  We report on a study that compares the properties of magnetic clouds (MCs)
during the first 73 months of solar cycles 23 and 24 in order to understand the
weak geomagnetic activity in cycle 24. We find that the number of MCs did not
decline in cycle 24, although the average sunspot number is known to have
declined by ~40%. Despite the large number of MCs, their geoeffectiveness in
cycle 24 was very low. The average Dst index in the sheath and cloud portions
in cycle 24 was -33 nT and -23 nT, compared to -66 nT and -55 nT, respectively
in cycle 23. One of the key outcomes of this investigation is that the
reduction in the strength of geomagnetic storms as measured by the Dst index is
a direct consequence of the reduction in the factor VBz (the product of the MC
speed and the out-of-the-ecliptic component of the MC magnetic field). The
reduction in MC-to-ambient total pressure in cycle 24 is compensated for by the
reduction in the mean MC speed, resulting in the constancy of the dimensionless
expansion rate at 1 AU. However, the MC size in cycle 24 was significantly
smaller, which can be traced to the anomalous expansion of coronal mass
ejections near the Sun reported by Gopalswamy et al. (2014a). One of the
consequences of the anomalous expansion seems to be the larger heliocentric
distance where the pressure balance between the CME flux ropes and the ambient
medium occurs in cycle 24.
