1. Characteristics of severe thunderstorms over Bangladesh and neighborhood: Observations & WRF- ARW model simulations Senaka Basnayake Asian Disaster Preparedness Centre Thailand WRF Lecture Series, 20 – 24 September 2010 @ BCCR - Norway

3. “Safer communities and sustainable development through disaster risk reduction”

4. History of ADPC Established in 1986, at the initiative of WMO, UNDP and UNOCHA Served as the Outreach Center of Asian Institute of Technology, 1986-1999 Independent international foundation, July 1999 Inter-governmental charter signed, February 2005 Over 100 staffs, 19 nationalities

5. ADPC Organization Chart Board of Trustees 23 Members 16 Countries International Advisory Council (IAC) 95 members Executive Committee Regional Consultative Committee (RCC) 32 Members 26 Countries Urban Disaster Risk Management (UDRM) Public Health in Emergencies (PHE) Disaster Management Systems (DMS) Office of the Executive Director (OED) Climate Risk Management (CRM) Training Resource Group (TRG)

6. Severe thunderstorms or Nor’westers

7. Favorable Synoptic conditions for Nor’westers Presence of an active elongated trough of low over the Gangetic plains of north India across north Bangladesh on the mean seal level pressure chart Presence of southerly low level jet with a pole ward meridional component in the lower tropospheric wind flow High magnitude of moisture in the humidity field intruding from the Bay of Bengal into Bangladesh and thereafter north India Presence of sub-tropical jet stream with strong vertical wind shear in the low to middle troposphere levels over Bangladesh and neighborhood Intrusion of high convective available potential energy (CAPE) from the Bay of Bengal into Bangladesh and presence of a low convective inhibition energy (CINE) regime. A pocket of strong warm temperature advection at 850 hpa and cold temperature advection at 300 hpa

9. S. NoDateNo of events /dayReported StationReported Wind Speed km/h Wind Direction (’ly) Reported Time (UTC) 121.03.20091aRajshahi56NW1305-1308 1bRangpur41NE1535-1537 2 26.03.2009 1a44SW0949 1b52W0952 1c44W0955 2Rangpur63N2259-2302 3 29.03.2009 165-1130 2a46NW1756 2bM.M.O Dhaka65S1800 430.03.2009143SW1313 5 31.03.2009 1a52NW1445-1447 1b57NW1450 1c74NW1508 1d56NW1510-1513 1e44NW1524 2a56NW1730-1800 2bCox’sbazar46N1755-1757 602.04.2009148N1545 706.04.2009151W0915 808.04.20091Sylhet58NW2037-2040 909.04.2009170W0858 1017.04.2009 1a51E1025 1bHatiya51SE1402 2Rangpur83NW1405-1408 3aKutubdia93S1414 3bCox’sbazar83SWS1436 481 N 1524 1119.04.20091Sylhet70W1924 1229.04.20091Rangpur67E1855-1856 1301.05.20091Sylhet67NW1031-1033 246NW1725 2009 pre-monsoon

10. 2009 pre-monsoon season

11. (29) NW SE (2) 8) W S (3) NE (9 N (10) E (3) (4) SW 41 – 60 km/h ~ 41, 61 – 90 km/h ~ 27, 91 – 120 km/h ~ 2 2009 pre-monsoon season

12. CAPECINE LI SI Threshold Value >1500 0 > ( NEGATIVE) Week instability CAPE < 1000 J/kg Moderate instability 1000 J/kg < CAPE < 2500 J/kg Strong instability CAPE > 2500 J/kg Very Stable atmospheric condition LI ≥ 6.0 Stable condition - unlikely to form thunderstorms 1.0 < LI < 6.0 Slightly Unstable - possible thunderstorms with mechanical lifting -2.0 < LI < 0.0 Unstable - likely to form thunderstorms with strong mechanical lifting -6.0< LI < -2.0 Very Unstable - likely to form severe thunderstorms with strong mechanical lifting LI < -6.0 Possible showers or thunderstorms SI ≤ +3.0 Possible severe convective activitySI ≤ -3.0

13. TTISWEAT BRN Indicator of occurrence of thunderstorm TTI ≥ 40 Indicator of occurrence of thunderstorm with tornado intensity TTI ≥ 47 Indicator for potential strong convectionSWEAT = +250 Indicator for potential severe thunderstormsSWEAT = +300 ndicator for potential tornados SWEAT = +400 Thunderstorms unlikely due to too much wind shear BRN < 10 Possibility of Supercells10 < BRN < 45 Storms with multicells than supercellsBRN > 45

