thunderstorms - incois scale : characteristics ... the tropics than in the extra tropics. • due to...
TRANSCRIPT
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Thunderstorms
Naresh Kumar
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Planetary scale : Characteristics horizontal length ~ 5000 km
Synoptic scale : Characteristics horizontal length ~ 1000 km
Meso-scale : Characteristics horizontal length ~ 100 km
Micro scale : Characteristics horizontal length ~ 1 km
Scales of systems (Space):
Planetary scale : Characteristics horizontal length ~ 5000 km
Synoptic scale : Characteristics horizontal length ~ 1000 km
Meso-scale : Characteristics horizontal length ~ 100 km
Micro scale : Characteristics horizontal length ~ 1 km
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Planetary scale : Characteristics horizontal length ~ 5 days ormore
Synoptic scale : Characteristics horizontal length ~ 1day
Meso-scale : Characteristics horizontal length ~ 5 hrs
Micro scale : Characteristics horizontal length ~ 10 minutes
In general, larger the horizontal length scale, longer is the timescale
Scales of systems (Time):Planetary scale : Characteristics horizontal length ~ 5 days ormore
Synoptic scale : Characteristics horizontal length ~ 1day
Meso-scale : Characteristics horizontal length ~ 5 hrs
Micro scale : Characteristics horizontal length ~ 10 minutes
In general, larger the horizontal length scale, longer is the timescale
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Hazardous weather
Synoptic scale systems in tropics derive most of their
energy through meso-scale systems
Difficult to capture with synoptic scale observations
Due to importance of meso-scale systems, international
efforts have been made for special studies
FDP STORM has been taken up by SAARC countries
Importance of Meso-scale systems Hazardous weather
Synoptic scale systems in tropics derive most of their
energy through meso-scale systems
Difficult to capture with synoptic scale observations
Due to importance of meso-scale systems, international
efforts have been made for special studies
FDP STORM has been taken up by SAARC countries
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Convection: Mesoscale in Nature
Horizontal scale of ~ 10 sq km
Vertical extent averaging ~ 15 km
Time scale of about 1-6 hr
It interact with large-scale flow results in the
development of mesoscale convective systems like
SEVERE THUNDERSTORMS and associated severe
weather phenomenon like HAIL STORMS, SQUALL &
Lightning.
Tropical Convection Convection: Mesoscale in Nature
Horizontal scale of ~ 10 sq km
Vertical extent averaging ~ 15 km
Time scale of about 1-6 hr
It interact with large-scale flow results in the
development of mesoscale convective systems like
SEVERE THUNDERSTORMS and associated severe
weather phenomenon like HAIL STORMS, SQUALL &
Lightning.
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Thunderstorm Moderate Thunderstorm
Loud peals of thunder withfrequent lightning flashes,moderate to heavy rains andmaximum wind speed 29 to 74kmph
Severe Thunderstorm :
Continuous thunder andlightning, heavy rains andmaximum wind speed ≥ 75 kmph
Moderate Thunderstorm
Loud peals of thunder withfrequent lightning flashes,moderate to heavy rains andmaximum wind speed 29 to 74kmph
Severe Thunderstorm :
Continuous thunder andlightning, heavy rains andmaximum wind speed ≥ 75 kmph
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These are the most violent convective systems in theatmosphere and are associated with cumulonimbus (Cb)cloud.
One of the ingredients needed for thunderstormdevelopment is moisture, preferably in the lower and midlevels.
Originate mainly over the heated land masses that heats upthe air mass above it and initiates convection.
In India, these thunderstorms reach severity whencontinental air meets warm moist air from ocean.
The eastern and north eastern part of the country getsaffected by severe thunderstorms mainly during April-May.
The presence of upper level shear adds severity to thestorm since it differentiates the zone of the updraft formthe zone of downdraft at this stage. It also extends the lifetime of the cell.
Thunderstorm These are the most violent convective systems in the
atmosphere and are associated with cumulonimbus (Cb)cloud.
One of the ingredients needed for thunderstormdevelopment is moisture, preferably in the lower and midlevels.
Originate mainly over the heated land masses that heats upthe air mass above it and initiates convection.
In India, these thunderstorms reach severity whencontinental air meets warm moist air from ocean.
The eastern and north eastern part of the country getsaffected by severe thunderstorms mainly during April-May.
The presence of upper level shear adds severity to thestorm since it differentiates the zone of the updraft formthe zone of downdraft at this stage. It also extends the lifetime of the cell.
