Using MJO to predict late season W. ATL Trop. Cyclogenesis: usefulness overrated?

[GaWx]

I believe that the usefulness of using MJO phases to predict the likelihood of W. Atlantic Basin cyclogenesis during late season (TC's that form west of 70W 10/1+) is highly overrated due to a very small correlation, at best. I'll show why with hard, objective data from 1974-2010:

MJO Phase at cyclogenesis and # of TC's that formed W of 70W 10/1+ during 1974-2010 (1978 N/A):

1: 2

2: 4

3: 2

4: 3

5: 3

6: 1

7: 3

8: 2

(Total for Phases 1-8: 20. Also, 14 formed when the MJO was within the circle....so no phase was given for them. )

As one can see, there is a pretty symmetrical spread over all phases as opposed to concentrating within the supposedly favorable phases of 8, 1, and 2. You get a total of only 8 when adding those three phases together. With 20 storms, 20/8 or 2.5 per phase would be the expected amount/phase if it were totally random. So, if it were totally random, the expected number for phases 8, 1 and 2 combined would be 7.5. Yet, there were only 8, which is hardly above the 7.5. Look at phases 3-5, combined, a supposedly less favorable group of phases. They also add to 8. So, the not so favorable phases 3-5 produced as many western ATL basin late season storms as the favorable phases 8-2 during 1974-2010!

In case anyone is wondering, I found 16 of the 36 Oct.-Nov.'s with available MJO phase to have been largely within phases 8-2....i.e., nearly half dominated by these 3 phases of the total 8 phases. Only four of these 16 (25%) produced a TC within phases 8-2, which is quite underwhelming. The point of my mentioning these two things is to show that it isn't as if phases 8-2 are any less frequent than the other phases.

In case anyone is wondering, no, these late season W. basin forming TC's that later became MH's did NOT show any hint of favoring phases 8-2 either at time of TC formation or at time of upgrade to MH status. Regarding time of formation, there was one in phase 2, one in phase 4, and two in phase 7. So, only one of the four formed during phases 8-2. Regarding time of upgrade to a MH, one was in phase 3, one was in phase 5, one was in phase 7, and one was on the border of phases 7 and 8.

I'm respectfully challenging those who follow the MJO phases closely to convince me that my historical statistical based assertion is wrong or misleading and that there is, indeed, a nontrivial correlation between phases 8-2 and a higher than average chance for late season TC formation in the ATL basin west of 70W. A thorough but civil debate/discussion would be appreciated as I have a genuine concern about this. If I don't see any responses, I'll assume there's pretty good agreement on this.

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Historical Data sources:

MJO phase: http://www.bom.gov.au/climate/mjo/

TC tracks: http://weather.unisy...ntic/index.html

Individual storm Data:

MJO phase, # of TC's forming, List of TC's (MH's bolded)

1: 2 Marco of 90, Tammy of 05

2: 4 Gordon of 94, Michelle of 01, Odette of 03, Ida of 09

3: 2 Katrina of 81, Fabian of 91

4: 3 Jerry of 89, Katrina of 99, Wilma of 05

5: 3 Michael of 00, Matthew of 04, Paula of 10

6: 1 Richard of 10

7: 3 Karen of 89, Roxanne of 95, Lenny of 99

8: 2 Juan of 85, Marco of 96

[Ginx snewx]

What about amplitude?

[wxmx]

You might want to check out this paper Larry.

[CUmet]

You're talking about a really small sample size by restricting it to 1) TC activity west of 70W, and 2) Only October-December. I'm too lazy to put in the extra lines in the script to count up TC genesis events, but based on NSD, HD, and MHD...this comprises roughly 8-9% of total seasonal Atlantic basin activity, and only about 20-25% of the activity west of 70W. You can basically show anything with a sample size that small.

[HM]

I think an understanding of how the MJO works is in order here.

Octant graphs are EOFs weighing h2 winds, h85 winds and OLR anomalies. ENSO can seriously skew late-season activity and if the MJO registers. Sometimes the MJO registers in a phase but technically driven by something else while a CHI wave crosses the Atlantic.

I would assume before someone does a statistical analysis, you cross-checked your data for these issues?

[OKpowdah]

To add to HM's comments, here's the description of the MJO EOFs

http://cawcr.gov.au/staff/mwheeler/maproom/RMM/eof1and2.htm

Filtering the ENSO signal for ACTUAL MJO waves make some difference.

For applying the MJO wave in research, there needs to be a general understanding of this still-developing area of meteorology, beyond the two dimensional illustration that everyone loves.