Indices of Pacific Walker Circulation strength: trends, correlations and
uncertainty
Abstract
The strength of Pacific Walker circulation (PWC) significantly affects
the global weather patterns, the distribution of mean precipitation, and
modulates the rate of global warming. Different indices have been used
to assess the PWC strength. Evaluated on different datasets for various
study periods, the indices show large discrepancies between the reported
trends. In this study, we performed sensitivity analysis of 10 PWC
indices and compared them over the 1951-2020 period using the ERA5
reanalyses.
The time series of normalised indices
generally agree on the annual-mean PWC strength. The highest
correlations (exceeding r=0.9) are between the indices that describe
closely linked physical processes.
The trends of PWC
strength are strongly affected by the choice of representative time
period. For the commonly used 1981-2010 period, the trends show
strengthening of the PWC. However, trends computed for longer period
(i.e. 1951-2020) are mostly neutral, whereas the past two decades
(2000-2020) display weakening of the PWC, although it is statistically
not significant. The temporal evolution of trends suggests multidecadal
variability of PWC strength with a period of about 35 years, implying a
continued weakening of the PWC in the next decade.