On the Purelake Climate (and Roshar in general)

[Firesong she/her]

So, according to Coppermind.

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The Purelake has a tropical climate that is consistently both warm^[3] and humid,^[11] with calm breezes.^[12] The passing of the highstorm is the only time the temperature drops and the lake's climate turns cold.^[3] The Purelake's weather is similar to that of Hallandren, on the planet Nalthis.^[12]

But, the thing is, I feel it wouldn't be accurate to call it tropical. As if it was in the tropical region, Jah Keved and Alethkar would also be Tropical. 

I think instead it comes down to the high humidity making it feel more tropical. As humidity makes lower temperatures feel much hotter, due to the Heat Index. For example, humidity around the Caspain Sea is 75-80%.

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Annual Relative Humidity is the highest on the Caspian Sea shore (75-80%)

This would increase the perceived temperature, increasing it. And I feel that the temperature would be significantly higher, without it being tropical. It would also experience winds blowing from the Reshi Sea. 

It is actually the Reshi Sea and Endless Ocean that I feel make western Roshar so lively compared to the East. Alethkar is blocked off by the Unclaimed Hills. Others are able to get humid winds from the Reshi Sea and Endless Ocean. Makabak is blocked from it by the mountains surrounding it. Shinovar likely captures winds moving southeast and northwest, which get caught in the area due to the Misted Mountains, which is what makes the mountains so misty. I feel there is likely a cell in that straight north of Shinovar, which moves along the coast of Iri, southward into Shinovar, before curving back up and getting its moisture caught by the Misted Mountains. 

I feel it could also potentially have been caught continuing south, stripping moisture as it flows into Alm and Steen, while retaining some degree of moisture, allowing eastern Makabak to get more green than the rest of the region. 

 

Also, I feel that it does actually make sense for the Reshi isles to not be deserts despite the lack of axial tilt. As they are smallish islands surrounded by a ton of water. Which I feel would be able to keep the humidity up and prevent it from just having everything die. We also know the planet would necessarily be further away from the sun, which would cool down the experienced temperature as per the inverse square law. 

[alder24]

2 hours ago, Firesong said:

I think instead it comes down to the high humidity making it feel more tropical. As humidity makes lower temperatures feel much hotter, due to the Heat Index. For example, humidity around the Caspain Sea is 75-80%.

I think it's also important that the Reshi sea is a very warm place - the air and waters from it would travel south by currents and meet mountain ranges south of the Purelake, trapping the heat in this region, making it tropical and humid. Roshar has also no axial tilt, so the sun is always above the equator, which is north of the Rosharan continent (actually some Reshi Isles are north of the equator), and the heated water and air would travel by currents south, warming up the northern part of the continent (specifically western part, Reshi isles and Iri)

Edited September 17, 2023 by alder24

[Treamayne]

1 hour ago, Firesong said:

But, the thing is, I feel it wouldn't be accurate to call it tropical. As if it was in the tropical region, Jah Keved and Alethkar would also be Tropical. 

I think instead it comes down to the high humidity making it feel more tropical. As humidity makes lower temperatures feel much hotter, due to the Heat Index. For example, humidity around the Caspain Sea is 75-80%.

I feel like this is an example of generalities. There is a huge range of what is "tropical" (and i have no idea where the comparison to Hallendren comes from - they aren;t even close since one is a "bay", and the other a rainforest). For example - Koppen Climate Classification:

Spoiler

A (Tropical)	f (Rainforest) m (Monsoon) w (Savanna, dry winter) s (Savanna, dry summer)

Definition:

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Group A: tropical climates

This type of climate has an average temperature of 18 °C (64.4 °F) or higher every month of the year, with significant precipitation.^[1][10]

• Af = Tropical rainforest climate; average precipitation of at least 60 mm (2.4 in) in every month.
• Am = Tropical monsoon climate; driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with precipitation less than 60 mm (2.4 in), but at least 100−(TotalAnnualPrecipitation(mm)25).^[1][10]
• Aw or As = Tropical wet and dry or savanna climate; with the driest month having precipitation less than 60 mm (2.4 in) and less than 100−(TotalAnnualPrecipitation(mm)25).^[1][10]

Af: tropical rainforest climate

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All 12 months have an average precipitation of at least 60 mm (2.4 in). These climates usually occur within 10° latitude of the equator. This climate has no natural seasons in terms of thermal and moisture changes.^[9] When it is dominated most of the year by the doldrums low-pressure system due to the presence of the Intertropical Convergence Zone (ITCZ) and when there are no cyclones then the climate is qualified as equatorial. When the trade winds dominate most of the year, the climate is a tropical trade-wind rainforest climate.^[16]

Am: tropical monsoon climate

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This type of climate results from the monsoon winds which change direction according to the seasons. This climate has a driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with rainfall less than 60 mm (2.4 in), but at least 100−(TotalAnnualPrecipitation(mm)25) of average monthly precipitation.^[9]: 208

