Yana Virolainen

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.

Comparison of different techniques in atmospheric temperature-humidity sensing from space

Numerical closed-loop experiments on retrieving atmospheric temperature and humidity profiles by high-resolution measurements of the outgoing thermal infrared (IR) radiation using a Russian Fourier spectrometer (IRFS-2) were performed. Three techniques were used: multiple linear regression (MLR), the iterative physical-mathematical approach (IPMA), and artificial neural networks (ANNs). The MLR technique gives significant root mean square (RMS) errors in the retrieval of the temperature profile, especially in the troposphere region; these errors may be as great as 2–3 K. The ANN and IPMA techniques are considerably more accurate, giving approximately equal RMS errors of 1.0–1.5 K at altitudes of 2–30 km. For all interpretation techniques, a growth of errors of retrieval of temperature in the lower troposphere is observed and is especially substantial (up to 3 K for the near-surface temperature) in thermal sensing over land. The systematic errors of temperature retrieval for the ANN technique are practically zero, and for the other two techniques, they do not exceed 0.4 K. The differences in thermal sensing of the atmosphere over water and land manifest themselves in the appearance of an additional five determined coefficients of expansion of the spectral dependence of the IR emissivity of land in principal components. This leads to increased errors on thermal sensing in the lower troposphere, up to ~0.5 K for all interpretation techniques. The information content of the IRFS-2 device measurements with regard to the atmospheric humidity profile is relatively small because of the values of the errors of measurements of the outgoing radiation in the shortwave range, and in particular, in the water vapour absorption band 6.3 µm. The ANN technique makes it possible to determine relative humidity in the troposphere with RMS errors of 10–15%. In the case of observations over water, the mean errors of the ANN technique are practically equal to zero, and for the MLR and IPMA techniques, they are of an approximately equal order of magnitude, namely 2–4% of relative humidity. The IPMA and MLR techniques give RMS humidity errors of 15–20% and up to 40%, respectively.

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.

Synergetic ground-based methods for remote measurements of ozone vertical profiles

The technique of combining ground-based measurements in infrared and microwave spectral regions in order to achieve higher accuracy of ozone profile retrieval in extensive altitude ranges is described and analyzed. The information content, errors, altitude ranges and vertical resolution of ozone profile retrieval have been studied on the basis of numerical simulation of synergetic experiments. Optimal conditions of measurements are defined and requirements to additional information are formulated. The first results on ozone vertical profile retrieval using groundbased measurements of FTIR-spectrometer and microwave radiometer are given.

The atmospheric and surface sounding from the Meteor satellite (numerical simulation)

The main characteristics of the instruments onboard «Meteor-3M» satellite (IRFS-2, MTVZA-GYa, MSU-MR) measuring the outgoing radiation in visible, NIR, IR and microwave spectral ranges are presented. Characteristics of the informativity of outgoing radiation measurements (degrees of freedom, the Shannon information content) are analyzed under cloudless and cloudy conditions. Various techniques and software for interpreting the outgoing radiation measurements made by these instruments separately or in combination are developed and described. Mathematical basis of techniques is the Multiple Linear Regression (MLR) analysis and a nonlinear generalization of a method of statistical regularization. Numerical simulation of remote measurements is performed using the ensemble of realizations of the atmosphere and underlying surface state. As a result, potential errors of retrieving the atmospheric and surface parameters are estimated and analyzed under cloudless and cloudy conditions.

Ground-based measurements of atmospheric trace gases near Saint-Petersburg, Russia

Regular ground-based measurements of characteristics of atmospheric gas composition have been acquired at St. Petersburg State University (59°88’ N, 29°83’ E) since 1991. Equipment and techniques for interpreting the groundbased observations using measurements of spectra of direct solar IR radiation, zenith scattered UV and visible radiation are described. Main attention is centered on long-term variations of different trace gases, results of complex measurements of different atmospheric gases (O3, CO2, N2O, NO2, HF, HCl, HNO3 etc.) by Fourier spectrometer Bruker, comparisons of various ground-based methods for measuring the total columns of trace gases and the validation of different satellite measurements of total columns of trace gases.

Statistical models of aerosols and polar stratospheric clouds (PSC) for remote sensing

Algorithms to simulate the statistical microphysical and optical models for aerosol and polar stratospheric cloud (PSC) are described. Examples of such models for stratospheric and tropospheric aerosols and PSC are given. Different ways of applying the statistical aerosol and cloud models are discussed: - optimal parameterization of spectral dependences of aerosol extinction coefficient using the natural orthogonal basis; - multiple regression for estimating the optical parameter from measured one (for example, estimation of scattering coefficients from SAGE III multiwavelength measurements of aerosol extinction coefficients); - retrieval of microphysical properties of stratospheric aerosol and PSC from SAGE III extinction measurements; - lidar sounding.

Validation of Atmospheric Numerical Models Based on Satellite Measurements of Ozone Columns

The time series of ozone columns measured with the SBUV satellite instrument over three subarctic stations (Saint Petersburg, Harestua, and Kiruna) are analyzed. The daily and monthly mean ozone values in the layers of 0–25, 25–60, and 0–60 km are compared with the results of simulations with RSHU and EMAC numerical models for the period of 2000–2015. Model data are in good agreement with satellite data both in general and in the cases of rapid short-term ozone loss. However, there are some differences between the models and measurements as well as between the two considered models. These differences require the more detailed analysis in order to modify model parameters. Experimental data demonstrate the increase in ozone columns in the layer of 25–60 km which amounts to 2.1 ± 0.7, 2.4 ± 0.7, and 1.5 ± 0.8% per decade for Saint Petersburg, Harestua, and Kiruna stations, respectively. The results of numerical simulations do not contradict these estimates.