umu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Norqvist, Patrik
##### Publications (10 of 21) Show all publications
De Spiegeleer, A., Hamrin, M., Pitkänen, T., Volwerk, M., Mann, I., Nilsson, H., . . . Vaverka, J. (2017). Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail. Journal of Geophysical Research - Space Physics, 122(7), 7042-7056
Open this publication in new window or tab >>Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail
2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, p. 7042-7056Article in journal (Refereed) Published
##### Abstract [en]

Using plasma sheet data from Cluster 1 spacecraft from 2001 till 2011, we statistically investigate oscillatory signatures in the plasma bulk flow. These periodic oscillations are compared to high-speed and quiet flows. Periodic oscillations are observed approximately 8% of the time, while high-speed flows and quiet flows are observed around 0.5% and 12% of the time, respectively. We remark that periodic oscillations can roughly occur everywhere for x(gsm) < -10 R-E and |y(gsm)| < 10 RE, while quiet flows mainly occur toward the flanks of this region and toward x = -10 R-E. The relation between the geomagnetic and solar activity and the occurrence of periodic oscillations is investigated and reveal that periodic oscillations occur for most Kp values and solar activity, while quiet flows are more common during low magnetospheric and solar activity. We find that the median oscillation frequency of periodic oscillations is 1.7 mHz and the median duration of the oscillation events is 41 min. We also observe that their associated Poynting vectors show a tendency to be earthward (S-x >= 0). Finally, the distribution of high-speed flows and periodic oscillations as a function of the velocity is investigated and reveals that thresholds lower than 200 km/s should not be used to identify high-speed flows as it could result in misinterpreting a periodic oscillations for a high-speed flow.

##### Place, publisher, year, edition, pages
Washington: American Geophysical Union (AGU), 2017
##### Keywords
bursty bulk flows, plasma sheet, cluster observations, magnetic field, neutral sheet, magnetosphere, dependence, midtail
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
urn:nbn:se:umu:diva-139015 (URN)10.1002/2017JA024076 (DOI)000407627100008 ()
##### Funder
Swedish National Space Board, 271/14 Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2019-09-09Bibliographically approved
Pitkänen, T., Hamrin, M., Kullen, A., Maggiolo, R., Karlsson, T., Nilsson, H. & Norqvist, P. (2016). Response of magnetotail twisting to variations in IMF B-y: a THEMIS case study 1-2 January 2009. Geophysical Research Letters, 43(15), 7822-7830
Open this publication in new window or tab >>Response of magnetotail twisting to variations in IMF B-y: a THEMIS case study 1-2 January 2009
2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 15, p. 7822-7830Article in journal (Refereed) Published
##### Abstract [en]

Theoretical considerations, observations, and simulations have shown that the B-y component of the interplanetary magnetic field (IMF) may cause twisting of the magnetotail. However, the fundamental issues, the temporal and spatial responses of the magnetotail in the twisting process, are still unresolved. We report unique multipoint observations of the response of the magnetotail to the variations in IMF B-y on 1-2 January 2009. For the first time, estimates of the tail twisting response time at different (Time History of Events and Macroscale Interactions during Substorms, THEMIS) distances in the same event are inferred. Using cross-correlation and timing analyses, we find that the tail twisting propagates from farther out toward the Earth and the response time increases significantly to the inner magnetosphere.

##### Place, publisher, year, edition, pages
Wiley-Blackwell, 2016
##### Keywords
solar wind-magnetosphere interaction, magnetotail twisting, tail twisting temporal response, tail twisting spatial response
##### National Category
Probability Theory and Statistics Fusion, Plasma and Space Physics
##### Identifiers
urn:nbn:se:umu:diva-126750 (URN)10.1002/2016GL070068 (DOI)000383290300005 ()
Available from: 2016-10-19 Created: 2016-10-13 Last updated: 2018-06-09Bibliographically approved
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?
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 $\sim$ 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.

