Variation in Pedersen Conductance near Jupiter’s Main Emission Aurora: Comparison of Hubble Space Telescope and Galileo Measurements

We present the first large-scale statistical survey of the Jovian main emission (ME) to map auroral properties from their ionospheric locations out into the equatorial plane of the magnetosphere, where they are compared directly to in-situ spacecraft measurements. We use magnetosphere-ionosphere (MI) coupling theory to calculate currents from the auroral brightness as measured with the Hubble Space Telescope and from plasma flow speeds measured in-situ with the Galileo spacecraft. The effective Pedersen conductance of the ionosphere ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="ΣP*" display="inline"><m:mrow><m:mi mathvariant="normal">Σ</m:mi><m:msub><m:mi/><m:mi>P</m:mi></m:msub><m:msup><m:mi/><m:mo>*</m:mo></m:msup></m:mrow></m:math> ) remains a free parameter in this comparison. We first show that the field-aligned currents per radian of azimuth calculated from the auroral observations, found to be <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="I||=9.54+11.5-6.35" display="inline"><m:mrow><m:mi>I</m:mi><m:msub><m:mi/><m:mrow><m:mo stretchy="false">|</m:mo><m:mo stretchy="false">|</m:mo></m:mrow></m:msub><m:mo>=</m:mo><m:mn>9</m:mn><m:mo>.</m:mo><m:mn>5</m:mn><m:mn>4</m:mn><m:msup><m:mi/><m:mrow><m:mo>+</m:mo><m:mn>1</m:mn><m:mn>1</m:mn><m:mo>.</m:mo><m:mn>5</m:mn></m:mrow></m:msup><m:msub><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>6</m:mn><m:mo>.</m:mo><m:mn>3</m:mn><m:mn>5</m:mn></m:mrow></m:msub></m:mrow></m:math> MA rad and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="I||=10.64+11.1-6.11" display="inline"><m:mrow><m:mi>I</m:mi><m:msub><m:mi/><m:mrow><m:mo stretchy="false">|</m:mo><m:mo stretchy="false">|</m:mo></m:mrow></m:msub><m:mo>=</m:mo><m:mn>1</m:mn><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>6</m:mn><m:mn>4</m:mn><m:msup><m:mi/><m:mrow><m:mo>+</m:mo><m:mn>1</m:mn><m:mn>1</m:mn><m:mo>.</m:mo><m:mn>1</m:mn></m:mrow></m:msup><m:msub><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>6</m:mn><m:mo>.</m:mo><m:mn>1</m:mn><m:mn>1</m:mn></m:mrow></m:msub></m:mrow></m:math> MA rad in the north and south, respectively, are consistent with previous results. Then, we calculate the Pedersen conductance from the combined datasets, and find it ranges from <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="0.02<ΣP*<2.26" display="inline"><m:mrow><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>0</m:mn><m:mn>2</m:mn><m:mo><</m:mo><m:mi mathvariant="normal">Σ</m:mi><m:msub><m:mi/><m:mi>P</m:mi></m:msub><m:msup><m:mi/><m:mo>*</m:mo></m:msup><m:mo><</m:mo><m:mn>2</m:mn><m:mo>.</m:mo><m:mn>2</m:mn><m:mn>6</m:mn></m:mrow></m:math> mho overall with averages of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="0.14+0.31-0.08" display="inline"><m:mrow><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>1</m:mn><m:mn>4</m:mn><m:msup><m:mi/><m:mrow><m:mo>+</m:mo><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>3</m:mn><m:mn>1</m:mn></m:mrow></m:msup><m:msub><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>0</m:mn><m:mn>8</m:mn></m:mrow></m:msub></m:mrow></m:math> mho in the north and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="0.14+0.26-0.09" display="inline"><m:mrow><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>1</m:mn><m:mn>4</m:mn><m:msup><m:mi/><m:mrow><m:mo>+</m:mo><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>2</m:mn><m:mn>6</m:mn></m:mrow></m:msup><m:msub><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>0</m:mn><m:mn>9</m:mn></m:mrow></m:msub></m:mrow></m:math> mho in the south. Taking the currents and effective Pedersen conductance together, we find that the average ME intensity and plasma flow speed in the middle magnetosphere (10-30 R) R) are broadly consistent with one another under MI coupling theory. We find evidence for peaks in the distribution of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="ΣP*" display="inline"><m:mrow><m:mi mathvariant="normal">Σ</m:mi><m:msub><m:mi/><m:mi>P</m:mi></m:msub><m:msup><m:mi/><m:mo>*</m:mo></m:msup></m:mrow></m:math> near 7, 12, and 14 hours magnetic local time (MLT). This variation in Pedersen conductance with MLT may indicate the importance of conductance in modulating MLT- and local-time-asymmetries in the ME, including the apparent subcorotation of some auroral features within the ME.