2012 Fleetweek Parade of Ships on the Hudson

Posted on May 25, 2012 by

This week is Fleet Week in New York City, and my colleague Alex Sedunov captured this amazing time-lapse posted at YouTube and several great photos of the march of ancient sailing vessels up the Hudson yesterday.

Can you name any of these ships?

And this one is from our time-stamped monitoring camera at the Center for Secure and Resilient Maritime Commerce, where we have infra-red, radar and underwater acoustic monitoring.  Gotchya!

And one more time, if you missed that time lapse, it is linked here.

Thanks for the amazing coverage, Alex!  Last year’s photos are also captured in a blog post, when we had nicer weather and he took more military ship photos.

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Trees Tell the Story of 500 Years of NYC Drought History

Posted on April 29, 2012 by

by Neil Pederson

I didn’t see this coming. Yes, winter 2011-2012 has been quite unusual and it is becoming more obvious that almost anything can happen with our weather these days (see October snowstorm followed by days in winter 2012 when my house windows were opened). But, a moderate to severe drought just seven months after many of us were wondering if the rainstorms were going to stop? With the insight that my co-authors and I had looking over the past 500 years of drought history for the Greater NYC region, I didn’t expect this.

The Hudson River, September 2011

In a paper currently in revision with the Journal of Climate, we reconstructed drought history using tree rings back to the year 1531. We were wrapping up the manuscript in Summer 2011 when the march of the tropical storms was beginning. To talk about the drought reconstruction for a hike I was leading on Columbia’s Lamont-Doherty campus, I put together a record of the Palmer Drought Severity Index derived from meteorological measurements. When I first calculated annual and summer drought for the past 110 years, I thought I or the web source used to gather the data made a mistake because it looked odd, unnatural even. It looked like The Hockey Stick, but for moisture, not temperature.

Annual (top, dark blue line) and summer (bottom, light blue line) precipitation for the Hudson Valley. Adapted from: http://www.ncdc.noaa.gov/temp-and-precip/time-series/

I immediately showed the figure to co-authors and a few more folks in the lab. I cannot quote everything that was said; this blog is rated PG, I assume. Some things that can be quoted are, “Wow!”, “Bizarre…”, “Are you sure that is correct?” No, I wasn’t sure that it was correct. The online data source was fairly new, so it was conceivable that there was a bug in the program. So, I contacted other sources and acquired data elsewhere. The results were the same. The instrumental record indicated that the last decade had been extremely unusual. And, as the tropical storms marched up the eastern US, 2011 was only continuing that trend.

This ‘discovery’ was exciting in and of itself. It was so exciting, I squeezed it into the manuscript. But, looking at the series again was encouraging in a sense: I made three different attempts at reconstructing drought history for the NYC region prior to finalizing the manuscript, experiments if you will, and each indicated that the end of the 20th century appeared unusually wet. The indication from measured data that the end of the 20th century supported what the trees were saying.

—

The first drought reconstruction for the Hudson Valley, in 1977 (and the last tree-ring reconstruction specifically targeted for the larger Hudson Valley), showed for the first time that one could reconstruct drought in the humid eastern US. This was an advance because, well, it wasn’t too obvious at the time that trees that generally receive ~3.5 inches of rain each month (89 mm) would be sensitive to changes in moisture, at least, not compared with a semi-arid region like that of the Southwestern US. A collection of four different species for the first reconstruction nicely captured the variation of July drought from instrumental record. With Ed Cook as a collaborator, we now had 30+ tree ring records composed of at least a dozen species distributed across the valley. Most importantly, some of these records now stretch back to the 1400s. The original reconstruction most reliably went back to only 1700.  Interestingly, the original reconstruction ended just prior to the phenomenon that I had trouble believing was real in my first attempt at reconstructing drought for the NYC region.

—

Reconstructing drought for the NYC region was not something I planned to do with my dissertation data. But, after the results of a paper by Ed Cook using a chunk of this data and then some interesting work with some of this data by a group of Manhattan College students for a group project, I was inspired in 2007 to see how my collection of tree ring records across the Hudson Valley would perform in a drought reconstruction.

It was exciting to test my dissertation data from the Hudson Valley for a new drought reconstruction because it was diverse and spatially dense. What made the new tree-ring network derived from my dissertation most outstanding was the number of species used. A handful of new studies suggest that species replication might improve tree-ring based reconstructions (see here, here, and here). The new data set would be a good test of this hypothesis. Results do support the idea that species replication aids tree-ring based reconstructions. More work needs to be conducted in this arena, but the results are promising.

