Mesoscale Influences on Climate-Change Observations at an Arctic Site

Many of the long-term atmospheric observatories established for the multiagency, international Study of Environmental Arctic Change (SEARCH) are located in coastal regions or in regions of complex topography, or both. Such regions are known to produce mesoclimates which may vary greatly over relatively short distances and may respond differently to changes in large-scale climate forcing. This may explain why climate trends vary greatly on regional scales.

At Alert, Nunavut, both long-term historical data and shorter-term detailed surface energy budget and subsoil observations exist, permitting an evaluation of the principal processes producing the mesoclimate at Alert and an evaluation of changes in the frequency of occurrence of these processes. The processes forcing the climatic regimes and the annual surface energy budget cycle are examined in detail at Alert. Mesoscale processes important for the annual climate at this site are generally associated with a wind direction regime, and include terrain-induced flows and sea-breeze effects. Each atmospheric phenomenon provides distinct impacts on the surface energy fluxes, and can even be detected in soil temperatures in midwinter. Impacts of the mesoscale regimes on the annual climate and surface energy budget cycle are assessed. Then, historical wind and temperature data are used to compute temperature sensitivities to each mesoscale regime, which are combined with the long-term trends of the frequency of occurrence of each regime to explain the observed overall climatological temperature trend at Alert. The analysis for this site suggests that the future climate change at terrestrial Arctic sites will depend on the response of the dominant mesoscale processes to the large-scale Arctic changes, and may therefore not be of the same magnitude, nor sign, as the large-scale changes. This emphasizes the importance of understanding the processes producing the mesoclimate at Arctic long-term sites for interpretation of climate trends.