1. PBL simulated from different PBL Schemes in WRF during DICE
Wenyan Huang, Xinyong Shen, Qi Li
Nanjing University of Information Science and Technology
(Nanjing Institute of Meteorology)
Weiguo Wang, IMSG/NOAA

2. OUTLINE Motivation Experiment Design and PBL Schemes
Preliminary Results
a uncoupled SCM
b coupled SCM
Summary

3. 1. Motivation
Vertical transportations of atmospheric momentum, heat and moisture were presented in PBL schemes which play important roles in numerical prediction.
PBL schemes are advanced and new methods are also used in PBL parameterizations, but results from different PBL schemes are different from each other.
Single Column Models eliminating the feedback from large-scale forcing fields are outstanding tools for PBL schemes comparison.
SCM in WRFV3.5 was used in DICE to evaluate several PBL schemes' performance in DICE.
数值模式快速发展
模拟效果差异大

4. Coupled with Land-Surface WRF_SCM (coupled)
2. Experiment Design and PBL Schemes
Experiments Design
WRF_SCM (uncoupled)
Coupled with Land-Surface WRF_SCM (coupled)
Time Steps(s) 20
Vertical Levels 60
Microphysics
WSM6
Shortwave radiation
RRTM
Longwave radiation
Surface-layer
MYJ
Land-surface
None
Noah
Initial and large-scale forcing fields were provided by DICE
Simulation periods: :00 ～ :00 (LST)
Model center: E, N

5. Five PBL Schemes Five PBL schemes can employ MYJ Surface-layer scheme
MYNN2
BouLac UW
M-Y level 2.5，TKE Predicted
Local Closure
1.5 order closure
2 order closure
M-Y level 3，TKE Predicted
Local Closure
MYNN3
is turbulent exchange coefficient, is the mixing length， is the proportional coefficient， is turbulence kinetic energy, Great differences among PBL schemes were how to calculate and .
Five PBL schemes can employ MYJ Surface-layer scheme

6. 3. Uncoupled SCM Results
In SCM uncoupled with LSM, the boundary layer process is primarily driven by the observed surface fluxes, provided by DICE :
sensible heat flux
latent heat flux
momentum flux

7. 2 pm (LST) PT
24th th th
At daytime, turbulence mixes strongly in PBL and potential temperature can develop well in mixed-layer.
Mixed-layer from BouLac and UW schemes is deeper than the other three schemes.
Another major difference is that BouLac scheme's potential temperature is higher than the others.

8. 2 am (LST) PT
24th th th
At nighttime, because of cooling by surface radiation, inversion can be observed in PBL and above inversion layer is residual PBL.
All the schemes can simulate these characteristics well, so the difference is small.
BouLac scheme's potential temperature is higher than the others in residual PBL.

9. 2 pm (LST) MR
24th th th
At daytime, same as potential temperature, vapor mixed layer also can develop well in PBL. However, the Boulac and UW experiments show a deeper mixing than the other experiments.
The comparison results reveal slight distinctions among all the schemes, with small deviations from those observed.

10. 2 am (LST) MR
24th th th
At nighttime, inversion layer was observed in low level PBL at some time, and among these layers, simulations have apparent differences with observations, but residual PBL was simulated well.
There is little difference among all the schemes.

11. 2 pm (LST) WSP
24th th th
In general, wind speed profile is consistent with observations, but large differences can be found in lower level of PBL, e.g., 24th.
All schemes are similar.

12. 2 am (LST) WSP
24th th th
At nighttime, LLJ occurs in PBL, but the simulated speed of LLJ is smaller than the observations, e.g.,24th.
Near the surface, the differences among all schemes are obvious.

13. 2 pm (LST) WDR
24th th th
In general, the wind direction varies slightly with height in mixed layer.

14. 2 am (LST) WDR
24th th th
The simulated wind directions from all the schemes are less divergent at nighttime with slight biases.

15. 2 pm (LST) Kh 24th 25th 26th Kh shows the local exchange.
At daytime, Kh from UW scheme are much bigger than the others.

16. 2 am (LST) Kh
24th th th
At nighttime, Kh is small near surface, but we can see big values in residual PBL e,g,in 25th.

17. 2 pm (LST) Km
24th th th
At daytime, Km from UW scheme are much bigger than the others.

18. 2 am (LST) Km
24th th th
At nighttime, the values of 24th and 25th are bigger than that of 26th.

19. 2 pm (LST) TKE
24th th th
At daytime, turbulent kinetic energy (TKE) simulated by different schemes are divergent. Values from MYJ and UW scheme are weaker than the others.

20. 2 am (LST) TKE
24th th th
At nighttime, the results from all the schemes are less divergent.

21. PBL Height
The PBL height, directly output from the model, was diagnosed by different approaches.
For a fair comparison, the bulk Richardson number method was used to diagnose the PBL height.
Calculate Ri θ

22. Model output Ri-method
As is shown in the left figure, the simulated outputs vary significantly from each other because different schemes use different methods to diagnose PBL height. In comparison, the results from the bulk Richardson number method show slight discrepancies.
The PBL simulated by the Boulac and UW schemes are deeper than the others, which are in good agreement with higher potential temperature mixed-layer at daytime.

23. 3. Coupled SCM Results
In SCM coupled with LSM, the boundary layer process is primarily driven by the Noah land surface model and MYJ surface layer scheme.  
The suface fluxes is not given but calculated by the model.
LSM initial temperature and soil moisture are obtained from 10-yr spin-up data, provided by DICE.

24. Surface fluxes
The sensible heat flux simulated by SCM coupled with Noah land-surface model is greater at noon. However, the simulated latent heat flux is smaller at daytime.
The friction velocity of all the schemes fit well with the observations, except that a sudden change simulated by the BouLac scheme occurred in the second night.
In a word, the results from all the schemes are less divergent.
HFX LH
UST

25. PT
2 pm
2 am
24th th th
Results are similar to that from uncoupled SCM at daytime.
BouLac scheme simulated stronger turbulence in the second night, weaker inversion layer and higher potential temperature in PBL.

26. MR
2 pm
2 am
24th th th
Results are similar to that from uncoupled SCM, but negative difference of latent heat flux may lead to lower vapor mixing ratio at daytime. MR simulated by the coupled SCM is smaller than that of uncoupled SCM.

27. WSP
2 pm
2 am
24th th th
Results are similar to that from uncoupled SCM.
LLJ simulated by Boulac scheme is weaker and wind speed in low-level PBL higher because of stronger turbulence mixing in the second night, which also may lead to larger friction velocity in simulation using this scheme.

28. WDR
2 pm
2 am
24th th th
Results are same with uncoupled SCM .

29. Kh
2 pm
2 am
24th th th
Results are similar to that from uncoupled SCM. The major difference is that the exchange coefficient of turbulent heat and moisture simulated by Boulac scheme is larger, corresponding to stronger turbulence mixing in the second night.

30. Km
2 pm
2 am
24th th th
Results are similar to that from uncoupled SCM. The major difference is that the exchange coefficient of momentum simulated by Boulac scheme is larger in the second night, corresponding to stronger turbulence mixing during that night.

31. 4. Summary
Both uncoupled WRF-SCM and SCM coupled with Noah Land-surface model show good performance in simulating the PBL structure in DICE.
The results are different from different PBL schemes. Moreover, the daytime difference is more obvious than the nocturnal. The mixed layers simulated by BouLac and UW schemes are deeper than the others at daytime.
The sensible heat flux and friction velocity simulated by the SCM coupled with Noah land-surface model corresponds to the observations. The latent heat flux simulated by this model is smaller at daytime.
We are working on what might cause those differences.

32. Thank You