  Thermal atmospheric tides have a strong impact on the rotation of terrestrial
planets. They can lock these planets into an asynchronous rotation state of
equilibrium. We aim at characterizing the dependence of the tidal torque
resulting from the semidiurnal thermal tide on the tidal frequency, the planet
orbital radius, and the atmospheric surface pressure. The tidal torque is
computed from full 3D simulations of the atmospheric climate and mean flows
using a generic version of the LMDZ general circulation model (GCM) in the case
of a nitrogen-dominated atmosphere. Numerical results are discussed with the
help of an updated linear analytical framework. Power scaling laws governing
the evolution of the torque with the planet orbital radius and surface pressure
are derived. The tidal torque exhibits i) a thermal peak in the vicinity of
synchronization, ii) a resonant peak associated with the excitation of the Lamb
mode in the high frequency range, and iii) well defined frequency slopes
outside these resonances. These features are well explained by our linear
theory. Whatever the star-planet distance and surface pressure, the torque
frequency spectrum -- when rescaled with the relevant power laws -- always
presents the same behaviour. This allows us to provide a single and easily
usable empirical formula describing the atmospheric tidal torque over the whole
parameter space. With such a formula, the effect of the atmospheric tidal
torque can be implemented in evolutionary models of the rotational dynamics of
a planet in a computationally efficient, and yet relatively accurate way.
