Slush is life

Last night into this morning we had a little winter storm pass through. The precipitation forecast was tricky. Here in New York City we were, as we often are in winter, very close to the rain-snow line. In the end, we got maybe a couple inches of snow, plus some rain. Walking around today was messy business, with big sloppy puddles and lots of slush. Here’s a photo from my window down onto the street:


Many people don’t like this kind of weather. Many people would rather it were a little colder, so that we’d have nothing but clean white snow. (Of course in NYC it is only ever clean and white for a very short while, but never mind.) I get that. But actually, I like the slush.

Before saying anything else I have to admit that I don’t particularly like cold weather, period. I have mediocre circulation in my hands and feet. I get cold. I can enjoy some winter sports, but put me on the nicest ski slope around and then offer me the chance to be instantly transported somewhere warm and I’ll never say no. I grew up here and have lived here most of my life, but apparently I’m still not adjusted to the climate. I still find every winter a little harsh. And I know, a New York City winter is nothing compared to a lot of places.

Maybe that’s why I ended up working on tropical meteorology – thinking warm thoughts is part of my job. (And yes, occasionally I get to go to a conference or a field campaign in a tropical place when it’s winter here.)

So my appreciation for slush is partly about realizing that it could be even colder than it is. But it’s a little more than that. Slush tells us, in the most visceral way possible as it soaks through our shoes, how special a planet we live on. We can have slush only when the temperature is right near the freezing point of water, at which water can coexist in all three of its phases: solid, liquid, vapor.

A planet which has liquid water can support life. As scientists try to figure out if there’s life on Mars, looking for evidence of liquid water there seems to be most of the ballgame. And it’s only in a pretty narrow temperature range – compared to the range of possible planetary climates – that liquid water can exist; too cold and it all freezes (Mars, at least now), too warm and it all evaporates (Venus).

While we may need liquid water to support life, we don’t need ice. But the ice helps us appreciate the liquid. It shows us just how close we are to the edge. When it’s slushy, we can feel the transition between a frozen climate that is fundamentally inhospitable to life (sorry, Canadians, Midwesterners, Russians etc.) and one that isn’t. When I’ve been on a winter car trip to somewhere really cold and snowy, and I’m returning back to somewhere warmer, I always feel something magical at that slushy boundary in between.

On some days, we live right on that boundary. This was one of those days, in a particularly complete and interesting way. Let’s look at some data.

The picture below shows the local sounding — set of upper air measurements taken by weather balloon, plotted vs. height — from our National Weather Service station in Upton, New York (Long Island) from 7 AM local time this morning.


This is a “skew-T log-p diagram”. If you don’t know how to read one of these, I’m going to teach you what you need to know for today. It shows all the variables (temperature, humidity, wind) the balloon measured as functions of height, which is on the vertical axis just as you think it would be (see the white numbers just to the right of the vertical axis on the left, which give the height in meters; the blue letters to the left give the pressure, in hectoPascals). The higher you are on the plot, the higher the balloon was.

The two white lines are the temperature and dew point temperature. If they are on top of each other — as they are below about 5000 m (~3 miles up) — that means the atmosphere is saturated, relative humidity = 100%. Not a big surprise, as precipitation was falling when this balloon was flying.

More interesting is the temperature itself. The reason this is called a “skew-T” plot is that the axes are not at right angles — temperature is not on the horizontal axis, but rather on a tilted axis. The blue lines angling up to the right are lines of constant temperature, or isotherms. You can tell the temperature (in Celsius) of each one by the blue number where it hits the bottom. So a vertical line, for example, would mean the balloon is getting colder as it goes up, as it would be crossing blue lines with lower temperatures. In most soundings, from nearly everywhere on earth, the atmosphere does get colder with altitude, with only a few exceptions. (The word “inversion” is used to describe a layer where temperature increases with height; the word itself tells you right away that it’s an exception to a rule.)

Our balloon’s temperature trace, though, tracks right along one of the blue lines in a layer between about 1000 and 2500 m (or between 900 and 750 hPa, if you like). That means that in that layer, temperature was not decreasing with altitude, but staying the same – it was an isothermal layer. And not at any old temperature – the blue line is the one with a zero below it where it hits the bottom of the plot. That means that a roughly mile-thick slab of atmosphere was almost exactly at freezing.

