(ET) Streamline Configurations

(ET) Streamline Configurations(ET) Streamline Configurations

C

H H

C

HH

H

TradewindTradewindTroughTroughTradewindTradewindTroughTrough

MonsoonMonsoonTroughTroughMonsoonMonsoonTroughTrough

ConfluentConfluentWesterliesWesterliesConfluentConfluentWesterliesWesterlies

(ET) Streamline Configurations(ET) Streamline Configurations

C

H H

C

HH

H

TradewindTradewindTroughTroughTradewindTradewindTroughTrough

MonsoonMonsoonTroughTroughMonsoonMonsoonTroughTrough

ConfluentConfluentWesterliesWesterliesConfluentConfluentWesterliesWesterlies

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Diurnal EffectsDiurnal EffectsDiurnal EffectsDiurnal Effects

Temperature RangeTemperature RangeCloudsCloudsRainfallRainfall

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Diurnal EffectsDiurnal EffectsDiurnal EffectsDiurnal Effects

Temperature RangeTemperature Range– On small islands and coastlines 3-5°C On small islands and coastlines 3-5°C

with prevailing onshore flow.with prevailing onshore flow.– On inland locations or coasts 5-10°C On inland locations or coasts 5-10°C

with prevailing land breeze.with prevailing land breeze.– In the interior in the dry season > 10°C.In the interior in the dry season > 10°C.

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Diurnal EffectsDiurnal EffectsDiurnal EffectsDiurnal Effects

CloudsClouds–Oceans Oceans

Maximum (0400-0700L), Maximum (0400-0700L), minimum (1400L-1900L)minimum (1400L-1900L)

–Land Land Daytime maximum, Daytime maximum,

nocturnal minimumnocturnal minimum

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Diurnal EffectsDiurnal EffectsDiurnal EffectsDiurnal Effects

RainfallRainfall

– Nocturnal max over oceans, and Nocturnal max over oceans, and small islands.small islands.

– Shower maximum over land in Shower maximum over land in afternoon.afternoon.

– Monsoon areas and areas in Monsoon areas and areas in disturbances have night to early disturbances have night to early morning maximum.morning maximum.

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Tertiary CirculationsTertiary Circulations

Land and sea breezesLand and sea breezes– Sea-breeze characteristics.Sea-breeze characteristics.

Sets up a few hours after sunrise.Sets up a few hours after sunrise. Moves inland until late afternoon to evening.Moves inland until late afternoon to evening. Strong breezes may extend 30 - 50 miles inland.Strong breezes may extend 30 - 50 miles inland.

– Land-breeze characteristics.Land-breeze characteristics. Generally shallower with weaker winds than sea breeze.Generally shallower with weaker winds than sea breeze. Normally does not penetrate as far offshore as sea breeze Normally does not penetrate as far offshore as sea breeze

penetrates onshore.penetrates onshore. Land breeze front often triggers convection, especially Land breeze front often triggers convection, especially

converging land breezesconverging land breezes

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Prevailing flow onshore:Prevailing flow onshore:

Rainfall - Special CasesRainfall - Special Cases

Day

Night

Daytime max on inlandDaytime max on inlandslopesslopes

Nighttime max on coastlineNighttime max on coastline

Prevailing flow offshorePrevailing flow offshoreAfternoon max onAfternoon max oncoastlinecoastline

Sea BreezeSea Breeze

Land BreezeLand Breeze

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Sea Breeze

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Sea BreezeSea Breeze

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Land BreezeLand Breeze

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Tertiary CirculationsTertiary CirculationsTertiary CirculationsTertiary Circulations

Orographically-induced winds.Orographically-induced winds.– Valley breeze.Valley breeze.

Slopes warm during day.Slopes warm during day. Upslope wind.Upslope wind. Clouds and convection over peaks during daytime.Clouds and convection over peaks during daytime.

