some associated features of severe thunderstorms in ...international forum on tornado disaster risk...

International Forum on Tornado Disaster Risk Reduction for Bangladesh

-To Cope with Neglected Disasters-13-14 December 2009, Dhaka, Bangladesh

Some associated features of Severe Thunderstorms in Bangladesh extracted from conventional method and numerical modelling

Presenter: Md. Abdul Mannan, BMD

Collaboration with: Arjumand Habib, Md. Shah Alam and S. M. Quamrul Hassan

Contents of presentationVulnerability of Bangladesh in context of Severe

Thunderstorm and Tornado

Synoptic or conventional analysis of a Severe Thunderstorm in Bangladesh

Simulation of a Severe Thunderstorm using WRF model

Simulation of a Severe Thunderstorm using MM5 model

Conclusion

Tornado occurring areas in the world

1984Russia Ivanovo, YaroslavlTornado

400

1996BangladeshThe Tangail Tornado 440

1951ComoroThe Comoro Tornado 500

1964Bangladesh(Jessore)

The Narail-MaguraTornadoes

500

1851ItalyThe Sicily Tornado 500

1551MaltaThe Malta Tornado 600

1973 Bangladesh1973 Dhaka Tornado 681

March 18, 1925 United States (Missouri–Illinois–

Indiana)

The Tri-State Tornado695

1969 Bangladesh1969 East Pakistan Tornado

923

1989 Bangladesh(Manikganj)

The Saturia-ManikganjSadar Tornado

1,300

DateLocation Event Death Toll

Ten deadliest tornadoes

A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. Damage paths can be in excess of one mile wide and 50 miles long. 800 tornadoes are reported/Yr in USA.

What is a tornado?

Life stages: A sequence of images showing the birth of a tornado.

First, the rotating cloud base lowers.

This lowering becomes a funnel, which continues descending while winds build near the surface, kicking up dust and other debris.

Finally, the visible funnel extends to the ground, and the tornado begins causing major damage.

Types of Nor’wester associated with Severe Thunderstorm

A

BD

C

Develop over WB in the afternoon /late evening, speed 48-64 kph. 70-80% are of this type.

Sub mountainous districts of North Bengal during Night/EM, speed 16-32 kph. 10% are of this type.

Hills of N/L, Manipur & Mizoram, they are very rare.

Similar to “B”, but originate near Khashi hills & moves from N to S. 5% are of this type.

TYPE “A”

TYPE “B”

TYPE “C”

TYPE “D”

10%

13%

13%6%

42% 14%

0%2%

NE

E

SE

S

SW

W

NW

N

Fig: Distribution of Wind direction in March

In March about 42% severe thunderstorms are associated with northwesterly wind

14% are associated with westerly wind

13% are associated with northerly or southwesterly winds;

10% are associated with northeasterly wind.

There is no record of severe thunderstorms associated with easterly wind during this month.

Distribution of Wind direction related to severe thunderstorm in March

7%

9%

17% 3%

40%

21%

2%1%

NE

E

SE

S

SW

W

NW

N

Fig: Distribution of Wind direction in April

In April about 40% severe thunderstorms are associated with northwesterly wind,

21% severe thunderstorms are associated with westerly wind.

17% severe thunderstorms are associated with northerly wind and

7% and 9% are associated with northeasterly and southwesterly winds respectively.

Severe thunderstorms associated with easterly, southeasterly or southwesterly winds are very rare during this month.

Distribution of Wind direction related to severe thunderstorm in April

8%

7%

17%

2%

37%21%

4%4%

NE

E

SE

S

SW

W

NW

N

In May about 37% thunderstorms are associated with northwesterly

21% thunderstorms are associated with westerly and

17% severe thunderstorms are associated with northerly wind respectively.

The percentages of contribution of northeasterly and southwesterly winds are 8% and 7% respectively.

Severe thunderstorms associated with easterly, southeasterly or southerly winds are very rare wind during this month.

Distribution of Wind direction related to severe thunderstorm in May

Fig: Distribution of Wind direction in May

TIME OF OCCURRENCE

0

5

10

15

20

25

30

06-09 09-12 12-15 15-18 18-21 21-24 00-03 03-06

TIMES

BST

HAIL

A lower level warm & moist layer of air extending from surface to 5000-7000 ft.

An upper level cold & Dry layer of air.

