Oscillatory modes of extended Nile River records

• Main Authors: D. Kondrashov, Y. Feliks, M. Ghil
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.146.2013; http://www.atmos.ucla.edu/tcd/PREPRINTS/Nilegrl_Revised_Final.pdf

The historical records of the low- and high-water levels of the Nile River are among the longest climatic records that have near-annual resolution. There are few gaps in the first part of the records (A.D. 622–1470) and larger gaps later (A.D. 1471–1922). We apply advanced spectral methods, Singular-Spectrum Analysis (SSA) and the Multi-Taper Method (MTM), to fill the gaps and to locate interannual and interdecadal periodicities. The gap filling uses a novel, iterative version of SSA. Our analysis reveals several statistically significant features of the records: a nonlinear, data-adaptive trend that includes a 256-yr cycle, a quasi-quadriennial (4.2-yr) and a quasi-biennial (2.2-yr) mode, as well as additional periodicities of 64, 19, 12 and, most strikingly, 7 years. The quasi-quadriennial and quasibiennial modes support the long-established connection between the Nile River discharge and the El-Niño/Southern Oscillation (ENSO) phenomenon in the Indo-Pacific Ocean. The longest periods might be of astronomical origin. The 7-yr periodicity, possibly related to the biblical cycle of lean and fat years, seems to be due to North-Atlantic influences. 1.