Detection of the 11-yr sunspot cycle signal in Earth rotation

Abstract

Summary. A two-channel MESA or maximum entropy spectrum analysis (Morf et al. 1978) between ΔT°=ET–UT (Morrison 1973) and sunspot numbers spanning 1832–1975 yields the following results over a bandwidth 2–20yr: (1) The spectra of ΔT° and sunspot numbers are both dominated by a narrow band signal at 11.0 yr; (2) On average the coherency over the continuum is 0.14 while at 11.0yr it peaks at 0.83; (3) The 11-yr sunspot cycle signal in length of day (lod) has an amplitude of 0.16 ms, and in time lags that in sunspot numbers by 3.4yr. Estimates obtained from segmenting the series yield extremal values which grossly bound the above estimates: The narrow band signal has period range (10.5–11.4yr) coherency (0.8–1.0), amplitude (0.06–0.31 ms), and time lag (3.0–3.Syr). In addition, a two channel analysis of sunspot numbers with a new ΔTn series from 1861–1978 (Morrison 1979) and an earlier segment of ΔT°, as well as a single-channel analysis of ΔT° and ΔTn individually, further support the conclusion that the solar sunspot cycle in Earth rotation has been detected. These experimental results have implications in astronomy, solar physics, meteorology and climatology.