Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 21) Show all publications
Pitkanen, T., Kullen, A., Shi, Q. Q., Hamrin, M., De Spiegeleer, A. & Nishimura, Y. (2018). Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 2009. Journal of Geophysical Research - Space Physics, 123(9), 7486-7497
Open this publication in new window or tab >>Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 2009
Show others...
2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7486-7497Article in journal (Refereed) Published
Abstract [en]

We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-238923 (URN)10.1029/2018JA025688 (DOI)000448376600025 ()2-s2.0-85053662605 (Scopus ID)
Note

QC 20181122

Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2018-11-22Bibliographically approved
Karlsson, T., Kullen, A. & Marklund, G. (2017). Dawn-dusk asymmetries in auroral morphology and processes. In: Dawn-Dusk Asymmetries in Planetary Plasma Environments: (pp. 295-305). Wiley Blackwell
Open this publication in new window or tab >>Dawn-dusk asymmetries in auroral morphology and processes
2017 (English)In: Dawn-Dusk Asymmetries in Planetary Plasma Environments, Wiley Blackwell , 2017, p. 295-305Chapter in book (Other academic)
Abstract [en]

We address the dawn-dusk asymmetries in auroral emissions in the main auroral oval, and discuss their origins in terms of the underlying asymmetries of the precipitating particles. These, in turn, are associated with asymmetries in the mechanisms responsible for the transport and acceleration of the precipitating particles. We briefly discuss the reasons for the asymmetries of these processes, which include dawn-dusk asymmetries in particle drifts and in the ionospheric conductivity, the direction of the interplanetary magnetic field, and substorm-related asymmetries in field-aligned currents and flows. Finally, we briefly discuss dawn-dusk asymmetries associated with auroral emissions in the polar cap. 

Place, publisher, year, edition, pages
Wiley Blackwell, 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-236784 (URN)10.1002/9781119216346.ch23 (DOI)2-s2.0-85050325613 (Scopus ID)9781119216346 (ISBN)9781119216322 (ISBN)
Note

QC 20190109

Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-01-09Bibliographically approved
Karlsson, T., Eriksson, A. I., Odelstad, E., Andre, M., Dickeli, G., Kullen, A., . . . Richter, I. (2017). Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P. Geophysical Research Letters, 44(4), 1641-1651
Open this publication in new window or tab >>Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P
Show others...
2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 4, p. 1641-1651Article in journal (Refereed) Published
Abstract [en]

Electric field measurements from cometary environments are very rare but can provide important information on how plasma waves help fashion the plasma environment. The long dwelling time of the Rosetta spacecraft close to comet 67P/Churyumov-Gerasimenko promises to improve this state. We here present the first electric field measurements from 67P, performed by the Rosetta dual Langmuir probe instrument LAP. Measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of plasma density changes. Persistent wave activity around the local H2O+ lower hybrid frequency is observed, with the largest amplitudes observed at sharp plasma gradients. We demonstrate that the necessary requirements for the lower hybrid drift instability to be operating are fulfilled. We suggest that lower hybrid waves are responsible for the creation of a warm electron population, the origins of which have been unknown so far, by heating ambient electrons in the magnetic field-parallel direction.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-204075 (URN)10.1002/2016GL072419 (DOI)000396411100004 ()2-s2.0-85013420127 (Scopus ID)
Note

QC 20170329

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-11-29Bibliographically approved
Pitkanen, T., Hamrin, M., Norqvist, P., Karlsson, T., Nilsson, H., Kullen, A., . . . Milan, S. E. (2015). Azimuthal velocity shear within an Earthward fast flow - further evidence for magnetotail untwisting?. Annales Geophysicae, 33(3), 245-255
Open this publication in new window or tab >>Azimuthal velocity shear within an Earthward fast flow - further evidence for magnetotail untwisting?
Show others...
2015 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, no 3, p. 245-255Article in journal (Refereed) Published
Abstract [en]

It is well known that nonzero interplanetary magnetic field B-y 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 displacement of 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 V-perpendicular to y sign change, near the neutral sheet (B-x similar to 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 B-y and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between B-x and V-perpendicular to y 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.

Keywords
Magnetospheric physics, magnetospheric configuration and dynamics, magnetotail, plasma convection
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-166514 (URN)10.5194/angeo-33-245-2015 (DOI)000352159300001 ()2-s2.0-84923865761 (Scopus ID)
Funder
Swedish National Space Board
Note

QC 20150512

Available from: 2015-05-12 Created: 2015-05-11 Last updated: 2017-12-04Bibliographically approved
Carter, J. A., Milan, S. E., Fear, R. C., Kullen, A. & Hairston, M. R. (2015). Dayside reconnection under interplanetary magnetic field B-y-dominated conditions: The formation and movement of bending arcs. Journal of Geophysical Research - Space Physics, 120(4), 2967-2978
Open this publication in new window or tab >>Dayside reconnection under interplanetary magnetic field B-y-dominated conditions: The formation and movement of bending arcs
Show others...
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 2967-2978Article in journal (Refereed) Published
Abstract [en]

