Fig. 3. (a) The zonally resolved correlation coefficients between
tropical tropopause temperature anomalies, tropical SWV entry anomalies
and global SWV anomalies. The orange area indicates the IPWP region. The
bold line indicates that significance at the 90% confidence level. (b)
SST trends in the tropical Pacific and Indian Ocean from 1984 to 2020,
with the black box indicating the area of the IPWP (30°S to 30°N, 30°E
to 180°). Dots indicate significant trends at the 90% confidence level.
(c) The time series of the IPWP averaged SST anomalies from 1984 to
2020. This solid line indicates SST anomalies in the IPWP. The dashed
line is the linear regression line. The trend and uncertainty are shown
in the top right-hand corner. The uncertainties are expressed by 2σ
errors.
Fig. 4 shows the distribution of zonal mean SWV decreasing trends and
tropical tropopause cooling trends, with the left column showing the raw
trends and the right showing the trends after linearly regressing out
the warming IPWP signal. In SWOOSH, the significant dehydration trends
in the SWV below 30 hPa induced by the cooling trend in the tropical
tropopause are coherent with that shown before, and the only decreasing
trend is located above 30 hPa at high latitudes (Fig. 4a). And this is
consistent with Hegglin et al. (2014). In ERA5, the distribution of the
trend is significantly different. The decreasing trend is mainly in the
southern hemisphere, while the decreasing trend in the northern
hemisphere is weak (Fig. 4b). After removing the IPWP warming signal,
decreasing SWV trends become weaker in both data sets and even
increasing trend dominates the northern hemisphere in ERA5 (Figs. 4b,
4d). This implies that the recent decadal SWV trends may be connected
with IPWP warming. The IPWP warming signal is also shown in the cooling
trends of tropical tropopause. After removing the IPWP warming, the
significant cooling trends in tropical tropopause are relatively weak in
both ERA5 and JRA55 (Figs. 4f, 4h).