[Show abstract][Hide abstract] ABSTRACT: Long time series of ozone and NO 2 total column measurements in the southern tropics are available from two ground-based SAOZ (Système d'Analyse par Observation Zénithale) UV-visible spectrometers operated within the Net-work for the Detection of Atmospheric Composition Change (NDACC) in Bauru (22 • S, 49 • W) in S-E Brazil since 1995 and Reunion Island (21 • S, 55 • E) in the S-W Indian Ocean since 1993. Although the stations are located at the same lat-itude, significant differences are observed in the columns of both species, attributed to differences in tropospheric con-tent and equivalent latitude in the lower stratosphere. These data are used to identify which satellites operating during the same period, are capturing the same features and are thus best suited for building reliable merged time series for trend studies. For ozone, the satellites series best matching SAOZ observations are EP-TOMS (1995–2004) and OMI-TOMS (2005–2011), whereas for NO 2 , best results are obtained by combining GOME version GDP5 (1996–2003) and SCIA-MACHY – IUP (2003–2011), displaying lower noise and seasonality in reference to SAOZ. Both merged data sets are fully consistent with the larger columns of the two species above South America and the seasonality of the differences between the two stations, reported by SAOZ, providing reli-able time series for further trend analyses and identification of sources of interannual variability in the future analysis.
[Show abstract][Hide abstract] ABSTRACT: A representation of atmospheric chemistry has been included in the Integrated Forecasting System (IFS) of the European Centre for Medium-range Weather Forecasts (ECMWF). The new chemistry modules complement the aerosol modules of the IFS for atmospheric Composition, which is named C-IFS. C-IFS for chemistry supersedes a coupled system, in which the chemical transport model (CTM) MOZART 3 was two-way coupled to the IFS (IFS-MOZART). This paper contains a description of the new on-line implementation, an evaluation with observations and a comparison of the performance of C-IFS with IFS-MOZART. The chemical mechanism of C-IFS is an extended version of the CB05 chemical mechanism as implemented in the CTM TM5. CB05 describes tropospheric chemistry with 54 species and 126 reactions. Wet deposition and lightning NO emissions are modelled in C-IFS using the detailed input of the IFS physics package. A one-year simulation for 2008 at a horizontal resolution of about 80 km is evaluated against ozone sondes, CO MOZAIC profiles, European surface observations of ozone, CO, SO2 and NO2 as well as satellite retrievals of CO, tropospheric NO2 and formaldehyde. MACCity anthropogenic emissions and biomass burning emissions from the GFAS data set were used in the simulations by both C-IFS and MOZART. C-IFS (CB05) showed an improved performance with respect to MOZART for CO, upper tropospheric ozone, winter time SO2 and was of a similar accuracy for other evaluated species. C-IFS (CB05) is about ten times more computationally efficient than IFS-MOZART.
[Show abstract][Hide abstract] ABSTRACT: Current fire emission inventories apply universal emission factors (EFs) for the calculation of NOx emissions over large biomes such as boreal forest. However, recent satellite-based studies over tropical and subtropical regions have indicated spatio-temporal variations in EFs within specific biomes. In this study, satellite measurements of tropospheric NO2 vertical columns (TVC NO2) from the GOME-2 instrument and fire radiative power (FRP) from MODIS are used for the estimation of fire emission rates (FERs) of NOx over Eurasian and North American boreal forests. The retrieval of TVC NO2 is based on a stratospheric correction using simulated stratospheric NO2 instead of applying the reference sector method, which was used in a previous study. The model approach is more suitable for boreal latitudes. TVC NO2 and FRP are spatially aggregated to a 1° × 1° horizontal resolution and temporally averaged to monthly values. The conversion of the satellite-derived tropospheric NO2 columns into production rates of NOx from fire (Pf) is based on the NO2/NOx ratio as obtained from the MACC reanalysis data set and an assumed lifetime of NOx. A global land cover map is used to define boreal forests across these two regions in order to evaluate the FERs of NOx for this biome. The FERs of NOx, which are derived from the gradients of the linear relationship between Pf and FRP, are more than 30% lower for North American than for Eurasian boreal forest fires. We speculate that these discrepancies are mainly related to the variable nitrogen content in plant tissues, which is higher in deciduous forests dominating large parts in Eurasia. In order to compare the obtained values with EFs found in the literature, the FERs are converted into EFs. The satellite-based EFs of NOx are estimated at 0.83 and 0.61 g kg−1 for Eurasian and North American boreal forests, respectively, which is in good agreement with the value found in a recent emission factor compilation. However, recent fire emission inventories are based on EFs of NOx that are 3–5 times larger, which indicates that there are still large uncertainties in estimates of NOx from biomass burning, especially on the regional scale.
