Lecturer: Prof. Leon Ofman
Affiliation: NASA/Goddard Space Flight Center
and Catholic University of America
Abstract:
The Sun is a variable star with well-
documented activity cycle that manifests
itself most notably in photospheric
magnetic field (sunspots) and in related
phenomena. Coronal Mass Ejections
(CMEs) are the most important variable
components of solar activity that determine
space weather conditions and affect the
Earth through geomagnetic storms. These
ejections occur due to the accumulation of
magnetic flux, and related plasma
instabilities that lead to sudden acceleration,
shock formation, and release of magnetic
energy through magnetic reconnection.
CMEs carry solar magnetized plasma with
typical total mass of 10^12 kg at typical
speeds of ~500 - 1000 km/s into the
interplanetary space and produce energetic
particles. During maxima of solar activity
CMEs can occur several times per day, but
during minima only 1 - 2 CMEs occur per
week. Since CMEs erupt in all possible
directions - only a fraction is directed
toward the Earth causing geomagnetic
storms (i.e., geoeffective CMEs). Another
important aspect of solar activity is the
solar wind - a constant stream of
magnetized plasma that shapes the Earth's
Magnetosphere and expands to the outer
limits of the heliosphere. The solar wind
forms the background plasma in which
CMEs are propagating. The goal of Space
Weather research is to characterize the
plasma conditions and the energetic particle
flux in the heliosphere, and predict through
physics-based modeling the effects of solar
activity on Space Weather conditions. In
particular the likelihood of certain active
regions to form CMEs and the
determination of the geoffectiveness of
CMEs are important goals. Progress
towards these goals is achieved by
combining data from multiple satellite
observations, such as SDO, the twin
STEREO spacecraft, and early warning
from satellites between the Sun and the
Earth at L1 such as GOES, ACE, and Wind,
with global computer modeling.
Magnetospheric satellites, and earth based
stations measure the final effects of space
weather on the near-Earth environment.
However, important physical processes that
play a role in determining space weathered,
such as plasma instabilities, MHD
turbulence, waves, and kinetic dissipation
processes are not well understood and are
not fully addressed (or included
empirically) in global models.
I will discuss the physics of space weather
and the observationally guided theoretical
modeling effort under way aimed at
studying the details of the plasma physics
important for understanding space weather.