Responses of the electron radiation belt to high speed streams (Invited)

Details Responses of the electron radiation belt to high speed streams (Invited) Responses of the electron radiation belt to high speed streams (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm24a..06m&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM24A-06

Physics

[2730] Magnetospheric Physics / Magnetosphere: Inner, [2774] Magnetospheric Physics / Radiation Belts, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions

Scientific paper

High-speed solar wind streams (HSS), which have their origins in the outflow from coronal holes, form a large-scale repeatable driver for Earth’s magnetosphere and the parts of geospace coupled to it. HSS are interesting not only owing to their recurrent nature, but also owing to their wide-ranging effects in the geospace environment. Though they tend to produce relatively small geomagnetic storm disturbances they are the major contributor to adverse space weather during the declining phase of the solar cycle. However, in some cases, they can drive responses as severe as those during large storms near solar maximum. Thus, HSS provide the opportunity to study repeatable activity that is not only at the most extreme end of magnetospheric responses to solar wind driving, but spans a range of response levels. The effects of these HSS are seen across geospace, specially in the radiation belts. The Global Positioning System constellation now has 10 satellites (over 5 orbital planes) equipped with Combined X-Ray Dosimeters (CXDs), and due to its inclined, circular orbit (radius ~ 4 Re) is capable of sampling from L-values of 4 outward to beyond the region of trapped particles. The data density afforded by this constellation of CXDs gives good spatial and temporal coverage of the electron radiation belt. Predicting losses or enhancements of relativistic electron fluxes during stormtime has proven difficult, with only ~50% of Dst storms showing a net increase in fluxes and about 20% showing a net decrease. Under high-speed stream driving the predictability of net flux increases is enhanced by the Russell-McPherron effect but substantial variability is still observed. We present recent observations using the constellation of CXD instruments showing that dropouts extending to L*~4 are a consistent response to high-speed streams, irrespective of whether the stream drives a geomagnetic storm. Case studies show that these dropouts can occur on timescales of less than 3 hrs and recovery to pre-event count levels can take in excess of two weeks. We also show preliminary results of a statistical study of a set of prolonged electron dropouts observed with GPS and discuss how these different statistical and individual studies inform our understanding of the processes driving variability in the outer electron radiation belt.

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