Courtesy tree & j hensdill
Well, summer is officially over. The Weather Service switched to fall on September 1. The rest of the country likes to wait until the day after Labor Day. (The folks who hold out for the equinox are delusional, and best ignored.) So, it's time to update our on-going study comparing summer temperatures to winter temperatures.
For those of you just joining us, last February Buzz blogger extraordinaire Candace noted that the winter of 2008-2009 had been unusually warm. She asked if this meant the following summer would also be warm.
Well, I went to the website of the National Space Science and Technology Center, which very conveniently records the temperature for each month going back to December 1978. I crunched the numbers and found that, yes, there was a connection. Though summer temps fluctuate year-to-year, about half of that fluctuation can be tied to changes in winter temps.
Armed with this information, we anxiously awaited the temperature record from summer 2009. The results are in, and...
...well, this was obviously part of the other half. The winter of 2008-2009 was the 4th warmest in the recording period. The summer of 2009, however, was dead smack in the middle -- 16th out of 31. So disparate were these results that they actually brought down the average for the entire study period: the impact of winter temps on summer temps is now down to just 45%.
Still, for something as complicated as weather, that's a huge impact. So, while the winter-summer connection can't predict what will happen in any given year, over the long run it does still hold true.
Tune in next year for another exciting update!
Andrew Revkin, the blogger, is asking readers to send in photos or video (via Flickr or YouTube) of "...parts of your environs that you treasure, that are imperiled, or that otherwise matter." Doesn't say they have to be of New York, and Minnesotans know a thing or two about beautiful places and water in winter or both.
Last week, Candace asked whether there’s a connection between winter temperatures and summer temperatures. She noted that the winter of 2007-08 was pretty cold by recent standards, and the following summer was cool as well. Is there something going on here?
Liza searched the Web but couldn’t find anything definitive. I (after pooh-poohing the idea that this has been a warm winter – if you want to pay my heating bill, you’re welcome to it!) decided to crunch the numbers.
First, I went to this site. It records monthly average temperatures going back to December 1978.
Actually, it records temperature anomalies – whether the observed temperature in a given month is higher or lower than the average. They use the 20 years of 1979-1998 as their baseline. A reading of 1.00 means the temperature was 1 degree Centigrade (1.8 °F) warmer than expected. (One degree may not sound like much, until you realize it means 1 degree of every minute of every hour of every day. It quickly adds up to a lot of heat.) A reading of -1.00 means it was 1 degree cooler.
Using temperature anomalies is good for this exercise, as it removes the effects of global warming. Because global temperatures rose during the period under study, a “warm” winter in the late ‘70s might be considered only “average” today. In fact, that’s exactly what happened last winter. It was almost perfectly average by historical standards, but because recent winters have been so much warmer, it felt cold to us.
Getting back to Candace’s question: does a warm winter predict a warm summer? To answer this question, we have to calculate my all-time favorite statistical formula, the coefficient of correlation!
It sounds like a mouthful, but it’s a pretty easy concept to grasp. The coefficient of correlation measures how tightly two sets of numbers go together. For example, if you surveyed 100 people, and asked each one what year they were born, and how old they were, you would find that every single person born in 1990 was the exact same age. The first number (year of birth) and the second number (age) are linked together 100%.
OTOH, if you asked those people for the last digit in their telephone number, you would find no relationship whatsoever. A person born in 1990 is just as likely to have a phone number ending in 9 as ending in any other number, and the same goes for people born in every year.
Calculating the coefficient of correlation (or “coco,” as I affectionately call her), requires wading through a truly horrific battery of equations all to arrive at a number between 0 and 1. A coefficient of 1 means the two sets of numbers are perfectly synched together; a coefficient of 0 means there is no connection whatsoever.
So, I went back to the temperature data. First, I defined “winter” the same way the weather bureau does: December, January and February, the three coldest months of the year. (None of that solstice-equinox nonsense here!) I defined “summer” as the three warmest months: June, July and August, again following weather bureau standards. Using the Northern Hemisphere Land figures (sorry, they didn’t have anything Minnesota-specific), I came up with an average anomaly for every winter and every summer. I crammed the numbers into the formula, turned the crank, and came up with a coefficient of…
(drum roll, please)
OK, now what does that mean?
Well, in general, a score below 0.30 is considered inconclusive. It’s too close to zero—the “relationship” could just be random. A score between 0.30 and 0.50 is generally considered moderate—there’s a connection there, but it’s somewhat weak. A score over 0.50 is generally considered strong—there’s definitely something important going on there.
(This is especially true in highly complex systems, like weather, where a lot of different factors can affect your results. In a very simple system, you’d probably want a result much closer to 1.)
It all boils down to this: we can be more than 99% certain that, yes, there is a connection between a warm winter and a warm summer, or a cold winter and a cool summer. How much of a connection? For that, we need another figure, the coefficient of determination.
This one is much easier. Just square the coefficient of correlation. 0.71 squared yields 0.5041. That means 50% of the variability in summer temperatures is determined by the winter temperatures.
And “variability” is the key. Like I said, weather is an extremely complex system. Lots of things can affect the temperature for a day, a week, even a season. The fact that this winter is warmer than last winter does not guarantee that this coming summer will be warmer than last summer. (For example, the winter of 2003-04 was one of the warmest on record, but the following summer was one of the coolest in the study period.)
What this number does mean is, that of all the factors that will affect next summer’s temperatures, half of them seem to be connected to winter temperatures. And this winter was warmer than last winter.
Just for fun, I also ran the calculations the other way, to see if a warm summer predicts a warm winter. The coefficient of correlation was 0.54, and the coefficient of determination was 0.29. So, again, there is a connection, but it seems to b a good deal weaker.
