Md. Nazrul Islam(Bang. Univ. of Eng. and Tech.)

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• Md. Nazrul Islam(Bang. Univ. of Eng. and Tech.)
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• ??????(2000??3?????)
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AnalyArea
BAY OF BENGAL
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????????????

• Matsumoto(1992)??
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• Meghalaya??
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Seasons
Rainfall in 2000 averaged at stations in radar
sites
Dhaka/2000
Fig. 1A. Raingauge rainfall(mm/day) averaged for
BMD radar sites in 2000. Monsoon months in
Bangladesh are shown on the figure.
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• Ohsawa et al.(2001)
• 1995?6-8?
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Bangladesh RADAR

• Four RADAR data
• Dhaka RADAR is used mainly
• Intensive rawin sonde obs.

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Dhaka RADAR

• Continuous observations are conducted basically
  only for one hour duration for every other three
  hours, as follows
• 5-6, 8-9, 11-12, 14-15, 17-18, 20-21, 23-24BST.
• Almost all area of this country except for
  southeastern most part is covered.

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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
17 July
18 July
830, 1130, 1430, 1730, 2030, and 2330
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
830
17 July
18 July
No conv.
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
1130
17 July
18 July
SW scattering
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
1430
17 July
18 July
SW developing
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
1730
17 July
18 July
E forming
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
2030
17 July
18 July
E -gt NE Squall line
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Convection 17/18 July 2001
A typical pattern of the diurnal variation will
be shown using Dhaka RADAR data.
2330
17 July
18 July
NE spread
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Typical Diurnal Variation
Morning to afternoon Scattering convections over
the south western part of Bangladesh
Patterns are strikingly similar for two days 17
and 18 July 2001
indicating
This pattern should have been appeared under
some physical necessity
Evening to Midnight Organized convections over
the north eastern part of Bangladesh
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Comparison with prev. study
RADAR data
Ohsawa et al. (2001)
Midnight
Noon
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Summary(1)

• A typical pattern of diurnal variation of
  convection over Bangladesh is detected.
• Morning to afternoon Gradually organized
  scattering convections over SW part
• Evening to midnight Well organized convections
  over NE part
• Consistent with Ohsawa et al. (2001)

Rawin sonde observation ?
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Eventm
00LST 06LST 09LST 12LST
15LST 18LST 21LST
1613-1657
Fig. 2. Example of afternoon rain (mm/h)
estimated by Dhaka Radar at 1613LST, 15 April
2000 (left panel). Right panel is rain rate
averaged for 22 scans during a 45 minutes rainy
spell on that day .
Fig. 3. Example of morning rain (mm/h) in the
northern border of the country estimated by Dhaka
radar at 0504 LST on 2 June 2000.
BMD 2 June 2000
1-day
Fig. 4. Example of the distribution of rainfall
(mm/day) over the country estimated by Dhaka
radar in a day (25 April 2000). For a specific
time rainfall is averaged from all PPI scans in
that hour.
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m4m5
Fig. 6. Same as Fig. 5 except averaged for 1
May to 30 May 2000. Heavy rain is observed in
the northern border side of the country at 00,
06 and 09 LST. For 1-day, rain is moderated in
the western part of the country.
00
15
06
18
Fig. 5. Temporal and spatial variations of
rainfall (mm/day) estimated by Dhaka Radar,
averaged for 16 April to 30 April 2000. Left
panel top to bottom for 00, 06, 09, 12 while
right panel top to bottom for 15, 18, 21, 1-day.
Time unit is LST(UTC6 hours). Heavy rain is
observed in the northern and eastern parts of the
country.
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21
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Av.
Apr.
May
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m6m7
Fig. 8. Same as Fig. 5 except averaged for 1
July to 30 July 2000. In this month very light
rain is observed over the country. However, 1-day
rainfall shows relatively high rate in northern
border and southern costal region.
Fig. 7. Same as Fig. 5 except averaged for 1
June to 30 June 2000. Some places show heavy rain
in different time of the day. Northern border
shows maximum rain in night-morning while
southern costal region shows maximum in day time.
Jun.
Jul.
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8.1-8.30TA
Fig. 10. Same as Fig. 5 except averaged for 16
April to 30 August 2000. It seems that northern
and eastern parts of the country get much rain
comparing to western and southern parts during
the five monsoon months of this year.
Fig. 9. Same as Fig. 5 except averaged for 1
August to 30 August 2000. Rainfall is heavy
during night-morning time comparing to day time.
Aug.
Apr.-Aug.
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Rawin sonde (4-times daily)

• Dhaka station, 4-times daily
• 2001 summer (18 days total)
• June 28, 29
• July 4, 9, 10-11, 17-18, 21-22, 26-27, 30-31
• August 1, 5, 14-15

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Diurnal wind variations
Zonal wind velocity
Meridional wind velocity
SW
NE
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Meridional q transport
Specific humidity
Meridional wind velocity
qvgt0
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Convection and wind anomaly
In the daytime
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Convection and wind anomaly
In the midnight
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Summary (2)

• Diurnal wind anomaly transports water vapor
  northward
• i.e. qvgt0
• Diurnal wind variation is
• opposite to the land-sea breeze
• consistent with the diurnal variation of the
  convective activity

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Convection, wind, pressure
In the daytime
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Convection, wind, pressure
In the midnight
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Rawin-sonde

• 500-1000m?????(??????)
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2001, 4-times daily
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• BMD??
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• 1?4?
• 1992(4)-2001
• Dhaka,Chittagong
• ???1999-2001
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• 0.6, 0.9, 1.5, 2.1(, 3.0)km
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• 00Z(06LST)?????????????,06-12LST, 12-18LST,
  18-24LST, 24-06LST????????????????.

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