One or more of the following triggering actions:• Insolation• Inflow of moist wind from Bay• Eastward passage of Western Disturbance

Causes of Severe thunderstorms

Surface

L

20,000 ft

30,000 ft

7000 ft

*Cold & dry air

A low pressure over WB & Bihar during months of March to May.

Moist air from surface to 7,000 ft.

Cold & dry air within 20 to 30,000 ft .

Inversion layer between 10 to 15000 ft.

Low level warm andmoist air, 65 to 75 %

Cold & dry air

Inversion

*65 to 75 % RH

*Warm & moist air

FORMATION MECHANISM OF NOR’WESTER

FORMATION OF A TORNADO

TORNADOGETTING STRENGTHSOVER WATER BODIES

WIND GETS TWISTEDDRAWING DEBRISOVER GROUND

Severe thunderstorm in Bangladesh: 06May 2009

Severe thunderstorm in Bangladesh: 15May 2009

Synoptic analysis of severe thunderstorm

Synoptic analysisIn this method the following meteorological parameters are

carefully analyzed in each synoptic observation time based on the surface synoptic and upper air observation over the area of Bangladesh and its surroundings:Surface pressure, temperature, relative humidity, dew point

temperature fieldspressure change fields, temperature change fields during 24

hours and its lower time intervals; Pressure departure fields, temperature departure fields from

the normal valuesupper air temperature, humidity and wind field are analyzed based on the pilot balloon observation and Rawin Sondeobservational data in each observational period. The stability indices like SI, LI etc. are calculated for understanding the instability conditions of the troposphere.

Observed meteorological featuresa. surface and lower troposphere

Existence of a trough of low pressure over Uttar Prodesh and Bihar with its axis extending West-East direction across the plains.

The orientation of the axis and its intensity are affected by the passage of Western Disturbances in the form of low pressure area. In such a situation the accentuated axis of trough extends SE-wards into Gangetic West Bengal and Bangladesh.

Around the trough SW/S’ly wind normally blows from the Bay of Bengal upto a level of about 3000ft. (1Km) incurring moisture influx over the region covering Bangladesh, West Bengal and Assam.

Quite often through northeast Assam, ENE/NE’ly dry and cooler wind descends downwards to the West across the foot of the Himalayas.

In such a situation with the existence of ENE/E’ly wind over extreme north Assam and SW/S’ly wind from the South, East-West line of wind discontinuity takes place over north Bangladesh andupper Assam.

b. Upper troposphere

In the upper troposphere, westerlies or northwesterliesprevailed over Pakistan, North Indian Plains, Bangladesh and Assam.

The passage of upper air trough in the westerlies or the jet can often be detected at 30,000ft to 40,000ft (about 9.0 to 12.0 km) levels.

The superposition of upper divergence having association with a perturbation like a jet, jet-cum-trough or trough on the convergence having association with a low-level ‘low’ or even straight southerly flow upto 3000ft. (1 km) is quite a significant feature on the days of nor’westers over this area.

Forecasting Technique for severe thunderstormThe area over which nor’westers occur varies usually from one day to the other mostly depending on the synoptic situation at the surface and upper level. Identification of this area with positive threat of the storms is one of the most difficult problems for the forecasters.To observe the basic favourable conditions being fulfilled, a forecaster within a short span of time has to adopt certain quick techniques to make a decision about the occurrence or non-occurrence of nor’westers. These are:

determine the stability indices;locate the dynamic heat low over the vulnerable area like north Orissa,

Bihar, Gangetic West Bengal or southwestern part of Bangladesh;find out the middle and upper-level jet shear;see whether the positive area in greater than the negative area in the

thermodynamic chartfind out the 12 hour surface pressure fall;see the low-level moisture influx upto at least 3000ft from the pilot balloon

chartlocate the area of low-level convergence from the pilot balloon charts andcarefully interpret and follow the radar echoes observed by BMD radarsinterpret the satellite observation received by satellite receiving systems of

BMD

Gaps and needs• Occurrence time of thunderstorm is not forecasted precisely

• Occurrence area of thunderstorm is not forecasted precisely

• duration of thunderstorm is not forecasted

• Possibility of thunderstorm is not well informed to the public due to updated communication.

•People’s awareness is not in satisfactory level.

• Research on thunderstorms or severe thunderstorm related to tornado in Bangladesh is very limited.

