Tornadoes Storms of Destruction Mrs. Heathcott’s 7 th grade Navasota Jr. High December 8, 2005

Tornadoes are extremely rapid, rotating winds that form from cumulonimbus clouds that touch the ground.

Cumulonimbus clouds – reach high into the atmosphere, and are much larger and more vertically developed than cumulus clouds.

May 3, 1999 One of the deadliest series of tornadoes in U.S. history.  66 tornadoes touched down in Oklahoma and Kansas  F-5 tornado that moved along a 38-mile path  killed 46 people, injured 800, damaging 8,000 buildings  Caused at least $1.5 billion in damage

Every year, dozens of tornadoes rip through the U.S. and cause massive amounts of damage. Scientists work to understand where and how these storms originate and what powers them.

Tornado Classification Tornadoes are ranked by the amount of wind and damage they create. The Fujita Scale ranges from F0 to F5, with F0 being the least violent and F5 being the most violent.

Fujita Scale Fujita scale Wind speed mph Damage F0 <72Light: broken branches and chimneys F Moderate: roofs damaged, mobile homes upturned F Considerable: roofs torn off homes, large trees uprooted F Severe: trains overturned, roofs and walls torn off F Devastating: houses completely destroyed, cars picked up and carried elsewhere F Incredible: total demolition

Storm Mechanisms How are tornadoes formed ? What are the three major storm mechanisms that create tornadoes ?

Storm Mechanisms 1 Tornadoes have changes in air pressure.

Where are the high and low air pressures found in a balloon ? Where are the high and low air pressures found in a tornado ?

So……… Do winds blow from areas of low pressure to high pressure or from high pressure to low pressure ?

 Tornadoes are formed when a severe low pressure develops.  They operate like a ‘backwards’ balloon, air from high pressure rushes in to fill in the low pressure area.  Meteorologists closely monitor changes in air pressure (particularly decreases) because they can spawn tornadoes.

Storm Mechanisms 2 Tornadoes, hurricanes and thunderstorms have an ‘updraft’ mechanism. The upward movement of air is due to the process of convection.

Convection The Earth is heated by radiation from the sun (transporting energy via electromagnetic waves). Heating of earth's surface and atmosphere by the sun drives convection within the atmosphere and oceans, which produces winds and ocean currents.

Convection is the transfer of heat by the flow of a material.  Molecules move closer together, making air more dense, and air pressure rises. The process  Cold air sinks,  pushing up warm air,  which then cools and sinks,  pushing up more warm air.

 As instability occurs in the atmosphere, fronts move in and lower air layers break the upper layer cap.  Warm air can now rise.  As the warm, moist air rises, vapor condenses and precipitation occurs.  Thunderstorms and hail often occur with tornadoes. Movin’ On Up

Tornado Formation

 As moisture condenses it releases “latent” heat.  Latent heat is released during phase changes (such as…) Evaporation, freezing, melting …  The latent heat released helps the rising air stay warmer.  The air continues to rise and to gain speed (occasionally up to 150 mph!) Heating Up

Storm Mechanisms 3 The Coriolis Effect  Air and water turn left (CCW) in the southern hemisphere and right (CW) in the northern hemisphere due to the Earth’s rotation.  This rotation of the Earth also causes storm systems to rotate.

 Varying wind speeds at different levels cause the warm air to rotate and to gain even more speed.  This huge, rotating air mass is called a mesocyclone. Start the Spinning

 When a mesocyclone begins to move downward, it narrows and rotates even faster. But….  Only when the spinning air touches the ground does it officially become classified as a tornado. Touchdown! Tornadoes’ damage path ranges from less than 150 feet to more than a mile.

Where do Tornadoes Form? Thunderstorms (and tornadoes) form where warm moist air clashes with cool dry air. Tornadoes are common in a region of the U.S. called “Tornado Alley”. What are some features that may cause tornadoes to be so common here? Tornado Alley

Air from the western mountains produces winds that are cool and dry. Gulf of Mexico produces warm and moist air. The interaction of these 2 air masses can produce strong thunderstorms. Texas Interstate 35 roughly separates the dry west and humid east sides of our state. Rocky Mountains Gulf of Mexico Tornado Alley

So, where are the most damaging, most frequent tornados, where are the least damaging, least frequent and WHY?

How are tornadoes and hurricanes similar ?

Storm Similarities Both have….  Severe storms with vortex winds  Circulating winds due to the Coriolis effect  Updraft mechanisms due to convection  Considerable air pressure gradients

How do Tornadoes and Hurricanes differ?  Hurricanes are fueled by “heat of evaporation” and must form over warm oceans.  Tornadoes form (mostly) over land from convection updrafts and air pressure gradients.

Storm Mechanisms The interaction between temperature, air density, air pressure and convection currents are similar in thunderstorms, hurricanes and tornadoes.

Simulator Vortex Within this model, where are the areas of high and low pressure ? How are convection currents modeled ? How is the Coriolis Effect modeled? What limits this model from working like a real tornado ? Mist is used to show the simulator’s vortex. What is the visible vortex in a real tornado? The simulator’s vortex breaks up quickly. Describe why real tornadoes vortexes might also be short lived.

Simulator Vortex Predict what will happen when the simulator is modified by: –Columns are turned out –Top, middle and/or upper holes are plugged –Fan speed adjusted –Other alterations/modifications ?

Mr. Rushing for taking the time and energy to build this vortex simulator for NISD! A Texas twister sized Thank you to