SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Eglitis P) "

Sökning: WFRF:(Eglitis P)

  • Resultat 1-23 av 23
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Lockwood, M, et al. (författare)
  • Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF : relation to reconnection pulses and FTE signatures
  • 2001
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 19:10-12, s. 1613-1640
  • Forskningsöversikt (refereegranskat)abstract
    • We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ([X(GSM), Y(GSM), Z(GSM)] approximate to [2, 7, 9] R(E)). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is well-defined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events cor-relate well with swings of the IMF clock angle (in GSM) to near 90degrees. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10-15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvenic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R(E) in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.
  •  
2.
  • Syrjäsuo, M., Pulkkinen, T.I., Pellinen, R.P., Janhunen, P., Kauristie, K., Viljanen, A., Opgenoorth, H.J., Karllson, P., Wallman, S., Eglitis, P., Nielsen, E. and Thomas, C. (författare)
  • Observations of substorm electrodynamics using the miracle network.
  • 2001
  • Ingår i: The 4th International Conference on Substorms, ICS4. - : Terra Scient. Publ. Comp. Tokyo, Japan. Kaje Hamana, Japan.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
  •  
3.
  •  
4.
  • Boralv, E, et al. (författare)
  • The dawn and dusk electrojet response to substorm onset
  • 2000
  • Ingår i: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER-VERLAG. - 0992-7689. ; 18:9, s. 1097-1107
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occur
  •  
5.
  • Borälv, E., et al. (författare)
  • The dawn and dusk electrojet response to substorm onset
  • 2000
  • Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 18:9, s. 1097-1107
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetosphere's reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN) and incoherent (EISCAT) radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.
  •  
6.
  •  
7.
  •  
8.
  • Dhiman, Vinit, et al. (författare)
  • Multiband optical variability of the TeV blazar PG 1553+113 in 2019
  • 2022
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 519:2, s. 2796-2811
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the flux and spectral variability of PG 1553 + 113 on intra-night (IDV) to short-term time-scales using BVRI data collected over 91 nights from 28 February to 8 November 2019 employing 10 optical telescopes: three in Bulgaria, two each in India and Serbia, and one each in Greece, Georgia, and Latvia. We monitored the blazar quasi-simultaneously for 16 nights in the V and R bands and 8 nights in the V, R, I bands and examined the light curves (LCs) for intra-day flux and colour variations using two powerful tests: the power-enhanced F-test and the nested ANOVA test. The source was found to be significantly (>99 per cent) variable in 4 nights out of 27 in R-band, 1 out of 16 in V-band, and 1 out of 6 nights in I-band. No temporal variations in the colours were observed on IDV time-scale. During the course of these observations the total variation in R-band was 0.89 mag observed. We also investigated the spectral energy distribution (SED) using B-, V-, R-, and I-band data. We found optical spectral indices in the range of 0.878 +/- 0.029 to 1.106 +/- 0.065 by fitting a power law (F-nu proportional to nu(-alpha)) to these SEDs of PG 1553 + 113. We found that the source follows a bluer-when-brighter trend on IDV time-scales. We discuss possible physical causes of the observed spectral variability.
  •  
9.
  • Eglitis, P, et al. (författare)
  • New techniques for auroral irregularity studies with COSCAT
  • 1998
  • Ingår i: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 16:10, s. 1241-1250
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The COSCAT system enables the detection of E-region auroral backscatter with the EISCAT remote receivers at magnetic aspect angles close to 90 degrees. This is achieved by utilising a low-power transmitter stationed in Oulu, Finland. Many important observ
  •  
10.
  •  
11.
  •  
12.
  • Karlsson, SBP, et al. (författare)
  • Solar wind control of magnetospheric energy content: Substorm quenching and multiple onsets
  • 2000
  • Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 105:A3, s. 5335-5356
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we report coordinated multispacecraft and ground-based observations of a double substorm onset close to Scandinavia on November 17, 1996. The Wind and the Geotail spacecraft, which were located in the solar wind and the subsolar magnetosheat
  •  
13.
  •  
14.
  •  
15.
  • Marklund, Göran T., et al. (författare)
  • Astrid-2 and ground-based observations of the auroral bulge in the middle of the nightside convection throat
  • 2001
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 19:6, s. 633-641
  • Tidskriftsartikel (refereegranskat)abstract
    • Results concerning the electrodynamics of the nightside auroral bulge are presented based on simultanous satellite and ground-based observations. The satellite data include Astrid-2 measurements of electric fields, currents and particles from a midnight auroral oval crossing and Polar UVI images of the large-scale auroral distribution. The ground-based observations include STARE and SuperDARN electric fields and magnetic records from the Greenland and MIRACLE magnetometer network, the latter including stations from northern Scandinavia north to Svalbard. At the time of the Astrid-2 crossing the ground-based data reveal intense electrojet activity, both to the east and west of the Astrid-2 trajectory, related to the Polar observations of the auroral bulge but not necessarily to a typical substorm. The energetic electron fluxes measured by Astrid-2 across the auroral oval were generally weak being consistent with a gap observed in the auroral luminosity distribution. The electric field across the oval was directed westward, intensifying close to the poleward boundary followed by a decrease in the polar cap. The combined observations suggests that Astrid-2 was moving close to the separatrix between the dusk and dawn convection cells in a region of low conductivity. The constant westward direction of the electric field across the oval indicates that current continuity was maintained, not by polarisation electric fields (as in a Cowling channel), but solely by localized up- and downward field-aligned currents in good agreement with the Astrid-2 magnetometer data. The absence of a polarisation electric field and thus of an intense westward closure current between the dawn and dusk convection cells is consistent with the relatively weak precipitation and low conductivity in the convection throat. :Thus, the Cowling current model is not adequate for describing the electrodynamics of the nightside auroral bulge treated here.
  •  
16.
  •  
17.
  •  
18.
  • Nakamura, R, et al. (författare)
  • Substorm observations in the early morning sector with Equator-S and Geotail
  • 1999
  • Ingår i: Annales Geophysicae. - : SPRINGER VERLAG. - 0992-7689 .- 1432-0576. ; 17:12, s. 1602-1610
  • Tidskriftsartikel (refereegranskat)abstract
    • Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03-04 MLT) at a radial distance o
  •  
19.
  •  
20.
  • Uspensky, MV, et al. (författare)
  • CUTLASS HF radar observations of high-velocity E-region echoes
  • 2001
  • Ingår i: ANNALES GEOPHYSICAE. - : EUROPEAN GEOPHYSICAL SOCIETY. - 0992-7689. ; 19:4, s. 411-424 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magn
  •  
21.
  •  
22.
  • Uspensky, M, et al. (författare)
  • On auroral dynamics observed by HF radar: 1. Equatorward edge of the afternoon-evening diffuse luminosity belt
  • 2001
  • Ingår i: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER-VERLAG. - 0992-7689. ; 18:12, s. 1560-1575 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also
  •  
23.
  • Wild, JA, et al. (författare)
  • Multi-instrument observations of the electric and magnetic field structure of omega bands
  • 2000
  • Ingår i: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 18:1, s. 99-110 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • High time resolution data from the CUTLASS Finland radar during the interval 01:30-03:30 UT on 11 May, 1998, are employed to characterise the ionospheric electric field due to a series of omega bands extending similar to 5 degrees in latitude at a resolut
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-23 av 23

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy