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tokens: large SEP events (e.g., Gopalswamy 2018 ). SEP events need to be magnetically connected to the observer in order to be detected; type II bursts do not have such a requirement. Only 2 of the 44 cycle-23 limb halos are not associated with DH type II bursts; they are slow (800 km s −1 on 2000 October 24; 896 km s −1 on 2002 January 4) compared to the average speed of CMEs associated with cycle-23 DH type II bursts (1219 km s −1 ). The 2002 January 4 CME is associated with a metric type II burst, while the 2000 October 24 CME is radio-quiet. Nine cycle-24 halos have no DH type II association (see Table 1 ): five have metric type II bursts, three are quiescent filament-eruption events (which are only occasionally associated with DH type II bursts, Gopalswamy et al. 2015a ), and the slowest cycle-24 halo (2012 February 23). The four radio-quiet halos are slow (505 to 919 km s −1 ) compared CMEs associated with cycle-24 DH type II bursts (1059 km s −1 ). Thus, an overwhelming majority of limb halos (cycle 23: 98%; cycle 24: 90%) have type II bursts indicative of electron acceleration. 4. Discussion and Summary We analyzed large samples of limb-halo CMEs observed in cycles 23 and 24. We found that cycle-24 halos are slower than the cycle-23 ones. The limb CMEs that revealed wider width in cycle 24 did not show the speed difference (Gopalswamy et al. 2014a ). We introduced a new parameter—the height at halo time is readily determined for limb halos, but not for disk halos (the CME nose is hidden by the occulting disk of the coronagraph). The cycle-24 halo heights are significantly smaller. Combined with the result that cycle-24 halos are slower, we conclude that halos form at shorter heliocentric distances at lower speeds. Furthermore, we ruled out the possibility that the difference in CME properties is due to solar-source characteristics represented by soft X-ray flare size. Thus, we can pin down the heliospheric state as the main cause of the anomalous CME expansion in cycle 24. The number of limb halos (44) in cycle 23 is only slightly larger than the number (38) in cycle 24. This corresponds to a drop of only 14% in cycle 24. There was a 4 month SOHO data gap in cycle 23 (3 month in 1998 and one month in 1999). Assuming that the limb halos occurred at the cycle-averaged monthly rate (0.3 per month), we expect only one additional CME during the data gap. Then the drop is only 16%. This is much smaller than the 40% drop in the cycle-averaged total SSN from 81 to 49. Normalizing to SSN, we see that there are ∼42% more limb halos per SSN in cycle 24. This result was previously obtained by considering all LASCO halos in the first half of the two cycles (Gopalswamy et al. 2015b ). The effect of the heliospheric state on CMEs has important implications for space weather: lower geoeffectiveness is expected in SC 24 because lower speed and weaker CME magnetic field (due to expansion) result in a weaker storm. Furthermore, milder space weather is