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Additional file 3: Figure S3. Wavelet coherence between the tree-ring δ18O and (a) +JF, (b) +MA, and (c) +MJ NPGO index. Black contour indicates the 95% significant level, and white shade means the cone of influence.

Additional file 4: Table S1. Correlation coefficients between inverted MJ precipitation in Sendai and NPGO index.

Additional file 1: Figure S1. Same as Fig. 2, except for (a) monthly mean precipitation, (b) three-month average precipitation, (c) four-month average precipitation, (d) monthly mean relative humidity (RH), (e) three-month average RH, (f) four-month average RH, (g) two-month average temperature, (h) three-month average temperature, and (i) four-month average temperature.

Additional file 5: Figure S4. (a) MJ mean SLP anomalies for six events of negative tree-ring δ18O values (AD 1938, 1947, 1954, 1956, 1966 and 1981) using the 20th century Reanalysis V2 of NOAA ESRL (Compo et al. 2011). (b) Same as Fig. S4a, except for using the ERA-20C datasets (Poli et al. 2016). (c) MJ mean SLP anomalies for six events of positive tree-ring δ18O values (AD 1933, 1940, 1942, 1963, 1975 and 1987) using the 20th century Reanalysis V2 of NOAA ESRL (Compo et al. 2011). (d) Same as Fig. S4c, except for using the ERA-20C datasets (Poli et al. 2016). These anomalies were normalized to zero mean and one standard deviation during AD 1927â 2010.

Additional file 2: Figure S2. Results of MTM analysis for (a) tree-ring δ18O, (b) following year January-February (+JF), (c) following year March-April (+MA), and (d) following year May-June (+MJ) NPGO index. Analysis period is from AD 1950 to 2010. Red solid lines indicate 95 and 99% significant level. Black dot lines correspond to 3-, 5- and 30-year cycles.