Aw/As: tropical savanna climate

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Tropical savanna climate or tropical wet and dry climate is a tropical climate sub-type that corresponds to the Köppen climate classification categories Aw (for a dry "winter") and As (for a dry "summer"). The driest month has less than 60 mm (2.4 in) of precipitation and also less than 100−(Total Annual Precipitation (mm)25)mm of precipitation.^{[1]: 200–1}

This latter fact is in a direct contrast to a tropical monsoon climate, whose driest month sees less than 60 mm (2.4 in) of precipitation but has more than 100−(Total Annual Precipitation (mm)25) of precipitation. In essence, a tropical savanna climate tends to either see less overall rainfall than a tropical monsoon climate or have more pronounced dry season(s).

 

 

 Hallendren is likely to be an Af climate, whereas I would guess the Purelake to be a variant of the Tropical Savanna climate (because there would be no longer/shorter days on a planet without axial tilt - and if most of the precipitation comes from highstorms - which are much weakened - then the total rainfalll probably places the region well below Tropical Monsoon levels. 

1 hour ago, alder24 said:

(specifically western part, Reshi isles and Ire)

Do you perhaps mean iriali (not Ire - Elantrians are in Shadesmar AFAIK)?

Edited September 17, 2023 by Treamayne

[Firesong she/her]

5 hours ago, alder24 said:

I think it's also important that the Reshi sea is a very warm place - the air and waters from it would travel south by currents and meet mountain ranges south of the Purelake, trapping the heat in this region, making it tropical and humid. Roshar has also no axial tilt, so the sun is always above the equator, which is north of the Rosharan continent (actually some Reshi Isles are north of the equator), and the heated water and air would travel by currents south, warming up the northern part of the continent (specifically western part, Reshi isles and Iri)

Yeah, I mentioned the lack of tilt and how hot it would make the Reshi Isles. But how it would be a bit cooler than if Earth had no tilt, due to being further from their sun. It would still be rather unbearable to most people on Earth, though. I brought it up as it would likely be a desert, but the fact they are islands surrounded by a sea on a planet with what I think was like, 85% water, iirc. Which would keep it humid, instead of turning all dry. 

And I did also bring up that winds from the Reshi sea would warm up and bring more humidity to eastern and central Roshar. With Makabak being blocked off by the mountains, thus leaving the moisture captured on one side, making it even more lively on the opposite side. This is what I brought up as an explanation for Shinovar being so lively. With a cell in the north across that straight, which gets captured by the Misted mountains as it moves back north, which would be the reason why they are misty 

[Treamayne]

1 hour ago, Firesong said:

I brought it up as it would likely be a desert,

May I ask why you think it would be a desert? Do you know that desert conditions do not always involve temperature? The largest desert on Earth is Antarctica. . . (largest, not driest)

Spoiler

Antarctica is the coldest, windiest, and driest of Earth's continents.^[1]

Antarctica is a polar desert with little precipitation; the continent receives an average equivalent to about 150 mm (6 in) of water per year, mostly in the form of snow. The interior is dryer and receives less than 50 mm (2 in) per year, whereas the coastal regions typically receive more than 200 mm (8 in).^[71]

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life.

Deserts have been defined and classified in a number of ways, generally combining total precipitation, number of days on which this falls, temperature, and humidity, and sometimes additional factors.^[6]

Based on precipitation alone, hyperarid deserts receive less than 25 mm (1 in) of rainfall a year; they have no annual seasonal cycle of precipitation and experience twelve-month periods with no rainfall at all.^[31][32] Arid deserts receive between 25 and 200 mm (1 and 8 in) in a year and semiarid deserts between 200 and 500 mm (8 and 20 in).

Also, for a planet without axial tilt, the region would effectively be like the Carribean (between the equatorial line and what, on a planet with axial tilt, would have been roshar's version of Tropic of Capricorn) during the equinox (spring or fall) all year long. A tropical and semi-tropical high humidity environment. Unlikely to meet most (if any) definitions of "desert."

Edited September 18, 2023 by Treamayne
SPAG

[ΨιτιsτηεΒέsτ Male]

8 hours ago, Firesong said:

So, according to Coppermind.

But, the thing is, I feel it wouldn't be accurate to call it tropical. As if it was in the tropical region, Jah Keved and Alethkar would also be Tropical. 

I think instead it comes down to the high humidity making it feel more tropical. As humidity makes lower temperatures feel much hotter, due to the Heat Index. For example, humidity around the Caspain Sea is 75-80%.

This would increase the perceived temperature, increasing it. And I feel that the temperature would be significantly higher, without it being tropical. It would also experience winds blowing from the Reshi Sea. 

