Post on 17-Dec-2015
THUNDERSTORMS, THUNDERSTORMS, TORNADOES, AND TORNADOES, AND
HURRICANESHURRICANES
THUNDERSTORMSTHUNDERSTORMS ASSOCIATED WITH:ASSOCIATED WITH:
– Strong windsStrong winds– Gust frontsGust fronts– HailHail– Lightning and thunderLightning and thunder– TornadoesTornadoes– Extreme precipitation eventsExtreme precipitation events
MAY BE ISOLATED EVENT, A CLUSTER OF STORMS MAY BE ISOLATED EVENT, A CLUSTER OF STORMS OR A SQUALL LINE OF CUMULONIMBUS CLOUDS OR A SQUALL LINE OF CUMULONIMBUS CLOUDS EXTENDING 100S OF KILOMETERSEXTENDING 100S OF KILOMETERS
NEED:NEED:– Warm humid air rising in an unstable environmentWarm humid air rising in an unstable environment– Divergence of upper-level winds (jet stream) to enhance Divergence of upper-level winds (jet stream) to enhance
growthgrowth
TYPES OF THUNDERSTORMSTYPES OF THUNDERSTORMS
AIR MASS THUNDERSTORMAIR MASS THUNDERSTORM– Short-lived afternoon summer thunderstormsShort-lived afternoon summer thunderstorms– Form away from frontsForm away from fronts– Usually not associated with tornado activitiesUsually not associated with tornado activities
SEVERE THUNDERSTORMSEVERE THUNDERSTORM– Long-lived thunderstormsLong-lived thunderstorms– Form in strong vertical, wind shears along cold Form in strong vertical, wind shears along cold
frontsfronts– Associated with high winds, gust fronts, Associated with high winds, gust fronts,
microbursts, hail and tornadoesmicrobursts, hail and tornadoes
LIFE CYCLE OF LIFE CYCLE OF THUNDERSTORMSTHUNDERSTORMS
THE LIFECYCLE STAGES FOR AIR MASS AND THE LIFECYCLE STAGES FOR AIR MASS AND SEVERE THUNDERSTORMS ARE THE SAME SEVERE THUNDERSTORMS ARE THE SAME – AIR MASS LIFE CYCLE: APPROXIMATELY ONE AIR MASS LIFE CYCLE: APPROXIMATELY ONE
HOURHOUR– SEVERE LIFE CYCLES: MANY HOURS (SELF-SEVERE LIFE CYCLES: MANY HOURS (SELF-
SUSTAINING)SUSTAINING)
THREE STAGES:THREE STAGES:– CUMULUS EVENTCUMULUS EVENT– MATUREMATURE– DISSIPATINGDISSIPATING
CUMULUS EVENTCUMULUS EVENT
WARM, HUMID AIR RISES, COOLS, WARM, HUMID AIR RISES, COOLS, CONDENSESCONDENSES
RELEASE OF LATENT HEAT PROVIDESRELEASE OF LATENT HEAT PROVIDES ENERGY FOR CONTINUED GROWTHENERGY FOR CONTINUED GROWTH USUALLY NO PRECIPITATION – USUALLY NO PRECIPITATION –
UPDRAFTS TOO STRONGUPDRAFTS TOO STRONG SOMETIMES NO LIGHTNING OR SOMETIMES NO LIGHTNING OR
THUNDER AT THIS STAGETHUNDER AT THIS STAGE
MATURE STAGEMATURE STAGE UPDRAFTS STILL DOMINATE AS WARM UPDRAFTS STILL DOMINATE AS WARM
HUMID AIR CONTINUES TO BE LIFTEDHUMID AIR CONTINUES TO BE LIFTED RELEASE OF LATENT HEAT PROVIDES RELEASE OF LATENT HEAT PROVIDES
ENERGY FOR GROWTHENERGY FOR GROWTH DOWNDRAFTS BEGIN AS COOLER AIR SINKS DOWNDRAFTS BEGIN AS COOLER AIR SINKS
THROUGH CLOUDTHROUGH CLOUD PRECIPITATION BEGINSPRECIPITATION BEGINS ANVIL SHAPE AS TOP OF CLOUD HITS ANVIL SHAPE AS TOP OF CLOUD HITS
STABLE TROPOSPAUSESTABLE TROPOSPAUSE TORNADO FORMATION POSSIBLETORNADO FORMATION POSSIBLE
DISSIPATING STAGEDISSIPATING STAGE
DOWNDRAFTS DOMINATE OVER DOWNDRAFTS DOMINATE OVER UPDRAFTSUPDRAFTS
NO MORE WARM HUMID RISING AIR = NO MORE WARM HUMID RISING AIR = NO MORE RELEASE OF LATENT HEATNO MORE RELEASE OF LATENT HEAT
