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Publications (10 of 18) Show all publications
Pitkänen, T., Hamrin, M., Norqvist, P., Karlsson, T., Nilsson, H., Kullen, A., . . . Milan, S. M. (2015). Azimuthal velocity shear within an Earthward fast flow: further evidence for magnetotail untwisting?. Annales Geophysicae, 33, 245-255
Open this publication in new window or tab >>Azimuthal velocity shear within an Earthward fast flow: further evidence for magnetotail untwisting?
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2015 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, p. 245-255Article in journal (Refereed) Published
Abstract [en]

It is well known that nonzero interplanetary magnetic field By conditions lead to a twisted magnetotail configuration. The plasma sheet is rotated around its axis and tail magnetic field lines are twisted, which causes an azimuthal displacementof their ionospheric footprints. According to the untwisting hypothesis, the untwisting of twisted field lines is suggested to influence the azimuthal direction of convective fast flows in the nightside geospace. However, there is a lack of in situ magnetospheric observations, which show actual signatures of the possible untwisting process. In this paper, we report detailed Cluster observations of an azimuthal flow shear across the neutral sheet associated with an Earthward fast flow on 5 September 2001. The observations show a flow shear velocity pattern with a Vperpy sign change, near the neutral sheet (Bx  0) within a fast flow during the neutral sheet flapping motion over the spacecraft. Firstly, this implies that convective fast flows may not generally be unidirectional across the neutral sheet, but may have a more complex structure. Secondly, in this event tail By and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between Bx and Vperpy close to the neutral sheet and suggests that Cluster crossed the neutral sheet in the dawnward part of the fast flow channel. The magnetospheric observations are supported by the semi-empirical T96 and TF04 models. Furthermore, the ionospheric SuperDARN convection maps support the satellite observations proposing that the azimuthal component of the magnetospheric flows is enforced by a magnetic field untwisting. In summary,the observations give strong supportive evidence to the tail untwisting hypothesis. However, the T96 ionospheric mapping demonstrates the limitations of the model in mapping from a twisted tail.

Keyword
Magnetospheric physics, magnetospheric configuration and dynamics, magnetotail, plasma convection
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-100529 (URN)10.5194/angeo-33-245-2015 (DOI)000352159300001 ()2-s2.0-84923865761 (Scopus ID)
Funder
Swedish National Space Board, 78/11AB
Available from: 2015-03-04 Created: 2015-03-04 Last updated: 2017-12-04Bibliographically approved
Cresswell-Moorcock, K., Rodger, C. J., Kero, A., Collier, A. B., Clilverd, M. A., Häggström, I. & Pitkänen, T. (2013). A reexamination of latitudinal limits of substorm-produced energetic electron precipitation. Journal of Geophysical Research - Space Physics, 118, 6694-6705
Open this publication in new window or tab >>A reexamination of latitudinal limits of substorm-produced energetic electron precipitation
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2013 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, p. 6694-6705Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102630 (URN)10.1002/jgra.50598 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04
Aikio, A. T., Pitkänen, T., Honkonen, I., Palmroth, M. & Amm, O. (2013). IMF effect on the polar cap contraction and expansion during a period of substorms. Annales Geophysicae, 31, 1021-1034
Open this publication in new window or tab >>IMF effect on the polar cap contraction and expansion during a period of substorms
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2013 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1021-1034Article in journal (Refereed) Published
Abstract [en]

The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase.

