Saturday, September 22, 2007


The inversion modulation of the heliosphere magnetic field and Cosmic radiation

Plasma populations are embedded in a back ground neutral gas throughout the solar system, from the solar transition region, to planetary upper atmospheres, to the heliosphere’s interface with the interstellar medium. These populations transfer energy and momentum through multi-scale, nonlinear interactions which act to redistribute the bulk flows that, in turn, feed energy back into the original coupling system. For example, the upper atmospheres of planets, including Earth, are dramatically affected by energetic inputs originating at the Sun in the form of photons, particles, and fields.

How ever, there are many pathways by which that solar energy is transformed and redistributed throughout the atmosphere until the energy is ultimately re-radiated to space. Connected with these processes is much of the inherent variability of the atmosphere over daily to millennial time scales. The lower atmosphere is periodically pumped and heated, giving rise to a spectrum of small scale gravity waves and longer-period oscillations. These waves can propagate into the mesosphere and thermosphere depositing momentum. The atmospheric mean circulation is thereby modified, resulting in changes to the temperature structure and redistribution of radiation absorbers and emitters. The mean wind and temperature structures in turn influence the propagation of the waves and the manner in which they couple the lower and upper atmosphere.

Similar processes are also key to understanding the upper atmosphere weather and climate on Mars and Venus. The ionospheric electron density distribution depends on thermospheric composition and winds, together with electric fields that can be generated within the I-T system or im posed from the magnetosphere. In turn, the ionospheric plasma can inhibit or accelerate thermospheric winds that produce electric fields via an electrodynamic interaction. The interactions and feedback mechanisms remain a mystery due to a lack of simultaneous measurements of all the parameters that describe the fully coupled system. These interactions can occur on a global scale, but can also pro duce mesoscale structures, such as high latitude thermospheric density cells that affect satellite orbits, or midlatitude electron density enhancements that disrupt aircraft navigation systems being implemented by the FAA.

In addition, smaller scale structures cause ionospheric irregularities that degrade communication system performance. Turbulence is another example of a very important multi-scale, nonlinear process that transports particles and fields effectively, but is not well understood. Numerical simulations and laboratory experiments demonstrate that, in the presence of rotation or magnetic fields, turbulent motions create small-scale and large scale dissipative structures. In addition, electrodynamic and mass coupling along magnetic fields are fundamental physical processes that cut across many disciplines of space science. The interface between the heliosphere and the interstellar medium is a coupling region about which we are just beginning to learn. Finally, mass loading through ionization and charge exchange is a phenomenon of broad interest from planetary and atmospheric erosion to energetic particle creation and loss.

In an interesting paper we see shown that the heliomagnetic field (HMF) near Earth increased steadily over the past 580 years, exhibiting the strongest fields during the last 50 years. The estimates indicate that the HMF at sunspot minimum has exhibited steadily increasing “floors” between the several Grand Minima, similar to the one evident in satellite data since 1965.

This helps understand the step like changes in the satellite record temperature record.

Changes in the cosmic ray and heliomagnetic components of space climate, 1428–2005, including the variable occurrence of solar energetic particle events
Ken McCracken ASR 2007

