Occurrence rate of dipolarization fronts in the plasma sheet: Cluster observations

Sudong Xiao, Tielong Zhang, Guoqiang Wang, Martin Volwerk, Yasong Ge, Daniel Schmid, Rumi Nakamura, Wolfgang Baumjohann, Ferdinand Plaschke
2017 Annales Geophysicae  
<p><strong>Abstract.</strong> We investigate the occurrence rate of dipolarization fronts (DFs) in the plasma sheet by taking full advantage of all four Cluster satellites (C1–4) from years 2001 to 2009. In total, we select 466 joint-observation DF events, in which 318, 282, 254, and 236 DFs are observed by C1, C2, C3, and C4, respectively. Our findings are as follows: (1) the maximum occurrence rate is ∼ 15.3 events per day at <i>X</i><span class="thinspace"></span>∼ 15<span
more » ... class="thinspace"></span><i>R</i><sub>E</sub> in the <i>X</i><i>Y</i> plane, and the average occurrence rate is ∼ 5.4 events per day over the whole observation period; (2) the occurrence rate on the dusk side of the plasma sheet is larger and decreases with increasing <i>B</i><sub><i>X</i><i>Y</i></sub>∕<i>B</i><sub>Lobe</sub>; (3) the occurrence rate within |<i>Y</i>|<span class="thinspace"></span> &amp;lt; <span class="thinspace"></span>6<span class="thinspace"></span><i>R</i><sub>E</sub> increases gradually from <i>X</i> ≈ −19 to −15<span class="thinspace"></span><i>R</i><sub>E</sub> and then decreases from <i>X</i> ≈ −15 to −10<span class="thinspace"></span><i>R</i><sub>E</sub>; (4) the occurrence rate when AE &amp;gt; 200<span class="thinspace"></span>nT is much larger than that when AE &amp;lt; 200<span class="thinspace"></span>nT, indicating that DFs preferentially occur during high geomagnetic activity. The magnetic pileup and earthward and duskward ion flows could contribute to the increases in the occurrence rate from <i>X</i> ≈ −19 to −15<span class="thinspace"></span><i>R</i><sub>E</sub>. We suggest that both geomagnetic activity and multiple DFs contribute to the high occurrence rate of the DFs. In addition, the finite length of the DF in the dawn–dusk direction can affect the chance that a satellite observes the DF.</p>
doi:10.5194/angeo-35-1015-2017 fatcat:rp7iom2aazbffc4ouizly4s6rq