Abstract
Abstract. Solar absorption spectroscopy in the near infrared has been performed in Ny-Ålesund (78.9° N, 11.9° E) since 2002; however, due to the high latitude of the site, the sun is below the horizon from October to March (polar night) and no solar absorption measurements are possible. Here we present a novel method of retrieving the total column dry-air mole fractions (DMFs) of CO2 and CH4 using moonlight in winter. Measurements have been taken during the polar nights from 2012 to 2016 and are validated with TCCON (Total Carbon Column Observing Network) measurements by solar and lunar absorption measurements on consecutive days and nights during spring and autumn. The complete seasonal cycle of the DMFs of CO2 and CH4 is presented and a precision of up to 0.5 % is achieved. A comparison of solar and lunar measurements on consecutive days during day and night in March 2013 yields non-significant biases of 0. 66 ± 4. 56 ppm for xCO2 and −1. 94 ± 20. 63 ppb for xCH4. Additionally a model comparison has been performed with data from various reanalysis models.
Highlights
Since 1992 a Fourier transform infrared (FTIR) spectrometer (FTS) in Ny-Ålesund (78.9◦ N, 11.9◦ E) has been used for the ground-based observation of total column trace gas abundances in the Arctic via solar absorption spectroscopy (Notholt and Schrems, 1994)
After initial tests at the Bremen Total Carbon Column Observing Network (TCCON) site (Buschmann et al, 2015), a thermoelectrically cooled InGaAs diode detector was implemented in the Ny-Ålesund FTS and a time series of xCO2 and xCH4, the total column dry-air mole frac
Measurements are taken under cloud-free conditions for both the NDACC and TCCON networks during summer, and lunar absorption and atmospheric emission measurements are performed in winter
Summary
Since 1992 a Fourier transform infrared (FTIR) spectrometer (FTS) in Ny-Ålesund (78.9◦ N, 11.9◦ E) has been used for the ground-based observation of total column trace gas abundances in the Arctic via solar absorption spectroscopy (Notholt and Schrems, 1994). Since 2002, measurements in the near-infrared (NIR) spectral region have been performed to retrieve the dry-air mole fractions (DMFs) of CO2 and CH4 (denoted here as xCO2 and xCH4) and other gases (Warneke et al, 2005, 2006). These are, since 2005, part of the Total Carbon Column Observing Network (TCCON). After initial tests at the Bremen TCCON site (Buschmann et al, 2015), a thermoelectrically cooled InGaAs diode detector was implemented in the Ny-Ålesund FTS and a time series of xCO2 and xCH4, the total column dry-air mole frac-.
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