ENSO Anomalies over the Western United States: Present and Future Patterns in Regional Climate Simulations

Surface temperature, precipitation, specific humidity and wind anomalies associated with the warm and cold phases of ENSO simulated by WRF and HadRM are examined for the present and future decades. WRF is driven by ECHAM5 and CCSM3, respectively, and HadRM is driven by HadCM3. For the current decades, the ECHAM5-WRF, CCSM3-WRF and HadRM simulations are broadly consistent with the observed warm-dry and cool-wet teleconnection patterns over the Pacific Northwest (PNW) and the Southwest U.S. for warm and cold ENSO. Differences in the regional simulations originate primarily from the respective driving fields. For the future decades, the warm-dry and cold-wet teleconnection patterns in association with ENSO are still represented in ECHAM5-WRF and HadRM. However, there are indications of changes in the ENSO teleconnection patterns in CCSM3-WRF in the future, with wet anomalies dominating in the PNW and the Southwest U.S. for both warm and cold ENSO, in contrast to the canonical patterns of precipitation anomalies. Interaction of anomalous wind flow with local terrain plays a critical role in the generation of anomalous precipitation over the western U.S. Anomalous dry conditions are always associated with anomalous airflow that runs in parallel to local mountains and wet conditions with airflow that runs in perpendicular to local mountains. Future changes in temperature, precipitation and wind associated with the ENSO events in the ECHAM5-WRF and HadRM simulations appear to suggest weakening of teleconnection patterns for warm ENSO but strengthening of teleconnection patterns for cold ENSO.