bluuebunny/crossref_metadata_2025 huggingface dataset:
UVCS/SOHO catalog of coronal mass ejections from 1996 to 2005: Spectroscopic proprieties
Authors: Giordano S. , Ciaravella A. , Raymond J.C. , Ko Y.‐K. , Suleiman R.
Published: April 2013

Ultraviolet spectra of the extended solar corona have been routinely obtained by SOHO/UltraViolet Coronagraph Spectrometer (UVCS) since 1996. Sudden variations of spectral parameters are mainly due to the detection of coronal mass ejections (CMEs) crossing the instrumental slit. We present a catalog of CME ultraviolet spectra based upon a systematic search of events in the Large Angle and Spectrometric Coronagraph (LASCO) CME catalog, and we discuss their statistical properties. Our catalog includes 1059 events through the end of 2005, covering nearly a full solar cycle. It is available online at the URL http://solarweb.oato.inaf.it/UVCS_CME and embedded in the online LASCO CME catalog (http://cdaw.gsfc.nasa.gov/CME_list). The emission lines observed provide diagnostics of CME plasma parameters, such as the light‐of‐sight velocity, density, and temperature and allow to link the CME onset data to the extended corona white‐light images. The catalog indicates whether there are clear signatures of features such as shock waves, current sheets, O VI flares, helical motions, and which part of the CME structures (front, cavity, or prominence material) are detected. The most common detected structure is the cool prominence material (in about 70% of the events). For each event, the catalog also contains movies, images, plots, and information relevant to address detailed scientific investigations. The number of events detected in UV is about one tenth of the LASCO CMEs and about one fourth of the halo events. We find that UVCS tends to detect faster, more massive, and energetic CME than LASCO, and for about 40% of the events, it has been possible to determine the plasma light‐of‐sight velocity.
EMIC triggered chorus emissions in Cluster data
Authors: Grison B. , Santolík O. , Cornilleau‐Wehrlin N. , Masson A. , Engebretson M. J. , Pickett J. S. , Omura Y. , Robert P. , Nomura R.
Published: April 2013

Electromagnetic ion cyclotron (EMIC) triggered chorus emissions have recently been a subject of several experimental, theoretical and simulation case studies, noting their similarities with whistler‐mode chorus. We perform a survey of 8 years of Cluster data in order to increase the database of EMIC triggered emissions. The results of this is that EMIC triggered emissions have been unambiguously observed for only three different days. These three events are studied in detail. All cases have been observed at the plasmapause between 22 and 24 magnetic local time (MLT) and between − 15∘ and 15∘ magnetic latitude (λm). Triggered emissions are also observed for the first time below the local He+ gyrofrequency . The number of events is too low to produce statistical results, nevertheless we point out a variety of common properties of those waves. The rising tones have a high level of coherence and the waves propagate away from the equatorial region. The propagation angle and degree of polarization are related to the distance from the equator, whereas the slope and the frequency extent vary from one event to the other. From the various spacecraft separations, we determine that the triggering process is a localized phenomenon in space and time. However, we are unable to determine the occurrence rates of these waves. Small frequency extent rising tones are more common than large ones. The newly reported EMIC triggered events are generally observed during periods of large AE index values and in time periods close to solar maximum.
The plasma density distribution in the inner region of Saturn's magnetosphere
Authors: Persoon A. M. , Gurnett D. A. , Leisner J. S. , Kurth W. S. , Groene J. B. , Faden J. B.
Published: April 2013

Electron density measurements derived from the upper hybrid resonance frequency have been obtained from the Cassini Radio and Plasma Wave Science experiment over a 7 year period from 28 October 2004 through 7 November 2011. Additional density measurements inside the orbit of Enceladus and outside the orbit of Rhea have made it possible to expand a previously published density model to radial distances from 2.6 to 10.0 Saturnian radii (RS). The distribution of density data is compared to a simple scale height density model for a single‐species plasma within 8° of the magnetic equatorial plane. There is a broad peak in the equatorial density distribution between 4 RS and 5 RS with the plasma falling off both inward and outward from the peak region. The radial dependence of the equatorial density profile varies as R4.0 from 2.6 RS to 4 RS and as R–4.8 from 5 RS to 10 RS. The plasma distribution outside 5 RS remains consistent with earlier density models but additional density measurements inside 4 RS provide information on the plasma distribution in this inner region that will be the focus of the F‐Ring and proximal orbits near the end of the Cassini mission.
Out‐of‐plane electron currents in magnetic islands formed during collisionless magnetic reconnection
Authors: Huang Can , Lu Quanming , Wu Mingyu , Lu San , Wang Shui
Published: April 2013

