Another tidal surge in August end
This resurgence of high tides is most likely due to a unique astronomical phenomenon. According to astronomers, the amplitude (height) of tides fluctuates weekly with the phases of the moon. They also change over an 18.6-year tidal cycle due to changes in the alignment of the earth, moon and sun. In 2015, tide levels will be the highest in the present 18.6-year cycle. This means that we are near the peak of the tidal cycle. This happens at a time when the earth, moon and sun align such that they combine to create a greater than normal force over water bodies. This result in higher tides than normal, astronomers say.
Things are likely to improve after the first week of September but the tide will breach the 6-metre mark again in the last week of that month and this will continue till the first week of October. The worst affected are likely to be low-lying areas in south Kolkata, including Kalighat, Chetla, Rashbehari Avenue and the stretch from Naktala to Garia. Towards the north, all localities on the banks of the Hooghly are likely to get inundated.
In 2014, the highest tide level recorded for the three months starting July was on September 9. This was the only day when the high tide was measured at 6.1 metres. Since July this year, there have been several days when the tide level breached the 6.1-metre mark.
"It is a possibility that the high tide has something to do with the alignment of the earth with the sun and the moon's alignment with the earth. The earth's alignment with the sun's axis is 23.5 degrees. Similarly, the moon's axis with the earth is 5.5 degrees. After every 18.6 years, these two alignments get added. We call this a Major Lunar Standstill. This is when the declination of the moon is known to be at its maximum. After about nine years, we reach a phase known as the Minor Lunar Standstill. Tides are likely to be affected during both these phenomenon. This year, we are passing through a Minor Lunar Standstill and this may cause higher tides in the Hooghly. Astronomers have calculated its impact on monsoonal pattern, ocean currents and tides. The last Major Lunar Standstill occurred in 2005-06. It is likely to take place again in 2025," said M P Birla Planetarium director Debiprosad Duari.
Kolkata is the worst affected as its close to the coastline. Due to its proximity to the sea, there are two high tides and two low tides in the Hooghly in a span of 24 hours. The timings change as per the phases of the moon. The effects of the tides are not felt further upriver.
http://timesofindia.indiatimes.com/city/kolkata/Another-tidal-surge-in-August-end/articleshow/48408540.cms
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