Is solar variability reflected in the Nile River?

• Published in: Journal of Geophysical Research: Atmospheres
• Main Authors: Ruzmaikin, Alexander, Feynman, Joan, Yung, Yuk L.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2006
• Subjects: Indian; North Atlantic
• Online Access: https://doi.org/10.1029/2006JD007462

We investigate the possibility that solar variability influences North African climate by using annual records of the water level of the Nile collected in 622–1470 A.D. The time series of these records are nonstationary, in that the amplitudes and frequencies of the quasi-periodic variations are time-dependent. We apply the Empirical Mode Decomposition technique especially designed to deal with such time series. We identify two characteristic timescales in the records that may be linked to solar variability: a period of about 88 years and one exceeding 200 years. We show that these timescales are present in the number of auroras reported per decade in the Northern Hemisphere at the same time. The 11-year cycle is seen in the Nile's high-water level variations, but it is damped in the low-water anomalies. We suggest a possible physical link between solar variability and the low-frequency variations of the Nile water level. This link involves the influence of solar variability on the atmospheric Northern Annual Mode and on its North Atlantic Ocean and Indian Ocean patterns that affect the rainfall over the sources of the Nile in eastern equatorial Africa. © 2006 American Geophysical Union. Received 1 May 2006; revised 5 July 2006; accepted 9 August 2006; published 11 November 2006. We thank the reviewers for critical and helpful comments. We are grateful to Don Percival for providing the Nile data. We also thank the participants of the SORCE 2005 meeting and of Y. Yung's seminar at Caltech for helpful discussions of the results presented in this paper. A.R. thanks N. Huang and P. Flandrin for helpful advice on the application of the EMD. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Y.L.Y. was supported by NASA grant NNG04GN02G to the California Institute of Technology. Published - jgrd13171.pdf