Here’s a figure showing Judith Curry’s PDI as compared to calculations from my collation of the ATL track data previously archived, also comparing PDI – which is the integral of wind speed cubed against other measures: a count of hurricane-days, an integral of wind speed and an integral of wind speed squared (which I think is what they call “ACE”). I’ve plotted the data back to 1851 ti see what it looks like prior to truncations by Curry, HW, Eamnuel or others.
All of this is plotted here for the Atlantic and thus is biased through progressively improved measurements of eastern storms through the century. I haven’t done any smoothing since the data is simple enough that people should be allowed to look at the raw data – rather than take the risk that impressions are introduced through smoothing artifacts such as Emanuel’s end-point pinning.
As an impression, it looks to me like the transformations by which wind speeds are summed, then squared, then cubed, results in a difference between late 20th century levels and (say) late 19th century levels that isn’t present in the simple count. This indicates that the count of hurricanes is similar but that the average speed and/or average length of hurricane has increased in the later period. Obviously the measurement of wind speeds in the late 19th century was not done in the same way as in the late 20th century. Without parsing through the data on every storm, I don’t see how one can draw any conclusions based on this data as to whether the differences result from technical changes or from climatological changes.
One other observation from this data set: let’s say that Holland and Webster have hypothesized a model between SST and hurricanes based on the 1905-2005 period. This hasn’t used up all the available data as there is obviously a significant amount of 19th century hurricane data. I haven’t gone through the SST data yet, but my impression is that HadCRU and other temperature data show 19th century SSTs as lower than 20th century SSTs. This makes the high hurricane counts of the 1880s rather an interesting out-of-sample test. It’s hard to see that any plausible relationship between SST and hurricane counts will apply to the 1880s. Doesn’t this sort of verification seem like the sort of thing that a Holland and Webster article should have undertaken? They would presumably end up having to argue that 19th century hurricane counts have been overstated in Hurdat.
Figure 1. Atlantic Basin – hurricane (65 knots) days; and wind speed integrals.
West Division Only
If one looks at the same data using only West Division data which is almost certainly more homogeneous than total Atlantic data, we see a quite striking reversal of relative levels between previous high years 1886-87, 1933 and 2005.
Figure 2. Same for storms west of 69W (except for unavailable Curry comparandum)
East Division Only
Fig 3. Same for east of 69W
Here’s the calculation:
y< -tapply( !is.na(Track$wind)[temp1],Track$year[temp1],sum,na.rm=TRUE)
Here’s how I made this particular plot (there are some quite amazing R graphical techniques, but I’m only familiar with very workmanlike methods). This particular method gives control over axes and panels tho.
x0<-800;text(1851,x0,"Wind Speed Integral",font=2,pos=4)
x0<-30000;text(1851,x0,"Wind Speed^2 Integral",font=2,pos=4)#9*10^4
x0<-1000000;text(1851,x0,"Wind Speed^3 Integral",font=2,pos=4)#5*10^6