A multi-phase chronology of the Carrington storm of 1859 based on archival records of Trivandrum observatory

Abstract

The rediscovery of bifilar magnetometer records from Trivandrum Observatory—preserved within the historical archives of the National Library of Scotland—provides a rare and independent equatorial dataset crucial for reassessing the intensity and temporal structure of the 1859 Carrington storm. These archival materials reveal a nuanced sequence of geomagnetic disturbances, in as response to a sequence of likely coronal mass ejection (CME) impacts on 16th August and 29th August preceding the well-known super storm of 2nd September, and subsequent magnetospheric disturbances on 5th, 13th and 15th September due to weaker CME events and/or solar wind streams. The analyses of the archived Aide’s bifilar magnetometer data show that the 29th August and 2nd September events were of comparable magnitude (\(\Delta \)H ≈ −1851 nT and \(\Delta \)H ≈ −1926 nT) respectively, positioning the former as a newly calibrated benchmark for pre-Carrington CME activity. The records evidence disrupted diurnal periodicity in the horizontal magnetic field intensity on 16th August, 5th September, 13th September and 15th September, underscoring the magnetospheric fluctuations which may have been induced by successive interplanetary CME (ICME) impacts. By leveraging these meticulously preserved observatory logs, this study reconstructs a multi-phase chronology of the Carrington storm.