[Show abstract][Hide abstract] ABSTRACT: We report on the evolution of tropospheric nitrogen dioxide (NO2) over Spain, focusing on the densely
populated cities of Barcelona, Bilbao, Madrid, Sevilla and Valencia, during 17 years, from 1996 to 2012. This
data series combines observations from in-situ air quality monitoring networks and the satellite-based
instruments GOME and SCIAMACHY. The results in these five cities show a smooth decrease in the NO2
concentrations of ,2% per year in the period 1996–2008, due to the implementation of emissions control
environmental legislation, and a more abrupt descend of,7% per year from 2008 to 2012 as a consequence
of the economic recession. In the whole Spanish territory the NO2 levels have decreased by,22% from 1996
to 2012. Statistical analysis of several economic indicators is used to investigate the different factors driving
the NO2 concentration trends over Spain during the last two decades.
[Show abstract][Hide abstract] ABSTRACT: We investigated the effect of surface reflectance anisotropy, Bidirectional Reflectance Distribution Function (BRDF), on satellite retrievals of tropospheric NO2. We assume the geometry of geostationary measurements over Tokyo, which is one of the worst air-polluted regions in the East Asia. We calculated air mass factors (AMF) and box AMFs (BAMF) for tropospheric NO2 to evaluate the effect of BRDF by using the radiative transfer model SCIATRAN. To model the BRDF effect, we utilized the Moderate Resolution Imaging Spectroradiometer (MODIS) products (MOD43B1 and MOD43B2), which provide three coefficients to express the RossThick-LiSparseReciprocal model, a semi-empirical and kernel-based model of BRDF. Because BRDF depends on the land cover type, we also utilized the High Resolution Land-Use and Land-Cover Map by the Advanced Land Observing Satellite (ALOS)/Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2), which classifies the ground pixels over Tokyo into six main types: water, urban, paddy, crop, deciduous forest and evergreen forest. We first develop an empirical model of the three BRDF coefficients for each land cover type over Tokyo, and then apply the model to the calculation of land cover type dependent AMFs and BAMFs. Results show that the variability of AMF among the land types is up to several tens percent, and if we neglect the reflectance anisotropy, the difference from BRDF's AMF reaches 10% or more. The evaluation of the BAMFs calculated shows that not to consider variations in BRDF will cause large errors if the concentration of NO2 is high close to the surface, although the importance of BRDF for AMFs decreases for large aerosol optical depth (AOD).
