Tornadoes in the U.S., in Europe and elsewhere

tornadoes-hot-spots-around-the-world

Like the United States, Europe experiences its share of severe weather ranging from intense winter storms to violent thunderstorms accompanied by hail stones and even tornadoes. No continent remotely rivals North America when it comes to tornadoes. A vast majority of those tornadoes spawn within the 48 contiguous states of the U.S., mainly east of the Rocky Mountains. The Storm Prediction Center (SPC), headquartered in Norman, Oklahoma, keeps a history of tornadoes reported in the U.S. since 1950. The SPC is also situated in an area that has a relatively high frequency of strong to violent twisters. This band of intense tornadic activity, covering South Central states and most of the Midwest is referred to by the media as Tornado Alley.

tornado_alley_intense_tornadoes

Based on data pulled from the European Severe Weather Database (ESWD), 5,478 tornadoes have been reported from 1950 to 2015 in 42 countries. [Although waterspouts–generally weaker vortices over water–are included in the ESWD definition of a tornado, only those confirmed and verified, on land, were selected from the database for this article.] That comes to an average of 83 tornadoes per year in Europe. In December 2016, a research paper titled Tornadoes in Europe: An underestimated threat became available online with the purpose of raising public awareness as to the underestimated and under-reported threat of these funnel-shaped maelstroms of dangerous winds. Tornadoes were under-reported in the U.S. as well during earlier decades when reports of severe weather were handled by individual offices at the U.S. Weather Bureau, and overseen by the Environmental Science Services Administration (ESSA). For example, from 1953 to 2004, the average number of yearly tornadoes was 908. The annual average of U.S. tornadoes, based on the most recent 10-year period from 2005 to 2014, is 1,201. If you look at a 20-year span of tornadoes reported from 1995 to 2014, the average is higher at 1,239. A 30-year period, from 1985 to 2014, accounts for an average of 1,141 tornadoes.

In a PowerPoint presentation shared with North Jersey Weather Observers in May 2011 and published on SlideShare titled Overview of U.S. Tornadoes, I provided some explanations accounting for the increase in the number of tornadoes reported since 1990. [It is outlined on slide 22.]

  • Population increase: More tornadoes are observed and reported.
  • Better technology: More tornadoes are detected by meteorologists.
  • Greater knowledge: Fewer tornadoes are mistaken for straight line wind damage; downbursts; and gustnadoes, short-lived whirling gust fronts.
  • Confirmation: Fewer tornadoes are double counted by separate eye witnesses, reporting the same twister.

There was also an increased effort to improve severe weather forecasting and to effectively communicate likely and imminent hazardous weather alerts to the public.  So in 1966, ESSA formed a specialized branch of the U.S. Weather Bureau to do just that. And it was given the name: National Severe Storms Forecast Center (NSSFC). Part of the scope of the NSSFC was to centralize and verify severe weather data from radar, and eye witness accounts (observed and videotaped) from storm chasers, the media and individuals. In 1970, the U.S. Weather Bureau changed its name to the National Weather Service (NWS), and the ESSA was rebranded as the National Oceanic and Atmospheric Administration (NOAA). Later that decade the roll out of Real-time operational forecasts and warnings, using Doppler radar, had become a game changer for the NSSFC. By the end of the 1980’s, the network of advanced Doppler radars, referred to as  NEXRAD (short for ‘Next Generation Weather Radar’), had significantly improved lead times in predicting severe weather events, including ice storms, tornadoes, and flash floods.  In 1995, the NSSFC was renamed the Storm Prediction Center. [For more history on SPC, go here.]

People living in the U.S. understand the destructive powers of tornadoes, especially in the Great Plains region and in Southeast states where many families have storm shelters and emergency kits for such events. Civil defense sirens, as part of the Emergency Alert System (EAS), are sounded in the vicinity of imminent danger when tornado warnings are issued, simultaneously with radio and TV broadcasts, and smartphone alerts. And schools have practice drills designed for tornado preparedness. It is also a significant advantage when a common language–English–is spoken in every state. According to U.S. Census Bureau data from 2011 almost 80% of U.S. residents, age 5 and older, spoke English “very well” or “well”. It is easier to communicate watches and warnings, and to inform the general public on the hazards and safety measures of tornadoes when one language is predominantly spoken. It also helps to reduce the risk of serious injuries and fatalities from tornadoes and other severe weather events with effective and timely alerts.

