Investigations on the Extreme Space Weather Conditions During the Years 1841-1877 Using Geomagnetic Observations in Trivandrum, Singapore, Bombay and Madras

We have collected geomagnetic observations from low and equatorial latitudes during the 19th century to infer the intensity of geomagnetic storms during the years 1841-1877. Daily mean H observations during the above years in Trivandrum, Singapore and Madras is first scaled to Bombay observations and subsequently to the Dst index to infer the intensity of storms in modern units . These results are also compared with the intensity of these storms derived from mid latitudes. Extreme space weather events (ESW) are identified from the list of intense storms inferred during this period. The annual number of ESW events shows the characteristic double peak structure during the sunspot cycles 9-11. Space weather conditions during the sunspot cycle 11 (1867-1877) is found to be exceptional. A discussion on the true intensity of geomagnetic storms is also included.