My planet is tidally locked to a red dwarf, which itself orbits a yellow sun like our own. It has roughly the same atmospheric conditions as Earth (perhaps a slightly thicker atmosphere, but not extremely thick) and slightly less surface gravity (about 80% of Earth's). It is a stagnant lid planet (i.e., no plate tectonics).

NOTE: please do not comment or answer with "The planet wouldn't have an atmosphere because it's tidally locked. There are ways for such a planet to retain its atmosphere, so please just assume that it has one.

On the side facing the red dwarf, the planet receives more insolation than Earth when both suns are visible, and the annual average temperature at sea level at the point closest to the red dwarf (the planet's substellar point) is 64 C. On the other side (the antistellar point), it only receives insolation from the yellow sun during the day at about 40% of what Earth receives (similar to Mars). The temperature here at sea level is -44 C.

From the research that I've done, the dominant winds at ground/sea level would be from the cold side to the hot side, with the air being steadily heated before rising and returning back to the cold side at higher elevations. It seems that the planet would generally be pretty windy, and wind speeds would be high compared to most of Earth. I've also read that such a planet may have much more frequent precipitation than Earth.

On my planet, over 90% of its surface is ocean (or sea ice), most of it relatively shallow (average depth of about 2 km, alhough my story takes place on a large igneous province which has reduced regional average depths to about 100m), with a substantial sea ice cap on the cold side of the planet beginning at about 20 degrees towards the antistellar point from the terminator. The only land masses are volcanic hotspot islands. While many of these islands are the size of such islands on Earth (like the Hawaiian islands or Iceland), there are a handful of massive shield volcanoes like the ones found on Mars, which make up the largest land masses on the planet. They range in size from 500 km to 1500 km in width and can range in height from 4 km to 12 km.

The three primary islands where my story takes place are located as follows: enter image description here

This is a rough draft map that I've made which shows the beginning of the antistellar ice cap on the left at about 20 degrees towards the antistellar point, and extends to about 50 degrees towards the substellar point. The rough scale is about 7000 km x 5000 km. The map does not show elevation or climate, just water, sea ice, and land. This is NOT a full world map, just this portion of the planet.

From left to right:

  • Island 1 (bottom left): ~6-2 degrees towards the antistellar point (the cold/dark side). Average annual temperatures at sea level are about 6 degrees C on the coldest side of the island. The island is roughly 500 km wide and crescent-shaped. The volcano here is extinct and the island has been heavily eroded by wind and rain, but the summit of the island's mountains is still 4 km above sea level.
  • Island 2 (middle): ~4-14 degrees towards the substellar point (the hot side). Average annual temperatures at sea level are 12 C on the coldest side of the island, and 18 C on the hottest side. The island is roughly 1000 km wide and 1500 km long, and the volcano's summit is a towering 12 km, although the overall slope is fairly gentle (roughly 1 in 60).
  • Island 3 (top right): ~ 42-48 degrees towards the substellar point. Average annual temperatures at sea level are 35 C on the coolest side of the island and 39 C on the hot side. The island is roughly 800 km wide. This island's volcano is currently dormant, and it has a massive caldera crater at its peak. The caldera rim at the summit is about 7 km above sea level, but the caldera is 3km deep and approximately 100 km wide. The temperature on the caldera floor is about 16 C.

My question is, what are the types of climates and biomes you would find on such islands?

Because of the heightened precipitation, I would assume that deserts would be relatively rare, but would there be enough windward/leeward variation in precipitation for semi-arid climates such as steppes to develop on the leeward sides? Or would elevation be the primary determiner of climate on these islands? Would variation in insolation from the yellow sun due to eccentricity in the red dwarf's orbit around it be enough to produce noticeable seasons?

  • $\begingroup$ I might ad that the Earth doesn't have a single zone where the air rises or falls while it has a single insolation gradient from the equator to the poles. There are tree wind patterns on earth with the equator and the temperate zones having rising winds and the deserts and poles having falling winds. $\endgroup$ May 24, 2023 at 18:25


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