bluuebunny/crossref_metadata_2025 huggingface dataset:
Joint retrieval of aerosol and water-leaving radiance from multi-spectral, multi-angular and polarimetric measurements over ocean
Authors: Xu F. , Dubovik O. , Zhai P.-W. , Diner D. J. , Kalashnikova O. V. , Seidel F. C. , Litvinov P. , Bovchaliuk A. , Garay M. J , van Harten G. , Davis A. B.
Published: January 2016

Abstract. An optimization approach has been developed for simultaneous retrieval of aerosol properties and normalized water-leaving radiance (nLw) from multi-spectral, multi-angular, and polarimetric observations over ocean. The main features of the method are (1) use of a simplified bio-optical model to estimate nLw followed by an empirical refinement within a specified range to improve its accuracy; (2) improved algorithm convergence and stability by applying constraints on the spatial smoothness of aerosol loading and Chlorophyll-a (Chl-a) concentration across neighboring image patches and spectral constraints on aerosol optical properties and on nLw across relevant bands; and (3) enhanced Jacobian calculation by modeling and storing the radiative transfer (RT) in aerosol/Rayleigh mixed layer, pure Rayleigh scattering layers, and ocean medium separately and then coupling them to calculate the field at the sensor. This approach avoids unnecessary and time-consuming recalculations of RT in unperturbed layers in Jacobian evaluations. The Markov chain method is used to model RT in the aerosol/Rayleigh mixed layer and the doubling method is used for the uniform layers of the atmosphere-ocean system. Our optimization approach has been tested using radiance and polarization measurements acquired by the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) over the AERONET USC_SeaPRISM ocean site (6 February 2013) and near the AERONET La Jolla site (14 January 2013), which respectively reported relatively high and low aerosol loadings. Validation of the results is achieved through comparisons to AERONET aerosol and ocean color products and retrievals performed using the Generalized Retrieval of Aerosol and Surface Properties algorithm (Dubovik et al., 2011) on AirMSPI data. Uncertainties of aerosol and nLw retrievals due to random and systematic instrument errors are analyzed by truth-in/truth-out tests with three Chl-a concentrations, five aerosol loadings, three different types of aerosols, and nine combinations of solar incidence and viewing geometries.
Tropical tropospheric ozone columns from nadir retrievals of GOME-1/ERS-2, SCIAMACHY/Envisat, and GOME-2/MetOp-A (1996-2012)
Authors: Leventidou Elpida , Eichmann Kai-Uwe , Weber Mark , Burrows John P.
Published: January 2016

Abstract. Tropical tropospheric ozone columns are retrieved with the Convective Clouds Differential (CCD) technique using total ozone columns and cloud parameters from different European satellite instruments. Monthly mean tropospheric column amounts [DU] are calculated by subtracting the above cloud ozone column from the total column. A CCD algorithm (CCD_IUP) has been developed (as part of the verification algorithm development for TROPOMI on Sentinel 5-precursor mission) which was applied to GOME/ ERS-2 (1995-2003), SCIAMACHY/ Envisat (2002-2012), and GOME-2/ MetOpA (2007-2012) measurements. Thus a unique long-term record of monthly mean tropical tropospheric ozone columns (20°S–20°N) from 1996 to 2012 is now available. An extensive error analysis has been performed, estimating the tropospheric ozone column uncertainties being between 5 and 7 DU (25–36%). Validation with SHADOZ ozonesonde data show that tropospheric ozone columns from CCD and collocated integrated ozonesonde profiles from the surface up to 200 hPa are in good agreement with respect to range, inter-annual variations, and variances. Biases within ±5 DU and RMS errors of less than 10 DU are found. CCD comparisons using SCIAMACHY data with tropospheric ozone columns derived from Limb Nadir Matching have shown that CCD results are less noisy and correlate better with ozonesondes. The 17-year dataset can be helpful for evaluating chemistry models and performing climate change studies.
Characterization of anthropogenic methane plumes with the Hyperspectral Thermal Emission Spectrometer (HyTES): a retrieval method and error analysis
Authors: Kuai L. , Worden J. R. , Li K. , Hulley G. C. , Hopkins F. M. , Miller C. E. , Hook S. J. , Duren R. M. , Aubrey A. D.
Published: January 2016

Abstract. We introduce a retrieval algorithm to estimate lower tropospheric methane (CH4) concentrations from surface to 1 km with uncertainty estimates using Hyperspectral Thermal Emission Spectrometer (HyTES) airborne radiance measurements. After resampling, retrievals have a spatial resolution of 6x6 m2. Total error from single retrieval is approximately 20 %, with the uncertainties determined primarily by noise and spectral interferences from temperature, surface emissivity, and atmospheric water vapor. We demonstrate retrievals for a HyTES flight line over storage tanks near Kern River Oil Field (KROF), Kern County, California and find an extended plume structure in the set of observations with elevated methane concentrations (3.0±0.6 ppm to 6.0±1.2 ppm), well above mean concentrations (1.8±0.4 ppm) observed for this scene. With a 20 % estimated precision, plume enhancements with more than 1 ppm are distinguishable from the background noise. HyTES retrievals are consistent with simultaneous airborne and ground-based in situ CH4 mole fraction measurements within the reported accuracy of approximately 0.2 ppm (or ~8 %), due to retrieval interferences related to temperature or H2O or both.
High Resolution Tropospheric Carbon Monoxide Profiles Retrieved from CrIS and TROPOMI
Authors: Fu Dejian , Bowman Kevin W. , Worden Helen M. , Natraj Vijay , Worden John R. , Yu Shanshan , Veefkind Pepijn , Aben Ilse , Landgraf Jochen , Strow Lawrence , Han Yong
Published: January 2016

