Australian Cosmic Ray Modulation Research
M. L. Duldig , PASA, 18 (1), in press.
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Looking to the Future

In Section 4 some of the more recent instruments to be commissioned have been described. The neutron monitor latitude surveys will continue at least until the next solar minimum and should allow us to deduce the best neutron monitor yield functions to date. We should also obtain a much better assessment of the cosmic ray spectrum in the GV to tens of GV range where it is most influenced by solar modulation. The improved yield functions will also improve our GLE modelling and may make reconciliation between satellite and ground based measurements easier and more robust. The underground and surface muon telescopes in Tasmania will continue to operate in the short term. The surface telescopes at the University of Tasmania are the most threatened due to the retirement of the last staff member directly associated with the experiments and the pressures to use the space for other activities. The Mawson telescopes will continue to operate for the foreseeable future. Research with these instruments will continue to focus on modulation parameters and their variation throughout the solar cycle, variations in the structure of the Tail-In and Loss-Cone anisotropies with the solar cycle and studies of transient events such as Forbush decreases. There has been some evidence already from these instruments of precursor signatures to Forbush decreases and major geomagnetic storms (Munakata et al. 2000). The Australian neutron monitor network is in the process of being rationalized. With the last retirement mentioned above the Australian Antarctic Division has taken over responsibility for this research. Construction of a new neutron monitor facility at the Division's Kingston headquarters complex 20 km south of Hobart has been completed. The neutron monitor formerly at Brisbane airport has been relocated to this site and the Darwin monitor will be similarly relocated in October and November of 2000. The resulting monitor at Kingston will be of international standard size (18 counters) and the higher count rate will be valuable in analyses of both anisotropies and transient phenomena. The Hobart and Mt Wellington monitors will operate in parallel with the Kingston monitor for up to a year to allow cross calibration so that the long term record can be effectively extended. After that time these two monitors will be dismantled. Twelve counters will be relocated to Mawson to increase that monitor to the international standard and the remaining counters will be used to construct a second mobile monitor for the latitude survey studies. The Mawson cosmic ray laboratory will be extended over 2001-2 to house the larger monitor. The Mawson monitor will also be incorporated into a new collaboration known as ``Space Ship Earth''. This collaboration involves the Bartol Research Institute, Delaware, USA, IZMIRAN (Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation) Moscow, Russia and the Australian Antarctic Division. The aim is to determine the three-dimensional cosmic ray anisotropy in real or near-real time through the use of a series of nine polar neutron monitors carefully chosen to have equatorial viewing directions with narrow longitudinal spread and separated by $\sim$20^o in longitude. Two further monitors will provide polar views. Figure 37 shows the network. This exciting project will allow real time study of the cosmic ray anisotropy for the first time and may be used for alerting services at times of geomagnetic storms or GLEs. Construction of the additional observatories in Canada and Russia has already commenced and it is expected that the system could be operational by 2002 although the real-time data transfers may not be finalized for a year or so after that.

Figure 37: Asymptotic viewing directions of the ``Space Ship Earth'' collaboration neutron monitors showing the narrow angle equatorial coverage and the polar views. Existing stations, filled circles, stations planned or under construction, open circles.

One aspect of cosmic ray modulation research that is only just beginning to open is the long term study of past cosmic ray variations. The Greenland and Antarctic ice cores hold both isotope and chemical records that may tell us a great deal about cosmic rays in the heliosphere over the last 100,000 years or so. Evidence of GLE chemical signatures in the ice cores is mounting though the results are marginally significant at present. The isotope record in the ice cores is much more robust and may allow us to study cosmic ray density variations controlled by solar cycle activity over many tens or even hundreds of cycles. It may be possible to see differences during periods like the Maunder minimum and possibly to investigate cosmic ray changes in relation to global climate changes. This latter concept has gained credibility in recent times with evidence of global cloud cover varying with cosmic ray density at the Earth. The mechanism proposed is that variations in cosmic ray density change the ionization in the atmosphere. This ionization is one of the significant sources of nucleation sites on which raindrops can form. Next Section: Conclusion
Title/Abstract Page: Australian Cosmic Ray Modulation
Previous Section: Sidereal Anisotropies
Contents Page: Volume 18, Number 1