Torques responsible for evolution of atmospheric angular momentum during the 1982-83 El Nino

Atmospheric angular momentum (AAM) reached extremely high values during the large 1982-83 El Nino event. The mechanisms responsible for the anomalousl y high AAM are examined using mountain torque (tau(m)) and friction torque (tau(f)) time series computed from the National Centers for Environmental P rediction-National Center for Atmospheric Research reanalyses. AAM anomalie s, defined with respect to a 29-yr climatology (1968-96), are mostly positi ve from mid-1982 onward, but notably they double in amplitude over a 2-week period in early 1983. Analysis of the torque Series reveals that this shar p AAM increase is mostly related to anomalies in tau(m) primarily associate d with American and Eurasian orography. After reaching its peak value in Ja nuary, AAM anomalies decay slowly to near-normal values over the next three months, with anomalies in tau(f), especially over the subtropical North Pa cific, playing a dominant role in this downturn. The relevant anomalies in tau(m) and tau(f) are discussed in relation to rapid synoptic-scale variabi lity and longer-term, large-scale anomalous patterns in surface pressure an d winds that characterized this El Nino event.