So, we can now take drought history reliably back to the early-1500s. The new network reconstructs a longer season of drought, May-August, and accounts for more of the year-to-year change in moisture conditions from the instrumental record than the original reconstruction; I suspect the species diversity used here helps capture a broader window of drought. The new reconstruction reveals droughts in the past that make The 1960s Drought seem like a bad cough. For example, there were 23 straight years of below average moisture conditions in the 1500s. And, this drought falls only one year after a 5-yr drought and 10 years after an intense drought that began in 1543. If drought conditions only somewhat similar to the 1500s return, the NYC region will be in a heap of trouble.

Annual May-Aug drought (dashed line) for the Greater NYC Region. The solid line emphasizes decadal-scale changes in moisture availability including pluvials (above average moisture; blue) and drought (red).

So, why did it take me so many years to put this result up for review with our peers? Like the instrumental record I saw in Summer 2011, I didn’t believe the results. The new reconstruction shows the 20th century to be unusually wet. Importantly, the last 40 years, the time since The 1960s Drought, were especially wet, even in comparison to the rest of the century. It also revealed a long upward trend of increasingly moist conditions since the late-1800s. This could have been the result of how I processed the data. I sent the first version to Ed. He noticed something in some of the tree ring records that could use some improvement. So, I re-processed the data as Ed suggested, reconstructed drought, and got the same essential result. Hmm…I thought of one more test. I re-processed the tree ring data another way and got the same result. It seemed pretty robust. When cross-checked with four independent drought reconstructions across much of the eastern US, a similar, long-term trend is apparent. Therefore, it was time to see what my peers thought. The manuscript is now entering the last phase of peer review. So, if you want to see how much of the eastern US is wetting, you’ll have to wait until the publication comes out.

For myself, this finding of increasingly moist conditions in our region puts a different perspective on events and phenomena, especially given simulation modeling suggesting that this region is expected to continue to get wetter in the future. The beach closings because of sewage treatment overflow of last summer or the frustration of upstate residents because of reservoir water levels and stream quality? 2011 might be a signal that we will have to take on the issue of too much water so that we can swim in the summer. An acquaintance’s yard and basement is staying wet these days. They had the local government look for leaks in village’s water pipes. What if rising groundwater is causing this issue? What will the homeowner’s solution be? Someone asked me why trees on the edge of a local wetland were dying. My moisture-colored glasses can only think, again, of a rising water table playing a role (certainly it is more complex than this, correct?).

So, because of this long-term trend, I didn’t expect this year’s drought, despite the fact that I have been telling folks that the droughts of the past could come back and haunt us. We cannot predict just yet how the rest of this year, next 2-3 years, or decade will play out. Richard Seager has tried to determine what drives precipitation in this region. Turns out it is pretty difficult to understand with our current set of scientific tools. But, if this drought becomes more severe and extends itself for another 3-5 years, it will push those of us living in this region to think hard (again) about our water use during these wet years.

[This is a guest post by Neil Pederson, Assistant Research Professor at Columbia University's Lamont-Doherty Earth Observatory just up the Hudson in Palisades, NY]

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Central Park North Woods and Waterways

Posted on April 7, 2012 by

A week ago I went on a tour of Central Park’s northern end, lead by Ken Chaya, maker of the definitive map of the park.  We started at a pond called The Pool at 102nd Street, just inside the park from Central Park West.  We soon came across this stunning American Egret.

How amazing, a few yards inside a park in the nation’s largest city, and here is a pond that an egret somehow decided to call home, even if only for a short stop on a migration.

We made our way eastward into The Ravine, where this municipal-water fed stream runs over a few waterfalls, likely exaggerating the natural water flow that was here before Olmstead and Vaux had their way.

Here were some Mallard ducks on the stream down the Ravine.   The animals were very fearless of my standing within a few feet, which surprised me.  The area just east of the loop road here is a muddy, boggy area, with a very unusual feel for NYC.

An hour or so later, time for brunch … for the ducks, but not to mention the humans had to run and get crepes over on Columbus!

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Five Flavors of Fog Turn NYC Greyscale

Posted on March 21, 2012 by

Fogging over the Verazanno Bridge, date unknown. Credit: Jeff Colen

A rare but often beautiful sight around New York City is dense fog.  It might have to do with my vantage point, from Hoboken or Manhattan, where we often look over it from the outside.  It might not be so popular out in Brooklyn, which can get doused for days, or for people waiting through delays at airports.  And not to forget all those people who have bad hair days (Credit: Jennifer).

