This is Part 3 of my notes from the Vaisala Lightning Seminar. Please see the other entries in this series for definitions and more information.
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WHY ISN'T THERE MUCH LIGHTNING IN HURRICANES?
LIGHTNING IN HURRICANE HUMBERTO (ANIMATION)
This is something we've discussed before here on this blog. Despite what you see in the movies, lightning most often seen in the outer eyewall bands of hurricanes, far from the hurricane's high winds, where there are legitimate thunderstorms. There is also a small maximum of lightning in eyewalls, often during eyewall-replacement cycles.
Again, there is no relationship to the strength of the storm; Tropical Storms contain more inner-core lightning than tropical depressions or strong hurricanes, and 30 to 70% of tropical storms in general have some lightning during their lives.
There is some research that indicates that there is more inner-core lightning activity in tropical storms which are "steady state" -- neither increasing nor decreasing in strength, but more research is needed.
WHAT RELATIONSHIP DOES LIGHTNING HAVE TO TORNADOES OR SEVERE WEATHER?
Scientists once thought that a lot of positive lightning strikes might preceded tornadoes dropping to the ground, but when more cases were examined, the relationship was not found to be true. However, it was found that many severe weather (wind and hail) occurrences happen when Cloud Flashes are peaking and CG rates drop to near zero. If you look at overall CG lightning strikes, the map does not match areas of severe weather, including tornadoes.
WHY AREN'T MORE STORM CHASERS KILLED BY LIGHTNING?
The above statement may explain something I have always wondered: Why aren't more Plains storm chasers killed by lightning? They're always standing around in the open next to metal equipment and vehicles - a recipe for disaster! If what I said above is true, storm chasers in proximity to storms with severe weather are likely to arrive just as the CG count falls to near zero. This also means that storm chasers here in the East are in more danger because our storms are less likely to contain severe weather - and more likely to have CG lightning strikes.
RELATIONSHIP OF LIGHTNING TO SEVERE WEATHER?
WHY DO THEY SAY "GET AWAY FROM THE WINDOWS!"?
Why do people tell you to get away from windows during a storm? Well, aside from debris or hail smashing the window and hitting you with objects or shrapnel, a direct lightning strike to your house can shatter windows, and the splintered wood (see photo of this at my house when lightning struck in 1987) could injure you. Injury from wood splintering off a tree and shattering a window at high speed has also been documented.
WHY DO THEY SAY "GET OUT OF THE WATER!"?
Not being in a lake or ocean is good advice; scientists aren't sure how far the lethal electricity from lightning travels in water; it is probably tens of yards.
WHY DOES LIGHTNING DAMAGE SPIRAL AROUND TREES?
Scientists aren't sure; it may be due to the spiral nature of the magnetic field or it may depend on the way the bark peels from the tree when heated.
What should you do if you are caught in a field with a lone tree? Sadly, it's probably too late to do anything that would be helpful. Historically people have been taught to "lie flat" but even that may not help. The truth is, you should have evacuated that area before the lightning started. Large buildings or metal-topped vehicles are the only safe place.
WHAT ARE MASSIVE "SPIDER LIGHTNING FLASHES"?
Probably the coolest thing that I learned (aside from the note about storm chasers) was this story of how lightning detection is progressing our education on the topic. Vaisala, in partnership with the U.S. National Weather Service in Dallas, once observed (on the 3-d lightning network there) a lightning flash on the back end of an MCC [JessePedia] that extended out 190 kilometers from the thunderstorms in front, dropping CG's 50 kilometers apart, that were mixed polarity (positive and negative - something previously not seen from the same flash).
3-D SPIDER LIGHTNING
This was interesting because previously they had assumed that lightning on the back of MCC's was somewhat random, regular lightning strikes. In reality, there are specific regions of charge with MCC's.
Cross-Section of Lightning Regions in an MCC
CAN I DETECT WHEN LIGHTNING HAS HIT MY LIGHTNING ROD?
After lightning struck my house in 1987, my father suspended a lightning rod above the house, well grounded at both ends. He attached a small wire off of the cable near the ground, with a fuse in the middle. He claimed that would let us know if lightning ever hit the rod again. I asked the one of the Vaisala guys if they thought that would work, and they said it was plausible, although all the upward streamers coming up from the ground at that point could potentially set off the fuse and create a false alarm.
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