We suggest that B is a more fundamental parameter than V.

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[1] The observed modulation of galactic cosmic ray (GCR) intensity, on time and spatial scales, contains information regarding their transport in the heliosphere. One way to extract crucial information from the data is to study the rigidity dependence of modulation. A methodology is described to study the rigidity dependence of the short-term variations in galactic cosmic ray intensity Earth, in terms of the median rigidity of detector response (R m ) to cosmic ray spectrum. We define R m as the rigidity below which lies 50% of detector counting rate. For neutron monitors (NMs), it is easily calculated from the latitude survey obtained at sea level and higher elevations. We compute R m values for some NM sites; solar cycle dependence for them is shown to be small. Their practical utility is demonstrated in a study of transient cosmic ray solar modulation (Forbush decreases (FDs)), using data published in the literature. We plot the rigidity dependence of the amplitudes of three large Forbush decreases that occurred during the declining phase of three solar cycles (19, 20, and 21). We show that the Forbush decrease amplitude varies inversely with R m over a large range (1 to 300 GV) of GCR rigidities. Thereby, we rule out the existence of a ''transition rigidity'' suggested by Jokipii even for a short-term modulation (large Forbush decreases). We speculate that the force field model may be applicable to large Forbush decreases.

We have used neutron monitor data obtained at Deep River and Huancayo as well as the vertical underground muon telescope data obtained at Embudo to compute the cosmic ray transverse gradient (G,) for the 1965 to 1990 period. The computed mean value of G0, for a given qA epoch, changes sign with the change in the solar magnetic polarity in accordance with the predictions of some contemporary hypotheses. Also, we find that the magnitude of G0 undergoes a significant time variation during a given polarity epoch. It has the largest value near the solar polar field reversal epoch boundaries, when magnetic polarity in the solar northern hemisphere is positive (qA >0). For each of the three solar polar field reversals, the change in the magnitude of G0 is steeper across the epoch boundaries. There is a good correlation between G0 and the tilt angle of the heliospherie neutral current sheet (HNCS). Our results are in agreement with the reported piecemeal measurements of the latitudinal gradient made by spacecrafts, at different times, at lower primary energies, at far off distances from Earth's orbit. As such, their global significance is appreciable. Even so, it is not dear yet how these findings reflect upon the drift hypothesis in its present form. However, they do affirm the important role played by the tilt angle of HNCS in the modulation processes. 23,515 23,516 AHLUWAL•: BRIEF REPORT of the heliospheric current sheet tilt: 1992-1996, Geophys. Res. Lett., 20, 161-164, 1993. Thambyahpillai, T., and H. Elliot, Worldwide changes in the phase of the cosmic ray solar daily variation, Nature, 171, 918-920 1953.