A R C T E X

A R C T E X
Results of the Arctic Turbulence Experiments
www.arctex.uni-bayreuth.de
Long-term Monitoring of Heat Fluxes at a
high Arctic Permafrost Site in Svalbard
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A R C T E X
Results of the Arctic Turbulence Experiments
www.arctex.uni-bayreuth.de
CONTENT
Overview field experiments
Meso-scale atmospheric circulation pattern - Kongsfjord
Wind field and atmospheric stability
Typical diurnal patterns spring time
Disturbed temperature profile close to the surface
Ratio of buoyancy / shear production - Free Convection conditions
Surface energy budget of permafrost on Svalbard
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Direct near surface measurements of sensible heat fluxes in the
arctic tundra applying eddy-covariance and laser scintillometry
(supported by the DFG)
1 st Measurement experiment May 02, 2006 to May 20, 2006 -
Location: Ny-Ålesund, Spitzbergen (Svalbard), 79° North Latitude
Lüers, J and Bareiss, J (2010): The effect of misleading surface temperature estimations on the sensible heat
fluxes at a high Arctic site - The Arctic turbulence experiment 2006 on Svalbard (ARCTEX-2006),
Atmospheric Chemistry and Physics, 10 (1), 157-168.
Lüers, J and Bareiss, J: Direct near surface measurements of sensible heat fluxes in the arctic tundra
applying eddy-covariance and laser scintillometry - The Arctic Turbulence Experiment 2006 on Svalbard
(ARCTEX-2006), Theor Appl Climatol, in review 2010.
Westermann, S; Lüers, J; Langer, M; Piel, K; Boike, J (2009): The annual surface energy budget of a higharctic
permafrost site on Svalbard, Norway, The Cryosphere, 3 (2), 631-680.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
3

Diurnal variability of near surface sensible heat fluxes during summer
time over dry and wet high arctic Tundra using eddy-covariance and
laser scintillometer techniques in a typical footprint area on Svalbard
(DFG project LU 1400/2-1). 2 nd measurement experiment August 10,
2009 to August 20, 2009 - Location: Bayelva Catchment south-west of
Ny-Ålesund, 79° North latitude.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
4

Meso-scale atmospheric circulation pattern - Kongsfjord
Ny-Alesund
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
5

Wind field and atmospheric stability (Lüers & Bareiss, TAC 2010)
360
Ny-Alesund
NW SE NW SE NW SE
SE
NW
May 2006
0.8
2.0
315
0.7
1.5
wind direction ¨ [°]
270
225
180
135
90
45
0
0.0
07 08 09 10 11 12 13 14 15 16 17 18 19 20
Time [Day]
0.6
0.5
0.4
0.3
0.2
0.1
u * [m s -2 ]
u¨ [m s¨1]
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
stability z/L z/L ¨ [-] [-]
Interaction of micrometeorological atmospheric stability with change of wind direction
down (SE) or up (NW) Kongsfjord valley
Forced by change of thermal meso-scale atmospheric circulation pattern or synoptic
weather situation around Spitsbergen
Affected by
mountainous Islands covered by glaciers and sea-water filled Fjords
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
6

z/L z [ ]
z/L z [ ]
Ny-Alesund
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
NW
Typical diurnal patterns spring time (Lüers & Bareiss, TAC 2010)
z/L
QH ECV
00 01 02 03 03 04 04 05 05 06 06 07 07 08 08 09 09 10 10 11 12 11 13 12 14 13 1514 1615 1716 1817 19 18 20 19 21 20 22 23 21 00 22 23 00
Ny-Alesund
2.0
SE
z/L
SE
QH ECV
QH LC95 IR
QH SLS
CET [hour]
SE
SE
NW
QH LC95 IR
QH SLS
May 16, 11, 2006
10 20
00 01 02 03 03 04 04 05 05 06 06 07 07 08 08 09 09 10 10 11 12 11 13 12 14 13 1514 1615 1716 1817 19 18 20 19 21 20 22 23 21 00 22 23 00
CET [hour]
SE
NW
8
15
6
10
4
2
5
0
-2
-5
-4
-10
-6
-8
-15
-10 -20
May 16, 2006
10 20
NW
8
15
6
10
4
2
5
0
-2
-5
-4
-10
-6
-8
-15
-10 -20
QH [W m -2 ]
QH [W m -2 ]
10
8
6
4
2
0
-2
-4
-6
-8
-10
10
8
6
4
2
0
-2
-4
-6
-8
-10
Vh [ m s -1 ]
Vh [ m s -1 ]
May 11
Day time sustainable
neutral conditions with
strong SE winds
Night time stability
weak or calm NW
winds.
May 16 vice versa
Day time intermittent
turbulent exchange at
noon, calm winds
during change of
directions SE to NW.
Night time sustainable
neutral and windy
conditions during low
sun positions
(Both days were sunny
with some scattered
alto-level clouds.)
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
7

Disturbed temperature profile close to the surface (Lüers & Bareiss, ACP 2010)
Mean vertical profile of temperature and wind speed
Case A reflects strong surface cooling and a sharp inversion within 1 or 2 meter (5 h to 8 h or 17 to 22 h CET).
Case B occurs around noon (9 to 16 CET) indicating a disturbed profile caused by surface warming.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
8

Ratio of buoyancy / shear production - Free Convection conditions
Production of Turbulent Kinetic Energy TKE
B
=
g
θ
v
⋅ w′
θ′
v
Buoyancy production: This term represents effect of
thermal convection on the generation of TKE.
S
2
= u ∗
⋅
∆v
h
∆z
Shear production: This term represents
mechanical production of TKE or of turbulent eddies. Interaction of
the vertical wind profile with the kinematic stress against the surface.
Ratio B/S (B/S = flux Richardson number Ri f )
TKE produced or consumed by the buoyancy term B
versus
TKE produced by the mechanical or shear stress term S
Usable to assess the dynamical stability or the convective activity
of the atmospheric boundary layer.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
9

Ratio of buoyancy / shear production - Free Convection conditions
Ny-Alesund
May 2006
Ratio Buoyancy/Shear [ ]
12
9
6
3
0
-3
-6
-9
+1 or -3
Ratio B/S
12
9
6
3
0
-3
-6
-9
-12
07 08 09 10 11 12 13 14 15 16 17 18 19 20
Determination if a free convection event or extreme stability (Stull 2000)
B/S threshold of -3 buoyancy is three times greater than wind shear |B| > 3⋅|S|
high possibility to generate free convection.
B/S threshold of +1
Time [Day]
states dynamical stable, wave motion drive conditions.
Most of the time in May 2006 relation thermal vs. mechanical produced TKE is near zero.
Distinct, short periods of free convection or extreme stability (duration only 1 h to 2 h).
Events at Ny-Ålesund appear mostly around noon or afternoon.
-12
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
10

Surface energy budget of permafrost on Svalbard (Westermann, Lüers et al. TC 2009)
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

