The Influence of Upstream Solar Wind on Thermospheric Flows at JupiterJapheth N. Yates, Nick Achilleos, Patrick Guio

Simulate how solar wind dynamic pressure affects: 1. magnetosphere-ionosphere coupling currents, 2. momentum balance of atmospheric flows, 3. System’s energy budget

Talk Outline

• Introductioni. Model description

ii. Plasma angular velocity profiles.

• Resultsi. M-I coupling currents

ii. Momentum balance and thermospheric flows

iii. Energy budget

• Conclusionsi. Conclusion

ii. Future work2

Introduction to model

• Coupled magnetosphere, auroral conductivity and thermosphere model (Nichols and Cowley 2004, Cowley et al 2005, Grodent and Gerard 2001, Smith and

Aylward 2008,9).• Used three magnetospheric

configurations : compressed (A), average (B) and expanded (C).

• Super-corotation of thermosphere.

• Both thermosphere and magnetosphere sub-corotate to a greater degree with decreasing solar wind dynamic pressure.

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Yates et al (submitted to PSS)

Results – Magnetosphere-ionosphere coupling currents

• FAC densities peak at main auroral oval.

• Increase in FACs and thus auroral intensity with decrease in solar wind pressure.

• Compressed case (A) is interesting.

• Model suggests auroral features at the open-closed field line boundary.

• Oval location depends on Iρ at disc boundary.

• Strong downward FAC due to large gradients in ΣP 4

Yates et al (submitted to PSS)

Results – Thermospheric momentum balance 1

• Low altitude: Momentum imbalance leads to poleward flow, advection arises to balance momentum which accelerates the polewards flow. 5

Yates et al (submitted to PSS)

Acceleration / advection seen by a comoving observer

Results – Thermospheric momentum balance 2

• High altitude: Momentum almost perfectly balanced, advection insignificant, thus flow is equatorwards.

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Yates et al (submitted to PSS)

Sub-corotational jet

Super-corotational jet

Results – Energy budget

• Atmospheric power is sum of Joule heating and ion drag (Smith et al. 2007).

• Power dissipated by Joule heating and ion drag increases by ~190% from case A to C.

• Power used to accelerate magnetosphere towards corotation decreases slightly from case A-C.

• Closed field atmospheric and magnetospheric power in Cowley et al. 2007 comparable (~80%) to compressed and average cases. 7

Yates et al (submitted to PSS)

Conclusions

• Both thermosphere and magnetosphere sub-corotate to a greater degree with decreasing solar wind dynamic pressure.

• Increase in auroral intensity with decrease in solar wind pressure.

• Advection and ion drag play an important role in balancing momentum in the lower altitudes of the thermosphere (near the auroral ionization peak).

• The power dissipated within the thermosphere by Joule heating and ion drag respectively increases by 190 % and 185 % between our compressed and expanded models.

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