ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Source of the Dayside Cusp Aurora (2016)
    Wiley
    Details
    Publication Date: 2016-07-21
    Description: Monochromatic all-sky imagers at South Pole and other Antarctic stations of the Automatic Geophysical Observatory (AGO) chain recorded the aurora in the region where the THEMIS satellites crossed the dayside magnetopause. In several cases the magnetic field line threading the satellites when mapped to the atmosphere were inside the imagers’ field of view. From the THEMIS magnetic field and the plasma density measurements, we were able to locate the position of the magnetopause crossings and map it to the ionosphere using the Tsyganenko-96 field model. Field line mapping is reasonably accurate on the dayside sub-solar region where the field is strong, almost dipolar even though compressed. From these coordinated observations, we were able to prove that the dayside cusp aurora of high 630 nm brightness is on open field lines and it is therefore direct precipitation from the magnetosheath. The cusp aurora contained significant highly structured N 2 + 427.8 nm emission. The THEMIS measurements of the magnetosheath particle energy and density taken just outside the magnetopause compared to the intensity of the structured N 2 + 427.8 nm emissions showed that the precipitating magnetosheath particles had to be accelerated. The most likely electron acceleration mechanism is by Dispersive Alfvén Waves propagating along the field line. Wave-accelerated suprathermal electrons were seen by FAST and DMSP. The 427.8 nm wavelength channel also show the presence of a lower-latitudes hard-electron precipitation zone originating inside the magnetosphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) (2016)
    Wiley
    Details
    Publication Date: 2016-07-24
    Description: The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) was the first specifically dedicated instrument to observe lightning-induced transient luminous events (TLE) sprites, elves, halos, and gigantic jets from space. The Imager is an intensified CCD system operating in the visible wavelength region with a filter wheel to select from 6 positions with filters. The Imager has a 5°x20° (vertical x horizontal) field of view (FOV). The Spectrophotometer (SP) is populated with 6 photometers with individual filters for emissions from the far ultra-violet to the near-infrared. An Array Photometer with two channels operating in the blue and red provides altitude profiles of the emission over 16 altitude bins each. The Associated Electronics Package (AEP) controls instrument functions and interfaces with the spacecraft. ISUAL was launched May 21, 2004 into a sun-synchronous 890 km orbit on the Formosat-2 satellite and has successfully been collecting data ever since. ISUAL is running on the night side of the orbit and is pointed to the east of the orbit down towards the limb. The instrument runs continuously and writes data to a circular buffer. Whenever the SP detects a sudden signal increase above a preset threshold, a trigger signal is generated that commands the system to keep the data for about 400 msec starting from ~50 msec before the trigger. Over its lifetime of ~11 years the system recorded thousands of TLE and also successfully observed aurora and airglow.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    Secondary gigantic jets as possible inducers of sprites (2013)
    Wiley
    Details
    Publication Date: 2013-03-22
    Description: [1]  Three multi-TLE events, which were recorded by ISUAL on FORMOSAT-2 and shared a similar generating sequence, are reported. Each event began with a + CG-induced sprite, and a secondary gigantic jet (GJ) followed within ~30-50 ms. Then, 1 ms after the GJ, a new sprite occurred near the GJ without associated impulsive lightning signal. The associated electromagnetic signal for one of the events indicates that the GJ is a negative cloud-to-ionosphere discharge carrying a high peak current moment. Cross-analysis of the spectral, image and electromagnetic data of these three events indicates that the new sprites are likely induced by the secondary GJs, and the high current moment of the secondary GJs appears to be a crucial factor for the induction of the new sprites. Hence these secondary GJs may have played a role in inducing sprites much as the -CGs do for the occurrence of negative sprites.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Dynamic effects of restoring footpoint symmetry on closed magnetic field-lines (2016)
    Wiley
    Details
    Publication Date: 2016-03-29
