. , Harder H. , Otten C. , Platt U. , Pyle J. , Wagner T. , Pfeilsticker K.
Published: September 2002

Diurnal variations of the slant column amount of BrO (BrO‐SCD) measured at Kiruna/Esrange (67.9°N, 21.1°E) in winter/spring 1994/95 are compared with photochemical calculations using the SLIMCAT model. SLIMCAT assumes a total stratospheric bromine of 20 ppt, JPL‐97 kinetics but no tropospheric inorganic bromine. Observed local noon BrO‐SCDs are underestimated by the model by 20% to 40%. Sensitivity test of existing uncertainties in the stratospheric chemistry of bromine can not resolve the discrepancy. A tropospheric contribution to the total atmospheric BrO, corresponding to a vertical BrO column of 1 to 2×1013/cm², (or mixing ratios of 0.75 ppt to 2 ppt assuming an uniform tropospheric height profile) is suggested.
Regional nitric oxide enhancements in the North Atlantic flight corridor observed and modeled during POLINAT 2‐A case study
Authors: Schlager H. , Schulte P. , Flatoy F. , Slemr F. , van Velthoven P. , Ziereis H. , Schumann U.
Published: September 2002

In situ measurements of nitrogen oxides and other trace chemicals were performed aboard the DLR Falcon in September and October 1997 during POLINAT 2 over the eastern North Atlantic in areas with predicted high impact of aircraft emissions to search for flight corridor effects. During survey flights in the upper troposphere from the centre of the flight corridor to regions south of or below the major transatlantic aircraft routes, large‐scale enhancements in mixing ratios of NO of about 50 to 150 pptv were observed in corridor areas compared to the NO abundance measured outside the corridor. Using simultaneous tracer measurements, back trajectory analyses for the air masses sampled, the actual distribution of the North Atlantic air traffic, and comparisons of observed and predicted NO distributions from a regional model of simulations including or excluding aircraft emissions, these enhancements were attributed mainly to aircraft NOx.
Mountain Station pressure as an indicator of climate change
Authors: Toumi Ralf , Hartell Nigel , Bignell Ken
Published: September 2002

Surface temperature observations have been used to infer a global warming of about 0.7°K over the last century. Here, we present a new way of deriving temperature trends from observations of mountain surface pressure. From the hydrostatic equation it can be shown that a warming below the mountain increases the local pressure. This signal increases with height. The derived temperature trends from a few sites are consistent with reported regional warmings and a recent acceleration. These results provide independent confirmation of regional warming of the lower troposphere on a longer time scale than is currently available from radiosondes and satellites.
Sign‐singularity analysis of current disruption
Authors: Consolini Giuseppe , Lui Anthony T. Y.
Published: September 2002

The sign‐singular measure analysis is a new tool to investigate the scaling features of signals which oscillate in sign on an arbitrarily fine scale. In this work, we apply this new tool to the magnetic fluctuations observed before, during, and after tail current disruption (CD). The analysis shows that sign‐singularity is a genuine feature of the magnetic fluctuations in the near‐tail region, and that the character of the sign‐singularity changes during CD. Different values of the sign‐singularity scaling index, named the cancellation exponent κ, are obtained for periods before, during and after the CD. This change of the cancellation exponent is indicative of a reorganization phenomenon, occurring during CD. The results are discussed in connection with magnetospheric substorm onset as well as in the framework of self‐organized criticality and 2nd phase order transition.
On relationships between horizontal velocity structure and thermal ion upwellings at high latitudes
Authors: Kivanç Ö. , Heelis R. A.
Published: September 2002

Recent studies indicate that the vertical velocity of F region ion upwellings cannot be explained by frictional heating in the horizontal plane alone but requires additional energization sources. Processes involving velocity shear have recently been put forward as alternate mechanisms that can provide the energization in regions of smaller convection speeds. Studies show that structured flows can also give rise to significant upwelling of ions by seeding plasma waves that can potentially cause ion heating while Joule heating is relatively small. We provide a statistical analysis of the Dynamics Explorer 2 vertical and horizontal ion drift measurements that show further evidence for the significance of plasma wave energization process in regions of varying levels of Joule heating.
Spatial and temporal variations of Jupiter's H3+ emission deduced from image analysis
Authors: Satoh Takehiko , Connerney J. E. P.
Published: September 2002