Secondary islands are considered to play a crucial role in collisionless magnetic reconnection. Based on 2‐D particle‐in‐cell simulations, we investigate the characteristics of the out‐of‐plane electron currents in magnetic islands formed during collisionless magnetic reconnection with an initial guide field. In a primary island (formed simultaneously with the appearance of the X lines), due to the acceleration of the trapped electrons, the direction of the formed out‐of‐plane electron current is reverse to the original one. In the secondary island (formed in the vicinity of the X‐line), the out‐of‐plane electron current is generated due to the accelerated electrons by the reconnection electric field in the vicinity of the X line. In such a way, the direction of the out‐of‐plane electron current in a secondary island is found to be opposite to that in a primary island. Such characteristics are found to be related to the evolution of the magnetic islands and then electron dynamics in the islands, which are proposed in this paper to be a possible criterion to identify a secondary island formed during collisionless magnetic reconnection, especially in the magnetotail.
Ionospheric response to oscillatory flow braking in the magnetotail
Authors: Panov E. V. , Baumjohann W. , Nakamura R. , Amm O. , Kubyshkina M. V. , Glassmeier K.‐H. , Weygand J. M. , Angelopoulos V. , Petrukovich A. A. , Sergeev V. A.
Published: April 2013

We study the ionospheric response to oscillatory braking of bursty bulk flow observed by THEMIS on 17 March 2008 between 10:22 and 10:36 UT. By calculating different current components generated in the plasma sheet and correlating the space and ground observations, we discriminate the ionospheric current relevant to the large‐scale substorm wedge currents produced by the general reconfiguration of the magnetotail pressure gradient from the currents that appeared as a result of the flow oscillation. While the former currents are large and quasi‐stable, the latter (oscillating) currents are substantially (2–3 times) weaker and flow in opposite directions during earthward and tailward flow bursts. The oscillating currents include the polarization current and the current generated by the oscillating part of the pressure gradient. The two oscillating currents appear to produce modulation of the ionospheric currents (with about 2.5 min period) that was seen as Pi2 pulsations in the ground magnetometer observations. Our estimates of the ionospheric conductance suggest that the damping of the plasma sheet flow oscillation is due to heating the ionosphere through Pedersen currents. We also found that the all‐sky imager at Fort Yukon observed four auroral forms during the first two periods of the oscillatory flow braking: two auroral forms related to the earthward plasma sheet flows and the other two auroral forms related to the tailward rebounds of the earthward flow. The auroral forms evolve in accordance with the appearance and motion of the upward field‐aligned current spot of the modulated part of the ionospheric field‐aligned current.
Transient electron precipitation during oscillatory BBF braking: THEMIS observations and theoretical estimates
Authors: Panov E. V. , Artemyev A. V. , Baumjohann W. , Nakamura R. , Angelopoulos V.
Published: April 2013

We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) data acquired on 17 March 2008 between 10:22 and 10:32 UT to study the mechanism of transient electron injection into the loss cone during oscillatory bursty bulk flow (BBF) braking. During braking, transient regions of piled‐up magnetic fluxes are formed. Perpendicular electron anisotropy observed in these regions (presumably caused by betatron perpendicular electron heating) may be a free‐energy source of coexisting whistler waves. Parallel electrons with energies between 1 and 5 keV disappear inside these regions, and transient auroral forms (both rather discrete arcs and diffuse‐like aurora around the arcs) are observed simultaneously by the ground all‐sky imager at Fort Yukon. We use quasi‐linear theory of electron resonant interaction with whistler waves and also estimate the effectiveness of electron nonlinear capture by strong whistler waves. We suggest that electron injection into the loss cone is caused by: (1) scattering by whistler waves and (2) parallel acceleration of electrons captured by stronger whistler waves.
Ionospheric disturbances of the 2007 Bengkulu and the 2005 Nias earthquakes, Sumatra, observed with a regional GPS network
Authors: Cahyadi Mokhamad Nur , Heki K.
Published: April 2013

We studied ionospheric disturbances associated with the two large earthquakes in Sumatra, Indonesia, namely, the 2007 Bengkulu and the 2005 Nias earthquakes, by measuring the total electron contents (TEC) using a regional network of global positioning system (GPS) receivers. We first focus on coseismic ionospheric disturbances (CIDs) of the Bengkulu earthquake (Mw 8.5). They appeared 11–16 min after the earthquake and propagated northward as fast as ~0.7 km/s, consistent with the sound speed at the ionospheric F layer height. Resonant oscillation of TEC with a frequency of ~5 mHz continued for at least 30 min after the earthquake. The largest aftershock (Mw 7.9) also showed clear CIDs similar to the main shock. A CID propagating with the Rayleigh wave velocity was not observed, possibly because the station distribution did not favor the radiation pattern of the surface waves. This earthquake, which occurred during a period of quiet geomagnetic activity, also showed clear preseismic TEC anomalies similar to those before the 2011 Tohoku‐Oki earthquake. The positive and negative anomalies started 30–60 min before the earthquake to the north and the south of the fault region, respectively. On the other hand, we did not find any long‐term TEC anomalies within 4–5 days before the earthquake. Co‐ and preseismic ionospheric anomalies of the 2005 Nias earthquake (Mw 8.6) were, however, masked by strong plasma bubble signatures, and we could not even discuss the presence or absence of CIDs and preseismic TEC changes for this earthquake.
Microturbulence in the electron cyclotron frequency range at perpendicular supercritical shocks
Authors: Muschietti L. , Lembège B.
Published: April 2013

