Figure caption: Schematic showing the energy balance for the entire atmosphere north of 40°N. The left half with black numbers (annual/DJF) shows heat fluxes (PW) at the top, bottom and southern boundaries in the long-term control run of CM4C192. The right half with red numbers shows the heat flux anomalies during years 21–100 of the hosing experiment relative to the control. The positive and negative values indicate enhanced and reduced heat fluxes, respectively. Only the annual mean value is shown for the oceanic transport. The blue and yellow shadings denote the atmosphere and AMOC, respectively.
Due to its large northward heat transport, the Atlantic meridional overturning circulation influences both weather and climate at the mid-latitude Northern Hemisphere. In this study led by Geosciences Prof Jianjun Yin and Ming Zhao (NOAA/GFDL) use a state-of-the-art global weather/climate modeling system with high resolution (GFDL CM4C192) to quantify this influence focusing on the U.S. extreme cold weather during winter. They perform a control simulation and the water-hosing experiment to obtain two climate states with and without a vigorous Atlantic meridional overturning circulation. They find that in the control simulation with an overturning circulation, the U.S. east of the Rockies is a region characterized by intense north-south heat exchange in the atmosphere during winter. Without the northward heat transport by the overturning circulation in the hosing experiment, this channel of atmospheric heat exchange becomes even more active through the Bjerknes compensation mechanism. Over the U.S., extreme cold weather intensifies disproportionately compared with the mean climate response after the shutdown of the overturning circulation. Their results published in the journal Communications Earth & Environment suggest that an active overturning circulation in the present-day climate likely makes the U.S. winter less harsh and extreme.
An interview with Prof Jianjun Yin is featured at the University of Arizona News.