Boundary Layer Parameterization Issues in the MM5 and Other Models.

1. Boundary Layer ParameterizationIssues in the MM5 and Other Models. Cliff Mass, Eric Grimit, Jeff Baars, David Ovens, University of Washington

2. Apparent Problems During the past years a number of issues have become evident with the MM5 (and other) boundary layers, with the unproven implication that the PBL schemes or land surface schemes are to blame.

3. Basic Infrastructure • MM5 36, 12, and 4-km real-time runs over the Northwest • UW data collection effort (roughly 24-networks over the region) • UW Verification System

4. Some Observations • 10-m Winds are too geostrophic. • Positive wind biases (~2-3 knots) exist when all wind speeds are considered and turn negative for winds greater than three knots. • Difficult to maintain shallow pools of cold air or shallow cloud layers.

5. Domain-Wide Biases

6. 24h Forecast, Valid 12Z, all wind speeds-Night

7. 12-h Forecast, Valid 00 UTC-DAY Less Positive Bias at 00 UTC than 12 UTC

8. Questions • Does this error vary with wind speed? • Might part of it derive from wind sensor errors at slow speeds?

9. Instrument start threshold spd start threshold dir Met One 014A 1.0 mph - mph Met One 034B 0.9 0.9 RM Young 05103 2.2 2.4 RM Young 05106 "Marine" 2.2 2.4 RM Young 03001 "air quality" 1.1 1.8 RM Young 03101 "air quality" 1.1 1.8 Climatronics CS800 <1.0 <1.0 ASOS's F420 (company: n/a) 2.3 2.3 Vaisala WM30 <0.9 2.2 Vaisala WA15/WA25 <1.1 0.9 Looks like many networks are using the RM Young 05103. Agrimet does, the fixed/drifting buoy data does along with Vaisala, Schoolnet and RAWS show a picture of one on their website although Schoolnet mentions that stations installed prior to 1997 used a white cup/vane type.

14. Wind Direction • Winds generally too geostrophic by 5-10 degrees

16. Looks Worse for higher wind speeds… 4km is best

17. But things changed this year • Winds speeds developed a significant negative bias. • We changed the source of surface verification data…from using the lowest sigma and surface data to using the PBL scheme output directly.

18. Wind Speed Bias Valid at 12 UTC for 24 h Forecast

20. Less Change at 00UTC-- still generally underforecast.

22. Wind Direction…00UTC

23. 12 UTC 4-km MM5 is best by far!

24. Temperature Biases • Large temperature biases can occur at certain times: • When there is a shallow layer of cold air (few hundred m deep) that is mixed out. • During transition season (particularly spring, when land surface conditions are problematic) • During summer during warm periods.

25. 00 UTC

26. 12 UTC

27. Problems with Shallow Cold Air

28. January 6,2004 Well-Forecast Snow Event 2-4 inches

30. …but not the Freezing rain…because mixed Out the cold air Several days of freezing rain coasted Portland in a sheath of ice….PDX closed for THREE days

40. Shallow Fog…Nov 19, 2005 • Held in at low levels for days • MM5 held in the inversion…generally without the shallow mixed layer of cold air a few hundred m deep • MM5 could not maintain the moisture at low levels

47. Where are the problems? • PBL parameterizations? • Land surface models or surface specifications? • Dynamical models themselves (too much diffusion, etc)? • What happens at 1-10 km resolution when some PBL structures are beginning to be resolved? • Lack of verification/evaluation data/

48. Who is working on PBL parameterizations and evaluating current ones? • Generally a hollowing out of the U.S. efforts (e.g., UW Energy Transfer Group) • For MM5/WRF mainly Korean effort (Yonsei University) • Still activity in Europe…mainly Dutch? • Some interest in UW; Forest Service sponsored effort, Chris’s group. • No one at NCEP actively working on PBL parameterizations for mesoscale models.

49. Computer forecast models were nearly perfect for the onset and amount of snow over Puget Sound. They did not do a good job for the freezing rain over the east side and around Portland…. and we know why. The End