[Show abstract][Hide abstract] ABSTRACT: For the purpose of trace gas measurements and pollution mapping, the Airborne imaging DOAS instrument for Measurements of Atmospheric Pollution (AirMAP) has been developed, characterised and successfully operated from aircraft. From the observations with the AirMAP instrument nitrogen dioxide (NO2) columns were retrieved. A major benefit of the pushbroom imaging instrument is the spatially continuous, gap-free measurement sequence independent of flight altitude, a valuable characteristic for mapping purposes. This is made possible by the use of a frame-transfer detector. With a wide-angle entrance objective, a broad field-of-view across track of around 48° is achieved, leading to a swath width of about the same size as the flight altitude. The use of fibre coupled light intake optics with sorted light fibres allows flexible positioning within the aircraft and retains the very good imaging capabilities. The measurements yield ground spatial resolutions below 100 m. From a maximum of 35 individual viewing directions (lines of sight, LOS) represented by 35 single fibres, the number of viewing directions is adapted to each situation by averaging according to signal-to-noise or spatial resolution requirements. Exploitation of all the viewing directions yields observations at 30 m spatial resolution, making the instrument a suitable tool for mapping trace gas point sources and small scale variability. For accurate spatial mapping the position and aircraft attitude are taken into account using the Attitude and Heading Reference System of the aircraft. A first demonstration mission using AirMAP was undertaken. In June 2011, AirMAP has been operated on the AWI Polar-5 aircraft in the framework of the AIRMETH2011 campaign. During a flight above a medium sized coal-fired power plant in North-West Germany, AirMAP clearly detects the emission plume downwind from the exhaust stack, with NO2 vertical columns around 2 × 1016 molecules cm-2 in the plume center. The emission estimates are consistent with reports in the pollutant transfer register. Strong spatial gradients and variability in NO2 amounts across and along flight direction are observed, and small-scale enhancements of NO2 above a motorway are detected. The present study reports on the experimental setup and characteristics of AirMAP, and the first measurements at high spatial resolution and wide spatial coverage are presented which meet the requirements for NO2 mapping to observe and account for the intrinsic variability of tropospheric NO2.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen oxides (NOx) play key roles in atmospheric chemistry, air pollution, and climate. While the largest fraction of these reactive gases is released by anthropogenic emission sources, a significant amount can be attributed to vegetation fires. In this study, NO2 from GOME-2 on board EUMETSAT's MetOp-A and OMI on board NASA's Aura as well as fire radiative power (FRP) from the measurements of MODIS on board NASA's Terra and Aqua satellites are used to derive fire emission rates (FERs) of NOx for different types of vegetation using a simple statistical approach. Monthly means of tropospheric NO2 vertical columns (TVC NO2) have been analyzed for their temporal correlation with the monthly means of FRP for five consecutive years from 2007 to 2011 on a horizontal 1° × 1° grid. The strongest correlation is found to be largely confined to tropical and subtropical regions, which account for more than 80% of yearly burned area, on average, globally. In these regions, the seasonal variation of fire intensity, expressed by the FRP data, is similar to the pattern of TVC NO2. As chemical models typically require values for the amount of NOx being released as a function of time, we have converted the retrieved TVC NO2 into production rates of NOx from fire (Pf) by assuming a constant lifetime of NOx. The comparison between Pf and NOx emissions from the Global Fire Emissions Database (GFEDv3.1) over 5 characteristic biomass burning regions in the tropics and subtropics shows good agreement. By separating the monthly means of Pf and FRP according to land cover type, FERs of NOx could be derived for different biomes. The estimated FERs for the dominating types of vegetation burned are lowest for open shrublands and savannas (0.28-1.03 g NOx s-1 MW-1) and highest for croplands and woody savannas (0.82-1.56 g NOx s-1 MW-1). This analysis demonstrates that the strong empirical relationship between TVC NO2 and FRP and the following simplified assumptions are a useful tool for the characterization of NOx emission rates from vegetation fires in the tropics and subtropics. Possible factors affecting the magnitude of the obtained values are discussed.
[Show abstract][Hide abstract] ABSTRACT: The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice), which may affect atmospheric and biogeochemical cycles in the Arctic. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(ii)) in the atmosphere and its subsequent deposition to snow and ice. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic, some of which can enter ecosystems during snowmelt. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.
