Understanding the Features and Mechanisms of the Great Plains Low-Level Jet in the CMIP5 Models

The Great Plains low-level jet (GPLLJ) has been shown to significantly impact precipitation and severe weather outbreaks over the U.S. Great Plains during the spring and summer months. Therefore, it is extremely important that features of the GPLLJ, including the main atmospheric and oceanic drivers, are understood and simulated by global climate models accurately so Great Plains precipitation can be predicted reliably in the future. To examine sea surface temperature (SST) driving mechanisms of the GPLLJ, this study uses sea surface temperature (SST) data from HadISST1 along with data from the 20th Century, ERA-Interim, and NCEP CFSR reanalyzes, and historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Features of the GPLLJ are examined and show that CMIP5 historical models simulate a GPLLJ that is too weak, extends too late into the summer, and has a peak wind too low in the troposphere. Noting these errors in the simulation of the GPLLJ, the relationship between El Niņo Southern Oscillation (ENSO) and the GPLLJ in CMIP5 historical simulations is investigated. As observed in previous studies, observations and reanalysis show that ENSO has a significant negative correlation with the GPLLJ in the spring and a significant positive correlation with the GPLLJ in the summer. However, while the majority of CMIP5 historical simulations exhibit negative correlations in the spring, they fail to simulate the positive correlation in the summer. Causes of this failed simulation will be examined, including biases in the simulation of the GPLLJ and ENSO, and ability of the models to represent the atmospheric teleconnection with the Pacific. In addition to ENSO, SSTs in the Gulf of Mexico, Caribbean, and North Pacific (Pacific Decadal Oscillation) are also shown to impact the GPLLJ and will be examined in the CMIP5 simulations.