The Long Dark - surface conditions

I’ve talked about the peculiar day/night cycle on a world with a 90 degree axial tilt. That much is straightforward observation of how the sun would look at various points on the planet’s surface. But the next part of worldbuilding is a lot more speculative.

Most of a planet’s weather is driven by convection currents caused by temperature differences in its atmosphere and oceans. With that in mind, think about a planet where the sun hovers directly overhead at the pole, baking it remorselessly for months, then disappears for a whole half of the year plunging that same pole into darkness. To me, that adds up to massive temperature fluctuations across the globe during the course of a year.

I know the same thing happens on Earth at the poles, with six months day and six of night, but the sun stays low in the sky and the days stay cold. The poles don’t turn into the tropics at midsummer, and most of the Earth’s surface sees a reasonable day/night cycle all year round. On this planet, by contrast, periods of light and darkness are taken to extremes across most of its surface, and everywhere gets a dose of tropical heat at some point in the year.

One thing I think we can safely assume - there will be some pretty violent weather going on. Beyond that, I certainly have no way of knowing how it would look, so the rest is pure invention.

Earth has many stable circulation patterns, but its axis only wobbles 23 degrees back and forth relative to the sun during the course of a year. My world does a complete 180 and then back again, so any circulation patterns would completely reverse, which suggests a lot of turbulence to cope with.

In this world, a ‘year’ lasts about thirteen Earth years, so that gives a lengthy season. My worldbuilding has global weather patterns switching through a series of states as the seasons change. Each state is reasonably stable - though not necessarily benign - for a long stretch of time as the planet slowly turns new latitudes to the sun, then the pattern becomes unstable and flips in a rapid and violent transition to the next season.

The height of summer is the calmest time, and this is when most of the outdoor work is done. Meanwhile, in the winter hemisphere, temperatures bottom out at minus two hundred Celcius, lashing the winter pole with storms of nitrogen rain.

The most violent conditions arrive some time after midsummer, as the winter pole starts thawing and the summer pole plunges into darkness. Through the mid-seasons, convection currents in the atmosphere undergo dramatic shifts powered from the poles. I’m expecting storms and winds that would put an Earthly hurricane to shame.

On top of this, a red giant star itself is pretty active compared to our tranquil sun. Outbursts of solar flares make nearby space inhospitable to orbiting craft much of the time, and the colonists long ago gave up trying to keep satellites working. I’ve given the planet a powerful magnetic field to shield the surface from the worst of the solar storms, but it’s still a dangerous place to be. And all this electrical activity makes communications tricky at best. The colonists rely on land lines laid between permanent settlements, and short wave radio when conditions allow.