Simulations of thermal circulations over complex terrain during ESCOMPTE using Méso-

NH

Sophie Bastin+ and Philippe Drobinski

+: Current affiliation: NCAR, Boulder, CO, USA

Institut Pierre Simon Laplace/ Service d’Aéronomie

What is at stake?

• Better understanding and forecast of pollution episodes in the Marseille area:

numerous and intensive pollution events during summertime that are not well forecasted

Poor understanding of the atmospheric boundary-layer dynamical processes in this region that play a major role in the distribution of pollutants

• Improvement of chemistry-transport models Generalisation at other areas

Study of the atmospheric boundary layer dynamics at the scale of the ESCOMPTE area during summertime

Méso-NH simulations

• 50 vertical levels from the surface to 18 km:– 12 levels in the first 1000 m– 9 levels with a grid size less

than 100 m

• 2 simulations with 2 or 3 nested domains:– Resolution of the finest domain: 2 or 3 km

• Initialisation and forcing with ECMWF analyses

Triangles: model

Solid line: surface stations

25 June 2001 case study: pure sea breeze

• Development of the breeze everywhere along the coast

• Propagation speed: 10-20 km hr-1 (Bechtold et al., 1991)

25 June 2001 case study

Very good agreement

Bastin and Drobinski, QJRMS, in revision

coastline

WIND observations between 1645 &

1710 UTC

MESO-NH simulation at 1700

UTC

References H/v relationship H/v at 43.5°N

Rotunno (1983) N/(f2-2)1/2 146

Dalu and Pielke (1989) N/(f2+k2)1/2 75

Niino (1987); Steyn (1998)

N/ 138

Bastin et al. (AR, 2005) observations 200

25 June 2001 case study: pure sea breeze

Sea breeze front Structure

Turbulent Kinetic Energy (TKE)

e :

2, )(2

1iue ui

’: turbulent components of the wind

1200: convection over land where there is no sea breeze flow.

1400: strong upward and mixing at the breeze ‘head’

1700: decrease of upward and mixing

1900: no more TKE

sea

land

25 June 2001 case study: pure sea breeze

Sea breeze front

L

eC

x

eeLC

xu

g

x

uuueu

xt

e

jrefe

jrefvii

vk

ikikref

kref ref

2/32/1,,

3,, )(

1)(

1

advection Buoyant production

Shear production

Diffusion Dissipation

TKE budget:

Structure

12 14

17

19

25 June 2001 case study: pure sea breeze

Mass fluxes 14 UTC

0 – 300 m 300 – 1000 m

front

Slope winds

convergence

Slope winds + breeze

detrainment

Intensification of slope winds by the sea breeze Bastin and Drobinski, BLM, 2005

25 June 2001 case study: pure sea breeze

14 UTC 17 UTC

11 UTC

Massif Central wake

Vallon d’Ol

22 June 2001 case study: combination with Mistral

Bastin et al., MWR, in revision

Bastin et al., GRL, 2005

Vallon d’Ol

Westerly wind

North-westerly wind

22 June 2001 case study: combination with Mistral

Flow regime OnsetMaximum depth

Direction IntensityInland

penetration

Pure sea breeze

08-10 UTC

~ 1500 m

S 5 m s-1 100 km

Mistral/breeze11-17 UTC

< 1000 m

O/SO 5 m s-1 < 50 km

Publications

Bastin S., Drobinski P., Guénard V., Caccia J.L., Campistron B., Dabas A. M., Delville P., Reitebuch O., Werner C.: On the Interaction Between Sea Breeze and Summer Mistral at the Exit of the Rhône Valley. Mon. Wea. Rev., in revision

Bastin S., Drobinski P.: Sea Breeze Induced Mass Transport over Complex Terrain in Southeastern France: A Case Study. Quart. J. Roy. Meteorol. Soc., in revision

Bastin S., Champollion C., Bock O., Drobinski P., Masson F., 2005: On the Use of GPS Tomography to Investigate Water Vapor Variability During a Mistral/Sea Breeze Event in Southeastern France. Geophys. Res. Let, 32, L05808, doi:10.1029/2004GL021907

Bastin S., Drobinski P., Dabas A.M., Delville P., Reitebuch O., Werner C., 2005: Impact of the Rhône and Durance Valleys on Sea-Breeze Circulation in the Marseille Area. Atmos. Res., 74, 303-328

Bastin S., Drobinski P., 2005: Temperature and Wind Velocity Oscillations along a Gentle Slope during Sea-Breeze Events. Boundary Layer Meteorol., 114, 573-594