The cosmic-ray record has been used to study the variations in the space climate, 1428–2005. Inversion of the data shows that the heliomagnetic field (HMF) near Earth increased steadily over the past 580 years, exhibiting the strongest fields during the last 50 years. The estimates indicate that the HMF at sunspot minimum has exhibited steadily increasing “floors” between the several Grand Minima, similar to the one evident in satellite data since 1965. The cosmogenic data for the past 10,000 years contain an 2300 year periodicity, and it is proposed that the increasing HMF strength since the 15th century represents the first quarter cycle of a 2300 year quasi-periodicity. It is concluded that the 11-year average total magnetic flux of the Sun has increased by a factor of 4.5 over the past 580 years. It is speculated that this could indicate a factor of 9 variation over the 2300 year cycle. The cosmic ray data and theoretical considerations show that the 22-year periodicity in the cosmic radiation flux at Earth was more dominant at times of low solar activity, compared to the present epoch. Comparison of the occurrence of solar energetic particle events, and the estimated HMF, shows that a substantial decrease in the size and frequency of occurrence of GLE (ground level enhancements) after 1958 coincides with a substantial increase in the HMF. This is consistent with the conclusion of [McCracken, K.G., Dreschhoff, G.A.M., Smart, D.F., et al. A study of the occurrence of large-fluence solar proton events and the strength of the interplanetary magnetic field. Solar Phys., 224, 359–372, 2004.] that lower values of the solar magnetic fields result in increased values of the Alfven Mach number, and thence to more efficient acceleration of solar cosmic rays prior to 1958. It is suggested that the variability of the solar and heliospheric magnetic fields may have introduced long term changes into the nature of geomagnetic phenomena; particle acceleration throughout the heliosphere and heliosheath; and possibly to the luminosity of the facular network of the Sun.

The observed long term modulation of the cosmic radiation has led to the conclusion that the heliospheric magnetic field, and hence the open magnetic field of the Sun, has varied by a factor of 4.5 over the past 600 years. Section 5.4 has shown that this predicts long term changes in the acceleration of cosmic rays by the Sun, in accord with observation. The magnetic field has a pervasive influence on the physics of the solar wind, and the corona, and other long term effects can be expected. Several are suggested in the following for theoretical and experimental investigation in the future.
–Modulation of the interaction of the solar wind with the geomagnetic field, leading to long term changes in the nature of geomagnetic disturbances, and the efficiency of acceleration of auroral electrons.
–Substantial changes in the Alfven velocities leading to long-term changes in the acceleration of ions and electrons in shock waves throughout the heliosphere, at the termination shock, and in the heliosheath.

Lean et al. (1995) discussed the role of the photon emission from the network of faculae that normally covers the Sun, even during the sunspot minima in contemporary times. They speculated that the emission from the faculae would track the overall level of solar activity, being weaker during periods such as the Spoerer and Maunder Minima, and greater during periods similar to the present epoch. The faculae are magnetic phenomena, and this proposition appears plausible in view of the factor of 4.5 change of the solar magnetic flux inferred. Clearly, it is desirable to investigate the quantitative changes in the facular emission, and consequently the total solar irradiance of the Sun, as a consequence of this 4.5-fold change in the magnetic fields of the Sun.

The cosmic ray record has been used to investigate the variability of a number of the components of the space weather. Overall, this study shows that there have been large changes in a number of components of the “space climate” over the past 600 years and it further concludes that the space climate will exhibit an 2300 year periodicity.
The inversion process of Caballero-Lopez et al. (2004) has shown that the HMF increased steadily over the past 580 years, exhibiting the strongest fields during the last 50 years.

The inversion shows that the strength of the HMF at sunspot minimum was significantly less between 1901and 1944, compared to 1954, onwards. The estimates indicate that the HMF near Earth increased from an average of 2.5 nT for the sunspot minima in 1889 and 1901 (the Gleissberg minimum) to 3.5 nT averaged over the sunspot minimum of 1911–1944. Between 1944 and 1954, it increased to 5.2 nT, and the satellite and cosmic ray data show that the field at sunspot minimum remained at 5.2 nT between 1965 and 1996. Together, the cosmic ray and direct satellite measurements show that there was a step-wise and long lived increase in the strength of the HMF between 1944 and 1954.

The cosmogenic data for the past 10,000 years contain an 2300 year periodicity, and it is speculated that the increasing heliomagnetic field strength since the 15th century represents the first quarter cycle of a 2300 year periodicity in the HMF.
On the basis of these estimates, it is concluded that the total magnetic flux of the Sun has increased by a factor of 4.5 over the past 580 years. It is speculated that this could indicate a factor of 9 variation in solar magnetic flux over a 2300 year cycle.

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