High air temperature in the summer its density is relatively low, inhaling the combustible mixture in the cylinder than winter easy to ignite, need ignition breakdown voltage is relatively low, so the breakdown probability is small in the summer.
In winter temperatures lower its density is relatively high, so the density of the mixture formation within the cylinder, concentration is high, the spark plug electrode gas between the freedom of movement of the distance between ions and electrons, it is not easy to collision ionization.
So you must improve on the spark plug electrodes on the ignition voltage, increase the effect on the ion of the electric field force, and the ions accelerated motion collision ionization to spark breakdown.
Mixture density is big, the need of the higher breakdown voltage.
But there is no direct relationship between the breakdown voltage and temperature of the mixture, but is associated with the density of mixture, because the density of mixture, the greater the ions and electrons free movement distance will be shorter, thus not occur collision ionization.