Thunderstorms and Tornadoes Lecture 6 (EESA09) PDF

Thunderstorms and Tornadoes EESA09 Lecture 6 Forecast from Weather radar https://www.theweathernetwork.com/en/maps/radar  Tornadoes in Southwestern Ontario Hamilton, June 7, 201...

Thunderstorms and Tornadoes EESA09 Lecture 6 Forecast from Weather radar https://www.theweathernetwork.com/en/maps/radar  Tornadoes in Southwestern Ontario Hamilton, June 7, 2011 https://www.youtube.com/watch?v=i8hUOGlc3-c Outline Thunderstorm Primer What is a Thunderstorm Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Thunderstorms What is a thunderstorm? A violent storm that causes heavy precipitation, strong gusts of wind , and thunder and LIGHTNING. Every day more than 16 million Thunderstorms occur in the Worl d as a whole and about 2,000 are taking Place at any moment. About 100,000 occur in the Unite d States every year. Common in Southern Ontario in summer Only storm that has thunder and lightning Large thunderstorms can spawn tornadoes  Thunderstorms These are also known as Convective storm Caused by surface heating Forms cumulonimbus clouds air rises by convection inside THE cloud s As it rises it cools and some of ITS water vapor condenses This releases latent heat condensation, which warm the surrounding air  Thunderstorms Four categories Ordinary Multi-cell Supercell Mesoscale convective complexes (MCC)  Ordinary Thunderstorm Often develop within large air masses Not necessarily near a frontal system Little vertical wind shear Change of horizontal wind speed with height Ordinary Thunderstorm Three stages Differential surface heating induces upward flow in unstable air, updraft, cumulus cloud formation Mature phase – development of a downdraft with precipitation Gust front develops as downdraft air spreads along horizontal surface  Thunderstorms Gust front forces more air up into the updraft. Updraft and downdraft form a convective cell. When the gust front moves past the updraft, the updraft weakens. Rain starts to fall into the updraft, cutting off the rising humid air. Ordinary Thunderstorm Final stage Downdraft cuts off updraft and storm loses energy source and dissipates Relatively short-lived < 1 hour Diameter, 1 km or less  Multi-cell Thunderstorm Similar to ordinary except moderate wind shear Storm tilts Downdraft forms downwind of updraft Storm lasts longer Gust front of one storm initiates or induces another storm  Supercell Thunderstorm Form with strong vertical wind shear Surface winds (mT air) from south/southwest Upper level winds (cP air) from north/northwest Along cold front of a midlatitude cyclone 100 – 600 m in diameter Tornadoes can spawn  Supercell Downdraft does not cutoff updraft Storm can last for several hours Hail can form Microbursts can also form Supercell Plane view of thunderstorm Areas of updraft and downdraft Gust front Up level blow off (anvil extent) Microbursts Localized downdrafts Radial burst of surface wind The horizontal spreading of a microburst creates strong wind shear when it reaches the surface Aviation hazard A plane flying into the headwind of a microburst gets sudden increase in lift, which is replaced suddenly by a tailwind as it exits the downdrafts. Airplane crash, August 1985 at Dallas-Fort Worth Airport, 100 lives lost MCC Mesoscale convective complexes These are defined by oval or roughly circular organized systems containing several thunderstorms Multiple thunderstorms Circular fashion Covers over 100,000 square kilometers 12 hours or more, self sustaining Heavy precipitation Squall line A series of very vigorous cumulonimbus clouds that merge to form a continuous line and advances at right angles to the line itself Thus a String of thunderstorms start to form along a cold front Typically about 500 km in length The average squall line has a life span over 10 hours November 15, 1989 – The Huntsville Tornado is an example Hail and tornadoes formed  Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Lightning Special characteristic of thunderstorms Lightning is An electrical discharge that neutralizes a charge separation that has accumulated within a cloud between two clouds, or between a cloud and the ground Charge separation occurs in the cloud (charge is carried by the cloud droplets or ice crystals) Smaller particles tend to go to top of storm with positive charge, larger ones with negative charge to the bottom Acts like a magnet to attract positive charge at the surface Lightning Most (90%) lightning starts at cloud base and goes to the surface First step – a path of 50 m or so is ionized by 3 million volts of electricity Further steps of 50 to 100 m until surface is reached Lightning As surface is neared positive ions from the surface move upward Near the accumulated positive charge it is met by a return stroke, carrying positive charge back to the cloud and traveling along the same path of ionization. This return stroke is the main part of the flash. Lightning When the two connect, the luminous return stroke is seen Several cm in diameter Process can repeat leading to forked lightning Air heats to 30,000º C Generates shock wave – thunder! Sound travels more slowly than light Radio waves, sferics, are produced allowing for lightning detection worldwide http://www.youtube.com/watch?v=nCm2UCj6eDU&feature=related Real time Lightning Information World Wide Lightning Location Network  Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Hail Precipitation in the form of HAILSTONES, which are hard, more or less spherical pieces of ice. Largest form of solid precipitation and most damaging Canada has a new “heavy-weight” champion when it comes to hailstones. Coming in at 292.71 grams and measuring 123 millimetres in diameter, Western University’s Northern Hail Project (NHP) field team recovered this huge hailstone after Monday’s storm near Innisfail, Coffeyville hailstone at Kansas Alta. 757 grams (1.67 lbs)– 14 cm 2nd costliest natural weather disaster in Canada (after 1998 Ice Storm) https://www.theweathernetwork.com/en/news/weather/forecasts/canadas- largest-hailstone-found-in-alberta  