Friday, October 26, 2012
Storm Forecasting, The xkcd Version
xkcd is one of the most interesting commentaries I know on science, math, life, the universe, and everything... Today, they offer a highly amusing look back at the late 2005 hurricane season. If you haven't seen it, check it out at http://xkcd.com/1126/. And, as always, be sure to check out the mouseover.
Wednesday, October 24, 2012
Models and Forecasts: Sandy Edition
A few days ago, I blogged about the impossibility of predicting chaotic systems. One characteristics of chaotic systems is that the behavior of those systems over time can be said to be sensitively dependent on initial conditions. That means that small, seemingly insignificant differences in the inputs to the system may result in major differences in the behaviors of the system over time. The current forecast models for hurricane Sandy are a great example of this.
Sandy originated in the western Gulf of Mexico and is currently crossing over Jamaica, moving essentially due north toward Haiti and then the Bahamas. For the short-term forecast, nearly every forecast agrees, however, beginning Monday morning, there is a remarkable divergence in the forecast paths. Below are the model tracks from the National Weather Service Environmental Modeling Center at the National Center for Environmental Prediction.
There is a remarkable divergence of paths on this map, with a spread of nearly 120 degrees in the direction of motion of the storm, leading to predictions ranging from a landfall on the Delmarva Peninsula through landfalls all the way up the rest of the Northeast coast, to models showing Sandy turning harmlessly out toward the central Atlantic Ocean. One of the most widely respected models, the GFS model, shows Sandy looping east and then back west to come ashore in southern Maine, cross the White Mountains and dissipate over the Adirondack Mountains of northern New York. In addition to track uncertainty, there is considerable variation in the forecast central pressure, which has implication for winds, surge, and rainfall and therefore for potential hazards. MyFoxHurricane has some nice barometric pressure map visualizations of the European and GFS models.
Here is what the National Hurricane Center is saying about the long-range potential for Sandy:
Sandy originated in the western Gulf of Mexico and is currently crossing over Jamaica, moving essentially due north toward Haiti and then the Bahamas. For the short-term forecast, nearly every forecast agrees, however, beginning Monday morning, there is a remarkable divergence in the forecast paths. Below are the model tracks from the National Weather Service Environmental Modeling Center at the National Center for Environmental Prediction.
There is a remarkable divergence of paths on this map, with a spread of nearly 120 degrees in the direction of motion of the storm, leading to predictions ranging from a landfall on the Delmarva Peninsula through landfalls all the way up the rest of the Northeast coast, to models showing Sandy turning harmlessly out toward the central Atlantic Ocean. One of the most widely respected models, the GFS model, shows Sandy looping east and then back west to come ashore in southern Maine, cross the White Mountains and dissipate over the Adirondack Mountains of northern New York. In addition to track uncertainty, there is considerable variation in the forecast central pressure, which has implication for winds, surge, and rainfall and therefore for potential hazards. MyFoxHurricane has some nice barometric pressure map visualizations of the European and GFS models.Here is what the National Hurricane Center is saying about the long-range potential for Sandy:
THE INITIAL MOTION IS 015/11. THE SHORT-TERM TRACK FORECAST REASONING REMAINS UNCHANGED FOR THE FIRST COUPLE OF DAYS...AS SANDY SHOULD MOVE GENERALLY NORTHWARD INTO A BREAK IN THE SUBTROPICAL RIDGE OVER THE BAHAMAS AS IT INTERACTS WITH AN UPPER-LEVEL LOW TO ITS WEST. LATE IN THE PERIOD...THERE REMAINS CONSIDERABLE SPREAD IN THE GUIDANCE DUE TO DIFFERENCES IN HOW MUCH SANDY INTERACTS WITH ANOTHER TROUGH MOVING INTO THE NORTHEASTERN UNITED STATES. THE ECMWF HAS BEEN CONSISTENT IN SHOWING MORE INTERACTION AND A TRACK FARTHER WEST...WHILE THE GFS SHOWS SANDY TURNING EAST AND MISSING THE TROUGH. OVERALL MORE OF THE GUIDANCE HAS BEEN TRENDING TOWARD SHOWING MORE INTERACTION WITH THE EASTERN U.S. TROUGH LATE IN THE PERIOD. GIVEN THIS TREND...THE NHC FORECAST HAS BEEN ADJUSTED TO THE LEFT AT DAYS 4 AND 5...AND LIES ROUGHLY BETWEEN THE ECMWF AND THE TVCA MULTI-MODEL CONSENSUS. NEEDLESS TO SAY...THE TRACK FORECAST UNCERTAINTY REMAINS HIGH AT THE END OF THE PERIOD.
