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Sample records for dusk

  1. Dawn-dusk magnetosheath plasma asymmetries at 60 earth radii

    NASA Technical Reports Server (NTRS)

    Fenner, M. A.; Freeman, J. W., Jr.

    1975-01-01

    A study of data from the Apollo lunar surface suprathermal ion detector experiment (Side) package shows that plasma flow and energy parameters in the dusk magnetosheath are much better correlated with geomagnetic activity than those in the dawn magnetosheath. This result is in agreement with a dawn-dusk asymmetry in the magnetosheath magnetic field and in the bow shock configuration. The different orientations between the mean interplanetary magnetic field direction and the shock normal for the magnetosheaths suggest an explanation of the difference in the plasma parameters on the two sides.

  2. Dawn-dusk asymmetry in the northward IMF plasma sheet

    NASA Astrophysics Data System (ADS)

    Wing, S.; Johnson, J. R.; Newell, P. T.; Meng, C.

    2005-05-01

    During periods of northward IMF, as a result of large influx of the magnetosheath ions, the plasma sheet becomes cold and dense. During these periods, a large number of the plasma sheet ions have two components: hot (magnetospheric origin) and cold (magnetosheath origin). Based on their spectral distributions: one-component Maxwellian, two-component Maxwellian, and kappa (k), the characteristics of the plasma sheet ions were studied with DMSP satellites and a method of inferring plasma sheet ion properties from the ionospheric observations. The cold-component constituent of the two-component ions is hotter in the dawn than the dusk sector, consistent with the in situ studies that suggest that the magnetosheath ion is heated upon its entry along the plasma sheet dawn flank. This temperature asymmetry leads to a dawn-dusk asymmetry in the ion spectral distribution. The cold and hot components are closer together in temperature space, which increases the proportion of ions having (apparent) one-component distribution in the dawn flank while, in the dusk flank, the influx of the magnetosheath ions increase the density of the two-component ions. The dawn-dusk asymmetry in the cold magnetosheath ion profile should help determine the roles of various proposed magnetosheath entry mechanisms.

  3. Dawn-Dusk Asymmetries in Rapidly Rotating Magnetospheres

    NASA Astrophysics Data System (ADS)

    Jia, X.; Kivelson, M.

    2015-12-01

    Spacecraft measurements reveal perplexing dawn-dusk asymmetries of field and plasma properties in the magnetospheres of Saturn and Jupiter. Here we describe a previously unrecognized source of dawn-dusk asymmetry in a rapidly rotating magnetosphere. As plasma rotates from dawn to noon on a dipolarizing flux tube, it flows away from the equator at close to the sound speed. As plasma rotates from noon to dusk on a stretching flux tube, it is accelerated back to the equator by centrifugal acceleration at flow speeds typically smaller than the sound speed. Correspondingly, the plasma sheet remains far thicker in the afternoon than in the morning. Using two magnetohydrodynamic simulations, we analyze the forces that account for flows along and across the field in Saturn's magnetosphere and point out analogous effects at Jupiter. Different radial force balance in the morning and afternoon sectors produces net dusk to dawn flow, or equivalently, a large-scale electric field oriented from post-noon to pre-midnight.

  4. A dawn to dusk electric field in the Jovian magnetosphere

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Ip, W. I.

    1983-01-01

    It is shown that if Io-injected plasma is lost via a planetary wind-fixed Birkeland current system may result. This is due to the fact that the azimuthal centrifugal current flows across a density gradient produced by the loss of plasma through the planetary wind in the tail. The divergent centrifugal current is connected to field-aligned Birkeland currents which flow into the ionosphere at dawn and out of it at dusk. The closure currents in the ionosphere require a dawn to dusk electric field which at the orbit of Io is estimated to have a strength of 0.2 mV/m. However, the values of crucial parameters are not well known and the field at Io's orbit may well be significantly larger. Independent estimates derived from the local time asymmetry of the torus UV emission indicate a field of 1.5 mV/m.

  5. Dawn-dusk asymmetry in the Kelvin-Helmholtz instability at Mercury.

    PubMed

    Paral, Jan; Rankin, Robert

    2013-01-01

    The NASA MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft entered orbital phase around Mercury on 18 March 2011. A surprising consistent feature in the data returned is large-scale vortices that form exclusively on the dusk side of the magnetosphere. Here we present global kinetic hybrid simulations that explain these observations. It is shown that vortices are excited by a Kelvin-Helmholtz instability near the subsolar point, which grows convectively along the dusk-side magnetopause. Virtual time series along a track approximating a flyby of the MESSENGER show correspondence with the satellite data; the data contain sawtooth oscillations in plasma density, flow and magnetic field, and exhibit the observed dawn-dusk asymmetry. It is shown that asymmetry between dawn and dusk at Mercury is controlled by the finite gyroradius of ions and by convection electric fields. Mercury's magnetosphere offers a natural laboratory for studying plasma regimes not present in other planetary magnetospheres or the laboratory. PMID:23552060

  6. Exploration of tangential discontinuity structure of the dawn and dusk flank magnetopause

    NASA Astrophysics Data System (ADS)

    De Keyser, Johan; Maes, Lukas; Maggiolo, Romain; Haaland, Stein

    2015-04-01

    This contribution explores the tangential discontinuity configurations that are possible at the dawn and dusk flank magnetopause. The motivation for this study is the recent finding that the magnetopause current layer seems to be on average slightly thicker at the dawn flank than at dusk. The study is carried out by considering typical magnetosheath and magnetospheric plasma properties adjacent to the magnetopause and finding out which internal magnetopause structure is compatible with the given properties, if any. This is done by repeatedly running a kinetic model that self-consistently computes the internal structure of the tangential discontinuity magnetopause. The conclusions of this study support the viewpoint that, apart from dawn-dusk differences in the magnetosheath and/or magnetospheric conditions, one also has to consider an intrinsic asymmetry. For low magnetic shear in particular, the vxB electric field, with v the magnetosheath flow and B the geomagnetic field, points outward at dawn and inward at dusk. This convection electric field combines with the Chapman-Ferraro electric field that stems from the charge separation between the ions and electrons inside the magnetopause. Due to their different gyroradii, ions and electrons respond differently to a change of sign of the convection electric field, thus leading to dawn-dusk asymmetry of the internal structure of the magnetopause.

  7. Structure of the ionized lunar sodium and potassium exosphere: Dawn-dusk asymmetry

    NASA Astrophysics Data System (ADS)

    Yokota, Shoichiro; Tanaka, Takaaki; Saito, Yoshifumi; Asamura, Kazushi; Nishino, Masaki N.; Fujimoto, Masaki; Tsunakawa, Hideo; Shibuya, Hidetoshi; Matsushima, Masaki; Shimizu, Hisayoshi; Takahashi, Futoshi

    2014-04-01

    We present latitude and longitude distributions of Na+ and K+ fluxes from the Moon derived from Kaguya low-energy ion data. Although the latitude distribution agrees with previous ground-based telescope observations, dawn-dusk asymmetry has been determined in the longitude distribution. Our model of the lunar surface abundance and yield of Na and K demonstrates that the abundance decreases to approximately 50% at dusk compared with that at dawn due to the emission of the exospheric particles assuming the ion fluxes observed by Kaguya are proportional to the yield. It is also implied that the surface abundance of Na and K need to be supplied during the night to explain the observed lunar exosphere with dawn-dusk asymmetry. We argue that the interplanetary dust as well as grain diffusion and migration/recycling of the exospheric particles may be major suppliers.

  8. Dawn-dusk asymmetries in rotating magnetospheres: Lessons from modeling Saturn

    NASA Astrophysics Data System (ADS)

    Jia, Xianzhe; Kivelson, Margaret G.

    2016-02-01

    Spacecraft measurements reveal perplexing dawn-dusk asymmetries of field and plasma properties in the magnetospheres of Saturn and Jupiter. Here we describe a previously unrecognized source of dawn-dusk asymmetry in a rapidly rotating magnetosphere. We analyze two magnetohydrodynamic simulations, focusing on how flows along and across the field vary with local time in Saturn's dayside magnetosphere. As plasma rotates from dawn to noon on a dipolarizing flux tube, it flows away from the equator along the flux tube at roughly half of the sound speed (Cs), the maximum speed at which a bulk plasma can flow along a flux tube into a lower pressure region. As plasma rotates from noon to dusk on a stretching flux tube, the field-aligned component of its centripetal acceleration decreases and it flows back toward the equator at speeds typically smaller than 1/2 Cs. Correspondingly, the plasma sheet remains far thicker and the field less stretched in the afternoon than in the morning. Different radial force balance in the morning and afternoon sectors produce asymmetry in the plasma sheet thickness and a net dusk-to-dawn flow inside of L = 15 or equivalently, a large-scale electric field (E) oriented from postnoon to premidnight, as reported from observations. Morning-afternoon asymmetry analogous to that found at Saturn has been observed at Jupiter, and a noon-midnight component of E cannot be ruled out.

  9. Temporal variations in the dawn and dusk midlatitude trough position-modeled and measured (Ariel 3)

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Tulunay, Y. K.; Chen, A. J.

    1973-01-01

    The temporal development of the latitudinal position of the 600 km midlatitude electron density trough at dawn and dusk during the period 25-27 May 1967, which encompassed a large magnetic storm, was measured by the RF capacitive probe on the polar orbiting Ariel 3 satellite. The substorm-related changes in the L coordinate of the trough minimum and the point of most rapid change of density gradient on the low latitude side of the trough are similar. Oscillations of the trough position at dusk are in phase with substorm activity whereas movement of the trough at dawn is only apparent with the onset of the large storm. Near dusk there is evidence of structure in the form of a tail-like extension of the plasmasphere at the peak of the storm. Detailed model calculations assuming a spatially invariant equatorial convection E field which varies in step with K sub p index reproduces much of the observed behavior, particularly at dusk, and shows that more than one plasmapause-type transition may be identifiable in the trough region.

  10. Magnetosheath dawn-dusk asymmetries and their impact on solar wind - magnetosphere coupling processes

    NASA Astrophysics Data System (ADS)

    Dimmock, Andrew; Pulkkinen, Tuija; Nykyri, Katariina

    2016-07-01

    Through simulated and experimental investigations it is well established that from a statistical standpoint, the majority of plasma properties in the magnetosheath are asymmetric between the dawn (quasi-parallel) and dusk (quasi-perpendicular) flanks. To investigate this, we have compiled a 5 year database comprising of THEMIS magnetosheath measurements which are adjusted for boundary motion, planetary aberration, and changes in the upstream solar wind state. We quantify numerous asymmetries, determine their dependency on solar wind parameters, and show that coupling to solar wind properties vary between different asymmetries. In addition, using a combination our statistical data and local Hall MHD simulations, we show that magnetosheath dawn-dusk asymmetries play a role in the efficiency of the Kelvin Helmholtz Instability and its associated plasma transport. We also discuss the global impact from magnetosheath asymmetries on magnetospheric plasma conditions such as asymmetries reported in the cold dense plasma sheet.

  11. Simultaneous measurements of the thermospheric wind profile at three separate positions in the dusk auroral oval

    NASA Technical Reports Server (NTRS)

    Mikkelsen, I. S.; Friis-Christensen, E.; Larsen, M. F.; Kelley, M. C.; Vickrey, J.

    1987-01-01

    In the present three-dimensional wind field observations in the dusk auroral oval, the F region winds appear to be at the transition from a clockwise vortex centered at dusk to an antisunward flow at the nightside of the polar cap, while the E region winds seem to be part of a gravity wave with a wind amplitude of 125 m/sec. The wave period is found to be close to three hours, on the basis of the ratio of the magnitude of the wind component normal to the direction of wave propagation to the magnitude parallel to the direction of propagation. The observations show that significant energy resides in the divergent motions that are part of the transient response in the E region, at least in this case.

  12. The far-ultraviolet main auroral emission at Jupiter - Part 1: Dawn-dusk brightness asymmetries

    NASA Astrophysics Data System (ADS)

    Bonfond, B.; Gustin, J.; Gérard, J.-C.; Grodent, D.; Radioti, A.; Palmaerts, B.; Badman, S. V.; Khurana, K. K.; Tao, C.

    2015-10-01

    The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1.1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere.

  13. A dawn-to-dusk electric field in the Jovian magnetosphere

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.; Goertz, C. K.

    1984-01-01

    It is shown that if Io-injected plasma is lost via a planetary wind a sun-fixed Birkeland current system may result. This is due to the fact that a current flows across a density gradient produced by the loss of plasma through the planetary wind in the tail. The divergent current is connected to field-aligned Birkeland currents which flow into the ionosphere at dawn and out of it at dusk. The closure currents in the ionosphere require a dawn-to-dusk electric field which at the orbit of Io is estimated to have a strength of a few mV/m. Independent estimates derived from the local time asymmetry of the torus u.v. emission indicate a field of 1.5 mV/m.

  14. Light pollution alters the phenology of dawn and dusk singing in common European songbirds

    PubMed Central

    Da Silva, Arnaud; Valcu, Mihai; Kempenaers, Bart

    2015-01-01

    Artificial night lighting is expanding globally, but its ecological consequences remain little understood. Animals often use changes in day length as a cue to time seasonal behaviour. Artificial night lighting may influence the perception of day length, and may thus affect both circadian and circannual rhythms. Over a 3.5 month period, from winter to breeding, we recorded daily singing activity of six common songbird species in 12 woodland sites, half of which were affected by street lighting. We previously reported on analyses suggesting that artificial night lighting affects the daily timing of singing in five species. The main aim of this study was to investigate whether the presence of artificial night lighting is also associated with the seasonal occurrence of dawn and dusk singing. We found that in four species dawn and dusk singing developed earlier in the year at sites exposed to light pollution. We also examined the effects of weather conditions and found that rain and low temperatures negatively affected the occurrence of dawn and dusk singing. Our results support the hypothesis that artificial night lighting alters natural seasonal rhythms, independently of other effects of urbanization. The fitness consequences of the observed changes in seasonal timing of behaviour remain unknown. PMID:25780238

  15. Light pollution alters the phenology of dawn and dusk singing in common European songbirds.

    PubMed

    Da Silva, Arnaud; Valcu, Mihai; Kempenaers, Bart

    2015-05-01

    Artificial night lighting is expanding globally, but its ecological consequences remain little understood. Animals often use changes in day length as a cue to time seasonal behaviour. Artificial night lighting may influence the perception of day length, and may thus affect both circadian and circannual rhythms. Over a 3.5 month period, from winter to breeding, we recorded daily singing activity of six common songbird species in 12 woodland sites, half of which were affected by street lighting. We previously reported on analyses suggesting that artificial night lighting affects the daily timing of singing in five species. The main aim of this study was to investigate whether the presence of artificial night lighting is also associated with the seasonal occurrence of dawn and dusk singing. We found that in four species dawn and dusk singing developed earlier in the year at sites exposed to light pollution. We also examined the effects of weather conditions and found that rain and low temperatures negatively affected the occurrence of dawn and dusk singing. Our results support the hypothesis that artificial night lighting alters natural seasonal rhythms, independently of other effects of urbanization. The fitness consequences of the observed changes in seasonal timing of behaviour remain unknown. PMID:25780238

  16. The effects of selection for early (day) and late (dusk) mating lines of hybrids of Bactrocera tryoni and Bactrocera neohumeralis.

    PubMed

    Meats, A; Pike, N; An, X; Raphael, K; Wang, W Y S

    2003-11-01

    Bactrocera neohumeralis and Bactrocera tryoni are closely related tephritid fruit fly species. B. neohumeralis mates throughout the day (in bright light) and B. tryoni mates at dusk. The two species can also be distinguished by the colour of their calli (prothoracic sclerites) which are brown and yellow, respectively. The F1 hybrids can mate both in bright light just before dusk and during dusk and have calli that are partly brown and partly yellow. The F2 hybrids have a wider range of callus patterns and mating occurs more widely in the day as well as at dusk. We directly selected hybrid stocks for mating time, creating 'early' (day-mating) and 'late' (dusk-mating) lines. As an apparently inadvertent consequence, the two types of line respectively had predominantly brown and predominantly yellow calli and thus came to closely resemble the original two species in both behaviour and appearance. Lines that were evenly selected (half for day and half for dusk) essentially retained the mating pattern of F2 hybrids. Selection for callus colour alone also affected the distribution of mating times in a predictable way. We propose a genetical model to account for the results and discuss them in the light of the apparent maintenance of species integrity in nature. PMID:14686607

  17. Dawn-dusk asymmetry and adiabatic dynamic of the radiation belt electrons during magnetic storm

    NASA Astrophysics Data System (ADS)

    Lazutin, Leonid L.

    2016-09-01

    The changes of the latitudinal profiles of outer belt energetic electrons during magnetic storms are mostly explained by the precipitation into the loss cone caused by VLF and EMIC waves or by the scattering into the magnetopause. In present work, energetic electron dynamics during magnetic storm of August 29-30, 2004 we attributed at most to the adiabatic transformation of the magnetic drift trajectories and Dst effect. This conclusion was based on the analysis of dawn-dusk asymmetry of the electron latitudinal profiles measured by low altitude polar orbiter SERVIS-1 and on the coincidence of pre-storm and after-storm profiles of radiation belt electrons and protons.

  18. Dominance of toroidal oscillations in dawn/dusk sectors: A consequence of solar wind pressure variation

    NASA Astrophysics Data System (ADS)

    Sinha, A. K.; Rajaram, R.

    2003-02-01

    The pressure variations in the solar wind produce the oscillations in surface currents at the magnetopause boundary in order to nullify the pressure imbalance. These currents introduce compressional variations in the magnetic field within the magnetosphere. The response of transverse field line oscillations to such changes in the magnetic field has been brought out in perfectly reflecting ionospheric conditions. The analysis clearly shows that the fundamental toroidal modes are dominant in the dawn and the dusk sectors as revealed by the statistical studies of pulsations observed by the satellite AMPTE/CCE (Anderson et al., 1990). It is traditionally believed that such oscillations are mainly driven by Kelvin-Helmholtz (K-H) instability (Anderson et al., 1990). Our analysis shows that the dominance of fundamental toroidal modes in the dawn and dusk sectors can also be explained in terms of response to impressed pressure impulses without invoking K-H instability. The analysis also shows that poloidal modes do not exhibit any longitudinal structures. These results are consistent with the observations (Anderson et al., 1990).

  19. F region dusk ion temperature spikes at the equatorward edge of the high-latitude convection pattern

    NASA Astrophysics Data System (ADS)

    Goodwin, L.; St.-Maurice, J.-P.; Richards, P.; Nicolls, M.; Hairston, M.

    2014-01-01

    Using Poker Flat Incoherent Scatter Radar data from the International Polar Year, we observed unexpected short-lived enhancements of a few 100 K in the F region ion temperature, or "Ti spikes", in conjunction with sharp F region plasma density drops near the dusk plasmapause. The geomagnetic conditions were moderately to weakly disturbed and the dusk spikes were often the largest Ti values recorded within the day. Taking various other observations into consideration, we conclude that the radar observed ion frictional heating events driven by large ion-neutral relative drifts caused by temporary intensifications in the convection pattern. The heating rate was enhanced through an increase in the size of the convection pattern, causing the neutrals just poleward of the dusk plasmapause to be moving antisunward while ions were moving sunward.

  20. Coherent HF radar backscatter from small-scale irregularities in the dusk sector of the subauroral ionosphere

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.; Villain, J.-P.; Baker, K. B.; Newell, P. T.

    1988-01-01

    This paper describes the characteristics of backscatter from decameter-scale ionospheric plasma density irregualarities, observed with an impressive regularity by the Goose Bay (Labrador) high-frequency (HF) radar in the dusk sector of the winter ionosphere, and discusses the relation of the scatter to the midlatitude trough. It is shown that this dusk scatter can be readily distinguished from other types of late afternoon/early evening scatter by the extreme equatorward position of its source region and by the low values of its associated radar Doppler velocities (not above 200 m/s) and spectral widths (not more than 200 m/s). A comparison of the radar observations with nearly simultaneous particle precipitation data obtained with the DMSP F6 satellite demonstrated that the source region of the backscatter lies within the subauroral ionosphere. It is shown that the characteristics of dusk scatter are compatible with the Spiro et al. (1978) model of the electrodynamics of the midlatitude trough.

  1. The Dusk Chorus from an Owl Perspective: Eagle Owls Vocalize When Their White Throat Badge Contrasts Most

    PubMed Central

    Penteriani, Vincenzo; Delgado, Maria del Mar

    2009-01-01

    Background An impressive number of studies have investigated bird vocal displays, and many of them have tried to explain the widespread phenomenon of the so-called dawn and dusk chorus, the sunrise and sunset peaks in bird song output. As many as twelve non-exclusive hypotheses have been proposed to explain why twilight peaks in vocal display might be advantageous; but, even after more than two decades of study, the basis underlying the dusk and dawn chorus is still unclear. Moreover, to date, the majority of studies on this topic have focused on songbirds. Methodology/Principal Findings We investigate here a novel hypothesis on why nocturnal birds with patches of white feathers call at twilight. We propose that white plumage patches and the timing of visual signaling have co-evolved to maximize the effectiveness of social communication such as the dusk chorus. This hypothesis centers on the recent discovery that eagle owls can adopt specific forms of visual signaling and is supported by the observation that adult eagle owls possess a white throat badge that is only visible during vocal displays. By monitoring the calling of eagle owls at dusk, a peak time for bird call output, we found that white throat badges contrasted most with the surrounding background during the owls' twilight chorusing. Conclusions/Significance Crepuscular and nocturnal species appear to have evolved white patches that, shown in association with vocal displays, allow them to communicate in dark surroundings. The evolution of a white badge that operates jointly with call displays at dawn and dusk may be relevant to the eagle owls' social dynamics. Our explanation for the dusk chorus may possibly represent an overlooked but common pattern of signaling among crepuscular and nocturnal birds that combine patches of white feathers with twilight displays. Furthermore, our findings could be relevant to songbirds that breed in dark forest habitats and have contrasting white badges, as well as birds

  2. Possible Signatures Of Kelvin-Helmholtz Waves On The Dusk Flank Of The Kronian Magnetopause

    NASA Astrophysics Data System (ADS)

    Cutler, Jack; Masters, Adam; Dougherty, Michele; Lucek, Elizabeth; Kanani, Sheila

    2010-05-01

    A comprehensive survey of crossings of both Saturn's magnetopause and bow shock on the dusk side between January 2007 and December 2007 was compiled, using data from the Cassini fluxgate magnetometer and the Cassini electron spectrometer. Bow shock and magnetopause crossings were determined by the criteria discussed in Masters et al., 2008 and Masters et al., 2009 [1] respectively. 396 magnetopause crossings and 165 bow shock crossings were identified with large spatial variation; the high temporal frequency of crossings combined with the large radial variation was indicative of highly dynamic boundaries. A set of magnetopause crossings occurring near the nose of the magnetopause on the 30th June and 1st July 2007 were then analysed using minimum variance analysis (MVA) of the magnetic field vectors over the crossing interval to determine the direction of the boundary normal at each crossing. Using MVA analysis again to calculate the maximum variance direction of the magnetopause normals, I found a clear preferred direction of variance of the normals. The normals were found to deviate by an average of 30° about the average normal direction in the plane of maximum variance, but only by 12° in the perpendicular plane. The observed oscillation of dawn side crossing normals (Masters et al., 2009) was not present throughout the whole dusk set, but was present for subsets, which is suggestive of wave activity. Considering the orientation between the magnetospheric magnetic field and the direction of maximum variance of the normals, the Kelvin-Helmholtz (K-H) instability is the likely driving force of these boundary perturbations. Current work involves analyzing two further magnetopause crossing sets, one further dusk-ward and one closer to noon (SLT), to identify whether K-H waves are also present at these locations. [1] Masters, A.; McAndrews, H. J.; Steinberg, J. T.; Thomsen, M. F.; Arridge, C. S.; Dougherty, M. K.; Billingham, L.; Schwartz, S. J.; Sergis, N

  3. Neutral winds and electric fields in the dusk auroral oval. I - Measurements

    NASA Technical Reports Server (NTRS)

    Mikkelsen, I. S.; Jorgensen, T. S.; Kelley, M. C.; Larsen, M. F.; Pereira, E.; Vickrey, J.

    1981-01-01

    Two rockets carrying an upleg and downleg trimethyl aluminum chemical trail release and three barium cannisters were launched from Poker Flat, Alaska on Feb. 28, 1978 and Mar. 2, 1978 in order to study neutral winds and electric fields in the dusk auroral oval. Electric field measurements were also made with a radar system to supplement the barium cloud data. The barium cloud drifts on both days showed intense poleward electric fields in the subauroral region. The drifts were nearly latitude-independent and were equivalent to electric fields of 60 mV/m of February 2 and 40 mV/m on March 2. The data indicate that the Lorentz force and Joule heating had a strong influence on the observed neutral winds.

  4. Vertical velocities and momentum fluxes derived from wind measurements in the dusk auroral oval

    NASA Technical Reports Server (NTRS)

    Larsen, M. F.; Mikkelsen, I. S.

    1990-01-01

    Results are presented on a chemical release experiment carried out on March 20, 1985 in connection with NASA's Cooperative Observations of Polar Electrodynamics I campaign. Simultaneous neutral wind measurements in E region were carried out at three separate locations over a triangular region with sides of about 150 km in the dusk auroral oval, and the three wind profiles were used to calculate values of divergence and vorticity over the area. The vertical velocity over the hight range was calculated using the mass continuity equation, and the instantaneous vertical momentum fluxes in the E region were derived using the combination of horizontal-wind measurements and calculated vertical velocities. Results show that there is strong coupling between layers in the E region and that the momentum-flux-induced accelerations are at least comparable in magnitude to the pressure gradient and Coriolis force accelerations.

  5. Dawn and Dusk Set States of the Circadian Oscillator in Sprouting Barley (Hordeum vulgare) Seedlings

    PubMed Central

    Deng, Weiwei; Clausen, Jenni; Boden, Scott; Oliver, Sandra N.; Casao, M. Cristina; Ford, Brett; Anderssen, Robert S.; Trevaskis, Ben

    2015-01-01

    The plant circadian clock is an internal timekeeper that coordinates biological processes with daily changes in the external environment. The transcript levels of clock genes, which oscillate to control circadian outputs, were examined during early seedling development in barley (Hordeum vulgare), a model for temperate cereal crops. Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles. A dark-to-light transition influenced transcript levels of some clock genes but triggered only weak oscillations of gene expression, whereas a light-to-dark transition triggered robust oscillations. Single light pulses of 6, 12 or 18 hours induced robust oscillations. The light-to-dark transition was the primary determinant of the timing of subsequent peaks of clock gene expression. After the light-to-dark transition the timing of peak transcript levels of clock gene also varied depending on the length of the preceding light pulse. Thus, a single photoperiod can trigger initiation of photoperiod-dependent circadian rhythms in barley seedlings. Photoperiod-specific rhythms of clock gene expression were observed in two week old barley plants. Changing the timing of dusk altered clock gene expression patterns within a single day, showing that alteration of circadian oscillator behaviour is amongst the most rapid molecular responses to changing photoperiod in barley. A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod–insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod. The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states. PMID:26068005

  6. Weak auroral emissions and particle precipitations in the dusk auroral oval

    SciTech Connect

    Ono, T.; Hirasawa, T. ); Ching-I. Meng )

    1989-09-01

    Faint auroral displays in the low-latitude region of the duskside auroral oval were examined by using 5577 A, 6300 A, and 4861 A auroral images from three monochromatic all-sky television cameras at Syowa Station, Antarctica, and simultaneous precipitating auroral particle data obtained by the U.S. Air Force/Defense Meteorological Satellite Program (USAF/DMSP) F6 satellite. In the low-latitude region of the duskside auroral oval, we found three types of auroral displays with weak optical intensity: (1) proton auroras, (2) pulsating auroras, and (3) faint discrete auroral arcs distinct only in the 6300 A emission. In usual cases, the energy input into this region is mostly carried y proton precipitations to produce proton auroras mainly at wavelengths of 4861 A and 5577 A. Pulsating features are sometimes observed in the diffuse auroral region in the dusk sector. Comparing auroral images with the nearly simultaneous data of precipitating auroral particles, we confirmed that the pulsating auroras are associated with the intensification of precipitating electron flux from the central plasma sheet. Furthermore, electrons are the main contributors to the energy input into the duskside auroral oval in this case. We also found that discrete auroras sometimes appeared in the 6300 A images, but not in images at other wavelengths. They appear in the equatorial part of the dusk auroral oval. These 6300 A discrete auroras correspond to weak precipitation spikes of low-energy electrons simultaneously measured by DMSP satellites. The flux and average energy of these electron spikes are about 10{sup 8}/(cm{sup 2} sr s) and 100 eV, respectively. They are intense enough to excite 6300 A emissions but not 5577 A emissions, as detected from the ground observations. {copyright} American Geophysical Union 1989

  7. Sunbeams from mirrors in dawn-dusk orbit for earth solar power fields

    NASA Astrophysics Data System (ADS)

    Fraas, Lewis M.

    2013-09-01

    There are two problems limiting solar electric power. The amount of sunlight is limited and there is no sunlight during peak demand in the evening hours. These problems can be addressed by placing light weight mirror satellite constellations in sun synchronous dawn to dusk low earth orbits in space at an altitude of 1000 km. These satellites can deflect sunbeams down to an array of solar power stations distributed near major population centers around the earth. These solar PV earth stations are already being built. The additional solar energy provided in the early morning and evening hours can potentially reduce the cost of solar electricity at the ground sites to less than 6 cents per kWh. Herein, a specific mirror satellite design concept is proposed with the idea that if one practical mirror satellite can be built, it then can be replicated as many times as required for a specific mission. The proposed mirror satellite is comprised of a lightweight thin aluminized mirror membrane stretched flat by three radial spokes telescoping out from a central body. Control moment gyros similar to those used in the International Space Station (ISS) are mounted inside the central body of the mirror satellite for attitude control and sunbeam pointing. The three spokes collapse and the mirror membrane is folded such that several of these mirror satellites can potentially be stowed inside the fairing of today's available rockets for launch and deployment.

  8. MMS Observations of magnetospheric fast ion flows and magnetic dipolarization near the dusk-meridian flank

    NASA Astrophysics Data System (ADS)

    Pollock, Craig; Chen, Li-Jen; Wang, Shan; Torbert, Roy; Russell, Christopher; Reiff, Patricia; Giles, Barbara; Burch, James

    2016-04-01

    The concept of a magnetic dipolarization front propagating earthward through Earth's magnetotail and accompanied by fast earthward ion flows, both as consequences of magnetic reconnection occurring tail-ward of an observation point, is well known. Examples of this phenomenology have recently been referred to as reconnection fronts. It is less common to imagine similar signature sets in contexts other than the imagined noon-midnight magnetotail configuration. Nevertheless, signatures of 800 km/s earthward ion flows were observed contemporaneously with distinct but temporary increases in the GSE-z component of the magnetic field at a geocentric distance of the order of 10 RE, in the vicinity (but somewhat tail-ward) of Earth's equatorial dusk terminator on August 12, 2015. These observations were obtained using the Fast Plasma Investigation (FPI) and the Fields electric fields experiment on NASA's Magnetospheric Multiscale (MMS) mission. Several interesting questions arise as to the nature of the observed plasma and field signatures and their drivers in cases such as this. To what degree are they analogous to the magnetotail reconnection fronts previously alluded to? And, to the degree that they are, what kind of reconnection geometry can we envision as giving rise to these signatures at such a location? We will present sample observations and discuss their significance from this point of view.

  9. A DE-1/whistler study of the thermal plasma structure and dynamics in the dusk bulge sector of the magnetosphere

    NASA Technical Reports Server (NTRS)

    Carpenter, D. L.

    1992-01-01

    The objective of this research was to obtain new understanding of the thermal plasma structure and dynamics of the plasmasphere bulge region of the magnetosphere, with special emphasis on the erosion process that results in a reduction in plasmasphere size and on the manner in which erosion leads to the presence of patches of dense plasma in the middle and outer afternoon-dusk magnetosphere. Case studies involving data from the DE 1, GEOS 2, and ISEE 1 satellites and from ground whistler stations Siple, Halley, and Kerguelen were used. A copy of the published paper entitled 'A case study of plasma structure in the dusk sector associated with enhanced magnetospheric convection,' is included.

  10. Dawn-dusk asymmetry of the appearance of low-latitude mantle plasma in the magnetotail observed by ARTEMIS

    NASA Astrophysics Data System (ADS)

    Wang, C.; Lyons, L. R.; Angelopoulos, V.

    2013-12-01

    The mantle plasma sometimes appears at low latitudes in the magnetotail and at times is mixed with the plasma sheet boundary layer plasma. Because of its density is substantially higher than the lobe plasma, the low-latitude mantle provides more particles into the tail plasma sheet than do the lobes. To investigate where and when the low-latitude mantle plasma appears, we have identified its appearance using the two ARTEMIS satellites from Oct 2010 to Dec 2012 in the magnetotail from X ~ -40 to -80 Re. The mantle plasma flows tailward along magnetic field lines with speed from ~50 to 200 km/s, and at the same time drift toward midnight and toward the equator. Its density is similar to that in the plasma sheet but its temperature is about an order of magnitude lower. Its occurrence rate can be up to 50% near the flanks and it decreases with decreasing |Y| to nearly 0% at midnight. The appearance shows a clear dawn-dusk asymmetry that depends on the IMF By direction. In the region above (below) the current sheet, it appears dominantly in the post-midnight (pre-midnight) sector when IMF By is positive (negative). The occurrence rates and the dawn-dusk asymmetries are similar for both northward and southward IMF conditions. The BATS-R-US simulations for N IMF show that the magnetopause reconnection locations and the magnetopause shape in the magnetotail change significantly with the IMF clock angles. As IMF By becomes positively larger, the magnetopause reconnection site above (below) the current sheet moves toward lower latitudes to the dawn (dusk) side. Also the magnetopause shape becomes flatter with the Z distance from the magnetopause to the current sheet becomes smaller. As a result, the plasma mantles move to lower latitudes and become closer to the plasma sheet, and the appearance of the mantle plasma becomes more dawn-dusk asymmetric.

  11. SAR arc observation as the mapping of plasmasphere dusk-bulge during a magnetic storm

    NASA Astrophysics Data System (ADS)

    Ievenko, Igor; Parnikov, Stanislav

    2016-07-01

    The stable auroral red (SAR) arcs are the consequence of interaction of the outer plasmasphere (plasmapause) with energetic ions of the ring current. In this work we analyze the observation of aurorae and SAR arc with the all-sky imager (ASI) at the Yakutsk meridian (130ºE; 200ºE, geom.) during the magnetic storm main phase on March 17, 2015. ASI registers the SAR arc with a maximum of its intensity and the latitude on the westward horizon of station from the start of observations at ~1116 UT during the decrease of magnetic activity after the main phase onset of magnetic storm at ~0630 UT. The measurements of the thermal ion fluxes with ECT HOPE Instrument aboard the Van Allen Probes B satellite at ~1230 UT testify to a plasmapause location on L ~ 3.5 at the meridian ~1825 MLT. The inner boundary of the energetic H+ and O+ ions flux has been registered by the satellite on L ~ 2.8-3.3 at the meridian ~ 1800 MLT at 1210-1220 UT. At this time ASI observes SAR arc up to a meridian 1840 MLT on the westward horizon of station. Further the dynamics of aurorae in the 557.7, 630.0, 470.9 and 486.1 (Hβ) nm emissions owing to sharp changes in the solar wind and during three substorms is observed. We consider differences in the precipitation dynamics of energetic protons and electrons during substorms. It is shown that the SAR arc registered with ASI maps the ring current overlap with the region of plasmasphere dusk-bulge or plume. The research is supported by RFBR grant No 15-05-02372 a.

