Posted on by weatherlawyer

Weather (for want of a suitable category.)

The first tropical storm of the season has started in the southern hemisphere. Following the relinquished northern sphere of influence there was an hiatus of about 10 days without a tropical storm, longer if you don’t count the way that they petered out. There is no physics that explains the details of the phenomenon that affects the planet so completely twice each year. For my money it is all to do with the extent of the ice around Antarctica. The amount that occurs varies (with the seasons, obviously) but the amount that builds and melts in the seasons is controlled by a cycle of the moon that varies how far north and south the declination can go every month.

The declination of the moon varies a little each month covering as much as 10 degrees in as many years. You should know that the declination of the sun changes a little every day for six months during which time it runs from the southern reaches (The Tropic of Capricorn) to the northern most point (the Tropic of Cancer) and back again 6 months later. It crosses the equator twice in this time at spring and autumnal Equinoxes.

The sun moves exactly 23.5 degrees every 6 months but the moon moves in a much more complicated schedule, reaching about 5 degrees north of the tropics every 11 years. OTOH of course because of that 5 degree aberration the moon also fails to reach the tropics every 11 years. I believe this is called the nodes or nodal cycle.

I am pretty sure it isn’t the Saros, whatever.

147 Replies to “Weather (for want of a suitable category.)”

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