The Influence of Plasma Density Irregularities on Whistler-Mode Wave Propagation 

V.S. Sonwalkar 


Whistler mode (W-mode) waves are profoundly affected by Field- Aligned Density
Irregularities (FAI) present in the magnetosphere. These irregu- larities,
present in all parts of the magnetosphere, occur at scale lengths ranging from a
few meters to several hundred kilometers and larger. Given the spatial sizes of
FAI and typical wavelength of W-mode waves found in the magnetosphere, it is
convenient to classify FAI into three broad categories: large scale FAI, large
scale FAI of duct-type, and small scale FAI. We discuss experimental results and
their interpretations which provide physical insight into the effects of FAI on
whistler (W) mode wave propagation. It appears that FAI, large or small scale,
influence the prop- agation of every kind of W-mode waves originating on the
ground or in space. There are two ways FAI can influence W-mode propagation.
First, they provide W-mode waves accessibility to regions otherwise not
reachable. This has made it possible for W-mode waves to probe remote regions of
the magnetosphere, rendering them as a powerful remote sensing tool. Second,
they modify the wave structure which may have important consequences for
radiation belt dynamics via wave-particle interac- tions. We conclude with a
discussion of outstanding questions that must be answered in order to determine
the importance of FAI in the propagation of W-mode waves and on the overall
dynamics of wave-particle interactions in the magnetosphere. Key words: Field
aligned irregularities, whistler propagation, ducting, plasma inhomogeneity,
ionosphere

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Lect. Notes Phys., 687, 141Ð191, 2006