Identification of Large Scale Circulation Patterns Associated With Temperature Extremes Over North America in Observations and Climate Model Simulations of the 20th Century

To better anticipate how temperature extremes will be affected by climate change, it is important to understand the atmospheric circulation patterns associated with them. Working towards this goal we have extracted those events in the tails (i.e., below the fifth and above the ninety-fifth percentiles) of the daily temperature frequency distribution for locations in North America from a gridded observational data set for both daily maximum and minimum temperature during a 30 year period in the 20th century. Using reanalysis data, we calculated composite atmospheric circulation patterns for these events.. The identified patterns are then compared with known low frequency modes of climate variability that are understood to impact regional temperature behavior. Lastly, the same analysis techniques are applied to output from general circulation models to determine how similar the simulated relationships between temperature extremes and circulation are to the observed ones. The relationships identified using the observed data will aid in our understanding of how temperature extremes over North America will change in the future due to an anthropogenically enhanced greenhouse effect.