##### Keywords
Magnetospheric physics, magnetospheric configuration and dynamics, magnetotail, plasma convection
##### National Category
Fusion, Plasma and Space Physics
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: 2019-09-09Bibliographically approved
Hamrin, M., Pitkänen, T., Norqvist, P., Karlsson, T., Nilsson, H., Andre, M., . . . Dandouras, I. (2014). Evidence for the braking of flow bursts as they propagate toward the Earth. Journal of Geophysical Research - Space Physics, 119(11), 9004-9018
Open this publication in new window or tab >>Evidence for the braking of flow bursts as they propagate toward the Earth
2014 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 11, p. 9004-9018Article in journal (Refereed) Published
##### Abstract [en]

In this article we use energy conversion arguments to investigate the possible braking of flow bursts as they propagate toward the Earth. By using EJ data (E and J are the electric field and the current density) observed by Cluster in the magnetotail plasma sheet, we find indications of a plasma deceleration in the region -20 R-E < X < - 15 R-E. Our results suggest a braking mechanism where compressed magnetic flux tubes in so-called dipolarization fronts (DFs) can decelerate incoming flow bursts. Our results also show that energy conversion arguments can be used for studying flow braking and that the position of the flow velocity peak with respect to the DF can be used as a single-spacecraft proxy when determining energy conversion properties. Such a single-spacecraft proxy is invaluable whenever multispacecraft data are not available. In a superposed epoch study, we find that a flow burst with the velocity peak behind the DF is likely to decelerate and transfer energy from the particles to the fields. For flow bursts with the peak flow at or ahead of the DF we see no indications of braking, but instead we find an energy transfer from the fields to the particles. From our results we obtain an estimate of the magnitude of the deceleration of the flow bursts, and we find that it is consistent with previous investigations.

##### Keywords
bursty bulk flow, braking, energy conversion, dipolarization front, plasma sheet, flux pileup region
##### National Category
Fusion, Plasma and Space Physics
##### Identifiers
urn:nbn:se:umu:diva-99391 (URN)10.1002/2014JA020285 (DOI)000346792100021 ()
Available from: 2015-02-24 Created: 2015-02-07 Last updated: 2018-06-07Bibliographically approved
Pitkänen, T., Hamrin, M., Norqvist, P., Karlsson, T. & Nilsson, H. (2013). IMF dependence of the azimuthal direction of earthward magnetotail fast flows. Geophysical Research Letters, 40(21), 5598-5604
Open this publication in new window or tab >>IMF dependence of the azimuthal direction of earthward magnetotail fast flows
2013 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 21, p. 5598-5604Article in journal (Refereed) Published
##### Abstract [en]

Cluster magnetotail data together with ACE solar wind data from 2001 to 2009 are used to investigate the dependence of the azimuthal flow direction of earthward magnetotail fast flows on the interplanetary magnetic field (IMF). We find an indication that fast flows have favored azimuthal directions that have dependence on the IMF. Our results suggest that for positive IMF By, the favored azimuthal direction of the fast flows is dawnward in the northern plasma sheet and duskward in the southern plasma sheet. For negative IMF By, an opposite situation takes place, the favored azimuthal flow directions are then duskward and dawnward in the northern and southern plasma sheet, respectively. As a possible explanation for the results, it is suggested that the untwisting reconnected magnetic field lines may direct the fast flows in the magnetotail, the field line twist itself being dependent on the IMF.

##### Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2013
##### Keywords
fast flows, plasma sheet, magnetotail dynamics
##### National Category
Fusion, Plasma and Space Physics
Space Physics
##### Identifiers
urn:nbn:se:umu:diva-84715 (URN)10.1002/2013GL058136 (DOI)000327810800007 ()
Available from: 2014-01-17 Created: 2014-01-17 Last updated: 2018-06-08Bibliographically approved
Hamrin, M., Norqvist, P., Karlsson, T., Nilsson, H., Fu, H. S., Buchert, S., . . . Dandouras, I. (2013). The evolution of flux pileup regions in the plasma sheet: Cluster observations. Journal of Geophysical Research - Space Physics, 118(10), 6279-6290
Open this publication in new window or tab >>The evolution of flux pileup regions in the plasma sheet: Cluster observations
2013 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, no 10, p. 6279-6290Article in journal (Refereed) Published
##### Abstract [en]