Intensity distribution of H3+ emission across Jupiter's disk has been analyzed using 3.4‐µm IRTF/ProtoCAM images acquired in 1992. The apparent disk emission is approximated using a mathematical function, of which parameters characterize (i) the dependence on the solar illumination angle, (ii) limb brightening consistent with the line‐of‐sight effect, and (iii) the latitudinal variation. A simple atmospheric model reproduces the disk emission (corrected for the line‐of‐sight effect) well, with H3+ emission peak in an altitude range 700–750 km above P = 600 mb level.
Impact of aircraft emissions on NOx in the lowermost stratosphere at northern midlatitudes
Authors: Kondo Y. , Koike M. , Ikeda H. , Anderson B. E. , Brunke K. E. , Zhao Y. , Kita K. , Sugita T. , Singh H. B. , Liu S. C. , Thompson A. , Gregory G. L. , Shetter R. , Sachse G. , Vay S. A. , Browell E. V. , Mahoney M. J.
Published: September 2002

Airborne measurements of NOx, total reactive nitrogen (NOy), O3, and condensation nuclei (CN) were made within air traffic corridors over the U.S. and North Atlantic regions (35–60 °N) in the fall of 1997. NOx and NOy data obtained in the lowermost stratosphere (LS) were examined using the calculated increase in NOy (ΔNOy) along five‐day back trajectories as a parameter to identify possible effects of aircraft on reactive nitrogen. It is very likely that aircraft emissions had a significant impact on the NOx levels in the LS inasmuch as the NOx mixing ratios at 8.5–12 km were significantly correlated with the independent parameters of aircraft emissions, i.e., ΔNOy levels and CN values. In order to estimate quantitatively the impact of aircraft emissions on NOx and CN, the background levels of CN and NOx at O3=100–200 ppbv were derived from the correlations of these quantities with ΔNOy. On average, the aircraft emissions are estimated to have increased the NOx and CN values by 130 pptv and 400 STP cm−3, respectively, which corresponds to 70±30% and 30±20% of the observed median values.
Global mean surface air temperature and North Atlantic overturning in a suite of coupled GCM climate change experiments
Authors: Dixon Keith W. , Lanzante John R.
Published: September 2002

The effects of model initial conditions and the starting time of transient radiative forcings on global mean surface air temperature (SAT) and the North Atlantic thermohaline circulation (THC) are studied in a set of coupled climate GCM experiments. Nine climate change scenario experiments, in which the effective levels of greenhouse gases and tropospheric sulfate aerosols vary in time, are initialized from various points in a long control model run. The time at which the transition from constant to transient radiative forcing takes place is varied in the scenario runs, occurring at points representing either year 1766, 1866 or 1916. The sensitivity of projected 21st century global mean SATs and the THC to the choice of radiative forcing transition point is small, and is similar in magnitude to the variability arising from variations in the coupled GCM's initial three‐dimensional state.
Pre‐seismic slip on the 26 September 1997, Umbria‐Marche Earthquake fault? Unexpected clues from the analysis of 1951–1992 elevation changes
Authors: De Martini P. M. , Valensise G.
Published: September 2002

We studied 1951–1992 elevation changes recorded by a first order leveling line that intercepts the surface projection of the 26 Sep. 1997, Mw 6.0, Umbria‐Marche earthquake causative fault. The line documents 1951–1992 localized subsidence along a 12 km section above the fault. We calculated the expected 1997 coseismic elevation changes along the line using standard dislocation modeling and found that their trend has an amplitude three times larger than the trend of the observed pre‐1997 signal but with a similar shape. We suggest that this signal is the result of 10 cm of pre‐1992 slip along the northernmost 5 km of the 1997 earthquake fault, where coseismic slip was found to be less than the average estimated for the entire fault. This result implies unusually fast slip along this section of the fault and may suggest slip acceleration in preparation for the impending failure.
Anomalous aftershocks of deep earthquakes in Mariana
Authors: Wu Li‐Ru , Chen Wang‐Ping
Published: September 2002

Seismic moment of aftershocks during the August 23, 1995 deep earthquake sequence in the Mariana amounts up to 17% of that of the main shock (Mw 7.0). Such a high aftershock activity is extremely unusual. Based on the inversion of broadband P and SH waveforms, however, we found nothing anomalous in the source mechanisms. Among the 33 largest deep earthquakes (Mw≥7.0) since 1958, only events in the Mariana have high aftershock activity. We associate this observation with the unique configuration of the Mariana slab which seems to plunge sub‐vertically into the lower mantle with little distortion.
Anatomy of surface rupture zones of two stable continental region earthquakes, 1967 Koyna and 1993 Latur, India
Authors: Gupta Harsh K. , Rao R. U. M. , Srinivasan R. , Rao G. V. , Reddy G. K. , Dwivedy K. K. , Banerjee D. C. , Mohanty R. , Satyasaradhi Y. R.
Published: September 2002

