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Abstract The non-dipolar portions of Earth's main magnetic field constitute substantial differences between the geomagnetic field configurations of both.

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Presentation on theme: "Abstract The non-dipolar portions of Earth's main magnetic field constitute substantial differences between the geomagnetic field configurations of both."— Presentation transcript:

1 Abstract The non-dipolar portions of Earth's main magnetic field constitute substantial differences between the geomagnetic field configurations of both hemispheres. They cause in particular different magnetic field flux densities in the opposite polar regions and different offsets of the invariant poles with respect to the rotation axis of the Earth. The offset is presently considerable larger (factor ~2) in the Southern Hemi- sphere compared to the Northern, which has substantial implications for the coupled magnetosphere-ionosphere-thermosphere system under the influence of external drivers. Recent observations have shown that the ionospheric/thermospheric response to solar wind and IMF dependent processes in the magnetosphere can be very dissimilar in the Northern and Southern Hemisphere. We present statistical studies of both the high-latitude ionospheric convection and the patterns obtained from almost a decade of measurements starting in upper thermospheric circulation 2001 of the electron drift instrument (EDI) on board the Cluster satellites and an accelerometer on board the CHAMP spacecraft, respectively. Using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model, on the other hand, we simulated a 20-day spring equinox interval of low solar activity with both symmetric dipole and realistic (IGRF) geomagnetic field configurations to prove the importance of the hemispheric differences for the plasma and neutral wind dynamics. The survey of both the numerical simulation and the statistical observation results show some prominent asymmetries between the two hemispheres, which are likely due to the different geographic-geomagnetic offset, or even due to different patterns of geomagnetic flux densities. Plasma drift differences can partly be attributed to differing ionospheric conductivities. The forthcoming Swarm satellite mission will provide valuable observations for further detailed analyses of the North-South asymmetries of plasma convection and neutral wind dynamics. North-South differences in Earth's high-latitude upper atmosphere dynamics: influence of solar activity and seasonal variations Matthias Förster 1 and Ingrid Cnossen 2 1 - GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Telegrafenberg, D-14473 Potsdam, Germany, mfo @ gfz-potsdam.de 2 - British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom, inos @ bas.ac.uk EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

2 DIFFERENCES IN HIGH-LATITUDE PLASMA DRIFTS AND NEUTRAL WINDS BETWEEN THE NORTHERN AND SOUTHERN HEMISPHERE: THE ROLE OF MAGNETIC FIELD ASYMMETRY CONCLUSIONS EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

3 Outline Observational evidences - EDI/Cluster average ion drift pattern at high magnetic latitudes - CHAMP accelerometer neutral wind pattern at high latitudes Are there significant differences at high latitudes between the NH and SH ? What is the role of the geomagnetic field for M-I-T coupling processes ? Seasonal and solar cycle dependencies? Numerical experiment - Global first principle model GTIM (incl. TIE GCM) of the M-I-T system - High-latitude neutral wind and ion drift: magnitudes, variances, direction - Neutral wind and drift parameters versus UT and IMF orientation - Derived parameter: neutral wind vorticity EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

4 Cluster/EDI Average Convection Pattern EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

5 Cluster/EDI Average Convection Pattern EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

6 Wind Vector Distribution Pattern CHAMP accelerometer 01 Jan 2002 - 31 Dec 2003 North Hemisphere South Hemisphere EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

7 Vorticity of Wind Vector Distribution CHAMP accelerometer 01 Jan 2002 - 31 Dec 2003 North Hemisphere South Hemisphere cf.: M. Förster et al., Ann. Geophys., 29, 1, 181-186, 2011 EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

8 NorthSouth EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

9 NorthSouth EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

10 NorthSouth...with Altitude Adjusted Corrected Geomagnetic Coordinates (AACGM) EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

11 Model interval: March 20 – April 08, 2008 (20 days) Coupled M-I-T Model (CMIT) = Lyon-Fedder- Mobarry (LFM) magnetospheric MHD code plus the TIE-GCM Wiltberger et al., 2004, JASTP, 66, 1411-1423 Wang et al., 2004, JASTP, 66, 1425-1441 Wang et al., 2008, GRL, 35, L18105 Whole Heliosphere Interval (WHI 1) = Carrington Rotation 2068 Bisi et al., 2011, Solar Physics, 274 (1-2) Wiltberger et al., 2012, JASTP, 83, 39-50 EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

12 Neutral wind NH / SH & model run comparisons EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

13 Ion drift NH / SH & model run comparisons EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

14 Comparison NH/SH: Neutral wind versus UT EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

15 Comparison NH/SH: Ion drift versus UT EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

16 Neutral wind variance versus UT EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

17 Neutral wind vorticity maxima versus IMF sector EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

18 Neutral wind vorticity [mHz]: Min/Max values EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

19 Neutral wind vorticity [mHz]: Min/Max values EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

20 DIFFERENCES IN HIGH-LATITUDE PLASMA DRIFTS AND NEUTRAL WINDS BETWEEN THE NORTHERN AND SOUTHERN HEMISPHERE: THE ROLE OF MAGNETIC FIELD ASYMMETRY CONCLUSIONS CONCLUSIONS Numerical experiment for equinox conditions with two different model runs: - Symmetric geomagnetic dipole and - Asymmetric (“real”) IGRF configuration. The model results reveal substantial differences in the average ion drift and neutral wind parameters at high magnetic latitudes between NH and SH:  IGRF results suggest 10-15% NH > SH wind and ion drift magnitudes, but practically no differences for the symmetric dipole case;  the spatial variance of wind magnitudes is SH > NH for IGRF case only, showing a pronounced diurnal variation;  the variation of the ion drift & neutral wind versus IMF orientation shows the familiar Bz & By dependence in magnitude for both model realisations;  the average maxima & minima of wind vorticity show a ~10% difference and are in good coincidence with experimental results (CHAMP);  there is a factor ~2 difference in wind vorticity magnitudes and NH > SH differences between low (2006/8) and high (2002/3) solar activity. See: Förster and Cnossen, JGR, Vol. 118, 5951-5966, 2013. Follow-up studies clarify seasonal & solar activity dependences in more detail. EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

21 Average neutral wind magnitude [m/s] vs. DoY EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

22 Average neutral wind magnitude [m/s] vs. DoY EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

23 Neutral wind direction versus UT EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

24 Neutral wind direction versus UT EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

25 Neutral wind direction versus IMF sector

26 Solstice model intervals: December 2002 & June 2003 EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

27 Neutral wind vorticity [mHz]: Min/Max values EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

28 Average model neutral wind magnitude > 80 deg EGU 2014 Session ST 3.2 Vienna, Austria April 30, 2014

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