Impacts of Multi-Scale Solar Activity on Climate. Part I: Atmospheric Circulation Patterns and Climate Extremes |
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| Authors: | Hengyi WENG |
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| Institution: | State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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| Abstract: | The impacts of solar activity on climate are explored in this two-part
study. Based on the principles of atmospheric dynamics, Part I propose an
amplifying mechanism of solar impacts on winter climate extremes through
changing the atmospheric circulation patterns. This mechanism is supported
by data analysis of the sunspot number up to the predicted Solar Cycle 24,
the historical surface temperature data, and atmospheric variables of
NCEP/NCAR Reanalysis up to the February 2011 for the Northern Hemisphere
winters. For low solar activity, the thermal contrast between the low- and
high-latitudes is enhanced, so as the mid-latitude baroclinic ultra-long
wave activity. The land-ocean thermal contrast is also enhanced, which
amplifies the topographic waves. The enhanced mid-latitude waves in turn
enhance the meridional heat transport from the low to high latitudes, making
the atmospheric ``heat engine" more efficient than normal. The jets shift
southward and the polar vortex is weakened. The Northern Annular Mode (NAM)
index tends to be negative. The mid-latitude surface exhibits large-scale
convergence and updrafts, which favor extreme weather/climate events to
occur. The thermally driven Siberian high is enhanced, which enhances the
East Asian winter monsoon (EAWM). For high solar activity, the mid-latitude
circulation patterns are less wavy with less meridional transport. The NAM
tends to be positive, and the Siberian high and the EAWM tend to be weaker
than normal. Thus the extreme weather/climate events for high solar activity
occur in different regions with different severity from those for low solar
activity. The solar influence on the mid- to high-latitude surface
temperature and circulations can stand out after removing the influence from
the El Nino-Southern Oscillation. The atmospheric amplifying mechanism
indicates that the solar impacts on climate should not be simply estimated
by the magnitude of the change in the solar radiation over solar cycles when
it is compared with other external radiative forcings that do not influence
the climate in the same way as the sun does. |
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| Keywords: | solar impacts on climate surface thermal contrasts dynamical amplifying mechanism atmospheric circulations climate extremes |
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