Moisture Balance for Bidecadal Variability of Wintertime Precipitation in the North Pacific Using NCEP/NCAR Reanalysis

Abstract

Moisture budgets are analyzed using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data over the North Pacific for a Bi-Decadal Oscillation (BDO) in precipitation that was reported by Minobe and Nakanowatari (2002). BDO in wintertime precipitation is mostly associated with moisture flux convergence, with a minor contribution from evaporation. The moisture convergence is mainly due to anomalies of wind and moisture on time scales longer than a month, except at high-latitudes where transient eddy (time scales shorter than a month) contributions are greater. When the Aleutian low strengthens (weakens), the anomalous moisture flux convergence is due to a cyclonic (anti-cyclonic) wind circulation over 30°-60&deg:N and anti-cyclonic (cyclonic) wind circulation over 0°-30°N. This pair of anomalous circulations is also observed on interannual time scales, but they appear independent of El Ni&ntildeo;/Southern Oscillation (ENSO). The anomalous circulation over 0°-30°N is associated with sea-level pressure anomalies in the tropics (20°S-20°N) and this result is confirmed with the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and the NCEP real-time marine data. This low-latitude anomalous circulation plays a dominant role in precipitation variability in Hawaii on the bi-decadal and interannual time scales.