Supercritical perpendicular collisionless shocks are characterized by a fraction of the incoming ions being reflected at the steep front. These reflected ions accumulate and form a foot, where the relative drift of the reflected ion beam versus the electrons can easily excite an electron cyclotron drift instability (ECDI). Here, we analyze the resulting wave emissions by two approaches. First, our linear dispersion analysis shows that several electron Bernstein harmonics can be unstable, their number being proportional to the drift, yet limited by the ion beam temperature. Second, the three local populations (incoming electrons/ions and reflected ions) of the foot region are introduced in full electromagnetic particle‐in‐cell (PIC) periodic simulations in order to analyze the nonlinear regime of the ECDI. The main results are the following: (1) High gyroharmonics develop over a short time scale less than the lower hybrid period. (2) The spectral power shifts toward lower k modes to accumulate on the first harmonic under the effects of two complementary processes: (i) trapping of the reflected ion beam and (ii) resonance broadening. The latter acts to demagnetize the electrons in the dispersion relation. It initially applies to very high k modes (kρe>>1) and progressively, as time evolves, to lower k modes, invalidating the existence of all gyroharmonics except the first one. (3) In the late stage, a magnetic field component surprisingly develops in the energy spectrum that had so far been electrostatic. (4) The electrons are heated, which represents a source of preheating in the foot region of the shock front.
Observations of interstellar helium pickup ions in the inner heliosphere
Authors: Gershman Daniel J. , Gloeckler George , Gilbert Jason A. , Raines Jim M. , Fisk Lennard A. , Solomon Sean C. , Stone Edward C. , Zurbuchen Thomas H.
Published: April 2013

During the MESSENGER spacecraft's interplanetary trajectory to Mercury, the Fast Imaging Plasma Spectrometer (FIPS) measured the first helium pickup ion distributions at a heliocentric distance (R) ranging between 0.3 and 0.7 AU. From several transits of MESSENGER through the interstellar helium gravitational focusing cone, we map the cone structure in the ecliptic at R=0.3 AU and compare it with observations of He+ at R=1 AU made with the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE). Average downwind enhancements of ≈8 and average cone widths of ≈30° measured by each sensor match known models of neutral helium during this most recent, unusually quiet, solar minimum. The average cone center direction is calculated to be at J2000 ecliptic longitude λ∞=76.0°(±6.0°) and 77.0°(±1.5°) from FIPS and SWICS observations, respectively. These parameters are also in agreement with previous determinations of the downwind direction of interstellar flow and demonstrate the effectiveness of using pickup ion observations inside 1 AU to map the structure of the neutral helium distribution in the heliosphere, as well as to diagnose the conditions of the interstellar medium.
A statistical study of proton precipitation onto the Martian upper atmosphere: Mars Express observations
Authors: Diéval C. , Stenberg G. , Nilsson H. , Barabash S.
Published: April 2013

Due to the small size of the Martian magnetic pile‐up region, especially at the subsolar point, heated protons with high enough energy can penetrate the induced magnetosphere boundary without being backscattered, i.e., they precipitate. We present a statistical study of the downgoing ~ keV proton fluxes measured in the Martian ionosphere by the Analyzer of Space Plasma and Energetic Atoms experiment onboard the Mars Express spacecraft. We find that on the dayside, the events of proton penetration occur during 3% of the observation time; the precipitation is an intermittent phenomenon. The proton events carry on average ~0.2% of the incident solar wind flux. Therefore, the induced magnetosphere is an effective shield against the magnetosheath protons. The events are more frequent during fast solar wind conditions than during slow solar wind conditions. The sporadic proton penetration is thought to be caused by transient increases in the magnetosheath temperature. The precipitating flux is higher on the dayside than on the nightside, and its spatial deposition is controlled by the solar wind convective electric field. The largest crustal magnetic anomalies tend to decrease the proton precipitation in the southern hemisphere. The particle and energy fluxes vary in the range 104–106 cm–2 s–1 and 107–109 eVcm–2 s–1, respectively. The corresponding heating for the dayside atmosphere is on average negligible compared to the solar extreme ultraviolet heating, although the intermittent penetration may cause local ionization. The net precipitating proton particle flux input to the dayside ionosphere is estimated as 1.2 · 1021 s–1.
Heavy ion effects on substorm loading and unloading in the Earth's magnetotail
Authors: Liu Yanhua , Kistler Lynn M. , Mouikis Christopher G. , Klecker Berndt , Dandouras Iannis
Published: April 2013

We have performed a statistical study investigating how substorm triggering and unloading is affected by the heavy ion content of the magnetotail plasma sheet. During the substorm growth phase, magnetic flux is accumulated in the tail lobes until the magnetotail reaches an unstable state. A near‐Earth neutral line then forms, and this excess flux is reconnected. The increased lobe magnetic flux during the substorm growth phase increases the magnetopause flaring angle. As a result, a greater fraction of the solar‐wind dynamic pressure is observed in the tail lobes and plasma sheet. Therefore, the increase and decrease of the lobe magnetic flux can be monitored by observing the increase and decrease in the magnetotail pressure. Using Cluster data from 2001 to 2004, we have determined how the maximum pressure (or flaring angle) and the rate of change of pressure (or flaring angle) during substorms depend on the O+ content of the plasma sheet. In addition, we have estimated the maximum magnetic flux, and rate of change of the magnetic flux. Our results show that both the maximum tail pressure and the rate of change in the pressure are positively correlated with the amount of O+ in the plasma sheet. When the measurements are normalized to account for the external solar‐wind pressure and the different Cluster locations in the tail, the maximum accumulated flux and the unloading rate still correlate positively with the O+ density and O+/H+ ratio. This suggests that the additional O+ makes it more difficult to trigger the substorm onset, but once it is triggered, the unloading is faster. This could either indicate that the presence of O+ increases the reconnection rate, or that it initiates reconnection over a broader width of the tail.
Large‐scale ionospheric disturbances due to the dissipation of convectively‐generated gravity waves over Brazil
Authors: Liu H.‐L. , Vadas S. L.
Published: April 2013