Maybe there’s a little bit of envy in my heart for San Francisco and other West Coast locales where silky layers can sometimes rise up from the sea and pry ownership of the heavens from skyscrapers, or share the sky with glorious red cabled bridges.  But nothing smoothes out our manic city’s rough edges like a soothing greyscale layer flowing in past Verrazano Bridge.

Fog obscuring the Verrazano Bridge, March 20, 2012. Credit: Connor Hughes

Fog in our region comes in five different flavors, and a science paper recently cataloged them (PDF) and counted the events over twenty year’s time.  Some blow in from the ocean during the day, riding on the sea breeze – these are called advective fog events (~30% of total).  Some coalesce overnight amongst the buildings and shadows and huddle until the sun shoos them away – this type is called radiation fog due to the role of escaping heat, aka long-wave radiation, enabling condensation of humid air (10%).  Another is called precipitation fog, which arrives during rain events (40%).  And a common one in cooler seasons is cloud base fog, where fog sets in with clouds lowering down from above (20%).  The fifth, and one we perhaps don’t see in urban areas at all, is morning evaporation fog (2%).

A good example of advective fog came last April, and I blogged about how it blew in on the sea breeze and washed over Brooklyn and parts of Manhattan.  The heart of the city, however, is somewhat protected by its urbanization and the heat island phenomenon, while more rural areas get the most frequent fog episodes.

Sunrise on the Verrazano Bridge, March 18th, 2012. Credit: John Huntington

I’m not totally sure which type of fog we’ve had this week, but I think it’s mainly been advective fog.  The night of March 19-20 brought probably the most spectacular fog, and it arrived at 3:30 AM at Kennedy Airport, with a south wind.  But it arrived at 6:30 AM at La Guardia, with a northeast wind.  Radiation fog technically only occurs with light winds, so this was probably advection fog.  But they can also be a mix of these two types, where a marine air mass slowly moves in late in the day, and then the nighttime radiative cooling allows condensation.

But it’s nice to not be sure, because fog is supposed to be mysterious.

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Where are the Currents Weakest Around Manhattan?

Posted on March 5, 2012 by

A law firm recently contacted our oceanography research group with a request for research on whether or not the Marine garbage Transfer Station (MTS) proposed for 91st Street in Manhattan would cause navigational problems.  If we were willing to do some research into the question, they would be ready to have a “preliminary discussion about the cost and scope of our work”.  So, I plotted up a map of the typical average current around Manhattan, which reaffirmed for me that the site is actually very well-chosen for its safe navigational conditions.

Manhattan's average tidal currents

Map of the average tide-driven water speed in the vicinity of Manhattan, New York City, with longitude and latitude axes. The arrow shows the site of the proposed MTS, the location with the weakest currents. 1.0 m/s is equal to 2.2 mph. Estimates are based on the NYHOPS computer model.

A little background:  New York City is planning to build the MTS so that they can reduce emissions from garbage trucks and long-haul trucks, as well as to stop trucking our garbage through mid-town to neighborhoods in Newark and Jersey City.  This question of navigational safety is another front being opened in the Upper East Side community efforts to stop the MTS.  They have also claimed that we should stop the MTS because it will be bad for the environment, which I repudiated in a recent Op-Ed.

Representative Carolyn Maloney commented on the navigation issue in a July 2011 press release announcing that the ACE would solicit public comments on the MTS plan.  She said:

“The dock that the City is proposing to construct for this ill-conceived site for a garbage transfer station would pose a threat to the delicate marine habitat of the environmentally sensitive East River ecosystem and cause potential disruptions to maritime traffic in the aptly named Hell’s Gate section of the East River, an area of that busy waterway that is notoriously difficult to navigate[.]“

In 2008 testimony to the ACE regarding the MTS, State Sen. Liz Krueger said:

“The proposed MTS site would require a larger facility than the one that previously existed.  The new facility would be built out into the Hell’s Gate (sic) section of the East River.  The Hell’s Gate section of the East River is already difficult for ships to navigate and an expanded MTS would at the very least make the passage even more difficult to navigate and could increase the possibility of a serious accident.  For such an economically vital waterway we cannot allow this scenario to become a reality.”

