Decline in solar polar magnetic fields and heliospheric micro-turbulence levels: Are we headed towards a Maunder minimum?

Abstract

Sunspots or dark regions of strong magnetic fields on the solar photosphere are generated via magnetohydrodynamic processes in the solar interior that involve the cyclic generation of toroidal fields (sunspot fields) from pre-existing poloidal fields and the eventual regeneration of the poloidal fields. This cyclic process, referred to as the solar dynamo, leads to the well known solar activity cycle of waxing and waning sunspot numbers with a period of 11 years. The sunspot minimum at the end of solar cycle 23, however, was one of the deepest recorded in the past 100 years, with cycle 24 starting about 16 months later than expected. A detailed study of solar high latitude (≥ 45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∘</sup> ) or polar magnetic fields using ground based magnetograms has clearly shown a steady decline in polar field strength since mid-1990's [1, 2, 3] which has continued to the present, i.e. until the end of February 2013. Since sunspot fields are generated from polar fields, this long term decline in polar field strength would eventually effect the sunspot field strength in the subsequent solar cycles. A continued decline in the polar fields in the manner indicated by our analysis would imply that the polar field strength will approach zero by ∼2031. In addition, a detailed analysis of solar wind micro-turbulence in the inner heliosphere has also shown a steady decline in sync with the declining solar photospheric magnetic fields. The fact that both solar polar fields and inner-heliospheric micro-turbulence levels show a similar decline raises the question as to whether we are headed towards an extended period of very little or no sunspot activity in a manner similar to what was seen in the Maunder minimum?