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Free keywords:
Past climate change; Solar activity; General circulation model; Stratospheric–tropospheric coupling
DDC:
550 - Earth sciences
Abstract:
A model simulation of the climate during Maunder Minimum (MM) (1645–1715) was performed using the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM). A multi-year equilibrium integration with prescribed solar insolation, atmospheric composition and sea surface temperatures (SSTs) for MM conditions was compared with a present-day (PD) simulation. We find that during MM the stratosphere was significantly warmer (up to 3 K) than during PD, and dynamically more disturbed in winter. The warming is due to the dominant effect of the lower atmospheric CO2 concentration during MM, which leads to a reduced emission of long-wave radiation, and compensates the cooling due to the reduced solar irradiance. The troposphere was about 1–1.5 K cooler in the annual mean during MM. The global mean surface air temperature decreased by 0.86 K. Northern hemisphere winters were on average characterized by cooler and drier weather over the northern parts of the continents, with an increase in precipitation in the southern parts. These climate anomalies are shown to be related to a shift in the North Atlantic Oscillation (NAO) towards a predominantly low phase during MM. The simulated climate anomalies are in very good agreement with reconstructions from proxy-data. Changes in the dynamical coupling between the troposphere and stratosphere were found in the MM simulation, indicating the importance of the stratosphere for climate change.