– Mountain breeze.Mountain breeze. Slopes cool at night.Slopes cool at night. Downslope wind.Downslope wind. Clouds and convection in valleys at night.Clouds and convection in valleys at night.

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Tertiary CirculationsTertiary CirculationsTertiary CirculationsTertiary Circulations

Orographically-induced winds.Orographically-induced winds.– Mountain gap winds.Mountain gap winds.

Funneling through passes when surface gradient Funneling through passes when surface gradient across mountains is strong.across mountains is strong.

Example: Tehuantepecer winds off Mexico.Example: Tehuantepecer winds off Mexico.

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TehuantepecersTehuantepecers

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TehuantepecersTehuantepecers

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Tehuantepecers

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Tropical Upper-Tropospheric Trough Tropical Upper-Tropospheric Trough (TUTT)(TUTT)

Forms in summer hemisphere over mid-oceans.Forms in summer hemisphere over mid-oceans. Subtropical ridge - part that moves Subtropical ridge - part that moves

poleward over land masses (North America, poleward over land masses (North America, eastern Asia).eastern Asia).

Subequatorial ridge - part that stays near Subequatorial ridge - part that stays near equator over the ET.equator over the ET.

Upper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric Features

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Tropical Upper-Tropospheric Trough Tropical Upper-Tropospheric Trough (TUTT) - Continued -(TUTT) - Continued -

Level: Most intense - 200 mb.Level: Most intense - 200 mb.

Orientation: ENE-WSWOrientation: ENE-WSW

Season: Late April - Mid November (most Season: Late April - Mid November (most intense in Augustintense in August

Upper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric Features

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Tropical Upper-Tropospheric Trough Tropical Upper-Tropospheric Trough (TUTT) - Continued -(TUTT) - Continued -

Position: South of Surface Subtropical Position: South of Surface Subtropical Ridge over trade winds (convergent weather Ridge over trade winds (convergent weather associated with TUTT occurs in tradewinds) associated with TUTT occurs in tradewinds)

Major Convergent Weather: Few degrees Major Convergent Weather: Few degrees southeast of upper level centersoutheast of upper level center

Weather in axis or Cyclonic Cell Center: Weather in axis or Cyclonic Cell Center: Few clouds, general sinking motion Few clouds, general sinking motion

Upper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric Features

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Tropical Upper-Tropospheric Trough Tropical Upper-Tropospheric Trough (TUTT) - Continued -(TUTT) - Continued -

Temperature: Cold trough (3-5 degrees Temperature: Cold trough (3-5 degrees colder than environment, Isold TCU and colder than environment, Isold TCU and TSTMs in TUTT, and center of cellsTSTMs in TUTT, and center of cells

Axis Windshift: Often an abrupt 180 Axis Windshift: Often an abrupt 180 degree turn at trough axisdegree turn at trough axis

Cirrus Tracers: Indicates Cirrus Tracers: Indicates >> 50 kts either 50 kts either side of TUTT or embedded cell.side of TUTT or embedded cell.

Upper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric FeaturesUpper-Tropospheric Features

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OverviewOverviewOverviewOverview Upper-Tropospheric cyclones (cold lows).Upper-Tropospheric cyclones (cold lows).

•Strongest 200 to 300 mb and weaken downward.Strongest 200 to 300 mb and weaken downward.•TUTT cells are most common examples.TUTT cells are most common examples.

•CenterCenter•Usually clear due to subsidence, though deep cold Usually clear due to subsidence, though deep cold cells can have some core convection.cells can have some core convection.

•Periphery Periphery •Upper-level divergence, mostly SE side. Upper-level divergence, mostly SE side.

•Satellite ImagerySatellite Imagery•Ring of clouds about 140 nm from center.Ring of clouds about 140 nm from center.•Dark round area on water vapor image (best seen in Dark round area on water vapor image (best seen in water vapor!).water vapor!).

