EMS Annual Meeting Abstracts Vol. 7, EMS2010-PREVIEW, 2010 10th EMS / 8th ECAC © Author(s) 2010
High resolution climatology - towards climate change services
Regional energy and CO2 exchange over transitional grassland of Inner Mongolia - a weight-shift microlight aircraft study. S. Metzger (1), W. Junkermann (1), L. Wang (2), K. Butterbach-Bahl (1), X.H. Zheng (2), and T. Foken (3) (1) Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Garmisch-Partenkirchen, Germany (
[email protected]), (2) Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, (3) Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany
In environmental science spatial representativeness of measurements is a general problem. Often ground-based measurements can be commenced only at the expense of either scale or resolution. Airborne platforms have been shown to overcome this problem. However typical research aircraft are expensive to operate or not even applicable, e.g. in remote areas. Unmanned aerial vehicles do not yet allow a comprehensive sensor package due to payload restrictions. Here the Weight-Shift Microlight Aircraft (WSMA) can provide an alternative. After successfully applying a WSMA to aerial imagery, aerosol and radiation transfer studies, the feasibility of Eddy Covariance (EC) flux measurements in the Atmospheric Boundary Layer (ABL) was explored. Careful calibration and validation was followed by application of the WSMA to comprehensive ABL soundings over the grassland of the Xilin River Catchment (XRC) in Inner Mongolia, China. The XRC is subject to vast human activity, which influence to capture was objective of measurements from June to August 2009. Simultaneously to the WSMA soundings, half-hourly tower EC fluxes were measured at 3 control sites, two of them non-grazed (C4 dominated Leymus, C3 dominated Stipa) and one heavily grazed (3 sheep unit ha−1 y−1 , HG). The idea of this setup was to a) validate the spatial representativity of process-based regional flux simulation and b) allow for scenario study of advancing grassland degradation. WSMA soundings took place around sun apex, and followed multiple repetitions of 2 to 80 km long line transects, organized in vertical stacks. Operational results at lowest flight level (50 m, AC50) averaged to fluxes of sensible heat QH = -177±78 Wm−2 , latent heat QE = -78±40 Wm−2 and carbon dioxide QC = 0.02±0.2 mg CO2 m−2 s−1 throughout the campaign. At a radiation budget QS∗ = -412±86 Wm−2 , which was 16 % lower than the control sites, the energy balance from AC50 measurements was closed to 72±18 % on average. AC50 measured QH was found comparable in magnitude to the HG control site, whereas Leymus and Stipa sites were 30 % higher on average. The magnitude of QE was comparable to the Leymus site, QE from Stipa and HG were ≥35 % higher on average. AC50, Stipa and HG measurements indicate marginal CO2 release / uptake, only Leymus displayed notable CO2 assimilation (-0.07±0.3 mg CO2 m−2 s−1 ). The chronology of AC50 QH , QE , QC measurements throughout the campaign correlated best to Stipa, Stipa / HG and Leymus site, respectively. Ceilometer backscatter and radiosonde data allowed to determine the ABL height (1860±680 m) and to estimate the average QH VFG throughout the ABL (-0.12±0.08 Wm−3 campaign average). Stacked patterns however show that the QH VFG throughout the surface layer was significantly enhanced and more variable with -0.19±0.38 Wm−3 , indicating possible development of internal boundary layers. Consideration of stacked pattern VFGs during post-processing should improve comparability to control sites and the closure of energy balance. This study shows that the WSMA, which can be easily shipped to and operated from remote places, provides a suitable tool to close the gap between local and spatial measurements.
Regional energy and CO2 exchange over transitional grassland of Inner Mongolia – a weight-shift microlight aircraft study. S. Metzger1, 2, 3, W. Junkermann1, L. Wang2, M. Mauder1, K. Butterbach-Bahl1, X.H. Zheng2, H.P. Schmid1, and T. Foken3 (1) Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Garmisch-Partenkirchen, Germany (2) Chinese Academy of Sciences, Institute of Atmospheric Physics, Beijing, China (3) Bayreuth University, Department of Micrometeorology, Bayreuth, Germany
KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association
www.kit.edu
Motivation Bridging scales: regional measurements Fixed wing aircraft: wide range, but expensive Unmanned aircraft: flexible, but limited payload Alternative? Mengelkamp et al. (2006)
© Agriculture and Agri-Food Canada
2
© British Antartic Survey
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Weight-shift microlight aircraft Easy transport and certification Existing sensor package Surface imagery Aerosols and radiation
Eddy Covariance Fluxes?