The researchers who published Tornadoes in Europe: An underestimated threat understand the need to educate the public on tornado preparedness; and the importance of advancing forecasting products and services. The analysis of the tornado data led them to outline the following conclusions:

  1. Increase awareness of the threat of tornadoes to Europe
  2. Encourage further discussion within and between different European countries to (a) improve monitoring and recording of tornado occurrence, (b) better understand the local environments associated with tornadoes, and (c) eventually lead to the development of forecasting and warning systems
  3. Stimulate the interest of the scientific community
  4. Influence decision-makers to develop tornado preparedness and response programs

In Europe, the logistics of consistent and proficient communication is considerably more challenging since multiple languages and dialects are spoken across 40 plus countries. Notwithstanding some hurdles, the annual number of confirmed and verified tornadoes has been steadily rising. This most likely reflects an increase in the general public’s awareness and due diligence in reporting tornadic activity. For example, despite a well under-reported yearly mean of 50 European tornadoes from 1953 to 2004, the annual average of tornadoes from 2005 to 2014 was 258.

In 2006, Europe confirmed and verified a maximum of 414 tornadoes. The U.S. tallied its most prodigious year of tornadoes in 2004 with 1,817. That is over four times the annual record of tornadoes reported in all of Europe. To put it in perspective: the greatest number of U.S. tornadoes in a single month occurred in April 2011 when 758 twisters left a devastating path of destruction throughout most of the Southeast and Mid-Atlantic states. This single month record in the U.S. is greater than a recent 3-year total of 747 tornadoes that touched down in Europe from 2013 to 2015.

april-2011-tornado-reports-map

Although the United States has greater than four times as many tornadoes, Europe has more than twice the number of people living in the continent (742 million) compared with the U.S. population (323 million). There are other factors aside from population density and the likelihood of a tornado touching down: the preparedness of those in harm’s way, the lead time to respond accordingly, the time of day when it hits, the strength (damage potential) of the twister, and the duration and trajectory of the path in relation to people and property.

Tornadoes spawn outside of Europe and the United States. Canada reports as many as 100 tornadoes a year. Australia has up to 25 twisters reported annually. Tornadoes touch down in other countries, but not as frequent. Provided is a table with tornado stats by continent with annual average, percentage, square miles, average frequency per 100,000 square mile, and notes on the concentration of activity. The ‘Tornadoes per Year’ takes into account under-reporting, esp. in Europe where Earth scientists and meteorologists have estimated it to be closer to an average of 300.

annual-tornado-stats-from-around-the-world

 

Here is a pie chart representing the percentage of tornadoes around the world.

percentage-of-tornadoes-around-the-world

 

And here is a bar chart illustrating the annual average of tornadoes.

annual-average-of-tornadoes-around-the-world

No matter how the data is visually presented, it is clear to see the significant disparity of tornadoes in the United States versus Europe and elsewhere. However, there are regions in every continent, except for Antarctica, that are susceptible to tornadoes. Atmospheric scientists cannot prevent tornadoes from forming. However, meteorologists have a crucial role in predicting these powerful twisters, and in working with local agencies and the media to notify the public when there is a likelihood and presence of severe weather. The United States has mastered the art and science of forecasting tornadoes with a high degree of accuracy, educating the public of its dangers, and issuing warnings in a fast and effective way. It is a blueprint of success for European weather scientists as they endeavor to 1) improve forecasting and to 2) raise public awareness. Eventually, tornadoes will no longer be considered “an underestimated threat” in Europe.

 

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Mid-Atlantic Earthquake: Description and Comparison

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On the afternoon of August 23rd, 2011, an earthquake rocked the Mid-Atlantic region.  Seismometers recorded its signature at 1:51 PM as it measured a magnitude of 5.8 on the Richter scale.  The epicenter of the seismic discharge was located in northern Virginia, 38 miles northwest of Richmond.  The shock waves from the subterranean shift were felt in areas of New Jersey, as far north as Montreal, Quebec, east to Rhode Island and as far south as Georgia.

