Atmospheric integrated water vapour measured by IR and MW techniques at the Peterhof site (Saint Petersburg, Russia)

Abstract

Regular comparison of different systems for monitoring atmospheric integrated water vapour (IWV) is part of their testing and validation protocol. We compared coincident measurements of IWV over Saint Petersburg (Russia) from ground-based Fourier-transform spectrometer Bruker IFS 125 HR (FTIR) and microwave radiometer RPG-HATPRO (MW) at the Peterhof site between March 2013 and June 2015. This study is a contribution towards global efforts to make such inter-comparisons at various ground-based sites. Since FTIR measures solar radiance, the vast majority of coincident pairs correspond to the spring and summer seasons. The numbers of measurements in the dry season (from October to April) and in the wet season (from May to September) are almost identical, comprising 616 and 638 pairs, respectively. MW and FTIR data sets demonstrate a high level of agreement: the mean relative difference between MW and FTIR data is less than 3% (0.3 mm), with standard deviation from the means of about 4% (0.4 mm). Notwithstanding the short distance between both instruments (150 m), they can monitor different air masses: MW is a zenith-viewing instrument whereas FTIR follows the sun. We analysed the FTIR observation fields under different solar zenith and azimuth angles, taking into account the location of the Peterhof site between the Gulf of Finland and rural suburbs of Saint Petersburg. Although in general MW measurements slightly overestimated IWV in comparison with the FTIR data, we detected several episodes when FTIR gave higher values than MW. These episodes relate to the FTIR observations directed at the coastal region with more humid air than that above the measurement site. We may conclude at this stage of our investigations that the spatial inhomogeneity of humidity fields in the atmosphere causes the most significant differences between the two data sets. Detailed analysis of variation in spatial IWV, e.g. using a MW radiometer in angular scanning mode, is an issue for future research. ARTICLE HISTORY

Investigation of space-borne trace gas products over St. Petersburg and Yekaterinburg, Russia by using COCCON observations

“…XH2O shows a strong seasonal cycle with a maximal amount of ~4700 ppm in summer and minimal amount of ~320 ppm in winter. All products show quite similar behavior with high variability, which is similar to those in Semenov et al (2015), Timofeyev et al (2016) and Virolainen et al (2016. The GOSAT data have higher mean values since the measurement period covers only the time period from later spring to summer, during which higher XH2O is observed.…”

Solar FTIR measurements of NOx vertical distributions: Part I) First observational evidence for a seasonal variation in the diurnal increasing rates of stratospheric NO2 and NO

“…Accurate information on NO2 and NO columns are accessible via FTIR solar absorption spectrometry, which can cover the whole diurnal variation of NOx (Fischer, 1993). Since the first ground-based FTIR measurements of NO2 (Camy-Peyret et al, 1983) and NO (Hanst et al, 1982), some effort was made in monitoring seasonal trends and diurnal variation of stratospheric 70 and tropospheric NOx (Zhou et al, 2021;Yin et al, 2019;Virolainen et al, 2014;Hendrick et al, 2012;Flaud et al, 1988; https://doi.org/10.5194/egusphere-2023-1435 Preprint. Discussion started: 30 August 2023 c Author(s) 2023.…”