Basically, lighting conditions have to be just right to … basically, allow you to actually see your own white blood cells, in your own eyes, against the … background/everything you are seeing.
So my guess would be that in the summer, where you are, the … ambient light of the sky is too bright, it overwhelms this effect, but in the winter, maybe its mote generally humid, or the light is coming through more atmosphere , at more oblique angles, and is thus less intense.
Though if you are also seeing a… black tail, like… they’re followed by a black smear or a motion blur or something… that could be something else?
Basically, lighting conditions have to be just right to … basically, allow you to actually see your own white blood cells, in your own eyes, against the … background/everything you are seeing.
So my guess would be that in the summer, where you are, the … ambient light of the sky is too bright, it overwhelms this effect, but in the winter, maybe its mote generally humid, or the light is coming through more atmosphere , at more oblique angles, and is thus less intense.
Though if you are also seeing a… black tail, like… they’re followed by a black smear or a motion blur or something… that could be something else?