Boundary Layer Structure and Decoupling Luke b hande

Boundary Layer Structure and Decoupling

• Luke B Hande

• Monash University, Melbourne, Australia

• Under the supervision of:

• Steven T Siems and Michael J Manton

• Special thanks: Danijel Belusic

Previous Experiments

• SOCEX, ACE 1 and Morrison et al. (2010)

• Wang et al. (1999), Russell et al. (1998) and Jensen et al. (2000) also identifies an ‘intermediate layer’ above the boundary layer

Previous Experiments

• Sullivan and McWilliams show that waves influence the mean wind profiles, vertical fluxes of momentum and other scalars in the lower ABL

• Smedman observes momentum transport from waves into lower ABL in a ‘wave driven wind’ regime over Baltic sea.

Data

• Macquarie Island (54.6 S, 158.8 E)

Data

• Macquarie Island Soundings:

• High resolution 1995 - 2011

• 10 sec vertical resolution
• Approx 116 data points in lowest 2 km

• YOTC reanalysis 2008 - 2010

• 91 vertical levels
• Approx 18 data points in lowest 2 km

Boundary Layer Height

• BL height: main inv 0.01 K/m

• 84.4% of MAC

• 52.3% of YOTC

• MAC median = 1278 m

• MAC std = 624 m

• YOTC median = 1050 m

• YOTC std = 524 m

Boundary Layer Height

• BL height: secondary (decoupled) inv: 0.005 K/m

• 66.6% of MAC

• 22.7% of YOTC

• MAC median = 680 m

• YOTC median = 734 m

Vertical Structure

Vertical Structure

Vertical Structure

Vertical Structure

Boundary Layer Types

• Type 1: Single well mixed layer with

• 0.01 K/m

• Type 2: A decoupled BL with two inversions

• Type 3: A decoupled BL with shear over secondary inversion - ‘Buffer Layer’

• Type 4: No significant inversion

Boundary Layer Types

Type 2: Decoupled BL

Type 3: Buffer Layer

Ekman Spirals

• MAC = 53%

• YOTC = 83 %

Wind Shear over Cloud

Conclusions

• BL height is fairly well reproduced by YOTC, however frequency is underestimated

• Four types of BL structure where the decoupled BL and ‘Buffer Layer’ are underestimated in YOTC

• BL is principally driven by wind shear, which is significantly underestimated in YOTC

• Ekman spirals are frequently observed in MAC and YOTC

• Wind shear is dominant over cloud base

References

• Hande, L. B., S. T. Siems, and M. J. Manton (2012), Observed trends in wind speed over the Southern Ocean, Geophys. Res. Lett., doi:10.1029/2012GL051734.

• Hande, L. B., S. T. Siems, M. J. Manton, and D. Belusic (2012), Observations of wind shear over the Southern Ocean, J. Geophys. Res., doi:10.1029/2012JD017488.