It was a few minutes before 2 o’clock when I experienced the effects of the tremor (I was in my New Jersey apartment at the time).  At first, I looked out the window to see if there was a strong gust or a nearby truck that could have generated the vibration.  As the shaking gained momentum, I suspected it was an earthquake: how long would it last, how intense would it be, what danger was I in…there was no way to tell.

My cat was in the bedroom seemingly unable to move: her arms and legs were spread out as if to prevent herself from sliding.  I picked her up, moved under the door frame of the bathroom and waited for the seismic impulse to pass.  As I braced my arm against the door frame, I noticed the initial vibration gave way to a gentle sway: the resonance continued to build as if the apartment was slowly, rhythmically swinging on a giant pendulum.  The standing picture frames were shaking in synchronization; all the while, I heard a low rumbling coming from outside.  In the bedroom, the remote control hooked to the fan tower fell…at that moment the rocking stopped.  It was silent for a few moments following the tremor then a commotion of startled residents descended outside. The entire event lasted about 30 seconds, but it seemed to unfold in slow motion.

I checked online and turned on the television to the local channel—an earthquake was confirmed.  Many people I spoke with in the Tri-State area experienced the tremor.  My brother was in his house a few minutes north of me, yet he did not feel the effects from the propagating vibrations.  A friend living in Kentucky, west of the epicenter, did not notice the event.

The seismic waves of the Virginia quake traveled further distances and its effects were more intense compared with California tremors of equal size.  Unlike the West Coast, which sits between two sliding plates, the Eastern U.S. is situated in the middle of the North American plate.  The earth’s crust in the Eastern U.S. is more solid and dense, aiding in the propagation and amplification of the vibrations (the shaking).  Seismic waves travel faster through solid rock like granite compared to gravel and soil.  When subjected to strong shaking, moist sediment like silt (fine sand) becomes susceptible to liquefaction (process by which a solid behaves like a liquid).

Predicting the magnitude (size), intensity (effects), when and where an earthquake will hit is different from forecasting severe weather events such as tornadoes.  U.S. meteorologists use Doppler radar to identify Tornadic Vortex Signatures (TVS), bow echoes and hook echoes from mesocyclones—as the event takes shape.  Recent improvements in technology and training have led to a lower average lead time of 11 minutes for tornado warnings.

Japan has the most advanced early warning system for earthquakes.  On March 11th, 2011, Japan broadcast a nationwide alert within seconds after a powerful 8.9-magnitude quake was detected, yet Tokyo residents had a lead time of just 80 seconds before the devastating tremor reached the city.  Why?  The answer lies in the phase velocity of seismic waves.  Although tsunamis can reach speeds up to 500 miles per hour, seismic waves move significantly faster.

More about the velocity in a moment; let’s go over the four main types of seismic waves.  Primary or P-Waves compress and dilate the medium (i.e. rock; soil) in which it passes through as it propagates in the direction of the underground force.  Secondary or S-Waves oscillate perpendicular to the horizontal momentum of energy—up and down and side-to-side.  P-Waves and S-Waves are referred to as body waves because it radiates through the Earth’s body (from the hypocenter below the surface).  The other two distinct seismic vibrations are Love Waves and Rayleigh Waves, which are referred to as surface waves because it travels along the Earth’s surface (from the epicenter). Love Waves shift the ground side-to-side as it moves forward.  Rayleigh Waves roll along the vertical axis in an undulating motion.

The shorter P-Waves cause little to no damage, and are often too faint to be felt by people (some animals such as dogs and elephants can sense vibrations from P-Waves).  The longer S-Waves are typically the first vibrations we experience.  S-Waves are capable of causing ground shifts and structural damage to buildings.  Love Waves and Rayleigh Waves are more intense, causing the most damage, because the vibrations radiate along the ground instead of below the surface.

With respect to phase velocity, P-Waves are the fastest, followed by S-Waves then Love Waves and Rayleigh Waves.  Put another way: body waves radiate more quickly than surface waves.  The average velocity of an S-Wave is 2 – 3 miles per second; its speed varies depending on the composition of the Earth’s crust.  Located 230 miles southwest of the epicenter, Tokyo residents would have experienced the S-Wave from the March 11th quake in about 90 seconds.