Soil‐helium surveys in the surface rupture zones of the 1993 Latur (Mw 6.2) and the 1967 Koyna (Mw 6.3) stable continental region (SCR) earthquake sites in Peninsular India showed anomalies defining surface traces of the causative faults. Propagating from the Archaean crystalline basement through the Deccan basalt cover, the seismic fault produced a scarp by uplift along a thrust in the Killari area of the Latur earthquake, whereas the Koyna earthquake was associated with a strike‐slip fault which expressed itself as an en echelon fissure zone. Core drilling has confirmed that the fault at Killari extends downward from the surface rupture zone with an approximate dip of 50° towards SSW. The level differences of flow contacts obtained by drilling in the hanging wall and foot wall sides of the fault, do not unequivocally establish the amount of displacement, but suggest that it might be anything from 1 m to 6 m. If the higher figure of 6 m is accepted, it would indicate reactivation of an old fault. Drilling established a WNW dip of the Koyna fault, resolving a long‐standing debate.
3D simulations of multi‐segment thrust fault rupture
Authors: Magistrale Harold , Day Steven
Published: September 2002

Thrust faults, such as those that underlie the Los Angeles basin, are typically segmented by tear faults that offset the thrust fault segments. We perform 3D finite difference simulations of earthquake rupture to evaluate the effectiveness of these offsets in retarding rupture. The simulations include orthogonal, intersecting faults to model the interaction of the thrust fault segments with the tear fault. For reasonable assumptions for fault segment length, strength, and stress drop, rupture can jump offsets of up to 2 km if a tear fault is present, consistent with observations of well studied thrust earthquakes. Absent a tear fault, the maximum offset that can be breached is an order of magnitude smaller.
Acoustic, electromagnetic and ionospheric disturbances during the vibroseismic sounding
Authors: Kuznetsov Vladimir V. , Plotkin Valery V. , Khomutov Sergey Y.
Published: September 2002

The electromagnetic and acoustic phenomena during the powerful seismovibrator operation in frequency range from 5 to 10 Hz on horizontal distances up to 50 km were studied. The electromagnetic wave radiated on frequency of the seismovibrator and synchronous seismic and acoustic modes were detected. Ionospheric disturbances exhibited as a phase modulation of the sounding radiowave were registered. This effect is observed only in the daily sessions when the stable E‐layer exists in ionosphere. The delay between seismic and ionospheric signals is estimated to be about 7 minutes and it agrees with the time of the acoustic wave propagation to ionosphere.
Slip distribution of the Lake Tennyson earthquake, New Zealand, as inferred from static stress changes and off fault aftershocks
Authors: McGinty Peter , Robinson Russell
Published: September 2002

The fault plane of an earthquake can be estimated in many different ways. One is to examine the distribution of a well located aftershock sequence to see if a fault plane is evident. Here we present a new method where we take an earthquake aftershock sequence with distinguishable off fault clusters and vary the slip distribution to achieve a good correlation between regions of increased Coulomb failure stress (CFS) and aftershock occurrence. We find with the Lake Tennyson earthquake that simply taking an area outlined by aftershocks to estimate a fault plane may not be valid. If we do this, patterns of increased CFS have negative correlation with off‐fault aftershock occurrence. However if we restrict slip to only deeper regions, and over a smaller area, then the correlation between regions of increased CFS and aftershock off‐fault occurrence is good.
Astrometric and space‐geodetic observations of polar wander
Authors: Gross Richard S. , Vondrák Jan
Published: September 2002

Optical astrometric measurements of star positions taken during the past century have been recently re‐reduced using the final Hipparcos star catalog in order to determine variations in the mean location of the Earth's rotation pole with respect to the Earth's crust. This newly available polar motion series, which is the longest homogeneous polar motion series currently available, allows the drift in the pole path to be newly estimated. During the 1900.0 to 1992.0 span of the smoothed Hipparcos polar motion series, the Earth's rotation pole is observed to drift at a mean linear rate of 3.51±0.01 milliarcseconds/year (mas/yr) towards 79.2±0.2°W longitude. This new estimate for the observed trend in the pole path, which can be considered to be the present‐day expression of true polar wander, is nearly the same as that estimated in previous studies using the homogeneous ILS polar motion series.
Anthropogenic CO2 and CFCs in the North Atlantic Ocean ‐ A comparison of man‐made tracers
Authors: Körtzinger Arne , Rhein Monika , Mintrop Ludger
Published: September 2002

