Warm-Season North American Extreme Surface Air Temperature Relationships to Arctic Sea Ice Conditions

Abstract:

Growing amount of evidence points to a notable impact of the changing Arctic cryosphere on remote climates. Recent studies propose a series of events that makes the connection between Arctic amplification/sea ice decline and increased frequency of extreme weather events in the mid-latitudes plausible. This study examines relationships between 1978-2013 spring (MAM) and summer (JJA) extreme surface air temperature (SAT) conditions across North America (NA) and simultaneous Arctic sea ice concentration (SIC) conditions. Seasonal summaries of daily frequency of occurrence of extreme SATs are correlated to simultaneous mean seasonal SIC anomalies. Low MAM SICs coincide with higher-than-normal incidence of cool nights/days across central US and Canada and eastern in Canada and lower-than-expected incidence of cool nights/days is observed westward from Nevada and Arizona. At this time, large portions of northern and eastern Canada and NE US coincide with decreased frequency of warmest days/nights and large sections of the US southwest show a significant increase in the frequency of warmest days/nights when SICs are low. SAT extremes continue to be related to SIC conditions into JJA across large portions of northern and eastern NA where lower-than-expected SICs coincide with significantly lower frequencies of cool nights/days and higher frequency of warm days/nights. Also examined are various simultaneously-occurring atmospheric and synoptic flow conditions that may begin to suggest potential mechanisms behind the observed relationships. Initial analyses indicate the observed relationships are reflected in mean monthly SATs and atmospheric thickness conditions, as well as 500 and 250 hPa geopotential height and zonal wind anomaly patterns. Both seasons display strong north-south meandering of the 500 hPa surface. During low MAM ice seasons the mid-tropospheric flow resembles the positive phase of the AO with a well-developed polar vortex that dips south of the Great Lakes; low SIC JJA seasons are characterized by a low-high-low flow over NA with a ridge over the central-eastern sector. Zonal flow at the 500 hPa level is significantly weakened in JJA over eastern NA. Areas with greatest flow anomalies are associated with regions that display most notable SAT extreme frequency deviations.