Abstract. The Measurements of Pollution in the Troposphere (MOPITT) instrument is the only satellite-borne sensor in operation that uses both thermal (TIR) and near infrared (NIR) channels to estimate CO profiles. With more than fifteen years (2000 to present) of validated multi-spectral observations, this air quality and climate record provides the unique capability to separate CO in the Lower Most Troposphere (LMT, surface to 3 km (~ 700 hPa)) from the free tropospheric abundance. To extend this record, a new, hyper-spectral approach is presented here that will provide CO data products exceeding the capabilities of MOPITT instrument by combining the short wavelength infrared (SWIR, equivalent to the MOPITT NIR) channels from The TROPOspheric Monitoring Instrument (TROPOMI) aboard the European Sentinel 5 Precursor (S5p) satellite, and the TIR channels from the Cross-track Infrared Sounder (CrIS) aboard Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. We apply the MUlti- SpEctra, MUlti-SpEcies, MUlti-SEnsors (MUSES) retrieval algorithm, to quantify the potential of this joint CO product. CO profiles are retrieved from a single-footprint, full spectral resolution CrIS transect over Africa on August 27–28, 2013 coincident with significant biomass burning. Comparisons of collocated CrIS and MOPITT CO observations for the LMT show a mean difference of 2.8 ± 24.9 ppb, which is well within the estimated measurement uncertainty of both sensors. The estimated degrees of freedom (DOFS) for CO signals from synergistic CrIS/TROPOMI retrievals are 0.9 in the LMT and 1.3 above LMT, which indicates that the LMT CO can be distinguished near surface CO abundance information from the free troposphere, similar to MOPITT multiple spectral observations (0.8 in the LMT, and 1.1 above LMT). In addition to increased sensitivity, the combined retrievals reduce measurement uncertainty with ~ 15 % error reduction in LMT. With a daily global coverage and a combined spatial footprint of 14 km, the joint CrIS/TROPOMI measurements have the potential to extend and improve upon the MOPITT multi-spectral CO data records for the coming decade.
Measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground based observations of ozone and carbon monoxide lines in the 230–250 GHz region: Proof of concept
Authors: Newnham D. A. , Ford G. P. , Moffat-Griffin T. , Pumphrey H. C.
Published: January 2016

Abstract. Meteorological and atmospheric models are being extended up to 80 km altitude but there are very few observing techniques that can measure stratospheric-mesospheric winds at altitudes between 20 km and 80 km to verify model data-sets. Here we demonstrate the feasibility of horizontal wind profile measurements using ground-based passive millimetre-wave spectroradiometric observations of ozone lines centred at 231.28 GHz, 249.79 GHz, and 249.96 GHz. Vertical profiles of horizontal winds are retrieved from forward and inverse modelling simulations of the line-of-sight Doppler-shifted atmospheric emission lines above Halley station (75°37’S, 26°14’W), Antarctica. For a radiometer with a system temperature of 1400 K and 30 kHz spectral resolution observing the ozone 231.28 GHz line we estimate that 12hr zonal and meridional wind profiles could be determined over the altitude range 25–74 km in winter, and 28–66 km in summer. Height-dependent measurement uncertainties are in the range 3–8 m s–1 and vertical resolution ~8–16 km. Under optimum observing conditions at Halley a temporal resolution of 1.5hrs for measuring either zonal or meridional winds is possible, reducing to 0.5hr for a radiometer with a 700 K system temperature. Combining observations of the 231.28 GHz ozone line and the 230.54 GHz carbon monoxide line gives additional altitude coverage at 85±12 km. The effects of clear-sky seasonal mean winter/summer conditions, zenith angle of the received atmospheric emission, and spectrometer frequency resolution on the altitude coverage, measurement uncertainty, and height and time resolution of the retrieved wind profiles have been determined.
Dual-polarization radar rainfall estimation in Korea according to raindrop shapes using a 2D Video Disdrometer
Authors: Kim H.-L. , Suk M.-K. , Park H.-S. , Lee G.-W. , Ko J.-S.
Published: January 2016