  12. Dusk-to-nighttime enhancement of mid-latitude NmF2 in local summer: inter-hemispheric asymmetry and solar activity dependence

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Liu, L.; Le, H.; Wan, W.; Zhang, H.

    2015-06-01

    In this paper ionosonde observations in the East Asia-Australia sector were collected to investigate dusk-to-nighttime enhancement of mid-latitude summer NmF2 (maximum electron density of the F2 layer) within the framework of NmF2 diurnal variation. NmF2 were normalized to two solar activity levels to investigate the dependence of the dusk-to-nighttime enhancement on solar activity. The dusk-to-nighttime enhancement of NmF2 is more evident at Northern Hemisphere stations than at Southern Hemisphere stations, with a remarkable latitudinal dependence. The dusk-to-nighttime enhancement shows both increasing and declining trends with solar activity increasing, which is somewhat different from previous conclusions. The difference in the dusk-to-nighttime enhancement between Southern Hemisphere and Northern Hemisphere stations is possibly related to the offset of the geomagnetic axis from the geographic axis. hmF2 (peak height of the F2 layer) diurnal variations show that daytime hmF2 begins to increase much earlier at low solar activity level than at high solar activity level at northern Akita and Wakkanai stations where the dusk-to-nighttime enhancement is more prominent at low solar activity level than at high solar activity level. That implies neutral wind phase is possibly also important for nighttime enhancement.

  13. The dawn-dusk asymmetry of ion density in the dayside magnetosheath and its annual variability measured by THEMIS

    NASA Astrophysics Data System (ADS)

    Dimmock, Andrew P.; Pulkkinen, Tuija I.; Osmane, Adnane; Nykyri, Katariina

    2016-05-01

    The local and global plasma properties in the magnetosheath play a fundamental role in regulating solar wind-magnetosphere coupling processes. However, the magnetosheath is a complex region to characterise as it has been shown theoretically, observationally and through simulations that plasma properties are inhomogeneous, non-isotropic and asymmetric about the Sun-Earth line. To complicate matters, dawn-dusk asymmetries are sensitive to various changes in the upstream conditions on an array of timescales. The present paper focuses exclusively on dawn-dusk asymmetries, in particularly that of ion density. We present a statistical study using THEMIS data of the dawn-dusk asymmetry of ion density in the dayside magnetosheath and its long-term variations between 2009 and 2015. Our data suggest that, in general, the dawn-side densities are higher, and the asymmetry grows from noon towards the terminator. This trend was only observed close to the magnetopause and not in the central magnetosheath. In addition, between 2009 and 2015, the largest asymmetry occurred around 2009 decreasing thereafter. We also concluded that no single parameter such as the Alfvén Mach number, plasma velocity, or the interplanetary magnetic field strength could exclusively account for the observed asymmetry. Interestingly, the dependence on Alfvén Mach number differed between data sets from different time periods. The asymmetry obtained in the THEMIS data set is consistent with previous studies, but the solar cycle dependence was opposite to an analysis based on IMP-8 data. We discuss the physical mechanisms for this asymmetry and its temporal variation. We also put the current results into context with the existing literature in order to relate THEMIS era measurements to those made during earlier solar cycles.

  14. Additional stratifications in the equatorial F region at dawn and dusk during geomagnetic storms: Role of electrodynamics

    NASA Astrophysics Data System (ADS)

    Sreeja, V.; Balan, N.; Ravindran, Sudha; Pant, Tarun Kumar; Sridharan, R.; Bailey, G. J.

    2009-08-01

    The role of electrodynamics in producing additional stratifications in the equatorial F region (F 3 layer) at dawn and dusk during geomagnetic storms is discussed. Two cases of F 3 layer at dawn (0600-0730 LT on 5 October 2000 and 8 December 2000) and one case of F 3 layer at dusk (1600-1730 LT on 5 October 2000) are observed, for the first time, by the digital ionosonde at the equatorial station Trivandrum (8.5°N 77°E dip ˜ 0.5°N) in India. The unusual F 3 layers occurred during the geomagnetic storms and are associated with southward turning of interplanetary magnetic field B z , suggesting that eastward prompt penetration electric field could be the main cause of the F 3 layers. The dawn F 3 layer on 5 October is modeled using the Sheffield University Plasmasphere-Ionosphere Model by using the E × B drift estimated from the real height variation of the ionospheric peak during the morning period. The model qualitatively reproduces the dawn F 3 layer. While the existing F 2 layer rapidly drifts upward and forms the F 3 layer and topside ledge, a new layer forming at lower heights develops into the normal F 2 layer.

  15. Observations of Kelvin-Helmholtz Waves Along the Dusk-Side Boundary of Mercury's Magnetosphere During MESSENGER's Third Flyby

    NASA Technical Reports Server (NTRS)

    Boardsen, Scott A.; Sundberg, Torgjoern; Slavin, James A.; Anderson, Brian J.; Korth, Haje; Solomon, Sean C.; Blomberg, Lars G.

    2010-01-01

    During the third MESSENGER flyby of Mercury on 29 September 2009, 15 crossings of the dusk-side magnetopause were observed in the magnetic field data over a 2-min period, during which the spacecraft traveled a distance of 0.2 R(sub M) (where R(sub M) is Mercury's radius). The quasi-periodic nature of the magnetic field variations during the crossings, the characteristic time separations of approx.16 s between pairs of crossings, and the variations of the magnetopause normal directions indicate that the signals are likely the signature of surface waves highly steepened at their leading edge that arose from the Kelvin-Helmholtz instability. At Earth, the Kelvin- Helmholtz instability is believed to lead to the turbulent transport of solar wind plasma into Earth's plasma sheet. This solar wind entry mechanism could also be important at Mercury. Citation: Boardsen, S. A., T. Sundberg, J. A.Slavin, B. J. Anderson, H. Korth, S. C. Solomon, and L. G. Blomberg (2010), Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury s magnetosphere during MESSENGER's third flyby,

  16. Dawn-dusk asymmetry in solar wind ion entry and dayside precipitation: Results from large-scale simulations

    NASA Astrophysics Data System (ADS)

    Berchem, J.; Richard, R.; Escoubet, P.; Wing, S.; Pitout, F.

    2014-03-01

    We present the results of numerical studies of the interaction of solar wind ions with the dayside magnetospheric boundary for a southward interplanetary magnetic field and two solar wind speeds (250 and 500 km/s) using the results of global magnetohydrodynamics simulations in conjunction with large-scale kinetic calculations. Results of these studies show that a dawn-dusk asymmetry is found in the precipitation of low- to middle-energy ions over the high-latitude dayside magnetosphere. This asymmetry is consistent with statistical studies of DMSP data showing that ion precipitation from the mantle is predominantly seen over the morning and prenoon sector. Analysis of energy-latitude spectra and study of individual particle trajectories from the simulations revealed that low-energy ions can enter the magnetopause at high latitudes in regions where the parallel electric field associated with the magnetopause current is positive and strong enough for the ions to gain energies of the order of the parallel potential drop across the magnetopause. Because the parallel electric field in the Northern Hemisphere is positive in the prenoon sector and negative in the afternoon-evening sector, solar wind ions reaching the magnetopause in these regions are accelerated toward the ionosphere on the dawnside and outward on the duskside, creating the asymmetry in precipitation. The same dawn-dusk asymmetry is found in the Southern Hemisphere because both parallel electric field and magnetic field are reversed in direction.

  17. Dawn-Dusk Auroral Asymmetries as a Consequence of the Differential Inward Transport of Electrons and Protons (Invited)

    NASA Astrophysics Data System (ADS)

    Donovan, E.

    2013-12-01

    Electrons and ions are transported inwards in the magnetotail by quasi-steady and 'bursty' convection. Electrons and ions are drawn dawnward and duskward, respectively, by additional energy-dependent drifts, and the effects of the co-rotation electric field together conspire to create a highly asymmetric inner Central Plasma Sheet (CPS). These asymmetries have pronounced effects on the aurora, particularly so for diffuse aurora in the lower latitudes of auroral zone. Here I present an overview of these transport-related auroral asymmetries as seen in multi-spectral auroral observations from all-sky imagers and meridian scanning photometers, as well as topside in situ observations by the NASA FAST satellite. I will focus on how these asymmetries set the stage for different auroral mechanisms on the dusk and dawn sides.

  18. Dawn-dusk asymmetry in dayside ion precipitation for southward IMF: results from large-scale simulations

    NASA Astrophysics Data System (ADS)

    Berchem, J.; Richard, R. L.; Escoubet, C.; Wing, S.; Pitout, F.

    2013-12-01

    We present the results of numerical studies of the interaction of solar wind ions with the dayside magnetospheric boundary for a southward interplanetary magnetic field (IMF). These studies use the time-dependent electric and magnetic fields predicted by three-dimensional global magnetohydrodynamic (MHD) simulations to compute the trajectories of large samples of solar wind ions launched upstream of the bow shock. Energy-latitude spectra computed from the large scale kinetic (LSK) simulations show that a strong dawn-dusk asymmetry develops in the precipitation of low to middle energy ions over the high-latitude dayside magnetosphere. These results are consistent with statistical studies of DMSP data showing that ion precipitation from the mantle is predominantly seen over the morning and pre-noon sector.

  19. The Wonder and Enrichment of Teaching Wright Morris's "A Fight between a White Boy and a Black Boy in the Dusk of a Fall Afternoon in Omaha, Nebraska."

    ERIC Educational Resources Information Center

    McCaffrey, Jerrine

    2001-01-01

    Outlines a teaching method for Wright Morris's "A Fight Between a White Boy and a Black Boy in the Dusk of a Fall Afternoon in Omaha, Nebraska." Proposes that the story provides and opportunity to introduce stream-of-consciousness writing and to convey the significance of memory recall. (PM)

  20. Dawn-dusk asymmetry in ion pitch-angle anisotropy in the near-Earth magnetosphere and tail plasma sheet

    NASA Astrophysics Data System (ADS)

    Wang, C.; Zaharia, S. G.; Lyons, L. R.; Angelopoulos, V.

    2012-12-01

    We found a strong dawn-dusk asymmetry in ion pitch-angle anisotropy from spatial distributions statistically determined using THEMIS observations. The asymmetry varies significantly with ion energies and is a result of different processes. The anisotropy of ions below several hundreds eV in the tail plasma sheet (beyond X = 10 Re) and the near-Earth magnetosphere (inside r = 10 Re) is dominantly negative (relatively higher particle fluxes near 0 and 180 degree pitch-angle) and is more strongly negative in the post-midnight sector than the pre-midnight sector. The negative anisotropy is likely caused by field-aligned ionosphere outflow and the post-midnight enhancement is correlated with stronger electron precipitation energy fluxes that create stronger outflow. For ions between 1 to 10 keV in the near-Earth magnetosphere, anisotropy is found to be strongly positive (relatively higher fluxes near 90 degree pitch-angle) in the morning sector while near isotropic in the evening sector. Comparing the fluxes within the region of the positive anisotropy with other MLTs suggests that the positive anisotropy is caused by field-aligned ions not being able to drift as earthward as 90 degree ions. For ions of 10 keV and above, magnetic drift shell splitting results in strongly positive anisotropy on the dayside, while additional magnetopause shadowing causes strongly negative anisotropy in the post-midnight sector.

  1. A statistical study into the spatial distribution and dawn-dusk asymmetry of dayside magnetosheath ion temperatures as a function of upstream solar wind conditions

    NASA Astrophysics Data System (ADS)

    Dimmock, A. P.; Nykyri, K.; Karimabadi, H.; Osmane, A.; Pulkkinen, T. I.

    2015-04-01

    The magnetosheath contains the shocked solar wind and behaves as a natural filter to the solar wind plasma before it reaches the magnetosphere. The redistribution of kinetic energy at the bow shock results in significant thermalization of the solar wind plasma, resulting in a magnetosheath temperature profile which is highly nonhomogeneous and nonisotropic and differs between the dawn and dusk flanks. The present study attempts to study the spatial distribution of magnetosheath ion temperature as a function of upstream solar wind conditions. We pay particular attention to the dawn/dusk asymmetry in which we attempt to quantify using experimental data collected over a 7 year period. We also compare these data to simulated data from both the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme (BATS-R-US) MHD code and a kinetic hybrid model. We present evidence that the dawn flank is consistently hotter than the dusk flank for a variety of upstream conditions. Our statistical data also suggest a dependency on solar wind speed such that the level of asymmetry increases with faster speeds. We conclude that the dawn-favored asymmetry of the magnetosheath seed population is insufficient to explain the dawn asymmetry (30-40%) of cold component ions in the cold, dense plasma sheet, and therefore, other mechanisms are likely required.

  2. The dawn-dusk length of the X line in the near-Earth magnetotail: Geotail survey in 1994-2014

    NASA Astrophysics Data System (ADS)

    Nagai, Tsugunobu; Shinohara, Iku; Zenitani, Seiji

    2015-10-01

    The dawn-dusk length of the X line is investigated for magnetic reconnection in association with substorms in the near-Earth magnetotail on the basis of the 21 year Geotail plasma sheet observations. The X line is identified as a simultaneous plasma flow Vx and magnetic field Bz reversal inside the ion-electron decoupling region of magnetic reconnection. Forty-four X lines can be found at XGSM = -20 to -31 RE in the magnetotail. The X line length is estimated on the basis of occurrence of magnetic reconnection. Characteristics of flows and fields are investigated for magnetic reconnection and tailward flow events to verify the obtained X line length. The dawn-dusk length of the X line is most likely 6 RE with its center in the premidnight sector for moderate substorms. Hence, the magnetic reconnection site is mapped to approximately 1 h local time sector in the auroral ionosphere. The dawn-dusk length of the X line is extended mainly dawnward for larger substorms.

  3. Control of the Polarity of the Interplanetary Magnetic Field on the Dawn-Dusk Symmetry of the Magnetopause

    NASA Astrophysics Data System (ADS)

    Shue, J.; Jhuang, B.; Song, P.; Safrankova, J.; Nemecek, Z.; Russell, C. T.; Chen, S.

    2008-12-01

    The solar wind dynamic pressure is reduced when the solar wind flows around the magnetosphere due to the diversion of the flows. The magnetopause is the boundary where the reduced dynamic pressure is balanced with the magnetic pressure of the compressed magnetosphere by the solar wind. The size and shape of the magnetopause have long been considered among the most important parameters in Solar Terrestrial physics. Previous models of the size and shape of the magnetopause often assumed the axis- symmetry of the magnetopause with respect to the Sun-Earth line. With a large number of magnetopause crossings by ISEE-1 and -2, AMPTE/IRM, Hawkeye, Geotail, Interball-1, and Magion-4, we are able to consider the asymmetry of the magnetopuase. In the Shue et al. [1997] model, the magnetopause was modeled by two parameters, r0 and alpha, representing the subsolar standoff distance and the flaring level of the magnetopause, respectively. Parameter alpha was assumed to be independent of phi in the Shue et al. [1997] model, where phi is the angle between the Z axis and the mapping of the radial vector of the magnetopause on the YZ plane. In the present study we allow alpha to be a function of phi. We separate crossings with different phis and fit them in each bin to the new functional form proposed by Shue et al. [1997]. We find that the magnetopause is symmetric in the dawn-dusk direction for northward IMF. However, its size on the dawnside becomes larger when the IMF is southward. The function of alpha in terms of phi can be combined with the 2-D Shue et al. [1997] model into a 3-D magnetopause model. (Shue, J.-H., J. K. Chao, H. C. Fu, C. T. Russell, P. Song, K. K. Khurana, and H. J. Singer, A new functional form to study the solar wind control of the magnetopause size and shape, J. Geophys. Res., 102, 9497, 1997.)

  4. MHD instability with dawn-dusk symmetry in near-Earth plasma sheet during substorm growth phase*

    NASA Astrophysics Data System (ADS)

    Zhu, P.; Raeder, J.; Hegna, C.; Sovinec, C.

    2010-12-01

    Recent global MHD simulations of March 23, 2007 THEMIS substorm event using the OpenGGCM code have confirmed the presence of both high-ky ballooning modes and zero-ky instabilities in the near-Earth plasma sheet during the substorm growth phase [Raeder et al 2010]. These results are consistent with findings from earlier analyses [Siscoe et al 2009; Zhu et al 2009]. Here ky is the azimuthal wavenumber in the dawn-dusk direction. However, the nature and role of the ky=0 mode, as well as its interaction with the high ky ballooning modes, in the process leading to the expansion onset remain unclear. In this work, we focus on the stability properties of the ky=0 mode. A re-evaluation of the tail-tearing mode criterion by Sitnov and Schindler (2009) suggested that the dipolarization front (DF) structure identified in THEMIS observations [Runov et al 2009] could be tearing-unstable. Linear calculations using the NIMROD code have found a growing tearing mode in a generalized Harris sheet with a DF-like structure, which is also a unique feature closely correlated with the appearance of zero-ky mode in the OpenGGCM simulation. The ideal-MHD energy principle analysis is used to address the question whether the ky=0 mode is an ideal or resistive MHD instability. We further compare the linear and nonlinear tail-tearing mode in NIMROD simulations with the ky=0 mode from OpenGGCM simulations. *Supported by NSF Grants AGS-0902360 and PHY-0821899. References: Raeder, J., P. Zhu, Y.-S. Ge, and G. Siscoe (2010), Tail force imbalance and ballooning instability preceding substorm onset, submitted to J. Geophys. Res. Runov, A., et al. (2009), Geophys. Res. Lett., 36, L14106. Siscoe, G.L., M.M. Kuznetsova, and J. Raeder (2009), Ann. Geophys., 27, 3141. Sitnov, M.I. and K. Schindler (2010), Geophys. Res. Lett., 37, L08102. Zhu, P., J. Raeder, K. Germaschewski, and C.C. Hegna (2009), Ann. Geophys., 27, 1129.

  5. M-I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

    NASA Astrophysics Data System (ADS)

    Sandholt, P. E.; Farrugia, C. J.; Denig, W. F.

    2014-04-01

    We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δ Bz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross

  6. Low-Frequency Wave Activity Detected by MMS during Dusk Magnetopause Crossings and its Relation to Heating and Acceleration of Particles

    NASA Astrophysics Data System (ADS)

    Le Contel, O.; Roux, A.; Retino, A.; Mirioni, L.; Sahraoui, F.; Chust, T.; Berthomier, M.; Chasapis, A.; Aunai, N.; Leroy, P.; Alison, D.; Lavraud, B.; Lindqvist, P. A.; Khotyaintsev, Y. V.; Vaivads, A.; Marklund, G. T.; Burch, J. L.; Torbert, R. B.; Moore, T.; Ergun, R. E.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Macri, J.; Russell, C. T.; Magnes, W.; Strangeway, R. J.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Leinweber, H. K.; Anderson, B. J.; Nakamura, R.; Argall, M. R.; Le, G.; Slavin, J. A.; Kepko, L.; Baumjohann, W.; Pollock, C. J.; Mauk, B.; Fuselier, S. A.; Goodrich, K.; Wilder, F. D.

    2015-12-01

    Since the 9th of July, the MMS fleet of four satellites have evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and an apogee of 12 earth radii on the dusk side. In this study we report on ultra-low (1 mHz to ~10 Hz) and very-low (10 Hz to ~ 4 kHz) frequency wave activity measured by the four satellites during several crossings of the dusk equatorial magnetopause. Since the Larmor radius of magnetosheath protons is of the order of 50 km, this inter-satellite distance allows us to investigate in detail the physics of the magnetopause at proton scales including current structures related to Kelvin-Helmholtz instability as well as other energy transfer processes. From wave polarization analysis, we characterize the different types of emissions and discuss different mechanisms of heating and acceleration of particles. In particular, we focus on the electron heating by kinetic Alfvén waves and lower hybrid waves and the electron acceleration by oblique whistler mode waves, which have been suggested as possible mechanisms from previous Cluster and THEMIS measurements.

  7. Photoperiod-dependent changes in the phase of core clock transcripts and global transcriptional outputs at dawn and dusk in Arabidopsis.

    PubMed

    Flis, Anna; Sulpice, Ronan; Seaton, Daniel D; Ivakov, Alexander A; Liput, Magda; Abel, Christin; Millar, Andrew J; Stitt, Mark

    2016-09-01

    Plants use the circadian clock to sense photoperiod length. Seasonal responses like flowering are triggered at a critical photoperiod when a light-sensitive clock output coincides with light or darkness. However, many metabolic processes, like starch turnover, and growth respond progressively to photoperiod duration. We first tested the photoperiod response of 10 core clock genes and two output genes. qRT-PCR analyses of transcript abundance under 6, 8, 12 and 18 h photoperiods revealed 1-4 h earlier peak times under short photoperiods and detailed changes like rising PRR7 expression before dawn. Clock models recapitulated most of these changes. We explored the consequences for global gene expression by performing transcript profiling in 4, 6, 8, 12 and 18 h photoperiods. There were major changes in transcript abundance at dawn, which were as large as those between dawn and dusk in a given photoperiod. Contributing factors included altered timing of the clock relative to dawn, light signalling and changes in carbon availability at night as a result of clock-dependent regulation of starch degradation. Their interaction facilitates coordinated transcriptional regulation of key processes like starch turnover, anthocyanin, flavonoid and glucosinolate biosynthesis and protein synthesis and underpins the response of metabolism and growth to photoperiod. PMID:27075884

  8. Electrodynamics of the Inner Magnetosphere Observed in the Dusk Sector by CRRES and DMSP during the Magnetic Storm of June 4-6, 1991

    NASA Technical Reports Server (NTRS)

    Bruke, W. J.; Maynard, N. C.; Hagan, M. P.; Wolf, R. A.; Wilson, G. R.; Gentile, L. C.; Gussenhoven, M. S.; Huang, C. Y.; Garner, T. W.; Rich, F. J.

    1998-01-01

    We compare equatorward/earthward boundaries of convection electric fields and auroral/plasma sheet electrons detected by the DMSP F8 and CRRES satellites during the June 1991 magnetic storm. Measurements come from the dusk magnetic local time sector where the ring current penetrates closest to the Earth. The storm was triggered by a rapid increase in the solar wind dynamic pressure accompanied by a southward turning of the interplanetary magnetic field (IMF). Satellite data show the following: (1) all particle and field boundaries moved equatorward/earthward during the initial phase, probably in response to the strong southward IMF turning; (2) electric field boundaries were either at lower magnetic L shells or close to the inner edge of ring current ions throughout the main and early recovery phases. Penetration earthward of the ring current occurred twice as the polar cap potential increased rapidly; (3) electric potentials at subauroral latitudes were large fractions of the total potentials in the afternoon cell, twice exceeding 60 kV; and (4) the boundaries of auroral electron precipitation were more variable than those of electric fields and mapped to lower L shells than where CRRES encountered plasma sheet electrons. Observations qualitatively agree with predictions of empirical models for auroral electron and electric field boundaries.

  9. The reason "Why" graze cattle at dusk

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This work aimed and designed to assess the impact of timing of herbage allocation and fasting on patterns of ingestive behavior, herbage intake, ruminal fermentation, and nutrient flow to the duodenum. Treatments were daily herbage allocation in the afternoon (1500, AHA), morning (0800, MHA), AHA af...

  10. The dusk flank of Jupiter's magnetosphere.

    PubMed

    Kurth, W S; Gurnett, D A; Hospodarsky, G B; Farrell, W M; Roux, A; Dougherty, M K; Joy, S P; Kivelson, M G; Walker, R J; Crary, F J; Alexander, C J

    2002-02-28

    Limited single-spacecraft observations of Jupiter's magnetopause have been used to infer that the boundary moves inward or outward in response to variations in the dynamic pressure of the solar wind. At Earth, multiple-spacecraft observations have been implemented to understand the physics of how this motion occurs, because they can provide a snapshot of a transient event in progress. Here we present a set of nearly simultaneous two-point measurements of the jovian magnetopause at a time when the jovian magnetopause was in a state of transition from a relatively larger to a relatively smaller size in response to an increase in solar-wind pressure. The response of Jupiter's magnetopause is very similar to that of the Earth, confirming that the understanding built on studies of the Earth's magnetosphere is valid. The data also reveal evidence for a well-developed boundary layer just inside the magnetopause. PMID:11875558

  11. Let’s graze the cattle at dusk

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Research conducted in Argentina, US, Australia and Europe has shown significant variations in chemical composition of pasture throughout the day, which results in an increase in pasture digestibility and energy concentration as the day progresses. Cattle have adapted their grazing patterns during th...

  12. Linking pasture and animal processes. Why graze cattle at dusk?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This work aimed and designed to assess the impact of timing of herbage allocation and fasting on patterns of ingestive behavior, herbage intake, ruminal fermentation, and nutrient flow to the duodenum. Treatments were daily herbage allocation in the afternoon (1500, AHA), morning (0800, MHA), AHA af...

  13. Dusk Lighting of Layered Textures in 'Cape Verde'

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Full-shade lighting in the late Martian afternoon helps make details visible in this view of the layered cliff face of the 'Cape Verde' promontory making up part of the rim of Victoria Crater in the Meridiani Planum region of equatorial Mars.

    NASA's Mars Exploration Rover Opportunity used its panoramic camera (Pancam) to shoot the dozens of individual images that have been combined into this mosaic. Opportunity was inside Victoria Crater and near the base of the cliff when it took these images on the 1,579th and 1,580th Martian days, or sols, of the mission (July 2 and 3, 2008).

    Photographing the promontory from this position in Victoria Crater presented challenges for the rover team. The geometry was such that Cape Verde was between the rover and the sun, which could cause a range of negative effects, from glinting off Pancam's dusty lenses to shadowing on the cliff face. The team's solution was to take the images for this mosaic just after the sun disappeared behind the crater rim, at about 5:30 p.m. local solar time. The atmosphere was still lit, but no direct sunlight was illuminating the wall of Cape Verde.

    The result is a high-resolution view of Cape Verde in relatively uniform diffuse sky lighting across the scene.

    Pancam used a clear filter for taking the images for this mosaic. Capturing images in low-light situations was one of the main motivations for including the clear filter among the camera's assortment of filters available for use.

    The face of Cape Verde is about 6 meters (20 feet) tall. Victoria Crater, at about 800 meters (one-half mile) wide, is the largest and deepest crater that Opportunity has visited. It sits more than 5 kilometers (almost 4 miles) away from Opportunity's Eagle Crater landing site. Researchers sent Opportunity into Victoria Crater to study the rock layers exposed inside. The textures seen in the rock layers of Cape Verde suggest that the exposed layers were originally deposited by wind.

  14. Statistics of intense dawn-dusk currents in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Petrukovich, A. A.; Nakamura, R.; Zelenyi, L. M.

    2015-05-01

    We consider Cluster observations of events with an intense current density (>5 nA/m2) in the magnetotail current sheet. We use measurements by Cluster mission in the central magnetotail (X <- 16 RE, |Y|<10 RE, and |Bx|<10 nT) in the 2003 season when the spacecraft separation was about ˜300 km. For this season, when Cluster can probe very small scale currents, we collect the statistics of observations of strong current densities jy (in GSM coordinate system) and compare curlometer data with plasma parameters. The most intense currents are observed under disturbed conditions (plasma flow vx>300 km/s). We introduce the parameter vD/vTi (where vD=jy/ene, ne is an electron density, and vTi is a proton thermal velocity) and show that cases with vD/vTi˜1 correspond to the most intense currents observed in the vicinity of the reconnection regions. The comparison of electron and proton velocities demonstrates that electron often carry almost the entire current measured by a curlometer technique. The strong electron temperature anisotropy Te∥/Te⊥>1.2 corresponds to large magnitudes of By component of the magnetic field. We conclude that intense current sheets are often characterized by significant (more than 30%) contribution of electron curvature currents to the cross-tail current. The comparison of observations and models shows that the electron anisotropy level is likely controlled by competition of two processes: the electron scattering on fluctuations generated by fire-hose instability and the acceleration in sheared magnetic field configurations. We also suggest that current sheets embedded into the strong plasma flows (vx/vTi>0.1) can be balanced by ion flow anisotropy.

  15. From dusk till dawn: nocturnal and diurnal pollination in the epiphyte Tillandsia heterophylla (Bromeliaceae).

    PubMed

    Aguilar-Rodríguez, P A; Krömer, T; García-Franco, J G; MacSwiney G, M C

    2016-01-01

    In order to compare the effectiveness of diurnal and nocturnal pollinators, we studied the reproductive biology and pollinators of Tillandsia heterophylla E. Morren, an epiphytic tank bromeliad endemic to southeastern Mexico. Since anthesis in T. heterophylla is predominantly nocturnal but lasts until the following day, we hypothesised that this bromeliad would receive visits from both diurnal and nocturnal visitors, but that nocturnal visitors would be the most effective pollinators, since they arrive first to the receptive flower, and that bats would be the most frequent nocturnal visitors, given the characteristics of the nectar. Flowering of T. heterophylla began in May and lasted until July. The species is fully self-compatible, with an anthesis that lasts for ca. 15-16 h. Mean volume of nectar produced per flower was 82.21 μl, with a mean sugar concentration of 6.33%. The highest volume and concentration of nectar were found at 20:00 h, with a subsequent decline in both to almost zero over the following 12-h period. T. heterophylla has a generalist pollination system, since at least four different morphospecies of visitors pollinate its flowers: bats, moths, hummingbirds and bees. Most of the pollinating visits corresponded to bats and took place in the early evening, when stigma receptivity had already begun; making bats the probable pollinator on most occasions. However, diurnal pollinators may be important as a 'fail-safe' system by which to guarantee the pollination of T. heterophylla. PMID:25683682

  16. From dusk till dawn: the Arabidopsis thaliana sugar starving responsive network.

    PubMed

    Arias, Maria C; Pelletier, Sandra; Hilliou, Frédérique; Wattebled, Fabrice; Renou, Jean-Pierre; D'Hulst, Christophe

    2014-01-01

    Plant growth and development are tightly controlled by photosynthetic carbon availability. The understanding of mechanisms governing carbon partitioning in plants will be a valuable tool in order to satisfy the rising global demand for food and biofuel. The goal of this study was to determine if sugar starvation responses were transcriptionally coordinated in Arabidopsis thaliana. A set of sugar-starvation responsive (SSR) genes was selected to perform a co-expression network analysis. Posteriorly, a guided-gene approach was used to identify the SSR-network from public data and to discover candidate regulators of this network. In order to validate the SSR network, a global transcriptome analysis was realized on three A. thaliana starch-deficient mutants. The starch-deficient phenotype in leaves induces sugar starvation syndrome at the end of the night due to the absence of photosynthesis. Promoter sequences of genes belonging to the SSR-network were analyzed in silico reveling over-represented motifs implicated in light, abscisic acid, and sugar responses. A small cluster of protein encoding genes belonging to different metabolic pathways, including three regulatory proteins, a protein kinase, a transcription factor, and a blue light receptor, were identified as the cornerstones of the SSR co-expression network. In summary, a large transcriptionally coordinated SSR network was identified and was validated with transcriptional data from three starch-deficient mutant lines. Candidate master regulators of this network were point out. PMID:25295047

  17. From dusk till dawn: the Arabidopsis thaliana sugar starving responsive network

    PubMed Central

    Arias, Maria C.; Pelletier, Sandra; Hilliou, Frédérique; Wattebled, Fabrice; Renou, Jean-Pierre; D'Hulst, Christophe

    2014-01-01

    Plant growth and development are tightly controlled by photosynthetic carbon availability. The understanding of mechanisms governing carbon partitioning in plants will be a valuable tool in order to satisfy the rising global demand for food and biofuel. The goal of this study was to determine if sugar starvation responses were transcriptionally coordinated in Arabidopsis thaliana. A set of sugar-starvation responsive (SSR) genes was selected to perform a co-expression network analysis. Posteriorly, a guided-gene approach was used to identify the SSR-network from public data and to discover candidate regulators of this network. In order to validate the SSR network, a global transcriptome analysis was realized on three A. thaliana starch-deficient mutants. The starch-deficient phenotype in leaves induces sugar starvation syndrome at the end of the night due to the absence of photosynthesis. Promoter sequences of genes belonging to the SSR-network were analyzed in silico reveling over-represented motifs implicated in light, abscisic acid, and sugar responses. A small cluster of protein encoding genes belonging to different metabolic pathways, including three regulatory proteins, a protein kinase, a transcription factor, and a blue light receptor, were identified as the cornerstones of the SSR co-expression network. In summary, a large transcriptionally coordinated SSR network was identified and was validated with transcriptional data from three starch-deficient mutant lines. Candidate master regulators of this network were point out. PMID:25295047

  18. Seasonal Differences in the Dusk Equatorial Topside Ionosphere Measured by C/NOFS and DMSP

    NASA Astrophysics Data System (ADS)

    Hairston, M. R.; Coley, W. R.; Heelis, R. A.

    2009-12-01

    The C/NOFS spacecraft is in a near-equatorial elliptical orbit with an apogee of about 845 km which precesses through all local times over a period of about 66 days. The four operational DMSP spacecraft are in sun-synchronous circular polar orbits at roughly the same altitude as C/NOFS’s apogee. Thus the C/NOFS apogee overlaps with the DMSP duskside orbits every 66 days for a period of about two weeks. This work will present the analysis of three of these overlap periods during the northern winter (roughly December 30, 2008-January 12, 2009), the northern summer (roughly July 14-31, 2009), and one equinox period (roughly March 6-21, 2009) where we will use the combined C/NOFS and DMSP data to show the seasonal changes in ion density, composition, and temperature in the topside ionosphere. This will allow a further validation of the CINDI plasma instruments on C/NOFS as well as establishing a baseline of these geophysical parameters in the topside ionosphere through all seasons during the current extreme solar minimum conditions.

  19. Equatorial disc and dawn-dusk currents in the frontside magnetosphere of Jupiter - Pioneer 10 and 11

    NASA Technical Reports Server (NTRS)

    Jones, D. E.; Thomas, B. T.; Melville, J. G., II

    1981-01-01

    Observations by Pioneer 10 and 11 show that the strongest azimuthal fields are observed near the dawn meridian (Pioneer 10) while the weakest occur near the noon meridian (Pioneer 11), suggesting a strong local time dependence for the corresponding radial current system. Modeling studies of the radial component of the field observed by both spacecraft suggest that the corresponding azimuthal current system must also be a strong function of local time. Both the azimuthal and the radial field component signatures exhibit sharp dips and reversals, requiring thin radial and azimuthal current systems. There is also a suggestion that these two current systems either are interacting or are due, at least in part, to the same current. It is suggested that a plausible current model consists of the superposition of a thin, local-time-independent azimuthal current system plus the equatorial portion of a tail-like current system that extends into the dayside magnetosphere.

