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).