Lunisolar torque on the atmosphere and Earth's rotation

International audienceThe atmospheric effect on Earth's rotation is classically computed from atmospheric angular momentum (AAM) series by considering that the whole AAM variations are transmitted to the solid Earth. In fact, such a procedure is an approximation because it ignores that the atmosphere exchanges also angular momentum with the moon and the sun. The computation of the lunisolar gravitational torque on the atmosphere is the core of the present study. It is derived analytically and then estimated from pressure data over the period 19752000. The mean surface pressure is the main contributor, at the level of Full-size image (<1 K) for the equatorial component, Full-size image (<1 K) for the axial one, whereas the thermally driven pressure variations provide about 10% of the variance. This torque plays a significant role in the budget of the atmospheric angular momentum, but does not account for the inconsistency between the present series of the atmospheric angular momentum and the interaction torque between the solid Earth and the atmosphere. From the tidal waves of this torque we derive accurately the contribution of the atmosphere to the lunisolar precessionnutation of the Earth (Full-size image (