Why would that happen? Most likely the layer started out somewhere in the vicinity of zero C, but with more variation — part of the layer was colder, part warmer. Then precipitation (ice, liquid, or more likely some combination) started falling through it, and freezing and melting. Freezing liquid warms the air by the latent heat of fusion, while melting ice cools it for the same reason. So layers colder than zero would be warmed by freezing rain, while warmer layers would be cooled by melting snow or sleet. This would bring the temperature everywhere towards zero.

Just above the surface, the sounding shows an inversion layer, where temperature increases with height, so any frozen precip had a little more chance to melt before hitting the surface – which was, itself, exactly at zero C, about to become the perfect environment for slush as sunrise warmed it a bit above that temperature.

In other words, not just the ground, but the atmosphere itself was slushy. Organically, perfectly so.

And tonight, the temperature will drop, and we’ll have black ice. I don’t think I’ll be able to write such a happy meditation on that.

Climate Services: Two conferences on two continents

I spent this past week in Darmstadt, Germany, for the Climate Symposium. This was a conference organized by EUMETSAT (one of the European space agencies) and the World Climate Research Program.

The conference had a couple of goals. Perhaps most prominent was to “ascertain critical objectives to be achieved with satellite-based climate information, and identify gaps in the current space-based component of the climate observing system” – in other words, help EUMETSAT decide what new satellite instruments to build and launch in the coming years. The idea here was to present the current state and future needs of climate science in order to determine how new satellite observations could help. The climate science was presented through the lens of WCRP’s new Grand Challenges. (I am involved directly in one of these, on Clouds, Circulation and Climate Sensitivity, and interacting with the leaders of another, on Understanding and Predicting Weather and Climate Extremes.)

Climate science justifies its funding largely on the basis of its benefit (real or potential) to society, and that justification was particularly explicit at this conference. A lot of the program was devoted to “Climate Services”. This term refers to entities and people whose jobs lie in between the physical science of climate and “users” of climate information, also known as “stakeholders”. Climate Services involves translating the information that climate science can provide into terms that will be most useful for specific human purposes. (In the US, NOAA tried a few years ago – at the instruction of President Obama – to create a National Climate Service, with a status analogous to the National Weather Service. Congress, much of which hates even the word “climate”, killed it.) In practice, Climate Services is about taking the time to learn what specific users’ needs are, teaching those users what climate information current science can and can’t provide, and packaging the information to make it easier for them to digest.

Most of what I know about Climate Services comes from the International Research Institute for Climate and Society (IRI) at Columbia, which has been providing climate services since well before I (or most other people) ever heard the term. I was initially hired at Columbia through the IRI, which came into being a couple of years before I arrived here in January 2000. The IRI, in turn, exists because of the work of Mark Cane.

In the 1980s, Mark and his then student Steve Zebiak (later to become a founding member, and then director of IRI) developed the first numerical model that was capable of predicting the El Niño/Southern Oscillation (ENSO) phenomenon. They demonstrated this by making a successful prediction of the 1986/87 event.

While ENSO occurs in the equatorial Pacific, it has influences on climate and weather across much of the earth. An El Niño, for example, typically causes drought in Australia, Indonesia, southern Africa, and northeast Brazil, wet weather in southern California and unusually clear weather in the Pacific Northwest, and fewer hurricanes in the Atlantic, among other changes. Cane and Zebiak realized that the forecast capability they had developed had the potential to make a positive difference to the lives of a substantial fraction of the planet’s population. By knowing something about how the upcoming season or two would be likely to differ from the usual, people and governments could plan ahead across many sectors of activity: agriculture, water, health.

The IRI was created to realize that potential, and has been working with countries around the world for over 15 years to that end. While the notion of Climate Services now is as much about long-term anthropogenic climate change as it is about interannual variability (a la ENSO), ENSO and the IRI were at the start of it as much as anything, and are still a critically important component.

Tomorrow – Monday October 20 – we will start The Tropics Rule, a Symposium Honoring Mark Cane’s Contribution to Climate Science. This will be a two-day event on the occasion of Mark’s 70th birthday, featuring a long list of distinguished scientists presenting new research and historical reflections on Mark’s long career of truly amazing scientific achievements. It will take place in Monell Auditorium, the physical home of the IRI, on the Lamont Campus.