Abstract. The shapes of raindrops play an important role in inducing polarimetric rainfall algorithms with differential reflectivity (ZDR) and specific differential phase (KDP). The shapes of raindrops have a direct impact on rainfall estimation. However, the characteristics of raindrop size distribution (DSD) are different depending on precipitation type, storm stage of development, and regional and climatological conditions. Therefore, it is necessary to provide assumptions based on raindrop shapes that reflect the rainfall characteristics of the Korean peninsula. In this study, we presented a method to find optimal polarimetric rainfall algorithms on the Korean peninsula using the 2-Dimensional Video Disdrometer (2DVD) and Bislsan S-Band dual-polarization radar. First, a new axis ratio of raindrop relations was developed for the improvement of rainfall estimation. Second, polarimetric rainfall algorithms were derived using different axis ratio relations, and estimated radar-point one-hour rain rate for the differences in polarimetric rainfall algorithms were compared with the hourly rain rate measured by gauge. In addition, radar rainfall estimation was investigated in relation to calibration bias of reflectivity and differential reflectivity. The derived raindrop axis ratio relation from the 2DVD was more oblate than existing relations in the D < 1.5 mm and D > 5.5 mm range. The R(KDP, ZDR) algorithm based on a new axis ratio relation showed the best result on DSD statistics; however, the R(Zh, ZDR) algorithm showed the best performance for radar rainfall estimation, because the rainfall events used in the analysis were mainly weak precipitation and KDP is noisy at lower rain rates ( ≤ 5 mm hr−1). Thus, the R(KDP, ZDR) algorithm is suitable for heavy rainfall and R(Zh, ZDR) algorithm is suited for light rainfall. The calibration bias of reflectivity (ZH) and differential reflectivity (ZDR) were calculated from the comparison of measured with simulated ZH and ZDR from the 2DVD. The calculated ZH and ZDR bias was used to reduce radar bias, and to produce more accurate rainfall estimation.
Application of an online ion chromatography-based instrument for gradient flux measurements of speciated nitrogen and sulfur
Authors: Rumsey Ian C. , Walker John T.
Published: January 2016

Abstract. The dry component of total nitrogen and sulfur atmospheric deposition remains uncertain. The lack of measurements of sufficient chemical speciation and temporal extent make it difficult to develop accurate mass budgets and sufficient process level detail is not available to improve current air-surface exchange models. Over the past decade, significant advances have been made in the development of continuous air sampling measurement techniques, resulting with instruments of sufficient sensitivity and temporal resolution to directly quantify air-surface exchange of nitrogen and sulfur compounds. However, their applicability is generally restricted to only one or a few of the compounds within the de position budget. Here, the performance of the Monitor for AeRosols and GAses in ambient air (MARGA 2S), an commercially available on-line ion chromatography-based analyzer is characterized for the first time as applied for air-surface exchange measurements of HNO3, NH3, NH4+, NO3−, SO2 and SO42−. Analytical accuracy and precision are assessed under field conditions. Chemical concentrations gradient precision are determined at the same sampling site. Flux uncertainty measured by the aerodynamic gradient method is determined for a representative 3-week period in fall 2012 over a grass field. Analytical precision and chemical concentration gradient precision were found to compare favorably in comparison to previous studies. During the 3-week period, percentages of hourly chemical concentration gradients greater than the corresponding chemical concentration gradient detection limit were 86 %, 42 %, 82 %, 73 %, 74 %, and 69 % for NH3, NH4+, HNO3, NO3−, SO2, and SO42−, respectively. As expected, percentages were lowest for aerosol species, owing to their relatively low deposition velocities and correspondingly smaller gradients relative to gas phase species. Relative hourly median flux uncertainties were 31 %, 121 %, 42 %, 43 %, 67 %, and 56 % for NH3, NH4+, HNO3, NO3−, SO2, and SO42−, respectively. Flux uncertainty is dominated by uncertainty in the chemical concentrations gradients during the day but uncertainty in the chemical concentration gradients and transfer velocity are of the same order at night. Results show the instrument is sufficiently precise for flux gradient applications.
Measurement of nonvolatile particle number size distribution
Authors: Gkatzelis G. I. , Papanastasiou D. K. , Florou K. , Kaltsonoudis C. , Louvaris E. , Pandis S. N.
Published: January 2016

Abstract. An experimental methodology was developed to measure the nonvolatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (> 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a nonvolatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol (OA; 40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50–60 % of the particles had a nonvolatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon with an 80 % contribution, while OA was responsible for another 15–20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type of OA is of extremely low volatility.
Sensitivity of thermal infrared nadir instruments to the chemical and microphysical properties of UTLS secondary sulfate aerosols
Authors: Sellitto P. , Legras B.
Published: January 2016

