Observation of a tidal effect on the Polar Jet Stream

Abstract. Variations in the Polar Jet Stream directly affect weather across Europe and North America (Francis et al., 2012). Jet Stream dynamics are governed by the development of planetary Rossby waves (Dickinson, 1978) driven by variation of the Coriolis force with latitude. Here we show that increasing atmospheric tides induce the development of Rossby waves, especially during winter months. This changes the flow and direction of the Jet Stream, as measured by the Arctic Oscillation (AO). Although horizontal tidal forces are tiny (10⁷ smaller than gravity), they act over huge areas dragging the Jet Stream flow southwards in regular pulses as the earth rotates. This induces a changing Coriolis torque, which then distorts the Jet Stream flow. The data from eight recent winters are studied indicating that the AO is anti-correlated to the horizontal "tractional" component of tides acting between latitude 45 and 60° N. The observed 28 day cycle in Jet Stream flow and extent has a statistical significance > 99 %. A cross-correlation between all daily AO data since 1950 and the tractional tidal strength shows a significant anti-correlation with a lag time of ~ 5 days. The strongest correlation and largest excursions of the AO are observed during winter 2005/2006 – a maximum lunar standstill year. This declination dependence of tidal forces at high latitudes is the proposed cause of many previous reports of an 18.6 year dependence of continental rainfall and drought.