The typical speed of a tornado is 30 miles per hour; the fastest twisters move 60 plus miles per hour.  To put it into perspective, I felt the effects of the Mid-Atlantic earthquake approximately three minutes after the seismic discharge, which was 330 miles southwest of my location. Hence, the subterranean speed of the tremors traveled near 7,000 miles per hour!  In retrospect, the vibrations and effects I experienced that day were a series of distinct seismic waves arriving one after another.

[Side note: News and social media coverage of the Virginia earthquake was non-stop until the attention shifted to the approach of Hurricane Irene.  12 hours earlier at 1:46 AM EST on August 23rd, a quake, magnitude of 5.3, rattled Colorado (centered 180 south of Denver).  It was the second tremor originating from the same location within a 7-hour period (first temblor, magnitude 4.6, struck at 7:30 PM EST on August 22nd).  There was not as much coverage in the Denver news media or on twitter regarding the back-to-back events.  Earthquakes of magnitude 5+ are uncommon east of the Rocky Mountains.  The highest risk for seismic activity east of the Rockies is in the Ozark region.]

Another aspect of an earthquake’s power is the observed impact on built structures, above and below the ground, and its effect on the surrounding environment. This is referred to as an earthquake’s intensity. The modified Mercalli Intensity scale, the description of its values, and an approximate comparison to a quake’s seismographic measurement is provided in the following table.

Earthquake_Intensity v Magnitude_table_v2.png

The energy release from an earthquake is also determined by seismometers, and its magnitude is measured logarithmically. U.S. Geological Survey has an online calculator for comparing the size and strength of varying magnitude. Included is a table with differential references based on change in ground motion and energy release.

Earthquake_Magnitude v Ground Motion_table


References: Sites visited / links viewed in researching information and creating tables for this piece.

Date (mm/dd/yy) article published in parenthesis. [Hyperinks are checked periodically. Previously referenced URLs no longer available, and added links are noted in brackets.]

http://allshookup.org/quakes/wavetype.htm

http://aspire.cosmic-ray.org/labs/seismic/index.htm

http://earthquake.usgs.gov/learn/facts.php

http://earthquake.usgs.gov/learn/topics/mag_vs_int.php

http://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami

http://en.wikipedia.org/wiki/2011_Virginia_earthquake

http://en.wikipedia.org/wiki/Plate_tectonics

http://en.wikipedia.org/wiki/Richter_magnitude_scale

http://en.wikipedia.org/wiki/Seismic_wave

http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html

http://physics.info/intensity/

http://science.howstuffworks.com/environmental/earth/geophysics/question142.htm

http://science.howstuffworks.com/nature/natural-disasters/tsunami3.htm

http://tremblingearth.wordpress.com/2011/03/04/liquefaction-in-new-zealand/ (03/04/11)

http://www.alphadictionary.com/goodword/word/temblor

http://www.britannica.com/EBchecked/topic/532925/seismic-wave

http://www.csmonitor.com/Innovation/Latest-News-Wires/2011/0314/Japan-earthquake-How-Tokyo-got-an-80-second-head-start (03/14/11)

http://www.differencebetween.com/difference-between-earthquake-magnitude-and-vs-intensity/ (03/12/11)

http://www.nj.com/news/index.ssf/2011/08/earthquake_rocks_new_jersey_an.html (08/23/11)

http://www.npr.org/blogs/thetwo-way/2011/08/23/139892996/why-a-quake-in-virginia-isnt-as-rare-as-it-sounds?ft=1&f=1001 (08/23/11)

http://www.nytimes.com/2011/03/12/world/asia/12japan.html?pagewanted=all (03/11/11)

http://www.scientificamerican.com/article.cfm?id=fast-facts-japan (03/14/11)

http://www.time.com/time/world/article/0,8599,2059780,00.html (03/18/11)

http://www.differencebetween.info/difference-between-richter-scale-and-mercalli-scale [added 8/23/17]

http://www.diffen.com/difference/Mercalli_Scale_vs_Richter_Scale [added 8/23/17]

https://earthquake.usgs.gov/earthquakes/events/2011virginia/overview.php [added 8/23/17]

https://en.wikipedia.org/wiki/Mercalli_intensity_scale [added 8/23/17]

https://en.wikipedia.org/wiki/Moment_magnitude_scale [added 8/23/17]

https://pnsn.org/outreach/about-earthquakes/magnitude-intensity [added 8/23/17]