[Show abstract][Hide abstract] ABSTRACT: Record breaking loss of ozone (O3) in the Arctic transformations occurring in the Arctic polar vortex using total column and vertical profile data products for O3, bromine oxide (BrO), nitrogen dioxide (NO2), chlorine dioxide (OClO), and polar stratospheric clouds (PSC) retrieved from measurements made by SCIAMACHY (Scanning Imaging Absorption SpectroMeter for Atmospheric CHartography) onboard Envisat (Environmental Satellite), as well as total column ozone amount, retrieved from the measurements of GOME-2 (Global Ozone Monitoring Experiment) on MetOp-A (Meteorological Experimental Satellite). Similarly we use the retrieved data from DOAS (Differential Optical Absorption Spectroscopy) measurements made in NyÅlesund (78.55N, 11.55E). A chemical transport model (CTM) has been used to relate and compare Arctic winter– spring conditions in 2011 with those in the previous year. In late winter–spring 2010/2011 the chemical ozone loss in the polar vortex derived from SCIAMACHY observations confirms findings reported elsewhere. More than 70% of O3 was depleted by halogen catalytic cycles between the 425 and 525K isentropic surfaces, i.e. in the altitude range 16– 20 km. In contrast, during the same period in the previous winter 2009/2010, a typical warm Arctic winter, only slightly more than 20% depletion occurred below 20 km, while 40% of O3 was removed above the 575K isentrope (around 23 km). This loss above 575K is explained by the catalytic destruction by NOx descending from the mesosphere. In both Arctic winters 2009/2010 and 2010/2011, calculated O3 losses from the CTM are in good agreement to our observations and other model studies. The mid-winter 2011 conditions, prior to the catalytic cycles being fully effective, are also investigated. Surprisingly, a significant loss of O3 around 60 %, previously not discussed in detail, is observed in mid-January 2011 below 500K (around 19 km) and sustained for approximately 1 week. The low O3 region had an exceptionally large spatial extent. The situation was caused by two independently evolving tropopause elevations over the Asian continent. Induced adiabatic cooling of the stratosphere favoured the formation of PSC, increased the amount of active chlorine for a short time, and potentially contributed to higher polar ozone loss later in spring.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2014; 14:3247–3276. · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica in spring 2007, and BrO was measured by satellite-borne remote-sensing spectrometers using similar spectral regions and similar Differential Optical Absorption Spectroscopy (DOAS) analyses. Near-surface BrO was simultaneously measured in situ at Halley by Chemical Ionisation Mass Spectrometry (CIMS), and in an earlier year near-surface BrO was measured at Halley over a long path by a ground-based DOAS spectrometer. During enhancement episodes, total amounts of tropospheric BrO from the ground-based remote-sensor were similar to those from space, but if we assume that the BrO was confined to the mixed layer they were very much larger than values measured by either near-surface technique. This large apparent discrepancy can be resolved if substantial amounts of BrO were in the free troposphere during most enhancement episodes. Amounts observed by the ground-based remote sensor at different elevation angles, and their formal inversions to vertical profiles, demonstrate that much of the BrO was indeed often in the free troposphere. This is consistent with the ~5 day lifetime of Bry and with the enhanced BrO observed during some Antarctic blizzards.
Journal of Quantitative Spectroscopy and Radiative Transfer 01/2014; · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitrogen oxides (NOx) play key roles in atmospheric
chemistry, air pollution, and climate. While the largest fraction of
these reactive gases is released by anthropogenic emission sources, a
significant amount can be attributed to vegetation fires. In this study,
NO2 from GOME-2 on board EUMETSAT's MetOp-A and OMI on board
NASA's Aura as well as fire radiative power (FRP) from the measurements
of MODIS on board NASA's Terra and Aqua are used to derive fire emission
rates (FERs) of NOx for different types of vegetation using a
simple statistical approach. Monthly means of tropospheric
NO2 vertical columns (TVC NO2) have been analyzed
for their temporal correlation with the monthly means of FRP for five
consecutive years from 2007 to 2011 on a horizontal 1° ×
1° grid. The strongest correlation is found to be largely confined
to tropical and subtropical regions, which account for more than 80% of
yearly burned area on average globally. In these regions, the seasonal
variation of fire intensity, expressed by the FRP data, is similar to
the pattern of TVC NO2. As chemical models typically require
values for the amount of NOx being released as a function of
time, we have converted the retrieved TVC NO2 into production
rates of NOx from fire (Pf) by assuming a constant
lifetime of NOx. The comparison between Pf and
NOx emissions from GFEDv3.1 over 5 characteristic biomass
burning regions in the tropics and subtropics indicated good agreement.
