Integration of Neutron Monitor Data with Spacecraft Observations: a Historical Perspective |
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Authors: | Mcdonald Frank B |
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Institution: | (1) Institute for Physical Science and Technology, University of Maryland, College Park, MD, 20742, U.S.A. |
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Abstract: | Beginning in the early 1950s, data from neutron monitors placed the taxonomy of cosmic ray temporal variations on a firm footing,
extended the observations of the Sun as a transient source of high energy particles and laid the foundation of our early concepts
of a heliosphere. The first major impact of the arrival of the Space Age in 1957 on our understanding of cosmic rays came
from spacecraft operating beyond the confines of our magnetosphere. These new observations showed that Forbush decreases were
caused by interplanetary disturbances and not by changes in the geomagnetic field; the existence of both the predicted solar
wind and interplanetary magnetic field was confirmed; the Sun was revealed as a frequent source of energetic ions and electrons
in the 10–100 MeV range; and a number of new, low-energy particle populations was discovered. Neutron monitor data were of
great value in interpreting many of these new results.
With the launch of IMP 6 in 1971, followed by a number of other spacecraft, long-term monitoring of low and medium energy
galactic and anomalous cosmic rays and solar and interplanetary energetic particles, and the interplanetary medium were available
on a continuous basis. Many synoptic studies have been carried out using both neutron monitor and space observations. The
data from the Pioneer 10/11 and Voyagers 1/2 deep space missions and the journey of Ulysses over the region of the solar poles have significantly extended our knowledge of the heliosphere and have provided enhanced
understanding of many effects that were first identified in the neutron monitor data.
Solar observations are a special area of space studies that has had great impact on interpreting results from neutron monitors,
in particular the identification of coronal holes as the source of high-speed solar wind streams and the recognition of the
importance of coronal mass ejections in producing interplanetary disturbances and accelerating solar energetic particles.
In the future, with the new emphasis on carefully intercalibrated networks of neutron monitors and the improved instrumentation
for space studies, these symbionic relations should prove to be even more productive in extending our understanding of the
acceleration and transport of energetic particles in our heliosphere.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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