Magnetic data, over 100 years!

On September 1, 1859, British scientist Richard Carrington observed a sudden and intense brightening in one of the sunspots. Within a day of this event, Stewart recorded at the Kew Observatory violent fluctuations in the Earth’s magnetic field.

There were very large (several hundred gammas) and rapid changes in the field magnitude and direction.  Telegraph operators found it possible to operate their system without batteries since the potential drop generated by the magnetic field changes provided sufficient power. Arcing across lines and sparking at the telegraph keys were reported from telegraph stations geographically widely distributed. The event points to the fact that large magnetic storms can affect space weather with a potential to create hazards.

Studies have shown that magnetic storms can create power grid blackouts and inflict transformer damage.

A storm most unusual

The 1859 storm was most unusual. However, magnetic data obtained at the Kew Observatory did not really throw much light on the intensity of the storm. It is not well-known that this storm was also recorded at the Colaba Observatory. In 1910, Nanabhai Ardeshir Framji Moos, the Observatory’s first Indian director, analysed the data gathered over the previous 60 years and summarised his results in two volumes where, he categorised the 1859 event as a “most remarkable” one. Almost a hundred years after his accomplishment, the Colaba magnetic data is being revisited by teams of scientists from India and abroad.

After appropriate calibration, they have obtained a new measure of the intensity (nearing 1700 gammas, higher than any value recorded in the history of Very Large Magnetic Storms) and duration (between one and one and a half hours) of the 1859 storm - a super magnetic storm indeed.

The recordings are now being employed to discover what conditions in the sun-earth environment become conducive to the creation of storms of extreme magnitude and how one may employ the knowledge to predict a super storm.

We now know that space weather can have hazardous effects not only on satellite tracking equipment but also on sensitive electronics mounted on spacecraft. The forecasting of magnetic storms is now an important part of space weather studies.

The Colaba-Alibag Observatory has been gathering data for over 160 years, through vicissitudes and stormy periods that included two world wars and the events following the partition of India.  This is the only low-latitude magnetic observatory (situated, as it is, close to the current position of the magnetic equator) that can claim this distinction. Navigators of the Middle Ages used the lodestone to find their way in the sea, regarding variations in the direction it pointed as a supernatural phenomenon from the Heavens.

Magnetism through the years

William Gilbert (1600s) can be credited with having begun the scientific study of magnetism. Thirty years later, a secular variation of the Earth’s magnetic field and possible variations over millions of years were recognised. About a century later (1722), Graham, a London clockmaker, demonstrated transient rapid changes in the Earth’s magnetic field, irregular changes, magnetic disturbances, etc. superposed on regular daily variations and made the first distinction between geomagnetic quiet and magnetic disturbance. Alexander von Humboldt (1806) named large disturbances ‘magnetic storms’.

Celsius (Uppsala, Sweden; 1741) and Graham found that magnetic disturbances often happen simultaneously at two places, implying that magnetic ‘weather’ is as non-local as ordinary weather. The appearance of extraordinarily brilliant and beautiful moving lights in the aurorae seemed correlated with magnetic disturbances, as has been confirmed in a later age by satellite recordings of intense magnetic storms and simultaneous auroral displays.

Beginning 19th century, Poisson and Gauss developed methods of measuring the intensity and direction of magnetic fields in absolute units replacing noting of small movements of a compass needle. The first magnetic observatory equipped with ‘magnetometers’ (consisting of delicately suspended magnets bearing mirrors) was set up by Gauss (1834; Gottingen).

Von Humboldt assisted in establishing a network of observatories all over the world. The then President of the Royal Society of England chose three locations in India: Simla (Shimla), Madras (Chennai) and Trivandrum (Tiruvananthapuram). The first two were set up by the Royal Society and the third by Maharaja Swati Tirunal. The placement of the observatory at Colaba in Mumbai was by a fortunate accident.

An observatory was proposed to be established (1840) at Aden near the southwestern tip of the Arabian Peninsula but, due to some difficulties, the instruments were diverted to the then Bombay Port. They were then erected at the earlier-built Colaba Observatory, meant for astronomical observations and timekeeping, and which started to function as a magnetic observatory also. In 1906, it was shifted to Alibag to avoid magnetic noise caused by electric trams that replaced the horse-drawn street trams and renamed the Alibag-Colaba Observatory.  It is being operated since 1971 by The Indian Institute of Geomagnetism, Panvel, Navi Mumbai.

(The author is a retired professor, Dept of Mathematics, and Dean of Science, IISc)