Correlated changes in sunspot numbers and in corn and wheat yields


P. Bognár, Cs. Ferencz, Gy. Tarcsai

ABSTRACT

Time series of corn (Zea Mays) and wheat average yields from various countries of the world (including USA, Canada, Australia, Argentina and several countries of smaller area) exhibit periodicities which are similar in length and phase to those revealed by sunspot number studies. The various cycles in the sunspot number and yield time series were analyzed independently of each other, by means of a recursive parameter estimation technique. The longest yield time series used by us was that of the US corn covering the years between 1886 and 1988. Cycles with periods of 50-70 years were found in the yield data of several large crop producing countries. In particular, the 60 year long USA and Canada corn and wheat yield cycles were almost in the same phase as the respective sunspot cycle. In the lack of long enough yield time series, longer cycles, which are present in the solar data, could not be analyzed and compared. Going to shorter cycles, the 22 year magnetic sunspot cycle (which is present only in the sunspot polarity data and not in the sunspot number data) had its counterpart in some of the yield data (e.g. US corn), but could not be established very reliably. On the contrary, a roughly 11 year period could be identified on almost all yield data sets. Periods shorter than 11 years were found both in the solar and yield data with no apparent relationships between them.