The Köppen–Geiger climate classification made simpler (I hope so)

[Azélor]

All large scale circulation phenomena are better understood in the vertical plane than in the horizontal plane.
Also temperatures say generally more and are more causal for large scale features than pressures. This has a reason - energy exchages are better described by temperatures than pressures.
I have always seen that people who start modelling climates by trying to locate high and low pressure zones generally struggle to get Something consistent because the causalities are confusing.
The monsoon engine in the vertical plane is quite simple, one needs :
- a large land body (at rather low latitude, say around tropics)
- a large ocean body

As the ocean body is large, it is not far from being isothermal throughout the year.
The land body on the other hand strongly oscillates (the larger the amplitude, the stronger the effect) so that half of the year its temperature is above ocean and half of the year below.
Assuming N hemisphere, in summer the air above land is hot so it rises (corollary is that we have a low pressure but this is irrelevant)
Then in high altitude it must go somewhere. If it goes towards the ocean (here is the difficulty because it is not easy to say where the high altitude air will go) then it will sink above the ocean (corollary is that we have high pressure there).
Then because of mass conservation, the loop must be closed and the wet cold air goes again towards land on ground.
The result is that when this wet air rises again above the heated land, it expands and précipitations occur.

In winter it is opposite. It is the same vertical loop but it rotates in the opposite direction.

All this are necessary conditions but afaik the sufficient conditions for a monsoon regime to occur are not clearly known. Apparently the shape of the land/continent and oceanic currents (or their absence) play a role so that this becomes quite complicated.
For mapping purposes I have always adviced that if you have a large land mass beside an ocean (preferably eastwards) around the tropics and want a monsoon, just put it there.
You will find nobody who would argue that there should be none because nobody knows

I got this but the point I don't understand and as you said yourself:

In winter it is opposite. It is the same vertical loop but it rotates in the opposite direction.

the winter monsoon should be dry cold air but it is not and I want to know if my explanation above make sense.

Example:
https://en.wikipedia.org/wiki/Wuhan#Climate
https://en.wikipedia.org/wiki/Changsha#Climate
https://en.wikipedia.org/wiki/Nancha...hy_and_climate
https://en.wikipedia.org/wiki/Fuzhou
https://en.wikipedia.org/wiki/Hangzh...hy_and_climate

I could possibly ignore the winter monsoon of China, after all, a city like Wuhan receive possibly over 1200mm of rain during the 6 hottest months. It's enough to keep it humid.
But I would rather have it.

[Deadshade]

I got this but the point I don't understand and as you said yourself:


the winter monsoon should be dry cold air but it is not and I want to know if my explanation above make sense.

Example:
https://en.wikipedia.org/wiki/Wuhan#Climate
https://en.wikipedia.org/wiki/Changsha#Climate
https://en.wikipedia.org/wiki/Nancha...hy_and_climate
https://en.wikipedia.org/wiki/Fuzhou
https://en.wikipedia.org/wiki/Hangzh...hy_and_climate

I could possibly ignore the winter monsoon of China, after all, a city like Wuhan receive possibly over 1200mm of rain during the 6 hottest months. It's enough to keep it humid.
But I would rather have it.

It is not clear to me why you think that there is Something special to be explained.
There is no "winter monsoon" in this location - there is just a classical gaussian precipitation monsoon profile with a maximum around may-june. Precipitation in winter is low as expected.
The only phenomenon Worth to be noticed is that the temperature time derivative is strongest when passing from spring to summer. That means that the rate of temperature increase is at its maximum a bit before the summer when also the precipitation maximum is located.
If you want to understand what happens in that region (which is quite large going from Japan to East China) then there is a stationnary front (caused by the inverted monsoon like loop) where the wet air from pacific meets the very cold continental air.
This happens when the derivative is strongest (see above) and after that the front moves northwards so that the summer/fall are drier.
That shows that this is Something completely different from a monsoon - the cause of monsoon précipitations is adiabatic expansion while the cause of the east china-japan precipitation maximum is a stationary front.
Why the front is stationnary and regular, I don't know but it may be studied somewhere if I had the patience to Google "Meiyu front".

[Azélor]

You, I should recommend reading the whole guide before starting?

The north east is warmer... I was going to say that you confused east with west but I did it too in my previous message. The pink means it's 1 category warmer.
I think the blue is too cold to be on the coast, maybe on a closed sea it would be cold enough.

[ascanius]

You, I should recommend reading the whole guide before starting?

The north east is warmer... I was going to say that you confused east with west but I did it too in my previous message. The pink means it's 1 category warmer.
I think the blue is too cold to be on the coast, maybe on a closed sea it would be cold enough.

Yeah sorry, I forgot to proofread. Honestly I don't remember what I was trying to say. Anyway keep up the good work.

