Supplemental materials:
Figure S1. Difference of the improved GPI (contour) based on Tippett et al. (2011)
between the AP and IAP from June to September. The shaded GPI denote that the
differences are significant above the 90% confidence level by the Student’s t-test. It can
be seen that the spatial pattern of this new GPI version is generally consistent with that
in Figure 4c of the present manuscript.
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Figure S2. Difference of TC-removed GPI (contour) between the AP and IAP from
June to September. The shaded GPI denote that the differences are significant above the
95% confidence level by the Student’s t-test. After the removal of the TC-related field
in the 850-hPa vorticity and vertical wind shear from the GPI calculation, the GPI
pattern is quite similar to that in Figure 4c of the present manuscript.
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Figure S3. Monthly mean 850-hPa wind trend (vector; m s-1 20-1 yr-1) and precipitation
trend (shade; mm day-1 20-1 yr-1) from June to September for the period 1984-2003.
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Figure S4. The series of monthly PDO index averaged from June to September, and the
two dashed curves are the mean values of 1976-1997 and 1998-2011 respectively. The
PDO index is provided by the National Oceanic and Atmospheric Administration. The
decadal variation of PDO index shows obvious change in the late 1990s, which is
inconsistent with the decadal change of the SCS TC activity that occurred in the
mid-1990s.
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Figure S5. (a) Difference of SST (shade; °C) from June to September between the AP
and IAP. (b) The series of SST (°C) averaged over 10°N-20°N, 110°-120°E from June
to September, and the red curve is the linear trend.
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