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Mid-Latitude Climate Extremes

Atmospheric River

Visualization of atmospheric river simulated by the Weather Research and Forecasting (WRF) model (vertically integrated water vapor).

Daniel Swain is leading work focused on the atmospheric processes that connect the Earth's middle latitudes to equatorial and polar regions, with a particular emphasis on how the interaction between these latitudinal linkages and broader global climate change may drive extreme meteorological events.

Climate extremes occur over a wide range of spatial and temporal scales. Most atmospheric phenomena that are associated with day-to-day weather extremes--such as those leading to storms, floods, and heat waves--take place over the course of days or weeks and affect only a small portion of the planet at any particular time. For this reason, any tool used to investigate meteorological extremes must be able to resolve atmospheric behavior on a relatively fine scale.

One such instance of a characteristic mid-latitude feature associated with extreme precipitation events is that of "atmospheric rivers." These transient, highly-concentrated atmospheric moisture plumes are responsible for a significant fraction of wintertime precipitation along the Pacific Coast of North America and have been implicated in a large fraction of major wintertime flood events in this region. Recent research has evaluated atmospheric model simulations of these moisture plumes using a high-resolution version of the Weather Research and Forecasting Model (WRF). Findings suggest that the use of a high-resolution model is critical in resolving key structural features of these extreme events, which has important implications for the study of atmospheric rivers under both present and future climate. 

Ongoing work explores possible connections between enhanced atmospheric warming in the Arctic and changes in mid-latitude weather patterns. Such "Arctic amplification" of the global warming trend may disrupt prevailing westerly winds in the Northern Hemisphere mid-latitudes, potentially leading to increasing persistence of weather patterns in some regions and increasing the likelihood of certain types of extreme weather events.