A case study: 03 May 2009

020406080

May

03_0

001

May

03_0

101

May

03_0

201

May

03_0

301

May

03_0

401

May

03_0

501

May

03_0

601

May

03_0

701

May

03_0

801

May

03_0

901

May

03_1

001

May

03_1

101

May

03_1

201

May

03_1

301

May

03_1

401

May

03_1

501

May

03_1

601

May

03_1

701

May

03_1

801

May

03_1

901

May

03_2

001

May

03_2

101

May

03_2

201

May

03_2

301

Km

/hr

Recorded windon 03 May 2009

Recorded rainfall (mm)On 03 May 2009

03.05.2009: 0000UTC 03.05.2009: 0300UTC

03.05.2009: 0900UTC03.05.2009: 0600UTC

03.05.2009: 1200UTC 03.05.2009: 1500UTC

03.05.2009: 2100UTC03.05.2009: 1800UTC

03.05.2009: 0000UTC- 1000ft.

03.05.2009: 0000UTC- 2000ft.

03.05.2009: 0000UTC- 3000 and 5000ft.

03.05.2009: 0000UTC-7000 and 10,000ft.

May 03, 2009 at 6000UTC: 1000ft

May 03, 2009 at 6000UTC: 2000ft

May 03, 2009 at 6000UTC: 3000 and 5000ft

May 03, 2009 at 6000UTC: 7000 and 10000ft

May 03, 2009 at 1200UTC: 1000ft

May 03, 2009 at 1200UTC: 2000ft

May 03, 2009 at 1200UTC: 7000 and 10,000ft

May 03, 2009 at 1200UTC: 3000 and 5000ft

Stability indices: 01 May 2009:a. SI:+ 8.6b. LI :+ 7.602 May 2009:SI:- 4.9LI : -5.903 May 2009:SI:-6.6LI : -3.2

Chittagong Rajshahi Dhaka

Barisal Khulna Sylhet

MaxT_Field: 03May2009

Maximum temperature field:

On 03 May maximum temperature gradient was higher

MinT_Field: 03May2009

Minimum temperature field:

On 03 May uniform minimum temperature gradient was across northwest to northeast over the country.

MaxT_24hrsChange_03May09 MaxT_Departure_03May09

MinT_24hrsChange_03May09 MinT_Departure_03May09

WRF model Set up

WRF V3.1 MODELMay03_09_18hrsPoint in x-direction: 219 Lon: 87.68513- 94.12687ºEPoints in y-direction: 243 Lat: 20.74589- 27.27317ºNVertical levels: 27 Considered output: 60mNo. of Variables: 97Centered location:

Lat: 24.05ºN & Lon: 90.91ºEResolution: 3 km

Bay of Bengal

Bangladesh

Domain Area

WRF modelling for 03 May 2009

10m_WF_May03_09: 0100UTC

10m_WF_May03_09: 0600UTC

10m_WF_May03_09: 0300UTC

10m_WF_May03_09: 0400UTC

10m_WF_May03_09: 0500UTC

10m_WF_May03_09: 0200UTC

10m_WF_May03_09: 0700UTC

10m_WF_May03_09: 0800UTC

10m_WF_May03_09: 0900UTC

10m_WF_May03_09: 1000UTC

10m_WF_May03_09: 1100UTC

10m_WF_May03_09: 1200UTC

10m_WF_May03_09: 1300UTC

10m_WF_May03_09: 1400UTC

10m_WF_May03_09: 1500UTC

10m_WF_May03_09: 1600UTC

Simulated TF(2m) using WRF model: 03 May 2009

03May_0100UTC

03May_0500UTC

03May_0200UTC

03May_0600UTC 03May_0700UTC

03May_0300UTC 03May_0400UTC

03May_0800UTC

03May_0900UTC

Simulated TF(2m) using WRF model: 03 May 2009

03May_1300UTC

03May_1000UTC

03May_1400UTC

03May_1100UTC

03May_1500UTC

03May_1200UTC

03May_1600UTC

Simulated olr (W/m2) using WRF model: 03 May 2009

03May_0100UTC 03May_0200UTC

03May_0600UTC 03May_0700UTC

03May_0300UTC 03May_0400UTC

03May_0800UTC03May_0500UTC

03May_0900UTC

03May_1300UTC 03May_1400UTC 03May_1500UTC 03May_1600UTC

03May_1000UTC 03May_1100UTC 03May_1200UTC

Simulated olr (W/m2) using WRF model: 03 May 2009

BarisalChittagong

Dhaka Rajshahi

Model Predicted rainfall: 03 May 2009

Model DescriptionThe 5th generation PSU/NCAR mesoscale model (MM5) is a limited-area,

Non-hydrostatic and terrain-following sigma-coordinate model designed to simulate or predict mesoscale & regional scale atmospheric circulation.

