An observational study of slope air and free air wintertime temperatures in Whistler Valley, British Columbia, Canada

• Main Author: Erven, Lisa N.
• Language: English
• Published: University of British Columbia 2012
• Online Access: http://hdl.handle.net/2429/42468

Temperature structure within complex terrain is fundamental to determining stability, thermally-induced circulations, and mountain weather, all of which impact those living, working, and recreating within it, as well as those external to it that depend on water from snowmelt. While numerous studies and text books outline many factors affecting slope air and free air temperatures, the interactions of these factors with the complex terrain makes predictability of temperature structures very difficult. This is further compounded by sparse observational data that has limited representativeness due to numerous localized effects. In preparation for the 2010 Olympic and Paralympic Winter Games, temperature sensors were placed along the west slope of Whistler Mountain, and radiosondes were launched twice daily, creating a rare opportunity to investigate slope and free air temperature structure and evolution within a mountain valley. Daytime and nighttime temperature profiles are categorized by cloud cover, and very consistent lapse rates are found within categories. Profiles are compared for slope and free air within each category, and between categories. Case studies provide further detail in describing temperature structure evolution. Clear days give rise to the least uniform slope air temperature structure, but a consistent, fairly representative, linear lapse rate is nonetheless found. Overcast conditions effectively eliminate microclimates, producing a relatively linear slope air temperature structure. Additionally, consistent free air lapse rates are defined for each cloud cover category. While the majority of slope and free air lapse rates are statistically indistinguishable, significant slope-free air temperature differences still exist. Lastly, linear regression is used to develop an equation that successfully determines slope air temperatures from a given free air temperature, or vice versa. Together with the representative lapse rates, one is able to construct slope and free air temperature profiles given a single slope or free air temperature measurement. These results show that by separating profiles by weather condition, consistent temperature structures and relations can be extracted from a seemingly incoherent collection of complex mountain slope and free air profiles. In doing this, it becomes feasible to accurately predict these profiles, providing great utility to those impacted by mountain temperatures.