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Storm track variability and change in GCM simulations

PI: Edmund Chang
Institution: Stony Brook University
Additional Investigators: Xiaosong Yang, Xiaoming Xia, Isaac Held
In the mid-latitudes, day-to-day weather is basically controlled by the passages of cyclones and anticyclones. While society is faced with global warming due to increase in greenhouse gases, an issue that is not well understood is how the
storm tracks may change. Shifts in the location of the storm tracks, or changes in the storm track activity, can lead to droughts or floods, and affect the frequency of occurrence of severe weather, and is therefore one of the most important factors governing regional climate change. In addition, these storms are responsible for transporting huge amounts of heat, moisture, and momentum, hence changes in the storm tracks can also lead to changes in the global circulation.

While storm track changes are present in GCM simulations of global warming, few studies have been conducted to examine them in detail since previous generations of GCMs have poor simulations of storm tracks. With improvements in physical parameterizations as well as increase in model resolution, the current generation of GCMs does a much better job in simulating the climatological distribution of storm tracks. However, to date no detailed validation of how well storm track variability is simulated by GCMs has been conducted, making it impossible to assess how reliable GCM predicted storm track changes are.

In this project, GCM simulations of storm tracks and their variability and change will be assessed in detail, using a suite of diagnostic and modeling studies. The main goals are to quantitatively assess whether deficiencies in GCM storm track simulations could give rise to deficiencies in the GCMs prediction of how the storm tracks may change, and to achieve quantitative understanding of GCM predictions of storm track changes under global warming. Results from this project will enable the scientific community to assess the uncertainties present in such predictions.

In this project, GCM simulations of storm track variability will be compared in detail to observed storm track variability. Apart from statistical assessment of the fidelity of GCM simulated storm track variations, several prominent modes of storm track variability will be examined in detail. While there are other projects that focus on studying how storm track may change under various global warming scenarios, the novelty of this project is in the use of a combination of linear and nonlinear storm track and stationary wave models to quantitatively assess whether deficiencies in GCM simulations are of dynamical significance. In addition, dynamical models having various levels of complexity will also be employed to quantitatively understand and relate GCM predicted storm track and mean flow changes. In this study, simulations conducted using GFDL climate models will serve as reference, but other GCM simulations archived as part of the IPCC Fourth Assessment Report process will also be examined for comparison. This study is in collaboration with Dr. Isaac Held at GFDL.

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