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

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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

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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”