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

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1 International Forum on Tornado Disaster Risk Reduction for Bangladesh -To Cope with Neglected Disasters 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

2 Contents of presentation Vulnerability 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

3 Tornado occurring areas in the world

4 Ten deadliest tornadoes Death Toll Event Location Date 1,300 The Saturia-Manikganj Sadar Tornado Bangladesh (Manikganj) East Pakistan Tornado Bangladesh The Tri-State Tornado United States (Missouri Illinois Indiana) March 18, Dhaka Tornado Bangladesh The Malta Tornado Malta The Sicily Tornado Italy The Narail-Magura Tornadoes Bangladesh (Jessore) The Comoro Tornado Comoro The Tangail Tornado Bangladesh Ivanovo, Yaroslavl Tornado Russia 1984

6 What is a tornado? 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.

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

9 Types of Nor wester associated with Severe Thunderstorm TYPE A Develop over WB in the afternoon /late evening, speed kph % are of this type. TYPE B A B D Sub mountainous districts of North Bengal during Night/EM, speed kph. 10% are of this type. TYPE C C Hills of N/L, Manipur & Mizoram, they are very rare. TYPE D Similar to B, but originate near Khashi hills & moves from N to S. 5% are of this type.

10 Distribution of Wind direction related to severe thunderstorm 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. 42% 13% 10% 0% 2% NE 14% 6% 13% E SE S SW W NW Fig: Distribution of Wind direction in March N

11 Distribution of Wind direction related to severe thunderstorm 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. 40% NE 2% 17% 7% 1% E 3% SE 9% 21% S SW W NW Fig: Distribution of Wind direction in April N

12 Distribution of Wind direction related to severe thunderstorm in May 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. 37% 17% 8% 4% 4% 2% 7% 21% NE E SE S SW W NW Fig: Distribution of Wind direction in May N

13 TIME OF OCCURRENCE TIMES BST

16 HAIL

17 Causes of Severe thunderstorms A lower level warm & moist layer of air extending from surface to 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

18 FORMATION MECHANISM OF NOR WESTER 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 ft. 30,000 ft 20,000 ft 7000 ft Surface L *Cold & dry air *65 to 75 % RH *Warm & moist air Cold & dry air Inversion Low level warm and moist air, 65 to 75 %

19 FORMATION OF A TORNADO

20 TORNADO GETTING STRENGTHS OVER WATER BODIES WIND GETS TWISTED DRAWING DEBRIS OVER GROUND

21 Severe thunderstorm in Bangladesh: 15May 2009 Severe thunderstorm in Bangladesh: 06May 2009

22 Synoptic analysis of severe thunderstorm

23 Synoptic analysis In 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 fields pressure change fields, temperature change fields during 24 hours and its lower time intervals; Pressure departure fields, temperature departure fields from the normal values upper air temperature, humidity and wind field are analyzed based on the pilot balloon observation and Rawin Sonde observational data in each observational period. The stability indices like SI, LI etc. are calculated for understanding the instability conditions of the troposphere.

24 Observed meteorological features a. 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 SEwards 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 and upper Assam.

25 b. Upper troposphere In the upper troposphere, westerlies or northwesterlies prevailed 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 lowlevel low or even straight southerly flow upto 3000ft. (1 km) is quite a significant feature on the days of nor westers over this area.

26 Forecasting Technique for severe thunderstorm The 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 chart find out the 12 hour surface pressure fall; see the low-level moisture influx upto at least 3000ft from the pilot balloon chart locate the area of low-level convergence from the pilot balloon charts and carefully interpret and follow the radar echoes observed by BMD radars interpret the satellite observation received by satellite receiving systems of BMD

27 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.

28 A case study: 03 May 2009

80 60 40 20 0 Recorded wind on 03 May 2009 Km/hr May03_0001 May03_0101 May03_0201 May03_0301 May03_0401 May03_0501 May03_0601 May03_0701 May03_0801 May03_0901 May03_1001

29 Recorded wind on 03 May 2009 Km/hr May03_0001 May03_0101 May03_0201 May03_0301 May03_0401 May03_0501 May03_0601 May03_0701 May03_0801 May03_0901 May03_1001 May03_1101 May03_1201 May03_1301 May03_1401 May03_1501 May03_1601 May03_1701 May03_1801 May03_1901 May03_2001 May03_2101 May03_2201 May03_2301 Recorded rainfall (mm) On 03 May 2009

31 : 0000UTC : 0300UTC : 0600UTC : 0900UTC

32 : 1200UTC : 1500UTC : 1800UTC : 2100UTC

33 : 0000UTC- 1000ft : 0000UTC- 2000ft : 0000UTC and 5000ft : 0000UTC and 10,000ft.