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Squall
SQUALL: A sudden increase of wind speed by at least 29kmph(16 kts), the speed rising to 40 kmph (22 kts) or moreand lasting for at least one minute
Moderate: Surface wind speed ( in gusts) upto 80 kmph
Severe: Surface wind speed ( in gusts) > 80 kmph
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Win
d sp
eed
( kn
ot) R-29
R-27
R-11
Wind speed recorded at different Runways (R-29,R-27,R-11)during thunderstorm and squall on 22.10.2010.
Win
d sp
eed
( kn
ot)
Time (UTC)
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HailstormFrequency of
Hailstorms in 100years period
Slight Hailstorm :Sparse, usually small sizeand often mixed with rain
Moderate Hailstorm :Fall abundant enough towhiten ground
Heavy Hailstorm :Includes at least aproportion of large stones
Slight Hailstorm :Sparse, usually small sizeand often mixed with rain
Moderate Hailstorm :Fall abundant enough towhiten ground
Heavy Hailstorm :Includes at least aproportion of large stones
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Duststorms, which are raised dust in the air occur only inthe plains of Northwest India. Locally these are known as‘ANDHIS’.
Duststorm activity starts in April and continues up toJune. Their frequency of occurrence is at maximum inJune.
On a few occasions duststorms are followed bythundershowers.
Intense surface heating, western disturbances andwesterly trough are the causes of duststorms.
Duststorm Duststorms, which are raised dust in the air occur only in
the plains of Northwest India. Locally these are known as‘ANDHIS’.
Duststorm activity starts in April and continues up toJune. Their frequency of occurrence is at maximum inJune.
On a few occasions duststorms are followed bythundershowers.
Intense surface heating, western disturbances andwesterly trough are the causes of duststorms.
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Duststorms may be categorized into two types namely(i) The Pressure Gradient Type and (ii) The convective type. Pressure gradient type thunderstorm: When the seasonal low
pressure area over NW India becomes marked strong gradientbuilds up to the south of the low causing strong winds (about30 kts). These strong winds raise the dust particles in the airreducing the visibility below 1.0 km such pressure gradient typeduststorms occur frequently over Rajasthan in May and June. .
Convective type thunderstorm: It occurs in the later part ofthe day or night. In this type of duststorms the dust particlesare raised by the down draft winds of Cb-clouds in such casesthe dust particle may go up to a height of 2 to 3 kms.Convective type duststorms often go before thunderstorms.
DuststormDuststorms may be categorized into two types namely(i) The Pressure Gradient Type and (ii) The convective type. Pressure gradient type thunderstorm: When the seasonal low
pressure area over NW India becomes marked strong gradientbuilds up to the south of the low causing strong winds (about30 kts). These strong winds raise the dust particles in the airreducing the visibility below 1.0 km such pressure gradient typeduststorms occur frequently over Rajasthan in May and June. .
Convective type thunderstorm: It occurs in the later part ofthe day or night. In this type of duststorms the dust particlesare raised by the down draft winds of Cb-clouds in such casesthe dust particle may go up to a height of 2 to 3 kms.Convective type duststorms often go before thunderstorms.
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KALBAISAKHI / NORWESTERSThe eastern and northeastern parts of our country i.eGangetic West Bengal, Jharkahand, Bihar, Orissa, andStates in NE India get affected by severe thunderstormsduring pre-monsoon months of March to May.
These storms usually travel from northwest to southeastdirection and are called “Norwesters”. They are locallyknown as“Kalbaisakhi”.
These severe thunderstorms have very significant socio-economic importance for eastern and northeastern partsof the country.
The eastern and northeastern parts of our country i.eGangetic West Bengal, Jharkahand, Bihar, Orissa, andStates in NE India get affected by severe thunderstormsduring pre-monsoon months of March to May.
These storms usually travel from northwest to southeastdirection and are called “Norwesters”. They are locallyknown as“Kalbaisakhi”.
These severe thunderstorms have very significant socio-economic importance for eastern and northeastern partsof the country.
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Lightning
Source of lightning: the cumulonimbus cloud
• Collisions between supercooled cloud particlesand hail cause clouds to become charged
• Most of the base of the cumulonimbus cloudbecomes negatively charged – the restbecomes positively charged (positive electricdipole)
• Net transfer of positive ions from warmerobject to colder object (hailstone getsnegatively charged & fall toward bottom - icecrystals get + charge)
Lightning
Source of lightning: the cumulonimbus cloud
• Collisions between supercooled cloud particlesand hail cause clouds to become charged
• Most of the base of the cumulonimbus cloudbecomes negatively charged – the restbecomes positively charged (positive electricdipole)
• Net transfer of positive ions from warmerobject to colder object (hailstone getsnegatively charged & fall toward bottom - icecrystals get + charge)
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Development
of lightning
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The areas of highestactivity ofthunderstormsexceeding 120 days inthe year are seen overAssam, Sub HimalayanWest Bengal andwindward side of PirPanjal range in Jammuand Kashmir.
