More about Sandy -or- I have data!

I explained in an earlier blog post the significance of the sampling effort that was undertaken to understand the pattern of isotopic values, and how this changed over time, of precipitation coming from Superstorm Sandy as it made its landfall and slowly died over the interior of North America.

I ended my sampling effort on Saturday night after collecting a total of nine samples, one every twelve hours since about the time Sandy made landfall on Monday night, the 19th of October. There was only one span of time – on Halloween – when it did not rain sufficiently for me to collect a sample.

Precipitation samples from Superstorm Sandy collected at my house. Rain water was collected in a bucket (that was strapped down so it wouldn’t blow away!) then poured into vials at approximately twelve-hour intervals. The bucket was dried then set out again.

These nine fine samples are now on their way to the University of Utah where their isotopic values will be measured. But, see, I’m also an isotope geochemist. And I also have a water analyzer in my lab. And I might be just a tad impatient.

So I analyzed the waters before I sent them off.

Our water analyzer, Norm, analyzing the Sandy waters. This is a Los Gatos Liquid Water Isotope Analyzer.

Let’s think back on what I said before, about Rayleigh Distillation. So if a cloud rains, the isotopically heavier water (mass 19 or 20) is more likely to fall (because it’s heavier) than the more common, lighter (mass 18) water. So the rain is isotopically heavier than the cloud. After the rain has fallen, the cloud is isotopically lighter than it was before.

So, what happens when that cloud rains again?

When a big storm (like Sandy) moves inland, the rain causes the cloud to get lighter and lighter. And since the cloud water is getting lighter and lighter, so does the rain coming from the cloud, though it is always heavier than the cloud itself. This leaves a tell-tale pattern of heavier isotopes near the coastlines where the storm first came on land, to lighter and lighter isotopes further inland.

So what pattern would you expect if you did all your sampling in one place and a storm simply passed over? What if a storm parked over your house and rained for days and days? What would that look like?

Think about it. I’ll give you a few minutes. I need a glass of water.

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Keep thinking. I need to check my e-mail.

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Any ideas?

Well, it would stand to reason, that unless – somehow – heavy water vapor was getting back into the cloud, the isotopic values would get lighter and lighter over time.

So, one might predict that the rainwater that I collected would get lighter and lighter over time.

Let’s see:

Isotopic values from precipitation from Superstorm Sandy collected near Rochester. Blue lines and symbols are hydrogen; Red lines and symbols are oxygen. The patterns are very similar, as they should be. Hurricane Sandy makes landfall on the left side of the graph. Water samples are plotted according to when I collected the sample (at the end of the twelve-hour period). In the final analysis, it’ll probably be plotted by the mid-point of the sample interval.

The pattern we expected to see was completely borne out for the first three collections, from when Sandy made landfall, to when the center of the storm was supposed to be over the Rochester area, where the samples were being collected.

But then what happened? The values start to increase again. Any ideas?

Well, for one thing, Sandy was supposed to pass over Rochester on Halloween, but it didn’t. The bulk of the storm passed to the south. In fact, it didn’t rain at all on Halloween (which made trick-or-treating possible!). Superstorm Sandy swung south and then west of Rochester before becoming too diffuse to know where the core of the storm was.

Something happened. Something changed.

Well, maybe some heavier isotopes did make it into the vapor mass. Perhaps it was the arctic front that was swooping down from the north as Sandy struck from the east that brought the isotopically heavier rain. It definitely cooled off. It was snowing occasionally during those last two sampling intervals. I suppose it’s also possible that the storm picked up some moisture from the Great Lakes as well.

Again, this is the beauty of the larger project and sampling effort. With only one sample site, we can’t be sure. But once we have all the data from the 100+ sampling sites, we’ll be able to map in detail what was happening. It will be obvious of secondary vapor masses (clouds, storms) joined up with the remnants of Sandy. We’ll be able to tell where and when that occurred.

It’ll be a while before all those samples are gone through and analyzed. I sent my own samples off to Dr. Bowen, so he can re-analyze them using his own instrument and add the data to his huge database. In the meantime, I have this one tiny subsample of the data and a lot of excitement for what will be discovered when the entire data set is complete!

Stay tuned!

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