PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
the storm initial phase the strongest ULF geomagnetic pulsations are observed in the dayside polar cap due to
a direct penetration of the ULF waves from the solar wind. So, we could not expect to see this effect in the
ground ULF-index, calculated for auroral latitudes (Φ = 60°–70°), as well as in the magnetospheric ULFindex,
calculated applying the GOES data.
It is known that the main phase of the magnetic storm is accompanied by the development of magnetospheric
substorms accompanying by Pi3 irregular geomagnetic pulsations. It would seem that also the wave activity
during the main phase of storm must be concentrated in the night sector, and during the storm recovery phase
- in the dayside. It is well known [e.g., Afanasyeva, 1978]), that in the majority of the cases of Pc5 the
pulsations are observed in the auroral latitudes in the early morning sector after the end of the night
substorms.
Baker et al, (2003) found that at the
auroral latitudes there are two maxima
of Pc5 occurrence: one in the morning
and considerably weaker in the
afternoon time. Consequently, it can be
assumed that the basic contribution to
the dayside (03-18 MLT) ULF-index of
the pulsations activity consists of both
morning and afternoon Pc5 pulsation.
Thus, it is logical to divide up the values
of ULF-index into two parts - morning
(03-12 MLT) and afternoon (12-18
MLT). As an example we analyze the
strong magnetic storm on May 15, 1997.
The magnetograms (X and Y
components of magnetic field) for
several auroral stations, located at the
different longitudes, are given in Fig. 5.
Fig. 5 Magnetograms of X and Y components for the several
auroral stations on May 15, 1997; black diamonds –
local midnight, white triangle - noon
One can see that in the pre-midnight (MEA) and morning (NAQ) sectors there were observed the
development of the intensive substorm accompanied by strong pulsations.
The morning (blue) and afternoon (red) variations of the
ULF- index during this storm are presented in detail in Fig.
6, where the variations of the solar wind velocity (V) and
density (N), and the Dst index are shown too. The main
phase of this storm, as can be seen from Dst- index (Fig.
6), began about 07 UT. During the main phase of storm
(07-16 UT) the variations of the ULF- index demonstrated
three maxima simultaneously before noon and after noon.
The maps of the global scale distribution of the intensity of
geomagnetic pulsations in the frequency band of 2-5 mHz
(Fig. 7) were built for two stronger maxima (06-08 UT and
14-16 UT) in the coordinates: the corrected geomagnetic
latitude - local magnetic time (MLT).
As can be seen in upper panel of Fig. 7, at 06-08 UT the
most intensive pulsations were observed in two separated
longitudinal sectors - in the evening-night (18-22 MLT)
and in the early morning (02-08 MLT). The maximum of
ULF- index in 14-16 UT (Fig. 6) corresponds to the
excitation of the geomagnetic pulsations (Fig. 7, bottom
Fig. 6 Variations of the solar wind velocity panel) which were more intensive in the morning sector
(V) and density (N), Dst index and (03-08 MLT) than in the evening sector (16-19 MLT).
ULF- index: blue curve – morning, red Morning geomagnetic pulsations were observed during the
one - afternoon
recovery phase of morning substorm at MEA (Fig. 5).
As usual the activity of geomagnetic pulsations was higher
in the morning than after noon. This is clearly evident in Fig. 6 by the comparison of the values of the ULFindex
for the morning (03-12 MLT) and evening (12-18 MLT) pulsations.
144