ENSO-related Precipitation Seasonal Evolution and Multi-decadal Changes in Recent Reanalysis Datasets and CMIP5 Models

Abstract:

El Niño/Southern Oscillation (ENSO) is the single most important determinant of variability in global precipitation fields on seasonal to interannual time scales. It is important to understand and predict ENSO and ENSO-related precipitation due to its connection with many environmental and societal problems. However, since ENSO is associated with complex atmosphere-ocean coupling, it is still difficult for models to accurately simulate ENSO and the related precipitation. Our studies focus on comparing the ENSO and its related precipitation in the Coupled Model Intercomparison Project Phase 5 (CMIP5) models with the recent developed long-term 20^th Century Reanalysis (20CR) and the Reconstructed Precipitation (REC), in order to improve the ability of CMIP5 models to simulate ENSO and ENSO-related precipitation mean states and variations during the past century and to further understanding ENSO and the related precipitation. Currently we are using extended EOF (EEOF) to extract the ENSO-related precipitation seasonal evolution signals. The results show that all of models can simulate similar seasonal evolution of ENSO as the REC and the 20CR. We also use a moving block average method to form an ENSO-related precipitation index and use precipitation composites based on this index to compare the multi-decadal changes of the ENSO-related precipitation anomalies among the data. The results suggest that both DJF El Niño- and La Niña- related precipitation patterns and their extremes become significant stronger (on a significant level of 95%) in the 2^nd half of the 20^th Century in 20CR, REC and few CMIP5 models (e.g. MIROC5). By separating the related frequencies of ENSO into classic ENSO variability (period of 2-7 years) and decadal ENSO variability using a wavelet analysis, we are able to identify that the increase of the ENSO-related precipitation patterns and extremes in REC, 20CR and MIROC5 resides in the significant power increase of their classic ENSO variability. In the near future, we are also going to investigate how sea surface temperature and general atmospheric circulation in each dataset influence the behavior of its ENSO and ENSO-related precipitation, in order to further explain these seasonal and multi-decadal changes mentioned above, as well as the ENSO spatial differences among different datasets.