A couple of days ago, I posted up my attempt to replicate Emanuel 2005 Figure 1 (Atlantic PDI) and today post up a similar exercise on W Pacific PDI. While most hurricane discussion is focussed on the Atlantic, the PDI in the W Pacific is about 5 times larger. Emanuel said:
I maintain that current levels of tropical storminess are unprecedented in the historical record and that a global-warming signal is now emerging in records of hurricane activity This is especially evident when one looks at global activity and not just the 12% of storms that occur in the Atlantic.
In his Reply to Landsea on the endpoint pinning problem, Emanuel said:
As it happens, including the 2004 and 2005 Atlantic storms and correctly dropping the end-points restores much of the recent upswing evident in my original Fig. 1 and leaves the western Pacific series, correctly truncated to 2003, virtually unchanged….
Here is Emanuel’s Figure 2 showing PDI for the W Pacific against SST:
Emanuel 2005 Figure 2 | Annually accumulated PDI for the western North Pacific, compared to July–November average SST. The PDI has been multiplied by a factor of 8.3 * 10^-13 and the HadISST (with a constant offset) is averaged over a box bounded in latitude by 58Nand 158 N, and in longitude by 1308 E and 1808 E. Both quantities have been smoothed twice using equation (3). Power dissipation by western North Pacific tropical cyclones has increased by about 75% in the past 30 yr.
Below is my attempt to replicate the Figure using the archived Best Tracks data, done the same way as the Atlantic data. In the case of Atlantic storms, I gather that it’s not expected that there will be major additions to PDI during the balance of 2006; I have no idea what people expect in the W Pacific – so the 2006-to-date value is just illustrative. One difference between the graphics pertains to an adjustment to pre-1970 data by Emanuel, which was discussed by Landsea in his Comment. The Emanuel adjustment was based on Landsea 1993, but the adjustment is in controversy as discussed below.
Emulation of Emanuel 2005 Figure using Archived Data
Next here is the extension of smoothed data to 2005 and 2006 – again note the caveat on 2006 data expressed above.
Any impression of a "doubling" in recent years derived from this data obviously derives entirely from the adjustment to pre-1970 data applied by Emanuel. I get the impression from Landsea’s comments here (and also Landsea 2004) that his current view is that it’s the 1970-1990 data that need to be adjusted upward rather than the pre-1970 data being adjusted downward. As between the two scholars, I get the impression that Landsea is much more immersed in the data – a characteristic that I obviously believe to be important. At the end of his Reply to Landsea, Emanuel stated:
But I agree that there is a pressing need for a storm-by-storm reanalysis of tropical cyclones, not only in the North Atlantic, but also in the western North Pacific, where aircraft reconnaissance records also extend back to the 1940s.
In a recent article upon which I’ll post shortly, Landsea questioned whether the hurricane data set contained too many inhomogeneities of methodology and instrumentation to permit trend analysis – a question that I hope to return to some time.
The histogram of hurricane PDI and annual W Pacific PDI are shown below and look a bit different than the corresponding distributions for the Atlantic – the annual distrubtions are less skewed.