Abstract. Monitoring upper-tropospheric–lower-stratospheric (UTLS) secondary sulfate aerosols and their chemical and microphysical properties from satellite nadir observations is crucial to better understand their formation and evolution processes and then to estimate their impact on UTLS chemistry, and on regional and global radiative balance. Here we present a study aimed at the evaluation of the sensitivity of thermal infrared (TIR) satellite nadir observations to the chemical composition and the size distribution of idealised UTLS sulfate aerosol layers. The extinction properties of sulfuric acid/water droplets, for different sulfuric acid mixing ratios and temperatures, are systematically analysed. The extinction coefficients are derived by means of a Mie code, using refractive indices taken from the GEISA (Gestion et Étude des Informations Spectroscopiques Atmosphériques: Management and Study of Spectroscopic Information) spectroscopic database and log-normal size distributions with different effective radii and number concentrations. IASI (Infrared Atmospheric Sounding Interferometer) pseudo-observations are generated using forward radiative transfer calculations performed with the 4A (Automatized Atmospheric Absorption Atlas) radiative transfer model, to estimate the impact of the extinction of idealised aerosol layers, at typical UTLS conditions, on the brightness temperature spectra observed by this satellite instrument. We found a marked and typical spectral signature of these aerosol layers between 700 and 1200 cm−1, due to the absorption bands of the sulfate and bisulfate ions and the undissociated sulfuric acid, with the main absorption peaks at 1170 and 905 cm−1. The dependence of the aerosol spectral signature to the sulfuric acid mixing ratio, and effective number concentration and radius, as well as the role of interfering parameters like the ozone, sulfur dioxide, carbon dioxide and ash absorption, and temperature and water vapour profile uncertainties, are analysed and critically discussed. The information content (degrees of freedom and retrieval uncertainties) of synthetic satellite observations is estimated for different instrumental configurations. High spectral resolution (IASI-like pseudo-observations) and broadband spectral features (Moderate Resolution Imaging Spectroradiometer (MODIS) and Spinning Enhanced Visible and InfraRed Imager (SEVIRI)-like pseudo-observations) approaches are proposed and discussed.
UTLS water vapour from SCIAMACHY limb measurementsV3.01 (2002–2012)
Authors: Weigel K. , Rozanov A. , Azam F. , Bramstedt K. , Damadeo R. , Eichmann K.-U. , Gebhardt C. , Hurst D. , Kraemer M. , Lossow S. , Read W. , Spelten N. , Stiller G. P. , Walker K. A. , Weber M. , Bovensmann H. , Burrows J. P.
Published: January 2016

Abstract. The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) aboard the Envisat satellite provided measurements from August 2002 until April 2012. SCIAMACHY measured the scattered or direct sunlight using different observation geometries. The limb viewing geometry allows the retrieval of water vapour at about 10–25 km height from the near-infrared spectral range (1353–1410 nm). These data cover the upper troposphere and lower stratosphere (UTLS), a region in the atmosphere which is of special interest for a variety of dynamical and chemical processes as well as for the radiative forcing. Here, the latest data version of water vapour (V3.01) from SCIAMACHY limb measurements is presented and validated by comparisons with data sets from other satellite and in situ measurements. Considering retrieval tests and the results of these comparisons, the V3.01 data are reliable from about 11 to 23 km and the best results are found in the middle of the profiles between about 14 and 20 km. Above 20 km in the extra tropics V3.01 is drier than all other data sets. Additionally, for altitudes above about 19 km, the vertical resolution of the retrieved profile is not sufficient to resolve signals with a short vertical structure like the tape recorder. Below 14 km, SCIAMACHY water vapour V3.01 is wetter than most collocated data sets, but the high variability of water vapour in the troposphere complicates the comparison. For 14–20 km height, the expected errors from the retrieval and simulations and the mean differences to collocated data sets are usually smaller than 10 % when the resolution of the SCIAMACHY data is taken into account. In general, the temporal changes agree well with collocated data sets except for the Northern Hemisphere extratropical stratosphere, where larger differences are observed. This indicates a possible drift in V3.01 most probably caused by the incomplete treatment of volcanic aerosols in the retrieval. In all other regions a good temporal stability is shown. In the tropical stratosphere an increase in water vapour is found between 2002 and 2012, which is in agreement with other satellite data sets for overlapping time periods.
An automated gas chromatography time-of-flight mass spectrometry instrument for the quantitative analysis of halocarbons in air
Authors: Obersteiner F. , Bönisch H. , Engel A.
Published: January 2016

Abstract. We present the characterization and application of a new gas chromatography time-of-flight mass spectrometry instrument (GC-TOFMS) for the quantitative analysis of halocarbons in air samples. The setup comprises three fundamental enhancements compared to our earlier work (Hoker et al., 2015): (1) full automation, (2) a mass resolving power R = m/Δm of the TOFMS (Tofwerk AG, Switzerland) increased up to 4000 and (3) a fully accessible data format of the mass spectrometric data. Automation in combination with the accessible data allowed an in-depth characterization of the instrument. Mass accuracy was found to be approximately 5 ppm in mean after automatic recalibration of the mass axis in each measurement. A TOFMS configuration giving R = 3500 was chosen to provide an R-to-sensitivity ratio suitable for our purpose. Calculated detection limits are as low as a few femtograms by means of the accurate mass information. The precision for substance quantification was 0.15 % at the best for an individual measurement and in general mainly determined by the signal-to-noise ratio of the chromatographic peak. Detector non-linearity was found to be insignificant up to a mixing ratio of roughly 150 ppt at 0.5 L sampled volume. At higher concentrations, non-linearities of a few percent were observed (precision level: 0.2 %) but could be attributed to a potential source within the detection system. A straightforward correction for those non-linearities was applied in data processing, again by exploiting the accurate mass information. Based on the overall characterization results, the GC-TOFMS instrument was found to be very well suited for the task of quantitative halocarbon trace gas observation and a big step forward compared to scanning, quadrupole MS with low mass resolving power and a TOFMS technique reported to be non-linear and restricted by a small dynamical range.
Non-parametric and least squares Langley plot methods
Authors: Kiedron P. W. , Michalsky J. J.
Published: January 2016

