Deterministic signals in Southeast United States precipitation data

Abstract

Evidence for a signal in rainfall with period near 19 years is found in 54 out of 74 rain‐gauge records in Florida, Georgia, and South Carolina, while a term of period 10–11 years is evident in 58 instances. These are identified as induced by the 18.6‐year luni‐solar constituent M_n tide (M for moon and n for nodal), and a 10–11 year solar cycle S_c variation in the sun's luminosity of order 0.1%. M_n wavetrains display complex patterns with many experiencing 180° phase changes at epochs 1917.5, 1936.1, and 19733 (epochs are dates of maximum in tidal forcing). Polarity maps of wave maxima and minima at epochs show that at epoch 1898.9 only parts of South Carolina were dry, while at 1917.5 dryness had expanded over South Carolina and into Georgia and western Florida. By epoch 1936.1 a unipolar drought cell prevailed over the entire tri‐state region, and continued to prevail at epoch 1954.7. By epoch 1973.3, however, the monolithic dry cell had broken up into two smaller dry cells.