Amaya, D. J., A. J. Miller, S.-P. Xie and Y. Kosaka, 2020:
Physical drivers of the summer 2019 North Pacific marine heatwave
Nature Communications, 11, 1903.
Abstract.
Summer 2019 observations show a rapid resurgence of the Blob-like warm sea surface
temperature (SST) anomalies that produced devastating marine impacts in the Northeast
Pacific during winter 2013/2014. Unlike the original Blob, Blob 2.0 peaked in the summer, a
season when little is known about the physical drivers of such events. We show that Blob 2.0
primarily results from a prolonged weakening of the North Pacific High-Pressure System. This
reduces surface winds and decreases evaporative cooling and wind-driven upper ocean
mixing. Warmer ocean conditions then reduce low-cloud fraction, reinforcing the marine
heatwave through a positive low-cloud feedback. Using an atmospheric model forced with
observed SSTs, we also find that remote SST forcing from the central equatorial and, surprisingly,
the subtropical North Pacific Ocean contribute to the weakened North Pacific High.
Our multi-faceted analysis sheds light on the physical drivers governing the intensity and
longevity of summertime North Pacific marine heatwaves.
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