Many GCMs have exhibited unrealistic teleconnections between ENSO fluctuations and extratropical circulation patterns, driven in part from having poorly represented physical processes in the core ENSO region. CESM is a coupled climate model with land, atmosphere, ocean, and sea ice components that can be used to simulate the Earth's climate system, and is a strong candidate for investigating ENSO teleconnection patterns and extreme precipitation events for several reasons.

Using CESM, observational datasets, and the NCEP CFSR dataset, we analyze the characteristics of ENSO teleconnection patterns over the western U.S., and of ENSO over the tropics. Furthermore, we examine the skill with which CESM simulates synoptic storms over the western U.S., where water supplies, ecosystems and other vital systems are dependent upon the teleconnected signal between ENSO and precipitation. Comparisons are made between CESM and observations/reanalysis, and also between CESM and its predecessor, CCSM3 in order to show the vast improvements made in the newest version of this particular GCM. Notably, the magnitude and frequency of these patterns and events are simulated more realistically in CESM than in its predecessor, CCSM3. This is likely due to improvements in the atmospheric convection parameterization scheme utilized in CESM. Better parameterizations of cloud physics and atmospheric radiation in CESM have also improved simulations of precipitation type and amount. In addition, we investigate regional extreme precipitation events and introduce a method that accounts for the “wet bias” exhibited in many GCMs (including CESM) in simulating precipitation.

Economic entities like agricultural productivity and hydroelectric energy supply depend critically on sufficient available water resources. These resources are directly affected by prolonged precipitation minima (droughts), prolonged precipitation maxima (floods), and short but intense episodes of precipitation maxima (flash floods). It is therefore desirable to better understand mechanisms controlling the strength of the teleconnected signal between ENSO and precipitation. Climatically enhanced fluctuations in precipitation, including extreme wet or dry events, may then be anticipated and adapted to given better climate predictions.