New England Hurricanes, the forecast every time

12 11 2012

Kevin Anchukaitis

Let me start my first post here at Strange Weather by thanking Julien for the opportunity to join him here at his blog. I’ve been studiously preparing by listening to lots of Tom Waits albums, and although I hadn’t intended for my first post to be about hurricanes in the northeastern United States, some strange weather intervened.

I’m a recent arrival to the Massachusetts coast and now a scientist at the Woods Hole Oceanographic Institution, after spending the previous several years in New York City. While Superstorm Sandy, née Hurricane Sandy, was still several days from landfall in New Jersey, though, the region’s history of deadly hurricanes was already in the front of my mind. In August of 1991 Hurricane Bob scored a direct hit on Falmouth on Cape Cod in Massachusetts — my new home. At barbeques and gatherings this summer, my immediate neighbors were telling their stories of Bob’s “furious” landfall, the wind, the snapping trees, the storm surge, the flooding — and the long aftermath without power. So as Sandy lined up for her run at New England at the end of October, I admit I was somewhat nervously eyeing the tall but spindly locust trees near my house.

New England is not without a reason to keep one eye on the tropics in the late summer and autumn. Besides Bob, the New England Hurricane of 1938, the Great Atlantic Hurricane of 1944, Hurricane Carol in 1954, and Hurricane Donna in 1960. Wikipedia has a list of New England hurricanes. In 1821, a hurricane passed directly over New York City, resulting in 13 feet of storm surge and causing the East River to flow across lower Manhattan south of Canal Street. Yet another reason to be wary about hurricanes in New England lies in the mud and sand of the coastal marshes up and down the New England coast, several of which are disconcertingly within walking distance of my new home. These environments preserve a long record of storm activity in coastal New England going back hundreds or thousands of years.

Jeff Donnelly is a colleague of mine at Woods Hole Oceanographic Institution and one of the world’s experts in paleotempestology (Andrew Alden has a nice write-up on this science, here) — the study of past major storm activity from geological or biological evidence. Jeff uses sediments in coastal environments like marshes to identify and date past storms, but others have also used stable isotopes in tree rings, corals, and cave deposits, as well as historical records.

Marsh sediments from across New England tell a story of past hurricane strikes in the region, some clearly quite large. These environments record the passage of strong storms in the overwash deposits of sand that flood over their barrier with the sea during high waves and storm surges. Shore Drive in Falmouth is just such a barrier, and Sandy demonstrated quite clearly what an overwash deposit on its way to a backbarrier marsh looks like.

In a 2001 paper in the journal Geology, Jeff Donnelly and colleagues used multiple sediment cores extracted from a backbarrier march at Whale Beach, New Jersey, located between Ocean City and Sea Isle City, just to the south of Atlantic City, and close to where Hurricane Sandy made landfall, to reconstruct a history of beach overwash. They found deposits of sand associated with a 1962 nor’easter and another strong storm which they believed was the 1821 Hurricane. They dated a third deposit, thicker than the 1821 sand layer and probably related to an intense hurricane, to between 1278 and 1438 CE. In their article they note that the Whale Beach record suggests an annual landfall probability of 0.3%.

In a 2004 paper in Marine Geology, Donnelly and his team again looked at overwash deposits in New Jersey, this time from Brigantine, just to the north of Atlantic City. Here again they identified a layer of sand in the backbarrier marsh likely corresponding to the 1821 hurricane. They also dated large sand layers to the period between 550 – 1400 CE, which might correspond with the 13th or 14th century event identified at Whale Beach.

Donnelly et al. 2004, Marine Geology

Original caption from Donnelly et al. 2004, Figure 7: Cross-section of Transect 2 at Brigantine. ( p ) Location of radiocarbon-dated samples (see Table 1). Horizontal axis begins at the barrier/marsh boundary. The vertical datum is the elevation of the barrier/marsh interface (approximately mean highest high water).

