Study of space weather events and the occurrence of ionospheric plasma bubbles
in the Brazilian and Japanese sectors using ionospheric sounding data
ABSTRACT
The objective of this work is to study space weather events and the occurrence of
ionospheric plasma bubbles in the Brazilian and Japanese sectors using ionospheric
sounding data. Ionospheric sounding data obtained in the region of low latitude in the
Brazilian sector have been used to study the variations of large-scale equatorial
ionopheric irregularities with solar activity. An analysis of the ionospheric data obtained
at S.J. Campos (Brazil) during the period of October 2000 - September 2001 (high solar
activity - HSA) and March 2005 - February 2006 (low solar activity – LSA) has been
carried out and are compared with the ionospheric sounding observations obtained at
Okinawa (Japan) during this same period. Comparison between these two stations was
done because they have fairly similar latitudes but longitudes differ by 12 hours in local
time. Also, ionospheric sounding data from the UNIVAP network with digital
ionosondes localized at S.J. Campos (23.2º S, 45.9º O), Palmas (10.2º S, 48.8º O) and
Manaus (2.9º S, 60.0º O), Brazil, obtained during two space weather events with intense
(December of 2006) and very intense (November of 2004) geomagnetic disturbances
were used to study the influence on the equatorial and low-latitude F region in the
Brazilian sector. The comparisons during HSA and LSA at SJC showed that the
presence of spread-F is stronger, during HSA than LSA, however, at OKI the
occurrence of spread-F, in general, during HSA and LSA does not present much
difference. The comparisons between SJC and OKI during HSA showed that while SJC
presents maxim occurrence of spread-F during December solstice months, at OKI
during this period practically no spread-F is observed. On the other hand, during the
months of May to August (June solstice months), normally no spread-F occurs at SJC,
but during the months of July to September spread-F occurs at OKI. The comparisons
between SJC and OKI during the LSA did not show any clear tendency in the
occurrence characteristics at the two stations. In the two events investigated during
geomagnetic storms (November 2004, MAN and SJC located on either side of
geomagnetic equator); December 2006, PAL and SJC located on same side of
geomagnetic equator), both showed prompt penetrations of electric fields of
magnetospheric origin during the geomagnetic storm main phase, resulting in rapid
uplift of the F region during post-sunset period. Also, both the events showed the
presence of Traveling Ionospheric Disturbances (TIDs) propagating from south to north
associated with Joule heating in auroral region, resulting in strong oscillations in the F
region. The presence of plasma bubbles were detected in the first event ( November
2004) during the night of 06-07 (geomagnetically quiet), 07-08 e 08-09
(geomagnetically perturbed). It should be mentioned that on the nights of 09-10 e 10-11
November 2004, spread-F was observed only after mid night at MAN, because the
uplifting of F region during sunset time was inhibited by disturbances thermosphereic
wind. In the first event the variations in foF2 were more accentuated on the night of 10-
11 in comparison with average quiet days variations, with a MAN indicating positive
storm phase while SJC indicating negative storm phase. In the second event
(December 2006), plasma bubbles were observed on the nights of 13-14
(geomagnetically quiet) and 14-15 (geomagnetically perturbed), with post-sunset
uplifting more rapid during the geomagnetic disturbance (14 December). In the second
event, the variations in foF2 at PAL and SJC do not show much difference in
comparison with the average quiet days variations.
Keywords: Space weather, ionosphere, F region, ionosonde, plasma bubles,
geomagnetic-storms.