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