Fig. 6: Periodicity–variance spectrum of NH surface air temperature and its cross-correlation and cospectrum with sea ice extent.
From: Northern Hemisphere sea ice variability in a transient CGCM simulation of the past 2.6 Ma
The periodicity–variance spectrum of complete NH (here from 0° N–90° N) zonal mean surface air temperature during the (a) post-MPT, (b) MPT, and (c) pre-MPT periods (units show standardized variance). Purple lines at 70°N indicate the mean lowest latitudinal position of perennial sea ice. Dots show significance at red noise with a 95% confidence interval. d–f Cross-correlation of surface air temperature (solid black lines) with sea ice extent during the post-MPT, MPT, and pre-MPT periods, respectively. A positive lag means that changes in surface air temperature lead changes in sea ice extent. A zero lag shows synchronous changes in surface air temperature and sea ice extent. g–i Solid black lines show standardized cospectrum between surface air temperature and sea ice extent during the post-MPT, MPT, and pre-MPT periods.
