1. Statistics of turbulence profiles at Cerro Tololo
Tokovinin,
S. Baumont,
J. Vasquez
CTIO Seminar, September 5, 2002

2. Goals of the campaign: Contribution of ground layer
Predictions for SOAR AO
Understand seeing…
Use MASS and DIMM

3. What was measured?

4. Data overview All data for 0.5 microns at zenith!
Three months: April 29 to July 28, 2002
58 nights, 450 hours, profiles
21000 DIMM measurements
All data for 0.5 microns at zenith!

5. Examples

6. More examples…
July 14, 2002

7. Nightly median seeing

8. MASS-DIMM comparison

9. MASS-DIMM comparison
Two instruments based on different principles and calibrated independently agree very well!

10. Contribution of layers to seeing
Contributing
layers:
higher than 16 km
higher than 8 km
higher than 4 km
higher than 2 km
higher than 1 km
higher than 0.5 km
all layers : total
seeing

11. Numbers [arcseconds] 10% 25% 50% 75% 90% Total seeing 0.64 0.78 0.95
1.17
1.46
From 0.25km
0.28
0.38
0.55
0.83
1.24
From 2km
0.22
0.30
0.43
0.62
0.92
From 4km
0.19
0.26
0.37
0.53
0.73
From 8km
0.15
0.20
0.29
0.60
From 16km
0.10
0.12
0.16
0.21

12. Ground layer compensation
90%
75%
50%
25%
10%
Seeing
expectations
for different
levels of
layer
correction.

13. Temporal variation The lower layers change faster.
Characteristic evolution time between
15 min and
2 hours.

14. Turbulence vs. Jet Stream speed
Favorable
Jet-Stream
wind value
is m/s.

15. Total seeing vs. ground wind

16. Ground-layer seeing vs. ground wind

17. Four-day calm period Date Seeing median Free-atm. June 18 0.73 0.36
0.65
0.29
June 20
0.61
0.22
June 21
0.76
0.30
June 22
0.85
0.23
June 23
1.18
0.71

18. Conclusions Ground layer at Tololo contributes 50%
Free-atmosphere seeing never <0.15”, median 0.55”
Long periods of calm upper atmosphere
Low layers change faster
Seeing is dominated by local effects, fragile
“Lucky summits”? Modeling?