This Conference Is a "Drag"

I've been to perhaps 50 major scientific conferences in my career and the one I'm attending in Innsbruck this week is one of the best for both professional and personal reasons.  The quality of the science has been very high, and the area provides beautiful views and great brews for late-night discussions.  In addition, I've had an opportunity to see some excellent presentations covering new results in areas that interest me but lie outside my core research area.

One of these areas is something known as gravity wave drag.  Most of us are familiar with gravity waves, which include waves on the ocean, as well as so-called hydraulics generated by river flow over rocks.  Similarly, gravity waves are generated in the atmosphere by flow over mountains.  Under the right conditions, these waves can propagate to jet stream level and even into the stratosphere and mesosphere further aloft.  In some instances these waves break (the water analog is waves crashing on the beach), resulting in gravity wave drag, a deceleration of the flow at upper levels.

Source: The COMET Program

It turns out that these breaking waves are a major problem for weather and climate modeling.  The models lack the resolution to fully account for the effects of major mountain barriers (e.g., Andes, Rockies, New Zealand Alps, Alps, etc.).  The resulting underprediction of mountain-induced gravity waves and associated wave breaking leads to an overprediction of the flow at jet-stream level, which ultimately affects forecasts of the strength and timing of weather systems.  

This has been know for a few decades, and techniques have been developed to artificially add gravity wave drag to both weather and climate models.  However, these techniques make numerous assumptions and sometimes work well over one mountain range, but not another.

During the southern hemisphere winter of 2014, a major field program called DeepWave examined gravity waves generated over the New Zealand Alps that produce gravity wave drag and significant changes to the circulation of the upper atmosphere.  Early results from this field program are now coming to fruition and are guiding the development of new techniques to deal with gravity wave drag, as discussed during several talks this week.

Yup, this conference is most definitely a drag, but hopefully that will yield better forecasts in the future.