Yury Timofeyev

Ground-based validation of EOS-Aura OMI NO2 vertical column data in the midlatitude mountain ranges of Tien Shan (Kyrgyzstan) and Alps (France)

Ground-based UV-visible instruments for NO2 vertical column measurements have been operating at Issyk-Kul station, in Kyrgyzstan, and Observatoire de Haute-Provence (OHP), in France, since 1983 and 1992, respectively. These measurements have already been used for validation of ERS-2 Global Ozone Monitoring Experiment (GOME) and Envisat Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) NO2 column data. Building upon the successful missions of GOME and SCIAMACHY, the Ozone Monitoring Experiment (OMI) was launched by NASA onboard the EOS Aura satellite in July 2004. Here we present the results of recent comparisons between OMI NO2 operational data (standard product) and correlative ground-based twilight measurements in midlatitudes, at Issyk-Kul and OHP, in 2004–2006. The stratospheric NO2 columns, observed by OMI and our ground-based instruments, have been corrected for NO2 diurnal change and normalized to local noon values using a photochemical box model. According to our comparison, OMI stratospheric NO2 columns underestimate ground-based measurements by (0.3 ± 0.3) × 1015 molecules/cm2 and (0.7 ± 0.6) × 1015 molecules/cm2 at Issyk-Kul and OHP, respectively. The effect of tropospheric pollution on the NO2 measurements in both regions of observations has been identified and discussed.

Retrieval of ozone and nitrogen dioxide concentrations from Stratospheric Aerosol and Gas Experiment III (SAGE III) measurements using a new algorithm

[1] We describe a new inversion algorithm developed for the retrieval of atmospheric constituents from Stratospheric Aerosol and Gas Experiment III (SAGE III) solar occultation measurements. The methodology differs from the operational (NASA) algorithm in several important ways. Our algorithm takes account of the finite altitude and spectral resolution of the measurements by integrating over the viewing window spectrally and spatially. We solve the problem nonlinearly by using optimal estimation theory, and we use an aerosol parameterization scheme based on eigenvectors derived from existing empirical and modeled information about their microphysical properties. The first four of these eigenvectors are employed in the retrieval algorithm to describe the spectral variation of the aerosol extinction. We retrieve ozone and nitrogen dioxide number densities and aerosol extinction from transmission measurements at 41 channels from 0.29 to 1.55 mm. In this paper we describe the results of the gas retrievals. Numerical simulations test the accuracy of the scheme, and subsequent retrievals from SAGE III transmission data for the period between May and October 2002 produce profiles of O3 and NO2. Comparisons of the O3 and NO2 profiles with those obtained using the SAGE III operational algorithm and with those from independent measurements made by satellites, ozonesondes, and lidar indicate agreement in ozone measurements in the middle and upper stratosphere significantly closer than the natural variability and agreement in the lower stratosphere and upper troposphere approximately equal to the natural variability.

Intercomparison of satellite and ground-based measurements of ozone, NO2, HF, and HCl near Saint Petersburg, Russia

Regular intercomparison of different observing systems is a part of their testing and validation protocol, which gives the estimates of real measurement errors. The main objective of our study is the comparison of satellite and ground-based measurements of atmospheric composition near Saint Petersburg, Russia. Since early 2009, high-resolution Fourier Transform Infrared (FTIR) solar absorption spectra have been recorded at Peterhof station (59.82° N, 29.88° E), located in the suburbs of Saint Petersburg. We derived column amounts of O3, HCl, HF, and NO2 from these spectra using the retrieval codes SFIT2 and PROFFIT. We compared the data retrieved from Bruker 125 HR FTIR measurements with coincident satellite observations of the Microwave Limb Sounding (MLS), Ozone Monitoring Instrument (OMI), Fourier Transform Spectrometer from Atmospheric Chemistry Experiment (ACE-FTS), Global Ozone Monitoring Experiment (GOME and GOME-2), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments. The relative differences in ozone columns of FTIR from OMI-TOMS amount within (+3.4 ± 2.9)%, from GOME-2 are (+2.2 ± 3.0)%. The comparison of FTIR and MLS measurements of stratospheric ozone columns gives no mean and 5% of the RMS differences. Measurements of NO2 columns agree with the mean difference of +9% and the RMS differences within 14–16% for FTIR vs. GOME-2, SCIAMACHY, and OMI. FTIR vs. GOME comparison gives (+6 ± 31)%. HCl columns comparison for FTIR vs. MLS shows −4.5% in the mean and 12% in the RMS differences. FTIR vs. ACE-FTS comparison (nine cases) gives −8% and 10% for the mean and the RMS relative differences, respectively. Comparison of HF columns shows (−12 ± 6)% and (−12 ± 11)% for FTIR vs. ACE data v.2.2 and v.3.0, respectively. These figures show that the Peterhof ground-based FTIR measuring system can be used to support the validation of satellite data in the monitoring of stratospheric gases.

