Forcing for Multidecadal Surface Solar Radiation Trends Over Northern Hemisphere Continents

The long-term variation of North Pacific and North Atlantic sea surface temperatures (SSTs) is shown to be associated with multidecadal trends of surface solar radiation in North America, Europe, and Asia. Long-term, large-scale warm SST anomalies lead to a mid-level planetary wave anomaly pattern of geopotential height ridges over the warm water and dynamically-induced lower heights on either side, sometimes extending over adjacent continents. Geopotential height troughs over the continents encourage more cloud cover and dimming of surface solar radiation. Conversely, cool SST anomalies correspond to a pattern of lower mid-level geopotential heights over the cool water and compensating high pressure on either side that encourages decreasing cloud cover and brightening over the continents, if the wave positioning is favorable. Additionally, these effects are observed to be latitude dependent, showing stronger SST-geopotential height associations in the northern half of the Northern Hemisphere. The change from continental dimming to brightening and the reversal of North Pacific SST trends are nearly simultaneous. A similar SST-geopotential height association is seen in the North Atlantic and leads to brightening and dimming in Europe and North America, but there is a similar to 12-year lag between the transition of dimming to brightening and SST reversals there, which is yet unexplained. The next step is to support these connections and their latitudinal dependence with carefully designed numerical experiments that consider variable greenhouse gas and aerosol concentrations.