It is actually the Reshi Sea and Endless Ocean that I feel make western Roshar so lively compared to the East. Alethkar is blocked off by the Unclaimed Hills. Others are able to get humid winds from the Reshi Sea and Endless Ocean. Makabak is blocked from it by the mountains surrounding it. Shinovar likely captures winds moving southeast and northwest, which get caught in the area due to the Misted Mountains, which is what makes the mountains so misty. I feel there is likely a cell in that straight north of Shinovar, which moves along the coast of Iri, southward into Shinovar, before curving back up and getting its moisture caught by the Misted Mountains. 

I feel it could also potentially have been caught continuing south, stripping moisture as it flows into Alm and Steen, while retaining some degree of moisture, allowing eastern Makabak to get more green than the rest of the region. 

 

Also, I feel that it does actually make sense for the Reshi isles to not be deserts despite the lack of axial tilt. As they are smallish islands surrounded by a ton of water. Which I feel would be able to keep the humidity up and prevent it from just having everything die. We also know the planet would necessarily be further away from the sun, which would cool down the experienced temperature as per the inverse square law. 

Remember that it is fantasy.

I believe that Brandon has said something along the lines of: “ I try to make all the scientific weather causes and wind and ocean patterns and Geography realistic, but sometimes it just doesn’t work but I won’t get rid of it.”

I can’t find it on initial search, but I will see if i find it. It might have been in a podcast though. I will tell you if I find it.

[Firesong she/her]

Just now, Treamayne said:

May I ask why you think it would be a desert? Do you know that desert conditions do not always involve temperature? The largest desert on Earth is Antarctica. . .

  Reveal hidden contents

Antarctica is the coldest, windiest, and driest of Earth's continents.^[1]

Antarctica is a polar desert with little precipitation; the continent receives an average equivalent to about 150 mm (6 in) of water per year, mostly in the form of snow. The interior is dryer and receives less than 50 mm (2 in) per year, whereas the coastal regions typically receive more than 200 mm (8 in).^[71]

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life.

Deserts have been defined and classified in a number of ways, generally combining total precipitation, number of days on which this falls, temperature, and humidity, and sometimes additional factors.^[6]

Based on precipitation alone, hyperarid deserts receive less than 25 mm (1 in) of rainfall a year; they have no annual seasonal cycle of precipitation and experience twelve-month periods with no rainfall at all.^[31][32] Arid deserts receive between 25 and 200 mm (1 and 8 in) in a year and semiarid deserts between 200 and 500 mm (8 and 20 in).

Also, for a planet without axial tilt, the region would effectively be like the Carribean (between the equatorial line and what, on a planet with axial tilt, would have been roshar's version of Tropic of Capricorn) during the equinox (spring or fall) all year long. A tropical and semi-tropical high humidity environment. Unlikely to meet most (if any) definitions of "desert."

True, true. It wouldn't necessarily be a desert. I mostly just meant like, devoid of life. I do definitely see the confusion as that is definitely not an accurate way I worded that. 

[Firesong she/her]

16 minutes ago, ΨιτιsτηεΒέsτ said:

Remember that it is fantasy.

I believe that Brandon has said something along the lines of: “ I try to make all the scientific weather causes and wind and ocean patterns and Geography realistic, but sometimes it just doesn’t work but I won’t get rid of it.”

I can’t find it on initial search, but I will see if i find it. It might have been in a podcast though. I will tell you if I find it.

Yes, but it is very clear that it has specific wind cells that are indented, and I can find explanations for everything. This whole thread wasn't saying it is impossible, it was thinking of how it is actually reasonable and  possible. It all makes sense, and that was what I was trying to point out. 

I think you just missed the point of what I was saying, no offense. 

Edited September 18, 2023 by Firesong

[ΨιτιsτηεΒέsτ Male]

2 minutes ago, Firesong said:

Yes, but it is very clear that it has specific wind cells that are indented, and I can find explanations for everything. This whole thread wasn't saying it is impossible, it was thinking of how it is actually reasonable and  possible. It all makes sense, and that was what I was trying to point out. 

I think you just missed the point of what I was saying, no offense. 

I did. But it really is cool that he makes planets that works so well isn’t it?

[Firesong she/her]

36 minutes ago, ΨιτιsτηεΒέsτ said:

I did. But it really is cool that he makes planets that works so well isn’t it?

Yeah, the one I have the most issue with is Taldain. Which has a lot of accurate bits, like the stark difference in temperature between sides, and how that would create a massive storm between them due to pressure differences, and all of that. But it does underestimate the difference for plot reasons, as he wants both sides to be habitable. 

It does help that he has somebody with an astronomy degree (Peter has a minor in Astronomy, I think). 

It does also help that things like Roshar are pretty young in a geographic and astronomical sense. As Roshar's moons are definitely not stable on a large timescale. But they are stable on the timescale of the cosmere, being only a bit over 10,000 years. 

