Unfortunately, I can only find information suggesting that trees will BREAK dormancy based on soil temps, and that's what searches are turning up.
I am finding a bunch of info on "temperatures cooling, changes in day light/day length", but nothing definitive.
I'm pretty sure that ground temps climbing above 40°F initiate wakeup, so I'm inclined to believe that temps dropping below 40°F would also set in dormancy.
I also found info that suggested the leaves on trees have a built-in "temp gauge" that, given certain air temp, the leaves would send the signal to the plant to enter dormancy.
Not a botanist here...
I know seed break in many varieties is triggered by ground temps also ...
I'm inclined to believe length of day is less of a factor than ground temps.... but I also think that the presence of microclimates and concrete has the largest influence.