PRECIPITATION CONTINUES ALONG PRECIPITATION CONTINUES ALONG WITH STRONG WINDSWITH STRONG WINDS
TORNADO FORMATION POSSIBLETORNADO FORMATION POSSIBLE
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MAJOR DIFFERENCE BETWEEN MAJOR DIFFERENCE BETWEEN AIR MASS AND SEVERE AIR MASS AND SEVERE
THUNDERSTORMSTHUNDERSTORMS Air Mass Thunderstorms go through Air Mass Thunderstorms go through
three lifecycle stages in approximately three lifecycle stages in approximately one hourone hour– Updrafts cut off by downdraftsUpdrafts cut off by downdrafts
Severe Thunderstorms last for hoursSevere Thunderstorms last for hours– Tilted updrafts and downdrafts.Tilted updrafts and downdrafts.– Updrafts and downdrafts do not interfere Updrafts and downdrafts do not interfere
with each otherwith each other
TILTED UPDRAFTS IN A SEVERE TILTED UPDRAFTS IN A SEVERE THUNDERSTORMTHUNDERSTORM
A. Anvil Head
B. Overshooting top
C. Mammatus clouds
D. Flanking line
E. Precipitation (rain/hail)
F. Funnel Cloud/tornado
G. Rain-free downdrafts
H. Gust Front
CHARACTERISTICS OF SEVERE CHARACTERISTICS OF SEVERE THUNDERSTORMSTHUNDERSTORMS
GUST FRONTSGUST FRONTS MICROBURSTSMICROBURSTS LIGHTNING AND THUNDERLIGHTNING AND THUNDER HAILHAIL WIND SHEARWIND SHEAR MAMMATUS CLOUDSMAMMATUS CLOUDS OVERSHOOTING TOPOVERSHOOTING TOP MESOCYCLONEMESOCYCLONE TORNADOTORNADO
GUST FRONTS AND GUST FRONTS AND MICROBURSTSMICROBURSTS
Gust Fronts are a boundary that separates the cold Gust Fronts are a boundary that separates the cold downdrafts from the warm updrafts.downdrafts from the warm updrafts.– Act as a ‘wedge’ to push up warm air – producing more growth Act as a ‘wedge’ to push up warm air – producing more growth
for stormsfor storms Microbursts are localized downdrafts of air (about 4 Microbursts are localized downdrafts of air (about 4
km wide) that hit the ground and spread out km wide) that hit the ground and spread out horizontallyhorizontally– Windspeeds of 75 m/sec (~168 mph)Windspeeds of 75 m/sec (~168 mph)– May evolve into gust frontsMay evolve into gust fronts– Responsible for knocking down trees and associated with Responsible for knocking down trees and associated with
damage usually attributed to tornadoesdamage usually attributed to tornadoes– Responsible for several airline crashes on approach to Responsible for several airline crashes on approach to
landing:landing: 1982 727 in New Orleans, Louisiana1982 727 in New Orleans, Louisiana 1985 L1011 in Dallas-Forth Worth1985 L1011 in Dallas-Forth Worth
DOPPLER RADAR AND MICROBURSTSDOPPLER RADAR AND MICROBURSTS
Terminal Doppler Terminal Doppler Weather Radar (TDWR)Weather Radar (TDWR) is is located in 47 areas in the located in 47 areas in the United States. United States.
A big feature of A big feature of TDWRTDWR is is that it can actually look that it can actually look inside storms and measure inside storms and measure dangerous wind shifts, dangerous wind shifts, such as those linked to such as those linked to wind shear and tornadoes, wind shear and tornadoes, which pose a threat to which pose a threat to aircraft during take-off and aircraft during take-off and landing. landing.
