| 1. |
- Aikio, A. T., et al.
(författare)
-
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary
- 2008
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 26:1, s. 87-105
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromso (66.6 degrees cgmLat) and Longyearbyen (75.2 degrees cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5 degrees cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R-E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2 degrees during similar to 5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.
|
|
| 2. |
|
|
| 3. |
- Hølland, Vidar, et al.
(författare)
-
Nordic ionospheric sounding rocket seeding experiment (NISSE)
- 2009
-
Ingår i: Proc. 19th ESA Symposium on European Rocket and Balloon Programmes and Related Research, Bad Reichenhall, Germany, 7-11 June 2009. ; , s. 467-472
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 4. |
- Hølland, Vidar, et al.
(författare)
-
Nordic ionospheric sounding rocket seeding experiment (NISSE)
- 2009
-
Ingår i: Proc. 19th ESA Symposium on European Rocket and Balloon Programmes and Related Research, Bad Reichenhall, Germany, 7-11 June 2009. ; , s. 467-472
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Nordic Ionospheric Sounding rocket Seeding Experiment (NISSE) is a student research project in the REXUS student rocket experiment program. The NISSE experiment flew onboard a sounding rocket, the REXUS 6, which was launched at the Esrange rocket range on March 12, 2009. In the NISSE experiment about 8.3 kg of water was to be released into the ionosphere at the REXUS 6 apogee altitude of about 95 km. The EISCAT UHF incoherent scatter radar system located in Northern Fennoscandia, was in action for detection and observation of the effects of the released water on the upper atmosphere. Although NISSE was only partially successful, we are motivated to present here the conceptual description of the experiment and discuss the experience gained from an educational point of view.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Pitkänen, Timo, et al.
(författare)
-
Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm
- 2009
-
Ingår i: Annales Geophysicae. - : Copernicus Publications. - 0992-7689 .- 1432-0576. ; 27, s. 2157-2171
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager.The location of the polar cap boundary (PCB) is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE) boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7 of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB) is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1 equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines.East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD) region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet.The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs) in the same MLT sector. The results suggest that PBIs (typically 1.5 h MLT wide) are a consequence of temporarily enhanced longitudinally localized magnetic flux closure in the magnetotail.
|
|