Abstract. Langley plots are used to calibrate sun radiometers primarily for the measurement of the aerosol component of the atmosphere that attenuates (scatters and absorbs) incoming direct solar radiation. In principle, the calibration of a sun radiometer is a straightforward application of the Bouguer–Lambert–Beer law V = V0e−τ ⋅ m, where a plot of ln(V) voltage vs. m air mass yields a straight line with intercept ln(V0). This ln(V0) subsequently can be used to solve for τ for any measurement of V and calculation of m. This calibration works well on some high mountain sites, but the application of the Langley plot calibration technique is more complicated at other, more interesting, locales. This paper is concerned with ferreting out calibrations at difficult sites and examining and comparing a number of conventional and non-conventional methods for obtaining successful Langley plots. The 11 techniques discussed indicate that both least squares and various non-parametric techniques produce satisfactory calibrations with no significant differences among them when the time series of ln(V0)'s are smoothed and interpolated with median and mean moving window filters.
Carbon monoxide total columns from SCIAMACHY 2.3  µm atmospheric reflectance measurements: towards a full-mission data product (2003–2012)
Authors: Borsdorff T. , Tol P. , Williams J. E. , de Laat J. , aan de Brugh J. , Nédélec P. , Aben I. , Landgraf J.
Published: January 2016

Abstract. We present a full-mission data product of carbon monoxide (CO) vertical column densities using the 2310–2338 nm SCIAMACHY reflectance measurements over clear-sky land scenes for the period January 2003–April 2012. The retrieval employs the SICOR algorithm, which will be used for operational data processing of the Sentinel-5 Precursor mission. The retrieval approach infers simultaneously carbon monoxide, methane and water vapour column densities together with a Lambertian surface albedo from individual SCIAMACHY measurements employing a non-scattering radiative transfer model. To account for the radiometric instrument degradation including the formation of an ice-layer on the 2.3 µm detector array, we consider clear-sky measurements over the Sahara as a natural calibration target. For these specific measurements, we spectrally calibrate the SCIAMACHY measurements and determine a spectral radiometric offset and the width of the instrument spectral response function as a function of time for the entire operational phase of the mission. We show that the smoothing error of individual clear-sky CO retrievals is less than ±1 ppb and thus this error contribution does not need to be accounted for in the validation considering the much higher retrieval noise. The CO data product is validated against measurements of ground-based Fourier transform infrared spectrometers at 27 stations of the NDACC-IRWG and TCCON network and MOZAIC/IAGOS aircraft measurements at 26 airports worldwide. Overall, we find a good agreement with TCCON measurements with a mean bias b  = −1.2 ppb and a station-to-station bias with σ   = 7.2 ppb. The negative sign of the bias means a low bias of SCIAMACHY CO with respect to TCCON. For the NDACC-IRWG network, we obtain a larger mean station bias of b  = −9.2 ppb with σ  = 8.1 ppb and for the MOZAIC/IAGOS measurements we find b  = −6.4 ppb with σ  = 5.6 ppb. The SCIAMACHY data set is subject to a small but significant bias trend of 1.47 ± 0.25 ppb yr−1. After trend correction, the bias with respect to MOZAIC/IAGOS observation is 2.5 ppb, with respect to TCCON measurements it is −4.6 ppb and with respect to NDACC-IRWG measurements −8.4 ppb. Hence, a discrepancy of 3.8 ppb remains between the global biases with NDACC-IRWG and TCCON, which is confirmed by directly comparing NDACC-IRWG and TCCON measurements. Generally, the scatter of the individual SCIAMACHY CO retrievals is high and dominated by large measurement noise. Hence, for practical usage of the data set, averaging of individual retrievals is required. As an example, we show that monthly mean SCIAMACHY CO retrievals, averaged separately over Northern and Southern Africa, reflect the spatial and temporal variability of biomass burning events in agreement with the global chemical transport model TM5.
Comparison of GOME-2/Metop-A ozone profiles with GOMOS, OSIRIS and MLS measurements
Authors: Kauppi A. , Tuinder O. N. E. , Tukiainen S. , Sofieva V. , Tamminen J.
Published: January 2016