  20. From dawn till dusk: Shedding light on the recovery process by investigating daily change patterns in fatigue.

    PubMed

    Hülsheger, Ute R

    2016-06-01

    Although the notion that recovery is a process rather than a state lies at the heart of recovery theory, the continuous cycle of depletion and replenishment of resources itself has not yet been investigated empirically. In the present article, I therefore build on recovery theory and on evidence from chronobiological research and adopt a temporal research approach that allows investigating change trajectories in fatigue over the course of the day. Furthermore, the role of sleep quality and psychological detachment in these change trajectories is investigated. Hypotheses are tested in an experience-sampling study involving 133 employees who were asked to provide fatigue ratings 4 times a day over 5 consecutive workdays. Growth curve analyses revealed that on average fatigue decreased in the morning, reaching a nadir around midday and then increased until bedtime. Additionally, daily sleep quality explained variation in individuals' fatigue change trajectories: When sleep quality was low, next day fatigue decreased between morning and midday and then increased again until bedtime; when sleep quality was high, fatigue remained stable until midday and then increased again between the end of work and bedtime. Theoretical implications for the recovery literature and practical implications are discussed in conclusion. (PsycINFO Database Record PMID:26949820

  1. Dawn-dusk asymmetry of the tail region of the magnetosphere of Saturn and the interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.; Roederer, M.; Krimigis, S. M.

    1982-01-01

    In connection with the findings of the Voyager 1 mission, it appears that the tail lobe of Saturn is very different from that of earth and Jupiter, in that the latter are devoid of energetic particles, and magnetic field lines in this region are thought to be open and interconnecting with the interplanetary magnetic field at large distances in the antisolar direction. The present investigation is concerned with a possible explanation of these observations, taking into account a model of Saturn's magnetosphere. It is shown that the Voyager 1 spacecraft remained in the closed region of the magnetotail during its entire tail traversal and did not have an opportunity to penetrate into the high latitude lobe. It is concluded that Saturn probably has a tail lobe just like earth and Jupiter. However, this tail lobe was not traversed by Voyager.

  2. Cluster observations of the dusk flank magnetopause near the sash: Ion dynamics and flow-through reconnection

    NASA Astrophysics Data System (ADS)

    Maynard, Nelson C.; Farrugia, Charles J.; Burke, William J.; Ober, Daniel M.; Mozer, Forrest S.; Rème, Henri; Dunlop, Malcolm; Siebert, Keith D.

    2012-10-01

    Compared to the dayside, dynamics on the flanks of the magnetopause are poorly understood. To help bridge this knowledge gap we analyzed Cluster plasma and field measurements acquired during a 90-min period on 20 November 2003 when Cluster crossed the magnetopause four times in the vicinity of the sash. MHD simulations provide a context for Cluster observations. Crossings were between the magnetosheath and an S-shaped plasma sheet, rather than to the open-field lobes of the magnetotail. Cluster encountered two regions of MHD-breaking differences between perpendicular ion velocities and E × B convection. Ion adiabatic expansion parameter (δi) calculations show that ion gyrotropy was not broken during an episode of strong Alfvén wave activity in the magnetosheath. However, gyrotropy was broken (δi > 1) during the fourth magnetopause crossing. In the magnetosheath, ion guiding-center motion was maintained but inertial effects associated with temporally varying electric fields are probable sources of velocity differences. Regarding the magnetopause crossing, the generalized Ohm's law limits possible sources for breaking ion gyrotropy to inertial forces and/or electron pressure gradients associated with a nearby reconnection event. We suggest that Cluster witnessed effects of a temporally varying and spatially limited, flow-through reconnection event between open mantle field lines from the two polar caps adding new closed flux to the LLBL at the sash. Future modeling of flank dynamics must consider inertial forces as significant drivers at the magnetopause and in the adjacent magnetosheath.

  3. Investigation of sudden electron density depletions observed in the dusk sector by the Poker Flat, Alaska incoherent scatter radar in summer

    NASA Astrophysics Data System (ADS)

    Richards, P. G.; Nicolls, M. J.; St.-Maurice, J.-P.; Goodwin, L.; Ruohoniemi, J. M.

    2014-12-01

    This paper investigates unusually deep and sudden electron density depletions (troughs) observed in the Poker Flat (Alaska) Incoherent Scatter Radar data in middle summer of 2007 and 2008. The troughs were observed in the premidnight sector during periods of weak magnetic and solar activity. The density recovered to normal levels around midnight. At the time when the electron density was undergoing its steep decrease, there was usually a surge of the order of 100 to 400 K in the ion temperature that lasted less than 1 h. The Ti surges were usually related to similar surges in the AE index, indicating that the high-latitude convection pattern was expanding and intensifying at the time of the steep electron density drop. The convection patterns from the Super Dual Auroral Radar Network also indicate that the density troughs were associated with the expansion of the convection pattern to Poker Flat. The sudden decreases in the electron density are difficult to explain in summer because the high-latitude region remains sunlit for most of the day. This paper suggests that the summer density troughs result from lower latitude plasma that had initially been corotating in darkness for several hours post sunset and brought back toward the sunlit side as the convection pattern expanded. The magnetic declination of ~22° east at 300 km at Poker Flat greatly facilitates the contrast between the plasma convecting from lower latitudes and the plasma that follows the high-latitude convection pattern.

  4. Comparison of Dawn and Dusk Precipitating Electron Energy Populations Shortly After the Initial Shock for the January 10th, 1997 Magnetic Cloud

    NASA Technical Reports Server (NTRS)

    Spann, J.; Germany, G.; Swift, W.; Parks, G.; Brittnacher, M.; Elsen, R.

    1997-01-01

    The observed precipitating electron energy between 0130 UT and 0400 UT of January 10 th, 1997, indicates that there is a more energetic precipitating electron population that appears in the auroral oval at 1800-2200 UT at 030) UT. This increase in energy occurs after the initial shock of the magnetic cloud reaches the Earth (0114 UT) and after faint but dynamic polar cap precipitation has been cleared out. The more energetic population is observed to remain rather constant in MLT through the onset of auroral activity (0330 UT) and to the end of the Polar spacecraft apogee pass. Data from the Ultraviolet Imager LBH long and LBH short images are used to quantify the average energy of the precipitating auroral electrons. The Wind spacecraft located about 100 RE upstream monitored the IMF and plasma parameters during the passing of the cloud. The affects of oblique angle viewing are included in the analysis. Suggestions as to the source of this hot electron population will be presented.

  5. Melatonin Signal Transduction Pathways Require E-Box-Mediated Transcription of Per1 and Per2 to Reset the SCN Clock at Dusk

    PubMed Central

    Kandalepas, Patty C.; Mitchell, Jennifer W.; Gillette, Martha U.

    2016-01-01

    Melatonin is released from the pineal gland into the circulatory system at night in the absence of light, acting as “hormone of darkness” to the brain and body. Melatonin also can regulate circadian phasing of the suprachiasmatic nucleus (SCN). During the day-to-night transition, melatonin exposure advances intrinsic SCN neural activity rhythms via the melatonin type-2 (MT2) receptor and downstream activation of protein kinase C (PKC). The effects of melatonin on SCN phasing have not been linked to daily changes in the expression of core genes that constitute the molecular framework of the circadian clock. Using real-time RT-PCR, we found that melatonin induces an increase in the expression of two clock genes, Period 1 (Per1) and Period 2 (Per2). This effect occurs at CT 10, when melatonin advances SCN phase, but not at CT 6, when it does not. Using anti-sense oligodeoxynucleotides (α ODNs) to Per 1 and Per 2, as well as to E-box enhancer sequences in the promoters of these genes, we show that their specific induction is necessary for the phase-altering effects of melatonin on SCN neural activity rhythms in the rat. These effects of melatonin on Per1 and Per2 were mediated by PKC. This is unlike day-active non-photic signals that reset the SCN clock by non-PCK signal transduction mechanisms and by decreasing Per1 expression. Rather, this finding extends roles for Per1 and Per2, which are critical to photic phase-resetting, to a nonphotic zeitgeber, melatonin, and suggest that the regulation of these clock gene transcripts is required for clock resetting by diverse regulatory cues. PMID:27362940

  6. How long and when should I graze my cattle?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cattle instinctively concentrate grazing during dusk, when pasture is more nutritive. Afternoon allocations of fresh pasture increase duration and intensity of dusk grazing bouts and consequently pasture intake at that time of day, which certainly has demonstrated to improve animal performance when ...

  7. A Few Hours Grazing Session Seems To Be Enough

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cattle instinctively intensify grazing during dusk, when pasture is more nutritive. Afternoon allocations of fresh pasture (PM) increase duration and intensity of dusk grazing bouts and consequently pasture intake at that time of day, which certainly has demonstrated to improve animal performance wh...

  8. Solar wind control of the low-latitude asymmetric magnetic disturbance field

    NASA Technical Reports Server (NTRS)

    Clauer, C. R.; Mcpherron, R. L.; Searls, C.

    1983-01-01

    The extent to which the low latitude dawn-dusk magnetic asymmetry is controlled by the dawn-dusk solar wind motional electric field VBs and/or substorm processes measured by the westward auroral electrojet index AL is studied using the technique of empirical linear prediction filters. A new index, (ASYM), defined as the difference between dawn and dusk deviations in the X (geomagnetic Northward) magnetic field component, is used to measure the dawn-dusk asymmetry. Quantitative information which characterizes the coupling processes are provided by the empirically determined filters obtained from this analysis. Results indicate that some currents are directly driven by the solar wind-magnetosphere interaction and that their magnetic perturbations contribute to both the AL and ASYM indices. However, a portion of the AL index that is uncorrelated with VBs is correlated with ASYM which suggests that internal magnetospheric processes also contribute to AL and ASYM.

  9. Simultaneous conjugate observations of small-scale structures in Saturn's dayside ultraviolet auroras: Implications for physical origins

    NASA Astrophysics Data System (ADS)

    Meredith, C. J.; Cowley, S. W. H.; Hansen, K. C.; Nichols, J. D.; Yeoman, T. K.

    2013-09-01

    Conjugacy of Saturn's auroras was studied using unique near-equinox HST images. Dawnside patches are consistent with expectations for second harmonic ULF waves. Dusk transients are strictly non-conjugate, suggesting an open flux tube origin.

  10. Leishmaniasis

    MedlinePlus

    ... parasitic disease spread by the bite of infected sand flies. There are several different forms of leishmaniasis. ... prevent the disease is to protect yourself from sand fly bites: Stay indoors from dusk to dawn, ...

  11. Bug Bites and Stings

    MedlinePlus

    ... are most active (dawn and dusk); and apply insect repellent when kids go outside. When in tick country, ... pets to prevent them from being bitten. Use insect repellent when spending time outdoors camping, hiking, etc. Repellents ...

  12. West Nile Virus

    MedlinePlus

    ... avoid WNV is to prevent mosquito bites: Use insect repellent Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets or barrels Stay indoors between dusk and ... out NIH: National Institute of Allergy and Infectious Diseases

  13. West Nile Virus

    MedlinePlus

    ... appeared in the United States in 1999. Infected mosquitoes spread the virus that causes it. People who ... barrels Stay indoors between dusk and dawn, when mosquitoes are most active Use screens on windows to ...

  14. Leishmaniasis

    MedlinePlus

    ... disease spread by the bite of infected sand flies. There are several different forms of leishmaniasis. The ... the disease is to protect yourself from sand fly bites: Stay indoors from dusk to dawn, when ...

  15. West Nile Virus

    MedlinePlus

    ... protect themselves from mosquito bites by using mosquito repellent, especially at times when mosquitoes are most active, ... at dusk and dawn. The CDC recommends mosquito repellents that include one of the following ingredients: DEET ( ...

  16. WIDE AWAKE mediates the circadian timing of sleep onset.

    PubMed

    Liu, Sha; Lamaze, Angelique; Liu, Qili; Tabuchi, Masashi; Yang, Yong; Fowler, Melissa; Bharadwaj, Rajnish; Zhang, Julia; Bedont, Joseph; Blackshaw, Seth; Lloyd, Thomas E; Montell, Craig; Sehgal, Amita; Koh, Kyunghee; Wu, Mark N

    2014-04-01

    How the circadian clock regulates the timing of sleep is poorly understood. Here, we identify a Drosophila mutant, wide awake (wake), that exhibits a marked delay in sleep onset at dusk. Loss of WAKE in a set of arousal-promoting clock neurons, the large ventrolateral neurons (l-LNvs), impairs sleep onset. WAKE levels cycle, peaking near dusk, and the expression of WAKE in l-LNvs is Clock dependent. Strikingly, Clock and cycle mutants also exhibit a profound delay in sleep onset, which can be rescued by restoring WAKE expression in LNvs. WAKE interacts with the GABAA receptor Resistant to Dieldrin (RDL), upregulating its levels and promoting its localization to the plasma membrane. In wake mutant l-LNvs, GABA sensitivity is decreased and excitability is increased at dusk. We propose that WAKE acts as a clock output molecule specifically for sleep, inhibiting LNvs at dusk to promote the transition from wake to sleep. PMID:24631345

  17. Ecology of colors of firefly bioluminescence

    SciTech Connect

    Lall, A.B.; Seliger, H.H.; Biggley, W.H.; Lloyd, J.E.

    1980-10-31

    Dark-active North American fireflies emit green bioluminescence and dusk-active species emit yellow, in general. Yellow light and yellow visual spectral sensitivity may be adaptations to increase the signal-to-noise (that is, foliage-reflected ambient light) ratio for sexual signaling during twilight. The peaks of the electroretinogram visual spectral sensitivities of four species tested, two dark- and two dusk-active, correspond with the peak of their bioluminescent emissions.

  18. Gyroresonance of Kelvin-Helmholtz vortices with Na+ in Mercury's magnetotail

    NASA Astrophysics Data System (ADS)

    Gingell, Peter; Sundberg, Torbjorn; Burgess, David

    2015-04-01

    Observations of Mercury's plasma environment by the MESSENGER spacecraft have revealed that the planet hosts a strongly asymmetric magnetosphere as a result of an off-axis internal magnetic field, and significant finite Larmor radius effects at the boundary layer between magnetospheric and solar wind plasma environments. Linear analysis and global hybrid simulations suggest asymmetric growth of the Kelvin-Helmholtz instability between the dusk and dawn flanks of the magnetopause, and indeed Kelvin-Helmholtz waves have been observed almost exclusively at the dusk flank during northward IMF. A previous study has shown that Kelvin-Helmholtz waves at the dusk flank are observed predominantly at scales associated with the gyration of hot sodium ions - a population originating at the dayside exosphere, and distributed preferentially at the dusk flank. This suggests that a resonance may occur between sodium ion gyration and Kelvin-Helmholtz vortex growth. Using two- and three-dimensional local hybrid simulations of dusk and dawn boundaries, with varying magnetospheric sodium ion density, we have reproduced the main observational features: we see a strong peak in the Kelvin-Helmholtz wave spectra at sodium gyro scales at the dusk boundaries, and suppression of the growth of vortices at the dawn boundaries. We examine the mechanism of the resonant interaction between counter-gyrating sodium ions and K-H vortices using test particle simulations. Finally, we discuss the effect of the sodium ion population on cross-boundary particle transport.

  19. Cusp geometry in MHD simulations

    NASA Astrophysics Data System (ADS)

    Siscoe, George; Crooker, Nancy; Siebert, Keith; Maynard, Nelson; Weimer, Daniel; White, Willard

    2005-01-01

    The MHD simulations described here show that the latitude of the high-altitude cusp decreases as the IMF swings from North to South, that there is a pronounced dawn dusk asymmetry at high-altitude associated with a dawn dusk component of the IMF, and that at the same time there is also a pronounced dawn dusk asymmetry at low-altitude. The simulations generate a feature that represents what has been called the cleft. It appears as a tail (when the IMF has a By component) attached to the cusp, extending either toward the dawn flank or the dusk flank depending on the dawn dusk orientation of the IMF. This one-sided cleft connects the cusp to the magnetospheric sash. We compare cusp geometry predicted by MHD simulations against published observations based on Hawkeye and DMSP data. Regarding the high-altitude predictions, the comparisons are not definitive, mainly because the observations are incomplete or mutually inconsistent. Regarding the low-altitude prediction of a strong dawn dusk asymmetry, the observations are unambiguous and are in good qualitative agreement with the prediction.

  20. The impact of a hot sodium ion population on the growth of the Kelvin-Helmholtz instability in Mercury's magnetotail

    NASA Astrophysics Data System (ADS)

    Gingell, P. W.; Sundberg, T.; Burgess, D.

    2015-07-01

    Observations of Mercury's local plasma environment by MErcury Surface, Space ENvironment, GEochemistry, and Ranging have revealed that the planet hosts a strongly asymmetric magnetosphere as a result of an off-axis dipolar or quadrupolar internal field and significant finite Larmor radius effects at the boundary layer between magnetospheric and solar wind plasma environments. One important asymmetry appears in the growth and evolution of Kelvin-Helmholtz (K-H) waves at the dawn and dusk flanks of the magnetopause. Linear analysis and global hybrid simulations support a dusk-dawn asymmetry in the growth rate caused by finite Larmor radius effects, and indeed, K-H waves have been almost exclusively observed at the dusk magnetopause during northward interplanetary magnetic field. Observations of these K-H waves at sodium gyroscales invite investigation into the impact of the hot planetary sodium ion population, itself distributed preferentially on the dusk flank, on the growth of the K-H instability and associated plasma transport. We present local two-dimensional hybrid simulations of the dusk and dawn boundary layers, with varying magnetospheric sodium ion number density, and examine the associated changes in the growth rates of the K-H instability, K-H wave spectra, and cross-boundary particle transport. We show that gyroresonance between growing K-H vortices and sodium ion gyration introduces a strong spectral peak at sodium gyroscales at the dusk magnetopause, that an increase in sodium ion number density increases dawn-dusk asymmetry of K-H growth rates, and that cross-boundary particle transport decreases with sodium number density at the dawn flank.

  1. The impact of a hot sodium ion population on the growth of the Kelvin-Helmholtz instability in Mercury's magnetotail

    NASA Astrophysics Data System (ADS)

    Gingell, P.; Sundberg, T.; Burgess, D.

    2014-12-01

    Observations of Mercury's local plasma environment by MESSENGER have revealed that the planet hosts a strongly asymmetric magnetosphere as a result of an off-axis dipolar or quadrupolar internal field, and significant finite Larmor radius effects at the boundary layer between magnetospheric and solar wind plasma environments. One important asymmetry appears in the growth and evolution of Kelvin-Helmholtz (K-H) waves at the dawn and dusk flanks of the magnetopause. Linear analysis and global hybrid simulations support a dusk-dawn asymmetry in the growth rate caused by finite Larmor radius effects, and indeed K-H waves have been exclusively observed at the dusk magnetopause during northward IMF. Observations of these K-H waves at sodium gyro-scales invites investigation into the impact of the hot planetary sodium ion population, itself distributed preferentially on the dusk flank, on the growth of the K-H instability and associated plasma transport. We present local two- and three-dimensional hybrid simulations of the dusk and dawn boundary layers, with varying magnetospheric sodium ion number density, and examine the associated changes in the growth rates of the K-H instability, K-H wave spectra, and cross-boundary particle transport. We show that gyroresonance between growing K-H vortices and sodium ion gyration introduces a strong spectral peak at sodium gyro-scales at the dusk magnetopause, that an increase in sodium ion number density increases dawn-dusk asymmetry of K-H growth rates, and that cross-boundary particle transport increases with sodium number density.

  2. Surface waves on Saturn's magnetopause

    NASA Astrophysics Data System (ADS)

    Masters, A.; Achilleos, N.; Cutler, J. C.; Coates, A. J.; Dougherty, M. K.; Jones, G. H.

    2012-05-01

    Waves on the surface of a planetary magnetopause promote energy transport into the magnetosphere, representing an important aspect of solar wind-magnetosphere coupling. At Saturn's magnetopause it has been proposed that growth of the Kelvin-Helmholtz (K-H) instability produces greater wave activity on the dawn side of the surface than on the dusk side. We test this hypothesis using data taken by the Cassini spacecraft during crossings of Saturn's magnetopause. Surface orientation perturbations are primarily controlled by the local magnetospheric magnetic field orientation, and are generally greater at dusk than at dawn. 53% of all crossings were part of a sequence of regular oscillations arising in consecutive surface normals that is strong evidence for tailward propagating surface waves, with no detectable local time asymmetry in this phenomenon. We estimate the dominant wave period to be ∼5 h at dawn and ∼3 h at dusk. The role played by the magnetospheric magnetic field, tailward wave propagation, and the dawn-dusk difference in wave period suggests that K-H instability is a major wave driving mechanism. Using linear K-H theory we estimate the dominant wavelength to be ∼10 Saturn radii (RS) and amplitude to be ∼1 RS at both dawn and dusk, giving propagation speeds of ∼30 and ∼50 km s-1 at dawn and dusk, respectively. The lack of the hypothesized dawn-dusk asymmetry in wave activity demonstrates that we need to revise our understanding of the growth of the K-H instability at Saturn's magnetopause, which will have implications for the study of other planetary magnetospheres.

  3. MESSENGER Observations of Asymmetries at Mercury's Magnetotail Current Sheet

    NASA Astrophysics Data System (ADS)

    Poh, Gangkai; Slavin, James; Jia, Xianzhe; Raines, Jim; Sun, Wei-Jie; Genestreti, Kevin; Smith, Andy; Gershman, Daniel; Anderson, Brian

    2016-04-01

    Dawn-dusk asymmetries in the Earth's magnetotail current sheet have been observed and remain an active area of research. With an internal magnetic dipole field structure similar to Earth's, similar dawn-dusk asymmetries might be expected in Mercury's magnetotail current sheet. However, no observation of dawn-dusk asymmetries has been reported in the structure of Mercury's magnetotail. Using 4 years of MESSENGER's magnetic field and plasma data, we analyzed 319 current sheet crossings. From the polarity of Bz in the cross-tail current sheet, we determined that MESSENGER is on closed field lines about 90% of the time. During the other 10% MESSENGER observed negative Bz indicating that it was tailward of the Near Mercury Neutral Line (NMNL). The Bz magnetic field is also observed to be higher at the dawnside than the duskside of the magnetotail current sheet by approximately a factor of three. Further the asymmetry decreases with increasing downstream distance. A reduction (enhancement) in Bz should correspond to a more (less) stretched and thinned (thickened) current sheet. Analysis of current sheet thickness based upon MESSENGER's observations confirms this behavior with mean current sheet thickness and Bz intensity having dawn-dusk asymmetries with the same sense. Plasma β in the current sheet also exhibits a dawn-dusk asymmetry opposite to that of Bz. This is consistent with expectations based on MHD stress balance. Earlier studies had shown a dawn-dusk asymmetry in the heavy ion in Mercury's magnetotail. We suggest that this enhancement of heavy ions in the duskside current sheet, due to centrifugal acceleration of ions from the cusp and gradient-curvature drift from the NMNL, may provide a partial explanation of the dawn-dusk current sheet asymmetries found in this study.

  4. Interplanetary Electric Field Control of Field-Aligned Currents: Polar Magnetometer Observations

    NASA Astrophysics Data System (ADS)

    Fleishman, M.; Russell, C. T.

    2001-05-01

    ACE and Wind measurements of the solar wind velocity and interplanetary magnetic field have been used to calculate the interplanetary electric field during passages of the Polar spacecraft above the southern auroral oval. Periods of the quasi-steady interplanetary electric field have been identified when the Polar spacecraft was transiting the auroral and polar regions both just in front of the terminator above the lit ionosphere and just behind the terminator above the dark ionosphere. The east-west magnetic perturbation observed was then used as a measure of the local field-aligned current density and extrapolated to a common altitude. Independent of whether the interplanetary electric field (IEF) is from dawn to dusk or dusk to dawn a significant field-aligned current always exists. The magnitude of its perturbation field for dusk to dawn IEF is about 180 nT. For dawn to dusk IEF the magnetic perturbation is roughly proportional to the dawn-dusk component of the IEF. The strength of the field-aligned current does not depend on whether the ionosphere under the spacecraft is in sunlight or in darkness.

  5. Non-parametric entrainment by natural twilight in the microchiropteran bat, Hipposideros speoris inside a cave.

    PubMed

    Joshi, D S; Vanlalnghaka, C

    2005-01-01

    The study aimed to determine the influence of repeated natural dawn and dusk twilight pulses in entraining the circadian flight activity rhythm of the microchiropteran bat, Hipposideros speoris, free-running in constant darkness in a natural cave. The bats were exposed to repeated dawn or dusk twilight pulses at eight circadian phases. All bats exposed to dawn twilight pulses were entrained by advancing transients, and the stable entrainment was reached when the onset of activity occurred about 12 h before the lights-on of the pulses, irrespective of the initial phase at which the bats were exposed to twilight. All bats exposed to dusk twilight pulses, however, were entrained by delaying transients, and the stable entrainment was reached when the onset of activity occurred about 1.6 h after the lights-on of the pulses. The entrainment caused by dawn and dusk twilight pulses is discussed in the context of the postulated two photoreceptors: the short wavelength sensitive (S) photoreceptors mediating entrainment via dusk twilight, and the medium wavelength sensitive (M) photoreceptors mediating entrainment via dawn twilight. PMID:16147895

  6. Concerning the Motion of FTEs and Attendant Signatures

    NASA Technical Reports Server (NTRS)

    Sibeck, David G.

    2010-01-01

    We employ the Cooling et al. [2001] model to predict the location, orientation, and motion of flux transfer events (FTEs) generated along finite length component and anti parallel reconnection lines for typical solar wind plasma conditions and various interplanetary magnetic field (IMF) orientations in the plane perpendicular to the SunEarth line at the solstices and equinoxes. For duskward and northward or southward IMF orientations, events formed by component reconnection originate along reconnection curves passing through the sub solar point that tilt from southern dawn to northern dusk. They maintain this orientation as they move either northward into the northern dawn quadrant or southward into the southern dusk quadrant. By contrast, events formed by antiparallel reconnection originate along reconnection curves running from northern dawn to southern dusk in the southern dawn and northern dusk quadrants and maintain these orientations as they move anti sunward into both these quadrants. Although both the component and antiparallel reconnection models can explain previously reported event orientations on the southern dusk magnetopause during intervals of northward and dawn ward IMF orientation, only the component model explains event occurrence near the subsolar magnetopause during intervals when the IMF does not point due southward.

  7. Investigation of EMIC Waves During Balloon Detected Relativistic Electron Precipitation Events

    NASA Astrophysics Data System (ADS)

    Woodger, L. A.; Millan, R. M.

    2009-12-01

    Multiple relativistic electron precipitation (REP) events were detected by balloon-borne instrumentation during the MAXIS 2000 and MINIS 2005 campaigns. It has been suggested that resonance with EMIC waves caused these precipitation events (Lorentzen et al, 2000 and Millan et al, 2002) due to their location in the dusk sector. We present observations of dusk-side relativistic electron precipitation events, and use supporting satellite and theoretical data to investigate the relationship between EMIC waves and the detected REP. Satellite data can provide direct measurements of not only the waves themselves but also important resonance condition parameters. The data will be presented collectively with each event to showcase similarities and differences between events and the challenges that arise in trying to understand the relationship between dusk-side relativistic electron precipitation and EMIC waves.

  8. Intensity variation of ELF hiss and chorus during isolated substorms

    NASA Technical Reports Server (NTRS)

    Thorne, R. M.; Fiske, K. F.; Church, S. R.; Smith, E. J.

    1974-01-01

    Electromagnetic ELF emissions (100-1000 Hz) observed on the polar-orbiting OGO-6 satellite within three hours of the dawn-dusk meridian consistently exhibit a predictable response to isolated substorm activity. Near dawn, the emissions intensify during the substorm and then subside following the magnetic activity; the waves are most intense at L greater than 4, exhibit considerable structure and have been primarily identified as chorus. At dusk the response is entirely different; the wave intensity falls to background levels during substorm activity but subsequently intensifies, usually reaching levels well in excess of that before the disturbance. The emissions near dusk extend to low L, are relatively featureless, and have been identified as plasmaspheric hiss. These features are interpreted in terms of changes in the drift orbits of outer-zone electrons which cyclotron resonate with ELF waves.

  9. The resolution of a magnetic anomaly map expected from GRM data

    NASA Technical Reports Server (NTRS)

    Strangway, D. W.; Arkani-Hamed, J.; Teskey, D. J.; Hood, P. J.

    1985-01-01

    Data from the MAGSAT mission were used to derive a global scalar magnetic anomaly map at an average altitude of about 400 km. It was possible to work with 2 data sets corresponding to dawn and dusk. The anomalies which were repeatable at dawn and at dusk was identified and the error limits of these anomalies were estimated. The repeatable anomalies were downward continued to about 10 km altitude. The anomalies over Canada were correlated quantitatively with bandpass filtered magnetic anomalies derived from aeromagnetic surveys. The close correlation indicates that the repeatable anomalies detected from orbit are due to geological causes. This correlation supports the geological significance of the global anomaly map.

  10. Surveillance for Japanese encephalitis in villages near Madurai, Tamil Nadu, India.

    PubMed

    Mani, T R; Rao, C V; Rajendran, R; Devaputra, M; Prasanna, Y; Hanumaiah; Gajanana, A; Reuben, R

    1991-01-01

    A simple dusk index was developed to monitor the density of recognized vectors of Japanese encephalitis virus (JEV) based on hand catches around cattlesheds at dusk and parous rates. When used routinely in combination with sentinel animal studies for surveillance in villages with a high prevalence (46.2%) of neutralizing antibodies against JEV in children under 16 years, there was a peak in vector density and virus activity during the north-east monsoon period, October-December. The reasons for an unusual outbreak of cases of encephalitis during the summer months of 1984 are discussed. PMID:1653473

  11. Natural twilight phase-response curves for the cave-dwelling bat, Hipposideros speoris.

    PubMed

    Vanlalnghaka, C; Keny, V L; Satralkar, M K; Khare, P V; Pujari, P D; Joshi, D S

    2005-01-01

    Phase-response curves (PRCs) for the circadian rhythm of flight activity of the microchiropteran bat (Hipposideros speoris) were determined in a cave, employing discrete natural dawn and dusk twilight pulses. These PRCs are reported for the first time for any circadian system and they are unlike other PRCs constructed for nocturnal mammals. Dawn and dusk twilight pulses evoked advance and delay phase shifts, respectively. Advance phase shifts were followed by 3 to 4 advancing transients and a subsequent shortening of free-running period (tau); whereas, the delay phase shifts were instantaneous without any transients but with a subsequent lengthening of tau. PMID:16298767

  12. Older Drivers: How Health Affects Driving

    MedlinePlus

    ... see clearly, especially at dawn, dusk, and night. Eyes become more sensitive to glare from headlights, street lights, or the sun, making it difficult to see people, things, and movements outside your direct line of sight. Peripheral vision — the ability to see to the ...

  13. Remote Observations of Ion Temperatures in the Quiet Time Magnetosphere

    NASA Technical Reports Server (NTRS)

    Keesee, A. M.; Buzulukova, N.; Goldstein, J.; McComas, D. J.; Scime, E. E.; Spence, H.; Fok, M. C.; Tallaksen, K.

    2011-01-01

    Ion temperature analysis of the first energetic neutral atom images of the quiet -time, extended magnetosphere provides evidence of multiple regions of ion heating. This study confirms the existence of a dawn -dusk asymmetry in ion temperature predicted for quiescent magnetospheric conditions by Spence and Kivelson (1993) and demonstrates that it is an inherent magnetospheric feature.

  14. The Use of Technology in Literacy Instruction: Implications for Teaching Students from Low Socioeconomic Backgrounds. HBSK 4072, Section 3, Fall 2007

    ERIC Educational Resources Information Center

    Whitney, Jennifer D.

    2007-01-01

    Background: Almost every aspect of modern life is affected in some way by technology. Many people utilize technology from dawn to dusk to communicate; make decisions; reflect, gain, synthesize, evaluate or distribute information, among many other functions. One would be hard pressed to find a single professional, regardless of career field,…

  15. Temporal Links in Daily Activity Patterns between Coral Reef Predators and Their Prey

    PubMed Central

    Bosiger, Yoland J.; McCormick, Mark I.

    2014-01-01

    Few studies have documented the activity patterns of both predators and their common prey over 24 h diel cycles. This study documents the temporal periodicity of two common resident predators of juvenile reef fishes, Cephalopholis cyanostigma (rockcod) and Pseudochromis fuscus (dottyback) and compares these to the activity and foraging pattern of a common prey species, juvenile Pomacentrus moluccensis (lemon damselfish). Detailed observations of activity in the field and using 24 h infrared video in the laboratory revealed that the two predators had very different activity patterns. C. cyanostigma was active over the whole 24 h period, with a peak in feeding strikes at dusk and increased activity at both dawn and dusk, while P. fuscus was not active at night and had its highest strike rates at midday. The activity and foraging pattern of P. moluccensis directly opposes that of C. cyanostigma with individuals reducing strike rate and intraspecific aggression at both dawn and dusk, and reducing distance from shelter and boldness at dusk only. Juveniles examined were just outside the size-selection window of P. fuscus. We suggest that the relatively predictable diel behaviour of coral reef predators results from physiological factors such as visual sensory abilities, circadian rhythmicity, variation in hunting profitability, and predation risk at different times of the day. Our study suggests that the diel periodicity of P. moluccensis behaviour may represent a response to increased predation risk at times when both the ability to efficiently capture food and visually detect predators is reduced. PMID:25354096

  16. Timing of herbage and fasting allocation in strip grazed cattle: Effects on patterns of ingestive behavior, herbage intake, and nutrient supply

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Afternoon herbage allocations have shown to improve animal performance due to an increment in herbage intake during dusk, when herbage quality is higher. However, this phenomenon might not yet be maximized. This work aimed to assess the impact of timing of herbage and fasting allocation on patterns ...

  17. Spatial distribution of upstream magnetospheric geq50 keV ions

    NASA Astrophysics Data System (ADS)

    Anagnostopoulos, G. C.; Argyropoulos, G.; Kaliabetsos, G.

    2000-01-01

    We present for the first time a statistical study of geq50 keV ion events of a magnetospheric origin upstream from Earth's bow shock. The statistical analysis of the 50-220 keV ion events observed by the IMP-8 spacecraft shows: (1) a dawn-dusk asymmetry in ion distributions, with most events and lower intensities upstream from the quasi-parallel pre-dawn side (4 LT-6 LT) of the bow shock, (2) highest ion fluxes upstream from the nose/dusk side of the bow shock under an almost radial interplanetary magnetic field (IMF) configuration, and (3) a positive correlation of the ion intensities with the solar wind speed and the index of geomagnetic index Kp, with an average solar wind speed as high as 620 km s-1 and values of the index Kp > 2. The statistical results are consistent with (1) preferential leakage of sim50 keV magnetospheric ions from the dusk magnetopause, (2) nearly scatter free motion of sim50 keV ions within the magnetosheath, and (3) final escape of magnetospheric ions from the quasi-parallel dawn side of the bow shock. An additional statistical analysis of higher energy (290-500 keV) upstream ion events also shows a dawn-dusk asymmetry in the occurrence frequency of these events, with the occurrence frequency ranging between sim16%-sim34% in the upstream region.

