Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa51a1551c&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SA51A-1551
Physics
2407 Auroral Ionosphere (2704), 2411 Electric Fields (2712), 2431 Ionosphere/Magnetosphere Interactions (2736), 2447 Modeling And Forecasting
Scientific paper
Joule heating by high-latitude ionospheric electric fields is underestimated by global models, and the source of the underestimation is generally thought to be "electric field variability," which is often interpreted to mean structure in the electric field below the resolution of the electric field model. We investigate this and related issues by (1) comparing the Joule heating measured by the Sondrestrom incoherent scatter radar during a 40 hour period containing a storm with the Joule heating modeled by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure; and (2) employing an M-I coupling model to analyze the dependence of Joule heating estimates on the spatial-resolution of the inputs, to facilitate the AMIE and Sondrestrom comparison. We find that, as compared with Sondrestrom measurements, a much larger contribution from correlation between conductance and squared-electric-field (which is positive for AMIE, and negative for Sondrestrom) partially compensates for a much smaller mean-squared electric field, such that the overall average Joule heating rate modeled by AMIE is 29% less than measured by Sondrestrom. The underestimation of the mean-squared electric field was not associated with small-temporal-scale variability. Using the MI coupling model it is shown that one way to explain the correlation-contribution is by a difference in spatial resolution, although an alternative explanation is found in effects related to AMIE's reliance on magnetometers. Surprisingly, the M-I coupling model also finds that coarse spatial resolution causes overestimation of the Joule heating rate, due to the finding that the sub-resolution-scale spacial-fluctuations in conductance and squared-electric-field are anticorrelated. When comparing estimates of the total Joule heating over a period of time, the increased Joule heating arises as a larger contribution from temporal-correlation between conductance and squared-squared-electric-field, which overcompensates for the reduced mean-squared electric field.
Bahcivan Hasan
Cosgrove Russell B.
Heinselman Craig
Lu Gang
Matsuo Takeshi
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