  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).
