The size of the auroral belt during magnetic storms

Abstract. Using the auroral boundary index derived from DMSP electron precipitation data and the Dst index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its lowest latitude about one hour before Dst peaks. This time lag depends very little on storm intensity. It is also shown that during magnetic storms, the energy of the ring current quantified with Dst increases in proportion to Le–3, where Le is the L-value corresponding to the equatorward boundary of the auroral belt designated by the auroral boundary index. This means that the ring current energy is proportional to the ion energy obtained from the earthward shift of the plasma sheet under the conservation of the first adiabatic invariant. The ring current energy is also proportional to Emag, the total magnetic field energy contained in the spherical shell bounded by Le and Leq, where Leq corresponds to the quiet-time location of the auroral precipitation boundary. The ratio of the ring current energy ER to the dipole energy Emag is typically 10%. The ring current leads to magnetosphere inflation as a result of an increase in the equivalent dipole moment.Key words. Ionosphere (Auroral ionosphere) · Magnetospheric physics (Auroral phenomena; storms and substorms)

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The equatorial ring-current energy during magnetic storms as related to Dst activity indices

Journal of Atmospheric and Terrestrial Physics ◽

10.1016/0021-9169(94)e0004-7 ◽

1995 ◽

Vol 57 (6) ◽

pp. 719-724

Author(s):

M.A. Van Zele ◽

O. Schneider

Keyword(s):

Ring Current ◽

Magnetic Storms ◽

Current Energy ◽

Activity Indices

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Identification of the ground signatures of magnetospheric current systems as a function of latitude during intense magnetic storms

10.5194/egusphere-egu21-1436 ◽

2021 ◽

Author(s):

Vasilis Pitsis ◽

Georgios Balasis ◽

Ioannis Daglis ◽

Dimitris Vassiliadis

Keyword(s):

Solar Wind ◽

Magnetic Fields ◽

Geomagnetic Field ◽

Ring Current ◽

Magnetic Storms ◽

Quiet Time ◽

Maximum Correlation ◽

Current Form ◽

H Index ◽

Current Systems

We show that changes in the magnetospheric ring current and auroral currents during the magnetic storms of March 2015 and June 2015, are recorded in several specific ways by ground magnetometers. The ring current changes are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes from -50 to +50 degrees. The auroral currents changes are detected at high magnetic latitudes from 50 to about 73 degrees. Finally, for stations between 73 and about 85 degrees the measurements of the ground magnetometers seem to be directly correlated with the convection electric field VBSouth of the solar wind. Using the correlations among magnetic fields measured at stations ordered by latitude, a correlation diagram is obtained where the maximum correlation values for fields determined by the ring current form a distinct block. High-latitude magnetic fields from stations at higher latitudes, which are mainly determined by auroral currents, form a different block in the same diagram. This is in agreement with our earlier work using wavelet transforms on ground magnetic-field time series, where mid-latitude fields stations that are influenced mainly by the ring current, give a critical exponent greater than 2 while higher-latitude fields show a more complex dependence with two exponents. The maximum correlation values for mid-latitude fields correlated with the SYM-H index vary from 0.8 to 0.9, and, thus, we infer that those geomagnetic disturbances are mainly due to the ring current. The maximum correlations between the same fields and the solar wind VBSouth vary from 0.5 to 0.7. Fields at magnetic latitudes between 50 and 73 degrees exhibit greater correlation values for the AL index rather than the SYM-H index. This is expected since in the auroral zone, the convection- and substorm-associated auroral electrojets contribute significantly to the deviation of the geomagnetic field from its quiet-time value. In this case, maximum correlations vary between 0.6 and 0.7 for auroral latitude stations when compared with AL, as opposed to 0.4&#8211;0.5 when compared with SYM-H. Our results show how different measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems and of the solar wind &#8211; magnetosphere coupling.

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Geomagnetically Quiet Period Analysis of Relativistic Electrons, Auroral Precipitation, Joule Heating, and Ring Current During the Years of 1999, 2000 and 2004

Journal of Nepal Physical Society ◽

10.3126/jnphyssoc.v7i2.38633 ◽

2021 ◽

Vol 7 (2) ◽

pp. 126-137

Author(s):

R. K. Mishra ◽

A. Gautam ◽

P. Poudel ◽

N. Parajuli ◽

A. Silwal ◽

...

Keyword(s):

Relativistic Electron ◽

Joule Heating ◽

Time Variation ◽

Ring Current ◽

Time Lag ◽

Winter Season ◽

Relativistic Electrons ◽

Quiet Time ◽

Electron Population ◽

Cross Correlation Analysis

This work presents the study of the quietest time variation in relativistic electrons, auroral precipitation, ring current, and joule heating during 1999, 2000, and 2004. Geostationary Operational Environmental Satellite (GOES) data on relativistic electrons with energies above 0.6 MeV, 2 MeV, and 4 MeV were analyzed. The time-series analysis of the relativistic electrons over a 24-hour averaged interval reveals a precise 24-hour modulation of the relativistic electron population during all seasons for energies above 0.6 MeV and 2 MeV, and during the winter season for higher energies above 4 MeV. In addition, relativistic electron fluxes at energies above 0.6 MeV and above 2 MeV were higher during the descending phase of the solar cycle compared to the ascending and solar-maximum phases. The cross-correlation analysis presented a strong correlation of Joule heating, ring current, and auroral precipitation with the relativistic electron population in three energy bands considered, as indicated by the zero-time lag. Studying the quiet time variation of relativistic electrons will lead to more complete ionospheric models, which were previously limited to the geomagnetically disturbed period.

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