1. Analysis of Turbulence Development in the Morning
Based on Richardson Number
Josette Marquardt
Thishan Karandana
Yunpeng Shan

2. Outline Introduction to Richardson Number Evaluation to convection
Evaluation to wind shear
Conclusion

3. Introduction to Richardson Number
1. Calculation
Richardson Number = (-1)*(work by buoyancy)/(work by wind shear)
>0, Stable PBL condition
TKE decreases
Flux Richardson Number Ri
<0, Unstable PBL condition TKE increases
Gradient Richardson Number
Bulk Richardson Number

4. Introduction to Richarson Number
2. Development of Boundary Layer

5. Y Y X X Z Z X X Introduction to Richardson Number
3. Conversion of Richardson Number Y Y X X Z Z X X
There is no wind shear
Wind shear

6. Introduction to Richardson Number
4. Comparison between convection and wind shear
It seems that turbulence during daily time is dominated by dry convection, while turbulence at night is controlled by wind shear.
Observing data is used to check if this assumption is true.
(Wyngaard J. C. 1990)

7. Evaluation to convection
1. Convections caused by the Long Wave Radiation(LWR)
Here we can see that 15% out-coming long wave radiation is absorbed by atmosphere. We assume that a constant portion of this energy has been converted into TKE.
Heated atmosphere will show an increasing potential temperature which also means a positive Ri’’ and increasing TKE.

8. Evaluation to convection
2. Kinetic Energy Variation caused by Potential Temperature
After sun rising, TKE had an obvious increasing trend and stayed a fluctuate condition from 09:30. The same thing happened to flow kinetic energy(FKE).
After sun rising, surface temperature, potential temperature and long wave radiation increased obviously. As a result of it, more energy could be provided in order to maintain the turbulence.

9. Y X Evaluation of wind shear
1. Richardson Number variation caused by wind shear Y X
Wind shear =

10. Evaluation of wind shear
There was an increasing trend of wind shear, but TKE portion did not show any rising. It seems that the wind shear do not make a significant contribution to TKE
2. Turbulence caused by wind shear in the morning
After sun rising, there was an increasing trend for both TKE and FKE. When it came to 09:30, this increasing trend converted into a fluctuating condition. Although direction of horizontal wind varied, the increasing trend from 07:00 to 9:30 was obvious.

11. Evaluation of wind shear
3. Comparison of two physical mechanism
Increasing absolute value of w means more and more dry convection happened during this time.

12. Comparison of averaged 1min U,V and W data with calculated based on raw data

13. Conclusion
A modified Richardson Number was used in order to investigate contribution of long wave radiation and wind shear to TKE.
From sun rising to about 9:30, TKE and FKE increased obviously, while the ratio that TKE is divided by sum of TKE and FKE stayed constant.
Both TKE and FKE stayed in a fluctuation condition , rather than going on increasing, after 9:30 when surface received enough solar energy, although surface temperature kept rising.
By comparison, it seems that convection caused by long wave radiation make a larger contribution to developing turbulence after sun rising.

14. Thanks for
your attention