Search Publications
Evolution of the Sun's activity and the poleward transport of remnant magnetic flux in Cycles 21-24
Banerjee, Dipankar; Karak, Bidya Binay; Kumar, Pawan +4 more
Detailed study of the solar magnetic field is crucial to understand its generation, transport, and reversals. The timing of the reversals may have implications on space weather and thus identification of the temporal behaviour of the critical surges that lead to the polar field reversals is important. We analyse the evolution of solar activity and…
A new look at the frequency-dependent damping of slow-mode waves in the solar corona
Nakariakov, Valery M.; Kolotkov, Dmitrii Y.
Being directly observed in the Doppler shift and imaging data and indirectly as quasi-periodic pulsations in solar and stellar flares, slow magnetoacoustic waves offer an important seismological tool for probing many vital parameters of the coronal plasma. A recently understood active nature of the solar corona for magnetoacoustic waves, manifeste…
Synthetic solar cycle for active regions violating the Hale's polarity law
Abramenko, V.; Sokoloff, D.; Zhukova, A. +1 more
Long observational series for bipolar active regions (ARs) provide significant information about the mutual transformation of the poloidal and toroidal components of the global solar magnetic field. The direction of the toroidal field determines the polarity of leading sunspots in ARs in accordance with the Hale's polarity law. The vast majority o…
Cycle dependence of a quasi-biennial variability in the solar interior
Broomhall, A. -M.; Jain, K.; Tripathy, S. C. +3 more
We investigated the solar cycle dependence on the presence and periodicity of the Quasi-Biennial Oscillation (QBO). Using helioseismic techniques, we used solar oscillation frequencies from the Global Oscillations Network Group (GONG), Michelson Doppler Imager (MDI), and Helioseismic and Magnetic Imager (HMI) in the intermediate-degree range to in…
Forbush decreases associated with coronal mass ejections from active and non-active regions: statistical comparison
Melkumyan, A. A.; Belov, A. V.; Abunina, M. A. +4 more
In this paper, Forbush decreases (FDs) from 1997 to 2020 associated with coronal mass ejections from active and non-active regions are compared between themselves and to FDs caused by high-speed streams from coronal holes. The two types of sporadic FDs are also compared when corresponding solar wind (SW) disturbances contain, or do not contain, ma…
The recurrent nova U Scorpii from the 2010.1 to 2022.4 eruptions; the missed eruption of 2016.78 ± 0.10 and the critical complex period changes
Schaefer, Bradley E.
U Sco is a recurrent nova with 11 observed eruptions, most recently in 2010.1 and 2022.4. I report on my program (running since 1989) of measuring eclipse times and brightnesses of U Sco in quiescence, from 2010 to 2022. The orbital period suddenly increased by +22.4 ± 1.0 parts-per-million across the 2010.1 eruption. This period change is greater…
Forbush decreases caused by paired interacting solar wind disturbances
Belov, A. V.; Abunina, M. A.; Abunin, A. A. +3 more
The paper discusses changes in various characteristics of the solar wind, interplanetary magnetic field, geomagnetic activity, and cosmic rays during the registration of paired interacting solar wind disturbances on the Earth using the data base of Forbush effects and interplanetary disturbances - FEID. The cases of pair interaction are considered…
Path-lengths in the quiet Sun transition region using O IV lines from IRIS
Del Zanna, Giulio; Rao, Yamini K.; Mason, Helen E. +1 more
We use spectroscopic diagnostics to determine different plasma parameters in the transition region of the quiet Sun. The electron number density from O IV lines using high-resolution spectral observations from the Interface Region Imaging Spectrograph (IRIS) are estimated to be around 1010 cm-3, in agreement with literature v…
A holistic approach to understand helium enrichment in interplanetary coronal mass ejections: new insights
Yogesh; Chakrabarty, D.; Srivastava, N.
Despite helium abundance [AHe = (nH/nHe) × 100] being ~8 per cent at the solar photospheric/chromospheric heights, AHe can be found to exceed 8 per cent in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation, and …
A multi-instrument investigation of the frequency stability of oscillations above the acoustic cut-off frequency with solar activity
Broomhall, A. -M.; Kiefer, R.; Kosak, K.
Below the acoustic cut-off frequency, oscillations are trapped within the solar interior and become resonant. However, signatures of oscillations persist above the acoustic cut-off frequency, and these travelling waves are known as pseudo-modes. Acoustic oscillation frequencies are known to be correlated with the solar cycle, but the pseudo-mode f…