Fig. 7: Periodicity–variance spectrum of the mid-latitude and high-latitude net surface shortwave radiation and cross-correlation of summer incoming solar radiation at 65° N, surface air temperature, and sea ice with obliquity and precession indices from 0.0–2.6 Ma.
From: Northern Hemisphere sea ice variability in a transient CGCM simulation of the past 2.6 Ma
a–c The periodicity–variance spectrum of net surface shortwave radiation over the ocean (watts per square meter) in the mid-latitude (35° N–70° N) and high-latitude (>70° N) regions are shown in black and purple lines, respectively. Red (orange) lines show the red noise with a 95% confidence interval over the mid-latitude (high-latitude). The y-axis shows variance multiplied by 10. d Cross-correlation between summer incoming solar radiation at 65° N (purple line), high-latitude surface air temperature (SAT) (red line), sea ice extent (blue line), high-latitude/perennial sea ice (green line), and obliquity index. e Cross-correlation between summer incoming solar radiation at 65° N (purple line), mid-latitude SAT (red line), sea ice extent (blue line), mid-latitude/seasonal sea ice extent (green line), and precession index. A negative (positive) lag means that changes in the summer incoming solar radiation, SAT, and sea ice lag (lead) the orbital forcing (obliquity/precession index). A zero lag indicates synchronous changes.