LIGHTNINGLIGHTNING Lightning Lightning
– Produces temperatures ~54,000Produces temperatures ~54,00000FF– A response to Electric Potential Gradient within Cb A response to Electric Potential Gradient within Cb
clouds: 3 million volts/meter along 50 meter pathclouds: 3 million volts/meter along 50 meter path 100,000 amperes100,000 amperes
– Warmer cloud bases (with more liquid droplets) is Warmer cloud bases (with more liquid droplets) is slightly negatively charged.slightly negatively charged.
– Colder cloud tops (with more solid ‘crystals’) is Colder cloud tops (with more solid ‘crystals’) is slightly positively charged.slightly positively charged.
– Particles falling through cloud become ‘electrically Particles falling through cloud become ‘electrically charged’charged’
– Cloud-to-cloud lightning more common that cloud-Cloud-to-cloud lightning more common that cloud-to-groundto-ground
LIGHTNINGLIGHTNING Electrons rush to cloud base along Electric Electrons rush to cloud base along Electric
Potential GradientPotential Gradient Stepped LeaderStepped Leader: electrons descending from : electrons descending from
base of cloud – hesitant – 50 -100 meters at a base of cloud – hesitant – 50 -100 meters at a time (seeking ‘fastest’ path to surface)time (seeking ‘fastest’ path to surface)
Return StrokeReturn Stroke: positive charges rush up to : positive charges rush up to meet descending electrons – ‘FLASH!!’ – path meet descending electrons – ‘FLASH!!’ – path is complete and energy flows up to the cloudis complete and energy flows up to the cloud
Dart LeadersDart Leaders: subsequent lightning strokes : subsequent lightning strokes generally follow same original path – only generally follow same original path – only faster now that there is less resistance!faster now that there is less resistance!
THUNDERTHUNDER
Superheated air (54,000Superheated air (54,00000F) rapidly expands the F) rapidly expands the lightning channel (‘path) at 1100 feet/sec (~700 lightning channel (‘path) at 1100 feet/sec (~700 mph) – SPEED OF SOUND!mph) – SPEED OF SOUND!
Sound travels approximately 1 mile in 5 Sound travels approximately 1 mile in 5 secondsseconds
Closer to lightning: thunder is a ‘cracking’ or Closer to lightning: thunder is a ‘cracking’ or ‘clapping’ sound‘clapping’ sound
Farther from lightning: thunder is a ‘rumbling’ Farther from lightning: thunder is a ‘rumbling’ soundsound
HAILHAIL
Hail is a multi-layered ice ball thrown from top, Hail is a multi-layered ice ball thrown from top, side, bottom of Cb clouds.side, bottom of Cb clouds.
Layers form when a very tiny object (leaf, ice Layers form when a very tiny object (leaf, ice crystal, insect) is caught in a strong updraft crystal, insect) is caught in a strong updraft
Freezing on the way to top of cloud, melting Freezing on the way to top of cloud, melting and colliding with liquid droplets on the way and colliding with liquid droplets on the way down.down.
Multiple ‘elevator rides’ builds many layers of Multiple ‘elevator rides’ builds many layers of ice until Hail is too heavy to be lifted by ice until Hail is too heavy to be lifted by updraftsupdrafts
WIND SHEARWIND SHEAR Wind Shear is the Wind Shear is the
change in wind change in wind speed or wind speed or wind direction with direction with increasing height increasing height above the Earth’s above the Earth’s surface.surface.
This is most This is most commonly seen commonly seen in Cb cloudsin Cb clouds
OVERSHOOTING TOP AND OVERSHOOTING TOP AND MAMMATUS CLOUDSMAMMATUS CLOUDS
Overshooting Tops: develop if the Overshooting Tops: develop if the energy within the Cb is extremely strong energy within the Cb is extremely strong and updrafts can push up above the and updrafts can push up above the anvil head.anvil head.
Mammatus clouds: pouch-like structures Mammatus clouds: pouch-like structures that hang inverted from a cloud base, or that hang inverted from a cloud base, or the base of an anvil headthe base of an anvil head– Associated with Cb that produce tornadoesAssociated with Cb that produce tornadoes
Overshooting Top in Cb
Mammatus clouds
OVERSHOOTING TOPSOVERSHOOTING TOPS
MESOCYCLONE – TORNADO MESOCYCLONE – TORNADO BEGINNINGSBEGINNINGS
Mesocyclones are rising and spinning Mesocyclones are rising and spinning columns of air within a Cb cloudcolumns of air within a Cb cloud
They can be 5-10 km across and extend They can be 5-10 km across and extend to the top of the Cb – sometimes to the top of the Cb – sometimes producing the overshooting top.producing the overshooting top.