In a companion paper, we show that large‐scale secondary gravity waves and circulation cells are created by the body forces generated by the dissipation of convectively generated gravity waves over Brazil on 01 October 2005. In this paper, we show that these fluid perturbations cause large‐scale perturbations of the plasma drift and plasma density in the ionosphere by changing the wind dynamo and transport. These fluid perturbations modify both the amplitude and direction of the plasma drifts. Near the geomagnetic equator, the magnitude of the pre‐reversal enhancement can be increased or weakened, depending on the location and local time. Because the circulation cells persist from late afternoon through midnight, the modulation of the vertical drift near the geomagnetic equator persists until midnight. The largest changes of the wind‐driven currents can occur either in the E or F region and are determined by the magnitudes of the wind perturbations, conductivities, and conductivity perturbations. The contributions to the plasma transport changes are from advection by the neutral winds along field lines, plasma drifts, and ambipolar diffusion, in the order of their relative significance in the numerical results.
Jupiter's aurora in ultraviolet and infrared: Simultaneous observations with the Hubble Space Telescope and the NASA Infrared Telescope Facility
Authors: Radioti A. , Lystrup M. , Bonfond B. , Grodent D. , Gérard J.‐C.
Published: April 2013

We compare Jupiter's northern auroral emissions in infrared (IR) and ultraviolet (UV) using ground‐based IR observations from the NASA Infrared Telescope Facility and UV observations from Hubble Space Telescope on 16 December 2000, the only date for which simultaneous observations in the two wavelength regions exist. We use polar projections and longitudinal brightness cuts to compare the IR ( ions) and UV (H2, H, and Lyman‐alpha) aurorae, consisting of the main auroral emission, emission regions both poleward and equatorward of the main emission, and those associated with the Io footprint and its extended tail. We demonstrate that (1) the IR main emission and the equatorward diffuse emissions are generally good proxies for the UV and vice versa, (2) the spatial distribution and temporal behavior of UV and IR emissions within the main emission, at high magnetic latitudes, differ substantially, (3) UV and IR emissions associated with the Io interaction appear at the Io footprint and along an extended (downstream) tail but differ in relative brightness. While the UV aurora is excited directly, the IR aurora is a thermal emission, its intensity depends on both the number density of the ions and the temperature. Three main factors may contribute to the observed morphological differences of the simultaneous emissions in the two wavelengths, namely ion transport, local heating, and the energy of the precipitating electrons. We estimate the ion transport distances, based on the ion lifetime and suggest that ion transport cannot account for large‐scale morphological differences between the UV and IR emissions. We propose that neutral gas heating by particle precipitation and Joule heating locally enhances the emission with no UV counterpart. Additionally, we estimate that local temperature variations are reflected in the IR emission with a time lag of several hours with respect to the UV. Finally, high precipitating electron energies exceeding a certain value might lead to chemical loss of the low altitude ions, suppress the lower IR emitting layers, and contribute to the observed differences of the emissions between the two wavelength regimes.
Slow magnetosonic waves detected in reconnection diffusion region in the Earth's magnetotail
Authors: Cao J. B. , Wei X. H. , Duan A. Y. , Fu H. S. , Zhang T. L. , Reme H. , Dandouras I.
Published: April 2013

We studied the ULF waves with a period of 30 s in the ion diffusion region of reconnection observed by Cluster satellites on 21 August 2002. The fast convective tailward ion flow accompanied with a large southward magnetic field component, a strong Hall magnetic field, and a Hall electric field demonstrates that the Cluster satellites are located in the ion diffusion region of reconnection. The analyses of wave properties using minimum variance analysis and timing method indicate that this wave is an obliquely propagating slow magnetosonic wave which is characterized by the anti phase relation between the magnitude of the magnetic field and the ion number density and by a propagation angle of around 130° with respect to the ambient magnetic field. This wave is generated by periodic magnetic reconnection. The periodic oscillations in the By and Bx components are driven by the periodic Hall current system, while the oscillation in the Bz component is driven by quasiperiodic convective tailward ion flows. The slow magnetosonic wave significantly influences the frequency of whistler waves and low hybrid waves excited by magnetic reconnection by changing the magnitude of the local magnetic field and subsequently the electron cyclotron frequency.
Numerical modeling of the large‐scale neutral and plasma responses to the body forces created by the dissipation of gravity waves from 6 h of deep convection in Brazil
Authors: Vadas S. L. , Liu H.‐L.
Published: April 2013