Based upon a survey of global auroral images collected by the Polar Ultraviolet Imager, Kullen etal. (2002) subdivided polar cap auroral arcs into a number of categories, including that of bending arcs. We are concerned with those bending arcs that appear as a bifurcation of the dayside auroral oval and which subsequently form a spur intruding into the polar cap. Once formed, the spur moves poleward and antisunward over the lifetime of the arc. We propose that dayside bending arcs are ionospheric signatures of pulses of dayside reconnection and are therefore part of a group of transient phenomena associated with flux transfer events. We observe the formation and subsequent motion of a bending arc across the polar cap during a 30 min interval on 8 January 1999, and we show that this example is consistent with the proposed model. We quantify the motion of the arc and find it to be commensurate with the convection flows observed by both ground-based radar observations and space-based particle flow measurements. In addition, precipitating particles coincident with the arc appear to occur along open field lines, lending further support to the model.

Keywords
bending arcs, transpolar arcs, ionosphere
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-172265 (URN)10.1002/2014JA020809 (DOI)000354894800043 ()2-s2.0-84961315816 (Scopus ID)
Note

QC 20150819

Available from: 2015-08-19 Created: 2015-08-14 Last updated: 2017-12-04Bibliographically approved
Karlsson, T., Hamrin, M., Nilsson, H., Kullen, A. & Pitkänen, T. (2015). Magnetic forces associated with bursty bulk flows in Earth's magnetotail. Geophysical Research Letters, 42(9), 3122-3128
Open this publication in new window or tab >>Magnetic forces associated with bursty bulk flows in Earth's magnetotail
Show others...
2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 9, p. 3122-3128Article in journal (Refereed) Published
Abstract [en]

We present the first direct measurements of magnetic forces acting on bursty bulk flow plasma in the magnetotail. The magnetic forces are determined using Cluster multispacecraft measurements. We analyze 67 bursty bulk flow (BBF) events and show that the curvature part of the magnetic force is consistently positive, acting to accelerate the plasma toward Earth between approximately 10 and 20 RE geocentrical distances, while the magnetic field pressure gradient increasingly brakes the plasma as it moves toward Earth. The net result is that the magnetic force accelerates the plasma at distances greater than approximately 14 RE, while it acts to decelerate it within that distance. The magnetic force, together with the thermal pressure gradient force, will determine the dynamics of the BBFs as they propagate toward the near-Earth tail region. The determination of the former provides an important clue to the ultimate fate of BBFs in the inner magnetosphere. Key Points Direct measurements of magnetic force acting on BBF plasma BBF plasma is accelerated toward Earth until it reaches 15 RE, then braked Knowledge of the forces on BBFs provides clue to their fate close to Earth.

Keywords
bursty bulk flows, Cluster, curlometer, multipoint measurements
National Category
Geophysics
Identifiers
urn:nbn:se:kth:diva-170293 (URN)10.1002/2015GL063999 (DOI)000355878300008 ()2-s2.0-84930477445 (Scopus ID)
Funder
Swedish National Space Board, 78/11A-B
Note

QC 20150630

Available from: 2015-06-30 Created: 2015-06-29 Last updated: 2017-12-04Bibliographically approved
Liljeblad, E., Karlsson, T., Raines, J., Slavin, J., Kullen, A., Sundberg, T. & Zurbuchen, T. H. (2015). MESSENGER observations of the dayside low-latitude boundary layer in Mercury's magnetosphere. Journal of Geophysical Research - Space Physics, 120(10)
Open this publication in new window or tab >>MESSENGER observations of the dayside low-latitude boundary layer in Mercury's magnetosphere
Show others...
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 10Article in journal (Refereed) Published
Abstract [en]

Observations from MESSENGER's MAG and FIPS instruments during the first orbital year have resulted in the identification of 25 magnetopause crossings in Mercury's magnetosphere with significant low-latitude boundary layers (LLBLs). Of these crossings 72% are observed dawnside, and 65% for northward interplanetary magnetic field.

The estimated LLBL thickness is 450 ± 56 km, and increases with distance to noon. The Na+-group ion is sporadically present in 14 of the boundary layers, with an observed average number density of 22 ± 11% of the proton density. Furthermore, the average Na+-group gyroradii in the layers is 220 ± 34 km, the same order of magnitude as the LLBL thickness.

Magnetic shear, plasma β and reconnection rates have been estimated for the LLBL crossings, and compared to those of a control group (non-LLBL) of 61 distinct magnetopause crossings which show signs of nearly no plasma inside the magnetopause. The results indicate that reconnection is significantly slower, or even suppressed, for the LLBL crossings compared to the non-LLBL cases.

Possible processes that form or impact the LLBL are discussed. Protons injected through the cusp or flank may be important for the formation of the LLBL. Furthermore, the opposite asymmetry in the Kelvin-Helmholtz instability (KHI) as compared to the LLBL, rules out the KHI as a dominant formation mechanism. However, the KHI and LLBL could be related to each other, either by the impact of sodium ions gyrating across the magnetopause, or by the LLBL preventing the growth of KH waves on the dawnside.