Precursor to a funnel cloud dropping Precursor to a funnel cloud dropping from base of cloud to become a tornadofrom base of cloud to become a tornado
TORNADOESTORNADOES Tornadoes are rapidly rotating winds with intense Tornadoes are rapidly rotating winds with intense
central low air pressurecentral low air pressure Wind rotation speeds up to 230 mphWind rotation speeds up to 230 mph Counterclockwise rotation (Northern or Southern Counterclockwise rotation (Northern or Southern
Hemisphere)Hemisphere)– Coriolis Force Coriolis Force notnot a factor in rotation a factor in rotation
First indicators:First indicators:– Overshooting top (indicative of possible mesocyclone)Overshooting top (indicative of possible mesocyclone)– Wall cloud descends below base of cloud and slowly rotatesWall cloud descends below base of cloud and slowly rotates– Funnel cloud descends from wall cloudFunnel cloud descends from wall cloud– Tornado: not termed tornado until funnel cloud touches Tornado: not termed tornado until funnel cloud touches
groundground
Tornado in the United StatesTornado in the United StatesTornado AlleyTornado Alley
Tornadoes in United States most common across the Tornadoes in United States most common across the Midwest region from Texas to North Dakota – Midwest region from Texas to North Dakota – Tornado Tornado AlleyAlley
Average transit speed for tornadoes in this region is Average transit speed for tornadoes in this region is 20-40 knots 20-40 knots
Average direction from southwest to northeast Average direction from southwest to northeast following collision zone between mT air mass from following collision zone between mT air mass from Gulf of Mexico and cP air mass from Canada.Gulf of Mexico and cP air mass from Canada.– Collision zone shifts seasonallyCollision zone shifts seasonally
Largest Occurrence: SpringLargest Occurrence: Spring Lowest Occurrence: WinterLowest Occurrence: Winter
COLLISION ZONE BETWEEN mT AND cP AIR MASSES
Average number of tornadoes per 26,000 square km (10,000 sq miles)
Seasonal march of peak tornado activity
TORNADO LIFECYCLE STAGESTORNADO LIFECYCLE STAGES Stage 1: Dust whirlStage 1: Dust whirl
– Circulation of air on ground with funnel cloud extensionCirculation of air on ground with funnel cloud extension Stage 2: Organizing StageStage 2: Organizing Stage
– Funnel cloud continues droppingFunnel cloud continues dropping– Wind rotation speed increasingWind rotation speed increasing
Stage 3: Mature StageStage 3: Mature Stage– Funnel cloud at greatest widthFunnel cloud at greatest width– Wind rotation speed increasingWind rotation speed increasing– Funnel cloud on groundFunnel cloud on ground
Stage 4: Shrinking StageStage 4: Shrinking Stage– Funnel cloud ‘shrinks’ in diameter – increasing wind rotation Funnel cloud ‘shrinks’ in diameter – increasing wind rotation
speed to maximumspeed to maximum– Most dangerous stageMost dangerous stage
Stage 5: Decay StageStage 5: Decay Stage– Funnel cloud takes on a ‘ropey’ look – no longer vertical below Funnel cloud takes on a ‘ropey’ look – no longer vertical below
cloud basecloud base– Final stage for tornado: dissipates or is pulled back into cloudFinal stage for tornado: dissipates or is pulled back into cloud
Wall cloud
1st Stage Dust Whirl
3rd Stage: Mature
2nd Stage: Organizing
4th Stage: Shrinking
5th Stage: Decay Stage
Fujita Scale – Measuring tornadoesFujita Scale – Measuring tornadoes Measuring intensities of tornadoes based on Measuring intensities of tornadoes based on
a scale developed by Dr. Theodore Fujita, a scale developed by Dr. Theodore Fujita, University of Chicago (1960s)University of Chicago (1960s)
F0 – F5: F0 is the weakest and F5 is the F0 – F5: F0 is the weakest and F5 is the most violent possiblemost violent possible
HURRICANE KATRINA, AUGUST 2005HURRICANE KATRINA, AUGUST 2005
HURRICANESHURRICANES Largest of mid-latitude cyclonesLargest of mid-latitude cyclones
– A collection of large tropical thunderstorms rotating about a central low air A collection of large tropical thunderstorms rotating about a central low air pressurepressure