  18. The plasmapause revisited

    NASA Technical Reports Server (NTRS)

    Maynard, N. C.; Gebowsky, J. M.

    1976-01-01

    Saturation of the dc double probe instrument on Explorer 45 was used to identify the plasmapause. A data base was developed to statistically study the average position of the plasmapause over 14.5 hours of magnetic local time under differing magnetic conditions. The afternoon-evening bulge in the L coordinate of the plasmapause versus local time was found centered between 20 and 21 hours MLT during magnetically quiet periods and shifted toward dusk as activity increased, but always post dusk. During quiet periods a bulge in the L coordinate near noon was also seen, which disappeared as activity increased. The average local time distribution plasmapause position during high magnetic activity was irregular in the afternoon region where large scale convection models predict the creation of plasmatails or detached plasma regions from increases in the solar wind induced convection. The results suggest that solar wind induced convection is partially shielded from the dayside. As the intensity of the convection is increased, it more effectively penetrates the dayside, which shifts the post dusk bulge nearer to dusk and eliminates the quiet-time bulge near noon.

  19. The near-Earth magnetic field at 1980 determined from MAGSAT data

    NASA Technical Reports Server (NTRS)

    Langel, R. A.; Estes, R. H.

    1984-01-01

    Data from the MAGSAT spacecraft for November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the Earth's main magnetic field and its secular variation. Constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10. The first degree external terms and corresponding induced internal terms are given as a function of Dst. Preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contains a substantial field contribution from the equatorial electrojet current. The final data set is selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods: (1) November/December, 1979; (2) January/February; 1980; (3) March/April, 1980. A correction for the effects of the equatorial electrojet is applied to the dusk data utilized. The solution included calculation of fixed biases, or anomalies, for the observation data.

  20. Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015

    NASA Astrophysics Data System (ADS)

    Tulasi Ram, S.; Yokoyama, T.; Otsuka, Y.; Shiokawa, K.; Sripathi, S.; Veenadhari, B.; Heelis, R.; Ajith, K. K.; Gowtam, V. S.; Gurubaran, S.; Supnithi, P.; Le Huy, M.

    2016-01-01

    The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13°N and 25.98°S magnetic dip latitudes indicating their altitude development to ~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field Bz.

  1. Application of ground-truth for classification and quantification of bird movements on migratory bird habitat initiative sites in southwest Louisiana: final report

    USGS Publications Warehouse

    Barrow, Wylie C.; Baldwin, Michael J.; Randall, Lori A.; Pitre, John; Dudley, Kyle J.

    2013-01-01

    This project was initiated to assess migrating and wintering bird use of lands enrolled in the Natural Resources Conservation Service’s (NRCS) Migratory Bird Habitat Initiative (MBHI). The MBHI program was developed in response to the Deepwater Horizon oil spill in 2010, with the goal of improving/creating habitat for waterbirds affected by the spill. In collaboration with the University of Delaware (UDEL), we used weather surveillance radar data (Sieges 2014), portable marine radar data, thermal infrared images, and visual observations to assess bird use of MBHI easements. Migrating and wintering birds routinely make synchronous flights near dusk (e.g., departure during migration, feeding flights during winter). Weather radars readily detect birds at the onset of these flights and have proven to be useful remote sensing tools for assessing bird-habitat relations during migration and determining the response of wintering waterfowl to wetland restoration (e.g., Wetlands Reserve Program lands). However, ground-truthing is required to identify radar echoes to species or species group. We designed a field study to ground-truth a larger-scale, weather radar assessment of bird use of MBHI sites in southwest Louisiana. We examined seasonal bird use of MBHI fields in fall, winter, and spring of 2011-2012. To assess diurnal use, we conducted total area surveys of MBHI sites in the afternoon, collecting data on bird species composition, abundance, behavior, and habitat use. In the evenings, we quantified bird activity at the MBHI easements and described flight behavior (i.e., birds landing in, departing from, circling, or flying over the MBHI tract). Our field sampling captured the onset of evening flights and spanned the period of collection of the weather radar data analyzed. Pre- and post-dusk surveys were conducted using a portable radar system and a thermal infrared camera. Landbirds, shorebirds, and wading birds were commonly found on MBHI fields during diurnal

  2. Bimodal oscillations of cyclic nucleotide concentrations in the circadian system of the Madeira cockroach Rhyparobia maderae.

    PubMed

    Schendzielorz, Julia; Schendzielorz, Thomas; Arendt, Andreas; Stengl, Monika

    2014-10-01

    Pigment-dispersing factor (PDF) is the most important coupling factor of the circadian system in insects, comparable to its functional ortholog vasoactive intestinal polypeptide of the mammalian circadian clock. In Drosophila melanogaster, PDF signals via activation of adenylyl cyclases, controlling circadian locomotor activity rhythms at dusk and dawn. In addition, PDF mediates circadian rhythms of the visual system and is involved in entrainment to different photoperiods. We examined whether PDF daytime-dependently elevates cAMP levels in the Madeira cockroach Rhyparobia maderae and whether cAMP mimics PDF effects on locomotor activity rhythms. To determine time windows of PDF release, we searched for circadian rhythms in concentrations of cAMP and its functional opponent cGMP in the accessory medulla (AMe), the insect circadian pacemaker controlling locomotor activity rhythms, and in the optic lobes, as the major input and output area of the circadian clock. Enzyme-linked immunosorbent assays detected PDF-dependent increases of cAMP in optic lobes and daytime-dependent oscillations of cAMP and cGMP baseline levels in the AMe, both with maxima at dusk and dawn. Although these rhythms disappeared at the first day in constant conditions (DD1), cAMP but not cGMP oscillations returned at the second day in constant conditions (DD2). Whereas in light-dark cycles the cAMP baseline level remained constant in other optic lobe neuropils, it oscillated in phase with the AMe at DD2. To determine whether cAMP and cGMP mimic PDF-dependent control of locomotor activity rhythms, both cyclic nucleotides were injected at different times of the circadian day using running-wheel assays. Whereas cAMP injections generated delays at dusk and advances at dawn, cGMP only delayed locomotor activity at dusk. For the first time we found PDF-dependent phase advances at dawn in addition to previously described phase delays at dusk. Thus, we hypothesize that PDF release at dusk and dawn

  3. Solar terminator effects on middle- to low-latitude Pi2 pulsations

    NASA Astrophysics Data System (ADS)

    Imajo, Shun; Yoshikawa, Akimasa; Uozumi, Teiji; Ohtani, Shinichi; Nakamizo, Aoi; Demberel, Sodnomsambuu; Shevtsov, Boris Mikhailovich

    2016-08-01

    To clarify the effect of the dawn and dusk terminators on Pi2 pulsations, we statistically analyzed the longitudinal phase and amplitude structures of Pi2 pulsations at middle- to low-latitude stations (GMLat = 5.30°-46.18°) around both the dawn and dusk terminators. Although the H (north-south) component Pi2s were affected by neither the local time (LT) nor the terminator location (at 100 km altitude in the highly conducting E region), some features of the D (east-west) component Pi2s depended on the location of the terminator rather than the LT. The phase reversal of the D component occurred 0.5-1 h after sunrise and 1-2 h before sunset. These phase reversals can be attributed to a change in the contributing currents from field-aligned currents (FACs) on the nightside to the meridional ionospheric currents on the sunlit side of the terminator, and vice versa. The phase reversal of the dawn terminator was more frequent than that of the dusk terminator. The D-to- H amplitude ratio on the dawn side began to increase at sunrise, reaching a peak approximately 2 h after sunrise (the sunward side of the phase reversal region), whereas the ratio on the dusk side reached a peak at sunset (the antisunward side). The dawn-dusk asymmetric features suggest that the magnetic contribution of the nightside FAC relative to the meridional ionospheric current on the dusk side is stronger than that on the dawn side, indicating that the center of Pi2-associated FACs, which probably corresponds to the Pi2 energy source, tends to be shifted duskward on average. Different features and weak sunrise/sunset dependences at the middle-latitude station (Paratunka, GMLat = 46.18°) can be attributed to the larger annual variation in the sunrise/sunset time and a stronger magnetic effect because of closeness from FACs. The D-to- H amplitude ratio decreased with decreasing latitude, suggesting that the azimuthal magnetic field produced by the FACs in darkness and the meridional ionospheric

  4. The solar wind plasma entry and its effects on plasma sheet entropy

    NASA Astrophysics Data System (ADS)

    Wing, S.; Johnson, J. R.

    2008-05-01

    The solar wind enters the plasma sheet during northward and southward IMF. The connection between solar wind ions and plasma sheet cold-component ions has been demonstrated with in situ Geotail and inferred DMSP observations. The cold dense ions that originate from the solar wind are expected to decrease the entropies in the plasma sheet. Order of magnitude calculations of plasma sheet filling rate from reconnection and diffusion (either by K-H instabilities or kinetic Alfven waves) suggest that both entry mechanisms could result in roughly comparable filling rates, which are found consistent with DMSP observations. Previous studies have shown the presence of the dawn-dusk asymmetries in the plasma sheet temperatures and densities, which may be key in distinguishing various proposed entry mechanisms. This is investigated further with the entropy profiles and their dawn-dusk asymmetries during northward and southward IMF.

  5. Comparison of storm-time changes of geomagnetic field at ground and at MAGSAT altitudes, part 3

    NASA Technical Reports Server (NTRS)

    Dejesusparada, N. (Principal Investigator); Kane, R. P.; Trivedi, N. B.

    1982-01-01

    The latitudinal distributions of delta H, delta X, delta Y, and delta Z were studied for quiet and disturbed periods. For quiet periods, the average patterns showed some variations common to dusk and dawn, thus indicating probable ground anomaly. However, there were significant differences too between dusk and dawn, indicating considerable diurnal variation effects. Particularly in delta Y, these effects were large and were symmetric about the dip equator. For disturbed day passes, the quiet day patterns were considered as base levels and the latter were subtracted from the former. The resulting residual latitudinal patterns were, on the average, symmetric about the geographical equator. However, individual passes showed considerable north-south asymmetries, probably indicating meanderings of the central plane of the magnetospheric ring current.

  6. Observation of bow shock protons at the lunar orbit. M.S. Thesis; [particle trajectory analysis of solar protons in the lunar atmosphere

    NASA Technical Reports Server (NTRS)

    Benson, J. L.

    1974-01-01

    Protons with energies ranging from about 500 eV to 3,500 eV were observed by the Suprathermal Ion Detector Experiment (SIDE) on both the dusk and dawn sides of the magnetosphere. On each lunation these particles appeared as a rather continuous phenomenon for 3 to 5 days after crossing from the dawn-side magnetosheath into the solar wind and for about 2 days prior to entering the dusk-side magnetosheath. Data from the SIDE and from the Explorer 35 lunar orbiting magnetometer were analyzed and these data indicated that the transverse ion flows observed by the SIDE in the pre and post bow shock crossing regions of the lunar orbit are due to these deviated solar wind particles. A computer model based on drift trajectories for particles leaving the shock was developed and synthetic particle data produced by this model are in good agreement with the observed data.

  7. The relationship between the IMF B(y) and the distant tail (150-238 Re) lobe and plasmasheet B(y) fields

    NASA Technical Reports Server (NTRS)

    Tsurutani, B. T.; Smith, E. J.; Jones, D. E.; Lepping, R. P.; Sibeck, D. G.

    1984-01-01

    The relationships between the Solar Magnetospheric (SM) y-component of the interplanetary magnetic field (IMF) and the lobe and plasmasheet magnetic fields have been studied for the two ISEE-3 deep tail passes. It is found that for positive sector IMFs, 13 percent of the interplanetary magnetic field penetrates into the aberrated north-dawn and south-dusk lobe quadrants, and about the same amount in the north-dusk and south-dawn lobe quadrants for negative sector IMFs. For the above cases, field penetration is significantly less for opposite polarity IMFs. The former results are generally consistent with open magnetospheric models, but the latter (the lack of response in certain quadrants) are unexplained by theory at this time. If the magnitude of the plasmasheet B(y) fields are related to plasma pressure anisotropies, very small anisotropies of about 1.01 are expected.

  8. A statistical study of ion pitch-angle distributions

    NASA Technical Reports Server (NTRS)

    Sibeck, D. G.; Mcentire, R. W.; Lui, A. T. Y.; Krimigis, S. M.

    1987-01-01

    Preliminary results of a statistical study of energetic (34-50 keV) ion pitch-angle distributions (PADs) within 9 Re of earth provide evidence for an orderly pattern consistent with both drift-shell splitting and magnetopause shadowing. Normal ion PADs dominate the dayside and inner magnetosphere. Butterfly PADs typically occur in a narrow belt stretching from dusk to dawn through midnight, where they approach within 6 Re of earth. While those ion butterfly PADs that typically occur on closed drift paths are mainly caused by drift-shell splitting, there is also evidence for magnetopause shadowing in observations of more frequent butterfly PAD occurrence in the outer magnetosphere near dawn than dusk. Isotropic and gradient boundary PADs terminate the tailward extent of the butterfly ion PAD belt.

  9. Irregular structure of thermal ion plasma near the plasmapause observed from Ogo 3 and Pc 1 measurements.

    NASA Technical Reports Server (NTRS)

    Kikuchi, H.; Taylor, H. A., Jr.

    1972-01-01

    Independent measurements of the plasmapause and associated thermal plasma structure from Ogo 3 are compared with ground-based Pc 1 observations from the period 1966-67. Substantial agreement between the plasmapause crossing identified on the satellite and the Pc 1 occurrence positions observed on the ground at midlatitudes during the nighttime (including dawn and dusk) indicates that these nighttime Pc 1 events are closely associated with the plasmapause. A correlation of selected closely spaced events obtained in the nighttime under quiet to moderate activity provides good agreement in the proton concentrations near the plasmapause boundary. Preliminary results indicate Pc 1 excitation is associated with plasma irregularities near the plasmapause and is particularly favorable in the region of 'post-storm recovery' and in the region of diurnal 'plasma bulge' in the afternoon-dusk sector.

  10. Comparison of storm-time changes of geomagnetic field at ground and at MAGSAT altitudes, part 2

    NASA Technical Reports Server (NTRS)

    Dejesusparada, N. (Principal Investigator); Kane, R. P.; Trivedi, N. B.

    1982-01-01

    Geomagnetic field variations were studied by considering the parameter delta H which indicated H(observed) minus H(model), where H = (X squared + Y squared) (1/2) where X, Y, and Z are the components actually observed. Quiet time base values for 5 deg longitude belts were estimated. After subtracting these from the observed values, the residual delta H (dawn) and delta H (dusk) were studied for the two major storms. It was noticed that the dusk values attained larger (negative) values for a longer time, than the dawn value. Some changes in delta Y and delta Z were also noticed, indicating possibilities of either meridional currents and/or noncoincidence of the central plane of the ring current with the equatorial plane of the Earth. Other details are described.

  11. Diel changes in the near-surface biomass of zooplankton and the carbon content of vertical migrants

    NASA Astrophysics Data System (ADS)

    Hays, Graeme C.; Harris, Roger P.; Head, Robert N.

    Zooplankton biomass and the carbon content of vertical migrants were measured in the NE Atlantic (36.5°N, 19.2°W) between 11 and 18 July 1996 as part of the Plankton Reactivity in the Marine Environment (PRIME) programme. The increase in zooplankton biomass near the surface (0-100 m) at night compared to during the day suggested that diel vertical migration was an important feature at this site. For three species of vertically migrant copepods, Pleuromamma pisekii, P. gracilis and P. abdominalis, the carbon content of individuals collected at dusk was significantly less than for individuals collected at dawn, with this reduction being 6.2, 7.3 and 14.8%, respectively. This dawn-dusk reduction in carbon content is consistent with the diel pattern of feeding and fasting exhibited by vertical migrants and supports the suggestion that migrating zooplankton will cause an active export of carbon from the surface layers.

  12. Electron plasma oscillations in the near-earth solar wind: Preliminary observations and interpretations

    NASA Technical Reports Server (NTRS)

    Fredricks, R. W.; Scarf, F. L.; Green, I. M.

    1972-01-01

    Preliminary results and conclusions of a study of electric field oscillations in the upstream solar wind are reported. The OGO-5 orbits are on the dusk (three) and on the dawn (one) sides of the earth-sun line. It is concluded that there are electron streams produced at or near the bow shock. These streams penetrate the incoming solar wind plasma, and generate quasi-electromagnetic waves. The streams (as inferred from the wave levels) occur without regard to dawn-dusk location, as opposed to the low-frequency MHD upstream disturbances driven by backstreaming protons, which show a definitely strong preference for the dawn-noon sector. The presence of the suprathermal electron streams and associated wave turbulence indicates that some near-earth electron distributions are probably not representative of true solar wind distributions far away from the earth.

  13. Average field-aligned current configuration parameterized by solar wind conditions

    NASA Astrophysics Data System (ADS)

    Carter, J. A.; Milan, S. E.; Coxon, J. C.; Walach, M.-T.; Anderson, B. J.

    2016-02-01

    We present the first large-scale comparison of the spatial distribution of field-aligned currents as measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment, with the location and brightness of the average auroral oval, determined from the Imager for Magnetopause-to-Aurora Global Exploration far ultraviolet instrument. These distributions are compared under the same interplanetary magnetic field magnitude and clock angle conditions. The field-aligned currents and auroral oval drop to lower latitudes, as the interplanetary magnetic field becomes both increasingly stronger in magnitude and increasingly southward. We find that the region 2 currents are more closely aligned with the distribution of auroral UV emission, whether that be in the discrete auroral zone about dusk or in the postmidnight diffuse aurora sector. The lack of coincidence between the region 1 field-aligned currents with the auroral oval in the dusk sector is contrary to expectation.

  14. The inner edge of the plasma sheet and the diffuse aurora

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.; Vinas, A. F.

    1983-01-01

    Three dimensional measurements from the ISEE-1 low energy electron spectrometer are used to map the location of the inner edge of the plasma sheet and study the anisotropies in the electron distribution function associated with this boundary. Lower energy plasma sheet electrons have inner edges closer to the Earth than higher energies with the separations at different energies being larger near dawn and after dusk than at midnight. Lowest energy inner edges are frequently located adjacent to the plasmapause in the dawn hemisphere but are often separated from it in the dusk hemisphere by a gap of at least several Re. The energy dispersion is minimal in the afternoon quadrant where the inner edge is near the magnetopause and frequently oscillating on a time scale of minutes. The location of the inner edge is probably determined primarily by the motion of electrons in the existing electric and magnetic fields rather than by strong diffusion as has sometimes been supposed.

  15. Frequency variability of standing Alfvén waves excited by fast mode resonances in the outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Archer, M. O.; Hartinger, M. D.; Walsh, B. M.; Plaschke, F.; Angelopoulos, V.

    2015-12-01

    Coupled fast mode resonances (cFMRs) in the outer magnetosphere, between the magnetopause and a turning point, are often invoked to explain observed discrete frequency field line resonances. We quantify their frequency variability, applying cFMR theory to a realistic magnetic field model and magnetospheric density profiles observed over almost half a solar cycle. Our calculations show that cFMRs are most likely around dawn, since the plasmaspheric plumes and extended plasmaspheres often found at noon and dusk can preclude their occurrence. The relative spread (median absolute deviation divided by the median) in eigenfrequencies is estimated to be 28%, 72%, and 55% at dawn, noon, and dusk, respectively, with the latter two chiefly due to density. Finally, at dawn we show that the observed bimodal density distribution results in bimodal cFMR frequencies, whereby the secondary peaks are consistent with the so-called "CMS" frequencies that have previously been attributed to cFMRs.

  16. Lunar and daily spawning rhythms of Senegal sole Solea senegalensis.

    PubMed

    Oliveira, C; Dinis, M T; Soares, F; Cabrita, E; Pousão-Ferreira, P; Sánchez-Vázquez, F J

    2009-07-01

    A periodicity of 29 days was observed in spawning rhythms in Senegal sole Solea senegalensis, with an acrophase around the last quarter and the new moon. In both spring and autumn, a very marked nocturnal spawning rhythm was registered, with spawning beginning after dusk and the acrophase occurring around 2300 hours. When the photoperiod was artificially extended (from 10L:14D to 14L:10D), S. senegalensis synchronized to the new photoperiod: spawning took place after the new 'dusk', the beginning gradually shifting from 2100 to 2300 hours and the acrophase from 2325 to 0032 hours. Under continuous light conditions, fish sustained rhythmicity for 2 days, with an acrophase at 2249 hours, which suggested the existence of an endogenous pacemaker controlling the daily spawning rhythm. These findings provided new insights for better understanding the reproductive physiology of this species and for optimizing the timing protocols of egg collection and larvae production in S. senegalensis aquaculture. PMID:20738482

  17. Possible leakage of energetic particles from the magnetosphere into the upstream region on June 7, 1985

    NASA Technical Reports Server (NTRS)

    Kudela, K.; Sibeck, D. G.; Belian, R. D.; Fischer, S.; Lutsenko, V.

    1990-01-01

    Prognoz 10 observed a series of energetic ion (E not less than 10 KeV) and electron (E not less than 30 KeV) bursts whilst upstream of the dusk bow shock from 2000-2200 UT on June 7, 1985. The particles streamed away from the bow shock along the interplanetary magnetic field (IMF) during periods when the IMF connected the spacecraft to the bow shock/magnetosphere. Both ions and electrons were observed when the IMF connected the spacecraft to the subsolar bow shock, but only ions were observed when the IMF connected the spacecraft to the dusk bow shock. Simultaneous ground and magnetospheric observations are presented which indicate the onset of geomagnetic activity and an increase in magnetospheric energetic particle flux levels just prior to the series of particle bursts observed by Prognoz 10 upstream of the bow shock. The combined observations are consistent with a magnetospheric source for these upstream particle events.

  18. Viking observations of a reverse convection cell developing in response to a northward turning of the interplanetary magnetic field

    SciTech Connect

    Henderson, M.G.; Murphree, J.S.

    1996-04-15

    The authors report the development of a reverse sense convection cell in the polar ionosphere from auroral images coming from UV Viking probes. The cell was observed to grow on the dusk side of the north polar oval, near the transpolar arcs. As it grew it seemed to displace the arc system toward dawn. They compare their observations with a model in which magnetic merging in the magnetopause produces such convection cells, typically associated with horse-collar or teardrop auroral features.

  19. Comparison of storm-time changes of geomagnetic field at ground and MAGSAT altitudes

    NASA Technical Reports Server (NTRS)

    Dejesusparada, N. (Principal Investigator); Kane, R. P.; Trivedi, N. B.

    1982-01-01

    The MAGSAT data for the period Nov. 2-20, 1979 were studied. From the observed H, the HMD predicted by model was subtracted. The residue delta H = H-HMD shows storm-time variations similar to geomagnetic Dst, at least qualitatively. Delta H sub 0, i.e., equatorial values of delta H were studied separately for dusk and dawn and show some differences.

  20. Mapping high-latitude plasma convection with coherent HF radars

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.; Baker, K. B.; Villain, J.-P.; Hanuise, C.

    1989-01-01

    Several methods developed for mapping high-latitude plasma convection with a high-latitude HF radar are described, which utilize coherent backscatter from electron density irregularities at F-region altitudes to observe convective plasma motion. Several examples of two-dimensional convection-velocity maps are presented, showing instances of L-shell-aligned flow in the dusk sector, the reversal of convection near magnetic midnight, and counterstreaming in the dayside cleft.

  1. Distribution of larval fishes related to potential navigation impacts on the upper Mississippi River, pool 7

    USGS Publications Warehouse

    Holland, L.E.; Sylvester, J.R.

    1983-01-01

    Ichthyoplankton samples were collected twice monthly during spring and summer 1981 from a variety of habitats in Navigation Pool 7 of the upper Mississippi River. Larval-fish distributions in the pool and variations in those distributions were analyzed relative to potential impacts of increased commercial navigation. Although as many as 66 species of adults have been found in the area (33 considered common), only 17 taxa were identified from our collections. In April and May, most larvae were collected in main-channel and main-channel-border areas next to major expanses of shallow backwaters. White bass Morone chrysops, yellow perch Perca flavescens, and crappies Pomoxis spp. were predominant. Numerous catostomids also were taken. In June and July, most larvae were taken in the lower pool. Freshwater drum Aplodinotus grunniens and gizzard shad Dorosoma cepedianum predominated in these samples, which also included many cyprinids and centrarchids. Diel patterns of abundance varied with species and sampling location. Freshwater drums were more abundant near the surface at midnight than during the day. Common carp Cyprinus carpio were most abundant in collections at dusk, whereas all other cyprinids were most abundant at dusk and dawn. Numbers of gizzard shad also increased slightly at dusk. Total numbers of larvae collected were greatest at dusk in main-channel and main-channel-border samples; backwater areas produced the greatest catches at midnight and dawn. Seasonal, spatial, diel, and species-specific variations in larval fish abundances significantly influenced the proportion of the community potentially vulnerable to increased boat traffic through Pool 7.

  2. A consistent understanding of the ribbon structure for the Io plasma torus at the Voyager 1, 1991 ground-based, and Galileo J0 epochs

    NASA Astrophysics Data System (ADS)

    Smyth, William H.; Peterson, Charles A.; Marconi, Max L.

    2011-07-01

    A new four-dimensional (three spatial and local time) empirical model for the Io plasma torus is presented that includes several System III longitude asymmetries and a dawn-dusk electric field with variable direction and magnitude. The model is used to analyze and compare observations for the peak density structure of the plasma torus acquired at the 1979 Voyager 1, the 1991 ground-based, and the 1995 Galileo J0 epochs. The mean magnitude of the dawn-dusk electric field is determined to be much smaller at the 1991 ground-based epoch than at the Voyager 1 and Galileo J0 epochs. A consistent understanding of the radial structure for the density peaks in the plasma torus may then be achieved for these epochs if the dawn-dusk electric field departs by ˜20° from the true dawn-dusk direction and if account is taken of absolute density changes. The ratio of the electron density in the inner and outer plasma torus varies significantly for the three epochs and indicates different temporal evolutions in the balance of the plasma torus production and loss processes. The undisturbed electron density at Io's position in the plasma torus is calculated and has significantly different values at the three epochs; it is shown for each epoch to undergo large variations as Io changes its location in heliocentric phase angle and System III longitude. These large variations provide a wide variety of changing upstream plasma conditions for Io's atmospheric formation, local aurora and distant footprint emissions, and electrodynamic interaction.

  3. On chaotic conductivity in the magnetotail

    NASA Technical Reports Server (NTRS)

    Holland, Daniel L.; Chen, James

    1992-01-01

    The concept of chaotic conductivity and the acceleration of particles due to a constant dawn dusk electric field are studied in a magnetotail-like magnetic field. A test particle simulation is used including the full nonlinear dynamics. It is found that the acceleration process can be understood without invoking chaos and that the cross tail current is determined by the particle dynamics and distributions. It is concluded that in general there is no simple relationship between the electric field and the current.

  4. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    NASA Astrophysics Data System (ADS)

    Wright, D. M.; Yeoman, T. K.

    1999-07-01

    The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.

  5. Hydrogen density in the dayside venusian exosphere derived from Lyman-α observations by SPICAV on Venus Express

    NASA Astrophysics Data System (ADS)

    Chaufray, J.-Y.; Bertaux, J.-L.; Quémerais, E.; Villard, E.; Leblanc, F.

    2012-02-01

    A series of observations of the venusian hydrogen corona made by SPICAV on Venus Express are analyzed to estimate the amount of hydrogen in the exosphere of Venus. These observations were made between November 2006 and July 2007 at altitudes from 1000 km to 8000 km on the dayside. The Lyman-α brightness profiles derived are reproduced by the sum of a cold hydrogen population dominant below ˜2000 km and a hot hydrogen population dominant above ˜4000 km. The temperature (˜300 K) and hydrogen density at 250 km (˜10 5 cm -3) derived for the cold populations, near noon, are in good agreement with previous observations. Strong dawn-dusk exospheric asymmetry is observed from this set of observations, with a larger exobase density on the dawn side than on the dusk side, consistent with asymmetry previously observed in the venusian thermosphere, but with a lower dawn/dusk contrast. The hot hydrogen density derived is very sensitive to the sky background estimate, but is well constrained near 5000 km. The density of the hot population is reproduced by the exospheric model from Hodges (Hodges, R.R. [1999]. J. Geophys. Res. 104, 8463-8471) in which the hot population is produced by neutral-ions interactions in the thermosphere of Venus.

  6. Cool night-time temperatures induce the expression of CONSTANS and FLOWERING LOCUS T to regulate flowering in Arabidopsis.

    PubMed

    Kinmonth-Schultz, Hannah A; Tong, Xinran; Lee, Jae; Song, Young Hun; Ito, Shogo; Kim, Soo-Hyung; Imaizumi, Takato

    2016-07-01

    Day length and ambient temperature are major stimuli controlling flowering time. To understand flowering mechanisms in more natural conditions, we explored the effect of daily light and temperature changes on Arabidopsis thaliana. Seedlings were exposed to different day/night temperature and day-length treatments to assess expression changes in flowering genes. Cooler temperature treatments increased CONSTANS (CO) transcript levels at night. Night-time CO induction was diminished in flowering bhlh (fbh)-quadruple mutants. FLOWERING LOCUS T (FT) transcript levels were reduced at dusk, but increased at the end of cooler nights. The dusk suppression, which was alleviated in short vegetative phase (svp) mutants, occurred particularly in younger seedlings, whereas the increase during the night continued over 2 wk. Cooler temperature treatments altered the levels of FLOWERING LOCUS M-β (FLM-β) and FLM-δ splice variants. FT levels correlated strongly with flowering time across treatments. Day/night temperature changes modulate photoperiodic flowering by changing FT accumulation patterns. Cooler night-time temperatures enhance FLOWERING BHLH (FBH)-dependent induction of CO and consequently increase CO protein. When plants are young, cooler temperatures suppress FT at dusk through SHORT VEGETATIVE PHASE (SVP) function, perhaps to suppress precocious flowering. Our results suggest day length and diurnal temperature changes combine to modulate FT and flowering time. PMID:26856528

  7. Two encounters with the flank low-latitude boundary layer - Further evidence for closed field topology and investigation of the internal structure

    NASA Technical Reports Server (NTRS)

    Traver, D. P.; Mitchell, D. G.; Williams, D. J.; Frank, L. A.; Huang, C. Y.

    1991-01-01

    The structure of the flank low-latitude boundary layer (LLBL) is examined through differential energy spectra and particle angular anisotropies for traversals of the dawn flank (December 19, 1977) and dusk flank (July 7, 1978) during periods of predominantly northward magnetosheath field orientation. Spectra are presented that were obtained from combined ISEE 1 low-energy-proton and electron-differential-energy-analyzer and medium-energy-particle-instrument data extending over the 200-eV/q to 2-MeV energy range for the plasma sheet, stagnation region, outer LLBL, and magnetosheath regions. The stagnation region and the outer LLBL are each a mixture of plasma-sheet and magnetosheath populations, but the stagnation region contains a relatively higher fraction of plasma sheet particles, consistent with its placement earthward of the outer LLBL. Evidence for energization of thermal electrons appears during the dusk flank crossing. Bidirectional field-aligned ion distributions are observed with typically 5-to-1 enhancement of the flux along the magnetic field during certain portions of the dusk flank crossing.

  8. Coupled Magnetotail-Ionosphere Asymmetries from Ionospheric Hall Conduction

    NASA Astrophysics Data System (ADS)

    Lotko, W.; Smith, R. H.; Zhang, B.; Ouellette, J.; Brambles, O.; Lyon, J.; Wiltberger, M. J.

    2014-12-01

    Fast convective transport in the plasma sheet is more prevalent in the premidnight (dusk) sector relative to postmidnight. Ionospheric convection exhibits related asymmetries - more flux typically circulates in the dusk cell than in the dawn cell, and the nightside convection pattern is rotated clockwise when viewed over the North Pole. We show, using global simulations of the solar wind-magnetosphere-ionosphere interaction, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces asymmetries resembling observed distributions in plasmasheet flows and ionospheric convection (Figure, center panel). The primary causal agent in the simulations is a meridional gradient in ionospheric Hall conductance which, through Cowling polarization, regulates the distributions of i) electrical currents flowing within and between the ionosphere and magnetotail and ii) the nightside reconnection rate and resulting dawn-dusk distribution of plasma sheet fast flows. The asymmetry disappears in the simulation when the Hall conductance is taken to be uniform (left panel), and it reverses when the conductance is artificially depleted at auroral latitudes (right panel). The coupling between meridional currents and electric fields in the ionosphere and axial currents and electric fields in the plasmasheet is demonstrated by a simple model for non-ideal coupling of field-aligned currents flowing between the plasma sheet and the region of enhanced ionospheric conductance straddling the nightside convection throat.

  9. Mapping electrostatic potentials from the ionosphere to the magnetosphere

    NASA Technical Reports Server (NTRS)

    Sojka, J. J.; Foster, J. C.; Banks, P. M.; Doupnik, J. R.

    1983-01-01

    Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

  10. Mapping electrostatic potentials from the ionosphere to the magnetosphere

    NASA Astrophysics Data System (ADS)

    Sojka, J. J.; Foster, J. C.; Banks, P. M.; Doupnik, J. R.

    1983-11-01

    Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

  11. System III variations in apparent distance of Io plasma torus from Jupiter

    NASA Technical Reports Server (NTRS)

    Dessler, A. J.; Sandel, B. R.

    1992-01-01

    System III variations in apparent distance of the Io plasma torus from Jupiter are examined on the basis of data obtained from UVS scans across Jupiter's satellite system. The displacement of the dawn and dusk ansae are found to be unexpectedly complex. The displacements are unequal and both ansae are in motion with the motion of the approaching ansa being the lesser of the two. The radial motions, as measured from either the center of Jupiter or the offset-tilted dipole, are of unequal magnitude and have the System III periodicity. It is concluded that the cross-tail electric field that causes these torus motions is concentrated on the dusk ansa, varied with the System III period, and shows magnetic-anomaly phase control. It is found that the dawn-dust asymmetry in brightness is not explained simply by the cross-tail electric field. It is concluded that there is a heating mechanism that causes the dusk side of the Io plasma torus to be brighter than the dawn side.

  12. Hopkins Ultraviolet Telescope determination of the Io torus electron temperature

    NASA Technical Reports Server (NTRS)

    Hall, D. T.; Bednar, C. J.; Durrance, S. T.; Feldman, P. D.; Mcgrath, M. A.; Moos, H. W.; Strobel, D. F.

    1994-01-01

    Sulfur ion emissions from the Io plasma torus observed by the Hopkins Ultraviolet Telescope (HUT) in 1990 December have been analyzed to determine the effective temperature of the exciting electrons. Spectra were obtained with a long slit that extended from 3.1 to 8.7 Jupiter radii R(sub J) on both dawn and dusk torus ansae. The average temperature of electrons exciting S(2+) emissions from the dawn ansa is (4800 +/- 2400) K lower than on the dusk ansa, a dawn-dusk asymmetry comparable in both sign and magnitude to that measured by the Voyager Ultraviolet Spectrograph (UVS) experiment. Emissions from S(2+) ions are generated in a source region with electron temperatures in the range 32,000-56,000 K; S(3+) ion emissions are excited by electrons that average 20,000-40,000 K hotter. This distinct difference suggests that the S(3+) emission source region is spatially separate from the S(2+) source region. Estimated relative aperture filling factors suggest that the S(3+) emissions originate from a region more extended out of the centrifugal plane than the S(2+) emissions.

