Related papers: Is Solar Minimum 24/25 Another Unusual One?
Solar polar fields are essential for the solar cycle and the heliospheric magnetic field. Cycle 25 is now entering its declining phase, the critical period during which most of the cycle's polar fields are established. Therefore, reliable…
We report on a study that compares the properties of magnetic clouds (MCs) during the first 73 months of solar cycles 23 and 24 in order to understand the weak geomagnetic activity in cycle 24. We find that the number of MCs did not decline…
The dynamic activity of the Sun -- sustained by a magnetohydrodynamic dynamo mechanism working in its interior -- modulates the electromagnetic, particulate and radiative environment in space. While solar activity variations on short…
We report on the state of the corona over the minimum and ascending phases of Solar Cycle (SC) 25 on the basis of the temporal evolutions of its radiance and of the properties of coronal mass ejections (CMEs) as determined from white-light…
We test recent claims that the polar field at the end of Cycle 23 was weakened by a small number of large, abnormally oriented regions, and investigate what this means for solar cycle prediction. We isolate the contribution of individual…
Both direct observations and reconstructions from various datasets, suggest that conditions were radically different during the Maunder Minimum (MM) than during the space era. Using an MHD model, we develop a set of feasible solutions to…
This paper presents time series observations and analysis of broadband night sky airglow intensity 4 September 2018 through 30 April 2020. Data were obtained at 5 sites spanning more than 8500 km during the historically deep minimum of…
Solar coronal holes are sources of high-speed solar wind streams, which cause persistent geomagnetic activity especially at high latitudes. Here we estimate seasonal solar wind speeds at 1 AU for the last 100 years using high-latitude…
The maximum amplitude (Rm) of a solar cycle, in the term of mean sunspot numbers, is well-known to be positively correlated with the preceding minimum (Rmin). So far as the long term trend is concerned, a low level of Rmin tends to be…
Solar Cycle 24 is having a historically long and weak start. Observations of the Fe XIV corona from the Sacramento Peak site of the National Solar Observatory show an abnormal pattern of emission compared to observations of Cycles 21, 22,…
The Solar Cycle is reviewed. The 11-year cycle of solar activity is characterized by the rise and fall in the numbers and surface area of sunspots. A number of other solar activity indicators also vary in association with the sunspots…
Potential field extrapolations are widely used as minimum-energy models for the Sun's coronal magnetic field. As the reference to which other magnetic fields are compared, they have -- by any reasonable definition -- no global (signed)…
We have analyzed available full-disc data from the Michelson Doppler Imager (MDI) on board SoHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius.…
We have examined polar magnetic fields for the last three solar cycles, {$\it{viz.}$}, cycles 21, 22 and 23 using NSO Kitt Peak synoptic magnetograms. In addition, we have used SoHO/MDI magnetograms to derive the polar fields during cycle…
We report observations of a steady 20 year decline of solar photospheric fields at latitudes $\geq$45${^{o}}$ starting from $\sim$1995. This prolonged and continuing decline, combined with the fact that Cycle 24 is already past its peak,…
The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but…
We have studied the 27-day variations and their harmonics of the galactic cosmic ray (GCR) intensity, solar wind velocity, and interplanetary magnetic field (IMF) components in the recent prolonged solar minimum 23 24. The time evolution of…
The dependence of the sources and properties of the near-Earth solar wind on solar cycle activity is an important issue in solar and space physics. We use the improved two-step mapping procedure that takes into account the initial…
The relative abundance of alpha particles with respect to proton, usually expressed as $A_{He}$ = ($n_\alpha/n_p$)*100, is known to respond to solar activity although changes in its behaviour in the last four solar cycles are not known. In…
Solar variability occurs over a broad range of spatial and temporal scales, from the Sun's brightening over its lifetime to the fluctuations commonly associated with magnetic activity over minutes to years. The latter activity includes most…