Meaning/origin of 三寒四温【さんかんしおん】

Question

Recently I was introduced to the 四字熟語【よじじゅくご】:

三寒四温【さんかんしおん】

... to describe the type of changing weather one often experiences around late Winter/early Spring.

As to the literal meaning of this expression (and where it came from):

The 寒 and 温 in this expression are fairly obvious. For the 三 and 四, I automatically assumed a construction similar to the famous idiom: 七転び八起き【ななころびやおき】, where the "8" merely means "one more time than 7" and therefore something like "for every time you fall you get up, and then one".

With that perspective, 三寒四温 would be (very roughly) something like: "for every time it gets cold, it gets warm again". At any rate: some idea of a back-and-forth (ending on warm).

However, Wikipedia gives a completely different explanation:

三寒四温（さんかんしおん）とは冬季に寒い日が三日ほど続くと、そのあと四日ほど温暖な日が続き、また寒くなるというように7日周期で寒暖が繰り返される現象。

In their definition, the "3" and "4" correspond to somewhat specific durations, and together make a "one-week cycle" of cold and warm characteristic of the season.

As much as I hate to question a Japanese Wikipedia page, this seems surprisingly specific and does not sound particularly grounded in any scientific or folk theory I have ever heard of. The reference links on the Wikipedia page are more illustrations than explanations and not helpful there.

Has anybody ever heard of this expression and its possible origins? Is there any substance to this "one-week cycle" of late Winter in older Japanese folklore?

Answer 1

On this webpage by Japan Airlines, it says that the word originates from North Eastern China or Northern Korea to describe the winter climate where anticyclones from Siberia strengthen and weaken in a 7-day cycle, causing repetition of cold and warm days:

冬の時期に寒い日が３日くらい続くと、そのあとに比較的暖かい日が４日続くという意味の言葉で、寒暖の周期を表しています。 もとは中国の東北部や朝鮮半島北部で冬の気候を表す言葉として用いられました。冬のシベリア高気圧から吹き出す寒気が７日ぐらいの周期で、強まったり弱まったりすることに由来する言葉とされています[。]

And it goes on to say that it is actually rarely literally observed in Japan, and in recent Japanese, this word is used to describe early Spring rather than Winter. This is a departure from its original usage:

実際に日本では３日間寒い日が続いたあとに、４日間暖かい日が続くという周期が現れることはほとんどないのです。 ... その後、[この言葉は]日本に伝わりました。 ... 最近では ... 本来使われる冬ではなく、春先に使われることが多くなっています。日本では、早春に低気圧と高気圧が交互にやってきて、低気圧が通過し寒気が流れ込んで寒くなった後、今度は高気圧に覆われて暖かくなり、周期的な気温の変化を繰り返すことが多くなります。このため、日本では寒暖の変化がはっきりと現れる春先にこの言葉を用いる人が多くなったと考えられます。