Warning System Issues

Transcription

1 Other Forecast / Warning Sys issues Volcanologists are developing a ranked warning system for volcanic eruptions, applied case-by-case at volcanoes acting up, and is more now-casting than forecasting. Fear of over-warning and warning fatigue; under-warning Tiered warnings with lead time/accuracy problems (issue a watch when not sure, a warning when sure, usually less lead time) Ambiguous warnings a problem (Mt Ste Helens ash-fall example) Pre-planning, preparedness, awareness programs crucial to warning success: target area and audience needs to be briefed what to expect from forecast and warning system click here to watch the progress of the forecasts, the warnings, and the actual track of hurricane Charlie. Some residents of Pot Charlotte, where the small storm hit hardest, well south of Tampa Bay that appears to be the target for almost 48 hrs before landfall, claim they were not warned. But the NHC simply points out that the area was in the forecast cone and in the formal hurricane warning for 24 hrs before landfall.. From the NHC s repot on Charley (my emphais): Although the official track forecasts for the landfall of Charley on the Florida west coast did, in general, have a left bias, the hurricane made landfall within the area covered by the hurricane watch and warning. One day prior to the Florida landfall, the 24-h track forecast error was 40 n mi, which is below the long-term average. Table 7 lists all of the watches and warnings issued for Charley. It can be seen that a hurricane watch was issued for the southwest coast of Florida, including the landfall location, just less than 35 h prior to landfall on that coast. A hurricane warning was issued for the same area just less than 23 h prior to landfall. No one near the landfall location should have been surprised by the arrival of this hurricane. Warning System Issues Target Audience: handicapped, language, class, culture. Confirmatory behavior (audience often wants a second source to confirm what they hear) Differential response to content, delivery, source (some audiences may distrust sources; maybe government sources) Previous experience of the hazard, and hazard awareness (previous experience may heighten or lessen response; past near-misses may lessen response) You can get a sense of the problems of a warning system here: Play the Severe Weather Warning Game; Hot Seat The scoring system for Hot Seat tells you a bit about the challenge: issuing warning costs something, and getting them wrong costs more, lead time is good but don t leave old warnings up too long, etc. Scoring: Severe Thunderstorm Warning (SVR) Tornado Warning (TOR) Issuing a SVR costs 2000 points plus 50 points for every minute the warning is in effect Issuing a TOR costs 4000 points plus 50 points for every minute the warning is in effect A SVR verified by hail damage earns 10,000 points plus 100 points per minute of leadtime A TOR verified by hail damage earns 10,000 points plus 100 points per minute of leadtime A SVR verified by wind damage earns 10,000 points plus 100 points per minute of leadtime A TOR verified by wind damage earns 10,000 points plus 100 points per minute of leadtime A SVR verified by a tornado earns 2,000 points plus 50 points per minute of leadtime A TOR verified by a tornado earns 20,000 points plus 200 points per minute of leadtime Wind damage or hail where no warning was issued is a miss and costs 10,000 points A tornado where no warning was issued is a miss and costs 20,000 points These tips offer insights into the challenge (my bolds): When the scenario begins, there will be no warnings in effect. Get all your warnings out as quickly as possible BEFORE worrying about the path of the storms. Once you have the initial warnings issued and reports start coming in, place warnings out in front of the storms for lead time bonus points. Because warnings do cost you 50 points per minute, be sure to cancel them after the storm has passed. The key word here is "AFTER." Make sure that you're looking at the most recent radar scan when you are about to issue a warning. You can overlap warnings. The earliest warning you placed will be the one that verifies, thus giving you the largest possible leadtime bonus. The NWS frowns upon false alarms, but when you're issuing warnings that only cover several square miles, a few false alarms are inevitable. Remember that a missed event will cost you way more than a couple false alarms. After the scenario is over, you can cursor through the entire event to see which cells actually led to damage reports. Just because there were no damage reports for a certain cell doesn't mean there was no damage. It could mean that no one lives in that part of the state. Chap. 6: Earthquakes (Intro to tectonic hazards) -Earthquakes & Tsunamis are causes of largest single-event fatalities in the world Tangshan, China eq may have killed K. Already in 2010 Haiti eq caused over 200,000 deaths. -Several thousand deaths a year; and likely to be the big killer in the U.S. When LA of SF hit by major event. 1

