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The Carrington storm in 1859 September has been arguably identified as thegreatest geomagnetic storm ever recorded. However, its exact magnitude andchronology remain controversial, while their source data have been derived fromthe Colaba H magnetometer. Here, we have located the Colaba 1859 yearbook,containing hourly measurements and spot measurements. We have reconstructed theColaba geomagnetic disturbances in the horizontal component ({\Delta}H), theeastward component ({\Delta}Y), and the vertical component ({\Delta}Z) aroundthe time of the Carrington storm. On their basis, we have chronologicallyrevised the ICME transit time as =< 17.1 hrs and located the {\Delta}H peak at06:20 -- 06:25 UT, revealing a magnitude discrepancy between the hourly andspot measurements (-1691 nT vs. -1263 nT). Furthermore, we have newly derivedthe time series of {\Delta}Y and {\Delta}Z, which peaked at {\Delta}Y ~ 378 nT(05:50 UT) and 377 nT (06:25 UT), and {\Delta}Z ~ -173 nT (06:40 UT). We havealso computed the hourly averages and removed the solar quiet (Sq) fieldvariations from each geomagnetic component to derive their hourly variationswith latitudinal weighting. Our calculations have resulted in the disturbancevariations (Dist) with latitudinal weighting of Dist Y ~ 328 nT and Dist Z ~-36 nT, and three scenarios of Dist H ~ -918, -979, and -949 nT, which alsoapproximate the minimum Dst. These data may suggest preconditioning of thegeomagnetic field after the August storm ({\Delta}H =< -570 nT), which made theSeptember storm even more geoeffective.

Temporal Variations of the Three Geomagnetic Field Components at Colaba Observatory around the Carrington Storm in 1859