Figure 5.

The geometry for quantifying a “helical zippette”, a typical single reconnection event between flux tubes $X$ and $Y$ in the zipper phase of a coronal arcade that overlies an initial flux rope $Z$. The initial and final states are shown in (a) and (b), respectively. The reconnection occurs beneath $Z$, and thus produces an underlying tube, $U$. The other tube that is produced by the reconnection ($R$) overlies both $U$ and $Z$, and wraps one entire time around $Z$. The interior angles with flux rope $Z$ are indicated.