We study the response of the thermosphere and ionosphere to gravity waves (GWs) excited by 6 h of deep convection in Brazil on the evening of 01 October 2005 via the use of convective plume, ray trace, and global models. We find that primary GWs excited by convection having horizontal wavelengths of λH∼70–300 km, periods of 10–60 min, and phase speeds of cH∼50–225 m/s propagate well into the thermosphere. Their density perturbations are – 25% at z∼150 km and are negligible at z>300 km. The dissipation of these GWs creates spatially and temporally localized body forces with amplitudes of 0.2– 1.0 m/s2at z∼120–230 km. These forces generate two counter‐rotating circulation cells with horizontal velocities of 50–350 m/s. They also excite secondary GWs; those resolved by our global model have λH∼4000–5000 km and cH∼500–600 m/s. These secondary GWs propagate globally and have – 25% and 5–15% at z=250 and 375 km, respectively. These forces also create plasma perturbations of foF2′∼0.2–1.0 MHz, TEC′∼0.4– 1.5 TECU (total electron content unit, 1TECU  =1016 elm−2), and hmF2′∼5–50 km. The large‐scale traveling ionospheric disturbances (LSTIDs) induced by the secondary GWs have amplitudes of foF2′∼0.2–0.5 MHz, TEC′∼0.2– 0.6 TECU, and hmF2′∼5–10 km. In a companion paper, we discuss changes to the prereversal enhancement and plasma drift from these forces.
Modeling Jupiter's magnetosphere: Influence of the internal sources
Authors: Chané E. , Saur J. , Poedts S.
Published: April 2013

We introduce a new model to study Jupiter's magnetosphere and how it interacts with the solar wind. We first derive a set of one‐fluid MHD equations to consistently include the ion‐neutral collisions in Jupiter's ionosphere and the mass loading in the Io torus. The mass loading and the subsequent radial mass transport in Jupiter's magnetosphere leads to a deviation from full corotation of the magnetospheric plasma. Ion‐neutral collisions in Jupiter's ionosphere and subsequent transport of angular momentum out into the magnetosphere acts to spin up the magnetosphere's plasma. Our model explicitly includes mass loading in the Io plasma torus and an inner boundary region, which represents the effects of Jupiter's ionosphere. We present the results of five model runs where different mass loading rates and ionospheric conductances are used. For these model runs, we consider an antiparallel interplanetary magnetic field and a strong solar wind dynamic pressure, resulting in a compressed magnetosphere. The results are compared with analytical models, in situ measurements, and remote‐sensing observations. Our azimuthal velocity profiles and the position of the corotation breakdown are in quantitative agreement with theoretical predictions by Hill (1979, 2001) and Saur et al., (2004a), and Voyager observations. The total current flowing into and out of the ionosphere is 48.7 MA, which is in agreement with estimates from measurements and analytical models. Using the field aligned electric current j∥ to determine the position of the aurorae, we find that our main auroral oval is associated, as expected, with the position of the corotation breakdown (between 20.6 RJ and 30.1 RJ for the different model runs). The discontinuity in the main oval observed by Radioti et al. (2008) is also present in our results, where it is caused by an asymmetry in the pressure distribution, due to the interaction between the rotating plasma and the magnetopause.
An improved dispersion relation for parallel propagating electromagnetic waves in warm plasmas: Application to electron scattering
Authors: Chen Lunjin , Thorne Richard M. , Shprits Yuri , Ni Binbin
Published: April 2013

An improved dispersion relation, with thermal corrections retained, for parallel propagating electromagnetic waves in a warm plasma is developed for both left‒hand (L‒) and right‒hand (R‒) polarized modes. Compared with the cold plasma dispersion relation, the derived dispersion relation is in much better agreement with the full hot plasma dispersion relation (including the wave growth rate). The pitch angle scattering rates of energetic electrons are compared between using cold and full dispersion relation. Significant differences are found when evaluating pitch angle scattering rate of MeV electron caused by He+ band waves in multiple ion plasmas. Due to He+ ion cyclotron absorption, the He+band electromagnetic ion cyclotron waves, which are able to resonate with MeV electrons (at large wave number), tend to be strongly suppressed. Less significant differences in scattering rate of electrons between using cold and hot dispersion relation are found in the case of L‒mode waves in single H+ ion plasma and in the case of R‒mode waves.
Gravity wave coupling between the mesosphere and thermosphere over New Zealand
Authors: Smith S. M. , Vadas S. L. , Baggaley W. J. , Hernandez G. , Baumgardner J.
Published: April 2013