By separating the monthly means of Pf and FRP according to
land cover type, FERs of NOx could be derived for different
biomes. The estimated FERs for the dominating types of vegetation burned
are lowest for open shrublands and savannas (0.28-1.03 g NOx
s-1 MW-1) and highest for croplands and woody
savannas (0.82-1.56 g NOx s-1 MW-1).
This analysis demonstrates clearly that there are biome-specific,
diurnal, and regional differences in FERs for the dominating types of
vegetation burned in the tropics and subtropics. Possible factors
affecting the magnitude of the obtained values are discussed.
Atmospheric Chemistry and Physics 11/2013; 13(11):28453-28510. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Intercontinental long-range transport (LRT) events of NO2
relocate the effects of air pollution from emission regions to remote,
pristine regions. We detect transported plumes in tropospheric
NO2 columns measured by the GOME-2/MetOp-A instrument with a
specialized algorithm and trace the plumes to their sources using the
HYSPLIT lagrangian transport model. With this algorithm we find 3808 LRT
events over the ocean for the period 2007 to 2011. LRT events occur
frequently in the mid-latitudes, emerging usually from coastal
high-emission regions. In the free troposphere, plumes of NO2
can travel for several days to the polar oceanic atmosphere or to other
continents. They travel along characteristic routes and originate from
both continuous anthropogenic emission and emission events such as bush
fires. Most NO2 LRT events occur during autumn and winter
months, when meteorological conditions and emissions are most favorable.
The evaluation of meteorological data shows that the observed
NO2 LRT is often linked to cyclones passing over an emission
Atmospheric Chemistry and Physics 11/2013; 13(11):30945-31012. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Following polar sunrise in the Arctic springtime, tropospheric ozone
episodically decreases rapidly to near zero levels during ozone
depletion events (ODEs). Many uncertainties remain in our understanding
of ODE characteristics, including the temporal and spatial scales, as
well as environmental drivers. Measurements of ozone, bromine monoxide
(BrO), and meteorology were obtained during several deployments of
autonomous, ice-tethered buoys (O-Buoys) from both coastal sites and
over the Arctic Ocean; these data were used to characterize observed
ODEs. Detected decreases in surface ozone levels during the onset of
ODEs corresponded to a median estimated apparent ozone depletion
timescale (based on chemistry and the advection of
O3-depleted air) of 11 h. If assumed to be dominated by
chemistry, these timescales would correspond to larger-than-observed BrO
mole fractions based on known chemical mechanisms and assumed other
radical levels. Using backward air mass trajectories, the spatial scales
for ODEs (defined by time periods in which ozone mole fraction ≤15
nmol mol-1) were estimated to be ~900 km (median), while
areas estimated to represent major ozone depletions (<10 nmol
mol-1) had dimensions of ~280 km (median). These observations
point to a heterogeneous boundary layer with localized regions of
active, ozone-destroying halogen chemistry, interspersed among larger
regions of previously depleted air that retain reduced ozone levels
through hindered atmospheric mixing. Based on the estimated size
distribution, Monte Carlo simulations showed it was statistically
possible that all ODEs observed could have originated upwind, followed
by transport to the measurement site. Local wind speed averages were low
during most ODEs (median of ~3.6 m s-1), and there was no
apparent dependence on local temperature.