– Cyclones in Indian Ocean, Typhoons in Eastern PacificCyclones in Indian Ocean, Typhoons in Eastern Pacific– Last several weeks over open oceansLast several weeks over open oceans
Most destructive of all storm systemsMost destructive of all storm systems– Winds of 120 km/hour and higherWinds of 120 km/hour and higher
Size can be 220-700 km in diameterSize can be 220-700 km in diameter Northern Hemisphere Hurricane Season: June through November Northern Hemisphere Hurricane Season: June through November OrganizationOrganization
– Energy: Release of latent heat from transfer of sensible heat from warm Energy: Release of latent heat from transfer of sensible heat from warm tropical ocean to atmospheretropical ocean to atmosphere
– Unstable air aloft: cold upper air trough with diverging airUnstable air aloft: cold upper air trough with diverging air– Upper air divergence greater than lower atmosphere air convergenceUpper air divergence greater than lower atmosphere air convergence
Northern Hemisphere: surface convergence of air results in counterclockwise Northern Hemisphere: surface convergence of air results in counterclockwise rotation of air about Lowrotation of air about Low
Diverging air aloft enhances surface Low pressure developmentDiverging air aloft enhances surface Low pressure development FormationFormation
– Over warm tropical water (sea surface temp of 25Over warm tropical water (sea surface temp of 2500C)C)– In regions with little to no surface winds: “doldrums”In regions with little to no surface winds: “doldrums”– Latitudinal range: 5Latitudinal range: 50 0 – 25– 250 0 North or South of equatorNorth or South of equator
not at equator – insufficient Coriolis Force to start rotationnot at equator – insufficient Coriolis Force to start rotation
HURRICANES NEED WARM HURRICANES NEED WARM TROPICAL WATERSTROPICAL WATERS
Hurricanes track with global winds and feed off Hurricanes track with global winds and feed off Coriolis Force effects on ocean currentsCoriolis Force effects on ocean currents
Hurricane Season in Northern Hemisphere
CHARACTERISTICS OF CHARACTERISTICS OF HURRICANESHURRICANES
Inflow and OutflowInflow and Outflow– Updrafts so strong, more air is escaping the top of the clouds than can be Updrafts so strong, more air is escaping the top of the clouds than can be
brought inbrought in Eye Wall and Eye Wall CloudsEye Wall and Eye Wall Clouds
– Ring of violent super-cell Thunderstorms at the center of hurricaneRing of violent super-cell Thunderstorms at the center of hurricane– Tornadoes can be spawned hereTornadoes can be spawned here
EyeEye– Central low air pressure of hurricaneCentral low air pressure of hurricane– Region of relatively clear skies and calm windsRegion of relatively clear skies and calm winds– Air descending: compressional heating of air even though central air Air descending: compressional heating of air even though central air
pressure continues to droppressure continues to drop Storm SurgeStorm Surge
– Hurricane pulls up ocean water (“lifts the surface”) an average of 1cm for Hurricane pulls up ocean water (“lifts the surface”) an average of 1cm for each 1mb drop in pressureeach 1mb drop in pressure
– Regions along shores and coasts are inundated with water being pushed Regions along shores and coasts are inundated with water being pushed ahead of the hurricane, by intense precipitation and, sometimes, even ahead of the hurricane, by intense precipitation and, sometimes, even excessively high tides.excessively high tides.
outflowoutflow
inflow inflowEYE
Eyewall clouds Eyewall clouds
Storm SurgeStorm Surge
Storm Surge: Hurricane Katrina
HURRICANE DAMAGEHURRICANE DAMAGE
High winds are a primary cause of High winds are a primary cause of hurricane-inflicted loss of life and property hurricane-inflicted loss of life and property damage.damage.
A second cause is the flooding resulting A second cause is the flooding resulting from the coastal storm surge of the ocean from the coastal storm surge of the ocean and the torrential rains, both of which and the torrential rains, both of which accompany the storm.accompany the storm.
