[Peetwo]

The following is extracted from CSIRO David Griffin's latest 'MH370 - Drift Analysis' 

Summary



Analysis of the trajectories of satellite-tracked drifting buoys deployed in the Indian Ocean over the last 30 years confirms our earlier conclusion based on computer modelling that the MH370 flaperon found on La Reunion in July 2015 is consistent with MH370 having crashed near the 39°S-32°S segment of the 7th arc on 8 March 2014. With just one piece of MH370 found, however, the buoy data, like the computer modelling, can not significantly refine the ATSB's sea-floor search area - it just increases our confidence that the flight path analysis underpinning the choice of sea-floor search area is not wrong.

Introduction
Our 5 August news item described how the 29 July 2015 discovery of a flaperon (now confirmed as being from MH370) on La Reunion island did not cast doubt on the MH370 sea-floor search area chosen by the Australian Transport Safety Bureau based on analysis of the satellite ping data (see the ATSB Fact Sheet). This conclusion was based on ocean modelling. Here, we discuss additional information that lends further support to our 5 August conclusion.

The Global Drifter Program is a highly-valued legacy of the World Ocean Circulation Experiment. The satellite-tracked drifting buoys ('drifters') measure ocean surface temperature for calibration of satellites, and atmospheric pressure for improving the accuracy of weather forecasts. The trajectories of the drifters tells us about ocean surface currents.

The term 'surface current' however, needs discussion before we connect it with the drift of the flaperon.

The flaperon is buoyant, flat, and only a few meters long. Depending on exactly how it floated, it would have drifted at the velocity of the water averaged over the top 0.5-2m.

This is certainly close enough to the ocean surface for the effect of waves to be important, so the Stokes Drift would have contributed to its drift. If the flaperon had any non-negligible freeboard (projection into the air) then it would also catch the wind and 'sail' slowly through the water at some small fraction of the wind speed. This down-wind velocity is often referred to as 'leeway' and expressed as a percentage of the wind speed. We do not have an estimate of the leeway factor of the flaperon, so our modelling work was done for a range of plausible leeway factors. As an aside, we note that winds and waves are usually strongly correlated so empirical leeway factors will include the Stokes Drift if the influence of waves is not deliberately isolated.

Global Drifter Program drifters are fitted with 10m-long sea-anchors (or 'drogues') centred at about 15m depth so that, by design, they do not drift downwind like buoyant items such as the flaperon. There are several good reasons for this design, both scientific and practical. Fortunately for our present purpose, however, the drifters lose their sea-anchors after some time (Lumpkin et al. 2013), making them much more relevant to the question we now face with the flaperon than they were designed to be. Their leeway is possibly slightly higher than the flaperon's, but we think that the error associated with this is smaller than the errors of any other source of information available. We refer below to these as undrogued drifters. Trajectories of the drogued drifters are also shown to highlight the importance of the difference, and for comparison with models that have not included the effects of winds and waves, such as the recent GEOMAR study.

Results
We have extracted from the 1985-2015 database the trajectories of all undrogued drifters relevant to MH370, i.e. drifters that were near the present MH370 sea floor search area (the high-probability segment of the Inmarsat 7th arc between 39°S and 32°S) in February-April, or near La Reunion in April-July, in any of the last 30 years.


Forward drift from 39°S-32°S near 7th arc
Seventy four undrogued drifters (right, click to expand) passed through an area surrounding the present sea-floor search area for MH370 and reported data for at least 200 days after that. A substantial fraction of them went near La Reunion within 500 days. These are drifters that transited the blue rectangle within 6 weeks of 8 March. Relaxing that criterion, we see that trajectories at other times of the year were not very different. One drifter actually beached on La Reunion.

Water temperature and barnacles
The drifting buoys record the surface temperate of the ocean. These data, along with the general northward then westward drift post-crash, show that the flaperon probably entered water warmer than 18°C within a month or two of the crash, so barnacle nauplii may have started settling and growing on the flaperon for most of the voyage.

Forward drift from other segments of the 7th arc
We have also looked at the trajectories of drifters passing though segments of the 7th arc either south of 39°S or north of 32°S. Drifters passing through the southern region have an increased tendency to go east and a lower chance of going to La Reunion. Conversely, drifters passing through the northern region mostly went west across the Indian Ocean but passed north of La Reunion, several beaching on Madagascar or Africa in less than 300d. The flaperon finding is therefore too late as well as too far south to be consistent with a crash site north of the present sea-floor search region.

Comparison with model results
The undrogued drifter trajectories differ from our model trajectories in that the real drifters passed by La Reunion principally north of La Reunion, while our model drifters were principally south of La Reunion. This is precisely the sort of model error we had in mind when we said taking model errors into account in our 5 August news item.

Trajectories leading to La Reunion
Turning the question around, the origins of drifters that passed close to La Reunion any time in 1985-2015 were principally in the southern Indian Ocean, including regions near the supposed MH370 crash site, as shown at right. Selecting only those that arrived near La Reunion in April-July does not greatly alter the picture. What does change the picture, as mentioned above, is selecting for tracks of drogued drifters that (ultimately, possibly with the drogue off, like this one) go near La Reunion. These drifters are more likely to have originated in the tropical Indian Ocean. As discussed above, however, the flaperon floated close to the ocean surface, so the tracks of drogued drifters are much less directly relevant than those of the undrogued drifters.

Conclusion
Taking the modelling and drifter observations together, we stand by our earlier conclusions: the finding of the flaperon is not a reason to doubt the present choice of sea-floor search area. And with only one piece of MH370 found, the presence of ocean eddies makes it essentially impossible to refine the sea-floor search area with any confidence. The flaperon finding does, however, support the flight-path analysis conclusion that the 39°S-32°S segment of the 7th arc is indeed the highest-priority search region for MH370.

I am just a mere knuckledragger but this bit really makes one think that old mate Griffo has been tasked by the 'powers to be' to make the prognosis fit the synopsis...
 "...What does change the picture, as mentioned above, is selecting for tracks of drogued drifters that (ultimately, possibly with the drogue off, like this one) go near La Reunion. These drifters are more likely to have originated in the tropical Indian Ocean. As discussed above, however, the flaperon floated close to the ocean surface, so the tracks of drogued drifters are much less directly relevant than those of the undrogued drifters..."

If that is not the biggest load of presumptive codswallop, I don't know what is. If that is what they're basing their drift model on why then did they not bombard the 7th arc with SLDMBs that can simulate both floating & drogued drifters??- FCOBL...

MTF..P2