Characterization of orographic cloud and precipitation features over southern Baffin Island and surrounding area

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2014, 2014
Fargey, Shannon
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Taylor & Francis Publishing
John Wiley and Sons
Improved characterization of cloud and precipitation features are required to understand the impact of a changing climate in high latitude regions and accurately represent these features in models. The importance of cold season precipitation to regional moisture cycling and our limited understanding of orographic cloud and precipitation processes in the Arctic provide the motivation for this research. Using high-resolution datasets collected during the Storm Studies in the Arctic (STAR) field project this thesis examines cloud and precipitation features over southern Baffin Island in Nunavut. Cloud and precipitation features were shown to differ over orography compared to the adjacent ocean regions upstream. Gravity waves, terrain shape, atmospheric stability and atmosphere-ocean exchanges were all associated with precipitation enhancement. In addition, high sea ice extent, low-level blocking in the upstream environment and sublimation were factors that reduced precipitation. The nature of hydrometeors was variable and accretion and aggregation were found to be important determinants of whether precipitation reached the ground. The processes controlling a snowfall event over southern Baffin Island were found to be complex, representing a significant challenge for modelling in the region. Low-level convection over adjacent ocean regions, strong upslope flow over the terrain, and the passing of a weak trough collectively produced the event. Analysis of the Global Environmental Multi-scale limited area model (GEM-LAM 2.5) revealed that upstream convection and upslope processes were affected by model errors. Consequently, precipitation onset was delayed and total modelled accumulation was 50% less than observations. Further evaluation of a numerical weather prediction model during STAR cases provided descriptions of model errors and proficiencies for different synoptic forcing and surface environments. Overall the model overestimated temperature and had difficulties representing thermal inversions over sea ice. The model generally over-predicted moisture with the exception of profiles over sea ice and land. Wind speed was frequently underestimated, weakening upslope processes and errors in wind direction were large at times. Cloud-tops were usually too high and cloud-bases too low. Where multiple cloud layers were present, the dry layer depth was inaccurate. Model errors were shown to have implications for cloud and precipitation production and their forecast.
Arctic, cloud, precipitation
Fargey, S., Hanesiak, J., Stewart, R., and Wolde, M. (2014). Aircraft observations of orographic cloud and precipitation features over southern Baffin Island, Nunavut, Canada. Atmosphere-Ocean. 52, 54-76
Fargey, S., Henson, W., Hanesiak, J., and Goodson, R. (2014). Characterization of an unexpected snowfall event in Iqaluit, Nunavut during the Storm Studies in the Arctic Project. Journal of Geophysical Research-Atmos. 119, 5492-5511