2 A great earthquake occurs roughly annually. Hundreds of strong eg, each causing major damage and loss of life, occur each year around the world. There s no reason TO THINK THIS YEAR THAT WE RE SEEING MORE BIG QYAKES THAN STATISTICS WOULD SUGGEST. The geographic distribution of earthquake hazard is reasonably well known, mostly associated with tectonic plate boundaries. In fact, 2/3 of eq are along plate boundaries, especially subduction zones. Few intra-plate quakes with various causes: volcanism (e.g., hawaii); crustal rebound (from ice age, e,=.g., eastern Canada), and we don t know! A closer look at the U.S., shows the tectonic zone in the West, a off-shoot associated with orogeny (mountain-building) thru Utah and Idaho, and more rare mid-plate EQs in Missouri, SC, and Quebec. Earthquake Hazards Slippage along a fault in the earth s crust mostly due to build-up of tectonic forces (plate motion). Larger faults, and more slippage, means more intense quake (very biggest may have 15 meters of slippage) Intensity measured initially by magnitude of the Seismic Waves created by the fault motion, translated into a scale originally developed by Charles Richter (and later called the local magnitude or M L ) and now the moment magnitude (M W ) or just magnitude scaled to be similar to Richter. The dispersion of EQ hazard (ground shaking) from a given event varies across geography. The famous SF quake, with equivalent power, shook a much smaller area than the New Madrid quake in 1811, due to fewer faults in mid-continent attenuating the seismic energy. It is good that New Madrid quakes are very rare! BUT: these measures of energy release may not translate directly into impacts, depending on focal depth, distance, crustal composition, surface features, etc, and of course vulnerability of human systems (buildings, etc.) 2

3 Measuring EQ Magnitude Ancient cultures knew about seismic waves; some recorded them. The attempt to measure EQ magnitude illustrates problems with measuring any geophysical event: some arbitrary benchmarks are created to allow inter-comparison. Easier than some hazards because EQ s send out long-distance signals, measured all over the world! Seismology Modern development by Charles Richter, who created the first universal scale for measuring EQs; Richter Magnitude based on amplitude of seismic waves Opened-ended, each whole number is an order of magnitude (X10) increase in energy released. Empirically: 3 can be felt; 4 starts light damage; 5-6 significant damage starts; 7+ major damage How measured? Modern Richter standard is called the: local magnitude, M L : Log of standard seismograph trace in micrometers (10-3 mm); normalized to 100 km distance from epicenter (e.g., 1 mm amplitude = log 10 of 1,000 = M L 3) Energy release of EQ increases X 10 with each whole number increase in M L ---though actual ground motions can t increase that much! Rather, larger areas are shaken with the extra energy. Thus seismologist developed the Moment Magnitude Intensity also measured by impact/damage (Modified Mercalli Scale) and by rate of ground shaking (or motion at peak acceleration) as a percent of acceleration due to gravity or 1g Richter-derived scales (M L and M W ) are all about energy released at the rupture of a fault, and though obviously related it does not imply actual ground shaking which is what really matters in terms of hazards. Another scale, Mercalli, was developed to categorize the surface effects of an earthquake, all affected by magnitude of waves, type of surface, and type of human use. Many frightened and run outdoors Everyone runs outdoors Drivers of autos disturbed Waves seen on ground, line of sight distorted 3

4 Earthquake Hazards Slippage along a fault creates waves in the solid earth that propagate like air and water waves. Only brittle earth may deform permanently with passage of the wave. There are four main types of waves: (in the solid earth) Primary waves (p waves): compression waves, motion parallel to propagation, at 5-8 km/sec) Secondary waves (s waves, also shear waves): motion transverse or orthogonal to direction of propagation, at 3-4 km/sec Surface waves(sometimes all called L waves): As P and S waves reach the surface, they refract at interface of solid earth and atmosphere and cause large, amplitude low frequency waves to form: Rayleigh Waves: rolling waves, with spiral motion (like ocean waves) Love waves: sideways Rayliegh waves (type of L or surface wave) are akin to ocean waves. You can see the result of waves moving through the rigid surface and thru human constructions on the earth s surface, which often fail as they are compressed or sheared by P and S and L waves. Rayleigh and or Love Waves! Compression (and slip) Compression (maybe p waves) Some form of rolling surface wave (L probably) accelerated the ground up into these supports and they failed. 4

5 Faulting itself can express at the surface and also cause damage: Surface rupture w/ lateral slip along fault 1855! Wairarapa Earthquake (here s a vertical rupture, a classic, old fault scarp, worn down (eroded) over time to less slope) Watch the Puente Hills eq simulation: t/videos.html 5