Bursty bulk flows (BBFs) play an important role for the mass, energy, and magnetic flux transport in the plasma sheet, and the flow pattern in and around a BBF has important consequences for the localized energy conversion between the electromagnetic and plasma mechanical energy forms. The plasma flow signature in and around BBFs is often rather complicated. Return flows and plasma vortices are expected to exist at the flanks of the main flow channel, especially near the inner plasma sheet boundary, but also farther down-tail. A dipolarization front (DF) is often observed at the leading edge of a BBF, and a flux pileup region (FPR) behind the DF. Here we present Cluster data of three FPRs associated with vortex flows observed in the midtail plasma sheet on 15 August 2001. According to the principles of Fu et al. (2011, 2012c), two of the FPRs are considered to be in an early stage of evolution (growing FPRs). The third FPR is in a later stage of evolution (decaying FPR). For the first time, the detailed energy conversion properties during various stages of the FPR evolution have been measured. We show that the later stage FPR has a more complex vortex pattern than the two earlier stage FPRs. The two early stage FPR correspond to generators, E<bold></bold>J<0, while the later stage FPR only shows weak generator characteristics and is instead dominated by load signatures at the DF, E<bold></bold>J>0. Moreover, to our knowledge, this is one of the first times BBF-related plasma vortices have been observed to propagate over the spacecraft in the midtail plasma sheet at geocentric distances of about 18R(E). Our observations are compared to recent simulation results and previous observations.

##### Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2013
##### Keywords
dipolarization front, flux pileup region, flow vortices, energy conversion, generator, load
##### National Category
Astronomy, Astrophysics and Cosmology
##### Identifiers
urn:nbn:se:umu:diva-86346 (URN)10.1002/jgra.50603 (DOI)000330180600027 ()
Available from: 2014-02-24 Created: 2014-02-24 Last updated: 2018-06-08Bibliographically approved
Hamrin, M., Marghitu, O., Norqvist, P., Buchert, S., André, M., Klecker, B., . . . Dandouras, I. (2012). The role of the inner tail to midtail plasma sheet in channeling solar wind power to the ionosphere. Journal of Geophysical Research, 117(A6), A06310
Open this publication in new window or tab >>The role of the inner tail to midtail plasma sheet in channeling solar wind power to the ionosphere
2012 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no A6, p. A06310-Article in journal (Refereed) Published
##### Abstract [en]

In this article we use Cluster power density (E . J) data from 2001, 2002, and 2004 to investigate energy conversion and transfer in the plasma sheet. We show that a southward IMF B-z is favorable for plasma sheet energy conversion, and that there is an increased particle and Poynting flux toward the Earth at times when Cluster observes an enhanced energy conversion in the plasma sheet. Conversion from electromagnetic to kinetic energy is increasingly dominant farther down-tail, while the generation of electromagnetic power from kinetic energy becomes important toward the Earth with a maximum at roughly 10 R-E. By linking observations of the key quantity E . J to observations of the solar wind input and earthward energy flux, our results demonstrate the role of the inner tail to midtail plasma sheet as a mediator between the solar wind energy input into the magnetosphere and the auroral dissipation in the ionosphere.

##### Keywords
IMF, bursty bulk flows, energy conversion, magnetosphere-ionosphere interactions, plasma sheet, solar wind
##### National Category
Astronomy, Astrophysics and Cosmology
##### Identifiers
urn:nbn:se:umu:diva-56973 (URN)10.1029/2012JA017707 (DOI)000305147300008 ()
Available from: 2012-07-03 Created: 2012-07-02 Last updated: 2018-06-08Bibliographically approved
Hamrin, M., Marghitu, O., Norqvist, P., Buchert, S., Andre, M., Klecker, B., . . . Dandouras, I. (2011). Energy conversion regions as observed by Cluster in the plasma sheet. Journal of Geophysical Research, 116(A1)
Open this publication in new window or tab >>Energy conversion regions as observed by Cluster in the plasma sheet
2011 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no A1Article in journal (Refereed) Published
##### Abstract [en]

