object-oriented identification of coherent structures: a multi-case … · 2019. 10. 23. ·...
TRANSCRIPT
Object-oriented identification of coherent structures: A multi-case analysis of boundary-layer Large-Eddy Simulations
4 October 2019
Florent BrientFleur Couvreux, Catherine Rio, Rachel Honnert
CNRM/Météo-France/CNRS
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@z!0�0 + ↵(c� e) +Qrad
resolved parameterized
Turbulent and convective vertical transport
!0�0 = �K@�
@z
!0�0 = �!c(�c � �e)
turbulence
convection
Closure assumptions
Witek et. al 11
Errors in representing boundary-layer clouds significantly influence cloud feedbacks, the hydrological sensitivity, regional climate projections…
—> Investigating coherent structures in Large Eddy Simulations for better understanding of PBL motions (MESO-NH model)
Representing the boundary layer in climate models
Object-oriented sampling• Definition of coherent structures : 1. Ensemble of grid boxes satisfying the conditional sampling CS = {s’(x,y,z)>m*𝜎s(z)} based
on Couvreux et. al (10) (with s’(x,y,z) anomalies of tracer concentrations) 2. Object = Contiguous cells of positive CS (sharing face, edge, corner) 3. Selected object = Object with volume larger than Vmin
https://gitlab.com/tropics/objectsCollaborative project:
StCu by FIRE
Object-oriented sampling
• Advantages: • 3D geometrical coherence • Individual object characterisation • No a priori assumptions
of flow characteristics (𝜔, ql)
• Main results for StCu: • Objects cover 20% of the volume, but
contribute to ~80% of moisture and temperature resolved fluxes
• Coherent downdrafts matter !
StCu by FIRE
Brient et. al, 19 (GRL)
• Definition of coherent structures : 1. Ensemble of grid boxes satisfying the conditional sampling CS = {s’(x,y,z)>m*𝜎s(z)} based
on Couvreux et. al (10) (with s’(x,y,z) anomalies of tracer concentrations) 2. Object = Contiguous cells of positive CS (sharing face, edge, corner) 3. Selected object = Object with volume larger than Vmin
https://gitlab.com/tropics/objectsCollaborative project:
A diversity of boundary-layer situations
Clear-sky Stratus/Fog Stratocumulus St-to-Cu Cumulus
Continental
Marine
Are coherent structures consistent across boundary layers?
Clear-sky Stratus/Fog Stratocumulus St-to-Cu Cumulus
Continental
Marine
IHOP
FIRE ASTEX RICO
BOMEXCONSTRAIN
ARMCu
CGILS (s12)DYCOMS
AYOTTE
WarmCold
Microphysics
A diversity of boundary-layer situations
Clear-sky Stratus/Fog Stratocumulus St-to-Cu Cumulus
Continental
Marine
Are coherent structures consistent across boundary layers?
Clear-sky Stratus/Fog Stratocumulus St-to-Cu Cumulus
Continental
Marine
IHOP
FIRE ASTEX RICO
BOMEXCONSTRAIN
ARMCu
CGILS (s12)DYCOMS
AYOTTE
WarmCold
Microphysics
A diversity of boundary-layer situations
• A new tracer emitted above the domain-average cloud base —> Tracking structures entrained in the mixed layer
• Updrafts are separated by positive/negative vertical motions —> Returning shells
• Definition of “PBL-top” tracers for clear skies
First layer where:
Update since Brient et. al (19):
Clear-sky Stratus/Fog Stratocumulus St-to-Cu Cumulus
Continental
Marine
Are coherent structures consistent across boundary layers?
