The PDO index comes in at 1.25 for July. I would expect it to drop further as the El Niño fades .
If it goes negative I doubt it will go negative for long.
Question for AbruptSLR -
Is there a mechanism to adjust the PDO index to the rising SST trend in the Pacific ? If the El Niño in the Niño34 region for three months at +.5 is adjusted over time to trend I was wondering about the PDO.
Bruce,
As the issue that you raise is a little complicated (because the PDO index is reconstructed as the superimposition of both tropical forcing and extra-tropical processes), I provide the following link to the Wikipedia article about the PDO, which notes that linear inverse modeling (LIM) can be used to account for global trends for up to 4 seasons (see the following extract):
https://en.wikipedia.org/wiki/Pacific_decadal_oscillationExtract: “NOAA's forecast products do not include the PDO at this time. Alexander et al., explored the prediction skill of a linear inverse modeling (LIM) method to predict the PDO, LIM assumes that the PDO can be separated into a linear deterministic component and a non-linear component represented by random fluctuations.
Much of the LIM PDO predictability arises from ENSO and the global trend rather than extra-tropical processes and is thus limited to ~4 seasons. The prediction is consistent with the seasonal footprinting mechanism in which an optimal SST structure evolves into the ENSO mature phase 6–10 months later that subsequently impacts the North Pacific Ocean SST via the atmospheric bridge.
Skills in predicting decadal PDO variability could arise from taking into account the impact of the externally forced and internally generatedPacific variability. The difference in phasing of the PDO can provide predictive power for regional climate anomalies, such as is the case for the American West's drought cycle. The Great Salt Lake of Utah, for example, follows a distinct phase of this oscillation.
Commercial climate forecasting vendors such as MW&A, utilize solar factors to predict the PDO index. This vendor also utilizes the PDO, along with other parameters to forecast drought patterns in the American West.”
Best,
ASLR