Further to the east, in another 2001 paper Donnelly and his team used sediment cores from Succotash Marsh (near the fabulous Matunuck Oyster Bar near Point Judith in Rhode Island) to date hurricane strikes to known events in 1938 and 1954, as well as 1815 and the 1630s. Two other overwash deposits were dated to 1295-1407 and 1404-1446 CE. Donnelly and coauthors concluded that “at least seven hurricanes of intensity sufficient to produce storm surge capable of overtopping the barrier beach at Succotash Marsh have made landfall in southern New England in the past 700 yr”

One more, closer to home: In 2009, Anni Madsen and her coauthors (including Donnelly) published dates on hurricane deposits in Little Sippewissett Marsh in Falmouth, Cape Cod, Massachusetts, using optically stimulated luminescence (OSL) dating. This particular core shows a number of overwash deposits over the last 600 years, including probably Hurricane Bob and the 1976 Groundhog Day storm, but is also indicative of some of the difficulties and uncertainties in using backbarrier marshes to reconstruct hurricane strikes: Little Sippewissett Marsh doesn’t have sand layers that obviously date to recorded storms in 1938, 1944, 1954, 1815 and 1635, which include some of the largest to hit this region. Uncertainties arise from, amongst other things: a single core may not record all the storms at a site, storms themselves alter the height of the barrier and inlet channels, dating of events comes with analytical and depositional uncertainty, and in New England strong storms could be hurricanes or nor’easters.

Madsen et al. 2009, Geomorphology

Location of Little Sippewissett March, showing 19th and 20th century storm tracks across the region, from Madsen et al., A chronology of hurricane landfalls at Little Sippewissett Marsh, Massachusetts, USA, using optical dating, Geomorphology 109 (2009) 36–45, 2009

On Dot Earth, Andy Revkin has pointed toward his articles on Donnelly’s Caribbean research, as well as a 2002 paper by Anders Noren on millennium-scale storminess in the northeastern United States.

Bringing us back to Sandy, what does the history and geology of New England hurricanes tell us? There is evidence from all along the coast that powerful storms do occasionally make landfall in the region. The evidence from Whale Beach in New Jersey, near to where Sandy came ashore, records the very strong 1821 hurricane as well as another likely event in the 13th or 14th century. Other strong storms have hit the New England coast at other times in the past millennium. A 2002 article from the Woods Hole Oceanographic Institution quotes Donnelly:

“Most people have short memories,” says Donnelly. In fact, it is estimated that three-quarters of the population of the northeastern US has never experienced a hurricane. Donnelly’s research provides evidence to be heeded. “The geologic record shows that these great events do occur,” he says. “We need to make people aware that it can happen again. We’ve got to have better evacuation plans and we need to equip people to react to a big storm.”

I’m so far agnostic on the precise influence of human-caused climate changes on the track and characteristics of Sandy. The process of sorting out the influence of natural variability from the human-influence on this particular storm has just begun. As Justin Gillis notes in the New York Times Green Blog:

Some [climate scientists] are already offering preliminary speculations, true, but a detailed understanding of the anatomy and causes of the storm will take months, at least. In past major climate events, like the Russian heat wave and Pakistani floods of 2010, thorough analysis has taken years — and still failed to produce unanimity about the causes.

The influence of rising sea levels, particularly along the east coast of North America, no doubt has to be factored into understanding current and future storm surges. But what the geological and historical record indicate is that even in the absence of a human-influence on the strength, track, or magnitude of tropical storms, we would still need to be prepared for destructive coastal storms to strike areas of high population and considerable infrastructure. Paleoclimatology — in this case, paleotempestology — nearly always provides us with evidence of an even greater range and diversity of behavior of the climate system then we’ve witnessed over the relatively short period of instrumental observations, and gives an idea of some of the events — droughts, floods, and storms — that we need to keep in mind when figuring out how to build resilient communities.





The Heisenberg Principle of Climatology

17 02 2008

OK, I have to admit this is a pretty eccentric idea . It occurred to me around New Year’s time. Please read this as entertainment, not science – or at best, entertaining science. I assume the esteemed reader to be familiar with Heisenberg’s uncertainty principle .

These days, even small-time lawyers are using the concept – as we were reminded by the Coen brothers in the magnificently quirky “The Man who wasn’t there” :

Forgetting the Coen twist, the uncertainty principle states that there is a fundamental limit to the accuracy with which you can jointly determine the position (X) and the momentum (P) of a particle in quantum world. Which one can write :

\Delta X \Delta P \geq \frac{\hbar}{2}

wherein \Delta is the root mean square operator and \hbar is the familiar Planck’s constant.

This has pretty deep philosophical implications because it means that we must abandon utopias of ever knowing those quantities simultaneously with arbitrary accuracy. Most sobering is that it is a direct consequence of the fundamental principles of quantum mechanics.