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
Returning shells
Mean Precipitable Water (mm/day)
Convective Clear Sky (IHOP)
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Domain-mean resolved fluxes
Alti
tude
(km
)
X (m)
Y (m)
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
Domain-mean resolved fluxesMean Precipitable Water (mm/day)
Convective Clear Sky (IHOP)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
11% 1% 13%Domain-mean volume
All Structures
Entrained downdraftUpdraft
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Domain-mean resolved fluxesMean Precipitable Water (mm/day)
Alti
tude
(km
)
Convective Clear Sky (IHOP)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
11% 1% 13%
• Objects contribute to 74/86% of total heat/moisture fluxes (for 25% of volume)
All Structures
Entrained downdraftUpdraft
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Boundary-layer top
Domain-mean resolved fluxesMean Precipitable Water (mm/day)
Alti
tude
(km
)
Convective Clear Sky (IHOP)
Domain-mean volume
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
Liquid Water Content (g/m2)
All Structures
Entrained downdraftUpdraft
Sub-cloud downdraftStratocumulus (FIRE)
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
Liquid Water Content (g/m2)
1%
7%
All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
Alti
tude
(km
)
Domain-mean volume:
Stratocumulus (FIRE)
(K m/s) (g/kg m/s)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
Liquid Water Content (g/m2)
10%
All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
1%
7%
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
Domain-mean volume:
Stratocumulus (FIRE)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
Liquid Water Content (g/m2)
10%
All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
1%
7%
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
3%
Domain-mean volume:
Stratocumulus (FIRE)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers
Liquid Water Content (g/m2)
3%
All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
Domain-mean volume:
10%
1%
7%
• Objects contribute to 88/82% of total heat/moisture fluxes (for 21% of volume)
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
Stratocumulus (FIRE)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
Liquid Water Content (g/m2)
Cumulus (BOMEX)
Cloud top
Cloud base
Domain-mean resolved fluxes
!0✓0l !0q0t
(K m/s) (g/kg m/s)
Alti
tude
(km
)
Returning shells
X (m)
Y (m)
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
2%
6%
Liquid Water Content (g/m2)Domain-mean
volume:
Cumulus (BOMEX)
Domain-mean resolved fluxes
!0✓0l !0q0t
(g/kg m/s)
Alti
tude
(km
)
(K m/s)Cloud top
Cloud base
Returning shells
X (m)
Y (m)
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
2%
Liquid Water Content (g/m2)Domain-mean
volume:
2%
6%
Cumulus (BOMEX)
Domain-mean resolved fluxes
!0✓0l !0q0t
(g/kg m/s)
Alti
tude
(km
)
(K m/s)Cloud top
Cloud base
Returning shells
X (m)
Y (m)
Characteristics of boundary layers All Structures
Entrained downdraftUpdraft
Sub-cloud downdraft
2%
3%
Liquid Water Content (g/m2)Domain-mean
volume:
2%
6%
• Objects contribute to 90/85% of total heat/moisture fluxes (for 13% of volume)
Cumulus (BOMEX)
Domain-mean resolved fluxes
!0✓0l !0q0t
(g/kg m/s)
Alti
tude
(km
)
(K m/s)Cloud top
Cloud base
Returning shells
X (m)
Y (m)
Time evolution of boundary layersRelative Humidity (%)
Average contribution to fluxes
Entrained downdraftUpdraft
Sub-cloud downdraftReturning shells
65%
25%10%
Clear Sky
Time evolution of boundary layersRelative Humidity (%)
Average contribution to fluxes
Entrained downdraftUpdraft
Sub-cloud downdraftReturning shells
65%
25%10%
Clear Sky
Cloud Fraction (%)
50%35%4%4%
40%40%2%1%
Day Night
StCuAverage contribution
to fluxes
Time evolution of boundary layersRelative Humidity (%)
Average contribution to fluxes
Entrained downdraftUpdraft
Sub-cloud downdraftReturning shells
65%
25%10%
Clear Sky
Cloud Fraction (%)
50%35%4%4%
40%40%2%1%
Day Night
StCuAverage contribution
to fluxes
St-to-Cu
Cloud Fraction (%)
t+8h t+26h
60%5%4%5%
95%2%1%
17%
Contribution to fluxes
Time evolution of boundary layersRelative Humidity (%)
Average contribution to fluxes
Entrained downdraftUpdraft
Sub-cloud downdraftReturning shells
65%
25%10%
Clear Sky
Cloud Fraction (%)
50%35%4%4%
40%40%2%1%
Day Night
StCuAverage contribution
to fluxes
St-to-Cu
Cloud Fraction (%)
t+8h t+26h
60%5%4%5%
95%2%1%
17%
Contribution to fluxes
Cu
85%2%10%10%
Cloud Fraction (%)
Average contribution to fluxes
60%1%20%5%
sub-cloud only
Time evolution of boundary layersRelative Humidity (%)
Average contribution to fluxes
Entrained downdraftUpdraft
Sub-cloud downdraftReturning shells
65%
25%10%
Clear Sky
Cloud Fraction (%)
50%35%4%4%
40%40%2%1%
Day Night
StCuAverage contribution
to fluxes
St-to-Cu
Cloud Fraction (%)
t+8h t+26h
60%5%4%5%
95%2%1%
17%
Contribution to fluxes
Cu
85%2%10%10%
Cloud Fraction (%)
Average contribution to fluxes
60%1%20%5%
sub-cloud only
Coherent structures in observationsAre LES realistic?
