Solar Impacts on SST, Atmospheric Circulations and Extreme Climate Background in Boreal Winter

The impacts of solar activity on sea-surface temperature (SST), atmospheric circulations and extreme climate conditions in boreal winter are explored by data analysis. The sunspot number (SSN), SST and pressure-level climate variables with their respective available data records up to the 2009/2010 winter are used. Wavelet decomposition shows that warming or cooling trends in global SST on certain time periods are very likely to be influenced by the interaction and interference among various timescales of climate variables. These timescales are mainly resulted from the nonlinear resonance of the climate system to the multi-scale solar forcing. Based on the observed SSN and SST, as well as on the predicted weaker Solar Cycle 24, the global SST is very likely to be cooling in the coming decades with ups and downs on the interannual timescales. Composite analysis for pressure-level air temperature and winds for six solar minima (SCmin) and six solar maxima (SCmax) on the 11yr timescale during past six decades shows their distinct features in 3D space (up to 10hPa in pressure level). For SCmin, the easterly wind phase of the quasi-biennial oscillation (QBO) in both tropical and polar stratosphere, the warm phase of El Niño-Southern Oscillation (ENSO), the negative phase of the Arctic Oscillation (AO), and the stratospheric polar warming that sometimes connects to a blocking situation in the high-lat lower troposphere, are more likely to be enhanced by SCmin than SCmax. Besides, in the tropical stratosphere, there is an anomalously cold layer between 100-50hPa around the tropics, except for the Pacific region where the continuity is broken due to strong updraft during the warm phase of ENSO. However, for SCmax an anomalously warm layer between 50-20hPa is found around the tropics without apparent discontinuity. Walker circulation and zonally averaged meridional circulations are also apparently different between SCmin and SCmax. It is very likely that the zonally averaged meridional temperature gradient is enhanced for SCmin while weakened for SCmax. Thus, the mid-lat circulation has larger wave activity for SCmin than for SCmax. The combination of these anomalous circulations for SCmin or SCmax could lead to extreme climate background conditions. The anomalous 2009/2010 winter is such a case for SCmin. This winter seems to be influenced by both the prolonged solar minimum right before the start of Solar Cycle 24 and the negative phase of the current 88yr cycle, which has not reached its grand minimum yet. The climate background during such a low solar activity period favors large-amplitude negative phase of the AO and the stratospheric polar warming, which correspond to anomalously large meridional wind components causing strong north-south exchange in heat and moisture. The strong northerly wind components bring anomalously cold air to the mid-latitudes, causing record-breaking low temperature in many places. The central equatorial Pacific warming during the El Niño (Modoki) supplied abundant moisture to higher latitudes through abnormaly shifted meridional circulations causing many record-breaking snowfall events in mid-latitudes during the winter.