All‐sky images obtained with the Boston University all‐sky imaging system located at the Mount John University Observatory, New Zealand (43.98°S, 170.42°E) show clear evidence of dynamic coupling between the mesosphere and thermosphere. Gravity wave (GW) breaking events in the upper mesosphere at altitudes (z) of 80 to 100 km were observed in the 557.7 nm emission on the evening of 4 March 2009 from 08:40 to 13:50 UT. During this time, unusual oppositely propagating weak northwestward (NW‐ward) and strong southeastward (SE‐ward) GWs were observed in the all‐sky images of the thermospheric atomic oxygen O(1D) 630.0 nm emission at 250 km altitude. The waves appeared to originate from the same location over New Zealand, with phase fronts nearly parallel to the landmass axis of the South Island of New Zealand. Additionally, the southern portion of the wave train ends abruptly at the southern tip of New Zealand. The SE‐ward GWs were stronger and appeared for ~5 h, while the NW‐ward GWs were weaker and only appeared for ~1.75 h. We provide evidence that mountain waves were likely generated in the troposphere that evening. Momentum deposition from GW breaking excites secondary GWs. We model these secondary GWs and show that these GWs have a similar morphology and behavior as observed. Wind filtering in the thermosphere can account for the larger amplitudes and persistent appearance of the SE‐ward GWs and the smaller amplitudes and less persistent appearance of the NW‐ward GWs. Thus, the morphology and behavior of the 630.0 nm GWs suggest that they were secondary GWs generated from mountain wave breaking in the upper mesosphere. We also show that similar SE‐ward GWs have occurred in the 630.0 nm emission on other occasions.
Energetic electron (>10 keV) microburst precipitation, ~5–15 s X‐ray pulsations, chorus, and wave‐particle interactions: A review
Authors: Tsurutani Bruce T. , Lakhina Gurbax S. , Verkhoglyadova Olga P.
Published: April 2013

The fundamental features of ~0.1–0.2 s duration ~0.5 s spaced ionospheric electron precipitation “microbursts,” ~5 to 15 s microburst “trains,” and 5–15 s electron precipitation pulsations are reviewed in light of similar temporal structures of electromagnetic whistler mode “chorus” waves detected in the outer magnetosphere. Past observations of microbursts point to extremely rapid (ms timescale) wave‐particle interactions, probably between lower band chorus subelements (durations of ~10 to 100 ms) and energetic ~10 to 100 keV electrons. A recent theory explaining such rapid interaction rates observed in microbursts is briefly reviewed. Arguments are given why ~5–15 s X‐ray (and optical) pulsations are also associated with chorus scattering of energetic electrons. Comments about relativistic (E > 1 MeV) microbursts are also provided. There are, however, many other unsolved problems of outer zone energetic electron precipitation. The authors will attempt to indicate several of these for the interested reader. Finally, an appendix is provided for a brief review of two‐frequency chorus and some current problems with that topic.
Attribution of ionospheric vertical plasma drift perturbations to large‐scale waves and the dependence on solar activity
Authors: Liu H.‐L. , Richmond A. D.
Published: April 2013

In this study, we quantify the contribution of individual large‐scale waves to ionospheric electrodynamics and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi‐stationary planetary wave one (QSPW1), and nonmigrating semidiurnal westward wave one (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model simulations under solar minimum conditions, it is found that the mean winds and DW1 produce a wave two pattern in equatorial vertical E×Bdrift that is upward in the morning and around dusk. The modeled SW2 also produces a wave two pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and DW1. SW1 can cause large vertical drifts around dawn, while QSPW1 does not have any direct impact on the vertical drift. Wind components of both SW2 and SW1 become large at middle to high latitudes in the E‐region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift, likely through modulating the E‐region wind dynamo. The most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F‐region Pedersen conductivity and of the F‐region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background but also because the E‐region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases, and latitudinal and vertical structures of large‐scale waves are important in quantifying the ionospheric responses.
Energetic particle dynamics in Mercury's magnetosphere
Authors: Walsh B. M. , Ryou A. S. , Sibeck D. G. , Alexeev I. I.
Published: April 2013

We investigate the drift paths of energetic particles in Mercury's magnetosphere by tracing their motion through a model magnetic field. Test particle simulations solving the full Lorentz force show a quasi‐trapped energetic particle population that gradient and curvature drift around the planet via “Shabansky” orbits, passing though high latitudes in the compressed dayside by equatorial latitudes on the nightside. Due to their large gyroradii, energetic H+ and Na+ ions will typically collide with the planet or the magnetopause and will not be able to complete a full drift orbit. These simulations provide direct comparison for recent spacecraft measurements from MESSENGER. Mercury's offset dipole results in an asymmetric loss cone and therefore an asymmetry in particle precipitation with more particles precipitating in the southern hemisphere. Since the planet lacks an atmosphere, precipitating particles will collide directly with the surface of the planet. The incident charged particles can kick up neutrals from the surface and have implications for the formation of the exosphere and weathering of the surface.
Simultaneous conjugate observations of small‐scale structures in Saturn's dayside ultraviolet auroras: Implications for physical origins
Authors: Meredith C. J. , Cowley S. W. H. , Hansen K. C. , Nichols J. D. , Yeoman T. K.
Published: April 2013

Small‐scale features in Saturn's dayside UV auroras are examined using images obtained on 32 Hubble Space Telescope visits close to Saturn equinox when both northern and southern emissions were simultaneously observed, allowing their interhemispheric conjugacy to be investigated. Eastward‐propagating patches in the dawn‐to‐noon sector were observed on ~70% of visits, which when present were nearly always observed both north and south. The patches were generally not closely conjugate, however, but typically displaced in local time by ~0.5–1 h, with maxima in one hemisphere falling near minima in the other. Averaged angular velocities were ~80% of rigid corotation, larger than plasma angular velocities reported in the outer magnetosphere to which the emissions are likely conjugate. We suggest the patches are associated with field‐aligned currents of eastward‐propagating ULF waves, specifically second harmonic Alfvén resonances with typical azimuthal wave numbers m ≈ 20 and plasma rest frame periods ~80 min, plausibly driven by drift‐bounce resonance with hot magnetospheric water ions. Transient dusk sector emissions of ~10–30 min duration were also observed on ~40% of visits, and found to be strictly nonconjugate, with enhancements in one hemisphere, north or south, being unaccompanied by enhancements in the other. We suggest an association with open flux tubes, and discuss one scenario where hemispheric symmetry is broken on newly opened flux tubes via the interplanetary magnetic field Y component, plausibly consistent with nonconjugate events north and south, preferential postnoon occurrence, and time scales of a few tens of minutes, though the expected relationship with the Y component remains to be established.
Artificial plasma cusp generated by upper hybrid instabilities in HF heating experiments at HAARP
Authors: Kuo Spencer , Snyder Arnold
Published: April 2013