Abstract. This paper presents a comparison of vertical ozone profiles retrieved by the Ozone ProfilE Retrieval Algorithm (OPERA) (versions 1.14–1.24) from the Global Ozone Monitoring Experiment-2 (GOME-2) measurements on board the Meteorological operational Metop-A satellite with spaceborne high-vertical-resolution ozone profiles by Global Ozone Monitoring by Occultation of Stars (GOMOS), Optical Spectrograph and Infrared Imager System (OSIRIS) and Microwave Limb Sounder (MLS). The comparison, with global coverage, focuses on the stratosphere and the lower mesosphere and covers the period from March 2008 until the end of 2011. The comparison shows an agreement of GOME-2 ozone profiles with those of GOMOS, OSIRIS and MLS within ±15 % in the altitude range from 15 km up to  ∼ 35–40 km depending on latitude. The GOME-2 bias with respect to the reference instruments depends on season, with the strongest dependence observed at high latitudes. The GOME-2 ozone profiles retrieved from non-degradation corrected radiances have a tendency to a systematic negative bias with respect to the reference data above  ∼ 30 km. We have studied the influence of solar zenith angle and the effect of instrumental degradation correction. In addition, we have studied GOME-2 performance in Arctic ozone depletion case and demonstrated that GOME-2 data provide valuable information about ozone profiles.
Characterization of downwelling radiance measured from a ground-based microwave radiometer using numerical weather prediction model data
Authors: Ahn M.-H. , Won H. Y. , Han D. , Kim Y.-H. , Ha J.-C.
Published: January 2016

Abstract. The ground-based microwave sounding radiometers installed at nine weather stations of Korea Meteorological Administration alongside with the wind profilers have been operating for more than 4 years. Here we apply a process to assess the characteristics of the observation data by comparing the measured brightness temperature (Tb) with reference data. For the current study, the reference data are prepared by the radiative transfer simulation with the temperature and humidity profiles from the numerical weather prediction model instead of the conventional radiosonde data. Based on the 3 years of data, from 2010 to 2012, we were able to characterize the effects of the absolute calibration on the quality of the measured Tb. We also showed that when clouds are present the comparison with the model has a high variability due to presence of cloud liquid water therefore making cloudy data not suitable for assessment of the radiometer's performance. Finally we showed that differences between modeled and measured brightness temperatures are unlikely due to a shift in the selection of the center frequency but more likely due to spectroscopy issues in the wings of the 60 GHz absorption band. With a proper consideration of data affected by these two effects, it is shown that there is an excellent agreement between the measured and simulated Tb. The regression coefficients are better than 0.97 along with the bias value of better than 1.0 K except for the 52.28 GHz channel which shows a rather large bias and variability of −2.6 and 1.8 K, respectively.
Broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde
Authors: Washenfelder R. A. , Attwood A. R. , Flores J. M. , Zarzana K. J. , Rudich Y. , Brown S. S.
Published: January 2016

Abstract. Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and it strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99930 ± 0.00003 (1− reflectivity  =  700 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.43 km within the 1 m cell. We measure the cavity output over the 315–350 nm spectral region using a grating monochromator and charge-coupled device array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH2O and NO2 concentrations. Independent measurements of NO2 standard additions by broadband cavity-enhanced absorption spectroscopy and cavity ring-down spectroscopy agree within 2 % (slope for linear fit  = 1.02 ± 0.03 with r2 = 0.998). Standard additions of CH2O measured by broadband cavity-enhanced absorption spectroscopy and calculated based on flow dilution are also well correlated, with r2 = 0.9998. During constant mixed additions of NO2 and CH2O, the 30 s measurement precisions (1σ) of the current configuration were 140 and 210 pptv, respectively. The current 1 min detection limit for extinction measurements at 315–350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to trace gases, this approach will be appropriate for measurements of aerosol extinction in ambient air, and this spectral region is important for characterizing the strong ultraviolet absorption by brown carbon aerosol.
The uncertainty of the atmospheric integrated water vapour estimated from GNSS observations
Authors: Ning T. , Wang J. , Elgered G. , Dick G. , Wickert J. , Bradke M. , Sommer M. , Querel R. , Smale D.
Published: January 2016

Abstract. Within the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) there is a need for an assessment of the uncertainty in the integrated water vapour (IWV) in the atmosphere estimated from ground-based global navigation satellite system (GNSS) observations. All relevant error sources in GNSS-derived IWV are therefore essential to be investigated. We present two approaches, a statistical and a theoretical analysis, for the assessment of the uncertainty of the IWV. The method is valuable for all applications of GNSS IWV data in atmospheric research and weather forecast. It will be implemented to the GNSS IWV data stream for GRUAN in order to assign a specific uncertainty to each data point. In addition, specific recommendations are made to GRUAN on hardware, software, and data processing practices to minimise the IWV uncertainty. By combining the uncertainties associated with the input variables in the estimations of the IWV, we calculated the IWV uncertainties for several GRUAN sites with different weather conditions. The results show a similar relative importance of all uncertainty contributions where the uncertainties in the zenith total delay (ZTD) dominate the error budget of the IWV, contributing over 75 % of the total IWV uncertainty. The impact of the uncertainty associated with the conversion factor between the IWV and the zenith wet delay (ZWD) is proportional to the amount of water vapour and increases slightly for moist weather conditions. The GRUAN GNSS IWV uncertainty data will provide a quantified confidence to be used for the validation of other measurement techniques.
Mesospheric gravity wave characteristics and identification of their sources around spring equinox over Indian low latitudes
Authors: Sivakandan M. , Paulino I. , Taori A. , Niranjan K.
Published: January 2016

