the arctic boundary layer - ecmwf · 2015. 12. 31. · ian brooks, matthew shupe, thorsten...
TRANSCRIPT
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The Arctic boundary layer
Interactions with the surface, and clouds, as learned from observations (and some modeling)
Michael Tjernström
Department of Meteorology & the Bert Bolin Center
for Climate Research, Stockholm University
With the help of many: Ola Persson, Chris Fairall,
Ian Brooks, Matthew Shupe, Thorsten Mauritsen,
Joseph Sedlar, Cathryn Birch and many, many
others
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Context
• A few words about observations, or the lack thereof
• Boundary-layer structure
• Interaction with the surface: the seasonal story and what’s below
• Interactions with clouds
• Some modeling – here and there
2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
Surface obs
Soundings
Aircraft obs
Buoys &ships
A few words aboutobservations
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2011-11-08 / Michael Tjernström, Stockholm University
ASCOS 2008
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2011-11-08 / Michael Tjernström
Winter
Summer
Tjernström & Graversen 2009
Arctic troposphere vertical structureFrom SHEBA soundings
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2011-11-08 / Michael Tjernström
Winter
Summer
Tjernström & Graversen 2009
Arctic troposphere vertical structureFrom SHEBA soundings
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Arctic troposphere vertical structure
Winter
From SHEBA soundings
All seasons: Stable layer 200 m to ~2 km, near neutral 5-8 km & often near neutral PBL.
Winter: Additionally strong surface inversions ~ 50% of the time
Summer
Tjernström & Graversen 20092011-11-08 / Michael Tjernström
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2011-11-08 / Michael Tjernström
Surface inversion
Lifted inversion
”Boundary layer”
Winter Spring Summer Autumn
Surface 53% 15% 9% 61%
Lifted 47% 85% 91% 39%
Tjernström & Graversen 2009
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2011-11-08 / Michael Tjernström, Stockholm University
Inversion base height
Inversion strength
Inversion thickness
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2011-11-08 / Michael Tjernström, Stockholm University
Near-surface stability
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~400 m
~300 m
~300 m
~300 -600 m
2011-11-08 / Michael Tjernström, Stockholm University
Vertical thermal structure
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~1 km
~1.5 km
~600 m
~500 m
2011-11-08 / Michael Tjernström, Stockholm University
Vertical moisture structure
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2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
Winter
Spring
Summer
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA surface temperatures
Air temperature
Surface temperature
Sub-snow surface
Across the ice
Across the snow
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2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA Relative humidity
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA Relative humidity
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2011-11-08 / Michael Tjernström, Stockholm University
Winter
Spring
Summer
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2011-11-08 / Michael Tjernström, Stockholm University
Winter
Spring
Summer
SHEBA stability
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA sensible heat flux
Winter
Spring
Summer
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA latent heat flux
Winter
Spring
Summer
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2011-11-08 / Michael Tjernström, Stockholm University
Non-melt season: Variable Ts < 0° C
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2011-11-08 / Michael Tjernström, Stockholm University
Non-melt season: Variable Ts < 0° C
Melt season: Fixed Ts ≈ 0° C
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2011-11-08 / Michael Tjernström, Stockholm University
SHEBA Polar Night
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Momentum transfer to the surface
Tjernström et al. 20082011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
Surface sensible heat flux
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2011-11-08 / Michael Tjernström, Stockholm University
Surface latent heat flux
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Clouds in global models
2011-11-08 / Michael Tjernström, Stockholm University
Don’t use!
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2011-11-08 / Michael Tjernström, Stockholm University
Clouds in global models
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2011-11-08 / Michael Tjernström, Stockholm University
Winter conditions
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2011-11-08 / Michael Tjernström, Stockholm University
< 200 m100 m to 1 km
200 m to 1 km< 1km or >20 km
Summ
er conditions
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Clouds in regional models
2011-11-08 / Michael Tjernström, Stockholm University
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2011-11-08 / Michael Tjernström, Stockholm University
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Surface energybalance
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27 May, 2010 / Michael Tjernström
Sur
face
clo
udfo
rcin
g(W
m-2
)
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2011-11-08 / Michael Tjernström, Stockholm University
What is a cloud?
Cloud base (lidar)
Cloud top (radar)
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2011-11-08 / Michael Tjernström, Stockholm University
Surface basedboundary layer
Cloud generatedboundary layer
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Some reflections…• What we think we know about small scale features
such as low-troposphere vertical structure, clouds and surface fluxes rests on very “thin ice”. As a consequence modeling with out observational constraints is problematic; even reanalysis is difficult
• Some things stand out:
–The over-all boundary-layer structure is dominated by near-neutral conditions, but strong lasting surface inversions do occur in winter
–Three surface coupling regimes: melt (summer, fixed Ts), non-melt (spring, responsive Ts) and polar night (winter, no sun).
–Near-surface moisture remains close to saturation – almost always!– In winter, conduction through ice & snow is as important as sensible
heat flux and snow thickness is critical–Low clouds dominate, but clouds are sometimes optically thin. In
summer this is because of sometimes very low aerosol concentrations while cloud-water phase is also important, especially in winter
–Surface energy balance is dominated by (LW) radiation while turbulent heat fluxes are small ⇒ focus more on the momentum flux?
The Arctic boundary layer ��Interactions with the surface, and clouds, as learned from observations (and some modeling)ContextSlide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Surface energy�balanceSlide Number 38Slide Number 39Slide Number 40Some reflections…