Place, publisher, year, edition, pages
Blackwell Publishing, 2015
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-174177 (URN)10.1002/2015JA021662 (DOI)000366135200016 ()2-s2.0-84954385256 (Scopus ID)
Funder
Swedish National Space Board, 566176
Note

QC 20150107

Available from: 2015-10-01 Created: 2015-10-01 Last updated: 2017-12-01Bibliographically approved
Karlsson, T., Kullen, A., Liljeblad, E., Brenning, N., Nilsson, H., Gunell, H. & Hamrin, M. (2015). On the origin of magnetosheath plasmoids and their relation to magnetosheath jets. Journal of Geophysical Research - Space Physics, 120(9), 7390-7403
Open this publication in new window or tab >>On the origin of magnetosheath plasmoids and their relation to magnetosheath jets
Show others...
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 9, p. 7390-7403Article in journal (Refereed) Published
Abstract [en]

We investigate localized magnetosheath and solar wind density enhancements, associated with clear magnetic field changes, and therefore referred to as magnetosheath/solar wind plasmoids, respectively. Using Cluster data, we show that there are two distinct populations of magnetosheath plasmoids, one associated with a decrease of magnetic field strength (diamagnetic plasmoids), and one with an increased magnetic field strength (paramagnetic plasmoids). The diamagnetic magnetosheath plasmoids have scale sizes of the order of 1-10 R-E, while the paramagnetic ones are an order of magnitude smaller. The diamagnetic plasmoids are not associated with any change in the magnetosheath plasma flow velocity, and they are classified as embedded plasmoids in the terminology of Karlsson et al. (2012). The paramagnetic plasmoids may either be embedded or associated with increases in flow velocity (fast plasmoids). A search for plasmoids in the pristine solar wind resulted in identification of 62 diamagnetic plasmoids with very similar properties to the magnetosheath diamagnetic plasmoids, making it probable that the solar wind is the source of these structures. No paramagnetic plasmoids are found in the pristine solar wind, indicating that these are instead created at the bow shock or in the magnetosheath. We discuss the relation of the plasmoids to the phenomenon of magnetosheath jets, with which they have many properties in common, and suggest that the paramagnetic plasmoids can be regarded as a subset of these or a closely related phenomenon. We also discuss how the results from this study relate to theories addressing the formation of magnetosheath jets.

Place, publisher, year, edition, pages
Blackwell Publishing, 2015
Keywords
magnetosheath, solar wind, plasmoids, magnetosheath jets
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-177968 (URN)10.1002/2015JA021487 (DOI)000363876800022 ()2-s2.0-84945472590 (Scopus ID)
Note

QC 20151203

Available from: 2015-12-03 Created: 2015-11-30 Last updated: 2017-12-01Bibliographically approved
Kullen, A., Fear, R. C., Milan, S. E., Carter, J. A. & Karlsson, T. (2015). The statistical difference between bending arcs and regular polar arcs. Journal of Geophysical Research - Space Physics, 120(12), 10443-10465
Open this publication in new window or tab >>The statistical difference between bending arcs and regular polar arcs
Show others...
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 12, p. 10443-10465Article in journal (Refereed) Published
Abstract [en]

In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) B-y direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook-shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during B-y-dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90 degrees about 20min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF B-y and initial arc location. In our data set, the highest correlations are found with IMF B-y appearing at least 1-2 h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2015
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-183227 (URN)10.1002/2015JA021298 (DOI)000369180200022 ()2-s2.0-84957848598 (Scopus ID)
Funder
Swedish National Space Board
Note

QC 20160303

Available from: 2016-03-03 Created: 2016-03-03 Last updated: 2017-11-30Bibliographically approved
Mailyan, B., Shi, Q. Q., Kullen, A., Maggiolo, R., Zhang, Y., Fear, R. C., . . . Pu, Z. Y. (2015). Transpolar arc observation after solar wind entry into the high-latitude magnetosphere. Journal of Geophysical Research - Space Physics, 120(5), 3525-3534
Open this publication in new window or tab >>Transpolar arc observation after solar wind entry into the high-latitude magnetosphere
Show others...
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 5, p. 3525-3534Article in journal (Refereed) Published
Abstract [en]

Recently, Cluster observations have revealed the presence of new regions of solar wind plasma entry at the high-latitude magnetospheric lobes tailward of the cusp region, mostly during periods of northward interplanetary magnetic field. In this study, observations from the Global Ultraviolet Imager (GUVI) experiment on board the TIMED spacecraft and Wideband Imaging Camera imager on board the IMAGE satellite are used to investigate a possible link between solar wind entry and the formation of transpolar arcs in the polar cap. We focus on a case when transpolar arc formation was observed twice right after the two solar wind entry events were detected by the Cluster spacecraft. In addition, GUVI and IMAGE observations show a simultaneous occurrence of auroral activity at low and high latitudes after the second entry event, possibly indicating a two-part structure of the continuous band of the transpolar arc.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-171911 (URN)10.1002/2014JA020912 (DOI)000357869600019 ()2-s2.0-84934908198 (Scopus ID)
Note

QC 20150811

Available from: 2015-08-11 Created: 2015-08-10 Last updated: 2017-12-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0349-0645

Search in DiVA

Show all publications