1. OC 3750 Operational Oceanography
Cruise Report - Frank Price
Atmospheric Effects on Surface Based Ducts in comparison with ETA Model and Radiosonde Data.

2. OC 3750 Operational Oceanography Cruise Report
Introduction
Types of Ducts
Synoptic Pattern
Observed Data
Conclusion

3. Different Types of Ducts
Elevated Duct
300
200
100
Surface-based
Duct
Height (m)
Evaporation Duct
M (Modified Refractivity Index)

4. Synoptic Pattern
The Monterey Bay, San Francisco Bay and shortly offshore experienced southwesterly winds on the backside of High pressure and approaching cold front. These winds brought warm moist air under an existing colder more dense atmosphere. Thus setting up an unstable atmosphere. This is why the first cruise experience surface based ducting.
As front approached from the west the atmosphere became saturated and the surface duct disappeared.
Below is a series of charts correlating to ship’s cruises

5. January 23, 2007 January 24, 2007 January 25, 2007 January 26, 2007
Sonde Z
Sonde Z
January 24, 2007
Sonde Z
Sonde Z
Sonde Z
Sonde Z
January 25, 2007
Sonde Z
Sonde Z
Sonde Z
Sonde Z
Sonde Z
Sonde Z
Sonde Z
Sonde Z
January 26, 2007
Sonde Z
Sonde Z
Sonde Z
Sonde Z 2320Z Arrival Pier 27 San Francisco End Leg I

6. Jan Z
500mb Heights Surface SLP

7. Jan Z
500mb Heights Surface SLP

8. Jan Z
500mb Heights Surface SLP

9. Jan Z
500mb Heights Surface SLP

10. Jan Z
500mb Heights Surface SLP

12. 24/00Z
24/00Z 15 4 2 10
24/06Z
24/18Z 5 14
25/00Z
25/06Z 17
25/12Z 6
26/00Z 8
26/06Z
26/18Z
Pierside26/23Z

13. Conclusion
Synoptic weather pattern presented an unstable atmosphere such that the first leg observed surfaced based duct where the second leg did not.
12 KM ETA Model did not have great horizontal resolution below 1000mb further extracting surface model and making an assumption to the 1000mb level may have caused discontinuity with truth.
Temperature Inversions and Atmospheric Instabilities cause significant changes in modified refractivity indexes (M)