Extreme cyclone events in the Arctic: Wintertime variability and trends

Abstract

Typically 20–40 extreme cyclone events (sometimes called ‘weather bombs’) occur in the Arctic North
\nAtlantic per winter season, with an increasing trend of 6 events/decade over 1979–2015, according to
\n6 hourly station data from Ny-Ålesund. This increased frequency of extreme cyclones is consistent
\nwith observed significant winter warming, indicating that the meridional heat and moisture transport
\nthey bring is a factor in rising temperatures in the region. The winter trend in extreme cyclones is
\ndominated by a positive monthly trend of about 3–4 events/decade in November–December, due
\nmainly to an increasing persistence of extreme cyclone events. A negative trend in January opposes
\nthis, while there is no significant trend in February. We relate the regional patterns of the trend in
\nextreme cyclones to anomalously low sea-ice conditions in recent years, together with associated
\nlarge-scale atmospheric circulation changes such as ‘blocking-like’ circulation patterns (e.g.
\nScandinavian blocking in December and Ural blocking during January–February).