Collaborative Research: NSF-BSF--Tropospheric Response to Zonal Asymmetry of the Stratospheric Polar Vortex and Its Aapplication to Subseasonal to Seasonal (S2S) Prediction

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The stratosphere is the layer of the atmosphere that sits above the clouds and storms that affect weather at the earth's surface. But despite being above the weather the stratosphere still influences the weather, particularly when the eastward-moving vortex that forms in winter over the polar cap breaks down in events called sudden stratospheric warmings (SSWs). The expected tropospheric response to an SSW is higher surface pressure over the polar cap, more frequent occurrence of cold air outbreaks, and and more frequent coastal Nor'easter storms. SSWs are thus of great interest for subseasonal to seasonal (S2S) weather prediction, and the mechanisms through which SSWs influence surface weather have been intensively studied. Work under this award seeks to improve understanding of the effects of SSWs and other less extreme stratospheric polar vortex disruptions on tropospheric circulation and surface weather. A key issue is that some SSWs have a strong effect on the underlying troposphere while others do not, and the distribution of surface temperature anomalies can be quite different from one polar vortex disruption to another. The Principal Investigators hypothesize that differences in the tropospheric response are due in part to the pattern of distortions that occur over the course of a polar vortex disruption. For instance in some SSWs a "daughter" vortex forms after the stratospheric polar vortex breaks down, and the surface temperature response could vary depending on the location of the daughter vortex.The research involves analysis of observational datasets, output from simulations available through the Coupled Model Intercomparison Project (CMIP), and ensembles of subseasonal to seasonal (S2S) forecasts and hidcasts including those available through the National Multi-Model Ensemble (NMME). The data analysis effort is complemented by simulations from the Model of an Idealized Moist Atmosphere (MIMA), a simplified model capable of simulating realistic features of the Norhtern Hemisphere winter circulation including jet streams, stationary waves, and the stratospheric polar vortex. Experiments are conducted by using an artificial drag force to induce vortex disruptions with specific geographical distortions so that their effects on surface temperature can be assessed.The work is of societal as well as scientific interest given the connection between stratospheric vortex disruptions and extreme winter weather. One of the Principal Investigators maintains a blog that serves as a portal for technical and non-technical discussion of present and forecasted weather patterns for the Northern Hemisphere. The project also provides support and training for a graduate student and a postdoctoral associate.This is a project jointly funded by the National Science Foundation's Directorate of Geosciences (NSF-GEO) and the Israel Binational Science Foundation (BSF) in accord with the language in the Memorandum of Understanding between the NSF and the BSF. This Agreement allows a single collaborative proposal, involving US and Israeli investigators, to be submitted and peer-reviewed by NSF. Upon successful results of the NSF merit review and recommendation by the cognizant NSF Program of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.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.