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TUTT CellTUTT Cell

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TUTT cellTUTT cell

<------TUTT cell<------TUTT cell

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TUTT Cell------>TUTT Cell------>

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TUTT Cell------>TUTT Cell------>

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TUTT Cell ---------->TUTT Cell ---------->

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TUTT Cell ----------->TUTT Cell ----------->

in Multispectral Imageryin Multispectral Imagery

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NOGAPS 200 mb NOGAPS 200 mb temperaturestemperatures

<-----Trough<-----Trough

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Non-severe Weather Systems Non-severe Weather Systems and Tertiary Circulationsand Tertiary Circulations

Non-severe Weather Systems Non-severe Weather Systems and Tertiary Circulationsand Tertiary Circulations

•LinesLines•Tropical WavesTropical Waves•VorticesVortices•Land and Sea BreezesLand and Sea Breezes•Valley and Mountain BreezesValley and Mountain Breezes

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Non-severe LinesNon-severe Lines

Lines - Lines - synoptic scale convergence with synoptic scale convergence with length much greater than width.length much greater than width.

– Squall lines Squall lines

– Cold frontsCold fronts

– Shear linesShear lines

– Surge LinesSurge Lines

– Near Equatorial Convergence ZonesNear Equatorial Convergence Zones

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Shear LineShear Line

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Non-Severe Tropical WavesNon-Severe Tropical Waves

National Hurricane Center (NHC) National Hurricane Center (NHC) definition - a trough or cyclonic curvature definition - a trough or cyclonic curvature maximum in the trade-wind easterlies.maximum in the trade-wind easterlies.

Sometimes called “Tropical Easterly Sometimes called “Tropical Easterly Waves” in the Atlantic.Waves” in the Atlantic.

Originally, this term was based on older Originally, this term was based on older research on the tropics that was based on research on the tropics that was based on sparse surface and upper air data. sparse surface and upper air data.

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Non-Severe Tropical WavesNon-Severe Tropical Waves When NHC started using METSAT imagery When NHC started using METSAT imagery

in 1967, they saw new aspects of the so-called in 1967, they saw new aspects of the so-called “wave” that didn’t fit the theoretical model.“wave” that didn’t fit the theoretical model.

Not as common as previously thought; many Not as common as previously thought; many systems called waves were actually vortices systems called waves were actually vortices

This model is falling out of favor with many This model is falling out of favor with many in the tropical community.in the tropical community.

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TheThe““Tropical Easterly Wave”Tropical Easterly Wave”

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Non-Severe Tropical WavesNon-Severe Tropical WavesNon-Severe Tropical WavesNon-Severe Tropical Waves

CharacteristicsCharacteristics– Many stem from upper-level cyclones (cold Many stem from upper-level cyclones (cold

lows).lows).– Characteristics of Atlantic (easterly) waves.Characteristics of Atlantic (easterly) waves.

Form over Ethiopian Highlands June to October.Form over Ethiopian Highlands June to October. Move across baroclinic zone south of Sahara - Move across baroclinic zone south of Sahara -

often form squall lines.often form squall lines. Dampen under STR axis in eastern Atlantic and Dampen under STR axis in eastern Atlantic and

strengthen near Lesser Antilles.strengthen near Lesser Antilles.

40Inverted “Vee” or Screaming Eagle - really a circulationInverted “Vee” or Screaming Eagle - really a circulation

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Screaming EagleScreaming Eagle

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Non-Severe VorticesNon-Severe VorticesNon-Severe VorticesNon-Severe Vortices

Fair weather vortices - Fair weather vortices - (Equatorial (Equatorial anticyclone, heat low, and TUTT)…anticyclone, heat low, and TUTT)…

Bad weather vortices - Bad weather vortices - (Tropical cyclones, (Tropical cyclones, monsoon depression, west African cyclones, monsoon depression, west African cyclones, and mid Tropospheric cyclones).and mid Tropospheric cyclones).

