RCM sensitivity to domain size in summer and winter With the collaboration of: Jean-Philippe Morin...
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Transcript of RCM sensitivity to domain size in summer and winter With the collaboration of: Jean-Philippe Morin...
RCM sensitivity to domain size in summer and winter
With the collaboration of:
Jean-Philippe Morin (simulations)and Mathieu Moretti (diagnostics)
By Martin Leduc and René Laprise
The Big-Brother experiment
« Perfect-model » approach:
driving and nested model are the same.
differences between LB and BB fields are directly attributable to the nesting procedure.
Big-Brother Filtered Big-Brother Little-Brother
Measuring the RCM sensitivity to various parameters:
• Spatial resolution and the update frequency of the LBC: Denis et al. (2003), Antic et al. (2004) and Dimitrijevic and Laprise (2005)
• Errors in the nesting data: Diaconescu et al. (2007)
• Size of the domain: Leduc and Laprise (2008)
The domain-size issue (1)- LARGE domain -
Model is free to develop its own large-scale dynamics, differing from the nesting data.
Does spectral nudging is appropriate to solve this ?
"If you don't believe in the value of global climate models then there's no point in downscaling them” -Filippo Giorgi
Maybe not !
May be good: Small-scale physical processes can affect the large-scale dynamics.
constrain the RCM to follow the “good” large scales
let the RCM free to correct the “wrong” large scales
In other words:
• LBC exert a strong control on the solution (as for SN).
• Small-scale features have not enough time/space to develop.
The domain-size issue (2)- SMALL domain -
Leduc and Laprise (2008) :Effects related to the domain size have been studied for a winter case where the atmospheric flow is :
strong and westerly
Need to repeat the experiment with a summer flow.
Experimental framework
Simulations:
Big-Brother BB: 196x196
Little-Brothers LB1: 144x144 LB2: 120x120 LB3: 96x96 LB4: 72x72
Validation area: QC: 38x38
2 Periods: July 90 to 93 February 90 to 93
Sponge zone: 10 grid points
Summer and winter flows over Québec
SUMMER WINTER
ANIMATE !
700-hPa wind magnitude(temporal deviation)
Small scales
Large scales
SUMMER WINTER
Small-scale transient eddies of the 700-hPa wind magnitude
BB
LB1 LB2
LB3 LB4
(m/s)
R*LB1: 79%LB2: 68%LB3: 65%LB4: 78%
SUMMER
BB
LB1 LB2
LB3 LB4
R*LB1: 56%LB2: 50%LB3: 71%LB4: 44%
WINTER
(m/s)
Small-scale transient eddies of the 700-hPa relative humidity
(%)
R*LB1: 61%LB2: 49%LB3: 49%LB4: 50%
WINTERSUMMER
R*LB1: 90%LB2: 87%LB3: 89%LB4: 90% (%)
BB
LB1 LB2
LB3 LB4
BB
LB1 LB2
LB3 LB4
Small-scale transient variance ratio: LB / BB (wind magnitude)
WINTERSUMMER
(%) (%)
(%)
Small-scale transient variance ratio: LB / BB (relative humidity)
(%)
SUMMER WINTER
Did summer really heal our RCM ?
1- Flow characteristics (a high residency time)2- Intense convective processes3- Vertical turbulent fluxes
General conclusions
- Smaller domain can be used in summer -(for comparable skills)
Lateral boundary conditions control :
increases when the domain size is reduced, and is stronger in winter applied on large scales, it affects similarly the small ones
Magnitude of the small-scale features:
spin-up area in winter homogeneous spin-up in summer
Antic, S., R. Laprise, B. Denis and R. de Elía, 2004: Testing the downscaling ability of a one-way nested regional climate model in regions of complex topography. Climate Dynamics, 23, 473-493.
Denis, B., R. Laprise and D. Caya, 2003: Sensitivity of a regional climate model to the resolution of the lateral boundary conditions. Climate Dynamics, 20, 107-126.
Diaconescu, E. P., R. Laprise and L. Sushama, 2007: The impact of lateral boundary data errors on the simulated climate of a nested regional climate model. Climate Dynamics, 28, 333-350.
Dimitrijevic, M. and R. Laprise, 2005: Validation of the nesting technique in a RCM and sensitivity tests to the resolution of the lateral boundary conditions during summer. Climate Dynamics, 25, 555-580.
Leduc, M. and R. Laprise, 2008: Regional Climate Model sensitivity to domain size. Accepted in Climate Dynamics.
References
Taylor diagrams (ls)
Taylor diagrams (ss)
Spectral filters“T30” : 2160 to 1080 km
LPF : 2160 to 540 km
Small-scale transient variance ratio: LB / BB (relative vorticity)
700-hPa rvortSUMMER WINTER
Summer and winter flows over Québec
SUMMER WINTER