Carrington as a benchmark: comparisons of the September 1859 storm using newly digitised data for London

In September 1859, scientists observed what has gone down in history as the first ever Space Weather event, and which is also thought to be the greatest magnetic storm on record. At this time the development of magnetic observatory networks was in its infancy with few in existence and methods to continuously record the magnetic field variations were rare. Two competing London observatories, Greenwich and Kew were an exception and both recorded the Carrington storm on photographic paper. These magnetograms provide continuous measurements, from one or other of these two London observatories, for the entire Carrington storm. Over the past year, we have been running a project to glean time-series data from digital traces of these plots, as well as of fourteen other of the most powerful geomagnetic storms prior to the digital recording era. This has resulted in a new trove of data for studying these events. In this poster, we briefly describe the process of digitally-tracing, scaling and interpolation used to derive this data supply. We then go on to compare the results with other available data or the Carrington storm, including samples in observatory yearbooks. The results are also discussed in relation to the Dst results of Tsurutani et al (2003). Comparisons with other digitised storms are also made. Finally, we describe our efforts to derive dB/dt values from the analogue records, which are relevant for estimating Space Weather effects on technology.