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Fair Weather VorticesFair Weather VorticesFair Weather VorticesFair Weather Vortices

Equatorial anticyclonesEquatorial anticyclones– Found where monsoon trough is more than Found where monsoon trough is more than

10° from equator10° from equator– Surge from opposite hemisphere crosses Surge from opposite hemisphere crosses

equator and turns anticyclonicallyequator and turns anticyclonically– Curved band of cloud seen at leading edge Curved band of cloud seen at leading edge

of anticycloneof anticyclone

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Fair Weather VorticesFair Weather VorticesFair Weather VorticesFair Weather Vortices

Heat lows/ heat troughsHeat lows/ heat troughs– Low-level air rises over hot land with Low-level air rises over hot land with

subsidence aloft.subsidence aloft.– Lowest pressure coincides with highest Lowest pressure coincides with highest

temperature.temperature.– ExamplesExamples

Sahara and SW Asia in summer (may be part of Sahara and SW Asia in summer (may be part of monsoon trough).monsoon trough).

Southern South America, southern and eastern Southern South America, southern and eastern Africa all year.Africa all year.

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Bad Weather VorticesBad Weather Vortices

Mid-tropospheric cyclones.Mid-tropospheric cyclones.– Subtropical cyclones.Subtropical cyclones.

Cut-off portion of deep mid-latitude trough in Cut-off portion of deep mid-latitude trough in the tropics in winter.the tropics in winter.

Example: "Kona" storms in Hawaii, cause SW Example: "Kona" storms in Hawaii, cause SW winds and heavy rains.winds and heavy rains.

– Arabian Sea cyclonesArabian Sea cyclones Major rainmaker on west coast of India in SW Major rainmaker on west coast of India in SW

monsoon. monsoon. Cloud pattern resembles a typhoon.Cloud pattern resembles a typhoon.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Regional Effects Regional Effects Region normally dominated by NE trade windsRegion normally dominated by NE trade winds..

– Channeling causes 3 quasi stationary cyclones Channeling causes 3 quasi stationary cyclones on Pacific side of Central America which on Pacific side of Central America which anchor monsoon trough.anchor monsoon trough.

– Northern Hemisphere easterlies to north and Northern Hemisphere easterlies to north and Southern Hemisphere westerlies to south Southern Hemisphere westerlies to south maintain cyclones.maintain cyclones.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Panama Bay cyclonePanama Bay cyclone Strongest anchoring cyclone of the three.Strongest anchoring cyclone of the three.

– Reinforced by warm ocean currents.Reinforced by warm ocean currents.

– Southwesterly flow channeled cyclonically by Southwesterly flow channeled cyclonically by Andes year-round.Andes year-round.

– Persistent feature May through January.Persistent feature May through January.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Lake Nicaragua cycloneLake Nicaragua cyclone Anchored between Nicaragua and Costa Rica.Anchored between Nicaragua and Costa Rica. Weaker than Panama bay cyclone, persists May - Weaker than Panama bay cyclone, persists May -

November. November.

Gulf of Tehuantepec (Guatemalan) cyclone.Gulf of Tehuantepec (Guatemalan) cyclone. Weakest of the three.Weakest of the three. Maximum strength in OctoberMaximum strength in October Merges with NECZ to west, which is anchored over Merges with NECZ to west, which is anchored over

SST thermal maximum.SST thermal maximum.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

American Monsoons don't meet Ramage's American Monsoons don't meet Ramage's Criteria becauseCriteria because

Semi-annually reversing North-South pressure gradients do Semi-annually reversing North-South pressure gradients do not form.not form.

– Instead, Central America has a "transitional" Instead, Central America has a "transitional" monsoon.monsoon.