  13. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Jackman, C. M.; Thomsen, M. F.

    2016-04-01

    Reconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north-south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30RS downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure.

  14. Normal vision can compensate for the loss of the circadian clock.

    PubMed

    Schlichting, Matthias; Menegazzi, Pamela; Helfrich-Förster, Charlotte

    2015-09-22

    Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY. PMID:26378222

  15. IMF-By dependence of transient ionospheric flow perturbation associated with sudden impulses: SuperDARN observations

    NASA Astrophysics Data System (ADS)

    Hori, Tomoaki; Shinbori, Atsuki; Fujita, Shigeru; Nishitani, Nozomu

    2015-11-01

    A statistical study using a large dataset of Super Dual Auroral Radar Network (SuperDARN) observations is conducted for transient ionospheric plasma flows associated with sudden impulses (SI) recorded on ground magnetic field. The global structure of twin vortex-like ionospheric flows is found to be consistent with the twin vortices of ionospheric Hall current deduced by the past geomagnetic field observations. An interesting feature, which is focused on in this study, is that the flow structures show a dawn-dusk asymmetry depending on the combination of the polarity of SI and interplanetary magnetic field (IMF)-By. Detailed statistics of the SuperDARN observations reveal that the dawn-dusk asymmetry of flow vortices due to IMF-By appears during negative SIs, while such asymmetric characteristics are not seen during positive SIs. On the basis of the upstream observations, we suggest that this particular dawn-dusk asymmetry is caused by the interaction between the pre-existing round convection cell and a pair of the transient convection vortices associated with SIs.

  16. Label-free quantitative analysis of the casein kinase 2-responsive phosphoproteome of the marine minimal model species Ostreococcus tauri.

    PubMed

    Le Bihan, Thierry; Hindle, Matthew; Martin, Sarah F; Barrios-Llerena, Martin E; Krahmer, Johanna; Kis, Katalin; Millar, Andrew J; van Ooijen, Gerben

    2015-12-01

    Casein kinase 2 (CK2) is a protein kinase that phosphorylates a plethora of cellular target proteins involved in processes including DNA repair, cell cycle control, and circadian timekeeping. CK2 is functionally conserved across eukaryotes, although the substrate proteins identified in a range of complex tissues are often different. The marine alga Ostreococcus tauri is a unicellular eukaryotic model organism ideally suited to efficiently study generic roles of CK2 in the cellular circadian clock. Overexpression of CK2 leads to a slow circadian rhythm, verifying functional conservation of CK2 in timekeeping. The proteome was analysed in wild-type and CK2-overexpressing algae at dawn and dusk, revealing that differential abundance of the global proteome across the day is largely unaffected by overexpression. However, CK2 activity contributed more strongly to timekeeping at dusk than at dawn. The phosphoproteome of a CK2 overexpression line and cells treated with CK2 inhibitor was therefore analysed and compared to control cells at dusk. We report an extensive catalogue of 447 unique CK2-responsive differential phosphopeptide motifs to inform future studies into CK2 activity in the circadian clock of more complex tissues. All MS data have been deposited in the ProteomeXchange with identifier PXD000975 (http://proteomecentral.proteomexchange.org/dataset/PXD000975). PMID:25930153

  17. FORTRAN programs to process Magsat data for lithospheric, external field, and residual core components

    NASA Technical Reports Server (NTRS)

    Alsdorf, Douglas E.; Vonfrese, Ralph R. B.

    1994-01-01

    The FORTRAN programs supplied in this document provide a complete processing package for statistically extracting residual core, external field and lithospheric components in Magsat observations. To process the individual passes: (1) orbits are separated into dawn and dusk local times and by altitude, (2) passes are selected based on the variance of the magnetic field observations after a least-squares fit of the core field is removed from each pass over the study area, and (3) spatially adjacent passes are processed with a Fourier correlation coefficient filter to separate coherent and non-coherent features between neighboring tracks. In the second state of map processing: (1) data from the passes are normalized to a common altitude and gridded into dawn and dusk maps with least squares collocation, (2) dawn and dusk maps are correlated with a Fourier correlation efficient filter to separate coherent and non-coherent features; the coherent features are averaged to produce a total field grid, (3) total field grids from all altitudes are continued to a common altitude, correlation filtered for coherent anomaly features, and subsequently averaged to produce the final total field grid for the study region, and (4) the total field map is differentially reduced to the pole.

  18. Passive ranging redundancy reduction in diurnal weather conditions

    NASA Astrophysics Data System (ADS)

    Cha, Jae H.; Abbott, A. Lynn; Szu, Harold H.

    2013-05-01

    Ambiguity in binocular ranging (David Marr's paradox) may be resolved by using two eyes moving from side to side behind an optical bench while integrating multiple views. Moving a head from left to right with one eye closed can also help resolve the foreground and background range uncertainty. That empirical experiment implies redundancy in image data, which may be reduced by adopting a 3-D camera imaging model to perform compressive sensing. Here, the compressive sensing concept is examined from the perspective of redundancy reduction in images subject to diurnal and weather variations for the purpose of resolving range uncertainty at all weather conditions such as the dawn or dusk, the daytime with different light level or the nighttime at different spectral band. As an example, a scenario at an intersection of a country road at dawn/dusk is discussed where the location of the traffic signs needs to be resolved by passive ranging to answer whether it is located on the same side of the road or the opposite side, which is under the influence of temporal light/color level variation. A spectral band extrapolation via application of Lagrange Constrained Neural Network (LCNN) learning algorithm is discussed to address lost color restoration at dawn/dusk. A numerical simulation is illustrated along with the code example.

  19. Normal vision can compensate for the loss of the circadian clock

    PubMed Central

    Schlichting, Matthias; Menegazzi, Pamela; Helfrich-Förster, Charlotte

    2015-01-01

    Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY. PMID:26378222

  20. Electrodynamic Context of Magnetotail and Magnetopause Dynamics Observed by Magnetospheric Multiscal

    NASA Astrophysics Data System (ADS)

    Anderson, B. J.; Korth, H.; Waters, C. L.; Barnes, R. J.; Samara, M.; Russell, C. T.; Strangeway, R. J.; Plaschke, F.; Magnes, W.; Fischer, D.; Merkin, V. G.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Leinweber, H. K.; Le, G.; Bromund, K. R.; Chutter, M.; Slavin, J. A.; Kepko, L.; Le Contel, O.; Mauk, B.; Westlake, J. H.; Gjerloev, J. W.; Ruohoniemi, J. M.

    2015-12-01

    After successful launch and deployment on 14 March 2015, the four Magnetosphere Multiscale (MMS) spacecraft were commissioned during the first local time precession of the orbit line of apsides across the magnetotail from dawn to dusk. Prime science observations began in September 2015 when orbit apogee had moved to the dusk sector at magnetopause distances. Signatures of magnetotail dynamics were observed during payload and fleet commissioning. The electrodynamic context of the magnetotail events at MMS as well as observations at the dusk and afternoon magnetopause is assessed using correlative observations from low Earth orbit and ground-based instruments including the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE), SuperMAG, and SuperDARN. Substorm current onsets are prevalent in AMPERE data and are highly correlated with magnetotail injections and dipolarizations observed by MMS. To better constrain how the MMS magnetotail observations are related to global processes, we also examine the occurrence and prevalence of similar ionospheric onset signatures when MMS was at high altitudes in the magnetotail but observed no local signatures of injections or dipolarizations. For MMS magnetopause observations, we explore the relationship of magnetic reconnection signatures at MMS with the convection patterns derived from AMPERE and ionosphere observations to establish the relationship of the local MMS observations and global magnetospheric convective state.

  1. Solar wind influence on the Jovian inner magnetosphere observed by Hisaki/EXCEED

    NASA Astrophysics Data System (ADS)

    Murakami, G.; Yoshioka, K.; Yamazaki, A.; Tsuchiya, F.; Kimura, T.; Tao, C.; Kagitani, M.; Sakanoi, T.; Uemizu, K.; Kasaba, Y.; Yoshikawa, I.; Fujimoto, M.

    2015-12-01

    The dawn-dusk asymmetry of the Io plasma torus has been seen by several observations [e.g., Sandel and Broadfoot, 1982; Steffl et al., 2004]. Ip and Goertz [1983] explained this asymmetry can be caused by a dawn-to-dusk electric field in the Jupiter's inner magnetosphere. However, the question what physical process can impose such an electric field deep inside the strong magnetosphere still remains. The long-term monitoring of the Io plasma torus is a key observation to answer this question. The extreme ultraviolet (EUV) spectrometer EXCEED onboard the Hisaki satellite observed the Io plasma torus continuously during the two periods: from December 2013 to March 2014 and from November 2014 to May 2015. We found clear responses of the dawn-dusk asymmetry to rapid increases of the solar wind dynamic pressure. We statistically analyzed the relations between solar wind and IPT response. Furthermore, we investigated the influence of Io's volcanic activity, detected by Hisaki in January 2015, on the solar wind response of Jovian inner magnetosphere. We will report the initial results of this study.

  2. Precipitating and trapped ions and electrons observed at 840 km during the great magnetic storm of February 1986

    SciTech Connect

    Swider, W.

    1990-07-01

    A detailed picture is presented of the equatorward boundaries of the auroral ovals at dawn, morning, dusk, and evening for the three most disturbed days of February 1986. North-south symmetry for the boundaries of keV particles was good, and the differences between the ion and electron boundaries agreed with statistics which show the ion edge slightly equatorward of the electron edge at dusk, with the reverse for dawn. The electron boundary was most equatorward of the ion boundary for morning. Best symmetry and least difference were for evening, the sector nearest the central plasma sheet. Ions with energies from thermal to several hundred electron volts penetrated inward to L = 1.2. Initial penetration was confined mainly, if not exclusively, to the dawn sector. The sudden appearance of low-energy ions deep in the plasmasphere at dusk and evening after storm maximum suggests corotation from a plasmapause as low as L = 1.7 at dawn. Low-energy electrons rarely advanced equatorward of the deV electrons. On the other hand, keV electrons occasionally were detected about the equator, apparently in relation to the inward convection of the radiation belt. Very energetic, MeV, particles occurred near 52 deg MLAT, mainly after storm maximum and often unsymmetrically, which may reflect a characteristic akin to the South Atlantic Anomaly.

  3. Effects of the Dipole Tilt on Dayside Magnetic Reconnection in the Earth's Magnetosphere for Northward IMF

    NASA Astrophysics Data System (ADS)

    Park, K.; Ogino, T.

    2006-12-01

    Magnetic reconnection at the dayside magnetopause are dominantly affected by the relative orientation of the magnetic fields in the magnetosheath and magnetosphere, the relative perpendicular velocities of field lines both before and after reconnection, and the location of the minimum geomagnetic field. We have performed a high-resolution and time-dependent three dimensional MHD simulation of interaction between the solar wind and the Earth's magnetosphere when the dipole tilt, and By and Bz components of the IMF are simultaneously included in the whole volume of the simulation box. In the recent study of Park, K.S. et al. (2006) found that for positive dipole tilt (northern hemisphere is summer) and southward IMF (Bz = 5 nT, By = 5nT), the reconnection site shifts sunward and equatorward in the summer hemisphere, and moves tailward and away from equator in the winter hemisphere. The dipole tilt creates asymmetry that strongly affects the direction of the plasma flow due to reconnection. Moreover, the electric field in the northern "reconnection" region (antiparallel region) is 50% larger than that at the magnetic equator and twice that at the subsolar point. In present study, for the case of positive dipole tilt, and during the northward IMF (Bz = 5 nT, By = 5nT), magnetic reconnection occurs at high latitudes in the northern dusk due to antiparallel field condition in the summer hemisphere for By > 0 and creates open field lines. The open field lines which are generated in the dusk sector and their feet are on the northern ionosphere, move from dusk to dawn in the dayside magnetopause and then come back to dusk in the tail. Tail reconnection successively occurs in the slant and elevated plasma sheet. The polar cap potential in dusk cell is larger than that the dawn cell in summer hemisphere. Moreover three-cell pattern appears in the northern ionosphere. On the other hand, the negative potential is comparable to the positive potential in winter hemisphere and the

  4. Ionospheric vertical drift response at a mid-latitude station

    NASA Astrophysics Data System (ADS)

    Kouba, Daniel; Koucká Knížová, Petra

    2016-07-01

    Vertical plasma drift data measured at a mid-latitude ionospheric station Pruhonice (50.0 ° N, 14.6 ° E) were collected and analysed for the year 2006, a year of low solar and geomagnetic activity. Hence these data provide insight into the drift behaviour during quiet conditions. The following typical diurnal trend is evident: a significant decay to negative values (downward peak) at dawn; generally less pronounced downward peak at dusk hours. Magnitude of the downward drift varies during the year. Typically it reaches values about 20 ms-1 at dawn hours and 10 ms-1 at dusk hours. Maximum dawn magnitude of about 40 ms-1 has been detected in August. During daytime the vertical drifts increases from the initial small downward drifts to zero drift around noon and to small upward drifts in the afternoon. Night-time drift values display large variability around a near zero vertical drift average. There is a significant trend to larger downward drift values near dawn and a less pronounced decrease of the afternoon upward vertical drifts near sunset. Two regular downward peaks of the drift associated with the dawn and dusk are general characteristics of the analysed data throughout the year 2006. Their seasonal course corresponds to the seasonal course of the sunrise and sunset. The duration of prevailing negative drift velocities forming these peaks and thus the influence of the dawn/dusk on the drift velocity is mostly 1.5-3 h. The dawn effect on vertical drift tends to be larger than the effect of the dusk. The observed magnitude of the sunrise and sunset peaks show significant annual course. The highest variability of the magnitude is seen during winter. High variability is detected till March equinox and again after September equinox. Around solstice, both peaks reaches lowest values. After that, the magnitudes of the drift velocity increase smoothly till maxima in summer (August). The vertical drift velocity course is smooth between June solstice and September

  5. Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase

    NASA Technical Reports Server (NTRS)

    Le, G.; Russell, C. T.; Slavin, J. A.; Lucek, E. A.

    2008-01-01

    We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L greater than 5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L less than 5). The precipitation loss

  6. Earth's distant magnetotail current sheet near and beyond lunar orbit

    NASA Astrophysics Data System (ADS)

    Vasko, I. Y.; Petrukovich, A. A.; Artemyev, A. V.; Nakamura, R.; Zelenyi, L. M.

    2015-10-01

    We analyze the structure of the Earth magnetotail current sheet (CS) in middle, X∈[-50,-20] RE, and distant, X∈[-100,-80] RE, regions using data set of 573 CS crossings by Geotail in 1994-1995. For a subset of 213 CSs we determine the CS thickness L, average current density j0, and velocity vD=j0/en0 (n0 is the ion number density). We find similar dawn-dusk distributions of CS parameters for middle and distant tail: L is about 3000 km at the dusk flank and grows up to 12,000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2-3; and the most intense CSs (with higher vD) are observed near midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail in more than 50% of crossings. For observed CSs electrons likely provide the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). Weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. Intense CSs have thickness of about 3-7 thermal gyroradii and much smaller Bz implying more stretched field line configuration. Intense CSs are accompanied by fast ion flows: vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. The properties of the CS in middle and distant tail are compared with those found for the near-Earth tail.

  7. Ionospheric current contribution to the main impulse of a negative sudden impulse

    NASA Astrophysics Data System (ADS)

    Vichare, Geeta; Rawat, Rahul; Bhaskar, Ankush; Pathan, Bashir M.

    2014-12-01

    The geomagnetic field response to a moderate-amplitude negative sudden impulse (SI-) that occurred on 14 May 2009 at 10:30 UT was examined at 97 geomagnetic observatories situated all over the globe. The response signature contains a contribution from magnetospheric as well as ionospheric currents. The main impulse (MI) is defined as the maximum depression in the observed geomagnetic field. It is observed that for low-to-high latitudes, the amplitude of the MI is larger in the afternoon to post-dusk sector than in the dawn-noon sector, indicating asymmetry in the MI amplitude. We estimated the contribution at various observatories due to the Chapman-Ferraro magnetopause currents using the Tsyganenko model (T01) and subtracted this from the observed MI amplitude to obtain the contribution due to ionospheric currents. It is found that the ionospheric currents contribute significantly to the MI amplitude of moderate SI- even at low-to-mid latitudes and that the contribution is in the same direction as that from the magnetopause currents near dusk and in the opposite direction near dawn. The equivalent current vectors reveal a clockwise (anticlockwise) ionospheric current loop in the afternoon (morning) sector during the MI of the negative pressure impulse. This evidences an ionospheric twin-cell-vortex current system (DP2) due to field-aligned currents (FACs) associated with the dusk-to-dawn convection electric field during the MI of an SI-. We also estimated the magnetic field variation due to prompt penetration electric fields, which is found to be very small at low latitudes in the present case. The studied SI- is not associated with shock, and hence no preliminary reverse impulse was evident. In addition, the summer hemisphere reveals larger MI amplitudes than the winter hemisphere, indicating once again the role of ionospheric currents.

  8. Average thermospheric wind patterns over the polar regions, as observed by CHAMP

    NASA Astrophysics Data System (ADS)

    Lühr, H.; Rentz, S.; Ritter, P.; Liu, H.; Häusler, K.

    2007-06-01

    Measurements of the CHAMP accelerometer are utilized to investigate the average thermospheric wind distribution in the polar regions at altitudes around 400 km. This study puts special emphasis on the seasonal differences in the wind patterns. For this purpose 131 days centered on the June solstice of 2003 are considered. Within that period CHAMP's orbit is precessing once through all local times. The cross-track wind estimates of all 2030 passes are used to construct mean wind vectors for 918 equal-area cells. These bin averages are presented in corrected geomagnetic coordinates. Both hemispheres are considered simultaneously providing summer and winter responses for the same prevailing geophysical conditions. The period under study is characterized by high magnetic activity (Kp=4-) but moderate solar flux level (F10.7=124). Our analysis reveals clear wind features in the summer (Northern) Hemisphere. Over the polar cap there is a fast day-to-night flow with mean speeds surpassing 600 m/s in the dawn sector. At auroral latitudes we find strong westward zonal winds on the dawn side. On the dusk side, however, an anti-cyclonic vortex is forming. The dawn/dusk asymmetry is attributed to the combined action of Coriolis and centrifugal forces. Along the auroral oval the sunward streaming plasma causes a stagnation of the day-to-night wind. This effect is particularly clear on the dusk side. On the dawn side it is evident only from midnight to 06:00 MLT. The winter (Southern) Hemisphere reveals similar wind features, but they are less well ordered. The mean day-to-night wind over the polar cap is weaker by about 35%. Otherwise, the seasonal differences are mainly confined to the dayside (06:00-18:00 MLT). In addition, the larger offset between geographic and geomagnetic pole in the south also causes hemispheric differences of the thermospheric wind distribution.

  9. Surface waves on Saturn's magnetopause

    NASA Astrophysics Data System (ADS)

    Masters, A.; Achilleos, N.; Cutler, J. C.; Coates, A. J.; Dougherty, M. K.

    2011-10-01

    Waves on the surface of a planetary magnetopause lead to the transport of energy into the magnetosphere, making them an important aspect of solar wind-magnetosphere coupling. In the case of Saturn's magnetosphere it has been proposed that the growth of the Kelvin-Helmholtz (K-H) instability produces greater wave activity on the dawn side of the magnetopause than on the dusk side. Here we test this hypothesis using data taken by the Cassini spacecraft during 520 magnetopause crossings. We determine the surface normal for 477 of the crossings and show that perturbations of the surface orientation are predominantly in the direction perpendicular to the local magnetospheric magnetic field, due to the stabilizing influence of magnetic tension forces. There are two most likely orientations with respect to the magnetospheric magnetic field, and 45% of the crossings were part of a clear oscillation of consecutive normals. The only local time asymmetry in the surface orientation is a greater level of normal perturbations at dusk than at dawn. These results suggest that surface waves on Saturn's magnetopause are ubiquitous, and the K-H instability is the most plausible driving mechanism. The waves generally propagate tailward, with a typical period, wavelength, speed, and amplitude of 4 hrs, 10 Saturn radii (RS), 50 km s-1, and 1 RS, respectively. The lack of the hypothesized dawn-dusk asymmetry in wave activity means that we need to revise our understanding of the growth of the K-H instability at Saturn's magnetopause, which will have implications for the study of other planetary magnetospheres.

  10. Properties of low-latitude mantle plasma in the Earth's magnetotail: ARTEMIS observations and global MHD predictions

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Ping; Lyons, Larry R.; Angelopoulos, Vassilis

    2014-09-01

    The Earth's plasma mantle is one of the major suppliers of particles for the plasma sheet. To understand its plasma characteristics, spatial distributions, and dependencies on interplanetary magnetic field (IMF) direction, we statistically analyzed the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) observations in the low-latitude magnetotail (~10 RE above and below the current sheet) and investigated the predictions from global Block Adaptive Tree Solar wind-Roe-Upwind Scheme MHD simulations. The mantle plasma flows tailward along magnetic field lines (~50-200 km/s) and at the same time drifts toward midnight and toward the current sheet. The mantle plasma has similar temperature (~0.05-0.2 keV) to the magnetosheath plasma but has lower density (~0.1-1 cm-3). The mantle appearance is dawn-dusk asymmetric depending mainly on the IMF By direction. The occurrence rates, density, and V|| all decrease with decreasing |Y|. This density cross-tail profile suggests that the low-latitude mantle plasma mainly comes from the magnetosheath entering through the tail magnetopause along the open field lines. Density is highly and positively correlated with V||. These observations are qualitatively consistent with the MHD results. The simulations indicate that as IMF By becomes dominant, the source locations at the magnetopause for the mantle move to lower latitudes and become dawn-dusk asymmetric, and the tail cross section also becomes distorted with the magnetopause shape elongating and the current sheet tilting significantly. Degrees of these changes also vary with the downtail distances and IMF Bz direction. The source location change leads to the dawn-dusk asymmetric mantle appearance. The tail cross-section change alters the distance from the sources to the current sheet and thus the resulting mantle density distributions just outside the plasma sheet.

  11. Superposed epoch analysis of the ionospheric convection evolution during substorms: IMF BY dependence

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Milan, S. E.; Yeoman, T. K.; Sato, N.; Yukimatu, A. S.; Wild, J. A.

    2010-10-01

    We present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field (IMF). Observations of the ionospheric convection were provided by the Super Dual Auroral Radar Network (SuperDARN) and substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. We find that during the substorm growth phase the expected IMF BY-dependent dawn-dusk asymmetry is observed over the entire convection pattern, but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone. In the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk-dawn asymmetry being more closely related to the magnetic local time of substorm onset, itself only weakly governed by IMF BY. Owing to the preponderance of substorms occurring just prior to magnetic midnight, the substorm-asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector, a manifestation of the so-called “Harang discontinuity.” This results in the northern (southern) hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative (positive) IMF BY. When the preexisting convection pattern in the northern (southern) hemisphere is driven by positive (negative) IMF BY, the nightside auroral convection changes markedly over the course of the substorm to establish this same “Harang” configuration.

  12. The role of pollinators in maintaining variation in flower colour in the Rocky Mountain columbine, Aquilegia coerulea

    PubMed Central

    Thairu, Margaret W.; Brunet, Johanne

    2015-01-01

    Background and Aims Flower colour varies within and among populations of the Rocky Mountain columbine, Aquilegia coerulea, in conjunction with the abundance of its two major pollinators, hawkmoths and bumble-bees. This study seeks to understand whether the choice of flower colour by these major pollinators can help explain the variation in flower colour observed in A. coerulea populations. Methods Dual choice assays and experimental arrays of blue and white flowers were used to determine the preference of hawkmoths and bumble-bees for flower colour. A test was made to determine whether a differential preference for flower colour, with bumble-bees preferring blue and hawkmoths white flowers, could explain the variation in flower colour. Whether a single pollinator could maintain a flower colour polymorphism was examined by testing to see if preference for a flower colour varied between day and dusk for hawkmoths and whether bumble-bees preferred novel or rare flower colour morphs. Key Results Hawkmoths preferred blue flowers under both day and dusk light conditions. Naïve bumble-bees preferred blue flowers but quickly learned to forage randomly on the two colour morphs when similar rewards were presented in the flowers. Bees quickly learned to associate a flower colour with a pollen reward. Prior experience affected the choice of flower colour by bees, but they did not preferentially visit novel flower colours or rare or common colour morphs. Conclusions Differences in flower colour preference between the two major pollinators could not explain the variation in flower colour observed in A. coerulea. The preference of hawkmoths for flower colour did not change between day and dusk, and bumble-bees did not prefer a novel or a rare flower colour morph. The data therefore suggest that factors other than pollinators may be more likely to affect the flower colour variation observed in A. coerulea. PMID:25808657

  13. Strain- and sex-specific differences in daily flight activity and the circadian clock of Anopheles gambiae mosquitoes.

    PubMed

    Rund, Samuel S C; Lee, Samuel J; Bush, Brian R; Duffield, Giles E

    2012-12-01

    Anopheles gambiae, the primary African malaria vector, is currently speciating into two incipient species, the so-called "molecular forms" M and S. While some geographic areas may contain only one form, in many areas both forms are found coexisting, but reproductively isolated. It appears that spatial segregation of mating swarms may contribute significantly to reproductive isolation as in many locales single-form swarms exist almost exclusively even though they are in close geographic proximity. The mechanism causing this spatial segregation is not well understood. Here, we compare the locomotor flight activity of M and S form male and female An. gambiae mosquitoes with the goal of identifying potential strain-specific temporal differences that could potentially serve as a mating barrier. We use an infrared beam break method to monitor flight activity of individual mosquitoes with a minute-to-minute time resolution under both LD cycle and constant dark conditions. We compare daily total flight activity, activity onset, peak in early nocturnal activity, the build up of dusk-related activity, and the free-running circadian period length. Our investigations revealed strain- and sex-specific differences in total daily activity. In both forms, males commenced nightly flight activity earlier than females, and this corresponded with a significantly shorter circadian period length in males compared to females. We note strain-specific differences in this response to dusk as males of the M form have a pronounced build up in flight activity relative to the S form males prior to complete darkness. This is likely driven by a differential response to the decreasing light intensity at dusk. We hypothesize that this behavioral difference could be a temporal factor contributing to the assembly of single-form swarms. PMID:23068991

  14. Penetration Electric Fields and Inner Magnetosphere Dynamics: A Model and Data Comparison

    NASA Technical Reports Server (NTRS)

    Maynard, Nelson C.

    1998-01-01

    Significant progress has been made on the analysis of the June, 1991 storm. We have completed the analysis of the CRRES and DMSP data sets. We have been able to follow the evolution during the storm of the inner edge of the electric field patterns in the dusk sector and its relation to electron boundaries, ion boundaries and the ring current. Whereas the CRRES data provide radial cuts out through the plasmasphere every I 0 hours, DMSP provides snapshots every orbit of the potential and particle boundaries. Electric field and energetic particle measurements from CRRES and ion drifts and energetic particle measurements from DMSP provide the principal data sets. The combined data set provides high resolution definition of the boundary motions over the phases of the storm. L shell differences between the DMSP and CRRES particle boundaries are easily explained by inflation of the dusk sector by the ring current. The electric field boundaries are typically associated with the ion boundary and the inner edge of the ring current except during rapid increases in the cross-polar cap potential. A significant fraction of the dusk cell potential is found inside the plasmasheet electron inner edge. Twice during the storm this potential exceeded 60 kV. A paper (copy attached) has been prepared (Burke et al., 1998) and submitted to JGR. An invited paper will be presented by Burke at the spring AGU meeting. An abstract has also been submitted to the COSPAR meeting for presentation by Maynard. New simulations have been carried out with the Rice Convection Model for the magnetic storm of June 4-5, 1991, and comparisons have been made with CRRES and DMSP data.

  15. Observations of Thermospheric Horizontal Winds at Watson Lake, Yukon Territory (lambda=65 Deg N)

    NASA Technical Reports Server (NTRS)

    Niciejewski, R. J.; Killeen, T. L.; Solomon, Stanley C.

    1996-01-01

    Fabry-Perot interferometer observations of the thermospheric O I (6300 A) emission have been conducted from an airglow observatory at a dark field site in the southeastern Yukon Territory, Canada, for the period November 1991 to April 1993. The experiment operated in unattended, remote fashion, has resulted in a substantial data set from which mean neutral winds have been determined. Dependent upon geomagnetic activity, the nocturnal location of the site is either equatorward of the auroral oval or within oval boundaries. The data set is rich enough to permit hourly binning of neutral winds based upon the K(sub p) geomagnetic disturbance index as well as the season. For cases of low geomagnetic activity the averaged vector horizontal neutral wind exhibits the characteristics of a midlatitude site displaying antisunward pressure-gradient-driven winds. As the geomagnetic activity rises in the late afternoon and evening winds slowly rotate sunward in an anticlockwise direction, initially remaining near 100 m/s in speed but eventually increasing to 300 m/s for K(sub p) greater than 5. For the higher levels of activity the observed neutral wind flow pattern resembles a higher-latitude polar cap pattern characterized by ion drag forcing of thermospheric neutral gases. In addition, rotational Coriolis forcing on the dusk side enhances the ion drag forcing, resulting in dusk winds which trace out the clockwise dusk cell plasma flow. On the dawn side the neutral winds also rotate in an anticlockwise direction as the strength of geomagnetic disturbances increase. Since the site is located at a transition latitude between the midlatitude and the polar cap the data set provides a sensitive test for general circulation models which attempt to parameterize the contribution of magnetospheric processes. A comparison with the Vector Spherical Harmonic (VSH) model indicates several regions of poor correspondence for December solstice conditions but reasonable agreement for the

  16. The magnetospheric lobe at geosynchronous orbit

    SciTech Connect

    Thomsen, M.F.; Bame, S.J.; McComas, D.J.

    1994-09-01

    On rare occasions, satellites at geosynchronous altitude enter the magnetospheric lobe, characterized by extremely low ion fluxes between 1 eV and 40 keV and electron fluxes above a few hundred eV. One year of plasma observations from two simultaneously operating spacecraft at synchronous orbit is surveyed for lobe encounters. A total of 34 full encounters and 56 apparent near encounters are identified, corresponding to {approximately}0.06% of the total observation time. Unlike energetic particle (E>40 keV) dropouts studied earlier, there is a strong tendency for the lobe encounters to occur postmidnight, as late as 07 local time. The two spacecraft encounter the lobe with different rates and in different seasons. These occurrence properties are not simply explicable in terms of the orbital geometry in either the solar magnetic or the geocentric solar magnetospheric coordinate system. A composite coordinate system which previously organized more energetic particle dropouts is somewhat more successful in organizing the lobe encounters, suggesting that solar wind distortion of the magnetic equatorial plane away from the dipole location and toward the antisolar direction may be largely responsible for these dropouts. The authors results further suggest that this distortion persists even sunward of the dawn-dusk terminator. However, a simple dawn-dusk symmetric distortion does not fully account for all the seasonal and local time asymmetries in the occurrence of the lobe encounters; thus there is probably an additional dawn-dusk asymmetry in the distorted field. The lobe encounters are strongly associated with magnetospheric activity and tend to occur in association with rare magnetosheath encounters at synchronous orbit. It thus appears that the presence of the lobe at geosynchronous orbit is the result of major, probably asymmetric modifications of the magnetospheric field geometry in times of strong disturbance. 19 refs., 7 figs., 1 tab.

  17. Observations of a Unique Type of ULF Wave by Low-Altitude Space Technology 5 Satellites

    NASA Technical Reports Server (NTRS)

    Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

    2011-01-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three-microsatellite constellation deployed into a 300 x 4500 km dawn-dusk and Sun-synchronous polar orbit with 105.6deg inclination angle. Because of the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc2-3 frequency range. These Pc2-3 waves appear as wave packets with durations in the order of 5-10 min. As the maximum separations of the ST-5 spacecraft are in the order of 10 min, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc2-3 band; instead, the waves appear to be the common Pc4-5 waves associated with field line resonances. We suggest that these unique Pc2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-dusk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field line resonances.

  18. Observations of a unique type of ULF wave by low-altitude Space Technology 5 satellites

    NASA Astrophysics Data System (ADS)

    Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

    2011-08-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three-microsatellite constellation deployed into a 300 × 4500 km dawn-dusk and Sun-synchronous polar orbit with 105.6° inclination angle. Because of the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc2-3 frequency range. These Pc2-3 waves appear as wave packets with durations in the order of 5-10 min. As the maximum separations of the ST-5 spacecraft are in the order of 10 min, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc2-3 band; instead, the waves appear to be the common Pc4-5 waves associated with field line resonances. We suggest that these unique Pc2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-dusk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field line resonances.

  19. Observation of magnetopause fluctuations during a Cluster-THEMIS conjunction

    NASA Astrophysics Data System (ADS)

    Hwang, Kyoung-Joo; Goldstein, Mevlyn

    On April 27, 2007, THEMIS observed quasi-periodic magnetopause fluctuations for a prolonged time period (9 hrs) as they skimmed the dusk-side magnetopause, while Cluster detected 1.5-hour-long boundary undulations as they traversed the morning-side magnetopause. The com-parison between Cluster and THEMIS with ACE data implies that: 1) Similar periodicity and patterns of its variability between Cluster and THEMIS observations, with a certain time in-terval longer than is expected from the upstream magnetosheath travel time between THEMIS and Cluster locations, indicate that the dusk-side surface waves have been excited at the nearly subsolar region; 2) The complicated inner-LLBL fluctuations observed by THEMIS have been resulted from the development and modulation of the waves according to the local environment during convection along the LLBL, while Cluster observed the magnetopause fluctuations that appear to be more explicitly controlled by SW variations in the morning sector; 3) The intensity of KHW, often well characterized by Bm power spectra reflect the effects of IMF conditions, exhibiting a correlation with SW temperature and IMF clock angle, i.e., a more solid power law when IMF points due north or south rather than due dawn or dusk; 4) Steeper wavefront at the anti-sunward/sunward edge of KHW during southward/northward IMF support more rapid and turbulent evolution of KHW under southward IMF conditions [Hwang et al., 2010; Kuznetsova et al., 2008], and the steepening effects of the curvature forces of the magnetosheath flux tubes during northward IMF [Chen et al., 1997].

  20. Review of Solar Wind Entry into and Transport Within the Plasma Sheet

    NASA Astrophysics Data System (ADS)

    Wing, S.; Johnson, J. R.; Chaston, C. C.; Echim, M.; Escoubet, C. P.; Lavraud, B.; Lemon, C.; Nykyri, K.; Otto, A.; Raeder, J.; Wang, C.-P.