Measurements of Trace Gases at Saint-Petersburg State University (SPbSU) in the Vicinity of Saint-Petersburg, Russia

An overview of atmospheric trace gas measurements made using various spectroscopic ground-based instrumentation and measurement techniques at the Department of Physics of Atmosphere, St. Petersburg State University is given. The SPbSU trace-gas retrievals have been compared to independent ground-based and satellite measurements as well as to models. Temporal variations (from diurnal cycles to long-term trends) of trace-gases have been studied on the basis of experimental data.

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.

Case study of ozone anomalies over northern Russia in the 2015/2016 winter: Measurements and numerical modeling

Episodes of extremely low ozone columns were observed over the territory of Russia in the Arctic winter of 1

Study of Ozone Layer Variability near St. Petersburg on the Basis of SBUV Satellite Measurements and Numerical Simulation (2000–2014)

A comparison between the numerical simulation results of ozone fields with different experimental data makes it possible to estimate the quality of models for their further use in reliable forecasts of ozone layer evolution. We analyze time series of satellite (SBUV) measurements of the total ozone column (TOC) and the ozone partial columns in two atmospheric layers (0–25 and 25–60 km) and compare them with the results of numerical simulation in the chemistry transport model (CTM) for the low and middle atmosphere and the chemistry climate model EMAC. The daily and monthly average ozone values, short-term periods of ozone depletion, and long-term trends of ozone columns are considered; all data sets relate to St. Petersburg and the period between 2000 and 2014. The statistical parameters (means, standard deviations, variations, medians, asymmetry parameter, etc.) of the ozone time series are quite similar for all datasets. However, the EMAC model systematically underestimates the ozone columns in all layers considered. The corresponding differences between satellite measurements and EMAC numerical simulations are (5 ± 5)% and (7 ± 7)% and (1 ± 4)% for the ozone column in the 0–25 and 25–60 km layers, respectively. The correspondent differences between SBUV measurements and CTM results amount to (0 ± 7)%, (1 ± 9)%, and (–2 ± 8)%. Both models describe the sudden episodes of the ozone minimum well, but the EMAC accuracy is much higher than that of the CTM, which often underestimates the ozone minima. Assessments of the long-term linear trends show that they are close to zero for all datasets for the period under study.

Quality assessment of integrated water vapour measurements at St. Petersburg site, Russia: FTIR vs. MW and GPS techniques

The cross-comparison of different techniques for atmospheric integrated water vapour (IWV) measurements is the 10 essential part of their quality assessment protocol. We inter-compare the synchronised data sets of IWV values measured by Fourier-transform infrared spectrometer Bruker 125 HR (FTIR), microwave radiometer RPG-HATPRO (MW) and global navigation satellite system receiver Novatel ProPak-V3 (GPS) at St. Petersburg site between August 2014 and October 2016. Generally, all three techniques agree well with each other and therefore are suitable for monitoring IWV values at St. Petersburg site. We show that GPS and MW data quality depends on the atmospheric conditions; in dry atmosphere (IWV 15 smaller than 6 mm), these techniques are less reliable at St. Petersburg site than the FTIR method. We evaluate the upper bound of statistical measurement errors for clear-sky conditions as 0.33 ± 0.03 mm (2.0 ± 0.3 %), 0.54 ± 0.03 mm (4.5 ± 0.3 %), and 0.76 ± 0.04 mm (6.3 ± 0.7 %) for FTIR, GPS and MW methods, respectively. We conclude that accurate spatial and temporal matching of different IWV measurements is necessary for achieving the better agreement between various methods for IWV monitoring. 20