Wind Damage: Hurricane Katrina
Flood Damage: Hurricane Katrina
HURRICANE DEVELOPMENTHURRICANE DEVELOPMENT Tropical DisturbanceTropical Disturbance
– Mass of thunderstorms beginning to organizeMass of thunderstorms beginning to organize– Light wind circulationLight wind circulation
Tropical DepressionTropical Depression– Wind speed 20-34 knots (1 knot = 1.15mph)Wind speed 20-34 knots (1 knot = 1.15mph)– Central low pressure developing with rotation of thunderstormsCentral low pressure developing with rotation of thunderstorms
Tropical StormTropical Storm– 35-64 knots35-64 knots– Strong central low pressureStrong central low pressure– Increasing wind speedsIncreasing wind speeds– Forward movement across oceansForward movement across oceans
HurricaneHurricane– 64 knots64 knots– Well-development central low pressure: eye may be visibleWell-development central low pressure: eye may be visible– Moving to west along with global winds: NE or SE Trades, usually Moving to west along with global winds: NE or SE Trades, usually – Can move up to 50knots over open oceanCan move up to 50knots over open ocean– Highest wind speed on the ‘forward’ traveling sideHighest wind speed on the ‘forward’ traveling side
MEASURING HURRICANES MEASURING HURRICANES INTENSITYINTENSITY
Saffir-Simpson ScaleSaffir-Simpson Scale Measures the drop in central low air Measures the drop in central low air
pressure and the corresponding pressure and the corresponding increase in wind speedsincrease in wind speeds..
NAMING HURRICANESNAMING HURRICANES
Initial tracking of hurricane was by latitude and Initial tracking of hurricane was by latitude and longitude of origination.longitude of origination.– Too complicated since hurricanes move!Too complicated since hurricanes move!
World War II – use of military terms to identify World War II – use of military terms to identify individual hurricanesindividual hurricanes– Alpha, Bravo, Tango, etcAlpha, Bravo, Tango, etc
Early 1950s – use of female namesEarly 1950s – use of female names Late 1970s (post Women’s Lib movement) – Late 1970s (post Women’s Lib movement) –
Male and Female names are usedMale and Female names are used– Alternate male/female name for Pacific or Atlantic Alternate male/female name for Pacific or Atlantic
hurricaneshurricanes
HURRICANE NAMES: 2011 2011 Hurricane Names Arlene
BretCindyDonEmilyFranklinGertHarveyIreneJoseKatiaLeeMariaNateOpheliaPhilippeRinaSeanTammyVinceWhitney
HURRICANE DISSIPATIONHURRICANE DISSIPATION
Hurricanes need a constant source of warm, Hurricanes need a constant source of warm, humid airhumid air
If the hurricane travels over colder water, it If the hurricane travels over colder water, it will lose its source of energy: latent heatwill lose its source of energy: latent heat
If the hurricane travels over land, it will lose If the hurricane travels over land, it will lose its source of energy and encounter frictionits source of energy and encounter friction
DIFFERENCES BETWEEN DIFFERENCES BETWEEN HURRICANES AND OTHER MID-HURRICANES AND OTHER MID-
LATITUDE STORMSLATITUDE STORMS Energy sourcesEnergy sources
– Hurricanes need warm ocean water and release of latent heatHurricanes need warm ocean water and release of latent heat– Mid-latitude storms depend on temperature differences Mid-latitude storms depend on temperature differences
between contrasting air massesbetween contrasting air masses IntensityIntensity
– Hurricanes actually become weaker with higher altitudes Hurricanes actually become weaker with higher altitudes above the surfaceabove the surface
– Mid-latitude storms become stronger with higher altitudes Mid-latitude storms become stronger with higher altitudes above the surfaceabove the surface
CentersCenters– Hurricanes have a central column of warm descending air Hurricanes have a central column of warm descending air
(even with intensely low air pressure) which creates an ‘eye’(even with intensely low air pressure) which creates an ‘eye’– Mid-latitudes storms tend to have central columns of cool to Mid-latitudes storms tend to have central columns of cool to
cold air being forced to rise by dynamic low air pressure cold air being forced to rise by dynamic low air pressure processes in the upper atmosphere and they do not produce processes in the upper atmosphere and they do not produce an “eye”an “eye”