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Quantitative maps of geomagnetic perturbation vectors during substorm onset and recovery.

Pothier NM, Weimer DR, Moore WB - J Geophys Res Space Phys (2015)

Bottom Line: The fits obtained at onset time were subtracted from all subsequent fits, for each group of substorm events.We demonstrate an influence of the dipole tilt angle on the response to substorms.Our results indicate that there are downward currents poleward and upward currents just equatorward of the peak in the substorms' westward electrojet.

View Article: PubMed Central - PubMed

Affiliation: Department of Atmospheric and Planetary Sciences, Hampton University Hampton, Virginia, USA ; National Institute of Aerospace Hampton, Virginia, USA ; Bradley Department of Electrical and Computer Engineering, Center for Space Science and Engineering Research, Virginia Tech Blacksburg, Virginia, USA ; Department of Atmospheric, Oceanic, and Space Science, University of Michigan Ann Arbor, Michigan, USA.

ABSTRACT

: We have produced the first series of spherical harmonic, numerical maps of the time-dependent surface perturbations in the Earth's magnetic field following the onset of substorms. Data from 124 ground magnetometer stations in the Northern Hemisphere at geomagnetic latitudes above 33° were used. Ground station data averaged over 5 min intervals covering 8 years (1998-2005) were used to construct pseudo auroral upper, auroral lower, and auroral electrojet (AU*, AL*, and AE*) indices. These indices were used to generate a list of substorms that extended from 1998 to 2005, through a combination of automated processing and visual checks. Events were sorted by interplanetary magnetic field (IMF) orientation (at the Advanced Composition Explorer (ACE) satellite), dipole tilt angle, and substorm magnitude. Within each category, the events were aligned on substorm onset. A spherical cap harmonic analysis was used to obtain a least error fit of the substorm disturbance patterns at 5 min intervals up to 90 min after onset. The fits obtained at onset time were subtracted from all subsequent fits, for each group of substorm events. Maps of the three vector components of the averaged magnetic perturbations were constructed to show the effects of substorm currents. These maps are produced for several specific ranges of values for the peak /AL*/ index, IMF orientation, and dipole tilt angle. We demonstrate an influence of the dipole tilt angle on the response to substorms. Our results indicate that there are downward currents poleward and upward currents just equatorward of the peak in the substorms' westward electrojet.

Key points: Show quantitative maps of ground geomagnetic perturbations due to substorms Three vector components mapped as function of time during onset and recovery Compare/contrast results for different tilt angle and sign of IMF Y-component.

No MeSH data available.


Related in: MedlinePlus

(a–c) Examples of cases where a substorm was identified. The dotted lines show the outline of the curve that the automated program used to calculate a match with the “canonical substorm time series [Weimer, 1994].” Example of a case where the onset time required a manual adjustment by a few minutes. (d) Example of a case where the automated program had marked a time as having a substorm onset, but it was rejected in the visual check.
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fig03: (a–c) Examples of cases where a substorm was identified. The dotted lines show the outline of the curve that the automated program used to calculate a match with the “canonical substorm time series [Weimer, 1994].” Example of a case where the onset time required a manual adjustment by a few minutes. (d) Example of a case where the automated program had marked a time as having a substorm onset, but it was rejected in the visual check.

Mentions: The process was sufficiently flexible to allow for significant departure from the exponential curve, due to the rapid magnetic field variations that result from chaotic turbulence in the ionosphere and sharp conductivity variations [Pulkkinen et al., 2006]. Example events are shown in Figures 3a–3c. The dotted lines show the outline of the curve that the automated program had used to calculate a match with the “canonical substorm time series [Weimer, 1994].” The solid lines show the actual AU* and AL* indices.


Quantitative maps of geomagnetic perturbation vectors during substorm onset and recovery.

Pothier NM, Weimer DR, Moore WB - J Geophys Res Space Phys (2015)

(a–c) Examples of cases where a substorm was identified. The dotted lines show the outline of the curve that the automated program used to calculate a match with the “canonical substorm time series [Weimer, 1994].” Example of a case where the onset time required a manual adjustment by a few minutes. (d) Example of a case where the automated program had marked a time as having a substorm onset, but it was rejected in the visual check.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497481&req=5

fig03: (a–c) Examples of cases where a substorm was identified. The dotted lines show the outline of the curve that the automated program used to calculate a match with the “canonical substorm time series [Weimer, 1994].” Example of a case where the onset time required a manual adjustment by a few minutes. (d) Example of a case where the automated program had marked a time as having a substorm onset, but it was rejected in the visual check.
Mentions: The process was sufficiently flexible to allow for significant departure from the exponential curve, due to the rapid magnetic field variations that result from chaotic turbulence in the ionosphere and sharp conductivity variations [Pulkkinen et al., 2006]. Example events are shown in Figures 3a–3c. The dotted lines show the outline of the curve that the automated program had used to calculate a match with the “canonical substorm time series [Weimer, 1994].” The solid lines show the actual AU* and AL* indices.

Bottom Line: The fits obtained at onset time were subtracted from all subsequent fits, for each group of substorm events.We demonstrate an influence of the dipole tilt angle on the response to substorms.Our results indicate that there are downward currents poleward and upward currents just equatorward of the peak in the substorms' westward electrojet.

View Article: PubMed Central - PubMed

Affiliation: Department of Atmospheric and Planetary Sciences, Hampton University Hampton, Virginia, USA ; National Institute of Aerospace Hampton, Virginia, USA ; Bradley Department of Electrical and Computer Engineering, Center for Space Science and Engineering Research, Virginia Tech Blacksburg, Virginia, USA ; Department of Atmospheric, Oceanic, and Space Science, University of Michigan Ann Arbor, Michigan, USA.

ABSTRACT

: We have produced the first series of spherical harmonic, numerical maps of the time-dependent surface perturbations in the Earth's magnetic field following the onset of substorms. Data from 124 ground magnetometer stations in the Northern Hemisphere at geomagnetic latitudes above 33° were used. Ground station data averaged over 5 min intervals covering 8 years (1998-2005) were used to construct pseudo auroral upper, auroral lower, and auroral electrojet (AU*, AL*, and AE*) indices. These indices were used to generate a list of substorms that extended from 1998 to 2005, through a combination of automated processing and visual checks. Events were sorted by interplanetary magnetic field (IMF) orientation (at the Advanced Composition Explorer (ACE) satellite), dipole tilt angle, and substorm magnitude. Within each category, the events were aligned on substorm onset. A spherical cap harmonic analysis was used to obtain a least error fit of the substorm disturbance patterns at 5 min intervals up to 90 min after onset. The fits obtained at onset time were subtracted from all subsequent fits, for each group of substorm events. Maps of the three vector components of the averaged magnetic perturbations were constructed to show the effects of substorm currents. These maps are produced for several specific ranges of values for the peak /AL*/ index, IMF orientation, and dipole tilt angle. We demonstrate an influence of the dipole tilt angle on the response to substorms. Our results indicate that there are downward currents poleward and upward currents just equatorward of the peak in the substorms' westward electrojet.

Key points: Show quantitative maps of ground geomagnetic perturbations due to substorms Three vector components mapped as function of time during onset and recovery Compare/contrast results for different tilt angle and sign of IMF Y-component.

No MeSH data available.


Related in: MedlinePlus