juliane schwendike and sarah jones

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

in der Helmholtz-Gemeinschaft

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



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



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]



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


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



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



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)


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



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



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




Average over box B





Average over box C



Θ tendency for MCS over West Africa

Ascent

Descent



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



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



PV tendency for the whole boxes for MCS over West Africa

A CB

diabatic PV tendencyhorizontal componentvertical component



Potential Temperature Budget Analysis: Over Water

Average over box D




Potential Temperature Budget Analysis: Over Water

Average over box E


D

D

E

E

Θ tendency for strong ascent region

Θ tendency for strong descent region

Θ tendency for convective

system over the Ocean



D E

Diabatic PV tendency for the whole boxes

PV tendency for convective system over the Ocean

diabatic PV tendencyhorizontal componentvertical component



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



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



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).

juliane schwendike and sarah jones

Documents

hpa cosmo t

pv budget

ice kgm2 wind ms

cloud water

integral of humidity

n cosmorelative vorticity

n ecmwfrelative vorticity

water vapour