Figure 4

From: Atlantic hurricane activity during the last millennium

Figure 4

Time-series analyses of the Extended Hurricane Activity (EHA) index and comparison with natural external forcing (a) Changes in volcanic forcing52 (black line, upper panel) and (b) Total Solar Irradiance (TSI)50,51 (yellow and black). (c) PC3 sequence of lake-level change at Grape Tree Pond, Jamaica27 (grey) and the Extended Hurricane Activity (EHA) index (blue) calculated for the geographic region defined by the grid box 15–25°N, 70–80°W. The black line represents the section of the PC3 series anchored to the annually-resolved coral-based SST reconstruction from the Yucatan Peninsula30 (d) Annual basin-wide tropical cyclone counts from a coupled ocean-atmosphere climate model simulation35 (light blue), and from statistical model reconstructions driven by estimates of landfalling hurricane strikes from overwash sediment records36 (pink). (e) Morlet wavelet analysis applied to the PC3 sequence from Grape Tree Pond, Jamaica. Colours represent the signal strength, which is the squared correlation strength with the scaled morlet wavelet. The 95% confidence level is plotted as a contour and the cone of influence identifies the region of the wavelet spectrum in which boundary effects are present. (f) Bandpass filters applied to the PC3 sequence centred on interannual (5–8 years; grey) and interdecadal timescales (54–80 years; green). Intervals associated with the five grand solar minima are shaded in grey and those of the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) are represented in open boxes with dashed lines extended to the top of the figure.