We investigate how night side cooling and surface friction impact surface temperatures and large scale circulation for tidally locked Earth-like planets .
For each scenario , we vary the orbital period between P _ { rot } = 1 - 100 days and capture changes in climate states .

We find drastic changes in climate states for different surface friction scenarios .
For very efficient surface friction ( t _ { s,fric } = 0.1 days ) , the simulations for short rotation periods ( P _ { rot } \leq 10 days ) show predominantly standing extra tropical Rossby waves .
These waves lead to climate states with two high latitude westerly jets and unperturbed meridional direct circulation .
In most other scenarios , simulations with short rotation periods exhibit instead dominance by standing tropical Rossby waves .
Such climate states have a single equatorial westerly jet , which disrupts direct circulation .

Experiments with weak surface friction ( t _ { s,fric } = ~ { } 10 - 100 days ) show decoupling between surface temperatures and circulation , which leads to strong cooling of the night side .
The experiment with t _ { s,fric } = ~ { } 100 days assumes climate states with easterly flow ( retrograde rotation ) for medium and slow planetary rotations P _ { rot } = 12 - 100 days .

We show that an increase of night side cooling efficiency by one order of magnitude compared to the nominal model leads to a cooling of the night side surface temperatures by 80-100 K. The day side surface temperatures only drop by 25 K at the same time .
The increase in thermal forcing suppresses the formation of extra tropical Rossby waves on small planets ( R _ { P } = 1 R _ { Earth } ) in the short rotation period regime ( P _ { rot } \leq 10 days ) .