Comparison of AMIE‐modeled and Sondrestrom‐measured Joule heating: A study in model resolution and electric field–conductivity correlation

Abstract

[1] Joule heating by high-latitude ionospheric electric fields is thought to be underestimated by models, and it has been conjectured that the source of the underestimation is ''electric field variability,'' which is often defined as electric field structure below the resolution of the model. We investigate this and related issues by (1) comparing the Joule heating measured by the Sondrestrom incoherent scatter radar during a 40 h period containing a storm with that modeled by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure and (2) employing an magnetosphere-ionosphere (M-I) coupling model to analyze the theoretical dependence of Joule heating estimates on the spatial resolution of the inputs. We find that as compared with Sondrestrom measurements, a much larger contribution from correlation between conductance and squared electric field (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. Surprisingly, the M-I coupling model finds that coarse spatial resolution causes overestimation of the Joule heating rate, owing to the finding that the subresolution-scale spatial 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 electric field, which overcompensates for the reduced mean-squared electric field. Therefore, the difference in the Sondrestrom and AMIE correlation contributions might be explained by a difference in spatial resolution.

Density Perturbations in the Upper Atmosphere Caused by the Dissipation of Solar Wind Energy

“…Some of the more recent publications include those by Johnson and Heelis (2005), Zhang et al (2005), Vasyliunas and Song (2005), McHarg et al (2005), Hernandez et al (2005), Knipp et al (2005), Weimer (2005, Palmroth et al (2006), Rosenquist et al (2006, Wilson et al (2006), Fang et al (2007a, Deng and Ridley (2007), Rae et al (2007), Fujiwara et al (2007), , Hardy et al (2008), Deng et al (2008), Golovchanskaya (2008, Emery et al (2008), Matsuo and Richmond (2008), Cosgrove et al (2009), Aikio andSelkälä (2009), Burke et al (2010a, b); and references therein.…”

Predicting global average thermospheric temperature changes resulting from auroral heating

“…Most ignore the effects of variable conductivity. Cosgrove et al [2009] found that an anticorrelation between spatial fluctuations in conductance and squared electric field may partially compensate for the effects of the field variability.…”

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“…The computational efficiency of the empirical models makes them favorable in space weather forecasting applications; however, they cannot model the short‐lived, small‐scale perturbations, that is, PI and MI FACs, that occur during the interaction of solar wind with the Earth's magnetosphere (Boudouridis et al, ; Deng & Ridley, ; Weimer, ). Various studies (Codrescu et al, ; Cosgrove et al, ) have shown that the majority of Joule heating rate comes from such transient, localized electric field perturbations making the MHD‐driven electrodynamics a better tool to investigate the coupling between magnetosphere‐ionosphere‐thermosphere systems.…”