17 November 2014

The Transient Circulation Response to Radiative Forcings and Sea Surface Warming


Considering climate change, understanding where the jet stream and the imbedded turbulent wind are going to strike next is a difficult task. The magnitude of tropospheric shifts in a changing climate, and the attending regional hydrological changes, are difficult to project. To better understand the physical mechanisms behind these circulation shifts, scientists at the University of Utah and a U.S. Department of Energy researcher at Pacific Northwest National Laboratory observed over 1000 simulations. To investigate how previously proposed mechanisms shift the midlatitude jet they used ensembles of 90-day climate model simulations where the future scenario was turned on and off–like a switch–instead of waiting for seasons to change in real time. Simulations included perturbed greenhouse gas concentrations, stratospheric ozone concentrations, and sea surface temperatures. They then documented the direct and indirect transient responses of the zonal mean general circulation. The research found that the indirect effect of greenhouse gas forcing, sea surface temperature warming, is a much more potent forcing for the circulation change. In addition, both the direct and indirect wind responses begin in the lower stratosphere, despite that in the latter the response is driven from below. Changes in mid-latitude eddies are ubiquitous and synchronous with the mid-latitude zonal wind response. The enhanced wave reflection at the poleward flank of the jet may be the most probable cause for the jet shift in response to warming sea surface temperature, while the wave absorption near the critical latitudes are not primary factors.

Paul W Staten
University of Utah