Long-term energy flux measurements over a small ... - FMInetfam.fmi.fi/Lake10/Annika_Nordbo.pdf ·...
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www.helsinki.fi/yliopisto
Long-term energy flux measurements over a small boreal lake using eddy
covariance technique
A. Nordbo, S. Launiainen, I. Mammarella, M. Leppäranta, J. Huotari, A. Ojala and T. Vesala
16.9.2010
Department of Physics / Division of Atmospheric Sciences / Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique 1
Based on an article submitted to Journal of Geophysical research, revised 27.8.2010: Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique
2nd Workshop on Parameterization of Lakes in Numerical Weather Prediction and Climate Modelling
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www.enviroment.fi
Lakes in size classesFraction of water per area
1. Background
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Lake surface energy balance
Thermocline
T-profile
H LE
Q
Rn
n B F PR Q H LE Q Q Q
QB
QF
QP
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Motivation• Lakes described very crudely in weather prediction models
• Increasing resolution enables small lakes to be taken into account• Measurements for evaluation data needed
• Lake ecology: thermal structure, gas exchange (CO2, CH4…)• Energy balance closure in EC measurements
Our aims1. Detailed information on the thermal structure of a small
boreal lake2. Determine the energy closure of the lake with its
components and their driving factors3. Provide data for model evaluation
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2. Measurements
• Raft on Lake Valkea-Kotinen, Lammi (61°24'N, 25°03'E)• Open-water periods 2005-2008• Eddy covariance measurements H & LE
• sonic anemometer (Metek USA-1) • closed-path IR gas analyzer (LI 7000)
• Net radiation: MB-1, Astrodata, Tartu, Estonia• Near water meteorology• Water temperature profile Q
• 13 depths, 20cm – 4m
130m460m
N• Area 4.1 ha• Mean depth 2.5 m• Max depth 6 m• attenuation coefficient 6.3 m-1
20 Hz data 60min covariances
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Source areas of the 4 energy fluxes are different• H & LE: about 50m, source area depends on winddirection, atmospheric stability…• Rn: 3.6m radius of 80% contribution• Q: point measurements
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Matemaattis-luonnontieteellinen tiedekunta / Annika Nordbo/ Micrometeorology and energybalance of a small boreal lake
3. Results
Water temperature profile
Thermocline depth
Inverse stratification
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16.9.2010 8Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
Does the hypolimnion interact with the atmosphere?
• A FFT applied to water temperature data from 13 depths• 24h variation power selected• plotted as a function of depth per each month
April and Octoberisothermal
2007 Month numbershowsthermocline depth
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Maximum at noon and minumum in the night
Maximum in the morning and minumum in the afternoon
Maximum in the afternoonand minumum in the morning
Energy fluxes
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Comparison betweenmeasurement sites
Average diurnalcourse in July 2007
Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
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Closure comparable to numerous studies from forest sites
Energy balance closure
Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
n
H LER Q
nR Q H LE
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4. Conclusions
• Longest data set ever from small lakes
• Energy flux dynamics differ much from those at terrestrial sites should be included in NWPs and climate models data needed from different sized lakes
• An inexplicable unclosed energy balance also at a lake site (as othersites, too)
• Hypolimnion not important for energy balance during stratification
Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
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2006Ice free Turnover
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
5. Potential for model validation?
Rn
H & LE
T, U, p, RH, rrWater temperature Q
Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
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6. New measurement site
2.6km
320m Lake Kuivajärvi, Hyytiälä
61°50'N, 24°16'E
Aug 2009 - Feb 2010Jul 2010 - now
Rn, Q, H, LEMeteorology
Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
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www.helsinki.fi/yliopisto 16.9.2010 15Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi
Measurements also at a fen
61 49.961’ N, 24 11.567’ E
See the webpage on the ”Contact info” slide for furtherinformation
Rn, Q, H, LEMeteorology
CO2 and CH4 fluxes
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Matemaattis-luonnontieteellinen tiedekunta / Annika Nordbo/ Micrometeorology and energybalance of a small boreal lake
2. Discussion
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www.helsinki.fi/yliopisto 16.9.2010 17Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi
References
Nordbo A., S. Launiainen, I. Mammarella, M. Leppäranta, J. Huotari, A. Ojala and T. Vesala (2010), Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique. J.Geophys.Res. Revised on August 27.
Vesala T., J. Huotari, Ü Rannik, T. Suni, S. Smolander, A. Sogachev, S. Launiainen and A. Ojala (2006), Eddy covariance measurements of carbon exchange and latent and sensible heat fluxes over a boreal lake for a full open-water period, J. Geopys. Res., 111 (D11101), doi:10.1029/2005JD006365.
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www.helsinki.fi/yliopisto
Annika NordboDepartment of physicsP.O.Box 48 FI – 00014 University of Helsinki
[email protected]+358 41 4410053
http://www.atm.helsinki.fi/ Research Micrometeorology
16.9.2010 18Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi
Contact info
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www.helsinki.fi/yliopisto 16.9.2010 19Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi
EXTRA SLIDES
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16.9.2010 20Annika Nordbo/ Long-term energy flux measurements over a small boreal lake lake using eddy covariance technique
Vesala et al. 2006
Source area analysis of the turbulent fluxes
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16.9.2010 21Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi Nordbo et al. 2010
Meteorology at Lake Valkea-Kotinen
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16.9.2010 22Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi Nordbo et al. 2010
Cumulative heat storage of the lake
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16.9.2010 23Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi Nordbo et al. 2010
Spectral correction of the water vapor flux
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16.9.2010 24Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi
Nordbo et al. 2010
Driving factors of H and LE