Juliane Schwendike and Sarah Jones
http://www.sat.dundee.ac.uk/abin/geobrowse/MSG/2006/
The Interaction between Convection and African Easterly Waves: a Model Case
Study
Forschungszentrum Karlsruhe
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13/09/2006, 00 UTC
10/09/2006, 12 UTC
11/09/2006, 00 UTC
11/09/2006, 12 UTC
10/09/2006, 00 UTC
13/09/2006, 12 UTC
14/09/2006, 00 UTC
Tropical Depression
Tropical Storm
Meteosat images: http://www.sat.dundee.ac.uk/abin/geobrowse/MSG/2006/9Channel 5: water vapour 5.35 - 7.15 µm.
17/09/2006, 00 UTC
Hurricane Helene
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Hovmoeller between 6N and 16N
Relative vorticity in 700 hPa
05Sep
09Sep
07Sep
11Sep
13Sep
15Sep40°W 10°E0°20°W
TS Helene
Tropical Depression
The AEW in the 700-hPa ECMWF Analysis
• Propagation speed: ~10 m s-1
• 9 Sep: Initiation of convection ahead of the trough of the AEW
• 10-11Sep: crossing from Land to water
• 12 Sep: tropical depression
• 14 Sep: Tropical Storm Helene
• 16 Sep: Hurricane Helene
Convective system in satellite images
Developing tropical depression in satellite images
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Model simulations with COSMO 4.0
Model regions
• Forecast model of the Deutscher Wetterdienst (DWD): COSMO 4.0
• Horizontal resolution: 28 km and 2.8 km
• 50 levels• No
parameterisation of convection with 2.8km resolution
• 72-h forecasts• Initiated with
ECMWF analyses
100 200 400 800 12001000 1400 18001600 2000 2200 2400 2600
orography [m]
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10E35W
10Sep
11Sep
12Sep
12UTC
12UTC
12UTC
12UTC
Hovmoeller between 6N and 16N ECMWFRelative vorticity at 700 hPa
0° 10E
Hovmoeller between 6N and 16N COSMORelative vorticity at 700 hPa
35W
10Sep
11Sep
12Sep
12UTC
12UTC
12UTC
12UTC 0°
The AEW in the 700-hPa ECMWF Analysis and in COSMO COSMO, 28 km resolution
72h Forecast initialised at 9 September 2006, 12 UTCECMWF Analysis
19°W7°N
17°N
1°W
10/09/2006, 00 UTC
12h forecast initiated at 9 Sep 2006, 12 UTCHeight (1000 hPa) COSMO T+12Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
Convection over West Africa
30h forecast initiated at 9 Sep 2006, 12 UTCHeight (1000 hPa) COSMO T+30Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
19°W7°N
17°N
10/09/2006, 18 UTC
1°W
Image courtesy for the RTD Product of Météo France.
18°W 12°W 6°W8°N
12°N
16°N
18°W 12°W 6°W8°N
12°N
16°N
12h forecast initiated at 10 Sep 2006, 12 UTCHeight (1000 hPa) COSMO T+12Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
21h forecast initiated at 11 Sep 2006, 00 UTCHeight (1000 hPa) COSMO T+21Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
11/09/2006, 00 UTC
11/09/2006, 12 UTC
Convection over West Africa and the Atlantic
24°W 18°W 12°W
12°N
8°N
5°N28°W
10°N
22°W 16°W 10°W
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Becoming a Tropical Depression 12h forecast initiated at 12 Sep 2006, 00 UTCHeight (1000 hPa) COSMO T+12Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
12h forecast initiated at 13 Sep 2006, 00 UTCHeight (1000 hPa) COSMO T+12Vert. integral of humidity, cloud water and ice (kg/m2) + wind (m/s)
12/09/2006, 12 UTC
32°W5°N
17°N
11°W
13/09/2006, 12 UTC
32°W5°N
17°N
11°W
12°W30°W 24°W 18°W6°N
10°N
14°N
16°W22°W28°W34°W
8°N
12°N
16°N
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Tropical Storm Helene12h forecast initiated at 16 Sep 2006, 00 UTC Height (700 hPa) COSMO T+12Specific humidity (kg/kg) and wind (m/s)
16/09/2006, 12 UTC
Image courtesy of Jason Dunion, HRD & CIMSS.
Image courtesy to CIMSS.
56°W 50°W 44°W
14°N
18°N
22°N
TS Helene 16 Sep 2006,
12 UTC
Saharan Air Layer (SAL)
Convection over Land vs. Ocean West Africa
Atlantic
zonal wind (contours); vertical velocity (shaded) rel. vorticity (contours); diabatic heating (shaded)
B
D
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Potential Temperature Budget Analysis: Over Land
300
400
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
Average over box A
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Potential Temperature Budget Analysis: Over Land
Average over box B
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
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Potential Temperature Budget Analysis: Over Land
Average over box C
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
Θ tendency for MCS over West Africa
Ascent
Descent
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Potential Vorticity Budget
)vkf(gPV
)F(g)f(gPVv
t
PV
))F((g))vkf((gvPV)PVv(t
PV
Potential vorticity (PV):
PV budget:
PV budget:
Diabatic PV changes
Frictional PV changes
very small
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Potential Vorticity Budget
PV budget:
y
u
x
vf
pg
xp
u
yg
p
v
yxg
Diabatic PV tendency
=
“Horizontal component”
“Vertical component”
))F((g))vkf((gvPV)PVv(t
PV
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PV tendency for the whole boxes for MCS over West Africa
A CB
diabatic PV tendencyhorizontal componentvertical component
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Potential Temperature Budget Analysis: Over Water
Average over box D
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
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Potential Temperature Budget Analysis: Over Water
Average over box E
___ vertical advection - - - grid scale moist processes ….. horizontal advection turbulence radiation sum of all tendencies
D
D
E
E
Θ tendency for strong ascent region
Θ tendency for strong descent region
Θ tendency for convective
system over the Ocean
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D E
Diabatic PV tendency for the whole boxes
PV tendency for convective system over the Ocean
diabatic PV tendencyhorizontal componentvertical component
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West Africa Eastern Atlantic
Mean PV at the beginning and end of the convective system‘s life cycle
PV at the beginning PV at the end
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Summary
• Updraught, heating and rel. vorticity are tilted over West Africa and upright over the Atlantic
• Diabatic PV tendency at low-levels positive and negative at mid and upper levels
• Increased low-level PV could enhance low-level monsoon flow behind the system and strengthen the AEW trough and AEJ at 700 hPa
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Outlook: Interaction with SAL
30h forecast initiated at 17 Sep 2006, 12 UTC Height (700 hPa) COSMO T+30Specific humidity (kg/kg) and wind (m/s) 18 September 2006, 18UTC
Precipitable water (mm)
Image courtesy Naval Research Laboratory.www.nrlmry.navy.mil/sat_products.html
28°N
20°N
Modelling with COSMO-ART (Aerosol and Reactive Trace gases).
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