Southern Cosmic Ray Anisotropies

Compared to northern hemisphere data, the quantity of anisotropy information in the south is very sparse. It is only in the half decade energy range above eV that the total data set is large enough to be useful for comparison with that from the north. We have taken those southern data (Farley and Storey 1954, Chapman and Ryder 1957, Farley and Storey 1957, Escobar et al. 1960, Bird et al.\ 1989) and derived combined first and second harmonic anisotropies in the same way that we did for the north (Clay et al. 1997a,b). This gives us values of amplitude and phase of (0.33%, 19.7hrs) for the first harmonic and (0.09%, 1.2hrs) for the second harmonic (see Table 1). We can then estimate how the cosmic ray intensity varies over the southern sky in right ascension by combining these data as shown in Figure 1. It is important to include the second harmonic even though its data are of limited statistical significance since it defines the difference in flow between the north and the south which is not possible with the first harmonic alone. The latter would be the same in both the north and the south for simple diffusive flow. Figure 1 also shows the corresponding result which we found for the northern data (Clay et al. 1997b).

Table 1: First and second harmonics of the cosmic ray anisotropy in the energy range eV to eV. These were derived by combining all available data.

	First Harmonic		Second Harmonic
	Ampl. (%)	Phase (h)	Ampl. (%)	Phase (h)
Northern Latitudes
Southern Latitudes

 
Figure 1: Intensity distribution obtained by combining the first and second harmonics of the anisotropy from Table 1. The solid line is the result for the northern hemisphere data and the broken line is the result for the southern hemisphere data.

© Copyright Astronomical Society of Australia 1997