The High Frequency Active Auroral Research Program digisonde was operated in a fast mode to record ionospheric modifications by the HF heating wave. With the O mode heater of 3.2 MHz turned on for 2 min, significant virtual height spread was observed in the heater off ionograms, acquired beginning the moment the heater turned off. Moreover, there is a noticeable bump in the virtual height spread of the ionogram trace that appears next to the plasma frequency (~ 2.88 MHz) of the upper hybrid resonance layer of the HF heating wave. The enhanced spread and the bump disappear in the subsequent heater off ionograms recorded 1 min later. The height distribution of the ionosphere in the spread situation indicates that both electron density and temperature increases exceed 10% over a large altitude region (> 30 km) from below to above the upper hybrid resonance layer. This “mini cusp” (bump) is similar to the cusp occurring in daytime ionograms at the F1–F2 layer transition, indicating that there is a small ledge in the density profile reminiscent of F1–F2 layer transitions. Two parametric processes exciting upper hybrid waves as the sidebands by the HF heating waves are studied. Field‐aligned purely growing mode and lower hybrid wave are the respective decay modes. The excited upper hybrid and lower hybrid waves introduce the anomalous electron heating which results in the ionization enhancement and localized density ledge. The large‐scale density irregularities formed in the heat flow, together with the density irregularities formed through the parametric instability, give rise to the enhanced virtual height spread. The results of upper hybrid instability analysis are also applied to explain the descending feature in the development of the artificial ionization layers observed in electron cyclotron harmonic resonance heating experiments.
Coupling between mesosphere and ionosphere over Beijing through semidiurnal tides during the 2009 sudden stratospheric warming
Authors: Xiong Jiangang , Wan Weixing , Ding Feng , Liu Libo , Ning Baiqi , Niu Xiaojuan
Published: April 2013

Sudden stratospheric warming (SSW) in the winter of 2008/2009 is the strongest recorded SSW event. The enhancement in semidiurnal variation of ionospheric TEC (total electron content) with phase shift forward is shown during 22 to 27 January 2009, based on the TEC observations in Beijing (40.30°N, 116.19°E geographic, 39.73°N dip latitude). We focus on finding the reason for the TEC variation. Winds observed by an all‐sky meteor radar in the same observatory are used to study mesospheric variation. The semidiurnal solar tide in the mesosphere starts to increase before the SSW and maintains oscillation with period 16–20 days during the SSW. The semidiurnal lunar tides in TEC and wind start to increase on 17 and 15 January, respectively. Although the semidiurnal lunar tide in TEC over Beijing almost dies out on 1 February, that over equatorial ionospheric anomaly crest does not vanish until 15 February when lunar tide in wind tends to be very weak. The maximum of lunar tide in wind appears on 2 February at 96 km with amplitudes of 15 m/s and 21 m/s for zonal and meridional winds. The phase comparison shows that lunar tides in TEC and zonal wind reach their maxima at almost the same time, which is 2–4 h lag behind the meridional wind. The coupling between the mesosphere and ionosphere contributes to the semidiurnal variation of TEC through both solar and semidiurnal lunar tides. The enhancement in semidiurnal lunar tide is responsible for the TEC peak shift forward during the SSW.
Large‐scale structures in the equatorial ionosphere and their connection to the generalized Rayleigh‐Taylor instability
Authors: Dao E. , Kelley M. C. , Pfaff R. F. , Roddy P. A.
Published: April 2013

For the first time, electric field and density fluctuations have been simultaneously measured on the Communications/Navigation Outage Forecasting System satellite at large scales (>300 km). The ratio of their spectral power rises as k2, unlike scales from 20 m to 300 km where the ratio is independent of k. We suggest that gravity waves dominate these large scales and mix with density gradients via self‐generated electric fields to form δn/n0.
Iceland rising: Solid Earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling
Authors: Auriac A. , Spaans K. H. , Sigmundsson F. , Hooper A. , Schmidt P. , Lund B.
Published: April 2013

