The Lower-Stratospheric Response to 11-Yr Solar Forcing: Coupling to the Troposphere-Ocean Response

The origin of the tropical lower-stratospheric response to 11-yr solar forcing and its possible coupling to a troposphere-ocean response is investigated using multiple linear regression (MLR) analyses of stratospheric ozone and temperature data over the 1979-2009 period and tropospheric sea level pressure (SLP) data over the 1880-2009 period. Stratospheric MLR results, comparisons with simulations from a chemistry-climate model, and analyses of decadal variations of meridional eddy heat flux indicate that the tropical lower-stratospheric response is produced mainly by a solar-induced modulation of the Brewer-Dobson circulation (BDC), with a secondary contribution from the Hadley circulation in the lowermost stratosphere. MLR analyses of long-term SLP data confirm previous results indicating a distinct positive response, on average, during the northern winter season in the North Pacific. The mean response in the Northern Hemisphere resembles a positive Arctic Oscillation mode and can also be characterized as "La Nina-like," implying a reduction of Rossby wave forcing, a weakening of the BDC, and an increase in tropical lower-stratospheric ozone and temperature near solar maxima. However, MLR analyses of different time periods show that the Pacific SLP response is not always present during every cycle; it was most clearly detected mainly during the ~1938-93 period when 11-yr solar variability was especially strong. During the 1979-93 period, the SLP response was strongly present when the lower-stratospheric responses were large. But during the 1994-2009 period, the SLP response was much less significant and the lower-stratospheric responses were weak, supporting the hypothesis that the lower-stratospheric and surface climate responses are dynamically coupled.