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Forecasting the Apostle Islands ice caves

Ice Arch. (stock image)ANN ARBOR—U-M climate researchers and their partners, including the National Park Service, are developing a tool to predict the upcoming ice cave season at Apostle Islands National Lakeshore, off the Wisconsin shore of Lake Superior.

In winter when conditions are just right, thousands of visitors tread across frozen Lake Superior to explore the Apostle Island sea caves and ice formations that drape the red sandstone cliffs there. In 2014, the caves drew more than 138,000 tourists when a deep freeze made the caves accessible for the first time in nearly five years. For budget and staffing purposes, the park service would like to know ahead of time if the caves are likely to be accessible in the coming winter.

Previous climate research has shown that Great Lakes winter variables such as ice cover are correlated with global climate patterns such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation. Analysis of Apostle Islands ice data from 1973 to 2015 showed a sharp decline in ice cover in the late 1990s that was coincident with the strong 1997-98 winter El Niño. That drop in ice cover has been followed by a persistent period of below-average ice cover at the Apostle Islands, with occasional exceptions.

The U-M-led research team has developed a predictive model that provides seasonal projections of ice cover areal extent across the Great Lakes, as well as forecasts for specific locations, such as the Apostle Islands. Currently, the researchers feel that the status of the Pacific Decadal Oscillation is a more important predictor of Great Lakes ice than the El Niño Southern Oscillation. Their findings will be submitted for publication in a peer-reviewed scientific journal.

U-M researchers on the team include Richard Rood and Xiaolong Ji of the Department of Climate and Space Sciences and Engineering. Former U-M undergraduate Houraa Daher, now a graduate student at the University of Miami, started the work. Co-leaders of the project are U-M's Rood and Andrew Gronewold of National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor.

"Simulating and forecasting seasonal ice cover." Ji, X., Rood, R.B., Daher, H., Gronewold, A.D. and Bolinger, R. Poster MMA-10. Poster session 6-8 p.m. Wed., May 17, Cobo River Atrium.