In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

Keyword
Magnetospheric physics
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-102629 (URN)10.5194/angeo-31-1021-2013 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
Aikio, A. T., Pitkänen, T., Honkonen, I., Palmroth, M. & Amm, O. (2013). IMF effect on the polar cap contraction and expansion during a period of substorms. Annales Geophysicae, 31, 1021-1034
Open this publication in new window or tab >>IMF effect on the polar cap contraction and expansion during a period of substorms
Show others...
2013 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1021-1034Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102898 (URN)
Available from: 2015-05-09 Created: 2015-05-09 Last updated: 2017-12-04
Juusola, L., Kubyshkina, M., Nakamura, R., Pitkänen, T., Amm, O., Kauristie, K., . . . Whiter, D. (2013). Ionospheric signatures of a plasma sheet rebound flow during a substorm onset. Journal of Geophysical Research - Space Physics, 118, 350-363
Open this publication in new window or tab >>Ionospheric signatures of a plasma sheet rebound flow during a substorm onset
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2013 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, p. 350-363Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-102627 (URN)10.1029/2012JA018132 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04
Pitkänen, T., Aikio, A. T. & Juusola, L. (2013). Observations of polar cap flow channel and plasma sheet flow bursts during substorm expansion. Journal of Geophysical Research - Space Physics, 118, 774-784
Open this publication in new window or tab >>Observations of polar cap flow channel and plasma sheet flow bursts during substorm expansion
2013 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, p. 774-784Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102628 (URN)10.1002/jgra.50119 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04
Pitkänen, T., Aikio, A. T., Amm, O., Kauristie, K., Nilsson, H. & Kaila, K. U. (2011). EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere. Annales Geophysicae, 29, 299-319
Open this publication in new window or tab >>EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere
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2011 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 29, p. 299-319Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102623 (URN)10.5194/angeo-29-299-2011 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04
Hubert, B., Aikio, A. T., Amm, O., Pitkänen, T., Kauristie, K., Milan, S. M., . . . Gérard, J.-C. (2010). Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations. Annales Geophysicae, 28, 883-892
Open this publication in new window or tab >>Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations
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2010 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, p. 883-892Article in journal (Refereed) Published
Abstract [en]

We compare the location of the polar cap boundary (PCB) determined using two different techniques, and use them as proxies for the open-closed field line boundary (OCB). Electron temperatures from observations of the EISCAT radar facility are used to estimate the latitude of the PCB along the meridian of the EISCAT VHF beam. The second method utilizes global images of proton aurora obtained by the IMAGE satellite FUV SI12 instrument. These methods are applied to three different intervals. In two events, the agreement between the methods is good and the mean of the difference is within the resolution of the observations. In a third event, the PCB estimated from EISCAT data is located several degrees poleward of that obtained from the IMAGE FUV SI12 instrument. Comparison of the reconnection electric field estimated from the two methods shows that highresolution measurements both in time and space are needed to capture the variations in reconnection electric field during substorm expansion. In addition to the two techniques introduced above to determine the PCB location, we also use a search for the location of the reversal of the east-west component of the equivalent current known as the magnetic convection reversal boundary (MCRB). The MCRB from the MIRACLE magnetometer chain mainly follows the motion of the polar cap boundary during different substorm phases, but differences arise near the Harang discontinuity.

Place, publisher, year, edition, pages
Copernicus Publications, 2010
Keyword
Magnetospheric physics (Magnetopause, cusp, and boundary layers, Storms and substorms, Instruments and techniques)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-102622 (URN)10.5194/angeo-28-883-2010 (DOI)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
Hubert, B., Aikio, A. T., Amm, O., Pitkänen, T., Kauristie, K., Milan, S. M., . . . Gérard, J.-C. (2010). Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations. Annales Geophysicae, 28, 883-892
Open this publication in new window or tab >>Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations
Show others...
2010 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, p. 883-892Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102896 (URN)
Available from: 2015-05-09 Created: 2015-05-09 Last updated: 2017-12-04
Pitkänen, T., Aikio, A. T., Amm, O., Kauristie, K., Nilsson, H. & Kaila, K. U. (2010). Conjugate EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere. In: URSI Finnish XXXII Convention on Radio Science and Electromagnetism 2010 meeting, Oulu, Finland, 26 August 2010: . Paper presented at URSI Finnish XXXII Convention on Radio Science and Electromagnetism 2010 meeting, Oulu, Finland, 26 August 2010.
Open this publication in new window or tab >>Conjugate EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere
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2010 (English)In: URSI Finnish XXXII Convention on Radio Science and Electromagnetism 2010 meeting, Oulu, Finland, 26 August 2010, 2010Conference paper, Published paper (Other academic)
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
urn:nbn:se:umu:diva-102626 (URN)
Conference
URSI Finnish XXXII Convention on Radio Science and Electromagnetism 2010 meeting, Oulu, Finland, 26 August 2010
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2015-05-09
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5681-0366

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