The occurrence ofthunderstorms is mainlycontrolled by the localorography.
Ajit Tyagi (2009), Mausam
The areas of highestactivity ofthunderstormsexceeding 120 days inthe year are seen overAssam, Sub HimalayanWest Bengal andwindward side of PirPanjal range in Jammuand Kashmir.
The occurrence ofthunderstorms is mainlycontrolled by the localorography.
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Country as a whole recordsthe lowest number ofthunderstorms during winterseason.
It is primarily due to stableand dry atmosphericconditions prevailing overmost parts of thesubcontinent with theexception of Srilanka andsouthern Kerala.
Highest frequency duringthis season is over Sri Lanka(16 days) associated withnortheast monsoon activity.
Second maxima (13 days) isseen over windward side ofPir panjal range over Jammuand adjoining region. Thismaxima isassociated with westerndisturbances.
Country as a whole recordsthe lowest number ofthunderstorms during winterseason.
It is primarily due to stableand dry atmosphericconditions prevailing overmost parts of thesubcontinent with theexception of Srilanka andsouthern Kerala.
Highest frequency duringthis season is over Sri Lanka(16 days) associated withnortheast monsoon activity.
Second maxima (13 days) isseen over windward side ofPir panjal range over Jammuand adjoining region. Thismaxima isassociated with westerndisturbances.
Ajit Tyagi (2009), Mausam
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Pre monsoon season ischaracterized by increase inthunderstorm activity over allparts of the country withsignificant increase overnortheast India, Bangladesh,West Bengal, southpeninsula and Jammu region.
Topography, insolation andadvection of moisture underfavourable wind regimecontribute tothunderstorm maxima overthese areas.
Synoptically, WesternDisturbances and induced lowsin the north and easterlywaves in south providefavourable conditionsfor the occurrence ofthunderstorm over these
Pre monsoon season ischaracterized by increase inthunderstorm activity over allparts of the country withsignificant increase overnortheast India, Bangladesh,West Bengal, southpeninsula and Jammu region.
Topography, insolation andadvection of moisture underfavourable wind regimecontribute tothunderstorm maxima overthese areas.
Synoptically, WesternDisturbances and induced lowsin the north and easterlywaves in south providefavourable conditionsfor the occurrence ofthunderstorm over these
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Country as awhole outsideKerala records
the highestfrequency of
thunderstormsduring monsoon
season.Availability ofmoisture and
favourablesynopticfeatures
contribute togeneral increaseof thunderstormactivity over all
parts of thecountry outside
Kerala. Thehighest
thunderstormactivity in the
countrycontinues to be
overnortheastern
states,Bangladesh,
West Bengal andadjoining states,
which recordmore than 50
days
Country as a wholerecords the highestfrequency ofthunderstorms duringmonsoon season.
Availability of moistureand favourable synopticfeatures contribute togeneral increase ofthunderstorm activityover all parts of thecountry outside Kerala.
The highestthunderstorm activity inthe country continues tobe over northeasternstates, Bangladesh, WestBengal and adjoiningstates, which recordmore than 50 days
Country as awhole outsideKerala records
the highestfrequency of
thunderstormsduring monsoon
season.Availability ofmoisture and
favourablesynopticfeatures
contribute togeneral increaseof thunderstormactivity over all
parts of thecountry outside
Kerala. Thehighest
thunderstormactivity in the
countrycontinues to be
overnortheastern
states,Bangladesh,
West Bengal andadjoining states,
which recordmore than 50
days
Country as a wholerecords the highestfrequency ofthunderstorms duringmonsoon season.
Availability of moistureand favourable synopticfeatures contribute togeneral increase ofthunderstorm activityover all parts of thecountry outside Kerala.
The highestthunderstorm activity inthe country continues tobe over northeasternstates, Bangladesh, WestBengal and adjoiningstates, which recordmore than 50 days
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After the withdrawal ofmonsoon, country outsideTamil Nadu coastal APand Kerala witnessesmarked decrease inthunderstorm activity.
Highest number ofthunderstorms duringthis season occur overKerala (20 to 25 days)whereas neighbouringstate Tamil Nadu hasfrequency of 10 to 15due to northeastmonsoon.
After the withdrawal ofmonsoon, country outsideTamil Nadu coastal APand Kerala witnessesmarked decrease inthunderstorm activity.
