|Left: Ocean heights as observed by two satellites.|
Top: at 7:30 hours; Bottom, at 8:20 hours
Right: Computer simulations (black lines) and data
(red and purple lines) on the form of the tsunami.
NASA/JPL-Caltech/Ohio State University
The NASA press release is here.
Tuesday, December 6, 2011
Tohoku tsunami IN THE PACIFIC was a "merged tsunami" (Or was it? Why did I put IN THE PACIFIC in capital letters? Read on!)
The Fall meeting of the American Geophysical Union is in full swing and press releases are highlighting some interesting papers. One of these is on so-called "merged tsunamis," which I'll explain in a minute. However, if you Google "merged tsunamis" today, you'll find headlines like:
"Two merging tsunamis caused Japanese devastation" (TG Daily)
"Double Tsunami" Doubled Japan Destruction" (Eurasia Review)
"Rare "merging tsunami" contributed to Japan destruction" (Mother Nature Network)
Even mainstream newspapers:
"Japan was hit by a tsunami formed from TWO giant waves, reveal scientists" (Daily Mail, UK) (OOOPs, note added: one commenter pointed out that the Daily Mail should not be considered a mainstream newspaper...)
"Tsunami that struck Japan in March resulted from merging waves" (CNN, International)
Even academic publications:
"Merging tsunami" doubled destructive power along Japanese coast" (Environment360, from Yale.edu)
Many of the articles are accompanied by photos of the devastation on the coast of Japan.
But, wait a minute!! Here's the actual NASA/JPL news release. While the headline "NASA finds Japan tsunami waves merged, doubling power," might lead you to think that scientists are saying "The tsunami that hit Japan was caused by merged tsunami waves, doubling the power...", that is, in fact, not what the text of the article, nor the accompanying images show. If you look at the images shown on this post (which are the images in the press release) carefully, Japan is in the far upper left corner and the waves that were observed and are modeled are far out away from Japan in the Pacific Ocean. They were observed 7:30 and 8:20 hours AFTER the earthquake. In contrast, the waves that devastated northern Honshu struck in 20 minutes.
Unfortunately, I am not at AGU to hear the paper (which is not being given until Friday morning), but I find the press release to have very little content--it basically says that two satellites captured the above two images, that there was a "merged tsunami," and that this merging phenomenon may account for unexpected destructive power." And, I find the images to be baffling....what do the three black arrows point to? What is the purple line that runs up through the bottom image, and why is it red in the top image? What is the red arrow on the bottom of each image and why has it changed position? What am I supposed to be seeing in these images? The abstract of the actual paper (by Y. Tony Song and others) has a different figure). For info, I have attached the actual abstract at the bottom of this post.
Here's what I do see--in both images the red areas show water that is higher than an arbitrary zero-level (see the scale on the left image). The blue areas, in contrast, represent water that is below the zero level. These two areas correspond to the highest and lowest peaks in the model and data shown on the right side of the figure. All that I can pull out of the two images on the left side is that there isn't as much red or as much blue in the bottom image as in the top one--that is, the high water is less high, and the low water is less deep, which is what you expect as a tsunami spreads out to cover more and more area. My concept of a "merged tsunami" is that two high waves catch up with each other producing a bigger wave by constructive interference. I can't see that in these images.
Readers--HELP!! (And they did, see reader comments!)
And, JPL--shame on you for an ambiguous, if not downright misleading, headline. It did its job in attracting a lot of attention, but it created a lot of misinformation, and that's not the job of a scientific press release.
Posted by Susan W. Kieffer at 3:22 PM