We compare estimates of the anthropogenic CO2 content of seawater samples from the subpolar North Atlantic Ocean calculated on the basis of a back‐calculation technique with measurements of the chlorofluorocarbon CFC‐11. Estimated anthropogenic CO2 concentrations are in the range 10–80 µmol kg‐1, while CFC‐11 concentrations cover the full range from below detection limit to > 5 pmol kg‐1 in waters at atmospheric equilibrium. The majority of the data points show a linear correlation between anthropogenic CO2 concentrations and CFC‐11 saturation, which can only be explained by the strongly advective nature of the North Atlantic Ocean. Only deep eastern basin samples deviate from this general observation in that they show still significant concentrations of anthropogenic CO2 where CFC‐11 is no longer detectable. In order to remove the influence of the Revelle factor reflected in the anthropogenic CO2 concentrations we have calculated 'excess' pCO2, showing an even tighter linear correlation with atmospheric equilibrium concentrations of CFC‐11.
Impact of the GOCE Gravity Mission on ocean circulation estimates
Authors: LeGrand Pascal , Minster Jean‐François
Published: September 2002

The impact of a geoid model derived from the GOCE gravity mission on estimates of large‐scale oceanic transports is investigated using an inverse model of the North Atlantic. Because its precision would match the precision of satellite altimeters, GOCE would significantly improve estimates of ocean dynamic topography and would thus provide information on ocean surface velocities. The impact of this information in terms of uncertainties in volume transports would be limited in the deep ocean by the presence of noise in the density field, but it would be significant in the upper ocean, with for instance a 26% reduction of the uncertainty in the top 100 m layer at 48°N. This impact is comparable in magnitude to the impact on top‐to‐bottom transport uncertainties found by Ganachaud and co‐workers, but it is achieved here with realistic error bars in the density field. This result shows that the improvement in hydrographic data assumed by these authors is not a prerequisite to a significant impact of future gravity missions.
Are monoterpene emissions influenced by humidity?
Authors: Schade Gunnar W. , Goldstein Allen H. , Lamanna Mark S.
Published: September 2002

Monoterpene mixing ratios and fluxes were measured above a ponderosa pine plantation in the Sierra Nevada mountains from July to October 1998. Data were obtained during a variety of weather regimes including periods of extreme heat and dryness as well as during rain. Monoterpene emissions were highly elevated during and after the rain events, and the expected exponential increase of emissions with temperature did not occur during extremely hot and dry conditions, suggesting an influence of ambient humidity levels on monoterpene emissions. Therefore, we propose a modified emission algorithm based on responses to both temperature and humidity.
Partitioning of the global fossil CO2 sink using a 19‐year trend in atmospheric O2
Authors: Langenfelds R. L. , Francey R. J. , Steele L. P. , Battle M. , Keeling R. F. , Budd W. F.
Published: September 2002

O2/N2 is measured in the Cape Grim Air Archive (CGAA), a suite of tanks filled with background air at Cape Grim, Tasmania (40.7°S, 144.8°E) between April 1978 and January 1997. Derived trends are compared with published O2/N2 records and assessed against limits on interannual variability of net terrestrial exchanges imposed by trends of δ13C in CO2. Two old samples from 1978 and 1987 and eight from 1996/97 survive critical selection criteria and give a mean 19‐year trend in δ(O2/N2) of −16.7±0.5 per meg yr−1, implying net storage of +2.3 ± 0.7 GtC (1015 g carbon) yr−1 of fossil fuel CO2 in the oceans and +0.2 ± 0.9 GtC yr−1 in the terrestrial biosphere. The uptake terms are consistent for both O2/N2 and δ13C tracers if the mean 13C isotopic disequilibrium flux, combining terrestrial and oceanic contributions, is 93±15 GtC ‰ yr−1.
Condensation nuclei (CN) and ultrafine CN in the free troposphere to 12 km: A case study over the Jungfraujoch High‐Alpine Research Station
Authors: Nyeki S. , Kalberer M. , Lugauer M. , Weingartner E. , Petzold A. , Schröder F. , Colbeck I. , Baltensperger U.
Published: September 2002

Condensation nuclei (CN) were measured in the free troposphere (FT) above the Jungfraujoch (JFJ) high‐alpine research station (3454 m; Switzerland) from 4.5 to 12 km asl in a case study on July 30, 1997. Vertical profiles of CN concentration for d ≥ 5 nm (N≥5), d ≥ 15 nm (N≥1515) were measured, and indicated that ultrafine CN (UCN; 5 ≤ d ≤ 15 nm; N5‐15) exhibited a distinct increase with altitude. Some evidence for near‐constant values of d(logCN)/dz within discrete layers was found, which generally coincided with different airmasses as delineated by changes in the lapse rate dθ/dz at ∼ 5.5, 6.4, 9.0 and 10.6 km asl. In addition, CN concentration was mapped over a 40 × 75 km horizontal domain at 8.0 km asl centered above the JFJ. A pronounced variation in N≥5,N≥15 and specific humidity, but not in UCN, exhibited quasi‐stationary 2‐D features and was attributed to the chance encounter of a mountain wave. The case study provides further evidence that the upper FT may be a source of new particles.
Nighttime observation of the HO2 radical by an LIF instrument at Oki Island, Japan, and its possible origins
Authors: Kanaya Y. , Sadanaga Y. , Matsumoto J. , Sharma U. K. , Hirokawa J. , Kajii Y. , Akimoto H.
Published: September 2002

