  The annual temperature cycle of the earth closely follows the annual cycle of
solar flux. At temperate latitudes, both driving and response cycles are well
described by a strong annual sinusoidal component and a non-vanishing
semiannual component. A new analysis of historical weather station records in
the United States determines persistent annual and semiannual variation with
high precision. Historical annual temperature ranges are consistent with prior
studies. Semiannual temperature cycles were much stronger than expected based
on the semiannual solar driving. Instead, these cycles were consistent with
multiplicative effects of two annual cycles. Our methods provide a quantitative
window into the climate's nonlinear response to solar driving, which is of
potential value in testing climate models.
