Long-term variations of atmospheric angular momentum and torque

Abstract

In the absence of external torques, the earth system is a closed system and its angular momentum is conserved. The atmospheric angular momentum (AAM) exchange with the solid/liquid earth is achieved by friction and mountain torques. The variations of the AAM and torques are important indicators of global climate change. Using the NCEP/NCAR reanalysis data for 1948–2015, the long-term variations of the AAM and torques are analyzed. A weak positive AAM trend is detected, but an examination of the AAM budget shows that on annual to decadal scales, the signals of the AAM and total torque are inconsistent. During the study period, the total torque was mostly negative and had a decreasing trend, suggesting a decrease of the AAM. To check this inconsistency, we analyze the time series of the length-of-day anomalies, ΔLOD. It is found that ΔLOD is weakly correlated with the AAM, while the derivative of the earth’s core-induced ΔLOD is strongly correlated with the torque. If this is correct, then a core-induced climate change can indeed happen.