HO2 (hydroperoxy) radical of unexpectedly high concentration around 3 ppt was measured by an instrument based on laser‐induced fluorescence with NO addition at Oki Island, Japan, on the night of August 9/10, 1998. We confirmed that the interference by atmospheric organic peroxy (RO2) radicals was insignificant and concluded that the measured signal originated from nighttime HO2. Model calculations constrained to ancillary measurements indicated that HO2 and RO2 were produced primarily via the reactions of ozone with olefins, especially those with internal olefins, and that NO3 chemistry was relatively unimportant. HO2 concentration was kept high by nighttime NO (∼10 ppt) via RO2 + NO reactions. Low NO2 (∼150 ppt) slowed NO3 production rate. Thus, the high observed HO2 suggests that the reactions of O3 with olefins are important HOx primary production mechanisms in the relatively clean atmosphere.
Arctic clouds in multiyear satellite data sets
Authors: Schweiger Axel J. , Lindsay R. W. , Key J. R. , Francis J. A.
Published: September 2002

Cloud amounts from the International Satellite Cloud Climatology Project (ISCCP) D‐series data set and the TOVS Polar Pathfinder data set are compared to surface observations of cloud amount from the North Polar (NP) drifting station data set for the central Arctic. The results show that cloud observations in the ISCCP data set differ significantly from surface observations and the annual cycle of cloudiness in the Arctic is reversed from what is observed from the surface. In contrast, cloud amounts provided by the TOVS Polar Pathfinder data set represent the annual cycle of cloudiness well. Path‐P cloud retrievals also correspond well with surface observations (NP) at timescales greater than 4 days.
Low‐latitude quasiperiodic echoes observed with the Piura VHF Radar in the E region
Authors: Chau Jorge L. , Woodman Ronald F.
Published: September 2002

We present the first quasiperiodic (QP) echoes from 3‐m E region field‐aligned irregularities observed in the Southamerican sector, just outside the magnetic equator (7.5°N geomagnetic). These QP echoes occur only at night and between 105 and 120 km. In general, Piura QP echoes present periods close to the Brunt‐Väisälä period (5 to 10 min), striations with positive slopes and altitude rates of 20‐25 m s−1 (upward/northward), striations spacings of 3 to 10 km, and downward/southward Doppler velocities. These results are compared to midlatitude QP echoes from 3‐ and 6‐m irregularities observed between 13.3°N and 46.7°N geomagnetic. We found that the general characteristics that are common to our observations and other QP observations are the nighttime occurrence and the periods close to the Brunt‐Väisälä period. On the other hand, the discrepancies with some of the QP echoes observed at mid‐latitudes are found in the slope and spacing of the striations, the mean phase velocities, and the mean altitude location of the E layer containing the striations.
The electron heat flux in the polar solar wind: Ulysses observations
Authors: Scime Earl E. , Badeau Allen E. , Littleton J. E.
Published: September 2002

Ulysses measurements of the solar wind electron heat flux as a function of heliographic latitude are presented. Contamination from a light leak at the highest latitudes has been removed from the data by interpolating between uncontaminated pixels. After normalization by the radial gradient in the electron heat flux obtained during the inecliptic phase of the Ulysses mission, the electron heat flux is essentially constant from −80° to 80° of heliographic latitude. During brief periods of the fast latitude scan, both uncorrelated and anti‐correlated modulations of the electron heat flux and the solar wind velocity are observed. The implications of the observations with regards to different models of electron heat flux regulation are discussed.
SONEX airborne mission and coordinated POLINAT‐2 activity: Overview and accomplishments
Authors: Singh Hanwant B. , Thompson Anne M. , Schlager H.
Published: September 2002

The SASS (Subsonic Assessment) Ozone and NOx Experiment (SONEX) was an airborne field campaign conducted in October–November 1997 in the vicinity of the North Atlantic Flight Corridor to study the impact of aircraft emissions on NOx and ozone (O3). A fully instrumented NASA DC‐8 aircraft was used as the primary SONEX platform. SONEX activities were closely coordinated with the European POLINAT‐2 (Pollution from Aircraft Emissions in the North Atlantic Flight Corridor) program, which used a Falcon‐20 aircraft. Both campaigns focused on the upper troposphere/“lowermost” stratosphere (UT/LS) as the region of greatest interest. Specific sampling goals were achieved with the aid of a state‐of‐the art modeling and meteorological support system, which allowed targeted sampling of air parcels with desired characteristics. A substantial impact of aircraft emissions on NOx, O3, and CN in the UT/LS of the study region is shown to be present. This mission provided direct support for the highly nonlinear nature of the NOx‐O3 chemistry. The results are being published in Special Sections of GRL and JGR. This overview provides a context within which these publications can be understood.
A sensitivity simulation of tropospheric ozone changes due to the 1997 Indonesian fire emissions
Authors: Hauglustaine D. A. , Brasseur G. P. , Levine J. S.
Published: September 2002