DS
-18
DL
+41
Q H
-18
Q E
+0.7
Light Winter
15 Mar
to 15 Apr
DS
-41
DL
+33
Q H
-8
Pre melt 15 Apr
to 31 May
Q E
+2.5
C ~0
Q G
-5.9
Q G
+3
C +10.5
DS
-91
Q G
+12
DL
+43
Q Melt
+27
Snow melt
Jun
Q H
-6
Q E
+11
C +3
Light winter: Net short-wave radiation increasing à limited by high snow albedo.
Energy loss by ∆L compensated by sensible heat flux and short-wave radiation.
Snow heat flux negative à further cooling underlying soil column à lowest soil
temperatures.
Pre melt: Net short-wave radiation dominant energy supply. Sensible heat flux
add. melt energy.
Net long-wave radiation main balancing factor. Latent heat remains insignificant.
Snow and soil column start to warm (now positive snow heat flux).
Snow melt: Warming of snow pack towards 0°C à followed by snow melt.
Energy consumed by melting snow is dominant component.
Strong net short-wave radiation (albedo change) à Compensated by net longwave
radiation.
Total net radiation is much stronger energy suppler compared to Q H .
Snow melt almost entirely controlled by radiation.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Dark Winter
Oct to Mar
Summer Jul & Aug
DL
+28 Q H
-16
Q E
+2.5
Q G
-5
C -9
Dark winter: Long-wave radiation is main forcing
à Net long-wave radiation dominant energy loss
∆L loss is compensated by
negative sensible heat flux (warming of surface,
cooling of atmosphere)
Sig. positive latent heat fluxes (at high wind speed
& neutral stratification)
Sig. influence of other factors:
wind speed & precipitation (rain on snow)
Schematic diagram of the contributions of the surface energy budget for different
seasons. Arrows pointing away from the surface indicate positive fluxes.
The flux values are given in Wm - 2 .
DS
-122
Q G
+12
DL
+43
Q H
22.5
Q E
22.5
Summer: strong forcing by short-wave radiation
à absence of snow cover.
C +22
Net short-wave radiation ∆S is compensated by:
+ net long-wave radiation ∆L
+ sensible and latent heat flux
+ ground heat flux à Thawing of the active layer.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Surface energy budget of permafrost on Svalbard
Summer 1 Jul to 31 Aug 2008, Bayelva permafrost station
Sensible (red), latent (blue) and ground (green) heat
fluxes W m −2 (left axis).
Soil water content θ w - Time Domain Reflectometry at
0.1 m depth (right axis).
Average daily Bowen ratio vs. volumetric soil
water content θ w
Soil water content classes of widths of 0.02.
Error bars represent the standard deviation of
the Bowen ratio values within one class.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Surface energy budget of permafrost on Svalbard
Snow melt - June
Sensible (red), latent heat flux
(blue), W m −2 , left axis.
Light gray : snow-covered
Dark gray : snow-free
fraction of the surface area, right
axis.
Intermediate gray : uncertainty in
area fractions.
Until large snow-free patches appear
Air temperature between -1°C and +5°C à snow surface temperature remains close to 0°C à resulting temperature
gradient is small à weak Q H -flux à positive Q E -flux, causing cooling of surface, becomes significant (presence of water).
During snow melt
Infiltrating melt water à subsequent refreezing processes dominates snow pack, (isothermal close to 0°C).
Underlying soil still colder à resulting in a heat transport from snow-soil interface into the soil.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Surface energy budget (SEB) of permafrost on Svalbard
Annual cycle
During polar night - main components SEB:
* IR-radiation *sensible heat flux *heat input refreezing active layer
Determining factor surface temperature of snow:
*incoming atmospheric IR-radiation and *downward sensible heat flux
During spring - Apr/May - long-lasting snow cover - high albedo:
Limitation of *short-wave radiation
Dominant component: energy consumed by melting snow
Albedo change by snow melt is of critical importance for annual SEB
Marking transition point between two fundamentally different regimes
During polar day - Jul/Aug - snow-free period - system governed by
*short-wave radiation
Main balancing factors in the surface energy budget
*turbulent heat fluxes and *IR-radiation balance
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de

Conclusions : Process understanding
ARCTEX-2006 and 2009 + Understanding: variability and transport processes
+ Interaction: meso-scale atmospheric circulation pattern with micrometeorological
near surface atmospheric exchange conditions.
+ Wind field change: short, developed unstable situations
or even free-convection events (noon or early afternoon).
+ Positive feedback: snow and ice melt is supported by
free-convection or short unstable periods
+ Disturbed temperature profile close to surface: Decoupling major error source
to estimate heat fluxes and appropriate surface temperature
+ Comparison: heat-flux parameterizations with direct measurements.
Hydrodynamic three-layer temperature-profile model reliably reproduces
temporal variability of surface temperature
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
17

Conclusions : Practical recommendations
Main technical error source drifting snow and precipitation effects through flux sensor pathways (over- or
underestimation and misleading flux directions)
Solution
Measurement height should be recorded (variation of snow depth) and must be adjusted according to change of
seasons, service of a present weather detector (weather code, visibility).
Decoupling effect (disturbed temperature profiles) and the determination of the surface temperature
Solution
Additional meteorological data + near-surface vertical gradients of wind, temperature, humidity.
Surf. temp.: IR-Thermometer or pyrgeometer or extrapolation applying a hydrodynamic three-layer temperatureprofile
model (Lüers & Bareiss ACP 10/1).
Measurement height of instrumentation (eddy-covariance systems or gradient towers) should be in appropriate
layer within and above this disturbed wind and temperature profiles.
General
Adaptation to polar conditions of flux data corrections and quality assessment and quality control (QA/QC)
techniques (rotation of coordinate system).
Detection of intermittent turbulent conditions, of free-convection events, of wave motion.
Investigation of meso-scale circulation pattern and micro-scale near surface profiles.
Observation of variability of the snow and tundra soil surface conditions (e.g. Web-Cam).
Finding a compromise between conflicting nature of the effect of the disturbed temperature profile and the search
for an acceptable fetch and desired footprint area.
Johannes Lüers
DACH 2010 Bonn
Universität Bayreuth Bayreuther Zentrum für Ökologie und Umweltforschung
Abteilung Mikrometeorologie johannes.lueers@uni-bayreuth.de
18

Thanks
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