Characteristics of severe thunderstorms over Bangladesh and
neighborhood: Observations & WRF-
ARW model simulations
Senaka Basnayake
Asian Disaster Preparedness CentreThailand
WRF Lecture Series, 20 – 24 September 2010 @ BCCR - Norway
“Safer communities and sustainable development through disaster risk reduction”
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
ADPC Organization ChartBoard 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)
Severe thunderstorms
or Nor’westers
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
S. No Date No of events /day Reported Station Reported Wind Speedkm/h
Wind Direction
(’ly)
Reported Time (UTC)
1 21.03.2009 1a Rajshahi 56 NW 1305-1308
1b Rangpur 41 NE 1535-1537
2
26.03.2009
1a 44 SW 09491b 52 W 09521c 44 W 09552 Rangpur 63 N 2259-2302
3 29.03.20091 65 - 11302a 46 NW 17562b M.M.O Dhaka 65 S 1800
4 30.03.2009 1 43 SW 1313
5
31.03.2009
1a 52 NW 1445-1447
1b 57 NW 14501c 74 NW 15081d 56 NW 1510-1513
1e 44 NW 15242a 56 NW 1730-1800
2b Cox’sbazar 46 N 1755-1757
6 02.04.2009 1 48 N 15457 06.04.2009 1 51 W 09158 08.04.2009 1 Sylhet 58 NW 2037-2040
9 09.04.2009 1 70 W 0858
10 17.04.20091a 51 E 1025 1b Hatiya 51 SE 1402 2 Rangpur 83 NW 1405-1408
3a Kutubdia 93 S 1414 3b Cox’sbazar 83 SWS 1436 4 81
N
1524
11 19.04.2009 1 Sylhet 70 W 1924 12 29.04.2009 1 Rangpur 67 E 1855-1856
13 01.05.2009 1 Sylhet 67 NW 1031-1033
2 46 NW 1725
2009 pre-monsoon
2009 pre-monsoon season
(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
CAPE
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
31M
ay_0
0
Date/Time
CA
PE
(J/k
g)
Dhaka Guwahati Patna Agartala kolkata Ranchi
(b)
-3000
-2500
-2000
-1500
-1000
-500
0
500
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
Date/Time
CIN
E(J
/kg
)
Dhaka Guwahati Patna Agartala kolkata Ranchi
(c)
CINE
LI
-20
-15
-10
-5
0
5
10
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
31M
ay_0
0
Date/Time
Lif
ted
Ind
ex
Dhaka Guwahati Patna Agartala kolkata Ranchi
(c)
-25
-20
-15
-10
-5
0
5
10
15
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
11M
ay_0
13M
ay_0
15M
ay_0
16M
ay_0
18M
ay_0
24M
ay_0
25M
ay_0
26M
ay_0
29M
ay_0
31M
ay_0
Date/Time
Sh
ow
alte
r In
dex
Dhaka Guwahati Patna Agartala kolkata Ranchi
(c)
SI
Threshold Value >1500
0 > (NEGATIVE)Week instability CAPE < 1000 J/kgModerate instability 1000 J/kg < CAPE < 2500 J/kgStrong instability CAPE > 2500 J/kg
Week instability CAPE < 1000 J/kgModerate instability 1000 J/kg < CAPE < 2500 J/kgStrong instability CAPE > 2500 J/kg
Very Stable atmospheric condition LI ≥ 6.0Stable condition - unlikely to form thunderstorms 1.0 < LI < 6.0Slightly Unstable - possible thunderstorms with mechanical lifting -2.0 < LI < 0.0Unstable - likely to form thunderstorms with strong mechanical lifting -6.0< LI < -2.0Very Unstable - likely to form severe thunderstorms with strong mechanical lifting LI < -6.0
Very Stable atmospheric condition LI ≥ 6.0Stable condition - unlikely to form thunderstorms 1.0 < LI < 6.0Slightly Unstable - possible thunderstorms with mechanical lifting -2.0 < LI < 0.0Unstable - likely to form thunderstorms with strong mechanical lifting -6.0< LI < -2.0Very Unstable - likely to form severe thunderstorms with strong mechanical lifting LI < -6.0