Highest number ofthunderstorms duringthis season occur overKerala (20 to 25 days)whereas neighbouringstate Tamil Nadu hasfrequency of 10 to 15due to northeastmonsoon.
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Socio-Economic Impact of SevereThunderstorm
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• Single cell
• Multi-cell cluster
• Multicell line (squall line)
• Super cell
Thunderstorm Type• Single cell
• Multi-cell cluster
• Multicell line (squall line)
• Super cell
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Single cell
• Short-lived afternoon summer TS. 30- 60 minute duration.• Usually not associated with tornado• Moves with mean environmental wind over 5-7 km.• Rainfall can be moderate to heavy, small hail is possible.• Vertical wind shear is small.• Updrafts cut off by downdrafts
Cumulus Stage Mature Stage Dissipating Stage
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CUMULUS STAGE
• Sun heats the land
• Warm, humid air rises
• Condensation point isreached, producing acumulus cloud
• Grows quickly (minutes)
because of the release of
latent heat
• Updrafts suspend droplets
• ‘Towering cumulus’
CUMULUS STAGE
• Sun heats the land
• Warm, humid air rises
• Condensation point isreached, producing acumulus cloud
• Grows quickly (minutes)
because of the release of
latent heat
• Updrafts suspend droplets
• ‘Towering cumulus’
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MATURE STAGE
• Droplets large enough toovercome resistance ofupdrafts (rain/hail)
• “Entrainment” Drier air isdrawn in
• Air descends in downdraft,due to evaporative coolingand falling rain/hail
• Anvil head when stable layerreached (cloud followshorizontal wind)
• Strongest stage, withlightning and thunder
MATURE STAGE
• Droplets large enough toovercome resistance ofupdrafts (rain/hail)
• “Entrainment” Drier air isdrawn in
• Air descends in downdraft,due to evaporative coolingand falling rain/hail
• Anvil head when stable layerreached (cloud followshorizontal wind)
• Strongest stage, withlightning and thunder
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Mature, ordinary cell thunderstorm with anvil head
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Microbursts create aviation hazards
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DISSIPATING STAGE
• Downdrafts dominate overUpdrafts and cut off thestorm’s “fuel supply”
• No warm humid rising air
• No more release in latentheat
• Precipitation continuous alongwith strong wind
• Ordinary cell thunderstormsmay pass through all threestages in only 60 minutes
DISSIPATING STAGE
• Downdrafts dominate overUpdrafts and cut off thestorm’s “fuel supply”
• No warm humid rising air
• No more release in latentheat
• Precipitation continuous alongwith strong wind
• Ordinary cell thunderstormsmay pass through all threestages in only 60 minutes
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Review of Stages:
Developing (cumulus), mature and
dissipating
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Multicell Thunderstorm
Sometimes thunderstorms form in clusters with many cellsin various stages of development merging together.
Unlike ordinary single cells, cluster storms can last forseveral hours producing large hail, damaging winds, andisolated tornadoes.
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Squall Line
• A squall line is any line of convective cells.• It may be a few tens of km long or 1000 km long (>500 nm);• The characteristic squall line life cycle is to evolve from a narrow band
of intense convective cells to a broader, weaker system over time• Stronger shear environments produce stronger long-lived lines composed
of strong leading line convective cells
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Favourable factors :
1. Intense heating
2. Moisture Incursion
3. Instability
4. Triggering Mechanism
Forecasting of Thunderstorm
Favourable factors :
1. Intense heating
2. Moisture Incursion
3. Instability
4. Triggering Mechanism
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When convective instability and liftingmechanism are present, convection is favoured.Following meso-scale phenomena provide thesefavourable conditions:
1.Upper level jets
2.Low level strong wind
3.Dry line
4.Meso-scale low pressure systems
5.Gravity waves
Forecasting of ThunderstormWhen convective instability and liftingmechanism are present, convection is favoured.Following meso-scale phenomena provide thesefavourable conditions:
1.Upper level jets
2.Low level strong wind
3.Dry line
4.Meso-scale low pressure systems
5.Gravity waves
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Forecasting of Thunderstorm Essential component of thunderstorm monitoring Monitoring of weather parameters Knowlwdge of synoptic systems to trigger
convection Climatology of weather parameters and synoptic
systems based on observations Thermodynamic indices (current value and
climatology)
Essential component of thunderstorm monitoring Monitoring of weather parameters Knowlwdge of synoptic systems to trigger
convection Climatology of weather parameters and synoptic
systems based on observations Thermodynamic indices (current value and
climatology)
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The shear perpendicular to the convective linesupports updraftMost important is the shear in the lowest layer
reaching from the surface up to 2-3 kmCells developing within strong vertical shear
have long lifetime and severe weatherMost intense thunderstorms develop when
there is change both in speed and direction ofthe wind
Role of vertical wind shearThe shear perpendicular to the convective line
supports updraftMost important is the shear in the lowest layer
reaching from the surface up to 2-3 kmCells developing within strong vertical shear
have long lifetime and severe weatherMost intense thunderstorms develop when
there is change both in speed and direction ofthe wind
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• In broad strong windcurrent, the strongesthorizontal winds andvertical shear are generallyof meso-scale dimensions.