    Description: Here we present an event where simultaneous global imaging of the aurora from both hemispheres reveals a large longitudinal shift of the nightside aurora of about 3 h, being the largest relative shift reported on from conjugate auroral imaging. This is interpreted as evidence of closed field-lines having very asymmetric footpoints associated with the persistent positive y-component of the interplanetary magnetic field before and during the event. At the same time, the Super Dual Auroral Radar Network (SuperDARN) observes the ionospheric nightside convection throat region in both hemispheres. The radar data indicate faster convection towards the dayside in the dusk cell in the Southern Hemisphere compared to its conjugate region. We interpret this as a signature of a process acting to restore symmetry of the displaced closed magnetic field-lines resulting in flux tubes moving faster along the banana cell than the conjugate orange cell. The event is analysed with emphasis on Birkeland Currents (BC) associated with this restoring process, as recently described by Tenfjord et al. [2015]. Using data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) during the same conditions as the presented event, the large-scale BC pattern associated with the event is presented. It shows the expected influence of the process of restoring symmetry on BCs. We therefore suggest that these observations should be recognized as being a result of the dynamic effects of restoring footpoint symmetry on closed field-lines in the nightside.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    The 2‐D Structure of Foreshock‐Driven Field Line Resonances Observed by THEMIS Satellite and Ground‐Based Imager Conjunctions (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Recent studies of Pc5‐band (150–600 s) ultralow frequency waves found that foreshock disturbances can be a driver of dayside compressional waves and field line resonance, which are two typical Pc5 wave modes in the dayside magnetosphere. However, it is difficult to find spatial structure of dayside Pc5 waves using a small number of satellites or ground magnetometers. This study determines 2‐D structure of dayside Pc5 waves and their driver by utilizing coordinated observations by the THEMIS satellites and the all‐sky imager at South Pole during two series of Pc5 waves on 29 June 2008. These Pc5 waves were found to be field line resonances (FLRs) and driven by foreshock disturbances. The ground‐based all‐sky imager at South Pole shows that periodic poleward moving arcs occurred simultaneously with the FLRs near the satellite footprints over ~3° latitude and had the same frequencies as FLRs. This indicates that they are the auroral signature of the FLRs. The azimuthal distribution of the FLRs in the magnetosphere and their north‐south width in the ionosphere were further determined in the 2‐D images. In the first case, the FLRs distribute symmetrically in the prenoon and postnoon regions with out‐of‐phase oscillation as the odd toroidal mode in the equatorial plane. In the second case, the azimuthal wavelengths of the 350–500 s and 300–450 s period waves were ~8.0 and ~5.2 Re in the equatorial plane. It also shows a fine azimuthal structure embedded in the large‐scale arcs, indicating that a high azimuthal wave number (m ~ 140) mode wave coupled with the low‐wave number FLRs.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Temporal and radiometric statistics on lightning flashes observed from space with the ISUAL spectrophotometer. (2015)
    Wiley
    Details
    Publication Date: 2015-07-15
    Description: The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite was launched in 2004 and records Transient Luminous Events (TLEs). ISUAL is an instrument composed of an imager and a multichannel spectrophotometer which is able to measure the brightness from Far-Ultra Violet to Near-Infrared for TLEs and lightning flashes. Several types of TLEs have been identified, classified and documented between 2004 and 2014. However, no statistical analyses on lightning have already been realized. In this paper, we focus on lightning flashes which did not induce TLEs. Statistics about brightness or temporal dynamic are presented from fitted waveforms from Far-Ultra Violet to Near-Infrared, after having corrected for atmospheric effects for each spectrophotometer channels. We demonstrate that the lightning/satellite distance and the altitude of the lightning need to be taken into account. The lightning waveforms from each spectrophotometer channel could be modeled as an exponential pulsed function which the shape could be explained by the photon propagation in the cloud. The median values at 777.4 nm are 1.63×10 -6 W.m -2 for the maximum brightness, 5.85×10 4 J for the total energy at the source, 414 µs for the FWHM, 620 µs for the FWQM and 170 µs for the rise time. Results are compared with previous experiments performed from visible to Near-Infrared domains. The median temporal variables for NIR waveforms are shorter than the values of the UV waveforms.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    Birth and life of auroral arcs embedded in the evening auroral oval convection: A critical comparison of observations with theory (2012)
    Wiley
    Details
    Publication Date: 2012-12-14