Possible showers or thunderstorms SI ≤ +3.0Possible severe convective activity SI ≤ -3.0Possible showers or thunderstorms SI ≤ +3.0Possible severe convective activity SI ≤ -3.0
0
10
20
30
40
50
60
70
80
90
100
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
31M
ay_0
0
Date/Time
To
tal T
ota
ls In
dex
Dhaka Guwahati Patna Agartala kolkata Ranchi
(c)
TTI
0
200
400
600
800
1000
1200
1400
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
31M
ay_0
0
Date/Time
SW
EA
T In
dex
Dhaka Guwahati Patna Agartala Koltata Ranchi
(c)
SWEAT
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1May
_00
2May
_00
3May
_00
5May
_00
6May
_00
9May
_00
10M
ay_0
0
11M
ay_0
0
13M
ay_0
0
15M
ay_0
0
16M
ay_0
0
18M
ay_0
0
24M
ay_0
0
25M
ay_0
0
26M
ay_0
0
29M
ay_0
0
31M
ay_0
0
Date/Time
Bu
lk R
ich
ard
son
Nu
mb
er
Dhaka Guwahati Patna Agartala kolkata Ranchi
(c)
BRN
Indicator of occurrence of thunderstorm TTI ≥ 40
Indicator of occurrence of thunderstorm with tornado intensity TTI ≥ 47
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
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 Supercells 10 < BRN < 45
Storms with multicells than supercellsBRN > 45
Thunderstorms unlikely due to too much wind shear BRN < 10
Possibility of Supercells 10 < BRN < 45
Storms with multicells than supercellsBRN > 45
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 : 3rd 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
Date Model Simulated Time (UTC)
Observed Place Observed Wind Speed (km/h)
Observed Time (UTC)
Squall speed Nor’westers (41-60 km/h)
31 /03/2009 1900 Chittagong 56 1730
02/05/2009 0900 Dhaka 57 0505
2300 Cox's Bazar/Ctg 48 2251
05/05/2009 1400 Rangpur 59 1520
11/05/2009 1000 Dhaka 43 0945
18/05/2009 0500 Dhaka 44 0505
29/05/2009 0700 Dhaka 48 0737
31/05/2009 0900 Saidpur 52 0630
Light Nor'wester (61-90 km/h)
29/03/2009 1200 Dhaka 65 1130
1800 Dhaka 65 1800
01/05/2009 1100 Sylhet 67 1031
03/05/2009 0900 Dhaka 74 0836
13/05/2009 2000 Chittagong 63 2000
16/05/2009 0900 Chittagong 63 0922
Moderate Nor'wester (91-120 km/h)
17/04/2009 1600 Kutubdia 93 1414
11/05/2009 0900 Barrackpore, India 93 1240
S. No.
Parameter Squall speed Light Moderate
Obs. Model Obs. Model Obs. Model
1 Cloud Top Altitude (hPa) 150 110 102 115 120 100
2 Precipitation rate at surface (mm/h) 36 24 32 24 31 32
3 Direction of movement NWly NWly NNWly Wly WNWly NWly
4 Speed of movement (km/h) 53 51 52 46 59 75
5 Maximum wind speed at surface (m/s) 14 9 18 10 26 11
6 Length of squall line (km) 215 239 300 290 340 320
7 Altitude of Core pptn (hPa) N/A 830 N/A 800 N/A 750
8 Intensity of Core pptn (mg/kg) N/A 195 N/A 740 N/A 26
9 Updrafts speed (maximum) (cm/s) N/A 120 N/A 100 N/A 160
10 Downdrafts Speed (maximum) (cm/s) N/A 60 N/A 120 N/A 60
11 Liquid water Content (mg/kg) N/A 221 N/A 301 N/A 365
Composite Characteristics
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.
Acknowledgement
• SAARC Meteorological Research Centre (SMRC)
• Bangladesh Meteorological Department (BMD)
• Dr. Someshwar Das and research team at SMRC
Tusen Takk
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