Cosmic Rays and Global Warming

In reference [1] a correlation was demonstrated for ’low clouds’ (<3.2 km in altitude) between the changes in CC (the CC anomaly), and CR count rate as measured by the Hunacayo neutron monitor (see figure 1 of reference [1]). The CC anomaly was derived from the ISCCP D2 analysis using the infrared data [3]. It was then implied in [1] that the CR variation caused that in the CC. Since this may not be the case if both effects are correlated to a third variable, it is prudent to look for further evidence of such a causal connection. The first problem that arises is that the correlation is absent in the data for two other atmospheric depths: ‘middle levels’ (3.2 -6.5 km) and ‘high levels’ (>6.5 km altitude). This result is surprising in view of the fact that the CR ionization (mainly from muons and electrons) increases with height. Specifically the rate of production of ions, in cm -3 s -1 , for the 3 levels is estimated to be: high, 130(50); middle, 30(13) and low, 4(3) where the values are for 60 • N (the equator). A possibility, and one needed by the proponents of the CR-CC causal connection, is that the efficiency of the conversion from CR ions to cloud droplets (presumably by way of aerosols) falls with increasing height above sea level. Such behaviour cannot be ruled out but seems rather ad hoc. The implication would be that even in the low region the efficiency in not 100% and, as will be shown, there are already problems in this respect. that could be produced by CR (muons) at the lowest level. With a rate of ions, of 4 cm -3 s -1 and assuming they all give ‘small ions’ the rate of production of small ions will be the same, giving, for a mean lifetime of 50 s [4] 200 cm -3 . To produce significant nucleation rates much larger ion densities than this were required [5]. Hence the ionisation rate in CR could be too small to produce significant numbers of water droplets such as would be necessary in a cloud.

It is well known that the magnitude of the CR time variation, due to the 11 year solar cycle, varies with latitude. More accurately, it is a function of the vertical rigidity cut-off (VRCO), the reason being the effect of the geomagnetic field deflecting away more low energy particles as the geomagnetic equator (highest VRCO) is approached. Since this variation falls with increasing primary CR energy, the solar modulation is most severe in the polar regions. Hence one would expect larger changes in CC in the polar regions than at the Equator. Furthermore it is known that there is a delay of 6-14 months between the decrease in the CR intensity and the increase in the sun spot (SS) number with even numbered solar cycles showing smaller delays than the odd numbered [7]. Note that the CR count rate is anticorrelated to the SS number. We have studied this effect in some detail by plotting the CC for different VRCO bands and the results are given in Figure 1. The smooth curves in figure 1 show the best fit of the CC anomaly to the mean daily SS number (inverted) with a linearly changing background. We observe the same dip in CC as seen in [1] between the years 1985 and 1995. However, the expected rise in amplitude of this dip with increasing VRCO is not apparent. Furthermore, the dip in CC seen in solar cycle 22 (peaking in 1990) is not evident in solar cycle 23 (peaking in 2000) except in the equatorial region (high VRCO) where the solar modulation is least. To investigate this effect further and to check that the above result was not due to a latitude dependent ’efficiency’ the CC was determined in three strips of latitude and the amplitude of the dip in solar cycle 22 was measured for each as a function of VRCO. This was achieved by fitting the SS number variation to the observed CC again with a linearly decreasing background. The delay between the onset of the dip in CC and that of the SS number was also a free parameter in the fit. Figure 2 (upper panel) shows that the amplitude of the dip appears to be constant with VRCO rather than changing in an analogous manner to the observed CR modulation [6]. The measured value of the delay between the onset of the dip and the change in SS number fluctuates randomly rather than concentrates around a fixed delay (expected to be -7 months for solar cycle 22). Hence there is an imperfect time correlation between the start of the dip and the change in the CR rate. Thus the data in figure 2 do not corroborate the claim of

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