Influence of Meteorological Regimes on Cloud Properties over Ross Island, Antarctica: A Users Guide to AWARE Data

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Description

The ARM West Antarctic Radiation Experiment (AWARE) AMF-2 deployment at Ross Island sampled mixed-phase clouds with significant contrasts from the more thoroughly studied high Arctic. Influences on Antarctic clouds include substantial orographic forcing by mountainous terrain on local and regional scales, that induces much larger vertical velocities than observed in the Arctic. A colder and often more pristine atmosphere also influences contrasting ice cloud formation. The ultimate moderator of these effects is shifting weather patterns governed by Southern Ocean storm tracks. While AWARE data should thus be useful for testing the limits of current microphysical parameterizations in climate models, and perhaps developing improvements, making sense of the complex data (particularly the ARM research radars) can be a challenge for researchers working with Antarctic data for the first time. To assist researchers with understanding the AWARE data sets, we have identified the prevailing meteorological regimes throughout the yearlong AMF-2 deployment and developed a catalog listing when they occur in each season. Meteorological regimes are identified using k-means cluster analysis of daily 700-mb geopotential height anomalies from the ERA-Interim Global Reanalysis. We then use high-resolution Antarctic Mesoscale Prediction System (AMPS) forecasts to illustrate how the prevailing regimes influence the local scale meteorology at Ross Island, including the response of cloud formation and cloud microphysical properties. We identify three principal regimes: Pattern 1 – exhibiting strong ridging over the Amundsen Sea and weak low pressure over the Ross sea; Pattern 2- consisting of cyclonic flow over the Ross Sea; Pattern 3- with ridging over the Ross Sea and low pressure over the Bellingshausen Sea. In particular, Pattern 2 sets up intrusion of marine air into central West Antarctica, followed by southerly outflow over the RIS; along the western RIS complex atmospheric dynamics including low-level jets, vortices and waves form in response to orographic forcing from the Transantarctic Mountains, and Ross Island sees the greatest cloud amounts under this scenario in the form of ice and mixed-phase cloud systems.By identifying when these patterns occur, we hope that model developers can more easily find useful case studies in the AWARE data.