    2014-11-01

    The plasma sheet is populated in part by the solar wind plasma. Four solar entry mechanisms are examined: (1) double cusp or double lobe reconnection, (2) Kelvin-Helmholtz Instability (KHI), (3) Kinetic Alfvén waves (KAW), and (4) Impulsive Penetration. These mechanisms can efficiently fill the plasma sheet with cold dense ions during northward interplanetary magnetic field (IMF). The solar wind ions appear to have been heated upon entry along the plasma sheet dawn flank. The cold-component (solar wind origin) ion density is higher on the dawn flank than the dusk flank. The asymmetric evolution of the KAW and magnetic reconnection in association with the KHI at the dawn and dusk flank magnetopause may partly produce the dawn-dusk temperature and density asymmetries. Solar wind that crosses the magnetopause lowers the specific entropy ( s= p/ ρ γ ) of the plasma sheet along the flanks. Subsequent transport of the cold ions from the flanks to the midnight meridian increases s by a factor of 5. T i , T e , s i , and s e increase when the solar wind particles are transported across the magnetopause, but T i / T e is roughly conserved. Within the magnetotail, E× B and curvature and gradient drifts play important roles in the plasma transport and can explain the large features seen in the plasma sheet. Turbulence can also play a significant role, particularly in the cold plasma transport from the flanks to the midnight meridian. Total entropy ( S= pV γ ) conservation provides important constraints on the plasma sheet transport, e.g., fast flows.

  1. Turbulence in a Global Magnetohydrodynamic Simulation of the Earth's Magnetosphere during Northward and Southward Interplanetary Magnetic Field

    NASA Technical Reports Server (NTRS)

    El-Alaoui, M.; Richard, R. L.; Ashour-Abdalla, M.; Walker, R. J.; Goldstein, M. L.

    2012-01-01

    We report the results of MHD simulations of Earth's magnetosphere for idealized steady solar wind plasma and interplanetary magnetic field (IMF) conditions. The simulations feature purely northward and southward magnetic fields and were designed to study turbulence in the magnetotail plasma sheet. We found that the power spectral densities (PSDs) for both northward and southward IMF had the characteristics of turbulent flow. In both cases, the PSDs showed the three scale ranges expected from theory: the energy-containing scale, the inertial range, and the dissipative range. The results were generally consistent with in-situ observations and theoretical predictions. While the two cases studied, northward and southward IMF, had some similar characteristics, there were significant differences as well. For southward IMF, localized reconnection was the main energy source for the turbulence. For northward IMF, remnant reconnection contributed to driving the turbulence. Boundary waves may also have contributed. In both cases, the PSD slopes had spatial distributions in the dissipative range that reflected the pattern of resistive dissipation. For southward IMF there was a trend toward steeper slopes in the dissipative range with distance down the tail. For northward IMF there was a marked dusk-dawn asymmetry with steeper slopes on the dusk side of the tail. The inertial scale PSDs had a dusk-dawn symmetry during the northward IMF interval with steeper slopes on the dawn side. This asymmetry was not found in the distribution of inertial range slopes for southward IMF. The inertial range PSD slopes were clustered around values close to the theoretical expectation for both northward and southward IMF. In the dissipative range, however, the slopes were broadly distributed and the median values were significantly different, consistent with a different distribution of resistivity.

  2. Earth magnetotail current sheet near and beyond the Lunar orbit

    NASA Astrophysics Data System (ADS)

    Vasko, I.; Petrukovich, A. A.; Artemyev, A.; Nakamura, R.; Zelenyi, L. M.

    2015-12-01

    We analyze the structure of the Earth magnetotail current sheet (CS) in middle, -50 REdusk distributions of the CS parameters: L is about 3000 km at the dusk flank and grows up to 12000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2-3; the most intense CSs (with higher vD) are observed near the midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail regions in more than 50% of crossings. For observed CSs electrons provide likely the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). The weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. The intense CSs have thickness of about 3-7 thermal gyroradii and much smaller Bz implying a more stretched field line configuration. For intense CSs velocity vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. Intense CSs may be responsible for the Bursty Bulk Flow generation in the middle and distant tail regions.

  3. Evolution of ring current and radiation belt particles under the influence of storm-time electric fields

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Shinbori, A.; Ono, T.; Iizima, M.; Kumamoto, A.

    2007-06-01

    Electric field and potential distributions in the inner magnetosphere during geomagnetic storms have been investigated using the Akebono/EFD data. Using this electric field, we study injection of ring current particles and acceleration of radiation belt electrons by single-particle calculations. During the main phase, the dawn-dusk electric field is intensified especially in a range of 2 < L < 5 with a maximum amplitude of 6 mV/m on the duskside, and a two-cell convection pattern with a potential difference of 180 kV is identified. The convection pattern on the equatorial plane is significantly distorted with a large potential drop of 70 kV on the dawn and dusk sectors, indicating an intrinsic source of large-scale electric field in the inner magnetosphere. The plasma sheet ions are gathered into the dusk to premidnight sector in the inner magnetosphere in the region of enhanced electric field due to the strong E × B drift. The ions are transported into around 4 RE with an acceleration of more than 1 order of magnitude within 40 min, conserving the first adiabatic invariants. Relativistic electrons with initial energy of some hundreds of kiloelectron volts at 5 RE are energized to more than 100 keV for 3 hours. The energy spectrum during the recovery phase of 9 October 1990 geomagnetic storm observed by the CRRES satellite is reproduced without the radial diffusion or nonadiabatic acceleration by plasma waves. It is possible that this acceleration process is the inhomogeneity of the large-scale electric field, which corresponds to the ∇ × E term along orbits of electrons around the Earth.

  4. Effect of pressure pulse on geomagnetic field oscillations

    NASA Astrophysics Data System (ADS)

    Sinha, A. K.; Rajaram, R.

    The effect of solar wind pressure pulse on geomagnetic field oscillations has been computed by using Green's function technique. The dominance of toroidal oscillations during dawn/dusk sectors appears to be natural consequences of solar wind pressure pulse and may not be attributed to K-H instability at the magnetopause boundary caused by velocity shear. Pressure pulse generates surface waves at the magnetopause boundary and couples to the field oscillations to give rise such effects. The paper adopts the 3-dimensional approach to explain the phenomena.

  5. Cassini magnetometer measurements in the Jovian environment

    NASA Astrophysics Data System (ADS)

    Dougherty, M. K.

    2001-05-01

    M. K. Dougherty, and the Cassini magnetometer team The recent Cassini flyby of Jupiter had the spacecraft flying along the dusk flank of the magnetosphere, a region which has only been visited very briefly before during the Ulysses outbound pass. The unique Cassini flyby resulted in the spacecraft making numerous entries into the magnetosheath region as well as into the magnetosphere itself. Initial results from the magnetometer instrument will be described including information concerning the solar wind IMF, the large amount of mirror mode activity measured within the magnetosheath and incursions into the magnetosphere proper.

  6. Longitudinal asymmetries in aurora

    NASA Astrophysics Data System (ADS)

    Michell, R.; Samara, M.; Grubbs, G. A.

    2013-12-01

    We present a comparative study of auroral structure and dynamics over Poker Flat, Alaska and Tromso, Norway. These stations are at the same geomagnetic latitude but differ significantly (by 4 degrees) in geographic latitude. In the period of 25 November 2012 to 15 March 2013 we have optical imaging data from both stations. There is approximately a 12 hour difference in local time between them and therefore near winter solstice we have simultaneous observations in the dawn and dusk sectors. Differences in auroral morphology, for similar solar wind driving conditions, will be investigated.

  7. Opening the cusp. [using magnetic field topology

    NASA Technical Reports Server (NTRS)

    Crooker, N. U.; Toffoletto, F. R.; Gussenhoven, M. S.

    1991-01-01

    This paper discusses the magnetic field topology (determined by the superposition of dipole, image, and uniform fields) for mapping the cusp to the ionosphere. The model results are compared to both new and published observations and are then used to map the footprint of a flux transfer event caused by a time variation in the merging rate. It is shown that the cusp geometry distorts the field lines mapped from the magnetopause to yield footprints with dawn and dusk protrusions into the region of closed magnetic flux.

  8. Ramadan fasting and dental treatment considerations: a review.

    PubMed

    Shaeesta, Khaleelahmed Bhavikatti; Prabhuji, M Lv; Shruthi, J R

    2015-01-01

    During the sacred month of Ramadan, Muslims abstain from the consumption of food from dawn until dusk. Extended fasting hours produce changes in the body's metabolism during this period. A majority of the population who fast also restrict themselves from undergoing dental treatments due to a fear of breaking the fast. Even among health professionals, a certain amount of uncertainty prevails about the implications of treating a patient who is fasting. To help clinicians carry out safe and effective treatment without hampering a patient's religious beliefs, the present article focuses on the effect of Ramadan fasting on the body's metabolism and the ramifications for treatment aspects, including medications and dental procedures. PMID:26147170

  9. Hall current effect on tearing mode instability. [possible cause of magnetic field reconnection in space

    NASA Technical Reports Server (NTRS)

    Terasawa, T.

    1983-01-01

    From a linear 2-D eigenmode analysis, it is found that the Hall current effect on collisional tearing mode instability becomes important for the thin magnetic reversal layer whose width is comparable to the ion inertia length; Hall currents produce a three-dimensional field structure and increase the reconnection (growth) rate. Since the magnetaic reversal layer widths both in the magnetopause and in the magnetotail are reported to become as thin as the ion inertial length (several hundred km) when the reconnection process is supposed to occur, the Hall current effect may explain the appearance of the dawn-dusk component of the magnetic field in the magnetotail reconnection region.

  10. Structure of the plasmapause from ISEE 1 low-energy ion and plasma wave observations

    NASA Technical Reports Server (NTRS)

    Nagai, T.; Horwitz, J. L.; Anderson, R. R.; Chappell, C. R.

    1985-01-01

    Low-energy ion pitch angle distributions are compared with plasma density profiles in the near-earth magnetosphere using ISEE 1 observations. The classical plasmapause determined by the sharp density gradient is not always observed in the dayside region, whereas there almost always exists the ion pitch angle distribution transition from cold, isotropic to warm, bidirectional, field-aligned distributions. In the nightside region the plasmapause density gradient is typically found, and it normally coincides with the ion pitch angle distribution transition. The sunward motion of the plasma is found in the outer part of the 'plasmaspheric' plasma in the dusk bulge region.

  11. The Los Alamos Photon Counting Detector Debris Detection Project: An update

    SciTech Connect

    Ho, Cheng; Priedhorsky, W.; Baron, M.; Casperson, D.

    1995-03-01

    At Los Alamos, the authors have been pursuing a project for space debris detection using a photon counting detector with high spatial and time resolution. By exploiting the three dimensionality of the high quality data, they expect to be able to detect an orbiting object of size below 2 cm, using a moderate size telescope and state-of-the-art photon counting detector. A working tube has been used to collect skyward looking data during dusk. In this paper, they discuss the progress in the development of detector and data acquisition system. They also report on analysis and results of these data sets.

  12. Direct-driven mechanism for geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Arykov, A. A.; Maltsev, Yu. P.

    We have obtained the injection function for the part of the storm-time depression which is related to the cross-tail current and corresponding currents on the magnetopause. This injection function is QTC=-κU/S, where U is the electric potential difference between the dawn and dusk sides of the magnetosphere, S is the equatorial cross-section of the stable trapping region, and κ is a coefficient varying from 0.5 to 1.5 depending on the state of the magnetosphere and solar wind pressure. The injection function QTC appeared to be close to the observed one for the Dst-variation.

  13. A model of global convection in Jupiter's magnetosphere

    NASA Astrophysics Data System (ADS)

    Cheng, A. F.; Krimigis, S. M.

    1989-09-01

    Voyager observations of Jupiter's magnetosphere are compared with the planetary wind model in which corotation must break down outside some Alfven critical radius and a centrifugally driven wind outflow must develop. It is found that the model does not agree with the observations. A new global convection model for the Jovian magnetosphere is proposed, based on models of quasi-stationary plasma convection in the earth's magnetosphere. The model predicts a substantial dawn-dusk asymmetry in the structure, dynamics, and plasma composition of the magnetopause and magnetosheath. The model also predicts a region of cross-tail flow in the nightside plasma sheet containing a substantial admixture of solar wind plasma.

  14. Equatorial transport of Saturn's ionosphere as driven by a dust-ring current system

    SciTech Connect

    Ip, W.; Mendis, D.A.

    1983-03-01

    The diurnal modulation of the dust ring current of Saturn's D-ring causes field-aligned Birkeland currents ot flow near the dawn and dusk terminators and close across the mid-latitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionosheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.

  15. Managing diabetes during the Muslim fasting month of Ramadan.

    PubMed

    Velayudhan, M

    2012-06-01

    Target blood sugar levels in diabetes are achieved through manipulation of diet, exercise and medication. A change in any one of these three things can skew blood sugar levels and create complications associated with hyperglycemia or hypoglycemia. Fasting during the month of Ramadan is a religious activity that devout Muslims practice whether they are diabetic or not. Since such fasting involves abstinence from food and water for twelve hours or more during the day from dawn to dusk, it is evident that advice regarding exercise and medication will have to be modified during this period. PMID:23082439

  16. Estimates of the North--South electric field component in the magnetotail low latitude boundary layer

    SciTech Connect

    Candidi, M.; Orsini, S.

    1981-06-01

    The measurements of 0/sup +/ ions drift velocity in the magnetotail boundary layer are used to infer the North--South E/sub z/ component of the local electric field. It is shown that E/sub z/ is generally a substantial component of the field and that it reverses its sign from the dawn to the dusk side of the northern magnetotail between X/sub SM/ = -15 R/sub E/ and X/sub SM/ = -23 R/sub E/.

  17. Visual systems - The state of the art

    NASA Astrophysics Data System (ADS)

    Shorrock, David

    State-of-the-art, computer-generated image simulator visual systems typically encompass a data base which generates the model of the operating environment, an image generator, and a display system suitable for the applications envisaged. Two basic approaches to such systems are discernible: those employing hybrid raster/calligraphy and those using raster/continuous tone. Attention is presently given to such capabilities and elements of visual displays as texture effects, transparencies, fade level-of-detail management, animation effects, and image generator functions for daylight and night/dusk conditions, as well as prospective developments in this field.

  18. An experimental test of the electromagnetic ion cyclotron instability within the earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.; Mcpherron, R. L.

    1980-01-01

    Examples of propagating electromagnetic Alfven/ion cyclotron waves in plasma particle and magnetic field data observed by the ATS-6 geostationary satellite are discussed. These waves were viewed mainly near the afternoon and dusk regions of the earth's magnetosphere with normalized frequencies in the 0.05 to 0.5 range. Two wave events were analyzed: both appeared coincidentally with the encounter of cool plasma populations which joined the hot populations already present. An electromagnetic ion cyclotron instability was proposed as the wave generation mechanism; this theory was tested by evaluating the linear growth integrals under the measured anisotropic hot ion distribution.

  19. Aspects of Clock Resetting in Flowering of Xanthium 1

    PubMed Central

    Papenfuss, Herbert D.; Salisbury, Frank B.

    1967-01-01

    Flowering is induced in Xanthium strumarium by a single dark period exceeding about 8.3 hours in length (the critical night). To study the mechanism which measures this dark period, plants were placed in growth chambers for about 2 days under constant light and temperature, given a phasing dark period terminated by an intervening light period (1 min to several hrs in duration), and finally a test dark period long enough normally to induce flowering. In some experiments, light interruptions during the test dark period were given to establish the time of maximum sensitivity. If the phasing dark period was less than 5 hours long, its termination by a light flash only broadened the subsequent time of maximum sensitivity to a light flash, but the critical night was delayed. In causing the delay, the end of the intervening light period was acting like the dusk signal which initiated time measurement at the beginning of the phasing dark period. If the phasing dark period was 6 hours or longer, time of maximum sensitivity during the subsequent test dark period was shifted by as much as 10 to 14 hours. In this case the light terminating the phasing dark period acted as a rephaser or a dawn signal. Following a 7.5-hour phasing dark period, intervening light periods of 1 minute to 5 hours did not shift the subsequent time of maximum sensitivity, but with intervening light periods longer than 5 hours, termination of the light acts clearly like a dusk signal. The clock appears to be suspended during intervening light periods longer than 5 to 15 hours. It is restarted by a dusk signal. There is an anomaly with intervening light periods of 10 to 13 hours, following which time of maximum sensitivity is actually less than the usual 8 hours after dusk. Ability of the clock in Xanthium to be rephased, suspended, restarted, or delayed, depending always upon conditions of the experiment, is characteristic of an oscillating timer and may confer upon this plant its ability to respond to

  20. Recirculation and Acceleration of Ionospheric Plasma in the Martian Magnetospheres

    NASA Astrophysics Data System (ADS)

    Ip, Wing-Huen

    2012-07-01

    The presence of strong crustal remnant magnetic fields on Mars has important influence on the dynamical behavior of the ionospheric plasma. A model based on computational simulation of the time-varying configuration of the mini-magnetosphere is described to examine the possible process of acceleration and heating of photo electrons and ions embedded in the magnetic flux tubes as Mars rotates from dawn to dusk. The main idea is that ionospheric H+ and O+ ions pumped into the mini-magnetospheres on the dawn side could be subject to adiabatic heating during "depolarization" of the magnetic field as the local time approaches noon.

  1. Studying internal and external magnetic fields in Japan using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Fukushima, N. (Principal Investigator); Maeda, H.; Yukutake, T.; Tanaka, M.; Oshima, S.; Ogawa, K.; Kawamura, M.; Miyazaki, Y.; Uyeda, S.; Kobayashi, K.

    1980-01-01

    Examination of the total intensity data of CHRONIT on a few paths over Japan and its neighboring sea shows MAGSAT is extremely useful for studying the local magnetic anomaly. In high latitudes, the signatures of field aligned currents are clearly recognized. These include (1) the persistent basic pattern of current flow; (2) the more intense currents in the summer hemisphere than in the winter hemisphere; (3) more fluctuations in current intensities in summer dawn hours; and (4) apparent dawn-dusk asymmetry in the field-aligned current intensity between the north and south polar regions.

  2. On the equatorial transport of Saturn's ionosphere as driven by a dust-ring current system

    NASA Astrophysics Data System (ADS)

    Ip, W.-H.; Mendis, D. A.

    1983-03-01

    The diurnal modulation of the dust ring current of Saturn's D-ring causes field-aligned Birkeland currents to flow near the dawn and dusk terminators and close across the mid-latitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionospheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.

  3. Coherent radar observations of a storm sudden commencement having a preliminary reverse impulse

    SciTech Connect

    McDiarmid, D.R.; Nielsen, E. )

    1987-01-01

    Observations of the February 4, 1983, storm sudden commencement (ssc) by the STARE and SABRE radar systems are presented. The observing stations were in the dusk sector, where the ssc was accompanied by a preliminary reverse impulse (PRI). The radar data show the PRI to be a consequence of the ssc compression wave producing an initial antisunward flow. The polarization of the ssc electric field in the ionosphere is seen to have both longitudinal and latitudinal structure. The observations are discussed in terms of the propagation of the ssc disturbance throughout the magnetosphere.

  4. A simple model for polar cap convection patterns and generation of theta auroras

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.

    1985-01-01

    An addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. The model also accounts for field-aligned patterns within, and auroral arcs across, the polar cap. The qualitative predictions derived from the model express the electric field magnitudes, aurora intensity, sunward and antisunward flow, and the dusk-side reversal of the convection field in terms of the x and y components of the interplanetary magnetic field.

  5. Relativistic electron precipitation at International Space Station: Space weather monitoring by Calorimetric Electron Telescope

    NASA Astrophysics Data System (ADS)

    Kataoka, Ryuho; Asaoka, Yoichi; Torii, Shoji; Terasawa, Toshio; Ozawa, Shunsuke; Tamura, Tadahisa; Shimizu, Yuki; Akaike, Yosui; Mori, Masaki

    2016-05-01

    The charge detector (CHD) of the Calorimetric Electron Telescope (CALET) on board the International Space Station (ISS) has a huge geometric factor for detecting MeV electrons and is sensitive to relativistic electron precipitation (REP) events. During the first 4 months, CALET CHD observed REP events mainly at the dusk to midnight sector near the plasmapause, where the trapped radiation belt electrons can be efficiently scattered by electromagnetic ion cyclotron (EMIC) waves. Here we show that interesting 5-20 s periodicity regularly exists during the REP events at ISS, which is useful to diagnose the wave-particle interactions associated with the nonlinear wave growth of EMIC-triggered emissions.

  6. On the equatorial transport of Saturn's ionosphere as driven by a dust-ring current system

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.; Mendis, D. A.

    1983-01-01

    The diurnal modulation of the dust ring current of Saturn's D-ring causes field-aligned Birkeland currents to flow near the dawn and dusk terminators and close across the midlatitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionospheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.

  7. Ion measurements during Pioneer Venus reentry: Implications for solar cycle variation of ion composition and dynamics

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Hartle, R. E.; Kar, J.; Cloutier, P. A.; Taylor, H. A., Jr.; Brace, L. H.

    1993-01-01

    During the final, low solar activity phase of the Pioneer Venus (PV) mission, the Orbiter Ion Mass Spectrometer (OIMS) measurements found all ion species, in the midnight-dusk sector, reduced in concentration relative to that observed at solar maximum. Molecular ion species comprised a greater part of the total ion concentration as O(+) and H(+) had the greatest depletions. The nightside ionospheric states were strikingly similar to the isolated solar maximum 'disappearing' ionospheres. Both are very dynamic states characterized by a rapidly drifting plasma and 30-100 eV superthermal O(+) ions.

  8. Local time occurrence frequency of energetic ions in the earth's magnetosheath

    NASA Technical Reports Server (NTRS)

    Fuselier, S. A.; Hill, P.; Baumjohann, W.; Gosling, J. T.

    1993-01-01

    The occurrence frequency of energetic ions in the energy range from 8 to 40 keV/e as a function of local time in the magnetosheath is presented. Energetic ions are observed in the magnetosheath with a minimum probability of 25 percent for all local times. The occurrence frequency for the energetic ions is higher on the dawnside than on the duskside but shows a relative maximum postnoon in the local time range from 12 to 15 hours. The postnoon relative maximum is attributed to a magnetospheric source for the energetic ions while the dawn-dusk asymmetry is attributed to a quasi-parallel bow shock source.

  9. Heavy Ion Effects on Kelvin-Helmholtz Instability: Hybrid Study

    NASA Astrophysics Data System (ADS)

    Burgess, D.; Lin, D.

    2015-12-01

    Kelvin-Helmholtz instability (KHI) is a candidate mechanism for solar wind tansportation into the magnetosphere. The statistical study of Bouhram et al. 2005 has shown that heavy ions could dominate the magnetopause for as much as 30% of the time on the dusk side. Thus the influence of heavy ions in solar wind-magnetosphere coupling should not be neglected. However, the magnetohydrodynamic (MHD) linear theory for KHI does not include any ion effects, and people working on the heavy ion effects have not come to an agreement either. Whether the heavy ions promote or inhibit the KHI still remains not well addressed. With a two-dimensional hybrid model, we investigated the effects of ion mass number on the KHI growth rate, starting from the simplest case of uniform density and uniform magnetic field perpendicular to the shear flow. It is shown that the growth rate of the KHI is lower with a heavier mass number. We try to to derive the linear theory for the kinetic KHI and compare it with the hybrid simulation results. The linear theory with ion effects considered is going to be further verified with varying heavy ion fractions and finite magnetic shear. More implications for the dawn-dusk asymmetry of KHI on planetary magnetopause are desirable when comparing the results of opposite magnetic field directions relative to the flow vorticity.

  10. Tidal influence on O(1S) airglow emission rate distributions at the geographic equator as observed by WINDII

    NASA Technical Reports Server (NTRS)

    Shephere, G. G.; Mclandress, C.; Solheim, B. H.

    1995-01-01

    WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, observes winds, temperatures and emission rates in the upper mesosphere and thermosphere. In this paper we report on nighttime observations of the vertical distribution of the O(1S) 557.7 nm emission near the geographic equator for March/April, 1993. The airglow volume emission rate distribution is found to be strongly dependent on local time. Beginning at dusk, an intense airglow emission layer descends from a mean altitude of 95 km, reaching 89 km by midnight after which the emission rapidly decays. Shortly after midnight it reappears weakly at a higher altitude and remains at this level as the emission rate gradually increases towards dawn. This strong local time dependence leads us to conclude that the effect is tidally driven. Comparison with the Forbes (1982a,b) model suggest that total density perturbations and changes in the atomic oxygen mixing ratio may the cause of the changes in emission rate distribution between dusk and midnight. The reappearance of the emission after midnight may be caused by downward winds bringing oxygen-rich air from above.

  11. High-latitude currents and their energy exchange with the ionosphere-thermosphere system

    NASA Astrophysics Data System (ADS)

    Thayer, J. P.

    2000-10-01

    The transfer of electrical energy at high latitudes between the magnetosphere and ionosphere-thermosphere (IT) system is contained within the resulting currents and electric fields between the two systems. As such, the electrodynamic state of the IT system can influence how much of the electrical energy is transferred at any one time by modulating the currents that flow in the region. For this study, 1557 hours of detailed E region measurements by the Sondrestrom incoherent-scatter radar from 1993 through 1998 were collected, of which 95 hours were used to determine the local electromagnetic energy transfer rates within the IT system and evaluate the role of the IT system in modifying this energy transfer. The measurements have been organized into 59 periods of enhanced electrical energy transfer and cover all universal times but are local to the region above Sondrestrom at 74.2° magnetic latitude. In many of the events studied it was found that the IT system acted to reduce the net electromagnetic energy transferred from the magnetosphere owing to the presence of neutral winds. The dawn sector proved to have on average greater passive energy deposition rates than in the dusk sector. The reduction of this rate by neutral winds also proved stronger in the dawn sector. This enhanced modulation caused the dawn-dusk asymmetry in energy transfer to be less pronounced but still apparent in the electromagnetic energy transfer rate.

  12. Observational test of shock drift and Fermi acceleration on a seed particle population upstream of earth's bow shock

    NASA Technical Reports Server (NTRS)

    Anagnostopoulos, G. C.; Sarris, E. T.; Krimigis, S. M.

    1988-01-01

    The efficiency of proposed shock acceleration mechanisms as they operate at the bow shock in the presence of a seed energetic particle population was examined using data from simultaneous observations of energetic solar-origin protons, carried out by the IMP 7 and 8 spacecraft in the vicinity of the quasi-parallel (dawn) and quasi-perpendicular (dusk) regions of the earth's bow shock, respectively. The results of observations (which include acceleration effects in the intensities of the energetic protons with energies as high as 4 MeV observed at the vicinity of the dusk bow shock, but no evidence for any particle acceleration at the energy equal to or above 50 keV at the dawn side of the bow shock) indicate that the acceleration of a seed particle population occurs only at the quasi-perpendicular bow shock through shock drift acceleration and that the major source of observed upstream ion populations is the leakage of magnetospheric ions of energies not less than 50 keV, rather than in situ acceleration.

  13. Epithermal Neutron Evidence for a Diurnal Surface Hydration Process in the Moon's High Latitudes

    NASA Technical Reports Server (NTRS)

    McClanahan, T. P.; Mitrofanov, I. G.; Boynton, W. V.; Chin, G.; Parsons, A.; Starr, R. D.; Evans, L. G.; Sanin, A.; Litvak, M.; Livengood, T.

    2015-01-01

    We report evidence from epithermal neutron flux observations that show that the Moon's high latitude surfaces are being actively hydrated, dehydrated and rehydrated in a diurnal cycle. The near-surface hydration is indicated by an enhanced suppression of the lunar epithermal neutron leakage flux on the dayside of the dawn terminator on poleward-facing slopes (PFS). At 0600 to 0800 local-time, hydrogen concentrations within the upper 1 meter of PFS are observed to be maximized relative to equivalent equator-facing slopes (EFS). During the lunar day surface hydrogen concentrations diminish towards dusk and then rebuild overnight. Surface hydration is determined by differential comparison of the averaged EFS to PFS epithermal neutron count rates above +/- 75 deg latitude. At dawn the contrast bias towards PFS is consistent with at least 15 to 25 parts-per-million (ppm) hydrogen that dissipates by dusk. We review several lines of evidence derived from temperature and epithermal neutron data by a correlated analysis of observations from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) that were mapped as a function of lunar local-time, Lunar Observing Laser Altimeter (LOLA) topography and Diviner (DLRE) surface temperature.

  14. Polarized skylight does not calibrate the compass system of a migratory bat

    PubMed Central

    Lindecke, Oliver; Voigt, Christian C.; Pētersons, Gunārs; Holland, Richard A.

    2015-01-01

    In a recent study, Greif et al. (Greif et al. Nat Commun 5, 4488. (doi:10.1038/ncomms5488)) demonstrated a functional role of polarized light for a bat species confronted with a homing task. These non-migratory bats appeared to calibrate their magnetic compass by using polarized skylight at dusk, yet it is unknown if migratory bats also use these cues for calibration. During autumn migration, we equipped Nathusius' bats, Pipistrellus nathusii, with radio transmitters and tested if experimental animals exposed during dusk to a 90° rotated band of polarized light would head in a different direction compared with control animals. After release, bats of both groups continued their journey in the same direction. This observation argues against the use of a polarization-calibrated magnetic compass by this migratory bat and questions that the ability of using polarized light for navigation is a consistent feature in bats. This finding matches with observations in some passerine birds that used polarized light for calibration of their magnetic compass before but not during migration. PMID:26382077

  15. Ion trajectories in Mercury's magnetosphere

    NASA Astrophysics Data System (ADS)

    Sarantos, M.; Reiff, P.; Killen, R.

    2003-04-01

    The atmosphere of Mercury is eroded quickly by photoionization and electron impact ionization. Resulting ions are affected by both magnetic and electric field forces due to their small energy. The escape flux of these ions from Mercury's magnetosphere is believed to respond to the degree of solar wind - Hermean magnetosphere interaction. We present the structure of the Hermean magnetosphere obtained by the Toffoletto-Hill (JGR 98, 1339, 1993) model of an open magnetosphere, and supplement it with the Ding et al. (Phys. Space Plasmas, 1996) potential solver to represent the convection electric field. We follow thousands of Na and K ions in a tight grid of magnetic and electric fields at Mercury. Ions are created with a spatial distribution given from the neutral distribution to cover the entire dayside, and are launched at the surface, with an isotropic angular distribution. The initial energy is taken to be ˜1eV. We calculate the loci of points where the ions reimpact the planetary surface. We conclude that the dawn-dusk asymmetry and high-latitude enhancements in the sodium atmosphere are perpetuated by the pattern of ion redistribution due to a predominant dawn to dusk electric field. The solar wind ion sputtering effect will further amplify atmospheric patchiness.

  16. Impact of MHD shock physics on magnetosheath asymmetry and Kelvin-Helmholtz instability

    NASA Astrophysics Data System (ADS)

    Nykyri, K.

    2013-08-01

    We have performed 13 three-dimensional global magnetohydrodynamic (MHD) simulations of the magnetosheath plasma and magnetic field properties for Parker spiral (PS) and ortho-Parker spiral interplanetary magnetic field (IMF) orientations corresponding to a wide range of solar wind plasma conditions. To study the growth of the Kelvin-Helmholtz instability on the dawn and dusk flank magnetopause, we have performed 26 local two-dimensional MHD simulations, with the initial conditions taken from global simulations on both sides of the velocity shear layer at the dawn-dusk terminator. These simulations indicate that while the MHD physics of the fast shocks does not directly lead to strong asymmetry of the magnetosheath temperature for typical solar wind conditions, the magnetosheath on the quasi-parallel shock side has a smaller tangential magnetic field along the magnetosheath flow which enables faster growth of the Kelvin-Helmholtz instability (KHI). Because the IMF is statistically mostly in the PS orientation, the KHI formation may statistically favor the dawnside flank. For all the 26 simulations, the growth rates of the KHI correlated well with the ratio of the velocity shear and Alfvén speed along the wave vector, k. Dynamics of the KHI may subsequently lead to formation of kinetic Alfvén waves and reconnection in the Kelvin-Helmholtz vortices which can lead to particle energization. This may partly help to explain the observed plasma sheet asymmetry of cold-component ions, which are heated more on the dawnside plasma sheet.

  17. Plasma and convection reversal boundary motions in the high-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Chen, Y.-J.; Heelis, R. A.; Cumnock, J. A.

    2016-06-01

    In this paper we present a statistical study of the high-latitude ionospheric plasma motion at the convection reversal boundary (CRB) and its dependence on the location of the CRB and the interplanetary magnetic field (IMF) orientation by using the Defense Meteorological Satellite Program (DMSP) F13 and F15 measurements over the period from 2000 to 2007. During periods of stable southward IMF, we find a smaller variability in plasma drifts across the CRB over a 4 h segment in magnetic local time (MLT) around dawn and dusk compared to that for variable IMF. Across these segments, the plasma motion at the CRB is directed poleward at local times closer to local noon and equatorward at local times closer to midnight on both the dawn and dusk sides with a total potential drop ~10 kV, suggesting that the CRB behaves much like an adiaroic line. For variable IMF with no stability constraint, we see a relatively narrow distribution of plasma drifts across the CRB only in the 6-7 h and 17-18 h MLT and equatorward/poleward motions of the CRB when the CRB is located at the highest/lowest latitudes. The smaller local time extent of the adiaroic line for variable IMF (~1 h) may be associated with rotation of the dayside merging gap in local time or local contractions and expansions of the polar cap boundary.

  18. The interaction of a magnetic cloud with the Earth - Ionospheric convection in the Northern and Southern Hemispheres for a wide range of quasi-steady interplanetary magnetic field conditions

    NASA Technical Reports Server (NTRS)

    Freeman, M. P.; Farrugia, C. J.; Burlaga, L. F.; Hairston, M. R.; Greenspan, M. E.; Ruohoniemi, J. M.; Lepping, R. P.

    1993-01-01

    Observations are presented of the ionospheric convection in cross sections of the polar cap and auroral zone as part of the study of the interaction of the Earth's magnetosphere with the magnetic cloud of January 13-15, 1988. For strongly northward IMF, the convection in the Southern Hemisphere is characterized by a two-cell convection pattern comfined to high latitudes with sunward flow over the pole. The strength of the flows is comparable to that later seen under southward IMF. Superimposed on this convection pattern there are clear dawn-dusk asymmetries associated with a one-cell convection component whose sense depends on the polarity of the magnetic cloud's large east-west magnetic field component. When the cloud's magnetic field turns southward, the convection is characterized by a two-cell pattern extending to lower latitude with antisunward flow over the pole. There is no evident interhemispheric difference in the structure and strength of the convection. Superimposed dawn-dusk asymmetries in the flow patterns are observed which are only in part attributable to the east-west component of the magnetic field.

  19. Diel variation in ammonia excretion, glutamine levels, and hydration status in two species of terrestrial isopods.

    PubMed

    Wright, Jonathan C; Peña-Peralta, Mariasol

    2005-01-01

    Terrestrial isopods (suborder Oniscidea) excrete most nitrogen diurnally as volatile ammonia, and ammonia-loaded animals accumulate nonessential amino acids, which may constitute the major nocturnal nitrogen pool. This study explored the relationship between ammonia excretion, glutamine storage/mobilization, and water balance, in two sympatric species Ligidium lapetum (section Diplocheta), a hygric species; and Armadillidium vulgare (Section Crinocheta), a xeric species capable of water-vapor absorption (WVA). Ammonia excretion (12-h), tissue glutamine levels, and water contents were measured following field collection of animals at dusk and dawn. In both species, diurnal ammonia excretion exceeded nocturnal excretion four- to fivefold while glutamine levels increased four- to sevenfold during the night. Most glutamine was accumulated in the somatic tissues ("body wall"). While data support the role of glutamine in nocturnal nitrogen storage, potential nitrogen mobilization from glutamine breakdown (162 micromol g(-1) in A. vulgare) exceeds measured ammonia excretion (2.5 micromol g(-1)) over 60-fold. This may serve to generate the high hemolymph ammonia concentrations (and high P(NH3)) seen during volatilization. The energetic cost of ammonia volatilization is discussed in the light of these findings. Mean water contents were similar at dusk and dawn in both species, indicating that diel cycles of water depletion and replenishment were not occurring. PMID:15578188

  20. Asymmetries observed in Saturn's magnetopause geometry

    NASA Astrophysics Data System (ADS)

    Pilkington, N. M.; Achilleos, N.; Arridge, C. S.; Guio, P.; Masters, A.; Ray, L. C.; Sergis, N.; Thomsen, M. F.; Coates, A. J.; Dougherty, M. K.

    2015-09-01

    For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn-dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn-dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the "intrinsic" polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north-south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10-17°).

  1. Dynamics of Subauroral Polarization Stream (SAPS) Structures

    NASA Astrophysics Data System (ADS)

    Sazykin, S. Y.; Coster, A. J.; Huba, J.; Ridley, A. J.; Erickson, P. J.; Foster, J. C.; Baker, J. B. H.; Wolf, R.

    2015-12-01

    The Subauroral Polarization Stream (SAPS) flow structures are narrow ionospheric channels of fast (in excess of 100 m/s) westward drift just outside the equatorward edge of the diffuse aurora in the dusk-to-midnight local time sector. Other terms for this phenomenon include subauroral Ion Drift (SAID) events and Polarization Jets. SAPS structures represent a striking departure from the commonly-used two-cell convection pattern. They are thought to arise from the displacement of the downward region-2 Birkeland currents on the dusk side equatorward of the low-latitude boundary of the auroral oval during times of changing high-latitude convection. In this paper, we will use several event simulations with the SAMI3-RCM numerical model (a self-consistent ionosphere-inner magnetosphere model) and RCM-GITM (a self-consistent model of the ionosphere-thermosphere-inner magnetosphere) to analyze the relative roles of changes in the IMF Bz component, ionospheric electron density depletions, and thermospheric modifications in controlling the dynamics of SAPS. Simulation results will be compared to multi-instrument ionospheric observations.

  2. Distribution of H2 in the Lunar Exosphere from LAMP Observations

    NASA Astrophysics Data System (ADS)

    Hurley, Dana; Retherford, Kurt; Cook, Jason; Grava, Cesare; Greathouse, Thomas; Gladstone, Randy; Stern, Alan

    2014-11-01

    Hydrogen gas (H2) has been detected in the Moon’s exosphere. It was identified spectrally during the LCROSS impact plume (Gladstone et al., 2010). Then it was found in LAMP data from the nominal exosphere (Stern et al., 2013). We examine the distribution of H2 in the lunar exosphere using a Monte Carlo model and data from the Lyman Alpha Mapping Project (LAMP) FUV imaging spectrograph onboard the Lunar Reconnaissance Orbiter (LRO). LAMP observations made in twilight, i.e., through illuminated exosphere, but with a footprint on the nightside of the Moon, are routinely made with LRO. However, during times when the beta angle of the orbit is close to beta=90°, a great portion of the nightside orbit is in the twilight viewing geometry. Using data from just behind the terminator on the post-dusk and pre-dawn sides, we compile a cumulative spectrum throughout LAMP’s bandpass. A dawn/dusk asymmetry is detected in the H2 abundance. Modeling is used to decipher the release mechanism and source distribution of diatomic hydrogen that best fits the observations. We examine the source rate and the total mass of the H2 exosphere consistent with the observations.

  3. Differential success in sampling of Atlantic Forest amphibians among different periods of the day.

    PubMed

    Rocha, C F D; Siqueira, C C; Ariani, C V; Vrcibradic, D; Guedes, D M; Kiefer, M C; Almeida-Gomes, M; Goyannes-Araújo, P; Borges-Júnior, V N T; Van Sluys, M

    2015-05-01

    In general, anurans tend to be nocturnal, though diurnal activity is characteristic of some groups. Studies show that frog activity may be inferred based on the number of individuals collected at different periods of the day, during large-scale field surveys. We investigated the best period of the day to conduct amphibian sampling in nine Atlantic Rainforest areas in southeastern Brazil, based on intensive field surveys. At each locality we employed similar sampling effort during diurnal, crepuscular and nocturnal searches (totaling 704.5 sampling hours). We pooled data from all localities for each period and estimated the proportion of frogs of each species active at each period based on the total number of individuals and on the number of species found during all surveys for that period. We recorded a total of 817 individual frogs from 69 species. Species richness was highest at night (median = 12 species), intermediate at dusk (median = 8), and lowest during the day (median = 4). The percentage of the total number of individual frogs found (pooled species) was highest during the night (ca. 53%) and lowest during the day (ca. 14%). Analyzing each species separately, the number of individuals recorded was consistently higher at dusk and night for most species. Our study evidences a trend for nocturnal activity for most Atlantic Rainforest frogs, with few species having primarily diurnal habits. Those results may favor future studies and conservation efforts for amphibian species. PMID:26132005

  4. Extreme ultraviolet explorer satellite observation of Jupiter's Io plasma torus

    NASA Technical Reports Server (NTRS)

    Hall, D. T; Gladstone, G. R.; Moos, H. W.; Bagenal, F.; Clarke, J. T.; Feldman, P. D.; Mcgrath, M. A.; Schneider, N. M.; Shemansky, D. E.; Strobel, D. F.

    1994-01-01

    We present the first Extreme Ultraviolet Explorer (EUVE) satellite observation of the Jupiter system, obtained during the 2 day period 1993 March 30 through April 1, which shows a rich emission-line spectrum from the Io plasma torus spanning wavelengths 370 to 735 A. The emission features correspond primarily to known multiplets of oxygen and sulfur ions, but a blended feature near 372 A is a plausible Na II transition. The summed detected energy flux of (7.2 +/- 0.2) x 10(exp -11) ergs/sq cm(s) corresponds to a radiated power of approximately equal to 4 x 10(exp 11) W in this spectral range. All ansa emissions show a distinct dawn-dusk brightness asymmetry and the measured dusk/dawn ratio of the bright S III lambda-680 feature is 2.3 +/- 0.3, significantly larger than the ratio measured by the Voyager spacecraft ultraviolet (UV) instruments. A preliminary estimate of ion partitioning indicates that the oxygen/sulfur ion ratio is approximately equal to 2, compared to the value approximately equal to 1.3 measured by Voyager, and that (Na(+))/(e) greater than 0.01.

  5. Ionospheric and magnetospheric plasmapauses'

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Hoffman, J. H.; Maynard, N. C.

    1977-01-01

    During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of about 5.2 R sub e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2-5.4. The locations of the Explorer 45 plasmapause crossings during this month were compared to the latitudinal decreases of the H(+) density observed on ISIS 2 near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Vertical flows of the H(+) ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 kilometers/sec near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H(+) trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause.

  6. Toroidal quarter waves in the Earth's magnetosphere: observational perspective

    NASA Astrophysics Data System (ADS)

    Bulusu, Jayashree; Sinha, A. K.; Vichare, Geeta

    2015-05-01

    Quarter waves in the Earth's magnetosphere are standing Alfvén waves excited on geomagnetic field lines when the conjugate ionospheres display strong asymmetry in conductivity. In this paper, we have examined the characteristics of these waves by analyzing two years (2007-2008) of magnetometer data from the geostationary satellite GOES-11. These waves are predominantly identified during quiet geomagnetic conditions based on interhemispheric conductivity contrast and opposite signs of wave reflection coefficients at the conjugate ionospheres. The observed frequencies are used in a numerical model to compute the equatorial ion density by assuming that the plasma consists only of protons at geostationary height during quiet conditions. The number density of protons thus obtained is compared with an empirical model. The phase difference between the waves observed at the satellite and northern conjugate ground station is in accord with model expectations for quarter mode waves. We also for the first time report the occurrence of an event depicting harmonically structured quarter wave oscillations. Statistical analysis of the seasonal and MLT (Magnetic local time) dependence of these oscillations shows that they mostly occur during solstices and around terminators (i.e. dawn and dusk time). In addition, it is observed that occurrence is more prevalent during dawn in the June solstice and dusk during the December solstice.

  7. Effects of interrupted photoperiods on the induction of ovulation in anestrous mares.

    PubMed

    Malinowski, K; Johnson, A L; Scanes, C G

    1985-10-01

    The ability of interrupted photoperiods to induce early estrus and ovulation was examined. Horse mares were exposed to long (16 h light) or short (10 h light), noninterrupted photoperiods, ambient light, or various interrupted photoperiod treatments from December 1 to April 15 (135 d). Follicular development was assessed by rectal palpation and estrous behavior was determined by teasing with a stallion. Serum concentrations of progesterone were used as an indicator of corpus luteum function. Differences among the light treatment groups were compared for the following behavioral and ovarian characteristics: days to first detectable 3-cm follicle, days to first estrous behavior, days to first ovulation, the number of mares ovulating within the treatment period, and the number of ovulations within the treatment period per mare. Compared with the ambient and 10L:14D (L = h of light and D = h of darkness) photoperiod treatments, ovulation was advanced to the greatest extent by a photoperiod of 16L:8D and the interrupted photoperiod 10L:8D:2L:4D. These two stimulatory photoperiod treatments were characterized by the presence of light 8 to 10 h after dusk. Therefore, the present data are consistent with an external coincidence model for the induction of seasonal breeding in horses, with the photoinducible phase occurring within the period 8 to 10 h after dusk. PMID:4066545

  8. 3D PIC Simulation of the Magnetosphere during IMF Rotation from North to South: Signatures of Substorm Triggering in the Magnetotail

    NASA Technical Reports Server (NTRS)

    Nishikawa, Ken-Ichi; Cao. D/ S/; Lembege, B.

    2008-01-01

    Three dimensional PIC simulations are performed in order to analyse the dynamics of the magnetotail as the interplanetary magnetic field (IMF) rotates from northward to southward direction. This dynamics reveals to be quite different within meridian/equatorial planes over two successive phases of this rotation. First, as IMF rotates from North to Dawn-Dusk direction, the X-Point (magnetic reconnection) evidenced in the magnetotail (meridian plane) is moving earthward (from x=-35 Re to x=-17.5 ) distance at which it stabilizes. This motion is coupled with the formation of "Crosstail-S" patterns (within the plane perpendicular to the Sun-Earth mine) through the neutral sheet in the nearby magnetotail. Second, as IMF rotates from dawn-dusk to South, the minimum B field region is expanding within the equatorial plane and forms a ring. This two-steps dynamics is analyzed in strong association with the cross field magnetotail current Jy, in order to recover the signatures of substorms triggering.

  9. Diurnal variations in, and influences on, concentrations of particulate and dissolved arsenic and metals in the mildly alkaline Wallkill River, New Jersey, USA

    NASA Astrophysics Data System (ADS)

    Barringer, Julia L.; Wilson, Timothy P.; Szabo, Zoltan; Bonin, Jennifer L.; Fischer, Jeffrey M.; Smith, Nicholas P.

    2008-01-01

    Diurnal variations in particulate and dissolved As and metal concentrations were observed in mildly alkaline water from a wetlands site on the Wallkill River in northwestern New Jersey. The site, underlain by glacial sediments over dolomite bedrock, is 10 km downstream from a mined area of the Franklin Marble, host to Zn ores, also As and Mn minerals. In mid-September 2005, maxima and minima in dissolved-oxygen-concentration and pH, typically caused by photosynthesis and respiration, occurred at 2000 and 0800 hours. Concentrations of dissolved As (1.52-1.95 μg/L) peaked at dusk (2000 hours), whereas dissolved Mn and Zn concentrations (76.5-96.9 and 8.55-12.8 μg/L, respectively) were lowest at dusk and peaked at 1000 hours. These opposing cycles probably reflect sorption and desorption of As (an anion), and Mn and Zn (cations) as pH varied throughout the 24-h period. Doubly-peaked cycles of B, Cl, SO4, and nutrients also were observed; these may result from upstream discharges of septic-system effluent. Both recoverable amd particulate Al, Fe, Mn, and Zn concentrations peaked between 0200 and 0600 hours. The particulate metals cycle, with perturbations at 0400 hours, may be influenced by biological activity.

  10. Variations in 13C discrimination during CO2 exchange by Picea sitchensis branches in the field.

    PubMed

    Wingate, Lisa; Seibt, Ulli; Moncrieff, John B; Jarvis, Paul G; Lloyd, Jon

    2007-05-01

    We report diurnal variations in (13)C discrimination ((13)Delta) of Picea sitchensis (Bong.) Carr. branches measured in the field using a branch chamber technique. The observations were compared to predicted (13)Delta based on concurrent measurements of branch gas exchange. Observed (13)Delta values were described well by the classical model of (13)Delta including isotope effects during photorespiration, day respiration and CO(2) transfer through a series of resistances to the sites of carboxylation. A simplified linear of model (13)Delta did not capture the observed diurnal variability. At dawn and dusk, we measured very high (13)Delta values that were not predicted by either of the said models. Exploring the sensitivity of (13)Delta to possible respiratory isotope effects, we conclude that isotopic disequilibria between the gross fluxes of photosynthesis and day respiration can explain the high observed (13)Delta values during net photosynthetic gas exchange. Based on the classical model, a revised formulation incorporating an isotopically distinct substrate for day respiration was able to account well for the high observed dawn and dusk (13)Delta values. PMID:17407538

  11. Take-off time of the first generation of the overwintering small brown planthopper, Laodelphax striatellus in the temperate zone in East Asia.

    PubMed

    Sanada-Morimura, Sachiyo; Otuka, Akira; Matsumura, Masaya; Etoh, Tomoki; Zhu, Yeqin; Zhou, Yijun; Zhang, Gufeng

    2015-01-01

    Overseas migration of the small brown planthopper, Laodelphax striatellus (Fallén), occurs during the winter wheat harvest season in East Asia. Knowing the take-off time of emigrating L. striatellus is crucial for predicting such migrations with a simulation technique because winds, carriers of migratory insects, change continuously. Several methods were used in China and Japan from late May to early June 2012 and again in 2013 to identify the precise timing of take-off. These methods included: a tow net trap mounted to a pole at 10 m above the ground, a helicopter-towed net trap, and a canopy trap (which also had video monitoring) set over wheat plants. Laodelphax striatellus emigrated from wheat fields mainly in the early evening, before dusk. The insects also emigrated during the daytime but rarely emigrated at dawn, showing a pattern that is unlike the bimodal emigration at dusk and dawn of two other rice planthoppers, the brown planthopper, Nilaparvata lugens (Stål), and the white-backed planthopper, Sogatella furcifera (Horváth). There was no significant difference in the temporal pattern of take-off behavior between females and males of Japanese L. striatellus populations. PMID:25780936

  12. Take-Off Time of the First Generation of the Overwintering Small Brown Planthopper, Laodelphax striatellus in the Temperate Zone in East Asia

    PubMed Central

    Sanada-Morimura, Sachiyo; Otuka, Akira; Matsumura, Masaya; Etoh, Tomoki; Zhu, Yeqin; Zhou, Yijun; Zhang, Gufeng

    2015-01-01

    Overseas migration of the small brown planthopper, Laodelphax striatellus (Fallén), occurs during the winter wheat harvest season in East Asia. Knowing the take-off time of emigrating L. striatellus is crucial for predicting such migrations with a simulation technique because winds, carriers of migratory insects, change continuously. Several methods were used in China and Japan from late May to early June 2012 and again in 2013 to identify the precise timing of take-off. These methods included: a tow net trap mounted to a pole at 10 m above the ground, a helicopter-towed net trap, and a canopy trap (which also had video monitoring) set over wheat plants. Laodelphax striatellus emigrated from wheat fields mainly in the early evening, before dusk. The insects also emigrated during the daytime but rarely emigrated at dawn, showing a pattern that is unlike the bimodal emigration at dusk and dawn of two other rice planthoppers, the brown planthopper, Nilaparvata lugens (Stål), and the white-backed planthopper, Sogatella furcifera (Horváth). There was no significant difference in the temporal pattern of take-off behavior between females and males of Japanese L. striatellus populations. PMID:25780936

  13. Observations of IMF and seasonal effects in high-latitude convection

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.

    1995-01-01

    Strong interplanetary magnetic field (IMF) and seasonal effects in the convection of nightside ionospheric plasma are described. The findings are based on a statistical analysis of observations made with the Johns Hopkins University/ Applied Physics Lab (JHU/APL) HF radar located at Goose Bay, Labrador. For positive sign of the IMF dusk-dawn component, By greater than 0 the dawn cell is more crescent shaped and the dusk cell more round while for BY less than 0 these pairings of size and shape are reversed. The more extreme crescent /round cell dichotomy is obtained for BY greater than 0. The return flows associated with the crescent-shaped cell dominate at midnight MLT (magnetic local time); the reversal in the zonal velocity in the 67 deg-69 deg lambda (magnetic latitude) interval occurs 2.5 hr earlier in summer than in winter. The maximum effects are obtained on the nightside for the pairings By greater than 0, summer and BY less than 0, winter; the first produces the more structured cell in the morning, the second in the evening, and this cell dominates the return flow at midnight. The difference in the zonal flow reversals for these pairings exceeds 4 hr in MLT.

  14. MESSENGER Orbital Observations of Large-Amplitude Kelvin-Helmholtz Waves at Mercury's Magnetopause

    NASA Technical Reports Server (NTRS)

    Sundberg, Torbjorn; Boardsen, Scott A.; Slavin, James A.; Anderson, Brian J.; Korth, Haje; Zurbuchen, Thomas H.; Raines, Jim M.; Solomon, Sean C.

    2012-01-01

    We present a survey of Kelvi\\ n-Helmholtz (KH) waves at Mercury's magnetopause during MESSENGER's first Mercury year in orb it. The waves were identified on the basis of the well-established sawtooth wave signatures that are associated with non-linear KH vortices at the magnetopause. MESSENGER frequently observed such KH waves in the dayside region of the magnetosphere where the magnetosheath flow velocity is still sub -sonic, which implies that instability growth rates at Mercury's magnetopau are much larger than at Earth. We attribute these greater rates to the limited wave energy dissipation in Mercury's highly resistive regolith. The wave amplitude was often on the order of ' 00 nT or more, and the wave periods were - 10- 20 s. A clear dawn-dusk asymmetry is present in the data, in that all of the observed wave events occurred in the post-noon and dusk-side sectors of the magnetopause. This asymmetry is like ly related to finite Larmor-radius effects and is in agreement with results from particle-in-cell simulations of the instability. The waves were observed almost exclusively during periods when the north-south component of the magnetosheath magnetic field was northward, a pattern similar to that for most terrestrial KH wave events. Accompanying plasma measurements show that the waves were associated with the transport of magnetosheath plasma into the magnetosphere.

  15. The origin of life and the left-handed amino-acid excess: the furthest heavens and the deepest seas?

    PubMed

    Goodman, Geoffrey; Gershwin, M Eric

    2006-11-01

    The origin of life is an extraordinary problem that leads back to the structure and dynamics of the cosmos and early development of organic molecules. Within that wider question lies an unsolved problem that has troubled biologists for 150 years. What is the origin of the dominant presence of left-handed stereoisomers of amino acids in nature even though their synthesis normally results in an equal mixture of the right- and left-handed molecular forms? We propose that asymmetric Earth rotation caused at dawn and dusk circularly polarized UV light (CPUVL) of opposite polarity and reversed temperature profiles in the oceans. Destruction of the d-isomer by CPUVL at dusk in a sea surface hotter than at dawn created a daily l-isomer excess protected from radiation by nightfall, preserved by down-flow (diffusive, mechanical) into cold, darker regions, eventually initiating an l-amino-acid excess embodied in early marine forms. Innumerable mechanisms have been proposed for the origin of l-chiral dominance in amino acids and none proven. Since the thalidomide tragedy, homochirality of amino acids has been a growing practical issue for medicine. Understanding its origin may bring further and unexpected benefits. It may also be a modest pointer to the possibility of positive answers to whether intelligent life will have the capacity to continue to protect itself from conditions inimical to survival. PMID:17060678

  16. Diurnal variations in, and influences on, concentrations of particulate and dissolved arsenic and metals in the mildly alkaline Wallkill River, New Jersey, USA

    USGS Publications Warehouse

    Barringer, J.L.; Wilson, T.P.; Szabo, Z.; Bonin, J.L.; Fischer, J.M.; Smith, N.P.

    2008-01-01

    Diurnal variations in particulate and dissolved As and metal concentrations were observed in mildly alkaline water from a wetlands site on the Wallkill River in northwestern New Jersey. The site, underlain by glacial sediments over dolomite bedrock, is 10 km downstream from a mined area of the Franklin Marble, host to Zn ores, also As and Mn minerals. In mid-September 2005, maxima and minima in dissolved-oxygen-concentration and pH, typically caused by photosynthesis and respiration, occurred at 2000 and 0800 hours. Concentrations of dissolved As (1.52-1.95 ??g/L) peaked at dusk (2000 hours), whereas dissolved Mn and Zn concentrations (76.5-96.9 and 8.55-12.8 ??g/L, respectively) were lowest at dusk and peaked at 1000 hours. These opposing cycles probably reflect sorption and desorption of As (an anion), and Mn and Zn (cations) as pH varied throughout the 24-h period. Doubly-peaked cycles of B, Cl, SO4, and nutrients also were observed; these may result from upstream discharges of septic-system effluent. Both recoverable amd particulate Al, Fe, Mn, and Zn concentrations peaked between 0200 and 0600 hours. The particulate metals cycle, with perturbations at 0400 hours, may be influenced by biological activity. ?? 2007 Springer-Verlag.

  17. Vasoactive intestinal polypeptide mediates circadian rhythms in mammalian olfactory bulb and olfaction.

    PubMed

    Miller, Jae-Eun Kang; Granados-Fuentes, Daniel; Wang, Thomas; Marpegan, Luciano; Holy, Timothy E; Herzog, Erik D

    2014-04-23

    Accumulating evidence suggests that the olfactory bulbs (OBs) function as an independent circadian system regulating daily rhythms in olfactory performance. However, the cells and signals in the olfactory system that generate and coordinate these circadian rhythms are unknown. Using real-time imaging of gene expression, we found that the isolated olfactory epithelium and OB, but not the piriform cortex, express similar, sustained circadian rhythms in PERIOD2 (PER2). In vivo, PER2 expression in the OB of mice is circadian, approximately doubling with a peak around subjective dusk. Furthermore, mice exhibit circadian rhythms in odor detection performance with a peak at approximately subjective dusk. We also found that circadian rhythms in gene expression and odor detection performance require vasoactive intestinal polypeptide (VIP) or its receptor VPAC2R. VIP is expressed, in a circadian manner, in interneurons in the external plexiform and periglomerular layers, whereas VPAC2R is expressed in mitral and external tufted cells in the OB. Together, these results indicate that VIP signaling modulates the output from the OB to maintain circadian rhythms in the mammalian olfactory system. PMID:24760863

  18. Vasoactive Intestinal Polypeptide Mediates Circadian Rhythms in Mammalian Olfactory Bulb and Olfaction

    PubMed Central

    Miller, Jae-eun Kang; Granados-Fuentes, Daniel; Wang, Thomas; Marpegan, Luciano; Holy, Timothy E.

    2014-01-01

    Accumulating evidence suggests that the olfactory bulbs (OBs) function as an independent circadian system regulating daily rhythms in olfactory performance. However, the cells and signals in the olfactory system that generate and coordinate these circadian rhythms are unknown. Using real-time imaging of gene expression, we found that the isolated olfactory epithelium and OB, but not the piriform cortex, express similar, sustained circadian rhythms in PERIOD2 (PER2). In vivo, PER2 expression in the OB of mice is circadian, approximately doubling with a peak around subjective dusk. Furthermore, mice exhibit circadian rhythms in odor detection performance with a peak at approximately subjective dusk. We also found that circadian rhythms in gene expression and odor detection performance require vasoactive intestinal polypeptide (VIP) or its receptor VPAC2R. VIP is expressed, in a circadian manner, in interneurons in the external plexiform and periglomerular layers, whereas VPAC2R is expressed in mitral and external tufted cells in the OB. Together, these results indicate that VIP signaling modulates the output from the OB to maintain circadian rhythms in the mammalian olfactory system. PMID:24760863

  19. Polarized skylight does not calibrate the compass system of a migratory bat.

    PubMed

    Lindecke, Oliver; Voigt, Christian C; Pētersons, Gunārs; Holland, Richard A

    2015-09-01

    In a recent study, Greif et al. (Greif et al. Nat Commun 5, 4488. (doi:10.1038/ncomms5488)) demonstrated a functional role of polarized light for a bat species confronted with a homing task. These non-migratory bats appeared to calibrate their magnetic compass by using polarized skylight at dusk, yet it is unknown if migratory bats also use these cues for calibration. During autumn migration, we equipped Nathusius' bats, Pipistrellus nathusii, with radio transmitters and tested if experimental animals exposed during dusk to a 90° rotated band of polarized light would head in a different direction compared with control animals. After release, bats of both groups continued their journey in the same direction. This observation argues against the use of a polarization-calibrated magnetic compass by this migratory bat and questions that the ability of using polarized light for navigation is a consistent feature in bats. This finding matches with observations in some passerine birds that used polarized light for calibration of their magnetic compass before but not during migration. PMID:26382077

  20. The CUSP as a Source of Magnetospheric Particles

    NASA Technical Reports Server (NTRS)

    Fritz, Theodore A.; Chen, Jiasheng

    1999-01-01

    Observations made by the Polar satellite have shown that plasma of solar wind magnetosheath origin is rammed into the high altitude polar cusp creating a diamagnetic cavity of large dimensions. The Earth's dipole field can be excluded from this region in it turbulent manner with the magnitude of the field strength reaching close to zero nT at times. At such times energetic particles are produced in this region in intensities which exceed those measured in the trapping regions of the magnetosphere beyond L = 6.5. These particles can then flow back out of the cusp along field lines that form the magnetopause. A fraction of these particles can enter the magnetosphere along the magnetopause on the dusk and dawn flanks. Due to existing gradients in the geomagnetic field, cusp accelerated ions can enter the magnetosphere along the dawn flank and electrons along the dusk flank. For those particles entering near the geomagnetic equatorial plane with pitch angles close to ninety degrees they will drift along contours of constant magnetic field strength reaching deep into the nightside inner magnetosphere. From observations made by the Polar ATS-6, and ISEE satellites it is argued that this cusp source appears to be capable of providing energetic ions to the magnetosphere and possibly energetic electrons which form the source population of the Subsequent radial diffusion and formation of the radiation belts.

  1. Asymmetric Magnetosphere Deformation Driven by Hot Flow Anomaly(ies)

    NASA Technical Reports Server (NTRS)

    Safrankova, J.; Goncharov, O.; Nemecek, Z.; Prech, L.; Sibeck, D. G.

    2012-01-01

    We present a case study of a large deformation of the magnetopause on November 26, 2008. The investigation is based on observations of five THEMIS spacecraft located at the dawn flank in the magnetosphere and magnetosheath, on Cluster measurements at the dusk magnetosheath, and is supported by ACE solar wind monitoring. The main revelation of our study is that the interaction of the IMF discontinuity with the bow shock creates either one very elongated hot flow anomaly (HFA) or a pair of them that is (are) simultaneously observed at both flanks. Whereas the dusk HFA is weak and does not cause observable deformation of the magnetopause, the pressure variations connected with the dawn HFA lead to a magnetopause displacement by approx. = 5 R(sub E) outward from its nominal position. This is followed by a rapid inward motion of the magnetopause approx. = 4 R(sub E) inward with respect to the model location. The surface deformation is so large that the outermost THEMIS spacecraft was in the magnetosphere, whereas the spacecraft located 9 R(sub E) inbound entered into the magnetosheath at the same time. The whole event lasted about 5 minutes.

  2. Substorm Current Wedge as a Combined Effect of Wedgelets

    NASA Astrophysics Data System (ADS)

    Liu, J.; Angelopoulos, V.

    2014-12-01

    Understanding how the substorm current wedge (SCW) is formed is crucial to solving the substorm mystery. One recent idea on the SCW formation is the "wedgelets" picture, which proposes that dipolarizing flux bundles (DFBs) are the building elements of an SCW. (A DFB is a ~1-3 RE wide flux tube with stronger magnetic field than the ambient plasma in the magnetotail; its leading edge is known as a "dipolarization front", or "reconnection front", the product of near-Earth reconnection). Although each DFB carries field-aligned currents (FACs) in similar configuration to an SCW, it is unclear how the DFBs combine to become the large-scale (several magnetic local times wide) region-1-sense (towards Earth at the dawn sector of the magnetotail and away from Earth at the dusk sector) FACs of the SCW. To answer this question, we investigate the FACs of DFBs statistically using THEMIS data. Our results suggest that at the dawn (dusk) sector of the magnetotail, a DFB has more FAC towards (away from) Earth than away from (towards) Earth, so that the net FAC is towards (away from) Earth. The combined effect of many DFBs is therefore the same as the large-scale region-1-sense SCW, supporting the idea that "wedgelets" comprise the large scale substorm current wedge.

  3. Solar wind driving of asymmetries in the magnetosheath - magnetosphere system

    NASA Astrophysics Data System (ADS)

    Dimmock, Andrew; Pulkkinen, Tuija; Osmane, Adnane; Nykyri, Katariina

    2015-04-01

    Over the decades of in-situ measurements of the terrestrial magnetosphere it has been suggested and experimentally shown that various parameter dawn-dusk asymmetries arise. What is also apparent is that such asymmetries are delicately coupled to the properties of the solar wind. The IMF configuration has a considerable impact since its orientation dictates the shock geometry, thus driving different dawn-dusk plasma properties downstream. Magnetosheath asymmetries are notably important since the magnetosheath effectively modifies and reconfigures plasma before it enters the inner magnetosphere and therefore may play a role in driving asymmetries in the inner magnetosphere. We apply our existing statistical mapping tool which uses over 7 years of THEMIS and OMNI data to create statistical maps of plasma properties in the global magnetospheric system. We look at asymmetries of both steady state properties (e.g. B, V, n), and also transient/kinetic features such as mirror mode activity. We focus specifically on 1. solar wind dependence and 2. the co-dependence between the magnetosheath and magnetospheric regions.

  4. Penetration of the solar wind electric field into the magnetosphere/ionosphere system

    NASA Astrophysics Data System (ADS)

    Kelley, Michael C.; Makela, Jonathan J.; Chau, Jorge L.; Nicolls, Michael J.

    2003-02-01

    On April 17, 2002 an intense, long duration electric field penetration event was captured by the Jicamarca incoherent scatter radar. Other radars in the U. S. chain detected the event as well, although not with as much clarity. The Interplanetary Electric Field (IEF) is available from the ACE satellite as well. The ratio of the dawn-to-dusk component of the IEF to the dawn-to-dusk electric field in the equatorial ionosphere for periods less than about two hours is 15:1. We suggest that this corresponds to the ratio of the size of the magnetosphere to the length of the connection line between the Interplanetary Magnetic Field (IMF) and the Earth's magnetic field. Simultaneous magnetic field measurements at Piura (off the magnetic equator) and at Jicamarca (under the magnetic equator) in Peru, reveal the same high frequency components and suggest that a chain of stations or an equatorial fleet of satellites in low earth orbit could be used to monitor the connection length continuously.

  5. Low-frequency wave activity related to dipolarization fronts detected by MMS in the magnetotail

    NASA Astrophysics Data System (ADS)

    Le Contel, O.; Retino, A.; Breuillard, H.; Mirioni, L.; Roux, A.; Chust, T.; Chasapis, A.; Lavraud, B.; Lindqvist, P. A.; Khotyaintsev, Y. V.; Vaivads, A.; Fu, H.; Marklund, G. T.; Nakamura, R.; Burch, J. L.; Torbert, R. B.; Moore, T. E.; Ergun, R.; Goodrich, K.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Russell, C. T.; Magnes, W.; Strangeway, R. J.; Le, G.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Leinweber, H. K.; Anderson, B. J.; Argall, M. R.; Slavin, J. A.; Kepko, L.; Baumjohann, W.; Pollock, C. J.; Mauk, B.; Fuselier, S. A.

    2015-12-01

    Dipolarization fronts are often associated to reconnection jets in the magnetotail current sheet and are sites of important energy dissipation and particle energization. Since the launch on March 12th and until the 9th of July 2015, the MMS constellation has been moving from dawn to dusk in a string of pearls formation. Although particle instruments were rarely operating and only FIELDS instrument suite was often gathering data, the MMS spacecraft have detected numerous dipolarization fronts, in particular on May 15th. Since 9th of July, the MMS evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and was still able to detect dipolarization fronts in the dusk magnetotail. As the Larmor radius of thermal protons is about 500 km in this region and dipolarization fronts have a typical thickness of the order of the Larmor radius, such a separation allows us to investigate in detail the microphysics of dipolarization fronts. In this study, we focus in particular on low-frequency electromagnetic wave activity related to the fronts and discuss possible mechanisms of particle heating and acceleration both at large scales (string of pearls configuration) and at kinetic scales (tetrahedral configuration).

  6. Spatial Distribution of Rolled up Kelvin-Helmholtz Vortices at Earth's Dayside and Flank Magnetopause

    NASA Technical Reports Server (NTRS)

    Taylor, M. G. G. T.; Hasegawa, H.; Lavraud, B.; Phan, T.; Escoubet, C. P.; Dunlop, M. W.; Bogdanova, Y. V.; Borg, A. L.; Volwerk, M.; Berchem, J.; Constantinescu, O. D.; Eastwood, J. P.; Masson, A.; Laakso, H.; Soucek, J.; Fazakerley, A. N.; Frey, H. U.; Panov, E. V.; Shen, C.; Shi, J. K.; Sibeck, D. G.; Pu, Z. Y.; Wang, J.; Wild, J. A.

    2012-01-01

    The Kelvin-Helmholtz Instability (KHI) can drive waves at the magnetopause. These waves can grow to form rolled-up vortices and facilitate transfer of plasma into the magnetosphere. To investigate the persistence and frequency of such waves at the magnetopause we have carried out a survey of all Double Star 1 magnetopause crossings, using a combination of ion and magnetic field measurements. Using criteria originally used in a Geotail study made by Hasegawa et al. (2006) (forthwith referred to as H2006), 17 candidate events were identified from the entire TC-1 mission (covering 623 orbits where the magnetopause was sampled), a majority of which were on the dayside of the terminator. The relationship between density and shear velocity was then investigated, to identify the predicted signature of a rolled up vortex from H2006 and all 17 events exhibited some level of rolled up behavior. The location of the events had a clear dawn-dusk asymmetry, with 12 (71 %) on the post noon, dusk flank suggesting preferential growth in this region.

