EGU2015 ST 3 1 Open Session on the

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EGU-2015 ST 3. 1, Open Session on the Ionosphere and Thermosphere Low-latitude field-aligned and

EGU-2015 ST 3. 1, Open Session on the Ionosphere and Thermosphere Low-latitude field-aligned and radial currents deduced by Swarm Hermann Lühr, Guram Kervalishvili, Jan Rauberg, Ingo Michaelis and the CAT-2 Team Deutsches Geo. Forschungs. Zentrum GFZ, Potsdam, Germany Vienna, 13 April 2015 No. 1

Motivation In the ionospheric F-region there are certain types of currents to be expected.

Motivation In the ionospheric F-region there are certain types of currents to be expected. For example, the inter-hemispheric field -aligned currents (IHFAC) which balance the potential differences between the Sq systems in the two hemispheres. Based on ground observations predictions have been made. There is a major current expected flowing from winter to summer around noon. (Fukushima, 1979) The Swarm constellation provides for the first time the possibility to record these currents reliably. No. 2

Measuring field-aligned currents with the Swarm constellation Using Ampère‘s integral in discrete form 2

Measuring field-aligned currents with the Swarm constellation Using Ampère‘s integral in discrete form 2 dℓ 1 1 Sw. A 3 dℓ 4 4 Sw. C Integration area: Along-track variation, BX, is derived from two subsequent measurements dt=5 sec dl 1, 3=38 km Cross-track separation is 1. 4° in longitude. Vertical current, j. Z, is projected on the field direction, to get FAC. (Ritter et al. , 2013, EPS) No. 3

Local time dependence of inter-hemispheric field-aligned currents We find the main current, as expected

Local time dependence of inter-hemispheric field-aligned currents We find the main current, as expected around noon from the winter to the summer hemisphere. In the morning and evening currents are flowing in the opposite direction. In the evening this is different from prediction. Somewhat surprising is the northbound current around 03 MLT. No. 4

Inter-hemispheric FACs, June solstice north ward The IHFACs from Swarm show a distinct longitude

Inter-hemispheric FACs, June solstice north ward The IHFACs from Swarm show a distinct longitude distribution. Around 330° longitude the noontime FAC is week. south ward The IHFACs from CHAMP agree in general with those from Swarm. The anomalous distribution around 330°E is related to the SAA. south ward SAA (Park et al. , 2011, Ann. Geo) north ward No. 5

The wind-driven dynamo in the F-region Concept of wind-driven dynamo Rishbeth (1972) CHAMP analysis:

The wind-driven dynamo in the F-region Concept of wind-driven dynamo Rishbeth (1972) CHAMP analysis: Lühr and Maus (2006); Park et al. (2010) No. 6

Swarm radial currents at low latitudes At low latitudes IHFACs appear as radial currents

Swarm radial currents at low latitudes At low latitudes IHFACs appear as radial currents with opposite signs in the two hemispheres. Right above the equator there are weak downward currents around noon and upward in the evening. No. 7

F-region dynamo current from CHAMP, 2001 - 2004 CHAMP results show the same local

F-region dynamo current from CHAMP, 2001 - 2004 CHAMP results show the same local time variation, downward around noon, upward in the evening. Around June solstice the currents are weakest. Park et al. , 2010 No. 8

Radial currents at low latitudes, noon time longitude distribution Around noontime the IHFACs flowing

Radial currents at low latitudes, noon time longitude distribution Around noontime the IHFACs flowing from south to north are dominating at low latitude. At the longitude around 300°E FACs in opposite direction appear. They can be related to the South Atlantic Anomaly. No. 9

Longitudinal distribution of noontime radial currents at equator The vertical currents around noontime are

Longitudinal distribution of noontime radial currents at equator The vertical currents around noontime are stronger in the 0°- 180° longitude sector. Over that range the dipequator is located in the northern (summer) hemisphere, i. e. higher ionospheric conductivity.

Longitudinal distribution of evening radial currents at equator During the evening hours the equatorial

Longitudinal distribution of evening radial currents at equator During the evening hours the equatorial radial current is strongest in the 160°E- 290°E sector, over the Pacific Ocean. Here the geomagnetic field has an eastward declination, and fluxtubes are well aligned with the evening terminator during summer. No. 11

Summary and Conclusions Ø The Swarm dual-satellite approach provides reliable results for low-latitude currents.

Summary and Conclusions Ø The Swarm dual-satellite approach provides reliable results for low-latitude currents. Initial results from June and Sep equinox Ø Inter-hemispheric field-aligned currents (IHFAC) are flowing from the winter to summer hemisphere around noon and in the opposite direction during morning and evening. Ø There is an unexpected nightime IHFAC into the summer hemisphere around 03 MLT. Ø The IHFACs is weak in the 300°- 330° longitude sector. This is related to the SAA where the Sq system seems to be strong, e. g. comparable to the northern summer conditions. Ø The F-region wind dynamo causes downward currents above the equator around noontime and upward currents in the evening. Ø The downward currents around noon are stronger over Africa and Asia, where the dip-equator is located in NH. The upward currents in the evening are stronger over the Pacific, where the fluxtubes are well aligned with the terminator No. 12

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