A global chemical transport model, called MOZART, is used to investigate the photochemical impact of the 1997 Indonesian fires on tropospheric ozone and its precursors in the tropics. Due to the high release of carbon monoxide by peat fires, CO increases by up to 1000 ppbv in the free troposphere over Indonesia. As a consequence of increased photochemical production, ozone is significantly perturbed over source regions (Sumatra and Kalimantan). The tropospheric O3 column increases by 20–25 DU and the ozone mixing ratio reaches 50 ppbv in the mid‐troposphere in November. South of the source region, low ozone mixing ratios of 20–25 ppbv are calculated in the boundary layer due to marine air influence and reduced photochemical activity in presence of biomass burning aerosols. The particular transport regime prevailing during the 1997 El Niño event is not considered in our calculations. This limitation precludes any definitive conclusion regarding the relative role played by photochemistry and transport processes on the distribution of species during the 1997 fires.
Large plasma density gradients in the low‐altitude low‐latitude ionosphere observed during the TSS‐1R mission
Authors: Vannaroni G. , Dobrowolny M. , De Venuto F. , Iess L. , Zolesi B.
Published: September 2002

We present results of in situ ionospheric density measurements performed during the TSS‐1R tether mission. The almost equatorial orbit of TSS‐1R was such that the descending node was syncronous with the day‐to‐night terminator and the measurements refer to 4 consecutive magnetic equator crossings. The most important feature of the observations is given by the indication of very deep density minima, centered at the magnetic equator, with density values up to a factor 100 smaller than those predicted by the IRI ionospheric model. We will show that a plausible explanation of these pronounced minima can be found in terms of the prereversal enhancement of the E×B drift which is one of the dominant features of the equatorial anomaly. Our data indicate therefore that, near the magnetic equator, the IRI model needs to be updated to include more accurately the sunset strengthening of the plasma drift.
Wobble motion of a particle's guiding center and the related magnetic moment
Authors: Huang Tian‐Sen
Published: September 2002

Because of the change in a magnetically trapped particle's instantaneous drift velocity, its guiding center does not bounce exactly along a field line but rather wobbles about it, when viewed in a frame of reference that moves with the bounce‐averaged drift velocity. On the particle's drift shell the wobble orbit forms two linking narrow loops with a width of the order of the gyroradius. Each loop results in a magnetic moment distributed along the guiding field line. The line density of this “wobble magnetic moment” is comparable in magnitude with the line density of the usual (gyro) magnetic moment when the latter is distributed along the field line according to the time spent by the particle in each line element. The direction of the magnetic moment is perpendicular to the field line in the former, instead antiparallel to it in the latter; for one of the loops it points “outward” (i.e., in the direction of the outward field line normal), while for the other loop it points “inward.” In addition, the direction of the wobble magnetic moment is independent of the particle's charge. In a plasma with a pressure gradient an electric current parallel to the magnetic field results from the wobble magnetic moment, just as a perpendicular diamagnetic current arises from an inhomogeneous gyromagnetic moment distribution. This parallel current turns out to be of the same order of magnitude as the parallel current derived from the divergence of the drift current in the same plasma. General expressions are derived for the wobble of a particle's guiding center, the line density of the wobble magnetic moment, and the magnetization current in a plasma due to the wobble magnetic moment. For illustration, examples of particle motion in two‐dimensional (line) dipole and three‐dimensional (loop) dipole magnetic fields are shown.
Properties and radial trends of coronal mass ejecta and their associated shocks observed by Ulysses in the ecliptic plane
Authors: Riley Pete , Gosling J. T. , McComas D. J. , Forsyth R. J.
Published: September 2002

