Atmospheric Blocking Trends and Seasonality around the Antarctic Peninsula

We analyze the seasonal evolution and trends of atmospheric blocking from 1979 to 2018 using a geopotential-height-based method over two domains, one located to the west (150 degrees-90 degrees W, 50 degrees-70 degrees S) and the other over and to the east (90 degrees-30 degrees W, 50 degrees-70 degrees S) of the Antarctic Peninsula. Spatial patterns of geopotential heights on days with blocking feature well-defined ridge axes over and west of much of South America, and days with the most extreme blocking (above the 99th percentile) showed upper-tropospheric ridge and cutoff low features that have been associated with extreme weather patterns. Blocking days were found to be more frequent in the first half of the period (1979-98) than the second (1999-2018) in all seasons in the west domain, whereas they seem to be more common over the eastern (peninsula) domain in 1999-2018 for austral winter, spring, and autumn, although these differences were not statistically significant. West of the Antarctic Peninsula, blocking days occur most frequently when the Antarctic Oscillation (AAO) is negative, whereas they are more frequent over the peninsula when the AAO is positive. We propose that our blocking index can be used to indicate atmospheric blocking affecting the Antarctic Peninsula, similar to how the Greenland blocking index has been used to diagnose blocking, its trends, and impacts over the Arctic.