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Reducing errors on estimates of the carbon uptake period based on time series of atmospheric CO2

Kariyathan, Theertha and Bastos, Ana and Marshall, Julia and Peters, Wouter and Tans, Pieter and Reichstein, Markus (2023) Reducing errors on estimates of the carbon uptake period based on time series of atmospheric CO2. Atmospheric Measurement Techniques (AMT), 16 (12), pp. 3299-3312. Copernicus Publications. doi: 10.5194/amt-16-3299-2023. ISSN 1867-1381.

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Official URL: https://dx.doi.org/10.5194/amt-16-3299-2023


High-quality, long-time-series measurements of atmospheric greenhouse gases show interannual variability in the measured seasonal cycles. These changes can be analyzed to better understand the carbon cycle and the impact of climate drivers. However, nearly all discrete measurement records contain gaps and have noise due to the influence of local fluxes or synoptic variability. To facilitate analysis, filtering and curve-fitting techniques are often applied to these time series. Previous studies have recognized that there is an inherent uncertainty associated with this curve fitting, and the choice of a given mathematical method might introduce biases. Since uncertainties are seldom propagated to the metrics under study, this can lead to misinterpretation of the signal. In this study, we use an ensemble-based approach to quantify the uncertainty of the derived seasonal cycle metrics. We apply it to CO2 dry-air mole fraction time series from flask measurements in the Northern Hemisphere. We use this ensemble-based approach to analyze the carbon uptake period (CUP: the time of the year when the CO2 uptake is greater than the CO2 release): its onset, termination and duration. Previous studies have diagnosed CUP based on the dates on which the detrended, zero-centered seasonal cycle curve switches from positive to negative (the downward zero-crossing date, DZCD) and vice versa (upward zero-crossing date, UZCD). However, the UZCD is sensitive to the skewness of the CO2 seasonal cycle during the net carbon release period. Hence, we develop an alternative method proposed by Barlow et al. (2015) to estimate the onset and termination of the CUP based on a threshold defined in terms of the first derivative of the CO2 seasonal cycle. Using the ensemble approach, we arrive at a tighter constraint to the threshold by considering the annual uncertainty; we call this the ensemble of first derivative (EFD) method. Further, using the EFD approach and an additional curve-fitting algorithm, we show that (a) the uncertainty of the studied metrics is smaller using the EFD method than when approximated using the timing of the zero-crossing date (ZCD), and (b) the onset and termination dates derived with the EFD method provide more robust results, irrespective of the curve-fitting method applied to the data.

Item URL in elib:https://elib.dlr.de/200021/
Document Type:Article
Title:Reducing errors on estimates of the carbon uptake period based on time series of atmospheric CO2
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Kariyathan, TheerthaMPI für Biochemie, Jena, Germanyhttps://orcid.org/0000-0003-4969-8844UNSPECIFIED
Bastos, AnaWageningen University, Wageningen, NLhttps://orcid.org/0000-0002-7368-7806UNSPECIFIED
Marshall, JuliaDLR, IPAhttps://orcid.org/0000-0003-2648-128XUNSPECIFIED
Peters, WouterWageningen University, Wageningen, NLhttps://orcid.org/0000-0001-8166-2070UNSPECIFIED
Tans, PieterUniversity of Colorado, Boulder, CO USAUNSPECIFIEDUNSPECIFIED
Reichstein, MarkusMPI für Biochemie, Jena, GermanyUNSPECIFIEDUNSPECIFIED
Date:27 June 2023
Journal or Publication Title:Atmospheric Measurement Techniques (AMT)
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:Yes
Page Range:pp. 3299-3312
Publisher:Copernicus Publications
Keywords:carbon uptake period, time series analysis, carbon dioxide, atmospheric mixing ratios
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:other
DLR - Research area:Raumfahrt
DLR - Program:R - no assignment
DLR - Research theme (Project):R - no assignment
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Marshall, Julia
Deposited On:29 Nov 2023 15:40
Last Modified:29 Nov 2023 15:40

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