The heliospheric Hale cycle over the last 300 years and its implications for a “lost” late 18th century solar cycle

Abstract

A Hale cycle, one complete magnetic cycle of the Sun, spans two complete Schwabe cycles (also referred to as sunspot and, more generally, solar cycles). The approximately 22-year Hale cycle is seen in magnetic polarities of both sunspots and polar fields, as well as in the intensity of galactic cosmic rays reaching Earth, with odd-and even-numbered solar cycles displaying qualitatively different waveforms. Correct numbering of solar cycles also underpins empirical cycle-to-cycle relations which are used as firstorder tests of stellar dynamo models. There has been much debate about whether the unusually long solar cycle 4 (SC4), spanning 1784-1799, was actually two shorter solar cycles combined as a result of poor data coverage in the original Wolf sunspot number record. Indeed, the group sunspot number does show a small increase around 1794-1799 and there is evidence of an increase in the mean latitude of sunspots at this time, suggesting the existence of a cycle ''4b''. In this study, we use cosmogenic radionuclide data and associated reconstructions of the heliospheric magnetic field (HMF) to show that the Hale cycle has persisted over the last 300 years and that data prior to 1800 are more consistent with cycle 4 being a single long cycle (the ''no SC4b'' scenario). We also investigate the effect of cycle 4b on the HMF using an open solar flux (OSF) continuity model, in which the OSF source term is related to sunspot number and the OSF loss term is determined by the heliospheric current sheet tilt, assumed to be a simple function of solar cycle phase. The results are surprising; Without SC4b, the HMF shows two distinct peaks in the 1784-1799 interval, while the addition of SC4b removes the secondary peak, as the OSF loss term acts in opposition to the later rise in sunspot number. The timing and magnitude of the main SC4 HMF peak is also significantly changed by the addition of SC4b. These results are compared with the cosmogenic isotope reconstructions of HMF and historical aurora records. These data marginally favour the existence of SC4b (the ''SC4b'' scenario), though the result is less certain than that based on the persistence of the Hale cycle. Thus while the current uncertainties in the observations preclude any definitive conclusions, the data favour the ''no SC4b'' scenario. Future improvements to cosmogenic isotope reconstructions of the HMF, through either improved modelling or additional ice cores from well-separated geographic locations, may enable questions of the existence of SC4b and the phase of Hale cycle prior to the Maunder minimum to be settled conclusively.

Seasonal Variability of Rainfall and its Decadal Anomaly over Nigeria: Possible Role of Solar and Geomagnetic Activities

“…Other authors such as [16], [17], [18] have obtained similar periodicities between solar indices and climatic parameters. It has been reported that solar activity varies between active and quiet phases with 11 year solar cycle known as Schwabe cycle, 22 year polarity reversals called Hale cycle and 80 year cycle known as Gleissberg cycle [19], [20]. The Schwabe, Hale, and Gleissberg cycles can be stretched or shortened, leading to different harmonics [21].…”

Near‐Earth heliospheric magnetic field intensity since 1750: 2. Cosmogenic radionuclide reconstructions

“…Five independent sets of data would yield a standard deviation of ~5.5% for the annual paleocosmic ray data, 0.3 nT for the annual estimates of the heliospheric magnetic field near Earth, and would allow smaller solar energetic particle events to be detected and eliminated from B[GCR‐MB2]. It would also permit the time profile of the 11 year cycle in the PCR to be determined for individual cycles (“sharp rising ” or “flat topped”) thereby identifying the polarity of the solar dipole into the past [ Potgieter , ; Owens et al , ]. Extending the annual PCR record back to 1000 before present (B.P.). (950 Common Era (C.E.))…”

Influence of solar and geomagnetic activity on climate change in Nigeria

“…Researchers have shown that solar activity alternates between active and quiet phases with an average duration of 11 year (Schwabe cycle), 22 year solar magnetic cycle polarity reversals (Hale cycle) and probably an ~80 year cycle (Gleissberg cycle), with short term periodicities (Nayar, 2006;Kane, 2005;El Mallah and El Sharkawy, 2011;Nagaya et al, 2012;Owen et al, 2015). The Schwabe, Hale and Gleissberg cycles can be stretched/shorten, leading to different harmonized (Miyahara et al, 2009).…”