It occurred to me the other day while having a shower (which is a well-known fountain of ideas), that one could formalize a similar principle in climatology. Indeed, the basic curse of paleoclimatology is that the farther back in time you try to estimate temperatures, the more uncertain they become. We think we know last year’s globally average temperature pretty well (say within 0.05 C ). Last decade might have similar or even lower uncertainties because of the central limit theorem knocking down some measurement errors for you… but try going back 100 years and the measurement error and sampling bias become so large you’ll be lucky to have an accuracy of 0.5 C. And that is during a period broadly known in the field as “instrumental”, that is to say the one over which we have a reasonable number of physical measurements of temperature. As you can see on the following graph from Brohan et al, 2006, this uncertainty grows back in time rather quickly already.

Uncertainty in global temperatures (HadCRUT3 dataset)

Before about 1850 A.D., we no longer have enough direct measurements, so we have to rely instead on proxy indicators. All of them (corals, tree rings, ice cores, sediments, documentary evidence) have their pros and cons, but even if they can give a surprisingly coherent view of past climates, they are necessarily approximate. Hence, go back 1000 years and arguably, we don’t know this within 0.7 C, perhaps even 1 C (this is a very controversial number and I’d be surprised if no one picks up on it… With wacky ideas come rather loose numbers that one should not take too literally). Go back 10,000 years and a degree C or two might be all that you could hope for. And so on and so forth : the more time elapses and eons pass by, the more water flows under bridges, the more overprinted, worn and tired is the geologic record – and so grows the uncertainty in the estimated temperature.

Say you are trying to estimate said temperature, T, over some period \tau (or equivalently, the frequency \omega). The longer the period (i.e., the smaller the frequency), the more uncertain the estimate, so one could write something of the form :

\Delta T  \omega \geq \gamma.

Which is pretty naive and assumes an inverse relationship between the two variables, and \gamma is by no means a “universal” constant. More generally one could write :

\frac{\Delta T} {\Delta T_{\circ}} =  \beta \left ( \frac{\omega} {\omega_{\circ}} \right )^{-\alpha}

where the subscript \circ denotes a reference period (say, the last decade), and \beta and \alpha are a positive constants, whose precise values are as yet undetermined. So one could play games with that and try to estimate them from a linear fit in log-log space… I’m not sure they would mean much, but who knows ? Perhaps one day we’ll have enough reliable data to be able to characterize this \alpha and it won’t seem so quirky. In any case, it’s now pretty far from Heisenberg, who must be shifting in his grave and the mere idea that I am using is august name for such silliness. Nevertheless, it is an uncertainty principle of sorts. And for no more fundamental reason that the degradation of geological records over time, which I guess one could view as a broad consequence of disequilibrium thermodynamics. But only loosely so, because bioturbation holds a large part of the blame, and darned if we have a consistent theory of living organisms that’s grounded in statistical mechanics. But I digresss.

In my defense, I would like to declare that this nonsense was scribbled on a piece of paper while leaning on a garbage can outside the Metropolitan Avenue subway station in Williamsburg, Brooklyn. Which we all know to be home to some pretty crazy stuff.

Now here’s the truly insane part of the story. The next day was my adoptive bigger sister’s birthday. ( If you happen to live far from home, I highly recommend you adopt, or get adopted by, a bigger sister. It’s loads of fun, especially when they have the same linguistic schizophrenia as yours). I was working from the Columbia University library that day, and decided to drop by to bring her a gift (she lives around the corner). I had no sooner entered her building and stepped into the elevator that a white-haired gentleman nimbly entering the lobby asked me to hold the doors. I happily obliged, and he promptly jumped into the cage a few seconds afterwards, with a mischievous smile on his face.

– “Piso cuatro, por favor “, he said with a distinguished Spanglish accent.

– “Si señor”, I replied, and pushed button 4.

He looked at me from top to bottom and asked in a spotless New England English (I must have looked really freaky) :

– “Are you a physicist ?”

– “Almost”, I replied, “I’m a geophysicist”.

– “Ah well, I am a physicist”, he went on. “And I recently had a very interesting epiphany about Heisenberg’s uncertainty principle.”

 

Before I could pick up my jaw from the floor, Mr Heisenberg Jr had disappeared into the depths of the 4th floor, only perceptible through the rustling of his raincoat as his walked down the corridor. And so it was decided that even though my Heisenberg idea might not pass into posterity past breakfast, it should at least be worthy of a little post.