Climatic consequences of two Polar Oceans and a Circumspecting Landmass

Question

On a certain planet, the sole continent of land is a large circumspecting ring about the equatorial regions, with a width averaging 500 miles. Rotational north and south are entirely pelagic. Various shallow seas exist on this continental stripe; some of these seas could join the surface layers of the two oceans. The planet is tectonically inactive, in that the mantle is unperforated and unbroken, and I suspect that it would be quite stable, barring some cataclysm.

Mass is roughly 1.5 times that of the Earth, and atmosphere is of mostly the same as here on Earth. Diurnal period, or rotation about its internal axis, is roughly 36 chronal hours with our SI units. Photosynthesis uses chlorophyll and soils are mostly the same as Earth also. In short, it is like a larger copy of the Earth with a different arrangement of oceans and land.

Its sole satellite, which is approximately one-third its mass and at slightly more twice the distance between Earth and Luna, orbit each other with nearly parallel axes.

Their axial tilt with respect to solar plane is approximately 28° arc. The parameters of their solar orbit is almost the same as that of the Earth.

The sun is Main Sequence, and lies somewhere between the G and K spectral classes.

Obviously my numbers are not precise yet.

Anyway, I expect that the large oceans would produce strong wind currents which would shift direction twice during the solar orbit, with the moist air causing seasonal variations of arid and soggy in some places as a result of the rain shadow. Otherwise, however, the climes should be mostly temperate.

What would be the climate equilibrium state, if any?

Answer 1

Basic answer...not taking into account axial tilt and sun details etc. Just basic climatology.

Landmass

500 mile width. On Earth the distance between each degree of latitude is about 69miles. So on Earth, your landmass would average 3.5-4 degrees latitude either side of equator. On your larger planet, it would be less!

Coriolis at the equator Earth rotates west to east, this rotation causes surface waters and winds to flow east to west.

Coriolis causes surface waters and winds to be deflected to the right in the northern hemisphere and left in the southern.

BUT, at the equator the is little to no deflection. We call it the 'doldrums'. So your coastal water currents will probably be fairly weak (if no other drivers can be found).

Oceanic circulation. As mentioned by Palarran, there will be no complete ocean circulation. On Earth, all our oceans are connected and combines to create the thermohaline circulation. This transfers cold polar water to the equator and beyond and warm equatorial water to the poles. But I don't see why you can't have two separate thermohaline circulation systems.

Your planet has ocean from the poles to pretty much the equator (barring a few degrees). Your cold polar waters will extend alot further inwards than on Earth. Eg in the northern hemisphere the cold oceans are mostly barred by eurasia and north America. In the south, the cold currents have near free reign and have formed a large antarctic circumpolar current.

You will have two of these, North and south. But I believe it may be 'wider'. This will result in larger ice caps affecting air temperatures. The cold water will sink until it hits the ocean surface and then travel underwater towards the equator (you will need some sunken landmass to direct it there). When it reaches the equator it may rise and bring nutrients to the surface. See areas of upwelling on Earth.

Depending on how wide a continental shelf you have, your coastal waters will therefore be colder than expected. Shallow coast, weaker and warmer current; steeper shelf, stronger current influenced by the upwelling cold current.

Such a strong polar ocean current would also result in very little surface mixing with the water in the mid-latitudes. So thinking the problem through, you will have a excessively strong polar current and a very weak equatorial current. You may have a narrow third current between the two. A mid-latitude current. Where the equatorial and polar currents interact. I'd imagine it would be mainly driven by any atmospheric circulation as there will be no landmass to drive or focus the direction.

Atmospheric circulation. I don't think it will be similar to Earth's hadley-ferrel-polar cell circulation. If it is, it will be a mutated version.

You will most certainly have a large strong polar cell. The polar cell has subsiding air at the poles and rising air at the polar front. On Earth about 60degrees.

With such a narrow landmass at the equator, you won't have a very strong zone of ascending warming air. Resulting in a weaker and smaller Hadley cell. This means that less warm air is going to be transported up into the upper atmosphere and down to the poles. Your tropics(where all the moisture falls back out if the sky) will also not reach to the 30 degree latitude and probably fall between 10-20 degrees (if that).

Your ferrel cell. This is where a very large amount of uncertainty lies. If it exists... Maybe just an interaction cell. Purely to exist to separate the cold polar air from the warmer equatorial air. It would be more of a buffer zone than an actual atmospheric cell.

In summary I believe you have created a very cold planet. Your polar icecaps will dominant the weather. Most moisture will be locked in the salter than Earth's oceans and poles. The air will be dryer. It will rain alot on your equator landmass, as the rain band is that much narrower than on Earth. There will be strong polar winds. Storm surges onto your landmass probably won't be uncommon. Expect lots of coastal flooding in low-lying areas.

Answer 2

The state of your planet is unstable.

The two oceans will have different sea levels, and even more: One of the two oceans will raise at the cost of the other. The result will be sooner or later an overflow from the higher level ocean to the lower one, creating as a net result a channel between the two oceans (similar to the Bosporus between the Mediterranean Sea and the Black Sea).