1. Advisors: Fuqing Zhang and Eugene Clothiaux
Large eddy simulation of multi-layer Arctic mixed-phase stratocumulus clouds:
Sensitivity to cloud condensation nuclei and ice nuclei number concentrations
Hui-Wen Lai
Advisors: Fuqing Zhang and Eugene Clothiaux
Group meeting 12 Dec. 2016

2. Introduction
The downwelling solar and longwave radiative fluxes in the Arctic are strongly impacted by Arctic Mixed-Phase Stratocumulus (AMPS) clouds (Curry et al., 1996).
Mixed-phase clouds are composed of a mixture of supercooled liquid water and ice crystals in a single or multiple stratiform layers. There are many factors that influence ice crystal growth conditions in mixed phase clouds, for example temperature, saturation ratio, and updraft speed (Morrison et al., 2012).
Liquid
Ice
Mixed-phase

3. Multi-layer Mixed-phase cloud
Multi-layer AMPS cloud layers near the boundary layer have been frequently observed but are poorly understood (Curry et al., 1996).
Cloud condensation nuclei (CCN) and ice nuclei (IN) may have a large impact on the formation of AMPS clouds.
Schematic diagram of multi-layer AMPS from McInnes and Curry (1995a, b)
Warm air
Temperature and humidity inversion
Radiative cooling induce mixing
Cool air
Cool surface
Most modeling studies of AMPS clouds have focused on single-layer clouds
Previous studies: Luo et al. (2008), Morrison et al. (2012), Solomon et al. (2011; 2014; 2015)

4. Case study of a multi-layer mixed-phase cloud
On 2 May 2013, a weak surface trough extended from the north towards Barrow, Alaska.
(NCEP/DOE AMIP-II Reanalysis (Reanalysis-2) GrADS image) L H

5. Large eddy simulation setting
Time:
Initial condition:
Water vapor mixing ratio: ERA-interim reanalysis
Other variables: NCEP Global Forecasting System final analysis
d01
d01 : 70 ×70 × 130 (25km)
d02 : 101 ×101 ×130 (5km)
d03 : 251 ×161 ×130 (1km)
d04 : 201 ×201 ×130 (0.2km)
Vertical resolution below 2km is 40 m
05/01
1800UTC
05/03
0000UTC
05/02
d04 started
d01, d02 and
d03 started
Physics Options in LES-WRF
Cumulus Parameterization:
Grell-Freitas ensemble scheme (d01, d02)
PBL Schemes:
Yonsei University scheme (d01, d02)
Cloud microphysics scheme:
Morrison 2-moment scheme

6. Sensitivity test to CCN and IN number concentration
Cloud condensation nuclei (CCN)
In Morrison two-moment scheme: 250 cm-3
Observation: 100 cm-3 (Bigg, 1996)
Experiments
Description
CCN (cm-3)
IN (m-3)
CNTR
Control run
250
NIN
deCCN
Decrease CCN
100
deIN
Decrease IN
0.5×NIN
inIN
Increase IN
2.0×NIN
Ice nuclei (IN)
Primary nucleation
N IN =0.005exp −T
Previous studies: Luo et al. (2008), Morrison et al. (2012), Solomon et al. (2011; 2014; 2015)

7. Simulated cloud water
deCCN
deIN
CNTR
inIN
(Z)

8. NTU triple-moment microphysical scheme
Morrison two-moment scheme
- Mixing ratio (mass concentration with fixed density)
- Number concentration
NTU triple-moment scheme
- Zeroth moment (number)
- Second moment (surface area)
- Third moment (volume concentration)
Adaptive growth habit of pristine ice crystals

9. NTU scheme Parameterization Hour (UTC) Hour (UTC) (a) Water vapor
(f) Water vapor
(b) Cloud water
(g) Cloud water
(c) Rain
(h) Rain
<
(d) Cloud ice
(i) Cloud ice
(e) Snow
Hour (UTC)
Hour (UTC)

10. Summary
The AMPS cloud in our case is sensitive to changes in CCN and IN number concentration. Changing both the CCN and IN number concentrations resulted in an absence of the second cloud layer in the simulation.
NTU microphysical scheme which allows ice crystal shape change may give a better description of multi-layer AMPS.

12. Introduction
Solomon et al. [2015] demonstrated that sustained ice nuclei (IN) number concentration through a drying subcloud layer and additional activation of IN are sufficient to maintain ice production and regulate liquid production in a decoupled AMPS.

13. Introduction
Solomon et al. [2015] demonstrated that sustained ice nuclei (IN) number concentration through a drying subcloud layer and additional activation of IN are sufficient to maintain ice production and regulate liquid production in a decoupled AMPS.
LES resolves the eddies that contain most of the kinetic energy and carry most of the fluxes in turbulent flows. Since AMPS clouds develop with and within the boundary layer, LES is able to resolve the turbulence in these shallow clouds.

14. Heat and moisture fluxes

15. Liquid water path and radiation fluxes

16. Cloud ice
deCCN
deIN
CNTR
inIN
deCCN

17. Multiple cloud layers assumption:
Paper review
Multiple cloud layers assumption:
Herman and Goody (1976)
Tsay and Jayaweera (1984)
McInnes and Curry (1995a, b)
Solar radiation
Temperature and humidity inversion
Longwave
ascent/entrainment
Radiative cooling induce mixing
Cool
Local evaporation
Advective cloud
Longwave
Warm air
Cool surface

18. HSRL and KAZR observation

19. HSRL and KAZR observation

20. HSRL and KAZR observation

21. m05

22. sfs

23. m25

24. m10