Vikas  Sonwalkar

Observations, Simulations, and Modeling of Space Plasma Waves: A Perspective on Space Weather

The Earth’s upper atmosphere, comprising of the thermosphere, ionosphere and magnetosphere, is a highly dynamic and complex system.  It contains cold and hot plasma that is strongly influenced by the geomagnetic field.  Electromagnetic fields permeate throughout the upper atmosphere. Interactions between the sun, solar wind, and upper atmosphere lead to adverse conditions in the Earth’s space environment that may cause disruption of satellite operations, communications, navigation, and electric power grid.  In general, the term space weather is used to refer to conditions on the sun, in the solar wind and in the upper atmosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health.  Space weather monitoring and forecasting is an important scientific and technological challenge facing the global community of space scientists.

The Earth's upper atmosphere supports a wide variety of plasma wave phenomena in the frequency range extending from a few hertz to a few megahertz.  The term plasma wave is used to denote a wave that is either generated within the ionospheric/magnetospheric plasma or which has its characteristics significantly modified by the ionospheric/magnetospheric plasma.  Most of the plasma waves are generated by the conversion of free energy residing within the space plasma into wave  energy through a variety of plasma-wave processes.   Significant contributions to plasma waves observed in space are also made by worldwide lightning activity and ground transmitters, particularly those operating below 100 kHz.  Plasma waves are important partly because they influence the behavior of the ionosphere and magnetosphere and partly because we use them as experimental tools in our investigations of the upper atmosphere.  Potentially, plasma waves could serve as one of the key indicators of space weather.

This lecture presents a review of the advances made in the last fifty years in the space-borne and ground-based observations and the theoretical interpretations of plasma waves. 

We shall find that many important questions, particularly those concerning the generation mechanisms of plasma waves, remain unanswered.  The lecture explores the relationship between plasma waves and other space weather indicators such as geomagnetic storms.   The lecture concludes with a discussion of how ground-based and space-borne plasma wave observations coupled with simulations and modeling can be used to monitor and predict space weather.