Answer:
Radiation
Explanation:
The radiation that comes from the sun is the one that causes the ground to warm up in sunny days, radiation brings energy form the sun all the way to the earth and warms up all of the things that touches or reaches, on cloudy days it is harde for radiation to reach the ground so it doesn´t get warmed up, so the answer to why in sunny days the ground is warmer would be because of radiation.
