Deterministic signals in USA precipitation records: Part I

Abstract

Abstract Evidence for the 18–6‐year luni‐solar M N signal is found in 220 out of 288 rain‐gauge records (76 per cent detection ratio) in the states of California, Colorado, Kansas, Missouri, North Carolina, Ohio. Oregon, Washington, and West Virginia, with a mean period of 18·4 ± 1·5 years. This detection ratio is less than that for the nation, which is 1015 out of 1219 records, or 83 per cent. The solar cycle S c signal was found in 70 per cent of these records, with a period of 10·6 ± 0·5 years. For Colorado, and states directly to the east as far as Illinois, minima in most 19‐year M n wavetrains were generally in phase with epochs 1898·9 through to 1954·7 (epochs are dates of maximum in tidal forcing). However, by 1973‐3 virtually all records east of Colorado had experienced a 180° phase switch and wave maxima were in phase with this epoch. In Oregon and Washington most M N waves recorded maxima in wetness at epoch 1898·9 through to 1973·3, and thus have historically been out of phase with the continental interior. California records displayed evidence for two 180° phase switches in the past 100 years. The apparent reason for this is that California is near the edge of a fairly stable continental interior cell that has historically been dry at epochs; and when the dry cell waxes or wanes in areal extent, frequent 180° phase switches are produced in areas adjacent to it. The phenomena described have been found in other regions of the USA, and in records of air temperature and air pressure world‐wide.