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A correlative study between the intensity of a geomagnetic storm (given by the Dst index) and the peak value reached by some solar wind parameters (velocity and density) and the southward component of the interplanetary magnetic field (IMF) is made. This study has been performed by using hourly values of the Dst index and measurements taken by the ACE spacecraft in the period 2000-2005, for which 72 geomagnetic storms were considered. It is confirmed that peak Dst is correlated to the maximum negative component B z of the IMF better than the maxima of n and V (solar wind number density and speed, respectively). By considering all the storms, the correlation coefficient was found to be 0.88. If we consider the geomagnetic storms for which −200 nT < peak Dst < −60 nT, a lower correlation coefficient of 0.63 is obtained.

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[1] Values of the F2 region maximum electron density height (hmF2) calculated using ground ionosonde data at South American latitudes are used to check the validity of the International Reference Ionosphere (IRI) to predict this variable. With this in mind we compare hmF2 predictions given by the model when measurements of critical frequency of F2 region and propagation parameter M(3000)F2 were used as input parameter in IRI (hmF2 IRI-Exp ), against those obtained using the standard International Radio Consultative Committee (CCIR) option (hmF2 IRI-CCIR ). In this paper we used hmF2 IRI-Exp values because hmF2 measurements were not available for the considered cases. Moreover, a comparison of the measured M(3000)F2 values with the CCIR predictions have been done. The results show that, in general, the standard predictions follow the diurnal tendency observed in the hmF2 IRI-Exp values. At low latitudes the hmF2 IRI-Exp values show oscillations not reproduced by the standard option. Cases with disagreements for 24 hours have been observed at high latitudes. Other cases with good agreement have been also obtained. The results suggest that, in general, the standard option of the model gives good hmF2 predictions at South American latitudes. Few cases showed deviation between 15 and 25%. As we expected, the obtained results suggest that the deviation between predicted and measured M(3000)F2 values is the main contribution for the deviation between hmF2 IRI-CCIR and hmF2 IRI-Exp . The comparison with the results obtained in previous work shows that the IRI performance in predicting M(3000)F2 and hmF2 is better than in predicting foF2.