Ogive

Title

Some considerations about the

Application of ogive analysis for quality control and spectral correction of eddy covariance fluxes
Christof Ammann, Albrecht Neftel

Content

Content
 Motivation for spectral/ogive analysis: methodological flux measurement problems at the Swiss CarboEurope grassland site  Some basics about ogives  Application examples:  High-frequency damping/correction  Analysis for intermittency/stationarity of turbulence  Conclusions

Site region

Measurement Site near Oensingen

0

N

annual distribution of wind directions

Site plots/fetch

Experimental Plots
200
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N
150 100

EC systems

local SN scale [m]

Hi
50

g

y wa h

0

-50

- aerodyn. measurement height: z = 0.7 –1.2 m - sensor separation (lateral): s = 16 cm

-100

-150

-200 -300

-250

-200

-150

-100

-50

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50

100

local WE scale [m]

Site wind

Nocturnal Wind Conditions
50.0 10

CO2 flux windspeed
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CO2 flux [umol/m2/s]

windspeed ca. 1m above ground (Jun-Oct 2002)

6 0.0 4

frequency of occurrence [rel. units]

daytime nighttime

2

-50.0 20.07.2002 00:00

20.07.2002 12:00

21.07.2002 00:00

21.07.2002 12:00

22.07.2002 00:00

22.07.2002 12:00

0 23.07.2002 00:00

0

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7

wind speed [m/s]

windspeed [m/s]

Site motivation

Motivation for spectral/ogive analysis
 Relatively small fields  low measurement height:  strong high-frequency damping  footprint problems (cf. talk by A. Neftel)  Frequent calm nights  weak/intermittent turbulence, non-stationary conditions  enhanced dew formation (on open-path sensor)

? Are parameterised spectral models for the correction of high-frequency damping accurate enough? ? Are integral turbulence characteristics (e.g.  /u*) specific enough for w optimum quality control?

Intro Ogive0

Wh tsa “ a i n ogive” ?
 statistics: cumulative frequency distribution curve