ENSO-induced anomalies over North America in historical and future climate simulations
This work seeks to improve understanding of how internal climate modes may change under externally forced climate change and how teleconnections to remote regions may be modified in the future. This research seeks to address three linked questions that explored whether downscaling ESM output to drive a regional climate model modifies implied ENSO teleconnections. We perform WRF simulations at convection-permitting resolution nested with LBC from the HadGEM2 ESM. Two paired simulations are run: a strong El Niño and a weak La Niña phase for the historical and future years. The HadGEM2-WRF simulation output is compared to the ENSO anomalies derived from the NOAA ENSO Climate Normals dataset. We quantify ENSO teleconnections to temperature and precipitation anomalies in the historical and future climate over the entire eastern North America at high resolution and find:
- Regional modeling of ENSO teleconnections with WRF using LBC from HadGEM2 shows a poor degree of agreement with differences in Tmax, Tmin, and PPT under different ENSO phases as manifest in the observed NOAA ENSO Climate Normals.
- When the HadGEM2-WRF results are placed in the context of the HadGEM2 output, the modification of the teleconnections at a regional scale is the result of inherent bias in the HadGEM2 model. There is evidence to suggest that WRF can drive its own response to ENSO phase. In areas of weaker signal from the LBC, WRF generates a regional teleconnection response.
- A reversal in the sign of the difference in Tmax and Tmin under different ENSO phases in the future climate relative to the historical climate is manifest in this model chain for this very high external climate forcing scenario.
The El Niño Southern Oscillation (ENSO) is a prominent mode of internal climate variability and is a critical source of temperature and precipitation anomalies across a wide range of countries particularly during the Northern Hemisphere winter. Because of the global impact of ENSO teleconnections, it is the leading source of forecast skill on seasonal to interannual time scales. Here we present the first (to our knowledge) downscaling simulations performed at a convection-permitting resolution to explore how regional temperature and precipitation anomalies over North America due to ENSO may be modified as the global climate warms.
Projected changes to the El Niño Southern Oscillation (ENSO) climate mode have been explored using global Earth System Models (ESMs). Regional expressions of such changes have yet to be fully advanced and require the use of regional downscaling. We perform simulations with the Weather Research and Forecasting (WRF) model applied at convection-permitting resolution and nested in output from the HadGEM2 ESM. We quantify ENSO teleconnections to temperature and precipitation anomalies in the historical and future climate over eastern North America. Two paired simulations are run: a strong El Niño (positive ENSO phase) and a weak La Niña (negative ENSO phase) for the historical and future years. The HadGEM2 direct output and HadGEM2-WRF simulation output are compared to the anomalies derived from the NOAA ENSO Climate Normals dataset. Near-surface temperature and precipitation differences by ENSO phase, as represented by HadGEM2-WRF historical simulations, show a poor degree of association with the NOAA ENSO Climate Normals due to large biases in HadGEM2. Downscaling with WRF does improve agreement with the observations but large discrepancies remain. The model chain HadGEM2-WRF reverses the sign of the ENSO phase response over eastern North America under simulations of the future climate with high greenhouse gas forcing, but due to the poor agreement with the NOAA ENSO Climate Normals, it is difficult to assign confidence to this prediction.