  Coronal dimmings, localized regions of reduced emission in the EUV and soft
X-rays, are interpreted as density depletions due to mass loss during the CME
expansion. They contain crucial information on the early evolution of CMEs low
in the corona. For 62 dimming events, characteristic parameters are derived,
statistically analyzed and compared with basic flare quantities. On average,
coronal dimmings have a size of $2.15\times10^{10}$ km$^{2}$, contain a total
unsigned magnetic flux of $1.75\times10^{21}$ Mx, and show a total brightness
decrease of $-1.91\times10^{6}$ DN, which results in a relative decrease of
$\sim$60% compared to the pre-eruption intensity level. Their main evacuation
phase lasts for $\sim$50 minutes. The dimming area, the total dimming
brightness, and the total unsigned magnetic flux show the highest correlation
with the flare SXR fluence ($c\gtrsim0.7$). Their corresponding time
derivatives, describing the dimming dynamics, strongly correlate with the GOES
flare class ($c\gtrsim 0.6$). For 60% of the events we identified core
dimmings, i.e. signatures of an erupting flux rope. They contain 20% of the
magnetic flux covering only 5% of the total dimming area. Secondary dimmings
map overlying fields that are stretched during the eruption and closed down by
magnetic reconnection, thus adding flux to the erupting flux rope via magnetic
reconnection. This interpretation is supported by the strong correlation
between the magnetic fluxes of secondary dimmings and flare reconnection fluxes
($c=0.63\pm0.08$), the balance between positive and negative magnetic fluxes
($c=0.83\pm0.04$) within the total dimmings and the fact that for strong flares
($>$M1.0) the reconnection and secondary dimming fluxes are roughly equal.