Can we observe boundary-layer coherent structures?
Image Satellite Suomi07/09/2019
Coherent structures in observationsAre LES realistic?
Can we observe boundary-layer coherent structures?
100 km
Image Satellite Suomi07/09/2019
Coherent structures in observations
Updrafts
Returning shells?
Are LES realistic?Can we observe boundary-layer coherent structures?
100 km
Image Satellite Suomi07/09/2019
Coherent structures in observations
Updrafts
Returning shells?
Entrained downdraftSaturated
environment
Are LES realistic?Can we observe boundary-layer coherent structures?
100 km
Image Satellite Suomi07/09/2019
Conclusions
Future work about boundary-layer coherent structures:
Coherent structures in LES using the MESO-NH model
Updrafts contribute the most to heat and moisture transportDowndrafts contribute significantly to transport only in StCu simulations (FIRE)Downward coherent structures exist below the cloud base and ressemble coherent downdrafts of convective clear-sky situations (IHOP)
Returning shells are close to updrafts but contribute only to ~10% of fluxes
Conclusions
Future work about boundary-layer coherent structures:
• Building better unified parameterizations for low-cloudsHow should be represented downward motions? Is the top-hat approximation relevant for downdrafts?
• Process-oriented analysis of the meso-scale low-cloud organisationWhat are the drivers of boundary-layer characteristics? Is the distance between updrafts important?
• Low-cloud feedback mechanismsChanges in coherent structures drive changes in cloudiness. How do coherent structures will change with global warming?
Coherent structures in LES using the MESO-NH model
Updrafts contribute the most to heat and moisture transportDowndrafts contribute significantly to transport only in StCu simulations (FIRE)Downward coherent structures exist below the cloud base and ressemble coherent downdrafts of convective clear-sky situations (IHOP)
Returning shells are close to updrafts but contribute only to ~10% of fluxes
Extra
Physical understanding of downdrafts
Zhou and Bretherton (19)
StCu (FIRE)
Physical understanding of downdrafts
Zhou and Bretherton (19)
Downdraft objects Updraft objects
StCu (FIRE)
Physical understanding of downdrafts
Zhou and Bretherton (19)
Downdraft objects Updraft objects
StCu (FIRE)
rH · V (s-1)Divergence
Physical understanding of downdrafts
Zhou and Bretherton (19)
Downdraft objects Updraft objects
• Divergence at the top of updrafts
• Convergence where downdrafts start (20-30m below the updraft’s divergence)
• Updrafts trigger downdrafts? Then, amplify by buoyancy reversal?
StCu (FIRE)
rH · V (s-1)Divergence
! (m s-1)Vertical velocity
Physical understanding of downdrafts
Witek et. al (11)
Downdraft objects
Updraft objects
• Divergence at the top of updrafts
• Convergence where downdrafts start (20-30m below the updraft’s divergence)
• Updrafts trigger downdrafts? Then, amplify by buoyancy reversal, or not?
Clear-sky (IHOP)
Divergence(s-1)rH · V
Vertical velocity! (m s-1)