Two way nested domains i.e. coarse domain (D1) of ~9 km resolutions and fine domain (D2) of ~3 km resolutions with grid cells 57x57 and 93×93 and have been prepared using MM5.

These domains have covered the areas 18.670-27.6721 N; 84.75-94.8875 E for coarse grid mesh and 21.760-26.674 N; 87.420-92.901E for fine grid mesh.

The topography in the model has been obtained from six resolutions (1 , 30, 10, 5 and 2 minutes, and 30 seconds) USGS (United States Geological Survey) land cover data set.

At the boundaries of the coarse domain, 1x1 degree resolution NCEP data have been provided at every 6 hrs as input.

Model Description continue

The model has then been run using the Grell or Anthes-Kuo(Anthes, 1977) option for cumulus parameterization and MRF for the boundary layer parameterization (Hong and Pan, 1996).

The simple ice scheme of Dudhia (Dudhia, 1996) is employed for explicit treatment of moisture and water vapor. Cloud radiation interaction is allowed for radiation anticipation. Five layer soil option is used for soil temperature. The model is run with 22 sigma levels in the vertical from the ground to the 100 hPa top surface.

The time frames of simulation for five cases in this study are 0000 UTC of 21 April to 0000UTC of 23 April 2007;

Precipitation outputs of MM5 have been generated at 30 minute intervals and processed using Grid Analysis and Display system (GrADS) software for visual and calculation purpose.

Simulated PF using MM5 model: 21-22 April 2007

21 May_0300UTC 21 May_0600UTC 21 May_0900UTC 21 May_1200UTC

21 May_1500UTC 21 May_1800UTC 21 May_2100UTC 22 May_0000UTC

22May_0300UTC 22May_0600UTC 22May_0900UTC 22May_1200UTC

22May_1500UTC 22May_1800UTC 22May_2100UTC 23May_0000UTC

Simulated PF using MM5 model: 21-22 April 2007

21May_0300UTC

21May_1800UTC21May_1500UTC 22May_0000UTC

21May_0600UTC 21May_0900UTC 21May_1200UTC

21May_2100UTC

Simulated TF using MM5 model: 21-23 April 2007

22May_0300UTC 22May_0600UTC

22May_1500UTC 22May_1800UTC 22May_2100UTC

22May_0900UTC 22May_1200UTC

23May_0000UTC

Simulated TF using MM5 model: 21-23 April 2007

21May_0300UTC 21May_0600UTC

21May_1800UTC 21May_2100UTC

21May_0900UTC 21May_1200UTC

22May_0000UTC21May_1500UTC

Simulated WF using MM5 model: 21-23 April 2007

22May_0300UTC 22May_0600UTC

22May_1500UTC 22May_1800UTC

22May_0900UTC

22May_2100UTC

22May_1200UTC

23May_0000UTC

Simulated WF using MM5 model: 21-23 April 2007

21 April 2007 (D1) 21 April 2007 (D2)

22 April 2007 (D1) 22 April 2007 (D2)

21 April 2007 -Raingauge

21 April 2007 -Raingauge

ConclusionMeteorology is a relatively young science and the study of tornadoes is

newer still. Although researched for about 140 years and intensively for around 60 years, there are still aspects of tornadoes which remain a mystery.

Scientists have a fairly good understanding of the development of thunderstorms and mesocyclones, and the meteorological conditions conducive to their formation.

Reliably predicting tornado intensity and longevity remains a problem, as do details affecting characteristics of a tornado during its life cycle and tornadolysis.

Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued.

Numerical modeling also provides new insights as observations and new discoveries are integrated into our physical understanding and then tested in computer simulations which validate new notions as well as produce entirely new theoretical findings, many of which are otherwise unattainable.

Importantly, development of new observation technologies and installation of finer spatial and temporal resolution observation networks have aided increased understanding and better predictions.

Therefore more active research are very much essential.