This site isn’t really in what’s typically perceived by mariners to be Hell Gate (see below), so much as it is in a calm-water embayment off to the side (it should be given a name — how about “Barrio Bay”).  Ship traffic mostly follows East River out to Long Island Sound, so doesn’t go behind the small island (Mill Rock) into this embayment, so there is no obvious reason why the new expanded MTS would cause navigational danger or problems of any sort.  Historically, at least prior to about ~1915, there actually were many piers in Barrio Bay, and these were eventually filled in and covered by the highway (check out the “greatest grid” exhibit at the Museum of City of New York).

So, to me, this is just another one of many flailing efforts to stop the MTS with any means possible (and with high-priced law firms).  Yes, one must respect the reasonable concerns of residents that the trucks could worsen safety or air quality locally in Yorkville.  However, nothing presented so far has convinced me, or the City Council, or the State Department of Environmental Quality (Impact Review PDF), that these changes will be anything more than incremental — currently, a highway runs right past here, and many large trucks already speed down avenues in this area (York and First Ave).  I live in the neighborhood and fully support their building the MTS.

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Blowing out the Ocean’s Waters

Posted on February 28, 2012 by
A fellow blogger over at Spoonbeams read my post on king tides and beachcoming  and asked what caused this Sunday’s extreme low tide in the Hudson way up near Germantown, which was baring previously unseen underwater obstacles.

Photo credit: Spoonbeam (Do you have any pictures of this past weekend's low sea levels? If so, pass them on!)

Here’s a plot showing how the sea level near there, at Norrie Point, varied over the past week, demonstrating how low the tides fell.  This was observed all over the entire region’s tidal waterways and beaches.

Time history of water elevation in feet: tide predictions (blue), NYHOPS model predictions (magenta) and observations (red dots) at Norrie Point along the Hudson (near Poughkeepsie). Zero elevation is mean-lower-low-water (MLLW), the typical daily low tide level. Not doing bad, NYHOPS!

It was actually driven by strong winds blowing from west to east — it pushed New Jersey coastal ocean waters offshore and can have an effect similar to the height of the tide, basically a reverse storm surge, a “blowout”.  Here’s some wind data — get my point?

Wind observations at JFK Airport, from the Urban Ocean Observatory (which is the parent site of SSWS).

Winds were blowing 22-30 knots (25-35 mph) from the west (arrows toward the right) on February 25th for about a day straight.  That’ll do it … I looked at 3-month view of data in SSWS for a few winters and you can see that this is about the lowest water level that is ever seen, as she surmised.  It occurs typically 1-2 times per winter.  It’s impressive that Spoonbeams noticed – it’s nice to know people with their eyes on the water who notice these things!

For future reference, instead of tide-tables or other tide prediction websites, people in our area should check http://stevens.edu/SSWS for tide predictions that incorporate this effect, as well as rain-driven water level changes that can be large in the Hudson.

Interestingly Earth’s rotation was also likely at play, causing Long Island coastal waters to also be deflected toward the right if the wind blows over a day or longer, which it did. That’s the Coriolis effect, and would let the west winds blow the water toward the southeast, also offshore.

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“Winter” 2011-2012: Hitting 50+ degrees Every Week

Posted on February 10, 2012 by

It keeps striking me how we seem to hit 50+ degree temperatures every week this winter, so I checked it out.  Here’s a plot showing hourly temperature data at Central Park and La Guardia.  Not only have we hit 50+ every single week all winter, there’s also an interesting periodicity to the data.

Air temperatures from December 1st, 2011, through February 10th, 2012, measured at Central Park (red) and La Guardia (blue). Also shown are horizontal lines marking the 50-degree and 32-degree mark (freezing). Data from NYHOPS, http://stevens.edu/NYHOPS .

The periodicity is caused by weak weather systems pushing through the US northeast, presumably riding on periodic north-to-south waves of the jetstream.  These systems bring cooler air but but the colder arctic airmasses have been trapped up north this year, unlike the winter of 2010-2011.

Also, it hasn’t dropped below 30 degrees in three weeks, though that’s changing this weekend.  Obviously the ground can’t freeze when it barely gets down to 32 at night, so it’s no surprise that we have shoots sprouting in the core of “winter”.  Many weeks have even hit 60+ degrees.

The latest forecast finally suggests we’ll have a full week or more without hitting 50 degrees F, though there’s a chance, with forecasts highs of about 47-48 by the end of the week.

[update 2/17/2012 - we hit 50+ today too, as I just noticed LGA was 50F at 3pm. Not sure about Central Park... and if you look back a year, the last time we didn't hit 50+ in a given calendar week was early February 2011.  So that's over a year with a 50+ degree day in every week in NYC.  Tomorrow it's forecast to be even nicer - get out and play!]

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