In this article we present a review of recent studies of observations of localized energy conversion regions (ECRs) observed by Cluster in the plasma sheet at altitudes of 15–20RE. By examining variations in the power density, E · J, where E is the electric field and J is the current density, we show that the plasma sheet exhibits a high level of fine structure. Approximately three times as many concentrated load regions (CLRs) (E · J > 0) as concentrated generator regions (CGRs) (E · J < 0) are identified, confirming the average load character of the plasma sheet. Some ECRs are found to relate to auroral activity. While ECRs are relevant for the energy conversion between the electromagnetic field and the particles, bursty bulk flows (BBFs) play a central role for the energy transfer in the plasma sheet. We show that ECRs and BBFs are likely to be related, although details of this relationship are yet to be explored. The plasma sheet energy conversion increases rather simultaneously with increasing geomagnetic activity in both CLRs and CGRs. Consistent with large-scale magnetotail simulations, most of the observed ECRs appear to be rather stationary in space but varying in time. We estimate that the ECR lifetime and scale size are a few minutes and a few RE, respectively. It is conceivable that ECRs rise and vanish locally in significant regions of the plasma sheet, possibly oscillating between load and generator character, while some energy is transmitted as Poynting flux to the ionosphere.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:umu:diva-50283 (URN)10.1029/2010JA016383 (DOI)
Available from: 2011-12-02 Created: 2011-12-02 Last updated: 2018-06-08Bibliographically approved
Minnhagen, P., Norqvist, P. & Wiklund, K. (2010). ABC-bok för fysiknyfikna. Umeå: Umeå universitet
Open this publication in new window or tab >>ABC-bok för fysiknyfikna
2010 (Swedish)Book (Other (popular science, discussion, etc.))
##### Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2010. p. 60
##### Keywords
Fysik, populärvetenskap
##### National Category
Physical Sciences Didactics
##### Identifiers
urn:nbn:se:umu:diva-44228 (URN)978-91-7459-081-4 (ISBN)
##### Note
LäromedelAvailable from: 2011-05-26 Created: 2011-05-26 Last updated: 2018-06-08Bibliographically approved
Hamrin, M., Norqvist, P., Marghitu, O., Buchert, S., Klecker, B., Kistler, L. M. & Dandouras, I. (2010). Geomagnetic activity effects on plasma sheet energy conversion. Annales Geophysicae, 28, 1813-1825
Open this publication in new window or tab >>Geomagnetic activity effects on plasma sheet energy conversion
2010 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, p. 1813-1825Article in journal (Refereed) Published
##### Abstract [en]

In this article we use three years (2001, 2002, and 2004) of Cluster plasma sheet data to investigate what happens to localized energy conversion regions (ECRs) in the plasma sheet during times of high magnetospheric activity. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have studied the influence on Concentrated Load Regions (CLRs) and Concentrated Generator Regions (CGRs) from variations in the geomagnetic disturbance level as expressed by the Kp, the AE, and the Dst indices. We find that the ECR occurrence frequency increases during higher magnetospheric activities, and that the ECRs become stronger. This is true both for CLRs and for CGRs, and the localized energy conversion therefore concerns energy conversion in both directions between the particles and the fields in the plasma sheet. A higher geomagnetic activity hence increases the general level of energy conversion in the plasma sheet. Moreover, we have shown that CLRs live longer during magnetically disturbed times, hence converting more electromagnetic energy. The CGR lifetime, on the other hand, seems to be unaffected by the geomagnetic activity level. The evidence for increased energy conversion during geomagnetically disturbed times is most clear for Kp and for AE, but there are also some indications that energy conversion increases during large negative Dst. This is consistent with the plasma sheet magnetically mapping to the auroral zone, and therefore being more tightly coupled to auroral activities and variations in the AE and Kp indices, than to variations in the ring current region as described by the Dst index.

##### Keywords
Energy conversion, load, generator, Earth's magnetosphere, geomagnetic activity, Kp, AE, Dst
##### National Category
Fusion, Plasma and Space Physics
Space Physics
##### Identifiers
urn:nbn:se:umu:diva-36512 (URN)10.5194/angeo-28-1813-2010 (DOI)000283653700001 ()
Available from: 2010-10-01 Created: 2010-10-01 Last updated: 2018-06-08Bibliographically approved

#### Search in DiVA

Show all publications