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Introduction

Importance of tail observation at –x = 50 to 100 Re suggested from plasma properties in the distant- to near-tail plasma sheet H. Hasegawa , M. Fujimoto, Y. Saito, & T. Mukai. Introduction

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Introduction

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  1. Importance of tail observationat –x = 50 to 100 Re suggested from plasma properties in the distant- to near-tail plasma sheetH. Hasegawa, M. Fujimoto, Y. Saito, & T. Mukai

  2. Introduction It has been believed that the normal (hot) plasma sheet results from magnetic reconnection at the Distant Neutral Line (DNL) located at –x= 100 to 150 Re. Plasma sheet

  3. Wind observation of an X-line X ~ -60 Re Flow reversal Øieroset et al., 2001; 2004 But, this observation suggests the existence of a steady X-line at x ~ –60 Re.

  4. Motivation: Are Geotail data consistent with the view that the DNL is located at –x = 100 to 150 Re? Data Analysis 12 sec resolution data from the Geotail LEP & MGF instruments •Analyzed period: Oct. 1993 to Dec. 1995 •XGSM’ = –10 to –210 Re •|YGSM’| < 10 Re (central part of the tail) •selected data points obtained exactly at the neutral sheet center, i.e., at moments when the sign of Bx reverses.

  5. Detection probability of Earthward & Tailward flows (X-dependence) The probabilities of earthward & tailward flows are roughly equal at –x = 50 to 80 Re. Dominant X-line at –x = 50 to 80 Re? Distant X-line?

  6. Plasma properties in the neutral sheet (Only Vx > 0 data are used here) Density at the neutral sheet Temperature The plasma properties are NOT consistent with the view that plasmas at –x = 100 to 150 Re are simply/directly transported toward the near-tail. Entropy S=P/(n5/3) ~60 Re

  7. Bz at the Neutral sheet X-line? The data seem to support that the most dominant DNL is at –x = 50 to 80 Re, rather than at –x = 100 to 150 Re.

  8. Proper models to explain our observations –x = 50-80 Re DNL that injects plasmas into the near-tail X = -200 Re

  9. However…, Geotail lacks data in the key region (–x = 50 ~ 100 Re) Observation of the plasma sheet at –x = 50 to 100 Re would be important to study the exact location & stability of the DNL(s), and their dependence on the solar wind conditions.

  10. Comment: The Wind satellite too observed the tail at –x = 50 to 100 Re, but it was not often for Wind to cross the neutral sheet in the central part (|y| < 10 Re) of the tail (according to our survey). So we still lack for a sufficient amount of data in the key region.

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