Also, as an extra note, I do love how he actually brings up how impossible Tai-na and such are in the books, by talking about how even scholars are confused about how they don't collapse under their own weight. As, yeah, even mixing together their aquatic nature, lower gravity, and higher oxygen, they are still impossible. And I also love the fact he made it low gravity and high oxygen in the first place, as that is perfect for megaflora and megafauna. 

It also makes Urithiru more feasible. It was all-in-all just a very clever choice. 

What I do wonder is how hot Ashyn must have been. I did the calculations of where Roshar should be in orbit, and it would force Ashyn to be close enough to the star to likely be out of the Habitable Zone. If my assumption of solar mass was accurate. 

Here is my little thread on it. 

But, from the short piece we have on Silence Divine, Ashyn does seem like it was genuinely just a hot place. As I don't think it would still be that hot on the surface from the Surgebinding alone. I think it possibly also comes from the closeness to the sun. 

Braize being uninhabitably cold is perfectly feasible with my maths. It would definitely be quite cold. Maybe uninhabitably so if it is far enough from Roshar. But it would be uninhabitable anyway due to a very thin atmosphere. Which would be hard (or impossible) to breathe in, and would retain less heat than a planet with a thicker atmosphere. As atmospheres are very important for heat retention. There is a reason Venus has a surface temperature of 475 C (900 F), and it is due to the thick carbon dioxide and sulfuric acid smog. 

This is the reason why the calculation for surface temperature of a planet (a bit too complex to put here as I don't know how to do math formatting on this forum, but I will try)

(I couldn't include it as it considers greek letters to be emojis, I guess, so I can't include the steffan-boltzmann constant)

seems so inaccurate. As it doesn't account for any greenhouse effects or anything. It is just the temperature a planet with little to no atmosphere would experience at a certain distance from a star of a specific luminosity. Like, for Earth, it would be 256 K or around -17 C (1.4 F). Which we can observe is very inaccurate. 

If my math is right, Roshar would be 261.815853715 K or -11.334146284999 C or 11.598536687 F (yeah, surprisingly close to the absolute value of C, if you are curious, it is exactly equal to the absolute value at -80/7 or -11.4285714286 C). On it being higher, this is due to the fact that the star is larger, and thus hotter (although this proportionality gets weird with really massive stars, but it works at the smaller end). Thus, despite being further away, it does experience slightly more heat. 

Also, this is assuming albedo of 0.29, which is equal to Earth. The fact it is has more water than Earth, and a greater water-to-land ratio, the albedo is likely different. 

Edited September 18, 2023 by Firesong

[ΨιτιsτηεΒέsτ Male]

It definitely is fascinating.

[Firesong she/her]

White Sand stuff

Spoiler

Taldain is definitely one that stresses me out, as the Luminosity of AisDa is going to be insane at the required distances (using Alcyone as a basis, a Blue Giant, I assumed a mere Giant due to the fact that a Supergiant is way too absurd and likely not accurate), At the furthest distance I could reasonably find, at 6.68 AU, which gets an angular size of around 0.741398 degrees, would have a Luminosity of -30.976. And I don't think it is that far away, meaning the luminosity is even higher. 

Even at this distance, I am not sure how it would be survivable to the people on it due to the temperatures that Tidally Locked planets reach. But for some reason nobody has asked Brandon about this. So we are left in the dark as, again, strangely nobody has asked him this in the 7 years since Taldain's introduction. And this is definitely one of the first things that would have come up with this planet, so I bet that he and his team have some explanation as to why.

Like, maybe Autonomy actively absorbs some of the heat to keep the temperatures reasonable. And maybe the luminosity is actually lower due to how she Invested AisDa, which might like, convert part of the radiated energy into Investiture instead of light and heat. 

I am just so curious as to how it all works. As there must be some kind of explanation. 

 

Update on Roshar, I did some testing to see how the ocean currents should work, and as it is south of the equator, the Purelake region would indeed get warm breezes flowing from the equator, and Jah Keved would likely get the cooler breezes as they flow back up towards the equator. The region east of the Unclaimed Hills should receive warm breezes as well. 

I found this 

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A quick tip: the western coast of a continent tends to have a cold current when between 10-45N/S, but a warm current from 45-60N/S (reverse this for the eastern coast).

Which I converted in Rosharan degrees, and this would make Aimia cold. But The Makabaki coast hotter. Both in the West. And in the East, we would get colder coastlines down by the Frostlands and Aimia, and warmer ones up by the Unclaimed Hills. 

Although Northern Alethkar would likely be getting colder winds from a cell north to it. And from the cold winds rising from the Reshi sea. (Which, as I noted, would be warmed around the Purelake area)

This all fits with the science as I understand it, and also seems to match very well with the map. Honestly surprising. 

Edited September 18, 2023 by Firesong