Small substorms: Solar wind input and magnetotail dynamics

We investigated properties of 43 small magnetospheric substorms. Their gene ral signatures were found to be consistent with the so-called contracted ov al or northern B-z substorms, Small but clear pressure changes in the tail corresponding to growth and expansion phases detected in about a half of ca ses testify that these substorms follow the same loading-unloading scheme a s the larger ones. However, rate of the solar wind energy accumulation in t he magnetosphere was low due to azimuthal IMF orientation with dominating I MF By and small fluctuating IMF B-z. Plasma sheet signatures could be very strong and likely were localized in their cross-tail size, Negative bags in auroral X magnetograms were of order of 100-300 nT, with maxima at Bear Is land station (71 degrees geomagnetic latitude) and in few cases were delaye d after magnetotail onsets by tens of minutes, Small substorms probably dif fer front their larger counterparts in a, way that coherency of the magneto tail reconfiguration in the inner and middle-tail regions and across the ta il is lost in smaller substorms.