Strange temperature changes around boundaries
 

I have been trying to calculate temperature field of air around a building.

The mesh in Z=0 plane around the building is shown in attachment 2.jpg.

I used RNG for viscous modelling and DO (solar loading) for radiation.
The absorption coefficient of air is 1.
building is 0.1.
ground is 0.2.

For building and ground, the Thermal mode is set as Mixed. I intended to use Coupled, however, the option does not show.

The strange calculation result is as shown in 1.jpg.

Anyone knows what the problem is?

Many thanks!