Wind measurement sophisticated Trike has rotational freedom
3
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Weight-shift microlight operation
4
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Setup for Eddy Covariance measurement 5 hole wind probe true airspeed, flow angles
Inertial navigation system groundspeed, attitude angles
50 μm Ni-Cr thermocouple air intrinsic temperature
Infrared gas analyzer H2O, CO2 concentration
Date acquistation at 10 Hz spatial resolution ~ 2.6 m
5
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Fast 3d wind: in situ comparison
Ground truth: Sonic Cup and vane SODAR
German Weather Service Lindenberg, meaasurement field ‘Falkenberg‘
6
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
3d wind: in situ comparison
Ground truth: Sonic Cup and vane SODAR
20 data couples RMSD < 0.4 ms-1 German Weather Service Lindenberg, meaasurement field ‘Falkenberg‘
7
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Application: Energy and CO2 fluxes in grassland
Distribution 6% 3% 4%
10% 4%
Aircraft: background fluxes Leymus: ungrazed C4 Stipa: ungrazed C3 Overgrazed: 3 sheep/ha
73% 8
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
How do blended aircraft fluxes compare to ‘pure’ tower fluxes? Sensible heat flux H [Wm-2]
Net radiation -Qs* [Wm-2] 700 600 500 400 300 200 100 0 -100 -200 -300 -400
700 600 500 400 300 200 100 0 -100 -200 -300 -400
Aircraft 16 % lower
CO2 flux [µg CO2 m-2s-1]
Latent heat flux LE [Wm-2] 700 600 500 400 300 200 100 0 -100 -200 -300 -400
700 600 500 400 300 200 100 0 -100 -200 -300 -400
Aircraft
9
Leymus C4
Stipa C3
Overgrazed
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia Stefan Metzger
Only Leymus C4 significant uptake
Aircraft
Leymus C4
Stipa C3
Overgrazed
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
What is the spatial resolution of aircraft measurements? flight altitude 50 m above ground 2 km flight legs downwind of 400 x 400 m Stipa C3
H [Wm-2]
Stipa C3 flux signal resolved during stationary condition
DIR Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 10 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Flux disaggregation Measured flux is linear combination of surface feature contributions
solve system of N equations for M regressors (Chen et al., 1999): Mengelkamp et al. (2006)
N: number of flux samples M: number of surface feature classes Fn: measured flux (regressand) Cnm: source weight Fm: surface feature flux (regressor) Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 11 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Flux disaggregation Source area of fluxes 2 km segments, N > 20 flux samples per flight Footprint model (Kormann and Meixner 2001)
solve system of N equations for M regressors (Chen et al., 1999): Mengelkamp et al. (2006)
N: number of flux samples M: number of surface feature classes Fn: measured flux (regressand) Cnm: source weight Fm: surface feature flux (regressor) Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 12 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
‘Tile‘ fluxes for flight on 2009-06-25 Sensible heat flux H [Wm-2] 500 400 300 200 100 0 -100
Latent heat flux LE [Wm-2]
UTM Northing
-200
500
-300
400
-400 dunes
300
marsh
steppe
arable
200 100 0 -100
CO2 flux [µg CO2 m-2s-1]
-200
-300 500 Only for steppe well determined. -400 400
H & LE:
R2
300
> 0.8, p200< 0.001
dunes
marsh
steppe
arable
100 0 -100 -200 UTM Easting -300 -400 dunes
marsh
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 13 Stefan Metzger
steppe
arable
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Weight-shift microlight as comprehensive environmental research aircraft Accurate turbulence measurement 3d wind RMSD < 0.4 ms-1 Sensible and latent heat RMSD < 15 %
Application in remote areas possible Convenient transport, certification and start / landing Comprehensive sensor package
Flux disaggregation must be improved to allow for regionalization Can solely land use explain flux variability? Footprint model sufficiently reliable? Can wavelet covariance aid by increasing sample size?
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 14 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Regional energy and CO2 exchange over transitional grassland of Inner Mongolia – a weight-shift microlight aircraft study. S. Metzger1, 2, 3, W. Junkermann1, L. Wang2, M. Mauder1, K. Butterbach-Bahl1, X.H. Zheng2, H.P. Schmid1, and T. Foken3 (1) Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Garmisch-Partenkirchen, Germany (2) Chinese Academy of Sciences, Institute of Atmospheric Physics, Beijing, China (3) Bayreuth University, Department of Micrometeorology, Bayreuth, Germany
KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association
www.kit.edu
3d wind: tunnel validation Specially designed 5 hole wind probe Objectives applicability of flow angle computation accuracy in the operational range
Performance in flow angle range ±17.5°: Flow angles: RMSD = 0.4°, R2 = 0.99 Dynamic pressure: RMSD = 0.4 kPa, R2 > 0.99
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 16 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
3d wind: upwash correction upwash scales with lift correlation COR(w,TAS): 0.79 → -0.11 COR(w,pch): -0.78 → 0.17
accuracy sd(w) / sd(uz): 3.8 → 2.7 % RMSD: 0.17 → 0.13 ms-1
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 17 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Sensible heat flux: ground truth comparison 1.00
9
0.80 WSMA leg LAS WSMA leg EC LAS EC 3 m EC 50 m EC 90 m
z / zi
0.60
0.40
0.20
0.00 0.00
0.20
0.40
0.60
0.80
1.00
QH / QH0
2
propagation of wind measurement uncertainties 4.3% for leg las (4.7 km) 3.9% for leg 2 (20 km)
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 18 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
The MAGIM research group Work topic part of DFG research group “MAtter fluxes of Grassland in Inner Mongolia as influenced by stocking rate“: Observing effects of increased animal based husbandry... …on matter fluxes… gaseous → climate effective trace gases; particles → sand storm; water → erosion, pollution; → research network of 11 German / Chines partner institutions.
...in semiarid grasslands.
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 19 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Application: energy and CO2 fluxes in grasslands
D
on i t a d a r eg
ss e c o r p
9.0 sheep/ha
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 20 Stefan Metzger
1.5 sheep/ha
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division
Internal boundary layers? Ceilometer ABL (1860±680 m) QH flux gradient 0.12 Wm-3 stacked patterns 0.19 Wm-3
Turbulent fluxes from weight-shift microlight aircraft over transitional grassland of Inner Mongolia 21 Stefan Metzger
Institute for Meteorology and Climate Research Atmospheric Environmental Research Division