In other words, "We don't know, either." Early next week, the storm will have moved far enough north that the uncertainty should have diminished somewhat. It could be an interesting Halloween, stay tuned.
Monday, October 22, 2012
Dark Day for Science
Today is a very bad day for seismology and for all of science. If you have not already heard, 6 Italian seismologists, including the Director of the National Earthquake Center, and the past-president of the National Institute of geophysics, were convicted of manslaughter, along with a former governmental official. The charges resulted from the belief that scientists were too reassuring in the aftermath of a couple of small tremors that turned out to be foreshocks of the deadly L'Aquila quake in 2009.
Many earth system behaviors are inherently chaotic, earthquakes included. These behaviors are, as a result, inherently unpredictable. There are small earthquakes more or less continuously in the Apennines, the modern front line of the ongoing collision between the African and Eurasian plates. The vast majority of these small quakes will be the harbingers of... nothing at all. When to issue a warning to the public is one of the most fundamental problems of earthquake hazards. Raise the alert level every time there is a minor tremor and pretty soon, people begin to ignore the alerts. Fail to issue an alert until you are sure there will be a quake and you might as well not have a warning system because you will never be sure. There is no research that says just how to walk this tightrope between too much warning and too little warning. This is the trap the Italian seismologists have found themselves in. The authorities, blessed with hindsight, have essentially said, "See, you had warning signs, you should have told every one."
A magnitude 5.5 earthquake happened just yesterday on the San Andreas fault in central California. Should Californians have been warned to evacuate because this is potentially a foreshock? Most of us would agree that this would be foolhardy. M 5 quakes happen regularly along the San Andreas and related fault systems in California without presaging anything. Yet one day, one of those shocks might very well be the foreshock of a much larger quake, one that wreaks devastation across a wide area. What is the responsible thing to do? Who should decide how much warning is appropriate?
Those convicted in Italy are among the top seismologists in the world. Even if these convictions are overturned, they will definitely inhibit important research in one of the most seismically active parts of the world. At this point the Italians have essentially guaranteed that they will have less information and less potential warning of future quakes, because no sane geophysicist would choose to work there. This ruling will undoubtedly also have a chilling effect on volcanological research and Italy is also the home of a number of dangerously active volcanoes. How sad for all involved, but especially how sad for the Italian people who, in the end, need more information, not less, in order to live as safely as they can in their active homeland.
Many earth system behaviors are inherently chaotic, earthquakes included. These behaviors are, as a result, inherently unpredictable. There are small earthquakes more or less continuously in the Apennines, the modern front line of the ongoing collision between the African and Eurasian plates. The vast majority of these small quakes will be the harbingers of... nothing at all. When to issue a warning to the public is one of the most fundamental problems of earthquake hazards. Raise the alert level every time there is a minor tremor and pretty soon, people begin to ignore the alerts. Fail to issue an alert until you are sure there will be a quake and you might as well not have a warning system because you will never be sure. There is no research that says just how to walk this tightrope between too much warning and too little warning. This is the trap the Italian seismologists have found themselves in. The authorities, blessed with hindsight, have essentially said, "See, you had warning signs, you should have told every one."
A magnitude 5.5 earthquake happened just yesterday on the San Andreas fault in central California. Should Californians have been warned to evacuate because this is potentially a foreshock? Most of us would agree that this would be foolhardy. M 5 quakes happen regularly along the San Andreas and related fault systems in California without presaging anything. Yet one day, one of those shocks might very well be the foreshock of a much larger quake, one that wreaks devastation across a wide area. What is the responsible thing to do? Who should decide how much warning is appropriate?
Those convicted in Italy are among the top seismologists in the world. Even if these convictions are overturned, they will definitely inhibit important research in one of the most seismically active parts of the world. At this point the Italians have essentially guaranteed that they will have less information and less potential warning of future quakes, because no sane geophysicist would choose to work there. This ruling will undoubtedly also have a chilling effect on volcanological research and Italy is also the home of a number of dangerously active volcanoes. How sad for all involved, but especially how sad for the Italian people who, in the end, need more information, not less, in order to live as safely as they can in their active homeland.
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