Atmospheric Chemistry and Physics 11/2013; 13(11):30233-30285. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Major gaseous and particulate pollutant levels over Europe in 2008 have been simulated using the offline-coupled WRFCMAQ chemistry and transport modeling system. The simulations are compared with surface observations from the EMEP stations, ozone (O3) soundings, ship-borne O3 and nitrogen dioxide (NO2) observations in the western Mediterranean, tropospheric NO2 vertical column densities from the SCIAMACHY instrument, and aerosol optical depths (AOD) from the AERONET. The results show that on average, surface O3 levels are underestimated by 4 to 7% over the northern European EMEP stations while they are overestimated by 7-10% over the southern European EMEP stations and underestimated in the tropospheric column (by 10-20%). Particulate matter (PM) mass concentrations are underestimated by up to 60%, particularly in southern and eastern Europe, suggesting underestimated PM sources. Larger differences are calculated for individual aerosol components, particularly for organic and elemental carbon than for the total PM mass, indicating uncertainty in the combustion sources. Better agreement has been obtained for aerosol species over urban areas of the eastern Mediterranean, particularly for nss-SO4(2), attributed to the implementation of higher quality emission inventories for that area. Simulated AOD levels are lower than the AERONET observations by 10% on average, with average underestimations of 3% north of 40°N, attributed to the low anthropogenic emissions in the model and 22% south of 40°N, suggesting underestimated natural and resuspended dust emissions. Overall, the results reveal differences in the model performance between northern and southern Europe, suggesting significant differences in the representation of both anthropogenic and natural emissions in these regions. Budget analyses indicate that O3 and peroxyacetyl nitrate (PAN) are transported from the free troposphere (FT) to the planetary boundary layer over Europe, while other species follow the reverse path and are then advected away from the source region.
Science of The Total Environment 10/2013; 470-471C:270-281. · 3.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Atmospheric aerosol, generated from natural and anthropogenic sources,
plays a key role in regulating visibility, air quality, and acid
deposition. It is directly linked to and impacts on human health. It
also reflects and absorbs incoming solar radiation and thereby
influences the climate change. The cooling by aerosols is now recognized
to have partly masked the atmospheric warming from fossil fuel
combustion emissions. The role and potential management of short-lived
climate pollutants such as aerosol are currently a topic of much
scientific and public debate. Our limited knowledge of atmospheric
aerosol and its influence on the Earth's radiation balance has a
significant impact on the accuracy and error of current predictions of
the future global climate change. In the past decades, environmental
legislation in industrialized countries has begun to limit the release
of anthropogenic pollutants. In contrast, in Asia as a result of the
recent rapid economic development, emissions from industry and traffic
have increased dramatically. In this study, the temporal changes/trends
of atmospheric aerosols, derived from the satellite instruments MODIS
(on board Terra and Aqua), MISR (Terra), and SeaWiFS (OrbView-2) during
the past decade, are investigated. Whilst the aerosol optical thickness,
AOT, over Western Europe decreases (i.e. by up to about -40% from 2003
to 2008) and parts of North America, a statistically significant
increase (about +34% in the same period) over East China is observed and
attributed to both the increase in industrial output and the Asian
Atmospheric Chemistry and Physics 10/2013; 13(10):26001-26041. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Since the establishment of the SCIAMACHY Quality Working Group (SQWG) in a joint inter-agency ESA-DLR-NSO effort in late 2006, the ESA operational Level 2 processor was significantly improved w.r.t. data quality and the product list was substantially enhanced with new parameters. Current operational Level 2 products correspond to version 5. Meanwhile the Quality Working Group has prepared the next product version 6. This paper summarises the key characteristics of the Level 2 version 5 and 6.
[Show abstract][Hide abstract] ABSTRACT: Filling-in of spectral features observed in scat- tered sunlight and known as the \Ring Eect" has a sig- nicant impact on the retrieval of atmospheric trace con- stituentsfrombothground-basedandsatelliteobservations. As clouds also have strong impacts on radiative transfer in the UV/visible spectral range, possible changes of the Ring Eect due to clouds have to be considered. Such investiga- tions require radiative transfer modeling explicitly account- ing for both cloud and Ring features. UV/visible ground and satellite based measurements, taken under cloudy con- ditions, were used to validate Ring and cloud modeling us- ingtheradiativetransfermodelSCIATRAN.Asanexample results of model applications are presentedfor bothground- based and satellite geometry. Two case studies are used to explain the sources of the observed Filling-in.
Geophysical Research Letters 08/2013; · 3.98 Impact Factor