Polar Cap Convection Structures: Relations to High Speed Streams and Plasma Sheet Dynamics

Details Polar Cap Convection Structures: Relations to High Speed Streams and Plasma Sheet Dynamics Polar Cap Convection Structures: Relations to High Speed Streams and Plasma Sheet Dynamics

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm32a..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM32A-01

Physics

[2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2475] Ionosphere / Polar Cap Ionosphere, [2764] Magnetospheric Physics / Plasma Sheet, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions

Scientific paper

The orientation and magnitude of the interplanetary magnetic field (IMF) and solar wind dynamic pressure are well known to affect the strength of convection. However, radar measurements of high-latitude ionospheric convection show evidence that ULF power in the IMF has an additional substantial effect on the strength of convection within the polar caps, and on the nightside within both the aurora ionosphere and the plasma sheet. Convection flows during periods of large north-south IMF fluctuations are observed to be as strong as for steady and large southward IMF periods, and substantially enhanced convection is observed for northward IMF intervals when the IMF exhibits high ULF power. Since ULF power is particularly high during high-speed solar wind streams (HSS), these effects are particularly important and likely a major contributor to disturbances within the magnetosphere-ionosphere-thermosphere system during HSS. However, observations during periods of Alfvénic magnetic fluctuations without high-speed solar wind indicate that the enhanced flows are at least in part directly due to the Alfvénic magnetic fluctuations and are not solely due to the high-speed solar wind. We furthermore find that the enhanced polar-cap convection driven by the ULF power in the solar wind is highly structured in time, and is associated with many substorms, including during periods of northward IMF. A possible cause of the connection to convection and disturbances within the plasma sheet is indicated by recent radar observations of flows within the polar cap. The observations suggest that meso-scale flow channels from deep within the region of open polar cap field lines may cross the nightside polar cap boundary into the closed field line region and contribute to the triggering of equatorward (earthward) meso-scale flows across the ionospheric (equatorial) end of plasma sheet fields lines and lead to PBIs and streamers. This includes the streamers that have been postulated to bring new plasma equatorward (earthward) and lead to substorm onset. Such a connection offers an explanation for the enhanced convection, plasma pressures, and substorm activity that has been observed within the plasma sheet during periods of enhanced ULF fluctuations, including during HSS.

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