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php [webpage no longer available]

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/ (03/11/11) [webpage no longer available]

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005ic9/ (08/22/11) [webpage no longer available]

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005idz/ (08/23/11) [webpage available but no longer maintained]

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005ild/ (08/23/11) [webpage no longer available]

http://churmura.com/lifestyle/environment/earthquake/20286/ (10/21/09) [webpage no longer available]

http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usb0001igm.php (02/21/11) [webpage no longer available]

http://wcatwc.arh.noaa.gov/physics.htm [webpage no longer available]

http://www.geo.mtu.edu/UPSeis/magnitude.html [webpage no longer available]

http://www.geology.siu.edu/people/pinter/pdf/EQMagIntensity.pdf [webpage no longer available]

http://www.theblaze.com/stories/why-was-virginias-earthquake-felt-all-the-way-in-canada/ (08/23/11) [webpage no longer available]

Tornadoes Strike Massachusetts

 

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Twister rumbling through downtown Springfield, MA on the afternoon of June 1st.

During the Memorial Day weekend, the Northeast had experienced a gradual warming trend coupled with an increase in humidity.  On Wednesday, June 1st, the temperature and heat index peaked for most of the region ahead of a cooler, drier air mass approaching from the Ohio Valley.  The cold front was preceded by a trough, adding further convection to an already unstable atmosphere.  That morning National Weather Service issued a Tornado Watch, effective from 1:00 PM to 8:00 PM, covering eastern Pennsylvania, most of New Jersey, New York lower Hudson Valley, parts of Connecticut, most of Massachusetts, all of New Hampshire, and southern Maine.

Around 4:30 PM, strong thunderstorms in western and central Massachusetts spawned multiple tornadoes (final count and strength had yet to be determined at the time of this article).  Initial reports showed extensive damage in the cities of Westfield and Springfield.  Several injuries were reported, including three fatalities.  Massachusetts Governor Deval Patrick had declared a state of emergency.

One of the twisters that struck Massachusetts was filmed crossing the Connecticut River in Springfield (video is posted at the end of the article).  The funnel had a siphon-like effect, channeling water into the vortex as it glided across the surface.  A tornado draws in air to replace the rapidly rising curtains in the mesocyclone—the violent, rotating updraft that forms the circulation.  The funnel cloud is essentially a spiraling updraft, picking up anything in its path.  The angular force of the wind and the whirling debris within the vicinity of the twister are what make this storm so deadly.

It had been three years since a tornado was reported in “The Bay State”.  The last fatality from a tornado was when a F4 twister struck the state in 1995.  The tornadoes on June 1stwere more destructive because of the populated areas it struck.  The NWS Storm Prediction Center had done its job, alerting the public well in advance that conditions were favorable for severe thunderstorms, accompanied with hail, gusty winds, and possibly tornadoes.  The weather forecast was not as ominous on June 9, 1953 when residents were caught completely off guard as a mammoth tornado ravaged Worcester County, staying on the ground for over an hour (first reported at 4:25 PM; last reported at 5:40 PM)!

Tornadoes are uncommon in New England.  From 1953 to 2004, Massachusetts has averaged slightly less than three tornadoes annually, including one strong twister (F2 or greater); Connecticut, Rhode Island, Vermont, New Hampshire and Maine have a combined average of near six tornadoes in total during the same span.  The other three states in the Northeast—Pennsylvania, New York and New Jersey—have an annual average of 12, 7 and 3 tornadoes, respectively.

Note of interest: New Jersey (3.8) and Massachusetts (3.6) have the highest concentration of tornadoes among the Northeast states (per 10,000 square miles) based on data reports from 1953 to 2004.

Overview of U.S. Tornadoes

This presentation was put together in May 2011, following a very active stretch of severe weather, esp. in the Southeast region.