E. S. Posmentier

Variations of solar coronal hole area and terrestrial lower tropospheric air temperature from 1979 to mid-1998: astronomical forcings of change in earth's climate?

Abstract The temperature anomaly of the terrestrial lower troposphere, inferred from the Microwave Sounding Unit (MSU) radiometers, is found to be inversely correlated with the area of the Sun covered by coronal holes. The correlation between the monthly time series of global tropospheric temperature anomaly and total coronal hole area from January 1979 to April 1998 has a Pearson coefficient of −0.46, which is different from zero at a 95% confidence level. Physical reasonings for the explained and unexplained parts of the correlation are discussed. The coronal hole area is a physical proxy for both the global-scale, 22-yr geometrical and shorter-term, dynamical components of the cosmic ray modulation, as well as the corpuscular emission of the Sun. Other solar parameters that may indicate a solar radiative effect on climate are also evaluated. It is concluded that variable fluxes either of solar charged particles or cosmic rays modulated by the solar wind, or both, may influence the terrestrial tropospheric temperature on timescale of months to years.

Comments on spectral analysis of core data

In a recent issue of Palaeogeography, Palaeoclimatology, Palaeoecology Schnitker (1982) suggested that f luctuations in benthic foraminiferal populations are rhythmic and occur with periodicities ranging from 350 to 5000 years. Schnitker speculated that these cycles are related to characteristic turnover times in deep ocean circulation. While Schnitker s final interpretat ion of North Atlantic paleo-oceanography may be valid we contend that it rests on a statistically weak foundat ion. In particular, we believe that Schnitker (1982) did no t use sufficient caution in assessing the effects of sample interval and temporal trends on spectral analysis. The highest f requency that can be resolved in any t ime-dependent data set is called the Nyquist f requency and is the reciprocal of twice the t ime interval between adjacent samples (Blackman and Tukey, 1958; Imbrie and Kipp, 1970). It is impor tant to note tha t in order to identify a spectral peak at the Nyquist f requency, it must be assumed that one-point peaks in the data are real. Ledbet ter and Ellwood (1976) have pointed out that many processes including random depositional events, sampling and analytical variations and (we add) stratigraphic problems including sporadic changes in sedimentation rate all lead to a lack of confidence in one-point peaks. They therefore suggest that a sample interval of 0.25 cycles per sample, rather than the 0.5 cycles per sample at the Nyquist f requency, is a more prudent sample interval for geologic data. We add that the unsmoothed spectral estimate at the Nyquist f requency has only one degree of f reedom, compared to two at all o ther frequencies. Fur thermore , the highest f requency that can be resolved in smoothed spectra is no t even as high as the Nyquist f requency. Schnitker (1982) analyzed two cores f rom the western North Atlantic. To place the down-core samples in a time framework he used the stratigraphy described in Balsam and Heusser (1976) and Schnitker (1979). The sedimentat ion rates in these cores are highly variable; in core V26--176 the rate varies f rom 11.2 to 37.4 cm per 1000 years, whereas in core GPC-5 it varies f rom 16.2 to 143.9 cm per 1000 years. Because of the wide variation in sedimenta t ion rates in these cores it is impor tant to know the shortest period that can be resolved between adjacent stratigraphic markers at Schnitker s