Abstract. We report OI557.7 nm night airglow observations with the help of a charged-couple device (CCD)-based all-sky camera from a low-latitude station, Gadanki (13.5° N; 79.2° E). Based on the data collected during March and April over 3 years, from 2012 to 2014 (except March 2013), we characterize the small-scale gravity wave properties. During this period, 50 gravity wave events were detected. The horizontal wavelengths of the gravity waves are found to ranging from 12 to 42 km with the phase velocity 20–90 m s−1. In most cases, these waves were propagating northward with only a few occurrences of southward propagation. In the present novel investigation from the Indian sector, each of the wave events was reverse-ray-traced to its source. The outgoing longwave radiation (OLR) suggested that tropospheric convection was a possible source for generation of the observed waves. It was found that approximately 66 % of the events were triggered directly by the convection.
The formation of multiple layers of ice particles in the polar summer mesopause region
Authors: Li H. , Wu J. , Zhou Z.
Published: January 2016

Abstract. This paper presents a two-dimensional theoretical model to study the formation process of multiple layers of small ice particles in the polar summer mesosphere as measured by rockets and associated with polar mesosphere summer echoes (PMSE). The proposed mechanism primarily takes into account the transport processes induced by gravity waves through collision coupling between the neutral atmosphere and the ice particles. Numerical solutions of the model indicate that the dynamic influence of wind variation induced by gravity waves can make a significant contribution to the vertical and horizontal transport of ice particles and ultimately transform them into thin multiple layers. Additionally, the pattern of the multiple layers at least partially depends on the vertical wavelength of the gravity wave, the ice particle size and the wind velocity. The results presented in this paper will be helpful to better understand the occurrence of multiple layers of PMSE as well as its variation process.
Radial dependence of ionization losses of protons of the Earth's radiation belts
Authors: Kovtyukh A. S.
Published: January 2016

Abstract. Coulomb losses and charge exchange of protons are considered in detail. On the basis of modern models of the plasmasphere and the exosphere, the radial dependences of the rates of ionization losses of protons, with μ from 0.3 to 10 keV nT−1, of the Earth's radiation belts near the equatorial plane are calculated for quiet periods. For calculation of Coulomb losses of protons we used data of ISEE-1 satellite (protons with energy from 24 to 2081 keV) on L from 3 to 9, data of Explorer-45 satellite (protons with energy from 78.6 to 872 keV) on L from 3 to 5 and data of CRRES satellite (protons with energy from 1 to 100 MeV) on L ≤  3 (L is the McIlwain parameter). It is shown that with decreasing L the rate of ionization losses of protons of the radiation belts is reduced; for protons with μ > 1.2 keV nT−1 in a narrow region (ΔL ∼  0.5) in the district of plasmapause in this dependence may form a local minimum of the rate. We found that the dependence from μ of the boundary on L between Coulomb losses and charge exchange of the trapped protons with hydrogen atoms is well approximated by the function Lb = 4.71μ0.32, where [μ]  =  keV nT−1. Coulomb losses dominate at L < Lb(μ), and at L > Lb(μ) dominates charge exchange of protons. We found the effect of subtracting the Coulomb losses from the charge exchange of protons of the radiation belts at low μ and L, which can simulate a local source of particles.
Ozone and temperature decadal responses to solar variability in the mesosphere and lower thermosphere, based on measurements from SABER on TIMED
Authors: Huang F. T. , Mayr H. G. , Russell III J. M. , Mlynczak M. G.
Published: January 2016

Abstract. We have derived ozone and temperature responses to solar variability over a solar cycle, from June 2002 through June 2014, 50 to 100 km, 48° S to 48° N, based on data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite. Results with this extent of coverage in the mesosphere and lower thermosphere have not been available previously. A multiple regression is applied to obtain responses as a function of the solar 10.7 cm flux (solar flux units, sfu). Positive responses mean that they are larger at solar maximum than at solar minimum of the solar cycle. From  ∼  80 to 100 km, both ozone and temperature responses are positive for all latitudes and are larger than those at lower altitudes. From  ∼  80 to 100 km, ozone responses can exceed 10 % (100 sfu)−1, and temperature responses can approach 4 °K. From 50 to  ∼  80 km, the ozone responses at low latitudes ( ∼  ±35°) are mostly negative and can approach  ∼  negative 3 % (100 sfu)−1. However, they are mostly positive at midlatitudes in this region and can approach  ∼  2 % (100 sfu)−1. In contrast to ozone, from  ∼  50 to 80 km, the temperature responses at low latitudes remain positive, with values up to  ∼  2.5 K (100 sfu)−1, but are weakly negative at midlatitudes. Consequently, there is a systematic and robust relation between the phases of the ozone and temperature responses. They are positively correlated (in phase) from  ∼  80 to 100 km for all latitudes and negatively correlated (out of phase) from  ∼  50 to 80 km, also for all latitudes. The negative correlation from 50 to 80 km is maintained even though the ozone and temperature responses can change signs as a function of altitude and latitude, because the corresponding temperature responses change signs in step with ozone. This is consistent with the idea that dynamics have the larger influence between  ∼  80 and 100 km, while photochemistry is more in control from  ∼  50 to 75 km. The correlation coefficients between the solar 10.7 cm flux and the ozone and temperature themselves from 2012 to 2014 are positive (negative) in regions where the responses are positive (negative). This supports our results since the correlations are independent of the multiple regression used to derive the responses. We also compare with previous results.
High-speed stereoscopy of aurora
Authors: Kataoka R. , Fukuda Y. , Uchida H. A. , Yamada H. , Miyoshi Y. , Ebihara Y. , Dahlgren H. , Hampton D.
Published: January 2016