So in summary, I got on a plane to fly to Germany for a conference where I heard about the present and future of Climate Services. Then I got back on a plane to fly home to attend another conference at my own institution, in honor of the scientist who, it is not a great exaggeration to say, invented the idea.

The size of it

What a day yesterday.

adam march photo

The organizers are saying 400,000 people. That is an astonishing number, but it did seem an endless throng. It didn’t move at all for the first couple of hours; we were wondering what was going on. Afterwards, I read somewhere that people filled the entire 4-mile length of the route, so some had to finish before others could start.

A friend who didn’t march said right after that she had thought she wouldn’t fit in because it was all “climate scientists and ex-hippies”. I said that wasn’t what I had seen. Ok, there were a few of both for sure, but you don’t get to 400K with just those factions. Most of the crowd looked pretty civilian to me.

I read a quote from someone today (can’t remember who now, nor find it) to the effect that this was the biggest political demonstration about anything in the USA in a very long time. True, no doubt; what came closest? Can’t have been anything more recent than the last Iraq war, if that. Certainly, I can remember no show of feet like this in my adult lifetime on any “environmental issue”, let alone climate.

The mass of the thing was profoundly heartening, because ignorance and denial still loom so large on this issue in this country, and nothing else seems able make a dent in the hard core of it. We know that facts from the mouths of scientists (or anyone) are not going to cut any ice with those who get their information from Fox News or the Wall Street Journal op-ed page – which unfortunately includes about half of Congress – because if they could, they would have by now. The only thing that will matter is sheer force of numbers. We showed that we had that.

On a much smaller scale, I carried an intentionally nerdy and obscure sign (thanks for the idea Michela) to create teachable moments. Indeed maybe half a dozen people asked me what it meant, allowing me to explain the mechanics of carbon emissions scenarios and IPCC assessments to interested citizens. Here’s a photo of me explaining it to one of New York’s finest:


We ended the day exhausted but happy. It was a privilege and a great thrill to have been able to march. We made the kids come, figuring that someday they’d appreciate  having been there. In the event, they seemed to appreciate it right then. There’s hope yet.

New York’s rainiest day

On August 12 and 13, a new record was set for the most rainfall in a 24-hour period at any location in New York State. 13.57 inches of rain fell in 24 hours at Islip MacArthur Airport in Long Island. (That’s about 345 mm, for anyone outside the US.) This breaks by about 2 inches the previous NY State record, set just three years earlier, in August 27-28 during Hurricane Irene in Tannersville, NY.

The new record was officially verified by the National Weather Service just this past Wednesday, in this Public Weather Statement put out by our local office, in Upton, NY (which happens also to be on Long Island, not far from where the record-breaking rainfall fell).

The same office has also put up a nice web page on the details of the event, featuring lots of maps and charts for weather nerds. Their summary of the meteorology reads as follows:

“An anomalously deep upper level trough was moving into the northeast the morning of August 13th, transporting deep moisture over Long Island. At the surface, a parent low pressure system was moving across southeast Canada, with secondary low development just south of New York City. Heavy precipitation focused along and just north of the warm front associated with the secondary low pressure system. The mean storm motion was parallel to the orientation of the warm front and was significant in helping maintain heavy rain over Islip, NY for several hours.”

You can watch the radar animation on the web page and see what was going on. Not only was the “mean storm motion … parallel to the orientation of the front”, but the shape of the storm, as evident in the radar reflectivity (which is a very close indication of where rain was falling and how hard), was roughly linear and oriented along the front. The storm was like a long thin snake moving almost exactly straight ahead, with no component of the motion perpendicular to itself. Any point below it stayed below it as it moved.

This is often how the very highest rainfall totals are achieved at single locations: not just a hard rain, but a hard rain staying in the same place for a good while. This means either a storm that sits still – as in the record-breaking floods in Boulder, Colorado last September – or one that is so large that it takes a long time to entirely pass over, even though it’s moving. Tropical cyclones in particular can rack up huge accumulations, as they are sometimes all of the above: big, dumping prodigiously, and slow. Irene in 2011, our previous record-breaker, was an example of this.

