Most climate change research is focused on the trends in different metrics (means, maximums, minimums, extremes, etc.) of temperature and/or precipitation. Beyond this, however, trends in other variables have been noted, including absolute moisture metrics, relative humidity, sea-level pressure and many other atmospheric variables and phenomena. This multivariate nature of the weather at any given location naturally underlies the concept of an air mass or weather type – a category of weather that defines the holistic atmospheric situation at a particular time. Thus, since temperature and precipitation trends over the last few decades are well-researched, but a changing climate can manifest itself in myriad ways, the simple aim of this research is to examine the changes in GWTC weather type (WT) frequency over North America since 1979. Generally, warm WTs (Humid Warm, Warm, Dry Warm) are increasing in frequency at the expense of the cool WTs (Humid Cool, Cool, Dry Cool), and the effects of Arctic Amplification are apparent. Humid Cool weather is significantly increasing in northwestern North America and transitional (frontal) weather types are increasing in the US and decreasing in Canada. The magnitude of changes is greater than we expected (+/- 30 to 40 days in some regions). We postulate that noting the extreme magnitude of the WT frequency changes found herein might be a more efficacious means (than explaining importance of a 2-3Â°C change) of communicating longer-term climate change trends to policymakers and the general public.
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Short-term sea-level fluctuations along the eastern seaboard of the US and their atmospheric connections03/21/2019
In this research, we assess the impact of short-term events, combined with sea-level rise, through synoptic climatological analysis, exploring whether circulation pattern identification can be used to enhance probabilistic forecasts of flood likelihood. Self-organizing maps (SOMs) were created for two discrete atmospheric variables: 700-hPa geopotential height (700z) and sea-level pressure (SLP). For each variable, a SOM array of patterns was created based on data spanning 25°-50°N and 60°-90°W for the period 1979-2014. Sea-level values were derived from tidal gauges between Cape May, New Jersey and Charleston, South Carolina, along the mid-Atlantic coast of the US. Both anomalous sea-level values, as well as nuisance flood occurrence (defined using the local gauge threshold), were assessed. Results show the impacts of both the inverted barometer effect as well as surface wind forcing on sea levels. With SLP, higher sea levels are associated with either patterns that were indicative of on-shore flow or cyclones. At 700z, ridges situated along the east coast are associated with higher sea levels. As the SOM matrix arranges atmospheric patterns in a continuum, the nodes of each SOM show a clear spatial pattern in terms of anomalous sea level, including some significant sea-level anomalies associated with relatively ambiguous pressure patterns. Further, multi-day transitions are also analyzed, showing rapidly deepening cyclones, or persistent onshore flow, can be associated with the greatest likelihood of nuisance floods.