Revisiting the post An obvious clue from tidal data, which is an analysis of this paper The effect of regional sea level atmospheric pressure on …

At the time, I did not try to duplicate the results, but after coming across it again, curiosity got the best of me. The program to duplicate the results is in this GIST: Analysis of SLP from PSMSL stations, using HadSLP2.

The author really didn’t clarify that the striations/bands/gaps in readings (above from paper and recreated below, left) were simply due to the discrete nature of monthly readings placed against a strong seasonal variation. For example, the NYC (The Battery) and Boston location have a significant seasonal SLP response due to the geographic characteristic of cold-season continental highs alternating with warm-season lower-pressure maritime regimes.

For New York, explain this figure [📷 nyc_monthly_slp.png]. On the right the values are replotted as (Month modulo 12) to indicate which months corresponded to the left.

Copilot response:

Of course there is other stuff lurking in the data, so it is good to have the HadSLP2 as an adjunct to the PSMSL data I am using here

Consider the Honolulu SLP data below. There’s a clear Hovmller-like sloped ridge in the data, as one’s eye can detect, emphasized by the highlighter.

The testing of lines in the rotated frame of the form u = p - s t finds this in the power spectrum. See It reads a HadSLP2 TSV, searches over diagonal slopes in rotated coordinates u = pressure – slope * time, identifies the strongest ridge, writes the power spectrum and ridge profile as TSVs, and saves a PNG with the ridge overplotted on the scatter plus the spectrum. See the previous GIST

A plausible explanation is a multidecadal modulation of the regional seasonal SLP cycle by North Pacific basin circulation variability, of which PDO/IPO variability is a plausible contributor.