Blar i forfatter "Ogawa, Yasunobu"

Viser treff 1-12 av 12

    • Aspect angle sensitivity of pump-induced optical emissions at EISCAT 

      Kosch, Michael J.; Bryers, Carl; Rietveld, Michael T; Yeoman, Timothy K; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-12-04)
      We investigate the aspect angle sensitivity of the pump-induced artificial optical emissions in the ionosphere over the European Incoherent Scatter Scientific Association (EISCAT) high-frequency transmitter facility at Ramfjord, Norway, as a function of the pump beam launch angle relative to the magnetic field line direction. The highest intensity optical emissions occur when the pump beam pointing ...

    • Auroral molecular-emission effects on the atomic oxygen line at 777.4 nm 

      Oyama, Shin-Ichiro; Tsuda, Takuo T.; Hosokawa, Keisuke; Ogawa, Yasunobu; Miyoshi, Yoshizumi; Kurita, Satoshi; Kero, Antti; Fujii, Ryochi; Tanaka, Yoshimasa; Mizuno, Akira; Kawabata, Tetsuya; Gustavsson, Björn Johan; Leyser, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-16)
      One of the representative auroral emission lines that radiates from F-region heights and is measurable on the ground is the 777.4 nm line from excited atomic oxygen. This line has been adopted, along with another E-region emission line, for example 427.8 nm, to estimate the mean energy and total energy flux of precipitating auroral electrons. The influence of emissions from part of the molecular ...

    • A case study on generation mechanisms of a sporadic sodium layer above Tromsø (69.6° N) during a night of high auroral activity 

      Takahashi, Toru; Nozawa, Satonaori; Tsuda, Takuo T.; Ogawa, Yasunobu; Saito, Norihito; Hidemori, Takehiro; Kawahara, Takuya D.; Hall, Chris; Fujiwara, Hitoshi; Matuura, Nobuo; Brekke, Asgeir; Tsutsumi, Masaki; Wada, Satoshi; Kawabata, Tetsuya; Oyama, Shinichiro; Fujii, Ryoichi (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-05)
      We have quantitatively evaluated generation mechanisms of a sporadic sodium layer (SSL) based on observational data obtained by multiple instruments at a high-latitude station: Ramfjordmoen, Tromsø, Norway (69.6° N, 19.2° E). The sodium lidar observed an SSL at 21:18 UT on 22 January 2012. The SSL was observed for 18 min, with a maximum sodium density of about 1.9 × 1010 m−3 at 93 km with a 1.1 km ...

    • Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm 

      Tanaka, Yoshimasa; Ogawa, Yasunobu; Kadokura, Akira; Partamies, Noora; Whiter, Daniel; Enell, Carl-Fredrik; Brändström, Urban; Sergienko, Tima; Gustavsson, Björn Johan; Kozlovsky, Alexander; Miyaoka, Hiroshi; Yoshikawa, Akimasa (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-09)
      We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were ...

    • Electron Energy Spectrum and Auroral Power Estimation From Incoherent Scatter Radar Measurements 

      Virtanen, Ilkka I.; Gustavsson, Björn Johan; Aikio, Anita; Kero, Antti; Asamura, Kazushi; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-23)
      Differential energy flux of electrons precipitating into the high‐latitude ionosphere can be estimated from incoherent scatter radar observations of the ionospheric electron density profile. We present a method called ELSPEC for electron spectrum estimation from incoherent scatter radar measurements, which is based on integration of the electron continuity equation and spectrum model selection by ...

    • First observation of the anomalous electric field in the topside ionosphere by ionospheric modification over EISCAT 

      Kosch, Michael; Vickers, Hannah; Ogawa, Yasunobu; Senior, Andrew; Blagoveshchenskaya, Natalya (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-10-24)
      We have developed an active ground-based technique to estimate the steady state field-aligned anomalous electric field (E*) in the topside ionosphere, up to ~600 km, using the European Incoherent Scatter (EISCAT) ionospheric modification facility and UHF incoherent scatter radar. When pumping the ionosphere with high-power high-frequency radio waves, the F region electron temperature is significantly ...