    Description: We present and analyze data on auroral arcs obtained during a pass of the FAST satellite over the field-of-view of the all-sky camera at Ft. Simpson (Canada), supported by ground-based magnetometer and SuperDARN radar data, and plasma data from THEMIS-A near the source region of the auroral currents. The auroral event took place at 19:00 MLT during substorm activity further east. Active auroral arcs were present over six degrees in latitude moving equatorward with significant changes in brightness and structure. New arcs were forming continuously at the polar border of the auroral oval which was marked by an Alfvénic arc. The data analysis revealed that the equatorward drift of the arcs was in part due to convective motion of the plasma frame but was rather dominated by proper motions of the arcs. Interpretation of these findings in the framework of theoretical work by one of the authors reproduces quantitatively the observed proper motion as a consequence of the progressive erosion of magnetic shear stresses. Most important was the possibility to deduce the interaction time scale between arc and source region. On average it corresponded to about six to eight transit times of an Alfvén wave between arc and source plasma or two fundamental eigenperiods of toroidal mode or azimuthally polarized Alfvén waves. However, large variations of the interaction times and corresponding proper motions were found. They are attributed to temporal and spatial variations of the energy input from the source plasma. The more remarkable is the fact that analysis on the basis of a quasi-stationary model produces consistent results. The progressive release of shear stresses during the equatorward motion of the arcs leads to the conclusion that they are dying after having reached the maximum of the poleward Pedersen current.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    ULF waves and discrete aurora (2012)
    Wiley
    Details
    Publication Date: 2012-09-27
    Description: We present results from the numerical study of ULF waves generated by the ionospheric feedback instability in density cavities. The goal of the study is to explain several spectral features of ULF waves detected on the ground in close vicinity of intense discrete auroral arcs. These features include (1) localization of the waves packages across the ambient magnetic field, (2) variation of the wave frequency in relatively small amplitude waves, and (3) presence of several discrete harmonics in the spectrum of the relatively large amplitude waves. Time-dependent, two-dimensional simulations based on the two-fluid MHD model performed in the dipole, axisymmetrical geometry of the ambient magnetic field with realistic parameters of the plasma density in the ionosphere and the magnetosphere demonstrate that the ionospheric feedback instability inside the density cavity indeed provides a good, quantitative explanation of these features of ULF waves observed at high latitudes during substorm onsets.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Full-kinetic elve model simulations and their comparisons with the ISUAL observed events (2012)
    Wiley
    Details
    Publication Date: 2012-07-31
    Description: A full kinetic elve model with a wide time range from microseconds to seconds and its spectral range from UV, visible to near-infrared wavelengths is developed. Not only the fast electron-impact emissions N2 1P (B3Πg - A3Σu+), N2 2P(C3Πu - B3Πg), N2 Lyman-Birge-Hopfield (a1Πg - X1Σg+), N2+ 1N (B2Σu+ - X2Σg+) and O2+ 1N (b4Σg− – a4Πu) but also the post-impulse chemiluminescenses, O2 atmospheric band (b1Σg+ – X3Σg−), O(1S – 1D) at 557.7 nm and O(1D – 3P) at 630 nm, are considered in the elve model. We calculate the dominant emissions and possible weak emissions in our elves model to analyze the relative importance of emission intensity, measured by the ISUAL imager with 5 selectable band pass filters (N21P, 762, 630, 557.7, 427.8 nm filter). The modeling emission intensities were well consistent with the measurements by Imager with different filters. This comparison could also be useful in designing the imager filters for future TLE survey missions in Earth orbit.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Tailward leap of multiple expansions of the plasma sheet during a moderately intense substorm: THEMIS observations (2012)
    Wiley
    Details
    Publication Date: 2012-07-26
    Description: A moderately intense substorm on 1 March 2008, from 0830 to 1000 UT, observed by THEMIS probes and the Ground Based Observatory (GBO) is examined to investigate the global evolution of substorm phenomena. During this interval, all five THEMIS probes are closely aligned along the tail axis near midnight covering a radial range from ∼9 Re to ∼18 Re. After the substorm onset, plasma sheet expansions take place successively at multiple locations in the magnetotail as measured by different probes. The positions of the plasma sheet expansions have a tailward leap progression with an average velocity of ∼36 km/s. There are two types of dipolarization detected in this substorm. The first type is the dipolarization front which is associated with the bursty bulk flow (BBF). While the second type, which we call ‘global dipolarization’, is associated with plasma sheet expansions. In the substorm studied, there are four intensifications as shown in the THEMIS AE index. We can detect the effects of localized and short-lived magnetic energy release processes occurring in the magnetotail corresponding to each of the four AE intensifications. Furthermore, the inner four probes can detect the global dipolarization signatures ∼4–15 min earlier than plasma sheet expansions, while the outermost probe (P1) cannot detect this before the plasma sheet expansion. These two phenomena are caused by the same process (magnetic energy release process) but the effects detected by probes locally appear delayed. The observations in this case are not sufficient to distinguish between the two competing substorm models.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...