• There are dynamicallyfavourable sectors (rightentrance and left exit inupper troposphericwesterly jet) for upwardmotion and convectivedevelopment.
Upper level Jet:• In broad strong wind
current, the strongesthorizontal winds andvertical shear are generallyof meso-scale dimensions.
• There are dynamicallyfavourable sectors (rightentrance and left exit inupper troposphericwesterly jet) for upwardmotion and convectivedevelopment.
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Low level WindThe low level strong wind locatedin the regions,
where the underlying surface haslarge variations of topography.
Heating of air during day timeand cooling of air at night time,
Strong gradient of temperatureand pressure.
The low level strong wind locatedin the regions,
where the underlying surface haslarge variations of topography.
Heating of air during day timeand cooling of air at night time,
Strong gradient of temperatureand pressure.
As a result, meso–scale regions of convergence anddivergence of low level winds get generated. Regions oflow level convergence are favourable for convection.
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• A dry line is a narrow, almost verticaltransition zone, across which there isa sharp moisture gradient.
• Separates moist and dry air.• Regions of these wind discontinuities
are also trough lines of low pressure.• Air on the moist side of the wind
discontinuity is convectively unstableand hence gives rise to CB cloudsthrough frictional convergence.
Dry line:• A dry line is a narrow, almost vertical
transition zone, across which there isa sharp moisture gradient.
• Separates moist and dry air.• Regions of these wind discontinuities
are also trough lines of low pressure.• Air on the moist side of the wind
discontinuity is convectively unstableand hence gives rise to CB cloudsthrough frictional convergence.
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Meso-scale low pressure systems:• Severe thunderstorms
sometimes occur in associationwith low pressure systemshaving diameters upto a fewhundred kms.
• Generally they are weaker inthe tropics than in the extratropics.
• Due to feebleness of mesolows and lack of high densitynetwork of observations,knowledge about meso lows isinadequate.
(a)0300 UTC (b)0600 UTC
(d)1200 UTC(c)0900 UTC
• Severe thunderstormssometimes occur in associationwith low pressure systemshaving diameters upto a fewhundred kms.
• Generally they are weaker inthe tropics than in the extratropics.
• Due to feebleness of mesolows and lack of high densitynetwork of observations,knowledge about meso lows isinadequate.
(d)1200 UTC(c)0900 UTC
•31st March 2009
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ENVIRONMENT FOR WIDE SPREAD THUNDERSTORM(Example :taken from IMD’s Forcasting Manual)
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Spatial and Temporal domains of Forecast
Nowcasting for next 6-12 hours(Venue/ location specific)
Short Range for next 72 hours (Location/District/State/Met Sub-division)
Medium Range for next 3-7 days(District)
Extended range for 10-15 days(Met Subdivision/State/ Homogeneous regions)
Long range for month/season(Homogeneous regions/country)
Nowcasting for next 6-12 hours(Venue/ location specific)
Short Range for next 72 hours (Location/District/State/Met Sub-division)
Medium Range for next 3-7 days(District)
Extended range for 10-15 days(Met Subdivision/State/ Homogeneous regions)
Long range for month/season(Homogeneous regions/country)
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NOWCAST FOR THUNDERSTORM
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Multi-hazard warning system
Systematic Warning Map for highimpact weather events
Colour system for highlighting Warning production and
dissemination in a single system Link between IMD and Disaster
management Relation with other stake holders
Systematic Warning Map for highimpact weather events
Colour system for highlighting Warning production and
dissemination in a single system Link between IMD and Disaster
management Relation with other stake holders
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Multi HazardWarning System
• Thundersquall withheavy rain over Assam ,Meghalaya, ArunachalPradesh & NMMT
• Moderate thundersquallover West Bengal , BiharJharkhand, Chattisgarhand Orissa .
• Isolated dust-storm overRajasthan.
• Thundersquall withheavy rain over Assam ,Meghalaya, ArunachalPradesh & NMMT
• Moderate thundersquallover West Bengal , BiharJharkhand, Chattisgarhand Orissa .
• Isolated dust-storm overRajasthan.
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ThanksThanks