5. the extreme march-may 2012 warm anomaly over the eastern united states: global context and multimodel trend analysis

TLDR: In this paper, the authors show that the record hot spring of 2012 over the eastern United States can be mainly explained by atmospheric dynamics, while large-scale circulations were favorable to anomalously high temperatures over this region in summer, other local factors, possibly linked to the exceptionally hot spring and persisting drought throughout summer, shaped the spatial pattern of the following summer heat wave.

Abstract: Conclusions. In conclusion, the record hot spring of 2012 over the eastern United States can be mainly explained by atmospheric dynamics. Conversely, while large-scale circulations were favorable to anomalously high temperatures over this region in summer, other local factors, possibly linked to the exceptionally hot spring and the persisting drought throughout summer, shaped the spatial pattern of the following summer heat wave. In a long-term climate perspective, Fig. 4.2b reveals a positive trend over the last 20 years (1993–2012) in spring maximum temperatures over the eastern United States, which is found to be statistically significant at the 5% level and consistent with the flow-analogue temperature reconstruction. By contrast, no significant trend is found in summer for maximum temperatures (Fig. 4.2c), albeit additional observations show a significant increase of 0.5 σ per decade over the past 40 years (1973–2012) for minimum temperatures, partially explained by f low-analogues (not shown). This trend analysis, nevertheless, reaches the limits of daily unadjusted GHCN temperatures, since homogenized USHCN monthly temperatures exhibit a one-to-two times larger warming over recent years (but still not significant for summer maximum temperatures). The contribution of potential changes in circulation to the recent long-term warming in the United States, therefore, requires further research.