20 research outputs found
A study of density modulation index in the inner heliospheric solar wind during solar cycle 23
The ratio of the rms electron density fluctuations to the background density
in the solar wind (density modulation index, )
is of vital importance in understanding several problems in heliospheric
physics related to solar wind turbulence. In this paper, we have investigated
the behavior of in the inner-heliosphere from 0.26 to 0.82 AU.
The density fluctuations have been deduced using extensive
ground-based observations of interplanetary scintillation (IPS) at 327 MHz,
which probe spatial scales of a few hundred km. The background densities ()
have been derived using near-Earth observations from the Advanced Composition
Explorer (). Our analysis reveals that and does not vary appreciably with heliocentric distance. We
also find that declines by 8% from 1998 to 2008. We discuss the
impact of these findings on problems ranging from our understanding of Forbush
decreases to the behavior of the solar wind dynamic pressure over the recent
peculiar solar minimum at the end of cycle 23..Comment: 13 Pages, 8 Figures, Accepted for publication in Ap
Solar cycle 24: an unusual polar field reversal
Aims: To investigate solar polar fields during cycle 24, using measurements
of solar magnetic fields in the latitude range 55 - 90 degree and 78 - 90
degree, to report a prolonged and unusual hemispheric asymmetry in the polar
field reversal pattern in solar cycle 24. Methods: This study was carried out
using medium resolution line-of-sight synoptic magnetograms from the magnetic
database of the National Solar Observatory at Kitt Peak (NSO/KP), USA for the
period between February 1975 and October 2017, covering solar cycles 21-24 and
high-resolution line-of-sight synoptic magnetograms from the Michaelson Doppler
Imager instrument onboard the Solar Heliospheric Observatory. Synoptic
magnetograms using radial measurements from the Heliospheric Magnetic Imager
instrument onboard the Solar Dynamics Observatory, covering solar cycle 23 and
24, were also used. Results: We show that the Southern solar hemisphere
unambiguously reversed polarity in mid-2013 while the reversal in the field in
the Northern solar hemisphere started as early as June 2012, was followed by a
sustained period of near-zero field strength lasting until the end of 2014,
after which the field began to show a clear rise from its near-zero value.
While this study compliments a similar study carried out using microwave
brightness measurements (Gopalswamy et al. 2016) which claimed that the field
reversal process in cycle 24 was completed by the end of 2015, our results show
that the field reversal in cycle 24 was completed earlier i.e. in late 2014.
Signatures of this unusual field reversal pattern were also clearly
identifiable in the solar wind, using our observations of interplanetary
scintillation at 327 MHz which supported our magnetic field observations and
confirmed that the field reversal process was completed at the end of 2014.Comment: 11 pages, 7 figures, Under review in A&
Preparing for Solar and Heliospheric Science with the SKAO: An Indian Perspective
The Square Kilometre Array Observatory (SKAO) is perhaps the most ambitious
radio telescope envisaged yet. It will enable unprecedented studies of the Sun,
the corona and the heliosphere and help to answer many of the outstanding
questions in these areas. Its ability to make a vast previously unexplored
phase space accessible, also promises a large discovery potential. The Indian
solar and heliospheric physics community have been preparing for this science
opportunity. A significant part of this effort has been towards playing a
leading role in pursuing science with SKAO precursor instruments. This article
briefly summarises the current status of the various aspects of work done as a
part of this enterprise and our future goals.Comment: 34 pages, 18 figures, accepted for publication in Journal of
Astronomy and Astrophysic