Changes in Summer Weather Type Frequency in Eastern North America

摘要

In this research, the Spatial Synoptic Classification (SSC), a weather type scheme, is used as an alternative method of demonstrating evidence of climate change in the Eastern United States and southern Canada. Changes in frequencies for the seven SSC weather types were assessed for summer trends (May-September) at thirty-eight stations and also at four regions of latitude between 1950 and 2015. Using the SSC, results show significant summer decreases in dry polar (DP) days and transitional (TR) days and significant increases in moist tropical (MT) days. The North region exhibited the greatest breadth of significant results among all weather types. The DP and TR decline was strongest at higher latitudes and weakened approaching the subtropics. The MT gain was strongest across the midlatitudes but statistically significant in all four regions. The four remaining SSC weather types showed more localized statistically significant trends. Results suggest that these trends in weather type frequency are an indicator of summer climate change, with some stations losing over 50 percent of their DP frequency, losing over 40 percent of their TR frequency, and gaining over 30 percent of their MT frequency since 1950.