[Azélor]

Step 6, precipitations:

General explanations:

What cause rain? : When the air gets colder. Colder air masses have a smaller moisture retention capacity than the hotter ones, and it fall to the ground.

· Rising air in low pressure areas: the Intertropical convergence zone (ITCZ) and the polar front.
· Polar front, when hot air masses encounter cold air masses. This is called a cold front.
· Orographic lift: Air rising above the mountains. Side facing the dominant winds is rainy.


General tips

· Precipitation tends to decrease when moving away from the source of water.
· In summer, some islands and peninsulas are drier than inland locations but wetter in winter. Ex: Nova Scotia.
· If the winds are blowing directly from sea to land, there are more precipitations.
· Inland precipitation follows the directions of the winds. See the Asian monsoon in Mongolia.
· Precipitation categories spread a lot over flatlands.
· Size and shape of wet systems are influenced by dry systems. It bends and is push it away. Ex: Africa ITCZ.
· Higher latitudes tend to be drier than those close to the equator.

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Transition map, it's not mandatory but it's meant to help figuring out where it rains.
Temporary green/wet and white/dry map

I recommend making maps like the ones below. For the sake of simplification, we can classify the different areas on the planet, according to whether it’s a dry air mass or a wet one mostly by using just the air pressure and wind directions. Here are the different zones. Green is for rainy areas, white is dry.

January and July

explanation pressure winds and rain Jan.png explanation pressure winds and rain July.png

1,2,3,4 are roughly the same thing. They are dry.
5 and 6 are pretty similar but have a different cause. They are wet.
7 It’s just to represent the fact that the cold polar air is drier but not completely dry either.

1· High pressure systems (H, for short) are dry and the areas receiving dry air are dry as well.
2· The equatorward east side of the oversea H is usually really dry.
3· Equatorward west of H is dry
4· Equatorward west side tend to be dry in winter. Dry but can have some rain at right angle from the sea. It never rain with cold currents. Orographic rain possible. In summer, they make the weather drier as in Brazil.
5· The west and poleward sides of H are wet. This is where the cold air from the poles and the hot air from the tropics collide. Strom formations are more common. They don’t travel as far west in winter as in summer because the continents have a higher air pressure.
6· Low pressure systems (L) are wet if there is water available and if the winds are not blocked by mountains. Inland winds are dry even if they are located in a low pressure area as it’s the case in North Africa in January.
7· In summer especially, the areas receiving the cold air from the pole are drier.


Mapping the precipitation using the 6 categories

Now, time to map the precipitation. I would recommend using the color scheme provided to paint it if you intend to use the script later.

There are 6 categories for precipitations, from 0 to 5:

Category 0: The first one is pink/magenta and is actually a penalty I added later to get a more precise results. It can have a huge impact on colder areas.
Category 1: The second category is transparent.
The other colors are as indicated in the document, 6 (whitish blue) being the wettest.

color rain.png

''Painting''

1· ITCZ (number 6 on the white/green map). It can cover rather large area. Cover the whole area until stopped by mountains.
It has the highest precipitations (5), the size depend on the winds and the moisture they carry. More moisture=larger wet area.
For example, Africa ITCZ is smaller than in South America presumably, because it receives half of its winds from the dry Sahara.
Ideally the ITCZ is centered on the center of the low pressure, following the direction of the winds

Information: the Amazonian forest generates 50-80% of its own rain with its own transpiration. Less trees means less precipitation.

January and July

jan itcz.png jul itcz.png


2· High latitudes dominant Westerlies: located mostly on west coasts. Number 6

Winter: Poleward of 30
Category 4 is on coasts at right angle mostly, on peninsulas and small islands.
Category 3 covers a distance of 10 to 15 degrees inland from the source of water. (1 degree is about 111,11km at the equator)
Category 2 is covering a large area 2000 or 3000 km from the sea.

Summer: Poleward of 40-45
Category 4 is at right angle with the sea.
Category 3 is almost the default at mid latitudes as far as 2000-2500 km inland.
Category 2 is near the poles instead of 3.
Outside the poles, Category 2 is only a transition to the dry areas.

January and July

jan westerlies.png jul westerlies.png


3· Extratropical storm path: Located in mid to high latitudes, west of oceanic high pressure centers. Number 5
Explanation: The High over the water pushes hot air toward the land and toward the pole, clashing with the colder air coming from the pole. The clash is a cold front, a rapid cooling of the air, generating the precipitations. Area is smaller in winter due to the H overland.
When the Westerlies become dominant, this influence gets weaker.

Winter: poleward of 20-25
Category 4 is on coasts if direct winds, can go 10 degrees inland near tropics, otherwise it’s marginal.
Peninsulas and direct onshore winds are wetter are also category 4.
Category 3 covers a distance of 10 to 15 degrees inland from the source of water.
Category 2 is a much shorter transition: 5 degrees or less.

