Examining Extratropical Cyclone Sensitivity to a Range of Environmental Conditions

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Tuesday, 4 August 2015: 2:00 PM
Republic Ballroom AB (Sheraton Boston )
Gregory Tierney, University of Michigan, Ann Arbor, MI; and J. Booth and D. J. Posselt

Extratropical cyclones (ETCs) are a key component of Earth's climate system. They transport energy and momentum meridionally, affect the top of atmosphere radiation budget, and produce the majority of the precipitation in the middle and high latitudes. Therefore, understanding how a warming climate might affect the extratropical cyclone life cycle is crucial for informing future climate change mitigation and preparation strategies. There are two potentially opposing influences of climate change on ETC strength: a weaker pole-to-equator temperature gradient may weaken the storm by decreasing baroclinicity, and an increase in atmospheric moisture content may strengthen the storm via increased latent heating. The interplay between these two influences is not well understood, given the range of scales involved. Although extratropical cyclones are synoptic events, they are influenced by a multitude of processes on the meso-, micro-, and molecular scale. These smaller-scale processes have complex feedbacks, complicating observation and theory-based explorations of ETC-environment interaction.

Our work presents a sensitivity analysis approach to untangling the interactions between a changing environment and ETC evolution. Using an idealized framework in the Weather Research and Forecasting (WRF) model, we first identify control variables relevant for consideration in a changing climate, including variations in baroclinicity, temperature, and moisture content. We examine the effect of discrete changes in each individual variable, tracking the effects on several output metrics, including minimum sea level pressure and eddy kinetic energy. Simulations conducted in a dry framework confirm that the storm response is consistent with previous studies. Experiments conducted in a moist environment allow further analysis via additional output metrics such as non-convective and convective precipitation, as well as latent heat release. We find that the introduction of moisture leads to non-linear and non-monotonic responses in the peak eddy kinetic energy of the system, as well as an increasing role of convection with increasing temperatures. In addition, we find that bulk temperature does not play a major role until moisture is included in the simulations, while baroclinicity plays a large role in both dry and moist simulations.