A broad uplift occurs in Iceland in response to the retreat of ice caps, which began circa 1890. Until now, this deformation signal has been measured primarily using GPS at points some distance away from the ice caps. Here, for the first time we use satellite radar interferometry (interferometric synthetic aperture radar) to constrain uplift of the ground all the way up to the edge of the largest ice cap, Vatnajökull. This allows for improved constraints on the Earth rheology, both the thickness of the uppermost Earth layer that responds only in an elastic manner and the viscosity below it. The interferometric synthetic aperture radar velocities indicate a maximum displacement rate of 24±4 and 31±4 mm/yr at the edge of Vatnajökull, during 1995–2002 and 2004–2009, respectively. The fastest rates occur at outlet glaciers of low elevation where ice retreat is high. We compare the observations with glacial isostatic adjustment models that include the deglaciation history of the Icelandic ice caps since 1890 and two Earth layers. Using a Bayesian approach, we derived probability density functions for the average Earth model parameters for three satellite tracks. Based on our assumptions, the three best fit models give elastic thicknesses in the range of 15–40 km, and viscosities ranging from 4–10× 1018 Pa s.
Elastic laboratory measurements and modeling of saturated basalts
Authors: Adam Ludmila , Otheim Thomas
Published: April 2013

Understanding the elastic behavior of basalt is important to seismically monitor volcanoes, subsea basalts, and carbon sequestration in basalt. We estimate the elastic properties of basalt samples from the Snake River Plain, Idaho, at ultrasonic (0.8 MHz) and seismic (2–300 Hz) frequencies. To test the sensitivity of seismic waves to the fluid content in the pore structure, measurements are performed at three saturation conditions: saturated with liquid CO2, water, and dry. When CO2 replaces water, the P‐wave velocity drops, on average, by 10%. Vesicles and cracks, observed in the rock microstructure, control the relaxation of pore‐fluid pressures in the rock as a wave propagates. The bulk and shear moduli of basalts saturated with liquid CO2 are not frequency dependent, suggesting that fluid pore pressures are in equilibrium between 2 Hz and 0.8 MHz. However, when samples are water saturated, the bulk modulus of the rock is frequency dependent. Modeling with Gassmann's equations predicts the measured saturated rock bulk modulus for all fluids for frequencies below 20 Hz but underpredicts the water‐saturated basalt bulk modulus for frequencies greater than 20 Hz. The most likely reason is that the pore‐fluid pressures are unrelaxed. Instead, the ultrasonic frequency rock moduli are modeled with high‐frequency elastic theories of squirt flow and Kuster–Toksöz (KT). Although KT's model is based on idealized pore shapes, a combination of spheres (vesicles) and penny‐shaped cracks (fractures) interpreted and quantified from petrographical data predicts the ultrasonic dry and saturated rock moduli for the measured basalts.
The instability of continental passive margins and its effect on continental topography and heat flow
Authors: Armitage J. J. , Jaupart C. , Fourel L. , Allen P. A.
Published: April 2013

The long geological history of passive margin evolution is complex yet typified by an initial ramp‐like tilting of the subaerial surface toward the continent‐ocean boundary, followed by episodic uplift and subsidence at a smaller wavelength. We argue that this behavior is due to changes in margin structure brought about by buoyancy‐driven lithospheric flow. Continental lithosphere is melt‐depleted, buoyant, and thick. It will resist convective breakdown into the asthenosphere below, but will be prone to lateral flow due to horizontal density contrasts. Changes in lithosphere thickness at the transition between continent and ocean will nucleate convection cells. Using a numerical model of viscous upper mantle flow, we show that stability or instability of the continental lithosphere at a passive margin is a function of the lithospheric rheology and composition. Increased compositional buoyancy leads to oceanward lateral flow of the continental lithosphere whereas decreased buoyancy has the opposite effect, causing landward lateral flow of the continental lithosphere. In model simulations, a continental lithosphere thought typical of Phanerozoic continental platforms experiences first a margin‐wide ramp‐like tilting, followed by topographic fluctuations due to an evolving array of convection cells in the mantle. The timing and magnitude of predicted changes in topography are similar to those observed at the eastern North American margin, suggesting that the tilting and episodic uplift and subsidence at continental passive margins are a natural consequence of the evolution of continental lithosphere after breakup and during mature seafloor spreading.
The use of GPS horizontals for loading studies, with applications to northern California and southeast Greenland
Authors: Wahr John , Khan Shfaqat A. , van Dam Tonie , Liu Lin , van Angelen Jan H. , van den Broeke Michiel R. , Meertens Charles M.
Published: April 2013

We describe how GPS measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements, to improve and extend GPS studies of surface loading. We show that the ratio of the vertical displacement to the horizontal displacement, combined with the direction of the horizontal motion, can help determine whether nearby loading is concentrated in a small region (for example, in a single lake or glacier), and where that region is. We illustrate this method by applying it to two specific cases: an analysis of GPS data from northern California to monitor the level of Lake Shasta, and the analysis of data from a single GPS site in southeast Greenland to determine mass variability of two large, nearby outlet glaciers: Helheim Glacier and Midgaard Glacier. The California example serves largely as a proof‐of‐concept, where the results can be assessed by comparing with independent observations (Lake Shasta tide gauge data, in this case). Our Greenland results show that both Helheim and Midgaard have experienced notable interannual variations in mass loss rate over the last decade. Helheim's mass loss accelerated rapidly in mid‐2003, decelerated in late 2005, and increased again in 2008–2009 before returning to about its pre‐2003 rate in late 2010. Midgaard's mass loss accelerated in mid‐2004, and remained more‐or‐less constant before returning to its pre‐2003 rate in late 2008.