Research Overview

Our research focuses on the dynamics of the climate system, with a specific emphasis on understanding the fundamental mechanisms that are involved in changes in climate.  Climate models are powerful tools for learning about such mechanisms, as they enable us to test hypotheses about climate system behavior by performing controlled experiments.  A substantial part of our research involves the simulation of past climates, such as the climate of the last ice age or the response of climate to changes in the earth's orbit. The value in studying past climates derives from the large changes in climate that have taken place over geologic time, which provide a framework for developing a better understanding of the key feedbacks and processes that determine how the climate system responds to external forcing.

In recent deacdes, human-induced climate change has grown in importance and is expected to be the dominant driver of climate change in the next century.  Thus we are also interested in understanding  the mechanisms that will govern the response of the climate system to anthropogenic forcing.  Such work is complementary to our research on past climates, for it is likely that similar mechanisms are involved.  An important point is that our goal is not to simply project future changes in climate, but also to understand the mechanisms by which such changes are expected to occur.  We are also working on techniques for taking  information from future climate projections and making it more useful to those who would like to anticipate the impacts of future changes in climate.

Current Projects

Orbital forcing of climate variations (with Amy Clement, Ben Lintner, Michael Erb, Damianos Mantsis)  Using idealized changes in Earth's orbital parameters and time-slice simulations from the Quaternary, we are studying the effects of changes in Earth's orbital configuration on climate.  We are  interested in understanding how orbital forcing affects the subtropical anticyclones, the South Pacific Convergence Zone (SPCZ), and the seasonal cycle of temperature in the tropical Pacific Ocean.  We are also interested in the role of radiative feedbacks in determining the climatic response.

Climate change and extreme precipitation over North America (with Steve Decker, Anthony DeAngelis)  Global warming simulations indicate an increase in the frequency of extreme precipitation events and observations suggest that a similar increase may be occurring in the real climate system.  

To study the physical mechanisms that underlie such chages, we are determining how well the CMIP multi-model ensemble can simulate the observed frequency and intensity of extreme daily precipitation events. determining if the simulated future changes conform to the 7% K^-1 scaling that would be expected from the Clausius-Clapeyron equation, and understanding the physical mechanisms responsible for any differences from such scaling.

The influence of the large-scale circulation on daily temperature extremes (with Paul Loikith)
Using observations and models, we are examining the realtionship between daily temperature extremes and large-scale atmospheric circulation.  Of particular interest is the relationship between major modes of climate variability (i.e., Pacific-North American pattern, Northern Annular Mode, El Nino-Southern Oscillation) and daily temperature extremes.  We are also evaluating how well current climate models simulate such relationships and how they are projected to change in a warming climate.

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