In this paper, magnetic and plasma measurements are used to analyze 17 interplanetary coronal mass ejections (CMEs) identified by Ulysses during its in‐ecliptic passage to Jupiter. We focus on the expansion characteristics of these CMEs (as inferred from the time rate of change of the velocity profiles through the CMEs) and the properties of 14 forward shocks unambiguously associated with these CMEs. We highlight radial trends from 1 to 5.4 AU. Our results indicate that the CMEs are generally expanding at all heliocentric distances. With regard to the shocks preceding these ejecta, we note the following: (1) There is a clear tendency for the shock speed (in the upstream frame of reference) to decrease with increasing heliocentric distance as the CMEs transfer momentum to the ambient solar wind and slow down; (2) 86% of the shock fronts are oriented in the ecliptic plane such that their normals point westward (i.e., in the direction of planetary motion about the Sun); (3) 86% of the shocks are propagating toward the heliographic equator; and (4) no clear trend was found in the strength of the shocks versus heliocentric distance. These results are interpreted using simple dynamical arguments and are supported by fluid and MHD simulations.
Observations of Pc5 field line resonance azimuthal phase speeds: A diagnostic of their excitation mechanism
Authors: Mathie R. A. , Mann I. R.
Published: September 2002

A number of recent publications have suggested that Pc5 field line resonance (FLR) azimuthal phase speeds may provide a diagnostic for determining pulsation excitation mechanisms. We analyze a subset of 27 multiple frequency FLR pulsation events identified from a total of 137 events observed with the IMAGE magnetometer array from March 1994, March 1995, and March 1996 to test the validity of this diagnostic. We show that during intervals of high solar wind speed, the frequency components within a pulsation event display a commonality of azimuthal phase speed, which may be related to the propagation speed of a shear‐flow instability on the magnetopause. In contrast, events observed during lower solar wind speed intervals often result in frequency components which have differing azimuthal phase speeds and may be more closely associated with impulses in the solar wind. Examining the local time dependence of each type of event reveals that the common phase speed events seem to be much more prevalent in the morning sector. We suggest that the local time dependence of the magnetospheric waveguide modes' boundary condition may account for the observed pulsation characteristics, in accordance with the theory of Mann et al. [1999]. Our observations provide some support for the hypothesis that many of the morning sector events are driven by magnetopause shear‐flow instabilities during intervals of enhanced solar wind speed and that these events are superposed on a background of more impulsively driven pulsations which may occur over a wider range of local time in response to solar wind discontinuities and buffeting.
The upper atmosphere during June 5–11, 1991
Authors: Litvin A. , Oliver W. L. , Picone J. M. , Buonsanto M. J.
Published: September 2002

Millstone Hill ionospheric incoherent scatter radar data collected during June 5–11, 1991, are analyzed to determine F region neutral and ion composition, density, and temperature. The 10.7‐cm solar flux index was at the very high level of 250, and the magnetic activity index Kp ranged up to the highest possible level of 9 during this period, making it of particular interest for understanding upper atmosphere behavior for such a nearly limiting combination of conditions experienced by the thermosphere. We find that the Mass Spectrometer Incoherent Scatter 86 (MSIS‐86) model overestimates the daytime exospheric temperature and the neutral O concentration for this high level of solar activity. These results differ substantially from storm periods analyzed previously. The ionospheric F region converts from largely atomic ions to largely molecular ions during the periods of strongest magnetic activity. We show that this condition leads to erroneous determination of neutral atmosphere parameters, including temperature, density, and drift velocity, if not accounted for in incoherent scatter data analysis.
An analytical theory of the morphology, flows, and shock compressions at corotating interaction regions in the solar wind
Authors: Lee Martin A.
Published: September 2002

An analytical theory for the structure of corotating interaction regions (CIRs) in the solar wind is developed. First, an approximate stream interface is determined by mapping the curve dividing fast and slow streams at the solar wind source surface into the solar wind, at the slow solar wind speed assuming a constant angular rotation rate of the Sun. The flow of the fast wind then impinges on this surface, creating a quasi‐perpendicular reverse (forward) shock in the fast (slow) stream, deflections of the shocked fast and slow flows tangential to the interface, and a modified location of the interface. Assuming a locally planar geometry and weak shocks, analytical expressions are derived and presented for both shock compression ratios and for the north–south and east–west components of the shocked fast and slow streams. These are evaluated for two representative curves dividing fast and slow streams at the solar wind source surface. Numerical results are also presented for shocks which may not be approximated as weak. It is shown that the weak shock approximation is valid well beyond its formal limit of validity. For characteristic solar wind parameters the shock and flow parameters are presented as functions of heliocentric radial distance r and the inclination of the stream interface at the solar wind source surface. Shock and flow parameters are also shown for a simulated spacecraft observation of a CIR at r = 5 AU during a 26‐day solar rotation period. The results of the model for the shocks and flows associated with CIRs are in apparent general agreement with observations by Ulysses and other spacecraft.
Heliopause imaging in EUV: Oxygen O+ ion 83.4‐nm resonance line emission
Authors: Gruntman Mike , Fahr Hans J.
Published: September 2002

