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We have reconstructed a new, homogeneous geomagnetic Dst indexfor 1932-2002,thus extending the original Dst index by 25 years,i.e. by more than one full solar magnetic cycle.The extension was done by using data from theoriginal set of four low-latitude stations for 1941-1956, and by usingthe nearby CTO station as a predecessor of the HER station for 1932-1940.Despite some open questions related to the composition of the originalDst index,the reconstructed index is quite similar to the original one duringthe overlapping time interval (1957-2002).However, the reconstructed Dst index correctsfor some known errors in the original Dst index, such asthe erroneously large daily UT variation in 1971.Also, despite the overall agreement, the reconstructed index deviatesfrom the original index even on the level of annual averages for several years.For instance, all annual averages of the reconstructed index are negative, andfor 1962-1966 they are systematically lower (more stormy) than thoseof the original index.Accordingly, we disagree with the uniquely positive annual average ofthe original index in 1965, which most likely is erroneous.We also find somewhat higher (less stormy) values than in theoriginal Dst index for the three lowest annual averages in1960, 1989 and 1991,out of which the lowest annual average is found in 1989 rather than in 1991.The annual averages of the geomagnetic Ap index and thereconstructed Dst indexcorrelate very well over this time interval, except in the beginningof the series in 1932-1940 and in the declining phase of solar cycles18, 20 and 21, where high speed solar wind streams cause enhanced geomagnetic activity.Using the superposed epoch method we also find that, on average, the stormsin the early extended period (1932-1956) are less intense but tend to havea longer recovery phase, suggesting that there are more HILDCAA-typemedium activity intervals during the early period than more recently.We also study the annually averaged storm structure over the 71-yeartime intervaland find that the most stormy years occur during thedeclining phase of solar cycles 17 and 21 and around the solarmaxima of cycles 19 and 22

A new reconstruction of the &lt;i&gt;D&lt;sub&gt;st&lt;/sub&gt;&lt;/i&gt; index for 1932-2002

A new reconstruction of the <i>D<sub>st</sub></i> index for 1932-2002