Examining the Effects of Pacific Decadal Oscillation and ENSO on Global Precipitation during the Satellite Era (1979–2014)

During the post-1979 period in which the satellite-based global precipitation measurements are available, global mean surface temperature rapidly increased up to late 1990s, followed by a period of temperature hiatus after about 1998/1999. Comparing observed surface temperature trends against the simulated ones by the CMIP5 historical experiments especially in the zonal mean context suggests that although the anthropogenic greenhouse-gases (GHG) forcing might have played an important role, in addition to the anthropogenic aerosols and various natural forcings, the effects from decadal-to-interdecadal-scale internal modes specifically the Pacific Decadal Oscillation (PDO) are also very strong. The PDO's effects on precipitation are thus assessed by means of the GPCP precipitation data and the CMIP5 historical simulations. The spatial patterns of observed precipitation trends in the Pacific, including reductions in the tropical central-eastern Pacific and increases in the tropical western Pacific and along the South Pacific Convergence Zone, primarily manifest the PDO's contribution. Removing the PDO effect from the total precipitation trends makes the spatial structures of precipitation trends more similar to those simulated by CMIP5 historical full forcing experiments particularly in the context of zonal-mean results.

On the interannual time scale, the so-called “Central Pacific El Nino” events appear more frequently after the 1997/1998 El Nino. How they have influenced global precipitation patterns, compared to the canonical “Eastern Pacific El Nino”, are explored by using the GPCP observation, the precipitation estimates from NASA/GSFC-Modern Era Retrospective-Analysis for Research and Applications (MERRA) project and the 20th Century Reanalysis (20CR), and the AMIP-type simulations from the NASA/GISS model. Composite spatial patterns of precipitation variations corresponding to these two distinct warm events are constructed and compared for both boreal winter and summer seasons. The comparisons between satellite-based measurements and reanalysis data can not only enhance our understanding of the effects of these two ENSO flavors, but also provide an assessment of the skills of these two reanalysis products. Composite spatial patterns of other components including tropospheric temperature and water vapor are further constructed and compared between satellite observations and reanalysis data.