March 15, 2012
Tornadoes And Seismic Activity
Joshua Kelly, Meteorology Correspondent for Redorbit.com
UPDATE (03.15.12): The seismic signals generated by tornadoes on February 29 and recorded by seismometers in southern Illinois were not unique, according to a spokesman for Engineering Analysis Inc. (http://www.mindspring.com/~eai/), which has been studying such signals for more than 20 years. Dr. Frank Tatom, the co-inventor of the seismic detector of tornadoes, reported that such long period seismic signals have been previously observed on at least seven different occasions, dating back to 1927. Tornadoes in Missouri, Ohio, Mississippi, Tennessee, and Texas have produced very similar signals and are generally associated with relatively strong storms.
The first is the minor earthquakes that occurred during the storms.
According to Indiana University: A recent “geophysical experiment detected unusual seismic signals associated with tornadoes that struck regions across the Midwest last week -- information that may have value for meteorologists studying the atmospheric activity that precedes tornado disasters.
The experiment by IU researchers involves deployment of more than 100 state-of-the-art digital seismographs in a broad swath of the U.S. midcontinent. One of the twisters that struck southeastern Missouri and southern Illinois on Feb. 29 passed through the seismic detection array.”
Here is an excerpt from Professor Michael Hamburger: “While examining the seismic stations three of our stations in Southern Illinois, showed unusual seismic activity.”
This may not sound like much and may not have many peopled concerned at this time, however it could give meteorologists a new method to help determine the strength of the tornado based on seismic returns. Also, this can be further used in helping to understand how tornadoes work because the stronger the return the more likely the storm was to have created a large damage impact.
(Image courtesy of Indiana University)
In the above image we can see the seismic stations that were in the path of the tornado that went through Southern Ill. Also the yellow line with an arrow is the actual tornado path. The darker colors show a stronger seismic return.
What could have caused these seismic stations to report such activity during the time of the tornado?
Although it is up to speculation, a good theory would be that the large pressure drop that occurred with the passage of the tornado caused the vibrations to occur. Also if you remember people are always talking about how when a tornado goes through it sounds like a freight train. Well, the tornado pushes its energy from up above to the surface so it acts like it may be a freight train hitting the ground at tremendous speeds causing the ground to vibrate.
So let´s examine why a tornado has such a pressure drop inside its core. To do this, it´s important to understand the makeup of a tornado. Tornadoes don´t just form. Certain things need to come together at the right place and right time for tornadoes to form. The biggest three things that need to come together are the warm-moist air from the Gulf of Mexico, the dry air from the Southwest United States and the very cold dense air from the Rockies.
The image below that I have created shows all three of these elements coming together.
(Image courtesy of Joshua Kelly)
If we look at the green arrow, we take note of the warm moist air coming in at the surface from the Southeast. The second arrow in yellow shows the dry warm air coming in from the Southwest. Thirdly, we have the blue arrow coming in from the Northwest out of the Rockies. It is important to know that all three of these arrows are from different heights also. This is an important piece of information as this provides clues as to why the winds turn with height, which is crucial in getting a storm to spin as needed for a tornado to form. Now we also need to look at the air coming in from the Rockies. It is higher in the air and colder which makes it want to sink towards the ground.
This helps us to understand why we see such a pressure change in a tornado.
Now we examine why some tornadoes may be stronger than others. The tornadoes that sound like freight trains are the stronger storms and these are the type of storms that are responsible for that seismic activity in Illinois. These storms get strong because they have a large amount of cold air present in them which is causing a rapid sink of the air towards the ground. This can also be proven by the images that NASA took that morning of the region. There infrared satellite images where scanning the atmosphere over this region and found cloud top temps to be very cold along the Polar front jet. This air was then being mixed in with the warm surface air that was present along the surface.
The best and simplest way to understand this outbreak is to think of cooking something. If you add too much of sugar it gets really sweet. This can be said of tornadoes as well. The more of the ingredient you add, the more punch the tornado will have.
So now to get back to this outbreak that occurred and why it might have been so significant. It could be related to the very strong push of cold air that was inserted over top of the well above normal and moist surface conditions that existed in the region. These types of surface conditions are more common during late May early June“¦not early March. That is one possible reason for this event to be so significant.
Is it likely that we could see more of these strong severe weather outbreaks in the year of 2012? While not a simple answer, it may be likely to see this type of outbreak again. These types of severe weather outbreaks are more common during an La-Nina type of pattern which we currently have in place.
How can you better prepare yourself for the next major outbreak or any severe weather that may happen. The best answer is to listen to the local National Weather Service (http://weather.gov/) and take their warnings seriously, as this will help cut down on potential loss of life. Another way that you can prepare yourself is to understand the methods that were mentioned above and how and when they come together.
So where are places to look for tornadoes to occur. There are several areas that are conducive of tornadoes, however the biggest pattern is along a squall line which forms ahead of the initial cold front. This line can generate rapidly forming rotating super-cell type thunderstorms which are common for rotating with height. Another spot that is common is near the center of the low on the warm sector and this is because we find the strongest spin in the atmosphere from the surface to heights well above the ground.
These are all things that meteorologists watch on a daily basis to determine if there is going to be severe weather and where will it form. So the best thing you can do is just tune into the local news or weather and listen for their warnings as they issue them.