Recent rainfall cycle in the Intermountain Region as a quadrature amplitude modulation from the Pacific decadal oscillation

Precipitation in the Intermountain Region has experienced a pronounced 10–20 yr cycle during the last four decades. We present evidence of a quadrature phase coupling of these 10–20 yr cycles between the Pacific Decadal Oscillation (PDO) and the Intermountain rainfall. The PDO has been linked to precipitation anomalies in the Northwest and Southwest U.S., while the Intermountain Region remains marginal. During the transition phase of a 10–20 yr cycle in the PDO, an anomalous circulation dipole over the Gulf of Alaska is formed. This circulation dipole modulates the synoptic activity that produces rainfall in the Intermountain Region. As a result, the Intermountain rainfall cycle has repeatedly lagged the PDO cycle by a quarter phase, amounting to about 3 to 4 years. Future understanding of the 10–20 yr cycle embedded in the PDO and its quadrature phase modulation may help predict the Intermountain climate.