PPPL-3809 is available in <a href="PPPL-3809.pdf">pdf</a> format (1.6 MB).

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<b>Near-earth Thin Current Sheets and Birkeland Currents during Substorm Growth Phase</b>
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<b>Authors:</b> Sorin Zaharia and C.Z. Cheng
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<b>Date of PPPL Report:</b> April 2003
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<b>Published in:</b> Geophysical Research Letters <b>30</b> No. 17 (September 4, 2003) 1883</p>


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Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (lXl ~ 9R<sub>E</sub>) thin cross-tail current sheet, as well as the equatorward shift of the ionospheric Birkeland currents. Our study is performed by solving the 3- D force-balance equation with realistic boundary conditions and pressure distributions. 

The results show a cross-tail current sheet with large current (J <font face="symbol"><sub>f</sub> ~ </font> 10 nA/m<sup>2</sup>) and very high plasma <font face="symbol">b</font> (<font face="symbol">b ~</font> 40) between 7 and 10 R<sub>E</sub>. The obtained region-1 and region-2 Birkeland currents, formed on closed field lines due to pressure gradients, move equatorward and become more intense (J<sub>llmax</sub> <font face="symbol">~ </font>3 <font face="symbol">m</font>A/m<sup>2</sup>) compared to quiet times. Both results are in agreement with substorm growth phase observations. Our results also predict that the cross-tail current sheet maps into the ionosphere in the transition region between the region-1 and region-2 currents.




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