15. (d) (e) (f)

17. Weather Research and Forecasting (WRF) Developed by the Mesoscale and Microscale Meteorology Division of National Centre for Atmospheric Research (NCAR) of USA National Centre for Environment Prediction (NCEP) real time analysis (FNL) data as initial and lateral boundary conditions (LBCs) at six hourly intervals Domain parameters & Model physics; Horizontal Resolution : 9 km No. of grid point along X : 153 No. of grid point along Y : 139 No. of Vertical sigma levels : 27 Iterative Time step : 50 seconds Integration scheme : 3 rd order Runga-Kutta mp_physics: WSM 3 Cumulus parameterization : Kain-Fritch scheme Sf_sfclay_physics : Monin-Obukhov with Carslon-Bolan viscous sub-layer option Sf_surface_physics : Noah LSM ra_lw_physics : RRTM ra_sw_physics : Dudhia Boundary layer parameterization : Yonsei University scheme

26. Date Model Simulated Time (UTC) Observed Place Observed Wind Speed (km/h) Observed Time (UTC) Squall speed Nor’westers (41-60 km/h) 31 /03/20091900Chittagong561730 02/05/20090900Dhaka570505 2300Cox's Bazar/Ctg482251 05/05/20091400Rangpur591520 11/05/20091000Dhaka430945 18/05/20090500Dhaka440505 29/05/20090700Dhaka480737 31/05/20090900Saidpur520630 Light Nor'wester (61-90 km/h) 29/03/20091200Dhaka651130 1800Dhaka651800 01/05/20091100Sylhet671031 03/05/20090900Dhaka740836 13/05/20092000Chittagong632000 16/05/20090900Chittagong630922 Moderate Nor'wester (91-120 km/h) 17/04/20091600Kutubdia931414 11/05/20090900Barrackpore, India931240

27. S. No. ParameterSquall speedLightModerate Obs.ModelObs.ModelObs.Model 1 Cloud Top Altitude (hPa)150110102115120100 2 Precipitation rate at surface (mm/h)362432243132 3 Direction of movementNW ly NNW ly W ly WNW ly NW ly 4 Speed of movement (km/h)535152465975 5 Maximum wind speed at surface (m/s)14918102611 6 Length of squall line (km)215239300290340320 7 Altitude of Core ppt n (hPa)N/A830N/A800N/A750 8 Intensity of Core ppt n (mg/kg)N/A195N/A740N/A26 9 Updrafts speed (maximum) (cm/s)N/A120N/A100N/A160 10 Downdrafts Speed (maximum) (cm/s)N/A60N/A120N/A60 11 Liquid water Content (mg/kg)N/A221N/A301N/A365 Composite Characteristics

28. Concluding Remarks…. Convective indices at Patna, Ranchi, Guwahati and Agartala stations are good indicators for identifying possible thunderstorm days over Bangladesh as the systems initiate or conceive over West Bengal, Assam and Meghalaya regions. Some of the factors which are essential for triggering of Nor’westers such as low level moist southerly jet from the head Bay of Bengal, mid-trophospheric cold dry westerly trough, etc. are well simulated by the model. WRF-ARW model is able to simulate some salient features of thunderstorms with some temporal and spatial shifting.

29. Acknowledgement SAARC Meteorological Research Centre (SMRC) Bangladesh Meteorological Department (BMD) Dr. Someshwar Das and research team at SMRC

30. Tusen Takk

31. Mission raising awareness and enhancing knowledge and skills ------------------------------------------------------------------------- strengthening sustainable institutional mechanisms ------------------------------------------------------------------------- facilitating exchange of information, experience and expertise ------------------------------------------------------------------------- developing and demonstrating innovative disaster risk reduction practices

32. Mainstream Disaster Reduction in Development Build and Strengthen Capacity Facilitate Partnerships and Exchange of Experiences Be recognized as a Proactive and Responsive Regional Resource Achieve Quality Service Through a Team Approach Goals

33. ADPC Highlights ADPC Projects and Programs: Longest serving regional center globally Proactive and responsive regional resource center 81 projects and programs across Asia Regional Early Warning Center provides services to 27 countries in the region