34 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

35 May 03, 2009 at 1200UTC: 1000ft May 03, 2009 at 1200UTC: 2000ft May 03, 2009 at 1200UTC: 3000 and 5000ft May 03, 2009 at 1200UTC: 7000 and 10,000ft

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

37 Chittagong Rajshahi Dhaka Barisal Khulna Sylhet

38 Maximum temperature field: On 03 May maximum temperature gradient was higher MaxT_Field: 03May2009 Minimum temperature field: On 03 May uniform minimum temperature gradient was across northwest to northeast over the country. MinT_Field: 03May2009

39 MaxT_24hrsChange_03May09 MaxT_Departure_03May09 MinT_24hrsChange_03May09 MinT_Departure_03May09

WRF model Set up WRF modelling for 03 May 2009 WRF V3.1 MODEL May03_09_18hrs Point in x-direction: 219 Lon: 87.68513-94.12687ºE Points in y-direction: 243 Lat: 20.74589-27.

40 WRF model Set up WRF modelling for 03 May 2009 WRF V3.1 MODEL May03_09_18hrs Point in x-direction: 219 Lon: ºE Points in y-direction: 243 Lat: ºN Vertical levels: 27 Considered output: 60m No. of Variables: 97 Centered location: Lat: 24.05ºN & Lon: 90.91ºE Resolution: 3 km Bangladesh Bay of Bengal Domain Area

41 10m_WF_May03_ 09: 0100UTC 10m_WF_May03_ 09: 0200UTC 10m_WF_May03_ 09: 0300UTC 10m_WF_May03_ 09: 0400UTC 10m_WF_May03_ 09: 0500UTC 10m_WF_May03_ 09: 0600UTC 10m_WF_May03_ 09: 0700UTC 10m_WF_May03_ 09: 0800UTC

42 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

43 03May_0100UTC 03May_0200UTC 03May_0300UTC 03May_0400UTC 03May_0500UTC 03May_0600UTC 03May_0700UTC 03May_0800UTC Simulated TF(2m) using WRF model: 03 May 2009

44 03May_0900UTC 03May_1000UTC 03May_1100UTC 03May_1200UTC 03May_1300UTC 03May_1400UTC 03May_1500UTC 03May_1600UTC Simulated TF(2m) using WRF model: 03 May 2009

45 03May_0100UTC 03May_0200UTC 03May_0300UTC 03May_0400UTC 03May_0500UTC 03May_0600UTC 03May_0700UTC 03May_0800UTC Simulated olr (W/m2) using WRF model: 03 May 2009

46 03May_0900UTC 03May_1000UTC 03May_1100UTC 03May_1200UTC 03May_1300UTC 03May_1400UTC 03May_1500UTC 03May_1600UTC Simulated olr (W/m2) using WRF model: 03 May 2009

47 Barisal Chittagong Dhaka Rajshahi

48 Model Predicted rainfall: 03 May 2009

Model Description The 5th generation PSU/NCAR mesoscale model (MM5) is a limited-area, Non-hydrostatic and terrain-following sigmacoordinate model designed to simulate or predict mesoscale & regional

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.

49 Model Description The 5th generation PSU/NCAR mesoscale model (MM5) is a limited-area, Non-hydrostatic and terrain-following sigmacoordinate 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 and have been prepared using MM5. These domains have covered the areas N; E for coarse grid mesh and N; E 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.

50 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.

51 21 May_0300UTC 21 May_0600UTC 21 May_0900UTC 21 May_1200UTC 21 May_1500UTC 21 May_1800UTC 21 May_2100UTC 22 May_0000UTC Simulated PF using MM5 model: April 2007

52 22May_0300UTC 22May_0600UTC 22May_0900UTC 22May_1200UTC 22May_1500UTC 22May_1800UTC 22May_2100UTC 23May_0000UTC Simulated PF using MM5 model: April 2007

53 21May_0300UTC 21May_0600UTC 21May_0900UTC 21May_1200UTC 21May_1500UTC 21May_1800UTC 21May_2100UTC 22May_0000UTC Simulated TF using MM5 model: April 2007

54 22May_0300UTC 22May_0600UTC 22May_0900UTC 22May_1200UTC 22May_1500UTC 22May_1800UTC 22May_2100UTC 23May_0000UTC Simulated TF using MM5 model: April 2007

55 21May_0300UTC 21May_0600UTC 21May_0900UTC 21May_1200UTC 21May_1500UTC 21May_1800UTC 21May_2100UTC 22May_0000UTC Simulated WF using MM5 model: April 2007

56 22May_0300UTC 22May_0600UTC 22May_0900UTC 22May_1200UTC 22May_1500UTC 22May_1800UTC 22May_2100UTC 23May_0000UTC Simulated WF using MM5 model: April 2007

57 21 April 2007 (D1) 21 April 2007 (D2) 21 April Raingauge 22 April 2007 (D1) 22 April 2007 (D2) 21 April Raingauge

58 Conclusion Meteorology 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.

Simulation of a Heavy Rainfall Event on 14 September 2004 over Dhaka, Bangladesh Using MM5 Model

Available Online Publications J. Sci. Res. 3 (2), 261-270 (2011) JOURNAL OF SCIENTIFIC RESEARCH www.banglajol.info/index.php/jsr Simulation of a Heavy Rainfall Event on 14 September 2004 over Dhaka, Bangladesh