  7. Studies of medium scale travelling ionospheric disturbances using TIGER SuperDARN radar sea echo observations

    NASA Astrophysics Data System (ADS)

    He, L.; Dyson, P.; Parkinson, M.; Wan, W.

    2004-12-01

    Seasonal and diurnal variations in the direction of propagation of medium-scale travelling ionospheric disturbances (MSTIDs) have been investigated by analyzing sea echo returns detected by the TIGER SuperDARN radar located in Tasmania (43.4° S, 147.2° E geographic; -54.6°Λ). A strong dependency on local time was found, as well as significant seasonal variations. Generally, the propagation direction has a northward (i.e. equatorward) component. In the early morning hours the direction of propagation is quite variable throughout the year. It then becomes predominantly northwest and changes to northeast around 09:00 LT. In late fall and winter it changes back to north/northwest around 15:00 LT. During the other seasons, northward propagation is very obvious near dawn and dusk, but no significant northward propagation is observed at noon. It is suggested that the variable propagation direction in the morning is related to irregular magnetic disturbances that occur at this local time. The changes in the MSTID propagation directions near dawn and dusk are generally consistent with changes in ionospheric electric fields occurring at these times and is consistent with dayside MSTIDs being generated by the Lorentz force.

  8. Sources of Local Time Asymmetries in Magnetodiscs

    NASA Astrophysics Data System (ADS)

    Arridge, C. S.; Kane, M.; Sergis, N.; Khurana, K. K.; Jackman, C. M.

    2015-04-01

    The rapidly rotating magnetospheres at Jupiter and Saturn contain a near-equatorial thin current sheet over most local times known as the magnetodisc, resembling a wrapped-up magnetotail. The Pioneer, Voyager, Ulysses, Galileo, Cassini and New Horizons spacecraft at Jupiter and Saturn have provided extensive datasets from which to observationally identify local time asymmetries in these magnetodiscs. Imaging in the infrared and ultraviolet from ground- and space-based instruments have also revealed the presence of local time asymmetries in the aurora which therefore must map to local time asymmetries in the magnetosphere. Asymmetries are found in (i) the configuration of the magnetic field and magnetospheric currents, where a thicker disc is found in the noon and dusk sectors; (ii) plasma flows where the plasma flow has local time-dependent radial components; (iii) a thicker plasma sheet in the dusk sector. Many of these features are also reproduced in global MHD simulations. Several models have been developed to interpret these various observations and typically fall into two groups: ones which invoke coupling with the solar wind (via reconnection or viscous processes) and ones which invoke internal rotational processes operating inside an asymmetrical external boundary. In this paper we review these observational in situ findings, review the models which seek to explain them, and highlight open questions and directions for future work.

  9. The global context of the 14 November 2012 storm event

    NASA Astrophysics Data System (ADS)

    Hwang, K.-J.; Sibeck, D. G.; Fok, M.-C. H.; Zheng, Y.; Nishimura, Y.; Lee, J.-J.; Glocer, A.; Partamies, N.; Singer, H. J.; Reeves, G. D.; Mitchell, D. G.; Kletzing, C. A.; Onsager, T.

    2015-03-01

    From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ˜20-30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

  10. Diurnal lighting patterns and habitat alter opsin expression and colour preferences in a killifish

    PubMed Central

    Johnson, Ashley M.; Stanis, Shannon; Fuller, Rebecca C.

    2013-01-01

    Spatial variation in lighting environments frequently leads to population variation in colour patterns, colour preferences and visual systems. Yet lighting conditions also vary diurnally, and many aspects of visual systems and behaviour vary over this time scale. Here, we use the bluefin killifish (Lucania goodei) to compare how diurnal variation and habitat variation (clear versus tannin-stained water) affect opsin expression and the preference to peck at different-coloured objects. Opsin expression was generally lowest at midnight and dawn, and highest at midday and dusk, and this diurnal variation was many times greater than variation between habitats. Pecking preference was affected by both diurnal and habitat variation but did not correlate with opsin expression. Rather, pecking preference matched lighting conditions, with higher preferences for blue at noon and for red at dawn/dusk, when these wavelengths are comparatively scarce. Similarly, blue pecking preference was higher in tannin-stained water where blue wavelengths are reduced. In conclusion, L. goodei exhibits strong diurnal cycles of opsin expression, but these are not tightly correlated with light intensity or colour. Temporally variable pecking preferences probably result from lighting environment rather than from opsin production. These results may have implications for the colour pattern diversity observed in these fish. PMID:23698009

  11. Effects of convection electric field on the distribution of ring current type protons

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Chen, A. J.

    1975-01-01

    The topology of the boundaries of penetration (or, inversely, the boundaries of the forbidden regions) of 90-deg pitch-angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment), complex structural features are expected in the proton energy spectra detected by satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to tail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large-scale convection field changes may be seen in the nose-like proton spectrograms observed near dusk by instrumentation on Explorer 45. These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to the Kp index through night-time equatorial plasmapause measurements.

  12. Dynamics of polar boundary of the auroral oval derived from the IMAGE satellite data

    NASA Astrophysics Data System (ADS)

    Lukianova, R.; Kozlovsky, A.

    2013-01-01

    Based on a new database on positions of the auroral oval boundaries including measurements made by the IMAGE satellite in 2000-2002 with correct determination of the glow boundaries, statistical estimations of the latitudinal position of the polar cap boundary (PCB) are obtained depending on the IMF B y and B z , and the PCB evolution during a magnetic storm is analyzed. At zero IMF in the noon (midnight) sector, PCB is located approximately at 80° (76°) CGMLat. The PCB displacement along the noon-midnight meridian is controlled by the IMF B z , and in the noon (midnight) sector it is equal to 0.45° (0.15°) CGMLat when B z changes by 1 nT. The PCB displacement along the dawn-dusk meridian depends on the IMF B y , and it equals 0.1° CGMLat when B y changes by 1 nT. Accordingly, the north polar cap as a whole is shifted to the dawn (dusk) side at B y > 0 ( B y <0). After northward turn of the IMF during the storm's recovery phase, the PCB on the dayside is shifted to the north practically without time delay. The night boundary requires 25 h or more in order to be shifted to the pole to a latitude corresponding to B z > 0.

  13. The global context of the 14 November 2012 storm event

    DOE PAGESBeta

    Hwang, K. -J.; Sibeck, D. G.; Fok, M. -C. H.; Zheng, Y.; Nishimura, Y.; Lee, J. -J.; Glocer, A.; Partamies, N.; Singer, H. J.; Reeves, G. D.; et al

    2015-03-01

    From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to thosemore » of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in-situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in-situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.« less

  14. The global context of the 14 November 2012 storm event

    SciTech Connect

    Hwang, K. -J.; Sibeck, D. G.; Fok, M. -C. H.; Zheng, Y.; Nishimura, Y.; Lee, J. -J.; Glocer, A.; Partamies, N.; Singer, H. J.; Reeves, G. D.; Mitchell, D. G.; Kletzing, C. A.; Onsager, T.

    2015-03-01

    From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in-situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in-situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

  15. Distribution of hydrogen and oxygen ion species in the plasmasheet

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Cao, Jinbin; Liu, Wenlong

    2016-07-01

    In this paper, using data obtained by Cluster 4 satellite from 2001 to 2012, we statistically investigate the spatial distributions of H+ and O+ in the magnetotail plasmasheet and their relation with geomagnetic indices. Our work outlines the existence of two regions with enhanced O+ concentration in the tail plasmasheet, one is located in the mid-tail plasmasheet at R > 17 RE, and the other is located near the inner boundary of plasmasheet at R < 10 RE. The existence of the depletion region of O+ between 10 RE < R < 17 RE indicates that the O+ ions in the mid-tail plasmasheet, which come from polar cap, are not likely to be able to make important contribution to the formation of ring current. Both the distributions of density and temperature of O+ ions have a dawn-dusk asymmetry. The number density of O+ during geomagnetic active time (Dst < -20 nT/AE > 200 nT/Kp ⩾ 3) is much larger than that during non-storm time (Dst > -20 nT/AE < 200 nT/Kp < 3). This dawn-dusk asymmetry and the number density of O+ varying with geomagnetic activity apply for both regions (R < 10 RE and R > 17 RE) of O+. Therefore both substorm and enhanced convection provide a large number of O+ ions to the plasmasheet, which makes favorable condition for the growth of the ring current.

  16. Ramadan fasting and patients with renal diseases: A mini review of the literature.

    PubMed

    Emami-Naini, Afsoon; Roomizadeh, Peyman; Baradaran, Azar; Abedini, Amin; Abtahi, Mohammad

    2013-08-01

    Fasting during the month of Ramadan is one of the five pillars of Islam. During this month, adult Muslims are obligated to refrain from eating and drinking from dawn to dusk. Although based on Islamic principles patients are exempted from fasting, each year, many Muslim patients express their willingness to observe the fast in Ramadan month to respect the cultural customs. There are concerns about the impact of fluid restriction and dehydration during Ramadan fasting for patients with renal diseases. In this study, we reviewed the PubMed, Google Scholar, EBSCO, SCIRUS, Embase, and DOAJ data sources to identify the published studies on the impact of Ramadan fasting on patients with renal diseases. Our review on published reports on renal transplant recipients revealed no injurious effect of Ramadan fasting for the renal graft function. Nearly all studies on this topic suggest that Ramadan fasting is safe when the function of the renal graft is acceptable and stable. Regarding the impact of Ramadan fasting on patients with chronic kidney disease, there is concern about the role of renal hypoperfusion in developing tubular cell injury. Finally, there is controversy between studies about the risk of dehydration in Ramadan in developing renal stones. There are uncertainties about the change in the incidence of renal colic in Ramadan month compared with the other periods of the year. Despite such discrepancies, nearly all studies are in agreement on consuming adequate amounts of water from dusk to dawn to reduce the risk of renal stone formation. PMID:24379850

  17. Daily rhythms in antennal protein and olfactory sensitivity in the malaria mosquito Anopheles gambiae

    PubMed Central

    Rund, Samuel S. C.; Bonar, Nicolle A.; Champion, Matthew M.; Ghazi, John P.; Houk, Cameron M.; Leming, Matthew T.; Syed, Zainulabeuddin; Duffield, Giles E.

    2013-01-01

    We recently characterized 24-hr daily rhythmic patterns of gene expression in Anopheles gambiae mosquitoes. These include numerous odorant binding proteins (OBPs), soluble odorant carrying proteins enriched in olfactory organs. Here we demonstrate that multiple rhythmically expressed genes including OBPs and takeout proteins, involved in regulating blood feeding behavior, have corresponding rhythmic protein levels as measured by quantitative proteomics. This includes AgamOBP1, previously shown as important to An. gambiae odorant sensing. Further, electrophysiological investigations demonstrate time-of-day specific differences in olfactory sensitivity of antennae to major host-derived odorants. The pre-dusk/dusk peaks in OBPs and takeout gene expression correspond with peak protein abundance at night, and in turn coincide with the time of increased olfactory sensitivity to odorants requiring OBPs and times of increased blood-feeding behavior. This suggests an important role for OBPs in modulating temporal changes in odorant sensitivity, enabling the olfactory system to coordinate with the circadian niche of An. gambiae. PMID:23986098

  18. Simultaneous measurements of energetic ion (50 keV and above) and electron (220 keV and above) activity upstream of earth's bow shock and inside the plasma sheet - Magnetospheric source for the November 3 and December 3, 1977 upstream events

    NASA Technical Reports Server (NTRS)

    Sarris, E. T.; Anagnostopoulos, G. C.; Krimigis, S. M.

    1987-01-01

    Simultaneous observations of energetic ions and electrons by the IMP 7 and 8 spacecraft are used here to separate temporal variations from spatial variations during the upstream ion events observed on December 3, 1977 and November 2-3, 1977, in order to determine the source of these particles. Analysis of the observations and comparison with theory shows that: (1) for each of the observed upstream enhancements, energetic ions and electrons were simultaneously present inside the plasma sheet; (2) the low-energy ion intensity profile inside the plasma sheet was relatively flat, while at higher energies there was considrable variability; (3) relativistic electron bursts were seen inside the plasma sheet and also upstream of the shock but at substantially reduced intensities; (4) the ion energy spectrum for the December 3 event, extended to energies of about 2 MeV, was identical in form with the plasma sheet and upstream of the shock; (5) ion anisotropies exhibited typically large dawn-dusk or dusk-dawn gradients and large field-aligned streaming away from the bow shock.

  19. Structure of kinetic/non-kinetic scale velocity shear layers and associated Kelvin-Helmholtz vortices: particle simulations

    NASA Astrophysics Data System (ADS)

    Nakamura, T.; Hasegawa, H.; Shinohara, I.

    2009-12-01

    Recent in-situ observations have revealed that Kelvin-Helmholtz (KH) vortices can roll-up not only at the Earth's magnetopause but also at the Mercury's magnetopause. Since kinetic effects cannot be neglected in Mercury-like small-scale situations, to universally understand the structure of the KH vortex the kinetic effects should be considered. Thus, in this study, we have performed 2D full particle (EM-PIC) simulations of KH vortices arising from kinetic and non-kinetic scale velocity shear layers. In this study, we focus on the basic situation in which the initial density, temperature and magnetic field are uniform and the magnetic field is perpendicular to the k-vector of KH instability. First, we investigated the kinetic equilibrium of velocity shear layers. In our simulation settings, particles are initialized with shifted Maxwellian velocity distributions having a bulk flow Vx0=±V0*tanh(Y/D0), where D0 is the initial half thickness of the velocity shear layer and V0 is the initial velocity jump across the shear layer. The +V0 (-V0) case corresponds to the dawn (dusk) case of the Earth’s and Mercury's situations. The Maxwellian loading of the particles, however, is only an approximation of equilibrium conditions, and past kinetic studies have shown that the true equilibrium condition is affected by the ion gyro-motion especially when D0<ρi, where ρi is the ion gyro radius. In this study, to exactly understand ion kinetic effects to the true equilibrium of various-scale velocity shear layer, we performed a parameter survey of D0 and V0. As a result, we found that in all cases until about 10 ion gyro-cycles the shear layer reaches the kinetic equilibrium, and further that when D0<ρi the thickness of the shear layer in the kinetic equilibrium always becomes 2ρi. It means there is a low threshold of the velocity shear layer which is determined by ρi. Moreover, we also found that the low threshold of the thickness in the dawn (dusk) case becomes thicker

  20. Quasi-periodic injections of relativistic electrons in Saturn's outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Roussos, E.; Krupp, N.; Mitchell, D. G.; Paranicas, C.; Krimigis, S. M.; Andriopoulou, M.; Palmaerts, B.; Kurth, W. S.; Badman, S. V.; Masters, A.; Dougherty, M. K.

    2016-01-01

    Quasi-periodic, short-period injections of relativistic electrons have been observed in both Jupiter's and Saturn's magnetospheres, but understanding their origin or significance has been challenging, primarily due to the limited number of in-situ observations of such events by past flyby missions. Here we present the first survey of such injections in an outer planetary magnetosphere using almost nine years of energetic charged particle and magnetic field measurements at Saturn. We focus on events with a characteristic period of about 60-70 min (QP60, where QP stands for quasi-periodic). We find that the majority of QP60, which are very common in the outer magnetosphere, map outside Titan's orbit. QP60 are also observed over a very wide range of local times and latitudes. A local time asymmetry in their distribution is the most striking feature, with QP60 at dusk being between 5 and 25 times more frequent than at dawn. Field-line tracing and pitch angle distributions suggest that most events at dusk reside on closed field lines. They are distributed either near the magnetopause, or, in the case of the post-dusk (or pre-midnight) sector, up to about 30 RS inside it, along an area extending parallel to the dawn-dusk direction. QP60 at dawn map either on open field lines and/or near the magnetopause. Both the asymmetries and varying mapping characteristics as a function of local time indicate that generation of QP60 cannot be assigned to a single process. The locations of QP60 seem to trace sites that reconnection is expected to take place. In that respect, the subset of events observed post-dusk and deep inside the magnetopause may be directly or indirectly linked to the Vasyliunas reconnection cycle, while magnetopause reconnection/Kelvin-Helmholtz (KH) instability could be invoked to explain all other events at the duskside. Using similar arguments, injections at the dawnside magnetosphere may result from solar-wind induced storms and/or magnetopause reconnection

  1. Investigation of storm time magnetotail and ion injection using three-dimensional global hybrid simulation

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Wang, X. Y.; Lu, S.; Perez, J. D.; Lu, Q.

    2014-09-01

    Dynamics of the near-Earth magnetotail associated with substorms during a period of extended southward interplanetary magnetic field is studied using a three-dimensional (3-D) global hybrid simulation model that includes both the dayside and nightside magnetosphere, for the first time, with physics from the ion kinetic to the global Alfvénic convection scales. It is found that the dayside reconnection leads to the penetration of the dawn-dusk electric field through the magnetopause and thus a thinning of the plasma sheet, followed by the magnetotail reconnection with 3-D, multiple flux ropes. Ion kinetic physics is found to play important roles in the magnetotail dynamics, which leads to the following results: (1) Hall electric fields in the thin current layer cause a systematic dawnward ion drift motion and thus a dawn-dusk asymmetry of the plasma sheet with a higher (lower) density on the dawnside (duskside). Correspondingly, more reconnection occurs on the duskside. Bidirectional fast ions are generated due to acceleration in reconnection, and more high-speed earthward flow injections are found on the duskside than the dawnside. Such finding of the dawn-dusk asymmetry is consistent with recent satellite observations. (2) The injected ions undergo the magnetic gradient and curvature drift in the dipole-like field, forming a ring current. (3) Ion particle distributions reveal multiple populations/beams at various distances in the tail. (4) Dipolarization of the tail magnetic field takes place due to the pileup of the injected magnetic fluxes and thermal pressure of injected ions, where the fast earthward flow is stopped. Oscillation of the dipolarization front is developed at the fast-flow braking, predominantly on the dawnside. (5) Kinetic compressional wave turbulence is present around the dipolarization front. The cross-tail currents break into small-scale structures with k⟂ρi˜1, where k⟂ is the perpendicular wave number. A sharp dip of magnetic field

  2. Penetration of Large Scale Electric Field to Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Chen, S. H.; Fok, M. C. H.; Sibeck, D. G.; Wygant, J. R.; Spence, H. E.; Larsen, B.; Reeves, G. D.; Funsten, H. O.

    2015-12-01

    The direct penetration of large scale global electric field to the inner magnetosphere is a critical element in controlling how the background thermal plasma populates within the radiation belts. These plasma populations provide the source of particles and free energy needed for the generation and growth of various plasma waves that, at critical points of resonances in time and phase space, can scatter or energize radiation belt particles to regulate the flux level of the relativistic electrons in the system. At high geomagnetic activity levels, the distribution of large scale electric fields serves as an important indicator of how prevalence of strong wave-particle interactions extend over local times and radial distances. To understand the complex relationship between the global electric fields and thermal plasmas, particularly due to the ionospheric dynamo and the magnetospheric convection effects, and their relations to the geomagnetic activities, we analyze the electric field and cold plasma measurements from Van Allen Probes over more than two years period and simulate a geomagnetic storm event using Coupled Inner Magnetosphere-Ionosphere Model (CIMI). Our statistical analysis of the measurements from Van Allan Probes and CIMI simulations of the March 17, 2013 storm event indicate that: (1) Global dawn-dusk electric field can penetrate the inner magnetosphere inside the inner belt below L~2. (2) Stronger convections occurred in the dusk and midnight sectors than those in the noon and dawn sectors. (3) Strong convections at multiple locations exist at all activity levels but more complex at higher activity levels. (4) At the high activity levels, strongest convections occur in the midnight sectors at larger distances from the Earth and in the dusk sector at closer distances. (5) Two plasma populations of distinct ion temperature isotropies divided at L-Shell ~2, indicating distinct heating mechanisms between inner and outer radiation belts. (6) CIMI

  3. Equatorial counterelectrojets during geomagnetic storms and their possible dynamos in the magnetosphere

    NASA Astrophysics Data System (ADS)

    Kikuchi, T.; Hashimoto, K. K.; Ebihara, Y.; Tsuji, Y.; Veenadhari, B.; Nishimura, T.; Tanaka, T.; Fujita, S.; Nagatsuma, T.

    2012-12-01

    During the substorm growth phase and storm main phase, the high pressure plasma accumulated in the cusp and mantle regions activates a dynamo for the dawn-to-dusk convection electric field and the Region-1 field-aligned currents (R1 FACs) [Tanaka, 1995]. The electric field and FACs are conveyed by the shear Alfven waves to the polar ionosphere and the electric field extends promptly to low latitude through the Earth-ionosphere waveguide [Kikuchi and Araki, 1979]. The electric field drives the DP2 currents at mid latitudes [Wilson et al., 2001; Tsuji et al., 2012] and intensifies the equatorial electrojet (EEJ) [Kikuchi et al., 1996, 2008]. The convection electric field extends to the inner magnetosphere promptly [Nishimura et al., 2009] and energizes the plasma in the partial ring current region with the help of the gradient and curvature drift [Ebihara and Ejiri, 2000], which in turn works as a dynamo for the dusk-to-dawn electric field and the R2 FACs. The dusk-to-dawn electric field causes the counterelectrojet (CEJ) at the equator when the IMF turns northward [Rastogi, 1975]. The CEJ often appears during substorms [Kobea et al., 2000; Kikuchi et al., 2000]. Both the R1 and R2 FACs are intensified by the substorm expansion, with the R2 FACs strong enough to cause the CEJ [Hashimoto et al., 2011]. The CEJ often occurs during the recovery phase of geomagnetic storms [Kikuchi et al., 2008; Tsuji et al., 2012], while the CEJ also appears during the storm main phase under the relatively stable southward IMF [Fejer et al., 2007; Veenadhari et al., 2010]. In this paper, we analyzed several storm events to identify the dynamo for the stormtime CEJ. The disturbance dynamo is a commonly accepted dynamo for the long lasting stormtime CEJ [Blanc and Richmond, 1980; Fejer and Scherliess 1997]. However, the observed rapid and periodic development of the CEJ should be attributed to the R2 FACs generated in the inner magnetosphere. Based on the magnetometer and radar

  4. Dynamics of the inner magnetosphere near times of substorm onsets

    NASA Astrophysics Data System (ADS)

    Maynard, N. C.; Burke, W. J.; Basinska, E. M.; Erickson, G. M.; Hughes, W. J.; Singer, H. J.; Yahnin, A. G.; Hardy, D. A.; Mozer, F. S.

    1996-04-01

    The electrodynamics of the inner magnetosphere near times of substorm onsets have been investigated using CRRES measurements of magnetic and electric fields, energetic electron fluxes, in conjunction with ground-based observations. Six events were studied in detail, spanning the 2100 to 0000 MLT sector and L values from 5 to 7. In each case the dawn-dusk electric field was enhanced over typical background electric fields, and significant, low-frequency pulsation activity was observed. The amplitudes of the pulsations were larger than the background electric fields. Dusk-dawn excursions of the cross-tail electric field often correlated with changes in currents and particle energies at CRRES and with ULF wave activity observed on the ground. Variations of the electric field and Poynting vectors with periods in the Pi 2 range are consistent with bouncing Alfvén waves that provide electromagnetic communication between the ionosphere and plasma sheet. Magnetic signatures of field-aligned current filaments directed away from the ionosphere, presumably associated with the substorm current wedge, were observed during three orbits. In all cases, ground signatures of substorm expansion were observed at least 5 min before the injection of electrons at CRRES. Field-aligned fluxes of counter-streaming, low-energy electrons were detected after three of the injections. We develop an empirical scenario for substorm onset. The process grows from ripples at the inner edge of the plasma sheet associated with dusk-dawn excursions of the electric field, prior to the beginning of dipolarization. Energy derived from the braking of the inward plasma convection flows into the ionosphere in the form of Poynting flux. Subsequently reflected Poynting flux plays a crucial role in the magnetosphere-ionosphere coupling. Substorms develop when significant energy (positive feedback?) flows in both directions, with the second cycle stronger than the initial. Pseudobreakups occur when energy flow

  5. Elements of M-I Coupling in Repetitive Substorm Activity Driven by Interplanetary CMEs

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Sandholt, P. E.

    2014-12-01

    By means of case studies we explore key elements of the magnetosphere-ionosphere current system associated with repetitive substorm activity during persistent strong forcing by ICMEs. Our approach consists of a combination of the magnetospheric and ionospheric perspectives on the substorm activity. The first aspect is the near-Earth plasma sheet with its repetitive excitations of the substorm current wedge, as monitored by spacecraft GOES-10 when it traversed the 2100-0300 MLT sector, and its coupling to the westward auroral electrojet (WEJ) centered near midnight during the stable interplanetary (IP) conditions. The second aspect is the excitation of Bostrom type II currents maximizing at dusk and dawn and their associated ionospheric Pedersen current closure giving rise to EEJ (WEJ) events at dusk (dawn). As documented in our study, this aspect is related to the braking phase of Earthward-moving dipolarization fronts-bursty bulk flows. We follow the magnetospheric flow/field events from spacecraft Geotail in the midtail (X = - 11 Re) lobe to geostationary altitude at pre-dawn MLTs (GOES 10). The associated M-I coupling is obtained from ground-satellite conjunctions across the double auroral oval configuration along the meridian at dusk. By this technique we distinguish between ionospheric manifestations in three latitude regimes: (i) auroral oval south, (ii) auroral oval north, and (iii) polar cap. Regime (iii) is characterized by events of enhanced antisunward convection near the polar cap boundary (flow channel events) and in the central polar cap (PCN-index events). The repetitive substorm activity is discussed in the context of the level of IP driving as given by the geoeffective IP electric field (E_KL), magnetotail reconnection (inferred from the PCN-index and spacecraft Wind at X = - 77 Re) and the storm SYM-H index. We distinguish between different variants of the repetitive substorm activity, giving rise to electrojet (AL)-plasma convection (PCN) events

  6. The search for Ar in the lunar atmosphere using the Lunar Reconnaissance Orbiter's LAMP instrument.

    NASA Astrophysics Data System (ADS)

    Cook, J. C.; Stern, S. A.; Feldman, P. D.; Gladstone, R.; Retherford, K. D.; Greathouse, T. K.; Grava, C.

    2014-12-01

    The Apollo 17 mass spectrometer, LACE, first measured mass 40 particles in the lunar atmosphere, and over a nine-month period, detected variations correlated with the lunar day (Hoffman et al., 1973, LPSC, 4, 2865). LACE detected a high particle density at dusk (0.6-1.0x104 cm-3), decreasing through the lunar night to a few hundred cm-3, then increasing rapidly before dawn to levels 2-4 times greater than at dusk. No daytime measurements were made due to instrument saturation. Given the LACE measurements' periodic nature, and the Ar abundance in lunar regolith samples (Kaiser, 1972, EPSL, 13, 387), it was concluded that mass 40 was likely due to Ar. Benna et al. (2014, LPSC, 45, 1535) recently reported that the Neutral Mass Spectrometer (NMS) aboard LADEE also detected Ar (mass 40) with similar diurnal profiles. We report on UV spectra of the lunar atmosphere as obtained by the Lunar Reconnaissance Orbiter (LRO). Aboard LRO is the UV-spectrograph, LAMP (Lyman Alpha Mapping Project), spanning the spectral range 575 to 1965 Å. LAMP is typically oriented toward the surface and has been mapping the Moon since September 2009. LAMP also observes the tenuous lunar atmosphere when the surface is in darkness, but the atmospheric column below LRO is illuminated. We have previously used nadir oriented twilight observations to examine the sparse lunar atmosphere (Feldman et al., 2012, Icarus, 221, 854; Cook et al., 2013, Icarus, 225, 681; Stern et al., 2013, Icarus, 226, 1210; Cook & Stern 2014, Icarus, 236, 48). In Cook et al., 2013, we reported an upper limit for Ar of 2.3x104 cm-3. Since then, we have collected additional data and refined our search method by focusing on the regions (near equator) and local times (dawn and dusk) where Ar has been reported previously. We have carefully considered effective area calibration and g-factor accuracies and find these to be unlikely explanations for the order of magnitude differences. We will report new results, which provide much

  7. Plasma convection in the nightside magnetosphere of Saturn determined from energetic ion anisotropies

    NASA Astrophysics Data System (ADS)

    Kane, M.; Mitchell, D. G.; Carbary, J. F.; Krimigis, S. M.

    2014-02-01

    The Cassini Ion and Neutral Camera measures intensities of hydrogen and oxygen ions and neutral atoms in the Saturnian magnetosphere and beyond. We use the measured intensity spectrum and anisotropy of energetic hydrogen and oxygen ions to detect, qualify, and quantify plasma convection. We find that the plasma azimuthal convection speed relative to the local rigid corotation speed decreases with radial distance, lagging the planetary rotation rate, and has no significant local time dependences. Plasma in the dusk-midnight quadrant sub-corotates at a large fraction of the rigid corotation speed, with the primary velocity being azimuthal but with a distinct radially outward component. The duskside velocities are similar to those obtained from earlier orbits in the midnight-dawn sector, in contrast to the depressed velocities measured at Jupiter using Energetic Particles Detector measurements on the Galileo spacecraft in the dusk-midnight quadrant. We find significant radial outflow in most of the nightside region. The radial component of the flow decreases with increasing local time in the midnight-dawn sector and reverses as dawn is approached. This and previous results are consistent with a plasma disk undergoing a centrifugally induced expansion as it emerges into the nightside, while maintaining partial rotation with the planet. The magnetodisk expansion continues as plasma rotates across the tail to the dawnside. We do not see evidence in the convection pattern for steady state reconnection in Saturn's magnetotail. The outermost region of the magnetodisk, having undergone expansion upon emerging from the dayside magnetopause confinement, is unlikely to recirculate back into the dayside. We conclude that plasma in the outer magnetodisk [at either planet] rotates from the dayside, expands at the dusk flank, but remains magnetically connected to the respective planet while moving across the tail until it interacts with and is entrained into the dawnside

  8. Energetic Neutral Atom Imaging at Low Altitudes from the Swedish Microsatellite Astrid: Images and Spectral Analysis. Paper 1

    NASA Technical Reports Server (NTRS)

    Brandt, Pontus C:son; Barabash, Stas; Norberg, Olle; Lundin, Rickard; Roelof, Rdmond C.; Chase, Christopher J.

    1999-01-01

    Observations of energetic neutral atoms (ENA) in the energy range 26- 52 keV are reported from four occasions during geomagnetically disturbed periods. The data were acquired by the ENA imager flown on the Swedish microsatellite Astrid in a 1000 km circular orbit with 83 deg inclination. The ENA imager separates charged particles from neutrals through an electrostatic deflection system in the energy range between 0.1 and 114 keV. ENA images obtained from vantage points in the polar cap and in the afternoon magnetic local time (MLT) hours looking into the antisunward hemisphere show intense ENA fluxes (approx. 10(exp 4)/sq cm sr s over 26-37 keV) coming from the dusk region and low altitudes (approx. 300 km). The morphology shows no relation to local magnetic field excluding the possibility of charged particle detection. It is concluded that the source of these ENAs are precipitating/mirroring ions from the ring current/trapped radiation interacting with the exobase on auroral L-shells and in the dusk region. The observed ENA fluxes show a relation with Kp and Dst geomagnetic indices. The observed ENA spectrum from a geomagnetic storm on February 8, 1995, is investigated in more detail and compared to the parent ion spectrum obtained by the Defense Meteorological Satellite Project (DMSP) satellite, Fl2, during the same period on L = 6 +/- 2 around dusk. The observed ENA spectral slope is used to derive the parent ion spectral temperature. The derived ion temperatures range is 3.0 - 6.0 keV for H and 4.5 - 8.5 keV for O. The higher of these ion temperatures comes closest in agreement to the extrapolated DMSP spectrum leading us to favor O over H as the species of the detected ENAS. It is shown that the detected ENAs must have been produced at L greater than or equal to 6 to reach the detector without atmospheric attenuation and that the main energy dependence of the ENA spectrum, apart from the parent ion spectrum, is governed by the energy dependence of the charge

  9. Dipolarization fronts as earthward propagating flux ropes: A three-dimensional global hybrid simulation

    NASA Astrophysics Data System (ADS)

    Lu, San; Lu, Quanming; Lin, Yu; Wang, Xueyi; Ge, Yasong; Wang, Rongsheng; Zhou, Meng; Fu, Huishan; Huang, Can; Wu, Mingyu; Wang, Shui

    2015-08-01

    Dipolarization fronts (DFs) as earthward propagating flux ropes (FRs) in the Earth's magnetotail are presented and investigated with a three-dimensional (3-D) global hybrid simulation for the first time. In the simulation, several small-scale earthward propagating FRs are found to be formed by multiple X line reconnection in the near tail. During their earthward propagation, the magnetic field Bz of the FRs becomes highly asymmetric due to the imbalance of the reconnection rates between the multiple X lines. At the later stage, when the FRs approach the near-Earth dipole-like region, the antireconnection between the southward/negative Bz of the FRs and the northward geomagnetic field leads to the erosion of the southward magnetic flux of the FRs, which further aggravates the Bz asymmetry. Eventually, the FRs merge into the near-Earth region through the antireconnection. These earthward propagating FRs can fully reproduce the observational features of the DFs, e.g., a sharp enhancement of Bz preceded by a smaller amplitude Bz dip, an earthward flow enhancement, the presence of the electric field components in the normal and dawn-dusk directions, and ion energization. Our results show that the earthward propagating FRs can be used to explain the DFs observed in the magnetotail. The thickness of the DFs is on the order of several ion inertial lengths, and the electric field normal to the front is found to be dominated by the Hall physics. During the earthward propagation from the near-tail to the near-Earth region, the speed of the FR/DFs increases from ~150 km/s to ~1000 km/s. The FR/DFs can be tilted in the GSM (x, y) plane with respect to the y (dawn-dusk) axis and only extend several Earth radii in this direction. Moreover, the structure and evolution of the FRs/DFs are nonuniform in the dawn-dusk direction, which indicates that the DFs are essentially 3-D.

  10. Food of young and colony-attendance of adult guillemots Uria aalge on Helgoland

    NASA Astrophysics Data System (ADS)

    Leopold, M. F.; Wolf, P. A.; Hüppop, O.

    1992-06-01

    The guillemot colony on Helgoland, Germany, was visited from June 5th to 21st 1990. The presence of adults and food delivery to chicks was studied on a ledge holding about 50 breeding pairs. Attendance varied through the day, with most birds present at mid-day. Food consisted only of fish, 94.6% Clupeidae (herring and sprat) and 5.4% sand-eel. On average, a chick received 2.72 fish per day. After a marked early morning peak of feeding, the number of feeds per hour levelled off to a constant rate during the rest of the day until dusk. At sea, high numbers of guillemots were present in front of the colony, with densities dropping steeply with distance. The birds are thought to forage at distances of more than 5 km away from the colony.