Copyright © National Academy of Sciences. All rights reserved.
Solar and Space Physics: A Science for a Technological Society
270
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
In situ measurements of the solar wind plasma velocity distribution functions and electromagnetic
fluctuations permit us to identify the dominant kinetic physics responsible for the generation and dissipation of Alfvénic fluctuations and other types of solar wind turbulence (motivations M1 and M3). Progress
has been made in measuring and understanding the types of turbulent fluctuations in the solar wind and
the likely dissipation mechanisms, but important questions remain. Observations from spacecraft—such as
Cluster, Wind, and ACE—and archival data from Helios have been used to probe the power in fluctuations
perpendicular and parallel to the local magnetic field as a function of scale and have demonstrated that
these fluctuations are highly anisotropic. Higher time-resolution measurements have allowed researchers to
trace the evolution of the turbulent cascade and dissipation past ion kinetic scales toward electron scales.
More work is needed to determine the relative fraction of fluctuations dissipated by ions and electrons
and to distinguish between different mechanisms for dissipation, such as ion-cyclotron resonance, kinetic
Alfvén waves, or the formation of small-scale current sheets. It is also unclear where broadband Alfvénic
fluctuations and other types of solar wind turbulence, such as 1/f noise, originate, either in the corona
or during propagation in the inner heliosphere. Further theoretical work and joint analysis of solar wind
plasma and electromagnetic fields will allow a determination of whether nonlinear plasma physics can
explain the highly nonadiabatic expansion of the solar wind.
FIGURE 10.5 Recent improvements in the accuracy and precision of measurements of total solar irradiance have resolved
several basic issues. The upper panel shows the original discordant measurements before recalibration. SOURCE: G. Kopp
and J. Lean, A new, lower value of total solar irradiance: Evidence and climate significance, Geophysical Research Letters
38(1):L01706, doi:10.1029/2010GL04577, 2011. Copyright 2011 American Geophysical Union. Reproduced by permission
of American Geophysical Union.
TSI corrected
Total Solar Irradiance Observations
Figure 10-5
Solar and Space Physics: A Science for a Technological Society
270
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
In situ measurements of the solar wind plasma velocity distribution functions and electromagnetic
fluctuations permit us to identify the dominant kinetic physics responsible for the generation and dissipation of Alfvénic fluctuations and other types of solar wind turbulence (motivations M1 and M3). Progress
has been made in measuring and understanding the types of turbulent fluctuations in the solar wind and
the likely dissipation mechanisms, but important questions remain. Observations from spacecraft—such as
Cluster, Wind, and ACE—and archival data from Helios have been used to probe the power in fluctuations
perpendicular and parallel to the local magnetic field as a function of scale and have demonstrated that
these fluctuations are highly anisotropic. Higher time-resolution measurements have allowed researchers to
trace the evolution of the turbulent cascade and dissipation past ion kinetic scales toward electron scales.
More work is needed to determine the relative fraction of fluctuations dissipated by ions and electrons
and to distinguish between different mechanisms for dissipation, such as ion-cyclotron resonance, kinetic
Alfvén waves, or the formation of small-scale current sheets. It is also unclear where broadband Alfvénic
fluctuations and other types of solar wind turbulence, such as 1/f noise, originate, either in the corona
or during propagation in the inner heliosphere. Further theoretical work and joint analysis of solar wind
plasma and electromagnetic fields will allow a determination of whether nonlinear plasma physics can
explain the highly nonadiabatic expansion of the solar wind.
FIGURE 10.5 Recent improvements in the accuracy and precision of measurements of total solar irradiance have resolved
several basic issues. The upper panel shows the original discordant measurements before recalibration. SOURCE: G. Kopp
and J. Lean, A new, lower value of total solar irradiance: Evidence and climate significance, Geophysical Research Letters
38(1):L01706, doi:10.1029/2010GL04577, 2011. Copyright 2011 American Geophysical Union. Reproduced by permission
of American Geophysical Union.
TSI corrected
Total Solar Irradiance Observations
Figure 10-5