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Polar mesocyclones (PMCs) occur frequently over the northern Sea of Japan. In the present study, topographic effects on PMC genesis in this region were investigated using long-term numerical simulations extending over 36 winter seasons. Sensitivity experiments showed that PMC genesis decreases in the part of the northern Sea of Japan when the mountain region at the eastern end of the Eurasian continent is removed. For instance, the generation of PMCs over offshore west of Hokkaido decreases significantly when the mountain range is removed, whereas the generation of PMCs over the Strait of Tartary remains unchanged. According to a composite analysis, this result can be attributed to the different responses of subregional oceanic surface wind to the removal of the mountains. In the experiment without mountains, cold air outbreaks from the continent blow directly over the Sea of Japan causing strong westerly winds over the offshore west of Hokkaido. Consequently, PMCs tend to make landfall earlier and before reaching maturity. The uniformly distributed westerly wind also has a negative impact on PMC genesis because of weakened horizontal wind shear and meridional temperature gradient. By contrast, the low-level wind over the Strait of Tartary before PMC genesis is unaffected by the mountains, and thus, topographic effects are not required for PMC genesis in this region. These results indicate that the responses of PMCs to topographic forcing have a regional variability.

The mid-1850s were a particularly interesting moment as regards instrumental meteorological observations, which were then given guidelines for their international standardization. It was also a period when the European nations and the USA showed eagerness to extend their colonial possessions and to establish intercontinental trade and shipping routes. At about the same time, Japan started to break up with its two-century old seclusion policy by concluding peace treaties with western nations. This presentation deals with the meteorological observations carried out by the naval physician Jean Barthe on board of the French frigate La Sibylle which took part in the Anglo-French naval operations conducted against Russian ships and defenses in the northern Pacific during the Crimean War. Barthe’s manuscript, a record of his observations from January 1855 to September 1857, was recently uncovered in the archives of the French Academy of Sciences in Paris. For each day, it contains the ship position and the five times-a-day weather measurements. Here we will focus on the observations performed during the summers of 1855 and 1856 at Hakodate, in Hokkaidō, on the Urup Island of the Kuril archipelago, on Sakhalin and in the Strait of Tartary.