Leaving home at 6:50 this morning, the sky held vivid contrails. About fifteen minutes after sunrise, white streaks stood out among clouds tinged rose by the morning sun.
♪ Longing for the sky, racing across the sky — that child’s life is a contrail ~ ♪
Humming Yumi’s “Contrail,” used this year as the theme song for Hayao Miyazaki’s “The Wind Rises,” I hurried to the station.
At Palaceside Building the sky was cloudless — another dazzling blue day. A warm one.
Contrails form in two main ways. First, exhaust from engines: at about 10,000 meters, temperature is roughly 60 degrees colder than on the ground — below minus 40. Engines compress and burn air, releasing 300–600°C exhaust; moisture freezes instantly into visible white cloud.
Second, vortices behind wings locally lower pressure and temperature, cooling moisture into contrails.
Weather firm “Idea”’s “Bioweather Service” site says contrails need matching pressure, temperature, humidity and wind — they form when aircraft fly through saturated or supersaturated air, may persist hours, and are common over Japan from autumn into early winter.
The site suggests Japanese began noticing contrails often from autumn 1944 (Showa 19), when B-29 raids on the home islands intensified. The first home-island raid was June 1944 from Chengdu targeting northern Kyushu; large-scale raids followed U.S. capture of the Marianas — first from there November 24, continuing until war’s end. B-29 altitude, speed and engines matched seasonal conditions for contrails. Japanese military records note “contrails always appear on high-altitude B-29 attacks.”
I wondered if contrails were a winter season word in haiku — summer has cumulus, autumn herring-scale clouds, winter winter clouds, cold clouds, “Fuji cap” clouds — but haiku using contrails are “non-season” (muki), not season words.