Climatology of katabatic winds in the McMurdo dry valleys, southern Victoria Land, Antarctica

Katabatic winds dramatically affect the climate of the McMurdo dry valleys, Antarctica. Winter wind events can increase local air temperatures by 30degreesC. The frequency of katabatic winds largely controls winter (June to August) temperatures, increasing 1degreesC per 1% increase in katabatic frequency, and it overwhelms the effect of topographic elevation (lapse rate). Summer katabatic winds are important, but their influence on summer temperature is less. The spatial distribution of katabatic winds varies significantly. Winter events increase by 14% for every 10 km up valley toward the ice sheet, and summer events increase by 3%. The spatial distribution of katabatic frequency seems to be partly controlled by inversions. The relatively slow propagation speed of a katabatic front compared to its wind speed suggests a highly turbulent flow. The apparent wind skip (down-valley stations can be affected before up-valley ones) may be caused by flow deflection in the complex topography and by flow over inversions, which eventually break down. A strong return flow occurs at down-valley stations prior to onset of the katabatic winds and after they dissipate. Although the onset and termination of the katabatic winds are typically abrupt, elevated air temperatures remain for days afterward. We estimate that current frequencies of katabatic winds increase annual average temperatures by 0.7degrees to 2.2degreesC, depending on location. Seasonally, they increase (decrease) winter average temperatures (relative humidity) by 0.8degrees to 4.2degrees (-1.8 to -8.5%) and summer temperatures by 0.1degrees to 0.4degreesC (-0.9% to -4.1%). Long-term changes of dry valley air temperatures cannot be understood without knowledge of changes in katabatic winds.