Frozen ground

I have really been enjoying the cold air at the lunchtime. I like the way that noise is deadened (apart from the ever present roar of motorised traffic of course) and my footsteps just make a thumping sound on the frozen ground.

My husband often likes to quote that if the air temperature is below 4C then it is cold enough for a ground frost. In fact there can be a difference of up to 5C between a thermometer placed on the ground and one placed 4 feet above it is the air is still and clear and there is low humidity. That is quite a difference.