A 20 year decline in solar magnetic fields and solar wind micro-turbulence levels: Are we heading towards a Maunder-like minimum?

摘要

Our study of solar high-latitude (≥45°) photospheric magnetic fields and interplanetary scintillation observations, at 327 MHz, of solar wind micro-turbulence levels showed a steady decline for the past 20 years. Also, the fact that cycle 24 has already past its peak, implies that high-latitude fields are likely to decline until ~2020. Based on a correlation between the solar high-latitude fields and the heliospheric magnetic fields (HMF), we estimated the HMF strength in 2020 and the floor value of the HMF, which were found to be 3.9 (±0.6) nT and 3.2 (±0.4) nT, respectively. Using estimated value of the HMF in 2020, the peak sunspot number for solar Cycle 25 was estimated to be 62 (±12). These results and the fact that solar magnetic fields continues to decline at present raise the question of a very low sunspot activity in near-future or another grand minimum similar to the Maunder minimum. So what is the possible impact of such a likely grand minimum on terrestrial ionospheric current systems? Our study night time F-region maximum electron density (a measure of terrestrial ionospheric currents) reveals that the impending minimum is not likely to have any adverse impact rather the period post cycle 25 will be useful for undertaking systematic ground based low-frequency radio astronomy as the night time ionospheric cutoff-frequency could be well below 10 MHz.