Solar Cycle Signal in Earth Rotation: Nonstationary Behavior

Science  23 Jan 1981:
Vol. 211, Issue 4480, pp. 386-389
DOI: 10.1126/science.211.4480.386


Following the discovery of the 11-year solar cycle signal in earth rotation, linear techniques were employed to investigate the amplitude and phase of the difference between ephemeris time and universal time (ΔT) as a function of time. The amplitude is nonstationary. This difference was related to Δ(LOD), the difference between the length of day and its nominal value. The 11-year term in Δ(LOD) was 0.8 millisecond at the close of the 18th century and decreased below noise level from 1840 to 1860. From 1875 to 1925, Δ(LOD) was about 0.16 millisecond, and it decreased to about 0.08 millisecond by the 1950's. Except for anomalous behavior from 1797 to 1838, ΔT lags sunspot numbers by 3.0 ± 0.4 years. Since ΔT lags Δ(LOD) by 2.7 years, the result is that Δ(LOD) is approximately in phase with sunspot numbers.