Schmid, H.P.

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Schmid, H. P.

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Surface-Atmosphere Exchange over Inhomogeneous Terrain:Seeing the Forest for the TreesHaPe Schmid, Institute for Meteorology and Climate Research, Research Centre Kalsruhe, Garmisch-Partenkirchen (Germany)Gibbs Roundsavall: "suburban sprawl" (detail) 19" x 24", enamel on aluminium, 2005Duluth, MN, neighborhood Morgan-Monroe State Forest, Indiana,USAPattern:     Spatial ScalesThe atmosphere sometimes organizes into patterns and distinct spatial scalesHomogeneous heatingRorationHeating gradient(from: Album of Fluid Dynamics)Landscape:Imposes Pattern and ScaleLandscape:Imposes Pattern and ScaleLandscape:Imposes Pattern and ScaleMexico City (source: Google) Measured Variability depends on Resolution: the Scale of MeasurementHomogeneous FieldPlant-Environment Interaction: CO2Scale of ApproachCO2Macroscopic Approach0.1 mmMicroscopic Approach• ecosystem exchange• transport• 102 - 103 m• hourly – multi-year• intercellular exchange• transformation, chemical pathways• 10-5 – 10-2 m• seconds – hourlyeverything in betweenMicrometeorological Flux Measurements: at what scale?Schmid 2002 (Agric. For. Meteorol. 113, 159-184)Flux FootprintSensorCO2SourceCO2The Flux Footprint:• What Part of the Ecosystem does the Flux Sensor ‘see’  ?• Is that Part Representative of the Ecosystem? (answer varies over time)• If yes: use data; if not: reject datae.g.: Schmid (2002, Ag. For. Met., 113, 159-184 )Schmid 1994 (Boundary-Layer Meteorol., 67, 293-318)Flux Footprint = spatial filter, “field of view”(convolution of the source distribution, QS, with the footprint, f )sensorInputs:• zm• z0• h• u*• σw• σv      ffs sQF d Q       x x x x xVancouver, B.C., Canada: Summer 1986Schmid et al., BLM 1991Does the Footprint Concept Actually Work?(after Schmid et al. 1991) "Field of View" / Footprint Varies with Time• Turns with wind direction• Small in unstable conditions• Larger in neutral/stable conditionsat full resolution (from airborne IR scanner)as "seen" by a flux sensor at 30 m in unstable conditions as "seen" by a flux sensor at 30 m in near-neutral conditions Vancouver Temperature Distribution variability reduced to 18% variability reduced to 4%Is the Vancouver Suburban Study Area Homogeneous?(regarding a turbulent flux sensor at 30 m)• in unstable conditions: expect spatial variability• in near-neutral/stable conditions: expect homogeneitySize of 0.5-level Source Area (m2 )104 1050510152025303540Inter -Site PeriodCalibration PeriodMeasured Spatial Variability of Sensible Heat Flux (QH)in Residential Vancouver Area (1986)Schmid, 1988; Schmid et al., BLM 1991; Schmid, AgForMet 1997QH variations within ~ 1 kminstrument uncertaintyQH variations decrease with increasing source area (= effective spatial averaging)spatial representativenessMorgan-Monroe State Forest (Indiana)Morgan-Monroe State Forest (Indiana) 39º 53’ N, 86º 25’ W South central Indiana – 275 mRed Oak, White Oak, TulipPoplar, Sugar Maple 60 – 80 year stand age 25 – 30 m canopy height 4.9 maximum Leaf Area Index 18.52  kg m-2 mean above-ground biomass 236 ~ 261 g C m-2 y-1 NEP(1998/99)500 m1000 mLocation and shape of the footprint ...500 m1000 mLocation and shape of the footprint ...... is variable (wind direction, stability)Is the tower optimally located ?What kind of location bias can we expect ?• Original NDVI:NDVI Variance: 0.053(= 100 %)• Original NDVI:NDVI Variance: 0.053(= 100 %)• Filtered NDVI:Unstable FSAM filterRemaining Variance:28 %FSAM Filter Size:• Original NDVI:NDVI Variance: 0.053(= 100 %)• Filtered NDVI:Unstable FSAM filterRemaining Variance:28 %• Histogram Comparison:HourlyFootprints2001:YD 217-YD 225Aug 5 –Aug 13HourlyFootprints2001:YD 217-YD 225Aug 5 –Aug 138-Day Flux Footprint CompositeLynn Basa: "Sprawl", acrylic on canvas, 12" x 12", 2007• Surface patterns impose atmospheric scales• Averaging over at least a pattern-unit provides a "scale of homoeneity"• Measurements at scales of homogneity are basis for generalisation and linking with models (e.g., at the micro-, stand-, or ecosystem-scale)ConclusionsThanks to...… with financial support from the US Dept. of Energy (TCP/Office of Science; NIGEC/NICCR); Canadian National Science and Engineering Research Council (NSERC); University of British Columbia (UBC); Indiana University; Research Centre Karlsruhe; German Federal Ministry of Education and Research (BMBF) through the Helmholtz Association Urban Meteorology, UBC Vancouver, CanadaForest Meteorology, Indiana University, Canada

Surface-atmosphere exchange over inhomogeneous terrain: Seeing the forest for the trees

https://publikationen.bibliothek.kit.edu/230075884/3815485

Surface-atmosphere exchange over inhomogeneous terrain: Seeing the forest for the trees

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