1. M. Yamauchi 1, H. Nilsson 1, I. Dandouras 2, H. Reme 2, R. Lundin 3, Y. Ebihara 4 (1) Swedish Institute of Space Physics (IRF), Kiruna, Sweden (2) CNRS and Universite de Toulouse, IRAP, Toulouse, France (3) Swedish Institute of Space Physics, Umeå, Sweden (4) Kyoto University, Uji, Japan Inbound-outbound asymmetry of Cluster perigee traversals as indicator of substorm dynamics

2. Ion’s are normally north-south symmetric (except seasonal effect) because these ions are bouncing between southern and northern hemispheres  Cluster (2001-2006): should be inbound-outbound symmetric because they are different only by 1-2 hours in both UT and LT.  Any asymmetry should reflect “event” such as substorms. We examined all perigee pass during 2001-2006 SC4 (about 670 traversals, with clean data of 460 traversals). Cluster perigee (L=4~6) ion patterns

3. (1) (2) (3)

4. (1) Westward drifting > 10 keV (2) Eastward drifting ~ few keV (mono-energy) (3) Eastward drifting wide-energy stripes < 1 keV Three major ion components in the dawn-to-noon sector:

5. symmetric patterns (1) (2) (3a) (3b)

6. 2001-9-4 (12 LT) 2001-7-18 (15 LT) 2002-6-2 (18 LT) other local times (3b)

7. statistics for (3b) “wedge”

8. However sometimes inbound- outbound asymmetry.  related to substorms! Examples of (2) & (3a) AE

9. Examples of (3b) “wedge-like structure”

10. Classify asymmetry in terms of basic patterns (1)Westward drifting > 10 keV * Intensity & energy @ same L (latitude) (2) Eastward drifting ~ few keV (mono-energy) * Intensity & energy @ same L (latitude) (3) Eastward drifting wide-energy stripes < 1 keV (3a) Vertical (extend from keV): * Intensity @ same L (latitude) (3b) Dispersed (extend from low energy) * Intensity & energy @ same L (latitude) * dispersion direction @ same L (latitude) Today

11. AE Asymmetry sometimes appears as (3c) internal structure (no model yet)

12. Statistics for (3a) 2003-3-15 (0 LT) |AL| > 400nT and the appearance of the vertical structure (type 3a) are related at midnight.

13. Statistics for (3b)/(3c) 2001-7-9 (16 LT) 2002-9-8 (12 LT) In many cases, “wedge” is enhanced within 2h of traversals and LT difference.

14. Hr from substorm onset cf. Viking dynamic-statistics 6 MLT 9 MLT 12 MLT 15 MLT 18 MLT

15.  ExB drift (+ co-rotation) is quite strong. The “wedge” is moving rather fast toward late afternoon

16. actually, simulation can re-produce the asymmetry!

17. SC-4

18. (a) Asymmetric in vertical stripes (1~10 keV ions)  * post-midnight peak * related |AL|>400nT substorm onset (b) Asymmetric “Wedge” (dispersed stripe at sub-keV) (c) Asymmetric internal structure of “Wedge”  * late-morning peak, but extends wide LT * quite soon (few hours) after substorm activity * right after onset@early morning Summary of asymmetric ion pattern We examined ion (CIS) data for all Cluster perigee traversals during 2001-2006 when the orbit is relatively north-south symmetric (2006 data is affected by orbit). Quite many cases are north-south asymmetric in the inner magnetosphere. On can guess the past history of substorm (+ E field) just from the ion spectrogram (if orbit is ideal).

19. Thank you for your attention

20. other substorms

21. V B  energy (mass independent) V ExB = constant (energy  mass) dispersed sub-keV ion = “wedge”