Typical Hail http://www.youtube.com/watch?v=PhcdBcmaazs Hail Formed in cumulonimbus clouds (thunderclouds) Formed through successive deposition of supercooled water onto an ice core Recycling through up- and downdrafts enable hailstone to grow until it is too heavy for the updraft 10 billion cloud droplets to form a golf ball sized piece of hail  Hail Distribution Anywhere thunderstorms can form Hail days in US range from 0 to 9 Leeward side of Rockies has most hail days Part III of lecture examines Canadian distribution of hail Hail days in Canada Hail compared to other Weather Hazards in Canada  Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Thunderstorm Distribution in US Maximum number in Florida Land/sea contrast Mid to late afternoon thunderstorm Worldwide Distribution Dai (2001) 15,000 stations around the globe, 1975-1997 Worldwide Distribution Seasonal distribution of thunderstorm probability Summer hemisphere Land versus ocean – mainly over land Tropics and midlatitudes Thunderstorm days  Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Tornadoes What is a tornado? Rapidly rotating column of air that reaches the ground Called “twisters” or “cyclones” “funnel cloud” precursor to tornado has not reached the surface http://www.youtube.com/watch?v=LfXDMgEFpb4 Tornadoes What is a tornado? (continued) Mostly counterclockwise 100 – 600 m diameter Usually last a few minutes Peak winds of 220 knots (400 km/h) Tornadoes How are they formed? Tornadoes are formed from supercell thunderstorms Thunderstorms often form along the cold front of a midlatitude cyclone  Tornado Conditions for formation cP cP air aloft mT air at surface Explosive development when stable level at 800 mT mb is eroded Tornado formation Wind shear Surface winds from south/southeast Upper level winds from west/northwest Cause air to rotate Vortex tube forms Tornado formation Updraft causes distortion of rotating air (vortex tube) Rotating column takes on vertical component This is the start of the tornado Tornado formation Fully developed tornadic conditions Vortex tube becomes vertical Funnel cloud forms first and becomes tornado when it hits the earth’s surface http://www.youtube.com/watch?v=006guBgSf14&NR=1  Tornado classification Fujita Scale F0 – Weak: 64 – 116 km/h Light Damage F1 – Weak: 117 – 180 km/h Moderate Damage F2 – Strong: 181 – 252 km/h Considerable Damage F3 – Strong: 253 – 330 km/h Severe Damage F4 – Violent: 331 – 416 km/h Devastating Damage F5 – Violent: 417 – 515 km/h Incredible Damage F6 – Violent: > 515 km/h Ted Fujita (1920-1998) Created in 1971 (University of Chicago) Damage scale – velocities are approximate Fujita Damage F0 F2 F1 Fujita Damage F4 F5 Limitations of Fujita Scale The original Fujita scale has several other weaknesses: Rankings are subjective and based solely on the damage caused by a tornado Difficult to apply with no damage indicators (if a tornado hits no structures, large trees, etc.) No account of construction quality and variability No definitive correlation between damage and wind speed Subject to biases of the surveyors Enhanced Fujita Scale The EF-scale was proposed by the National Weather Services (NWS) to the public and the full meteorological community early in 2006. On 1 February 2007, the Enhanced Fujita scale replaced the original Fujita scale in all tornado damage surveys in the United States The Enhanced Fujita scale is an estimate of peak wind speeds based on a damage assessment conducted by trained meteorologists from the NSW. https://weather.com/storms/tornado/news/enhanced-fujita-scale-20130206 Tornadoes in Canada Tropical Storm Classifications Saffir-Simpson Scale 1-5 rating scale Category One Hurricane 119-153 km/h (33 – 42.5 m/s), > 980 mb Category Two Hurricane 154-177 km/h (42.5 - 49 m/s), 965 – 979 mb Category Three Hurricane 178-209 km/h (49 – 58 m/s), 945 – 964 mb Category Four Hurricane 210-249 km/h (58 – 69 m/s), 920 – 944 mb Category Five Hurricane Greater than 249 km/h (> 69 m/s), < 920 mb Thunderstorms and Tornadoes How are thunderstorms and tornadoes related? Tornadoes are spawned from super cell (large) thunderstorms Tornadoes are formed from the thunderstorm base Thunderstorm is a necessary condition for a tornado but not vice versa  Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada Tornadoes in Canada Emergency Preparedness Canada Data base of natural disasters Tornadoes – 6th on the list 29 damaging tornadoes from 1900 to 1999 125 fatalities, 1777 injured, 7718 evacuated 1.2 billion dollars of damage Canadian Tornadoes Vaughn Tornado, 2009 Up to 45 houses and buildings have been deemed unsafe More than 600 homes have been damaged 200 home were damaged so badly that they will likely be demolished Likely an F2 Tornado http://www.youtube.com/watch?v=qNGohf5GU5A Tornado in Ottawa https://www.ctvnews.ca/video?clipId=1496164 Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada Tornados in Ontario Tornado Frequency during 1950- 2007 An upward trend is detected over time with 1.6 tornadoes/decade – statistically significant Examined the relationship between the multivariate ENSO index and tornado frequency and found that it is statistically significant ENSO years are associated with more tornadoes What do the results suggest under a changing climate condition? Outline Thunderstorm Primer Definitions Dynamics of Thunderstorms Lightning Hail World Distribution of Thunderstorms Tornado Primer Dynamics Devastation Famous Canadian Tornadoes Thunderstorms and ENSO Cao and Cai (2011) Detection of Tornado Frequency Trend Over Ontario, Canada  Discussion Questions What is the relationship between Thunderstorm and Tornadoes? What is the relationship between Midlatitude Cyclones and Thunderstorms ? How the 4 types of thunderstorms similar or different? What are some limitation of Fujita scales? How the Enhanced Fujita scale is different from Fujita scale? Discuss the Tornado Climatology in Canada/Ontario Next week Midterm on October 17th at 3 pm Detail will be posted at Quercus