A word of caution: one thing statisticians like to say is “correlation is not causation.” Partly because it’s fun to say, but mostly because it’s true. Just because two things are correlated does not mean one causes the other. We have not proven that warm winters cause warm summers. It could be that winter temps and summer temps are both boosted by some other factor – El Nino, perhaps. All we can say is that there is some sort of connection going on, and that it probably wouldn’t hurt to lay in some tanning cream now.
Courtesy jef safiHere in Minnesota, a whole lotta snow in the winter can lead to a whole lotta messy flooding in the spring. That's probably why the Federal Weather Folk--aka the National Oceanic and Atmospheric Administration or NOAA--base their National Operational Hydrological Remote Sensing Center up here in Chanhassen.
By looking at the snow conditions across the north, the NOHRSC can predict possible flooding when the seasons begin to change. The Star Tribune has an interesting article on how NOHRSC uses low flying planes and other forms of remote sensing to keep track of snow on the ground. Did you know that you can be a snow physicist?
So what can we expect this spring? Flooding is on the menu, and the folks at NOHRSC are flying around the north of the country to figure out where.
Courtesy vgm8383Its really cold where I live these days. It was 23 below zero Celsius (this is a science blog) this morning when I woke up. Bitter cold. An interesting phenomenon happens on roads when it gets this cold, a condition called black ice. It was in full effect this morning, with Twin City roads having over a dozen accidents and causing lengthy commute delays.
So, what is black ice (besides an AC/DC album)?
Black ice is a type of ice that is usually thin and forms without bubbles inside, making it harder to see. Because of its transparency, it usually takes on the color of whatever it is on, making it doubly hard to see and a hazard to drivers, bikers and walkers.
Black ice on roads is most common at night or in the early morning when temperatures are at their lowest, and before the sun has had a chance to warm the road surface. It can be mixed in with a wet road, and it can be hard to tell the difference between a road that is wet and a road that has black ice. Black ice can form more easily on bridges and overpasses as the very cold air can cool both the top and the bottom of the road at the same time, causing it to cool below freezing more quickly. Black ice can form from any source of moisture – light rain, meting and re-freezing snow or any other source of moisture on a road surface.
Here are some tips for driving on black ice. Drive safe my fellow Minnesotans – I’m going to be on the road with you this evening!
Courtesy Aaron SilversThis afternoon, in an announcement that surprised all, a rural Pennsylvanian groundhog emerged from a tree stump cage, and used magic to tell the world that it would be under the icy yolk of winter for at least six more weeks. Residents of the planet’s southern hemisphere were particularly disturbed.
Wisely deviating from the over relied upon scientific discipline of meteorology, experts have turned to the prognostications of the groundhog Phil, who uses centuries old magical techniques to reveal the secrets of immensely complex future weather patterns.
The determination was not without controversy, however. While the groundhog weather diviner West Indies Wilbur agreed with Phil – the most senior and important of extra-sensory rodents – several noted groundhogs took issue with the announcement. Wiarton Willy, Staten Island Chuck, Sir Walter Wally, Shubenacadie Sam, Malverne Mel, General Beauregard Lee, and Balzac Billy all argued the proclamation. However, as the National Climactic Data Center has stated groundhog accuracy to be around 39%, it makes sense that so many weather rodents would disagree with shrewd Phil.
This afternoon I saw a bald eagle circling over Irvine Park, just to the west of the museum. We're lucky: we see eagles a lot here in Minnesota and along the museum's stretch of the Mississippi River. Have you seen any eagles this winter? When and where?
It’s finally getting into real winter conditions here in Minnesota, but that still doesn’t mean it’s winter as normal.
Sunday’s snowfall led to three snowmobile crashes on lakes where drivers went through thin ice or open water. In one case, the snowmobile driver died. According to the press accounts, many snowmobile drivers like to “skip” their machines over open water. It got me wondering how this actually works.
It’s actually much like how a stone that is thrown at the right angle and speed skips across open water. Checking the web for snowmobile sites, I found out the specific details.
The snowmobile skip formula works this way: In order to skip, the snowmobile must be going at least 5 mph for every 150 lbs. of vehicle (or fraction thereof). For example, if a snowmobile and rider weighed 780 lbs., it would have to be going at least 30 mph to skip. The distance of water a snowmobile can cross is 2", plus 1/2" for every 5 mph over the minimum skip-speed. If the above-mentioned snowmobile was going 45 mph, it could cross 3 1/2" of water; at 75 mph, it could cross 6 1/2" of open water. There’s also friction, or drag, involved in this formula. A snowmobile decelerates 5 mph for every inch (or fraction) of water it "skips." The snowmobile above, crossing 6-1/2" inches of water at 75 mph, would be going only 40 mph when it got to the other side.
A snowmobile cannot change direction while "skipping" -- it can only go in a straight line. If a snowmobile doesn't make it across the open water, it sinks. It only takes one second for a snowmobile to sink to the bottom of a lake or river.
So, as they say on all the stunt shows, don’t try this at home….or on a lake near your home. Across the U.S. and Canada each winter about 50 people die from snowmobiles crashing and sinking into frigid waters.
Interestingly, a graduate from the University of Minnesota is developing a way to minimize the deaths of snowmobilers falling through the ice. John Weinel is now working with university students to come up with an automatic floatation device that could deploy from a snowmobile, much like an airbag in a car, when a snowmobile crashes into water. That work has already led to floatation equipment law enforcement officers can use at the scene a snowmobile water crash to help keep victims at the surface until better equipped rescuers can get to the scene.
Of course, the best thing to do if you're driving a snowmobile is to avoid driving it anywhere there is a chance to be open or thin ice. You and your snowmobile will be able to get around better and happier if you never go sinking into chilly water.