1. OC 3570 January 2006 Cruise Project
Differences in AREPS predicted near-surface refractivity conditions from measured radiosonde data, 12-HR ETA forecast, and 12-HR NOGAPS forecast
Leg January 2006
LT Keir D. Stahlhut

3. Should expect to see some evidence of ducting in time periods 1 through 5 based on Rosenthal (1979) synoptic thumb rule

4. Problem: ETA only computed to 1000 mb level over water (if fields available over water at all), and NOGAPS intermittently computed to 1013 mb level forecast model soundings do not contain high enough resolution near the surface to accurately display surface based ducting (and forget about seeing an evaporative duct).
Cruise data NOGAPS model

5. Cruise data ETA(12km) Model NOGAPS model
Jan 23, ~ 00Z

6. Cruise data ETA(12km) Model NOGAPS model
Jan 23, ~ 12Z

7. Cruise data ETA(12km) Model NOGAPS model
Jan 24, ~ 00Z

8. Cruise data ETA(12km) Model NOGAPS model
Jan 24, ~ 12Z

9. Cruise data ETA(12km) Model NOGAPS model
Jan 25, ~ 00Z

10. Cruise data ETA(12km) Model NOGAPS model
Jan 25, ~ 12Z

11. Cruise data ETA(12km) Model NOGAPS model
Jan 26, ~ 00Z

12. Jan 23, ~ 00Z Cruise/ETA/NOGAPS

13. Jan 23, ~ 12Z Cruise/ETA/NOGAPS

14. Jan 24, ~ 00Z Cruise/ETA/NOGAPS

15. Jan 24, ~ 12Z Cruise/ETA/NOGAPS

16. Jan 25, ~ 00Z Cruise/ETA/NOGAPS

17. Jan 25, ~ 12Z Cruise/ETA/NOGAPS

18. Jan 26, ~ 00Z Cruise/ETA/NOGAPS

19. Results: Estimated “maximum” detection ranges for “Generic AN/SPS-67-like” radar at 10 m height, of a “generic R/V-like” vessel with < 60 m detectable height
23/00z
23/12z
24/00z
24/12z
25/00z
25/12z
26/00z
Cruise
~ 25 km
~ 15
~ 10
ETA
~ 20
NOGAPS
Both Models Under predict - ETA shows some ducting, NOGAPS does not
Both Models Under predict - Both show some ducting
ETA Over predicts, NOGAPS Under predicts – ETA shows duct, NOGAPS does not
ETA Over predicts – ETA shows duct, NOGAPS show super refractive surface layer
Both Models Under predict – Both show some ducting
Both Models Under predict – ETA shows duct, NOGAPS show super refractive layer
Models good approximation to reality – environment has virtually no ducting
Conclusions:
No clear trends. It is possible that when there is no duct present, the models will better forecast propagation ranges, compared to when a duct is present.
Over ocean AREPS predictions near the surface using model data will most likely not be accurate due to lack of resolution at near-surface levels.