Modified

27 October 2026

Level-0: Preliminary flux calculations

Level 0 is a preliminary flux calculation with relaxed settings. Its results are not part of the dataset. They are used to choose the settings of the final calculation (Level 1):

  • to check that the flux processing works,
  • to check the wind direction across years,
  • to choose the time-lag windows for the final runs.

The Level-0 output of all EddyPro runs is merged into one record per gas analyser, and the checks below read that record. The method is described in the Swiss FluxNet flux processing chain.

NoteIRGA75 in progress

FP2026.1 contains the fluxes of the enclosed-path LI-7200 (IRGA72) only. The Level-0 results of the open-path LI-7500 (IRGA75) are shown here because they set up its final runs, which are in progress for FP2026.2. The IRGA75 fluxes are not part of FP2026.1.

TipNotebooks: merge and flux overview

Time lags from OPENLAG runs

TipNotebooks: time lag checks

The lag between the turbulent fluctuations of the vertical wind and of the gas was first searched in a wide time window (OPENLAG). For each setup period, the peak of the histogram of the lags found became the nominal (default) lag, and a window as narrow as possible around it became the lag search window of the final runs.

IRGA72 (2016 to September 2026)

  • The OPENLAG window was -1 s to +10 s from 2016 to 2018 and -1 s to +20 s from 2019 on. The wider window was needed because an artificial lag of about 8 s was introduced in 2019.
  • The window starts at -1 s rather than 0 s because EddyPro started the search at a later lag, for example +1 s, when the start value was 0 s.
Table 1: IRGA72 nominal (default) time lag and lag search window per setup period, in seconds, used for CO2 and H2O (LE) in the final flux calculations.
time period CO2 IRGA72 H2O IRGA72 Notes
2016_2 0.35, 0.05-1.00 0.55, 0.05-4.00 often faulty data
2016_3 0.30, 0.05-1.00 0.40, 0.05-4.00
2017_1+2 0.30, 0.05-1.00 0.45, 0.05-4.00
2018_1 0.35, 0.05-1.00 0.45, 0.05-4.00
2018_2 0.35, 0.05-1.00 0.40, 0.05-4.00
2018_3 only sonic only sonic low flow rate, no IRGA fluxes
2018_4+2019_1 0.30, 0.05-1.00 0.45, 0.05-4.00
2019_2 n.a. n.a. IRGA data empty
2019_4 8.40, 7.90-8.80 8.45, 8.00-13.00
2020_1 8.40, 7.90-8.80 8.45, 7.75-13.05
2021_1 8.40, 7.90-8.80 8.55, 8.00-13.00
(2021_2) n.a. n.a. unknown data format
(2022_1) n.a. n.a. unknown data format
2022_2 1.25, 0.95-1.40 1.40, 1.00-4.00
2022_3 8.95, 8.45-9.55 9.00, 8.20-13.05
2022_4 8.45, 8.00-9.30 8.55, 8.00-13.00
2023_1 8.45, 7.90-8.80 8.50, 7.75-13.05
2023_2 8.45, 7.90-8.80 8.50, 7.75-13.05
2024_1 8.45, 7.90-8.80 8.55, 7.75-13.05
2025_1 8.45, 7.90-8.80 8.55, 7.75-13.05 setup unchanged since 2023_2
2026_1 8.45, 7.90-8.80 8.50, 7.75-13.05 through September 2026

IRGA75 (2004 to 2017, 2019; in progress for FP2026.2)

Table 2: IRGA75 nominal (default) time lag and lag search window per setup period, in seconds, used for CO2 and H2O (LE) in the final flux calculations.
time period CO2 IRGA75 H2O IRGA75 Notes
2004 0.20, 0.05-0.75 same as CO2
2005_1+4 0.25, 0.05-0.75 same as CO2
2005_2 0.20, 0.05-0.75 same as CO2
2005_3 0.20, 0.05-0.75 same as CO2
2006 0.20, 0.05-0.75 same as CO2
2007 0.20, 0.05-0.75 same as CO2
2008_1+4 0.20, 0.05-0.75 same as CO2
2008_2+3 0.25, 0.05-0.75 0.30, 0.05-0.75 different lag for H2O
2009 0.25, 0.05-0.75 same as CO2
2010 0.25, 0.05-0.75 same as CO2
2011 0.30, 0.05-0.75 same as CO2
2012 0.25, 0.05-0.75 same as CO2
2013 0.25, 0.05-0.75 same as CO2
2014 0.25, 0.05-0.75 0.30, 0.05-0.75 different lag for H2O
2015 0.25, 0.05-0.75 same as CO2
2016_1 0.25, 0.05-0.75 same as CO2
2016_2+3 0.30, 0.05-0.75 0.25, 0.05-0.75 different lag for H2O
2017_1+2 0.30, 0.05-0.75 same as CO2
2019_3 12.20, 11.90-12.70 12.15, 11.90-12.70 artificial time lag added; different lag for H2O

Wind direction across years

TipNotebooks: wind direction checks

The wind directions were calculated with a sonic orientation of 209° to north. For each year, a histogram of the half-hourly wind directions (bin width 1°) was compared with that of a reference period. The offset is the number of degrees to add to the wind directions of a year to make its histogram most similar to the reference. All offsets are within ±3°, which indicates that the sonic orientation stayed close to 209° in all years.

IRGA72 (2016 to September 2026)

Reference period: 2024.

Table 3: Wind direction offsets of the IRGA72 years 2016-2026 (2026 through September), in degrees, against the reference period 2024, from the Level-0 OPENLAG runs.
YEAR OFFSET
2016 -2
2017 -3
2018 1
2019 0
2020 1
2021 1
2022 1
2023 2
2024 0
2025 1
2026 2

IRGA75 (2004 to 2017, 2019; in progress for FP2026.2)

Reference period: 2016-2017.

Table 4: Wind direction offsets of the IRGA75 years 2004-2017 and 2019, in degrees, against the reference period 2016-2017, from the Level-0 OPENLAG runs.
YEAR OFFSET
2004 1
2005 1
2006 1
2007 1
2008 1
2009 -1
2010 2
2011 1
2012 2
2013 3
2014 1
2015 0
2016 0
2017 0
2019 1
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