Or, a storm like this Islip system – long in one direction and moving in exactly that direction – can do it.

Mountains help. A strong wind carrying moist air into the side of a mountain – where it will be forced uphill, cooling as the pressure drops and condensing the vapor – is a key ingredient in a lot of records, including the previous one set in Irene in Tannersville. That town is in the Catskills, right up against Hunter Mountain, a popular ski resort with a summit 3200 feet high (a respectably big mountain in this part of the world). In this new Islip record, though, no mountains were involved. Long Island is quite flat.

While the new record is for the 24-hour rain total, the time series graph of rain rate and accumulation on the NWS page shows that most of it – about 10 inches – fell in just 2 hours. This rapid dump made for some very severe flash flooding. The page shows many photos of cars submerged and washed off the road, as described in the New York Times story the day after.

Yes, this is exactly the kind of thing we expect to happen more in a warming climate. A warmer atmosphere can contain more water vapor, and that gain can be realized in extreme precipitation events (even though global average rainfall will increase more slowly than water vapor does, because it is constrained by global energy balances which don’t track water vapor and can’t change as easily). So records like the one that just broke are going to break more frequently than they used to, and already are.

I’m sorry I wasn’t in Islip to see 13.57 inches of rain – or even in the city, which got a couple inches; I was out of town altogether. (I have seen a daily rainfall in that ballpark just once, in Darwin, Australia, where I had gone specifically to see it, which is a story I will write about another day.)  But just so we aren’t too awfully impressed, the global record for 24 hour rainfall is 1.825 meters, or 71.8 inches. That’s more than 5 times our new New York State record. This record was set on La Reunion, an island in the south Indian ocean – in a tropical cyclone, on the side of a mountain.

Emotional outburst due to lack of atmospheric one

I am currently frustrated, as it seems I often am, by the current display on our local weather radar. It has been unseasonably hot and humid here in New York City for about a week. Now, the climax that we residents of the humid eastern US habitually look forward to after waiting through such steamy periods is in sight. A solid line of thunderstorms (some of them severe) is stretching across Jersey and just south of the city. To get there it had to pass through NYC, but as it did it developed a gap, which we were in. We got jack diddly, at least here in northern Manhattan.

The cold front will pass through this evening regardless, and the heat will break – presumably for good, as we head into fall. And there’s a chance of more thunderstorms later. But still, I feel cheated.






Back to school heat in NYC

In New York City, today’s temperature was forecast to be hotter than any yet this summer (though it hasn’t got there yet, there is still time). This is a little unusual since it is already September. I got an inquiry from a reporter today, containing the following questions:

“This summer’s seemingly mild weather was actually warmer than average.  Has climate change caused us to have a new normal?  And while  a 92 degree day on September 2nd is not unheard of, is there a larger case of climate change going on?”

Here is the answer I sent, edited and expanded a bit for this post:

Yes, there is certainly a new normal as far as temperature is concerned. It was a cool summer compared to recent decades, but those have been warm compared to the longer-term historical record, due in large part to human-induced global warming. Thus this summer was still warm compared to the long-term average (which means, since the mid-19th

It’s worth also mentioning that the coolness this summer was limited to our half of the country; the west was extremely hot even compared to recent years, with bad forest fires in the Pacific NW, the drought in California etc.

One can’t assign the hot weather today to global warming though – at least not for the most part. It’s never a good idea to attribute a single day of weather to long-term trends, because the natural day-to-day (and even month-to-month or year-to-year) fluctuations are large. On the other hand, it is safe to say that global warming will mean more 92-degree days after Labor Day in years to come, compared to the past.

Because of natural variability, some summers are a little warmer, some are a little cooler. But global warming keeps continuously pushing them all warmer. So by sometime in mid-century, the coolest summer in any given decade is still very likely to be hotter than even the hottest summer that anyone alive now (or their parents, grandparents etc.) has yet experienced.

Climate Central did a nice piece recently which includes an online form allowing you to see how this summer stacked up against the historical record for many US cities. Here is the image I got by selecting San Francisco, where this summer broke the all-time record according to the graph – I’m not sure why the title is just “Near Record Warmth”. The bars are the different years ranked by their average temperature.