A prominent precipitation decrease occurred over the equatorial central Pacific in the late 1990s, accompanied by precipitation increase around the Maritime Continent and over the equatorial America. Previous studies attributed the above change to La Niña-like decadal mean sea surface temperature (SST) cooling associated with a positive to negative phase switch of the Pacific Decadal Oscillation (PDO). Results of numerical experiments with an atmospheric general circulation model reveal that both the interdecadal and interannual components of SST variations contribute to the late 1990s’ precipitation reduction over the equatorial central Pacific in all the four seasons and the precipitation increase around the Maritime Continent in winter and summer. The accompanying precipitation increase over the Central America is mainly induced by the interdecadal components of SST variations. The contribution of interannual SST variations to the equatorial central Pacific precipitation decrease mostly stems from a larger rate of precipitation change with SST in positive than negative SST anomaly years, which leads to a residual decadal mean precipitation being larger during the period before than after the late 1990s. The moisture budget decomposition demonstrates that the dynamic effect associated with the vertical motion change dominates the tropical decadal mean precipitation changes in all the four seasons and the thermodynamic effect associated with the moisture change is small. This applies to the equatorial central Pacific, the Maritime Continent, and the Central America in both interdecadal and interannual SST forced simulations.
This study is supported by the National Key Research and Development Program of China grant (2016YFA0600603) and the National Natural Science Foundation of China grants (41775080, 41530425, 41475081 and 41721004). The precipitation and wind data were obtained from https://www.esrl.noaa.gov/psd/. The SST data were obtained from https://climatedataguide.ucar.edu/climate-data/sst-data-hadisst-v11/.