Investigating the Baroclinic Annular Mode and its Predictability of Extreme Weather Events in the Midlatitudes

Purdue University, West Lafayette IN

Investigators

Abstract

The Baroclinic Annular Mode (BAM) dominates southern hemisphere midlatitude wind variance on subseasonal-to-seasonal time scales. Enhanced BAM activity has been linked to extreme weather events, such as heat waves and cold outbreaks, and an increase in the frequency of blocking events. The researcher has found that rainfall variability associated with the BAM is isolated to the south Pacific, suggesting the BAM may be a source of predictability for rainfall in this region, while its prominence in the hemispheric mean storm activity suggests it plays an important role in shaping the large-scale circulation and hydrological cycle of the southern hemisphere as a whole. The dynamical linkages between the BAM and extreme weather and blocking events are not well understood. The Intergovernmental Panel on Climate Change has also identified the future projections of large-scale coherent atmospheric modes like the BAM as highly uncertain. This project will investigate the gap in knowledge linking the BAM to extreme weather events and blocking, as well as a hypothesis for how BAM activity might be expected to change in a warming climate. The improved understanding of the BAM and its physical links to extreme weather and blocking will then be extended to other internal midlatitude modes of variability on subseasonal to seasonal time scales around the globe. This project has the potential to advance knowledge at the weather-climate interface in an area with high relevance to society. The strong focus on K-12 education is also a priority for increasing the future participation in STEM. The project will use a hierarchy of modeling studies, climate model output, and gridded data sets to carry out the research. Three hypotheses will be tested: 1) Certain BAM states are more conducive to blocking; 2) The BAM increases the frequency of blocking through synoptic eddy feedbacks; 3) Enhanced diabatic heating with global warming will enhance the BAM and blocking. Tasks include building a quantitative relationship between synoptic eddies, blocking patterns, and BAM states using a two-layer quasi-geostrophic model that can simulate key dynamical processes with limited interference from other atmospheric processes. The aim is to use two types of atmospheric general circulation models to investigate the role of climatological basic states and diabatic heating in determining the BAM and blocking. In a warming climate, the intensity of the BAM has been projected to increase. Given the dynamical connection identified in the PI’s preliminary results, in a warming climate, following an enhanced high BAM state, a more regular cluster of blocking events is expected, which has important implications for mitigating disasters for regions in the mid-latitudes. In combination, this project will enable the development of improved subseasonal-to-seasonal prediction and will also provide guidance to improve the ability of dynamical models to simulate extreme weather events. The researcher will support and mentor one undergraduate and one graduate student. The researcher will also work with Purdue’s College of Science K-12 outreach programs to create online resources for climate-based education in the local schools, working closely with educators in the public school system. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.