Oscillates north - south semiannually.Oscillates north - south semiannually. Location determined by strengths of NE trades and Location determined by strengths of NE trades and

Southern Hemisphere southwesterlies.Southern Hemisphere southwesterlies.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Monsoon SurgesMonsoon Surges– Often caused by low-latitude (10 - 20°N) Often caused by low-latitude (10 - 20°N)

tropical cyclones.tropical cyclones. Acceleration of southwesterlies from south of Acceleration of southwesterlies from south of

monsoon trough.monsoon trough.

NE flow aloft back into Southern Hemisphere.NE flow aloft back into Southern Hemisphere.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Monsoon Surges (Con’t)Monsoon Surges (Con’t) Atemporalado IndexAtemporalado Index

– ““Atemporalado”: term used to describe a winter Atemporalado”: term used to describe a winter rain event in Central America due to a vogorous rain event in Central America due to a vogorous cold front or shear line that crosses far enough cold front or shear line that crosses far enough south.south.

– Often results in Tehuanapecers.Often results in Tehuanapecers.

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The Central American MonsoonsThe Central American MonsoonsThe Central American MonsoonsThe Central American Monsoons

Monsoon Surges (Con’t)Monsoon Surges (Con’t) Rule of Thumb:Rule of Thumb:

Take SLP difference (Take SLP difference (P) between Merida P) between Merida Mexico and Houston TX. Mexico and Houston TX.

• If If P < 12 MB, no SURGEP < 12 MB, no SURGE

• If If P 12-14 MB, marginal SURGEP 12-14 MB, marginal SURGE

• If If P 15-19 MB, Nominal SURGEP 15-19 MB, Nominal SURGE

• If If P >20 MB, P >20 MB, STRONGSTRONG SURGE SURGE

53SurgeSurge

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Severe Weather In The TropicsSevere Weather In The TropicsSevere Weather In The TropicsSevere Weather In The Tropics

•Severe ThunderstormsSevere Thunderstorms•Non-Convective WindsNon-Convective Winds

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ThunderstormsThunderstormsThunderstormsThunderstorms

More common in tropics than in high More common in tropics than in high latitudeslatitudes

82 % of thunderstorms are over South 82 % of thunderstorms are over South America, Africa, and IndonesiaAmerica, Africa, and Indonesia

18% of thunderstorms are over water18% of thunderstorms are over water Most are not severe by mid-latitude Most are not severe by mid-latitude

(midwest) standards(midwest) standards

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Severe ThunderstormsSevere ThunderstormsSevere ThunderstormsSevere Thunderstorms HailHail

– Rare in tropicsRare in tropics The typical WBZ in tropics above 12,000 ft The typical WBZ in tropics above 12,000 ft

and is usually over 15,000 ftand is usually over 15,000 ft Tornadoes and waterspoutsTornadoes and waterspouts

– Most common in the U.S. and AustraliaMost common in the U.S. and Australia.. LocationLocation

– Most severe storms occur when continental polar Most severe storms occur when continental polar air penetrates the tropics and squall lines or shear air penetrates the tropics and squall lines or shear lines developlines develop

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Severe ThunderstormsSevere ThunderstormsSevere ThunderstormsSevere Thunderstorms

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Bad Weather VorticesBad Weather VorticesBad Weather VorticesBad Weather Vortices

Monsoon depressionsMonsoon depressions– Hybrid mid-latitude/tropical cyclone over Bay of Hybrid mid-latitude/tropical cyclone over Bay of

Bengal in summer.Bengal in summer.

West African cyclones.West African cyclones.– Mid-level cyclones that form south of heat trough Mid-level cyclones that form south of heat trough

in western Africa.in western Africa.– Causes dense stratiform clouds near coast, Causes dense stratiform clouds near coast,

convective clouds and squall lines north.convective clouds and squall lines north.– Move west and weaken over Atlantic.Move west and weaken over Atlantic.

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Monsoon DepressionMonsoon Depression

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Monsoon DepressionMonsoon Depression

65Monsoon DepressionMonsoon Depression

66Monsoon DepressionMonsoon Depression

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Monsoon DepressionMonsoon Depression

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