Quantifying the Impact of Atmospheric Blocking on the Mean State of the North Atlantic Sector of the Arctic

Blocked atmospheric flows over Greenland and the North Atlantic Arctic (NAA) can amplify persistent wind patterns that impact moisture transport and climate in this region both locally and remotely. Atmospheric blocking occurs when there is a slowing of synoptic-scale Rossby wave propagation resulting in a quasi-stationary high pressure system that redirects circulation, and typically results in a large-scale reversal of the meridional geopotential height gradient. This study seeks to quantify the impact of atmospheric blocking on the mean state of the NAA, by comparing a climatology of blocking events, identified using the Greenland Blocking Index (GBI), to blocking as represented in CMIP6 models.

In this study, daily geopotential heights and specific humidity from the ERA-Interim Reanalysis were composited for extreme values days of the upper 90th, 95th, 97th, and 99th percentiles of daily GBI. Anomalies of each variable were examined to better understand atmospheric conditions under unusual blocked and unblocked flows. Variability of integrated vapor transport (IVT) over Greenland was examined for the extremes of the GBI. Winter and summer seasonal analysis of extreme GBI days (99th percentile) from 1980-2017 reveal that there has been increase in frequency of extreme events from 2000-2017. When considering moisture transport, on an extreme blocking day (99th percentile) the probability of having above average moisture transport is 94% for winter months and 77% for summer. Similar analysis using the CMIP6 model output was conducted, and comparisons drawn between observed versus modeled blocking frequency and magnitude.