We explore the possibility of remote, from 1 AU, study of the heliopause by an observer outside the geocorona. We argue that the heliopause, a boundary that separates the solar wind and the galactic plasma of the local interstellar medium (LISM), can be imaged by detecting solar extreme ultraviolet (EUV) radiation reflected by interstellar ions. Such EUV imaging would map the heliopause and provide important insight into its three‐dimensional structure and the LISM parameters as well. We consider heliopause mapping in the oxygen O+ ion resonance line (83.4 nm); imaging in the helium He+ ion line (30.4 nm) will be considered in a future article. We show that the expected heliopause brightness map at 83.4 nm is essentially different from that of the foreground glow of the solar wind O+ pickup ions. The interstellar plasma glow is brighter in the upwind (with respect to the interstellar wind) direction, while the pickup ion glow dominates in the downwind direction. The spectral characteristics of the radiation scattered by the LISM plasma and by the pickup ions are significantly different. The all‐sky images at 83.4 nm are highly sensitive to the ionization state of the LISM and would allow one to probe the asymmetry of the interstellar magnetic field. We briefly discuss the experimental requirements to heliopause EUV mapping, which would require 3 orders of magnitude improvement in instrumentation sensitivity. This is a challenging but not impossible task.
Absolute differential and integral cross sections for charge transfer of keV O+ ions with O2
Authors: Sieglaff D. R. , Lindsay B. G. , Merrill R. L. , Smith K. A. , Stebbings R. F.
Published: September 2002

We report measurements of the absolute differential cross sections for charge‐transfer scattering of 0.5‐, 0.85‐, 1.5‐, 2.8‐, and 5‐keV O+ ions by O2 at scattering angles between 0.04° and 5.4° in the laboratory frame. Cross sections for both O+(4S) ground‐state and O+(2D, 2P) metastable ions are presented. The metastable differential cross section is somewhat more forward peaked than that for the ground state. Integral and total cross sections are also reported. The present O+(4S) cross section is consistent with previous measurements, but the present metastable‐state cross section is found to be substantially lower than previously reported in this energy range. These measurements provide information relevant to model calculations of O+ precipitation into the upper atmosphere during geomagnetic storms.
High‐latitude observations of ULF waves with large azimuthal wavenumbers
Authors: Yeoman T. K. , Wright D. M. , Chapman P. J. , Stockton‐Chalk A. B.
Published: September 2002

The Doppler Pulsation Experiment (DOPE) is an HF Doppler sounder deployed at Tromsø, northern Norway, for the investigation of the ionospheric signatures of ULF wave phenomena of magnetospheric origin. This high‐latitude Doppler sounder has been demonstrated to be a highly sensitive instrument for the investigation of ULF waves of large azimuthal wavenumber m. Such waves are assumed to be driven by magnetospheric wave‐particle interactions and are difficult to study by other ground‐based techniques owing to their strong spatial integration between the ionosphere and the ground. A new population of high‐m waves has been identified in the ground‐based data from DOPE, which could represent a significant new sink for ring current energy. These waves have m numbers of order 100 and are observed primarily in the morning sector. Their characteristics are described and compared to previous statistical observations from spacecraft. The DOPE sounder now offers routine measurements of the occurrence and characteristics of such high‐m wave populations.
Theory of thin‐filament motion in Earth's magnetotail and its application to bursty bulk flows
Authors: Chen C. X. , Wolf R. A.
Published: September 2002

An MHD theory has been developed for the motion of a thin magnetic flux tube through a two‐dimensional stationary medium that is in MHD equilibrium. The flux tube is represented as a one‐dimensional filament. Simple properties of the computed time development of the filament are explored analytically, including linear intermediate and slow‐mode waves, rotational discontinuities, and slow shocks. One numerical solution is presented in detail for a filament in the Earth's magnetotail that is initially underpopulated relative to its neighbors. The computed filament motion displays the strong earthward flow and reduced field line stretching that characterize bursty bulk flows, which are frequently observed in the plasma sheet of the Earth's magnetosphere. The solutions also display the propagation of MHD waves from the equatorial magnetosphere to the ionosphere, then partial reflection from the conducting ionosphere. The ionospheric end of the bursty‐bulk‐flow flux tube moves equatorward, but that motion is delayed relative to the earthward motion in the equatorial plane. The simulations illuminate the relationship between the interpretation of a bursty bulk flow (BBF) as an underpopulated flux tube and the fact that BBFs typically do not have significantly lower particle pressure than the neighboring plasma sheet. Though the simulated filament started out with lower particle pressure than its neighbors and thus started out as a “bubble” in the plasma sheet, its particle pressure rose to values comparable to, or sometimes greater than, its neighbors once its strong earthward motion developed.