Ed Gerber

Ed Gerber

Professor at the Courant Institute

Why does Europe tend to experience warmer winters following a major volcanic eruption?

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Major volcanic eruptions, especially those in the tropics, can inject sulfate aerosols into the stratosphere, where they scatter incoming radition and cool the planet. The effect, which lingers as long as the aerosols (1-2 years), was observed by the Romans, if not earlier civilizations. Paradoxically, there’s evidence that Northern Europe tends to warm following major eruptions. This points to a circulation impact of volcanic aerosols. In our new paper, The Circulation Response to Volcanic Eruptions: The Key Roles of Stratospheric Warming and Eddy Interactions, now in press with the Journal of Climate, we highlight the importance of the fact that stratospheric aerosols warm the lower stratosphere. This drives a poleward shift in the jet stream, which warms Europe. We also zero in on the role of eddies in the mechanism with a hierarchy of atmospheric models.

The image above shows the zonal mean temperature and zonal wind response to aerosol induced warming of the lower stratosphere, focusing on the boreal winter season. Note the poleward shifts in the jet streams in both hemispheres!

The study was led by Kevin DallaSanta in collabortation with Matt Toohey at GEOMAR in Kiel, Germany.

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See the forest and the trees!

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Congratulations to Dave Connelly, who just submitted his first paper! It is about the use of regression forest to represent atmospheric gravity wave momentum transport to JAMES! The manuscript makes two important steps forward. First, it shows that a “boosted forest” approach, where you train each subsequent decision tree on the residual (as sketched below), can out perform a “random forest” where you combine a number of decision trees, averaging the result. This was well known in the ML community, but less so in the climate sciences. Second, Dave found that techniques from interpretable AI could be used to improve the training of a data driven parameterization. Using feature importance metrics, he found that his origional boosted forest wasn’t using enough information about latitude. By forcing the method to predict the latitude as well, he could build trees that incorporate this information more effectively!

The graft-versus-host problem…

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Ofer Shamir just submitted a paper on the use of machine learning to represent atmospheric gravity wave momentum transport to QJRMS. He developed an idealized, one-dimensional model of the Quasi-Biennial Oscillation, where we could systematically compare different data-driven methods. In particular, how can one calibrate a data-driven scheme to work in a biased model (the graft-host problem), and how well can schemes generalize to new conditions, as in a climate change scenario?

Um, what happened to me?

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I flatter myself to think you may have stopped by my webpage over the last year and half and wondered, what happened to Ed? No new papers? No research? Did he drop off the face of the Earth? Sort of. I was on sabbatical at Free University Berlin and Ludwig Maximillian University, Munich for an academic year!