    • Ion-dispersion and rapid electron fluctuations in the cusp : a case study 

      Buchert, Stephan C; Lunde, June; Ogawa, Yasunobu; Hirahara, Masafumi; Seki, Kanako; Ebihara, Yuusuke; Sakanoi, Takeshi; Asamura, Kazushi; Okada, Masaki; Raita, Tero; Häggström, Ingemar (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

    • A new five-wavelength photometer operated in Tromsø (69.6°N, 19.2°E) 

      Nozawa, Satonori; Kawabata, Tetsuya; Hosokawa, Keisuke; Ogawa, Yasunobu; Tsuda, Takuo; Mizuno, Akira; Fujii, Ryoichi; Hall, Chris (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-11)
      A new fve-wavelength photometer was developed and installed at the EISCAT Tromsø site (69.6°N, 19.2°E) in January 2017. The photometer consists of two units: an optical unit and a control unit together with a PC. The photometer is capable of simultaneously observing auroral emissions with fve wavelengths. A uniqueness of the present system is its capability of precise pointing, which enables ...

    • Particle precipitations during NEIAL events : simultaneous ground based observations at Svalbard 

      Lorentzen, Dag Arne; Lunde, June; Gustavsson, B; Ogawa, Y; Løvhaug, U.P.; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)
      In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs) observed with the EISCAT Svalbard Radar (ESR). For the first time, long sequences of NEIALs are recorded, with more than 50 events within an hour, ranging from 6.4 to 140 s in duration. The events took place from ~08:45 to 10:00 UT, 22 January 2004. We combine ESR data with observations of optical aurora by a meridian scanning ...

    • The polarisation of auroral emissions: A tracer of the E region ionospheric currents 

      Bosse, Léo; Lilensten, Jean; Johnsen, Magnar Gullikstad; Gillet, Nicolas; Rochat, Sylvain; Delboulbé, Alain; Curaba, Stephane; Ogawa, Yasunobu; Derverchère, Philippe; Vauclair, Sébastien (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-20)
      It is now established that auroral emissions as measured from the ground are polarised. The question of the information given by this polarisation is still to be explored. This article shows the results of a coordinated campaign between an optical polarimeter and several ground-based instruments, including magnetometers, the EISCAT VHF radar, and complementary luminance meters in the visible ...

    • Reconstruction of precipitating electrons and three-dimensional structure of a pulsating auroral patch from monochromatic auroral images obtained from multiple observation points 

      Fukizawa, Mizuki; Sakanoi, Takeshi; Tanaka, Yoshimasa; Ogawa, Yasunobu; Hosokawa, Keisuke; Gustavsson, Björn Johan; Kauristie, Kirsti; Kozlovsky, Alexander; Raita, Tero; Brändström, Urban; Sergienko, Tima (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-12)
      In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochromatic PsA images obtained from three observation ...

    • The science case for the EISCAT_3D radar 

      McCrea, Ian W.; Aikio, Anita; Alfonsi, Lucilla; Belova, Evgenia; Buchert, Stephan C.; Clilverd, Mark; Engler, Norbert; Gustavsson, Björn Johan; Heinselman, C.; Kero, Johan; Kosch, Mike; Lamy, Herve; Leyser, Thomas; Ogawa, Yasunobu; Oksavik, Kjellmar; Pellinen-Wannberg, Asta; Pitout, Frederic; Rapp, Markus; Stanislawska, Iwona; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-29)
      The EISCAT (European Incoherent SCATer) Scientific Association has provided versatile incoherent scatter (IS) radar facilities on the mainland of northern Scandinavia (the EISCAT UHF and VHF radar systems) and on Svalbard (the electronically scanning radar ESR (EISCAT Svalbard Radar) for studies of the high-latitude ionised upper atmosphere (the ionosphere). The mainland radars were constructed ...