Abstract. We performed 100 fps stereoscopic imaging of aurora for the first time. Two identical sCMOS cameras equipped with narrow field-of-view lenses (15° by 15°) were directed at magnetic zenith with the north–south base distance of 8.1 km. Here we show the best example that a rapidly pulsating diffuse patch and a streaming discrete arc were observed at the same time with different parallaxes, and the emission altitudes were estimated as 85–95 km and > 100 km, respectively. The estimated emission altitudes are consistent with those estimated in previous studies, and it is suggested that high-speed stereoscopy is useful to directly measure the emission altitudes of various types of rapidly varying aurora. It is also found that variation of emission altitude is gradual (e.g., 10 km increase over 5 s) for pulsating patches and is fast (e.g., 10 km increase within 0.5 s) for streaming arcs.
The effects of the big storm events in the first half of 2015 on the radiation belts observed by EPT/PROBA-V
Authors: Pierrard V. , Lopez Rosson G.
Published: January 2016

Abstract. With the energetic particle telescope (EPT) performing with direct electron and proton discrimination on board the ESA satellite PROBA-V, we analyze the high-resolution measurements of the charged particle radiation environment at an altitude of 820 km for the year 2015. On 17 March 2015, a big geomagnetic storm event injected unusual fluxes up to low radial distances in the radiation belts. EPT electron measurements show a deep dropout at L > 4 starting during the main phase of the storm, associated to the penetration of high energy fluxes at L < 2 completely filling the slot region. After 10 days, the formation of a new slot around L = 2.8 for electrons of 500–600 keV separates the outer belt from the belt extending at other longitudes than the South Atlantic Anomaly. Two other major events appeared in January and June 2015, again with injections of electrons in the inner belt, contrary to what was observed in 2013 and 2014. These observations open many perspectives to better understand the source and loss mechanisms, and particularly concerning the formation of three belts.
Twin mesospheric bores observed over Brazilian equatorial region
Authors: Medeiros A. F. , Paulino I. , Taylor M. J. , Fechine J. , Takahashi H. , Buriti R. A. , Lima L. M. , Wrasse C. M.
Published: January 2016

Abstract. Two consecutive mesospheric bores were observed simultaneously by two all-sky cameras on 19 December 2006. The observations were carried out in the northeast of Brazil at two different stations: São João do Cariri (36.5° W, 7.4° S) and Monteiro (37.1° W, 7.9° S), which are by about 85 km apart. The mesospheric bores were observed within an interval of  ∼  3 h in the NIR OH and OI557.7 nm airglow emissions. Both bores propagated to the east and showed similar characteristics. However, the first one exhibited a dark leading front with several trailing waves behind and progressed into a brighter airglow region, while the second bore, observed in the OH layer, was comprised of several bright waves propagating into a darker airglow region. This is the first paper to report events like these, called twin mesospheric bores. The background of the atmosphere during the occurrence of these events was studied by considering the temperature profiles from the TIMED/SABER satellite and wind from a meteor radar.
Simultaneous multiplicative column-normalized method (SMART) for 3-D ionosphere tomography in comparison to other algebraic methods
Authors: Gerzen T. , Minkwitz D.
Published: January 2016

Abstract. The accuracy and availability of satellite-based applications like GNSS positioning and remote sensing crucially depends on the knowledge of the ionospheric electron density distribution. The tomography of the ionosphere is one of the major tools to provide link specific ionospheric corrections as well as to study and monitor physical processes in the ionosphere. In this paper, we introduce a simultaneous multiplicative column-normalized method (SMART) for electron density reconstruction. Further, SMART+ is developed by combining SMART with a successive correction method. In this way, a balancing between the measurements of intersected and not intersected voxels is realised. The methods are compared with the well-known algebraic reconstruction techniques ART and SART. All the four methods are applied to reconstruct the 3-D electron density distribution by ingestion of ground-based GNSS TEC data into the NeQuick model. The comparative case study is implemented over Europe during two periods of the year 2011 covering quiet to disturbed ionospheric conditions. In particular, the performance of the methods is compared in terms of the convergence behaviour and the capability to reproduce sTEC and electron density profiles. For this purpose, independent sTEC data of four IGS stations and electron density profiles of four ionosonde stations are taken as reference. The results indicate that SMART significantly reduces the number of iterations necessary to achieve a predefined accuracy level. Further, SMART+ decreases the median of the absolute sTEC error up to 15, 22, 46 and 67 % compared to SMART, SART, ART and NeQuick respectively.