Summer: poleward of 25 more or less
Category 4 can go10-15 degrees inland but the distance gets considerable shorter by getting close to the polar circle (60-66).
Past 40-45 of latitude: Category 4 becomes less common on coast but still possible inland
Category 3 is the default category at mid latitudes.
Category 2 is near the poles instead of 3.
Outside the poles, Category 2 is only a transition to the dry areas.

January and July

jan east coast storm.png jul east coast storm.png


4· Winter Monsoon: near the sea in winter, on the east coasts. Represented by 1,3,4
Need winds from ocean, strength of precipitation depend on the angle between the sea and the land . High at right angle but low or null if parallel (see graphic).
Precipitation decrease quickly when moving away from the coast.

Edit About China: there is a semi permanent low pressure system over the southern part of the country in winter possibly similar to what happens over North America = instability. It would be more appropriate in the category above.

January and july

jan winter monsoon.png jul winter monsoon.png


Poles summer: hotter water means more precipitations, with the eastern side usually drier than the west because of the dominant wind direction and warmer waters.

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Orographic lift effect

Precipitations fall because the cooling of the air saturates it with water. The water only falls if the air is saturated.

Notes
· Precipitations are centred on the flanks not on the ridges. (Actually, in Iraq, it's centered on the plains)
· Large areas have a larger effect and a rapid increase in elevation has also a bigger effect.
· High pressure zones with cold currents do not generate an Orographic lift: example Atacama Desert.
-Polar winds do not have orographic lift either.

Tip: when painting the precipitation related to the orographic lift, I've found it was easy to do it as follow. Select one level of precipitation and look at the elevation graphic to see at which altitude the precipitations should increase and use the paint tool on that color. This way, you will cover all the map in 1 click. Do this for the different altitude level if necessary.

Color altitudes for reference (see graphic)

Green: 0-1 km (the different colors don't have an impact below 1000, they could but it's just too complicated)

color altitude.png

Explanation: Take each category at a time and increasing the precipitation at these places only if the altitude is high enough.
When the default precipitation category at sea level is x (0-1 km), increase the precipitation.

Every ridge provoking an Orographic rain effect lowers the % moisture and makes the remaining air drier. It also means that in order to re-saturate the air of water, colder temperatures are needed.

I'm not sure what the mountain on the second line is for. Ignore it. I will try to find what it means.

altitude rain.png

Magenta, category 0

· The last part is to add the magenta penalty for the really dry places. This category is useful for moderate/cold areas that have low temperature but also low precipitations.
Without this some steppes appeared as lush forests.
· Should be put only where no other colors are present.
· Less likely at higher altitudes.
· Spread out on plains but close with rugged terrain.

Final results:

January
jan precipitation final.png
July
jul precipitation final.png

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[Gridello_Aspart]

i need help that tutorial make me so confuse i cant figure out where its dry or where its not pls HELP i m not even sure i did other parts right i really need help i read other tutorial i understand it well but it always crated some blanks so i tried that one but it makes me confuse

[Charerg]

i need help that tutorial make me so confuse i cant figure out where its dry or where its not pls HELP i m not even sure i did other parts right i really need help i read other tutorial i understand it well but it always crated some blanks so i tried that one but it makes me confuse

Just bumping this up since it showed up only now (your first posts need to be approved by a community leader before showing up on the forums). See the original post for the maps.

At first glance I admit I'm totally confused myself . Maybe start a bit slower and ask for feedback step-by-step? That way you usually end up with more feedback. Like start with the ocean currents for example. It might also be an idea to start a separate thread for your world, since I'm not sure how actively people check the tutorial thread.

[Azélor]

I fixed the attachments.
Using the 2.5 m resolution map instead is easy, since I keep the same colour scheme, I just need to change the base map.

Just bumping this up since it showed up only now (your first posts need to be approved by a community leader before showing up on the forums). See the original post for the maps.

At first glance I admit I'm totally confused myself . Maybe start a bit slower and ask for feedback step-by-step? That way you usually end up with more feedback. Like start with the ocean currents for example. It might also be an idea to start a separate thread for your world, since I'm not sure how actively people check the tutorial thread.

Woa, this just appeared out of nowhere.
I'd also recommend opening a new thread to avoid confusion.

[Azélor]

Meiyu, or plum rain start in late spring and continue during early summer: http://glossary.ametsoc.org/wiki/Mei-yu_front

Monsoon just mean an inversion on the winds pattern. It doesn't mean that it's going to be rainy. In this case roughly
summer: from sea to land
winter: from land to sea


My research so far had given me no satisfying answer. That is why I'm asking here, in case someone knew about it.


But if it's a stationary front, I just wanted to be sure.

[Deadshade]

My research so far had given me no satisfying answer. That is why I'm asking here, in case someone knew about it.


But if it's a stationary front, I just wanted to be sure.

Yes it is definitely a stationnary periodical front.