Following on from thoughts in the previous thread; weather will always take precedence in forecasts for the earth sciences until we learn how to make synoptic charts for seismic disturbances that are as good as the ones designed to forecast weather.
Unless you are one of the half-baked loony leftists that swallowed, hook line and sinker, the Glowballs/propaganda designed by Margaret Thatcher’s political advisers in the 1980’s, you will readily understand that according to gas laws (propounded centuries before she decided to destroy Britain’s coal mining industry) that warmer air rises faster than cold air.
Or to put it another way the hotter the atmosphere gets, the faster is sheds the heat. When the sea ice surrounding Antarctica grows past a certain critical point, the flow of the global conveyor changes to suit -and the ability for the region to sustain large cyclonic systems increases.
At the time of writing (27 July 2014) the extent of the Antarctic cyclones encompasses the southern tips of the three other continents in the southern hemisphere. This situation stops the fluid flow of the Hadley cells across the surrounding continents. And that situation causes the Inter-tropical Convergence Zone to move north.
Whatever happens, the tropics only get 12 hours of sunlight a day. In fact the cloud above the tropics is dense enough to prevent twilight from lasting long so it remains a 12 hour day out of every 24/7/52. But the further north you go. the longer the days become in the summer and the more sunlight there is to focus on the ocean surfaces in the subtropics. All the more so when the weather is anticyclonic, for such air is transparent to solar radiation.
August to February in the tropics. The equator is perpendicular to sunlight almost all the year through. And as the seas are or were clean (until we dropped all our bin bags there) the sunlight doesn’t glance off but penetrates to the full 300 feet it can go before being absorbed.
Coupled with the blanketing cloud at night the oceans in the tropics blend to keep the pressure of the ITCZ at 1016 millibars 24/7.
The Wikipedia states that the ocean circuit of the deep water takes 1000 years to complete. But the effect that increased cyclone diameters around the Antarctic has on distant oceans is almost immediate. The Warm Pools move north with the ITCZ and the sea level air pressures in the mid latitudes lose definition.
Here is a typical example, although it is early in the southern winter season and the ice has not grown out as far as it will by late September. Click to enlarge.
Here is the relevant southern ocean stuff for about the same time:
Since the gap between Cape Horn and Antarctica is so very narrow, the Pacific anticyclones approaching there are nearly always blocked from crossing oceans through the Drake Passage. They are blocked more or less the whole year through. But after that place, the channel between Antarctica and Australia is almost always the first to fill.
This is because the harmonics set up in its curve make it a natural resonator but also it is due to the amount of rain coming south from the equator through South America and Africa. The Congo and Venezuela have a region of more or less permanent thunderstorms. They are semi-permanent in all tropical rain forest too.
There is a super-abundance of hot moist air coming south from the tropics, more or less all the time.
The Antarctic climate is seasonal but there isn’t much of a season near the equator. This is why the behaviour of tropical storms has to be due to the margin of ice around Antarctica. There is no other explanation for their behaviour.
In northern latitudes the sun shines longer and longer every day until summer solstice in late June when the tropical storm season starts. And the decline is gradual until the ice melts from Antarctic coasts starting late in September. The tropical storm season runs until sea ice -if there is going to be any, starts to impact the climate of the North Pole.
From September the ITCZ begins to move south. It actually stays about 5 degrees north of the equator making the southern hemisphere’s tropical storm season longer but generally less energetic. (IMO.)
Twilight doesn’t have much effect on the earth’s surface but of course it is warming the upper atmosphere, it is sunlight after all. However none of this counts for much when there is cloud cover. And little of it has any affect on the weather nearer the equator whatever the sun or cloud.
But I was talking about the present situation with larger anticyclones in the tropics and subtropics.
Once the surface waters in the tropics reach the critical temperature of 29 degrees Centigrade, the region becomes liable to tropical storms. The other major factor in their development is the cross winds that can occur. These will dispose of all the heat column’s vorticity.
This is what can happen when the temperature is high enough and there is no wind shear:
What happens when such storms take place is that blocking lows occurs in both the North Atlantic and the North Pacific: