bluuebunny/crossref_metadata_2025 huggingface dataset:
Attribution of ozone radiative forcing trend to individual NOx sources
Authors: Dahlmann K. , Grewe V. , Ponater M. , Matthes S.
Published: April 2010

Abstract. Decadal means of ozone fields from transient E39/C climate-chemistry simulations (1960–2019) are analysed and temporally developing ozone radiative forcings (RF) are investigated which result from individual ozone precursor sources like road traffic, industry, air traffic, etc. We study how effective NOx emissions from different sources produce ozone. This ozone production efficiency is mainly dependent on the altitude of NOx emission and on the amount of background NOx. For example, our study shows that the ozone production efficiency of lightning and air traffic have a five and two time higher ozone production efficiency than ground based sources. The radiative efficiency of ozone (i.e. the radiative forcing per molecule) is mainly dependent on the surface temperature, but also, to a lesser degree, on the altitude of added ozone. Lightning, for example, causes the highest specific RF due to the fact that lightning primarily enhances ozone in low latitudes in the mid-troposphere. Superimposed on these effects, is a saturation effect which causes a decreasing RF efficiency with increasing background ozone. A consequence of this saturation effect is an underestimation of total RF by about 10% if the component RFs of individual ozone sources are calculated separately and added up afterwards. The results show that the time development of emissions (1960–2019) control the RF changes for most sources. RF changes are slightly reduced due to a changing atmospheric composition (10–25%) for all but the aircraft sources, and due to RF saturation (2–5%).
Spatial and temporal variability in surface ozone at a high elevation remote site in Nepal
Authors: Moore G. W. K. , Abernethy S. , Semple J. L.
Published: April 2010

Abstract. Ozone is an important atmospheric constituent due to its role as both a greenhouse gas and an oxidant. Recent measurements in the Mount Everest region indicate the presence of ozone at elevations from 5000 to 9000 m a.s.l. that are the result of both stratospheric and tropospheric sources. Here we examine the temporal variability in the surface ozone concentration measurements from the ABC-Pyramid Observatory in the Mount Everest region during 2006 and compare it to the total column ozone data from the OMI instrument as well as meteorological fields from the ECMWF Interim Reanalysis. Both the surface ozone at and the total column ozone over the ABC-Pyramid Observatory site have maxima in the pre-monsoon period. We show that during this period, there is a statistically significant correlation between the two suggesting that the stratosphere was an important contributor to the high levels of ozone observed during the period. There was a hiatus in the monsoon in June that resulted in a return of westerlies over northern Indian and southern Tibet and as a result, the aforementioned correlation extended into June. No such correlation exists during the monsoon and post-monsoon periods. Spatial correlation maps between the surface ozone and total column ozone as well as meteorological fields from the ECMWF Interim Reanalysis support the contention that there is a significant stratospheric contribution in the pre-monsoon period that is absent during and after the monsoon.
Information-based mid-upper tropospheric methane derived from Atmospheric Infrared Sounder (AIRS) and its validation
Authors: Xiong X. , Barnet C. , Wei J. , Maddy E.
Published: April 2010

Abstract. Atmospheric Infrared Sounder (AIRS) measurements of methane (CH4) generally contain about 1.0 degree of freedom and are therefore dependent on a priori assumptions about the vertical methane distribution as well as the temperature lapse rate and the amount of moisture. Thus it requires that interpretation and/or analysis of the CH4 spatial and temporal variation based on the AIRS retrievals need to use the averaging kernels (AK). To simplify the use of satellite retrieved products for scientific analysis, a method based on the information content of the retrievals is developed, in which the AIRS retrieved CH4 in the layer from 50 to 250 hPa below the tropopause is used to characterize the mid-upper tropospheric CH4 in the mid-high latitude regions. The basis of this method is that in the mid-high latitude regions the maximum sensitive layers of AIRS to CH4 have a good correlation with the tropopause heights, and these layers are usually between 50 and 250 hPa below the tropopause. Validation using the aircraft measurements from NOAA/ESRL/GMD and the campaigns INTEX-A and -B indicated that the correlation of AIRS mid-upper tropospheric CH4 with aircraft measurements is ~0.6–0.7, and its the bias and rms difference are less than ±1% and 1.2%, respectively. Further comparison of the CH4 seasonal cycle indicated that the cycle from AIRS mid-upper tropospheric CH4 is in a reasonable agreement with NOAA aircraft measurements. This method provides a simple way to use the thermal infrared sounders data to approximately analyze the spatial and temporal variation CH4 in the upper free tropospere without referring the AK. This method is applicable to derive tropospheric CH4 as well as other trace gases for any thermal infrared sensors.
Regional-scale correlation between CO2 fire emissions, burned areas, and mid-tropospheric CO2 daily variations over southern Africa
Authors: Chédin A. , Scott N. A. , Ciais P. , Rio C. , Hourdin F. , Crevoisier C. , Armante R.
Published: April 2010

Abstract. Monthly mean mid-tropospheric CO2 columns are retrieved from evening and morning observations of NOAA-10 satellite over the tropics during the period 1987–1991. We find that the difference between evening and morning CO2 columns (hereafter referred to as Daily Tropospheric Excess – DTE) increases by up to a few ppm over regions affected by fires. A high positive correlation (R2~0.8) is found between annual DTE and CO2 emissions derived from burned area (Global Fire Emission Database – GFEDv2) across 10 regions with contrasted vegetation cover in southern Africa. Seasonal variability comparison between DTE and GFEDv2 also shows a good general agreement. Only two regions south of 10° S, show a seasonal increase of DTE starting earlier and rising up more rapidly than seen in two burned area products: GFEDv2 and L3JRC, the latter established by the Joint Research Center. The phase of the L3JRC dataset is however closer to DTE observations. This misfit could come from limitations in current burned area detection algorithms (difficulty in detecting small fires). 3-D simulations of the DTE signal by the LMDz General Circulation Model, in which a pyro-thermal plume model is activated, confirm the observations. A large fraction of fire products are directly injected in the mid-troposphere, well above the boundary layer. This rapid uplift of CO2, combined with atmospheric transport patterns in southern Africa during the dry season, characterized by a fluctuating continental gyre, produces a daily DTE signal mainly positive above the source region and either positive or negative outside of the source region. On a monthly mean, this results in a persistent DTE signal above the source region of an order of 1 ppm, while the impact of large-scale advection vanishes. We conclude that the DTE signal is a quantitative proxy of fire emission spatial patterns, in particular before the ATSR or MODIS observation periods when better quality fire count and burned area data became available, and can also bring a constraint in the analysis of their present results.
Factors determining the effect of aerosols on cloud mass and the dependence of these factors on liquid-water path
Authors: Lee S. S. , Penner J. E.
Published: April 2010

Abstract. Increasing aerosols decreases the size of droplets and thus their collection efficiencies, leading to an inefficient conversion of droplets to precipitable raindrops. This, in turn, increases the mass of droplets suspended in the air by decreasing the removal of cloud mass by sedimentation and has been known to be a main mechanism which determines the effect of aerosols on cloud mass. However, a recent study showed that this mechanism played a negligible role in the determination of the cloud mass as compared to aerosol-induced feedbacks between microphysics and dynamics in thin stratocumulus clouds with LWP of ~50 g m
C3-C5 alkanes in the atmosphere: concentration, seasonal cycle and contribution to the atmospheric budgets of acetone and acetaldehyde
Authors: Pozzer A. , Pollmann J. , Taraborrelli D. , Jöckel P. , Helmig D. , Tans P. , Hueber J. , Lelieveld J.
Published: April 2010

Abstract. The atmospheric chemistry of C3-C5 alkanes has been incorporated in the atmospheric-chemistry general circulation model EMAC. Model output is compared with observations from the NOAA/ESRL GMD cooperative air sampling network. A new series of measurements is used to evaluate the model in representing C3-C5 alkanes (i.e. propane, isobutane, butane, isopentane and pentane). While the representation of propane is within the measurement standard deviation, some deviations are found for the other tracers. The model is able to reproduce the main features of the C3-C5 alkanes (e.g., seasonality). However, in the Northern Hemisphere during winter the mixing ratios of these alkanes are generally overestimated. Conversely, the model shows an underestimation in the Southern Hemisphere. Moreover, only for iso-pentane there is a net overestimation of the mixing ratios, while for the other alkanes, the results are at the higher end of the measurement range. The effects of the C3-C5 alkanes to atmospheric acetone and acetaldehyde are quantified. The total amount of acetone produced by propane, isobutane and isopentane oxidation is 11.6 Tg/yr, 4.2 Tg/yr and 5.8 Tg/yr, respectively. These chemical sources are largely controlled by the reaction with OH, while the reactions with NO3 and Cl contribute only to a little extent. Moreover, 3.1, 4.5, 1.9 and 6.7 Tg/yr of acetaldehyde are formed from the oxidation of propane, butane, pentane and isopentane, respectively. Also for acetaldehyde, the formation is controlled by the reaction of alkanes with OH. However, since isopentane is generally overestimated, its contribution to the production of these oxygenated compounds represents an upper limit.
Influence of semi-volatile species on particle hygroscopic growth
Authors: Villani P. , Sellegri K. , Monier M. , Laj P.
Published: April 2010

Abstract. The hygroscopic properties of aerosol particles are often related to their content of soluble material, on the basis of the Kohler theory. Recent studies, however, seem to indicate that the role of aerosol particle semi-volatile fraction properties has been underestimated. In this study, we use a novel method based on a Tandem Differential Mobility Analyser (TDMA) system combining particle volatilization and humidification conditioning (VH-TDMA) to test the effect of the gentle volatilization of a small fraction of the atmospheric particles on the particle hygroscopic growth in several environments (urban to remote). Results show that the particle hygroscopic properties can either be enhanced or decreased after thermal conditioning of the particle at moderate temperatures (50 to 110°C). The hygroscopic growth factor changes induced by volatilization indicate that some volatile compounds, although present at low concentrations, drastically influence the hygroscopic growth of particles in the way that can not be predicted by the Kohler theory at equilibrium.
Effects of absorbing aerosols in cloudy skies: a satellite study over the Atlantic Ocean
Authors: Peters K. , Quaas J. , Bellouin N.
Published: April 2010

Abstract. Aerosol effects, direct as well as indirect, constitute one of the biggest sources of uncertainty when it comes to quantifying human forcing of climate change. Understanding these will thus increase the credibility of climate predictions. This study focuses on aerosol effects when absorbing aerosols reside in cloudy skies. In cloudfree conditions, aerosols usually exert a negative radiative forcing (RF) at the top of the atmosphere (TOA) due to their scattering properties. When located above clouds, absorbing aerosols can reduce the shortwave local planetary albedo α, resulting in an often significant local positive direct radiative forcing (DRF). A method for deriving the aerosol radiative effects of absorbing aerosols in cloudy situations from satellite retrievals is presented. Data of 2005 and 2006 from various sensors aboard satellites of the "A-Train" constellation, restricted to the tropical and subtropical Atlantic ocean, is used. A multiple linear regression is performed to identify the dependence of α in cloudy scenes on cloud liquid water path (LWP) and aerosol optical depth (AOD), using the OMI UV-Aerosolindex (UV-AI) as an indicator for absorbing aerosols. The results show an increase of α with increasing aerosol load, and a relative decrease of α with increasing amount of absorbing aerosols in cloudy scenes. This allows to derive the direct aerosol effect of absorbing aerosols above clouds, with the effect of aerosol absorption over clouds in the Atlantic contributing +0.08±1.2×10-3Wm-2 to the global TOA RF.
Source apportionment of mercury in dust fallout at urban residential area of Central India
Authors: Pervez S. , Balakrishna G. , Tiwari S.
Published: April 2010

Abstract. The components and quantities of atmospheric dust fallout have been reported to be the pollution indicator of large urban areas. The multiplicity and complexity of sources of atmospheric dusts in urban regions (e.g. industrial complexes composed of a variety of industrial processes, automobiles, construction activities etc.) has put forward the need of source apportionment of these sources indicating their contribution to specific environmental receptor. The study presented here is focused on investigation of source contribution estimates of Mercury in urban dust fallout in an urban-industrial area, Raipur, India. Source-receptor based representative sampling plan using longitudinal study design has been adopted. Six sampling sites have been identified on the basis of land use for development plan of anthropogenic activities and factors related to the transportation and dispersion pattern of atmospheric dusts. 24 samples of dust fallout has been collected from each site (one in each month) and subjected to chemical analysis of selected chemical constituents known as markers of selected major dust emitting sources (Steel making average, Road traffic-borne dusts, construction activities, Auto mobile exhaust, and soils). Chemical composition of dust measured at sites marked for identified sources alongwith SPECIATE of USEPA has been used for the preparation of source profiles. Three classified residential receptors (ambient-outdoor, house-indoors and local street-outdoors) have been chosen for development of receptor compositional profiles. Source apportionment has been done using Chemical Mass Balance (CMB 8). Good fit parameters and relative source contribution has been analysed and documented. Dust fallout and respective mercury levels were found tobe higher compared to prescribed standards. Variation in relative contribution of selected sources from site to site within the study area has been occurred. Dominance of local line and area sources (road-traffic and construction borne dusts) on mercury levels measured at selected residential receptors compared to stationary industrial sources has been observed. Road-traffic has shown highest contribution of dust and mercury in house-indoors, while in case of ambient-outdoor the receptor has shown different higher susceptibility of identified sources for dust and mercury. The results of CMB output and regression data of source-receptor dust matrices have shown comparable pattern.
Atmospheric electric field anomalies associated with solar flare/coronal mass ejection events and solar energetic charged particle "Ground Level Events"
Authors: Kasatkina E. A. , Shumilov O. I. , Rycroft M. J. , Marcz F. , Frank-Kamenetsky A. V.
Published: April 2010

Abstract. We discuss the fair weather atmospheric electric field signatures of three major solar energetic charged particle events which occurred in on 15 April 2001, 18 April and 4 November, and their causative solar flares/coronal mass ejections (SF/CMEs). Only the 15 April 2001 shows clear evidence for Ez variation associated to SF/CME events and the other two events may support this hypothesis as well although for them the meteorological data were not available. All three events seem to be associated with relativistic solar protons (i.e. protons with energies >450 MeV) of the Ground Level Event (GLE) type. The study presents data on variations of the vertical component of the atmospheric electric field (Ez) measured at the auroral station Apatity (geomagnetic latitude: 63.8°, the polar cap station Vostok (geomagnetic latitude: −89.3°) and the middle latitude stations Voyeikovo (geomagnetic latitude: 56.1°) and Nagycenk (geomagnetic latitude: 47.2°). A significant disturbance in the atmospheric electric field is sometimes observed close to the time of the causative solar flare; the beginning of the electric field perturbation at Apatity is detected one or two hours before the flare onset and the GLE onset. Atmospheric electric field records at Vostok and Voyeikovo show a similar disturbance at the same time for the 15 April 2001 event. Some mechanisms responsible for the electric field perturbations are considered.
Aerosol direct radiative forcing during Sahara dust intrusions in the central Mediterranean
Authors: Perrone M. R. , Bergamo A. , Bellantone V.
Published: April 2010

Abstract. The clear-sky, instantaneous Direct Radiative Effect (DRE) by all and anthropogenic particles is calculated during Sahara dust intrusions in the Mediterranean basin, to evaluate the role of anthropogenic particle's radiative effects and to get a better estimate of the DRE by desert dust. The clear-sky aerosol DRE is calculated by a two stream radiative transfer model in the solar (0.3–4 μm) and infrared (4–200 μm) spectral range, at the top of the atmosphere (ToA) and at the Earth's surface (sfc). Aerosol optical properties by AERONET sun-sky photometer measurements and aerosol vertical profiles by EARLINET lidar measurements, both performed at Lecce (40.33° N, 18.10° E) during Sahara dust intrusions occurred from 2003 to 2006 year, are used to initialize radiative transfer simulations. Instantaneous values at 0.44 μm of the real (n) and imaginary (k) refractive index and of the of aerosol optical depth (AOD) vary within the 1.33–1.55, 0.0037–0.014, and 0.2–0.7 range, respectively during the analyzed dust outbreaks. Fine mode particles contribute from 34% to 85% to the AOD by all particles. The complex atmospheric chemistry of the Mediterranean basin that is also influenced by regional and long-range transported emissions from continental Europe and the dependence of dust optical properties on soil properties of source regions and transport pathways are responsible for the high variability of n, k, and AOD values and of the fine mode particle contribution. Instantaneous net (solar+infrared) DREs that are negative as a consequence of the cooling effect by aerosol particles, span the – (32–10) W m−2 and the – (44–20) W m−2 range at the ToA and surface, respectively. The instantaneous net DRE by anthropogenic particles that is negative, varies within −(13–8) W m−2 and −(17–11) W m−2 at the ToA and surface, respectively. It represents from 41 up to 89% and from 36 up to 67% of the net DRE by all particles at the ToA and surface, respectively. A linear relationship to calculate the DRE by natural particles in the solar and infrared spectral range is provided.
Technical Note: Detection and identification of radical species formed from α-pinene/ozone reaction using DMPO spin trap
Authors: Pavlovic J. , Hopke P. K.
Published: April 2010

Abstract. The reactions of ozone with monoterpenes proceed via the formation of multiple oxygen- and carbon-centered free radical species. These radical species are highly reactive and thus, have generally not been measureable. A method for their detection and characterization is needed to preserve these radicals for a sufficiently long time to permit analyzes to be performed. Radical-addition reactions, also called spin trapping techniques, allow the detection of short-lived radicals. This approach has been applied to products from the α-pinene/ozone reaction. Secondary organic aerosol (SOA) from a reaction chamber was collected on quartz fiber filters and extracted with a solution of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (spin trap) followed by analysis with ion-trap tandem mass spectrometry (MSn) using electrospray ionization (ESI) in the positive scan mode. The DMPO adducts with radical species appear as positive ions [DMPO−R+H]+, [DMPO−OR+H]+ and [DMPO−O−OR+H]+ in full MS spectra of the samples. Tandem mass spectrometry (MS2) was performed to identify the radical species. The DMPO adducts with the C-centered radical species [DMPO−R+H]+ are characterized by m/z 114 [DMPO+H]+ in the MS2 spectra and with peaks that represent the loss of [DMPO+H]+. The DMPO adducts with O-centered radical species (RO· and ROO·) are identified by m/z 130 [DMPO−OH+H]+ and m/z 146 [DMPO−O−OH+H]+, respectively, and with peaks that correspond to the loss of those adducts. DMPO was also able to capture OH radicals from the particle phase, and the product ion fragmentation confirmed DMPO/OH structure providing evidence for particle-bound OH radicals.
Interpreting the cloud cover – aerosol optical depth relationship found in satellite data using a general circulation model
Authors: Quaas J. , Stevens B. , Stier P. , Lohmann U.
Published: April 2010

Abstract. Statistical analysis of satellite data shows a positive correlation between aerosol optical depth (AOD) and total cloud cover (TCC). Here we compare the slope of the linear regression between the logarithm of TCC and the logarithm of AOD, or the strength of the relationship, as derived from three satellite data sets to the ones simulated by a global aerosol-climate model. We analyze model results from two different simulations with and without a parameterization of aerosol indirect effects, and using dry compared to humidified AOD. We find that none of the hypotheses discussed in the literature is able to uniquely explain the positive relationship. The most important contribution in the model is from the swelling of aerosol in the vicinity of clouds, where relative humidity is high. The model also shows contribution of the aerosol cloud lifetime effect to the positive relationship, which, however, is of lesser importance.
High-ozone layers in the middle and upper troposphere above Central Europe: strong import from the stratosphere over the Pacific Ocean
Authors: Trickl T. , Bärtsch-Ritter N. , Eisele H. , Furger M. , Mücke R. , Stohl A.
Published: April 2010

Abstract. Very dry high-ozone layers have been repeatedly observed with the ozone lidar in Garmisch-Partenkirchen (Germany) starting one or two days after the onset of high-pressure periods during the warm season. These episodes have been analysed by trajectory calculations and extended simulations with the FLEXPART particle dispersion model. Mixed contributions from the stratosphere over the Pacific Ocean and the boundary layers of East Asia and North America were found. The stratospheric influence is mostly dominating and caused by a rather shallow transfer from the stratosphere into these rapid upper- and mid-tropospheric air streams. The considerable vertical extent of these layers and peak ozone mixing ratios between 80 and 150 ppb suggest an important mechanism for stratosphere-to-troposphere transport.
Light-absorbing secondary organic material formed by glyoxal in aqueous aerosol mimics
Authors: Shapiro E. L. , Szprengiel J. , Sareen N. , Jen C. N. , Giordano M. R. , McNeill V. F.
Published: April 2010

Abstract. Light-absorbing and high-molecular-weight secondary organic products were observed to result from the reaction of glyoxal in mildly acidic (pH=4) aqueous inorganic salt solutions mimicking aqueous tropospheric aerosol particles. High-molecular-weight (500–600 amu) products were observed when ammonium sulfate ((NH4)2SO4) or sodium chloride (NaCl) was present in the aqueous phase. The products formed in the (NH4)2SO4 solutions absorb light at UV and visible wavelengths. Substantial absorption at 300–400 nm develops within two hours, and absorption between 400–600 nm develops within days. Pendant drop tensiometry measurements show that the products are not surface-active. The experimental results along with ab initio predictions of the UV/Vis absorption of potential products suggest that an aldol condensation mechanism is active in the glyoxal-(NH4)2SO4system, resulting in the formation of pi-conjugated products. If similar products are formed in atmospheric aerosol particles, they could change the optical properties of the seed aerosol over its lifetime.
Spatial and temporal UV irradiance and aerosol variability within the area of an OMI satellite pixel
Authors: Kazadzis S. , Bais A. , Balis D. , Kouremeti N. , Zempila M. , Arola A. , Giannakaki E. , Kazantzidis A. , Amiridis V.
Published: April 2010

Abstract. Results of an experimental campaign that took place in the greater Thessaloniki area were used to investigate temporal and spatial UV variability within an OMI satellite pixel. UV irradiance and aerosol optical depth measurements were performed for a one month period at three sites characterized as urban, rural and industrial, depending on their location and possible local aerosol sources. OMI showed a general UV irradiance overestimation compared to all three sites and for all atmospheric conditions. During the campaign the standard deviation calculated from the three sites for UV irradiance at 324 nm was of the order of 26%. For cloudless days with high spatial aerosol variability, UV differences reached ±20% within the OMI pixel. For cloudy days UV differences up to 100% were found at the three sites, a percentage that depends on the ground-based data integration time used for the comparison. Here we tried to focus on the limitations when trying to interpret results of UV irradiance comparisons between OMI satellite and ground based stations, taking into account the UV variability within an OMI pixel, due to such small scale spatial cloud and aerosol inhomogeneities.
n-Aldehydes (C6–C10) in snow samples collected at the high alpine research station Jungfraujoch during CLACE 5
Authors: Sieg K. , Starokozhev E. , Fries E. , Sala S. , Püttmann W.
Published: April 2010

Abstract. Samples of freshly fallen snow were collected at the high alpine research station Jungfraujoch, Switzerland, during the Cloud and Aerosol Characterization Experiments (CLACE) 5 in February and March 2006. Sampling was carried out on the Sphinx platform. Headspace-solid-phase-dynamic extraction (HS-SPDE) combined with gas chromatography/mass spectrometry (GC/MS) was used to quantify C6–C10 n-aldehydes in the snow samples. The most abundant n-aldehyde was n-hexanal (median concentration 1.324 μg L−1) followed by n-nonanal, n-decanal, n-octanal and n-heptanal (median concentrations 1.239, 0.863, 0.460, and 0.304 μg L−1, respectively). A wide range of concentrations was found among individual snow samples, even for samples taken at the same time. Higher median concentrations of all n-aldehydes were observed when air masses reached Jungfraujoch from the north-northwest in comparison to air masses arriving from the southeast-southwest. Results suggest that the n-aldehydes detected most likely are of direct and indirect biogenic origin, and that they entered the snow through the particle phase.
A QBO-signal in mesospheric water vapor measurements at ALOMAR (69.29° N, 16.03° E) and in model calculations by LIMA over a solar cycle
Authors: Sonnemann G. R. , Hartogh P. , Li S. , Grygalashvyly M. , Berger U.
Published: April 2010

Abstract. Microwave water vapor measurements between 40 and 80 km over a solar cycle (1996–2006) were carried out in high latitudes at ALOMAR (69.29° N, 16.03° E), Norway. Three larger interuptions in the winters of 1996/97 and 2005/06, and from spring 2001 to spring 2002, a few smaller interruptions of monitoring occurred during this period. The observed year-to-year variability is not directly related to the solar activity. The analysis of the observations by the Fast Fourier Transform (FFT) method revealed peaks close to two years, particularly in the upper monitoring domain. Model calculations by means of the real date model LIMA, Leibniz-Institute Middle Atmosphere model, reflect essential patterns of the water vapor variation. The FFT-analysis of the calculated water vapor mixing ratios also showed peaks of around two years. The real period of the QBO during the monitoring period ranged quite close to two years within the time interval considered, with the exception of the years 2001/02 when the period was essentially longer. Although the QBO is a phenomenon occurring in the zonal wind of the tropical stratosphere, we suppose an influence of the QBO on the water vapor distribution of the mesosphere of high latitudes controlled by transport processes. A possible link could be given by the planetary wave activity triggered by the QBO.
Satellite orbit determination using satellite gravity gradiometry observations in GOCE mission perspective
Authors: Bobojć A. , Drożyner A.
Published: April 2010

Abstract. Between the years 2004 and 2005 the launch of the first gradiometric satellite is planned. This satellite will be an important element of the Gravity Field and Steady – State Ocean Circulation Explorer Mission (GOCE). This mission is one of the reasons for performing the simulation research of the Satellite Gravity Gradiometry. Our work contains the theory description and simulation results of the satellite orbit determination using the gravity tensor observations. In the process of the satellite orbit determination the initial dynamic state vector corrections are obtained. These corrections are estimated by means of the gravity gradiometry measurements. The performed simulations confirm the possibility of satellite orbit determination by means of the gravity tensor observations.Key words. satellite geodesy, satellite gradiometry, satellite orbits
From the time-wise to space-wise GOCE observables
Authors: Reguzzoni M.
Published: April 2010

Abstract. The observables of the GOCE three-axis gradiometer are taken in time, along the orbit and, in the timewise proposal, filtered to stay in the measurement bandwidth, i.e. in the frequency interval between 0.005 and 0.1Hz. As a consequence, the resulting “observable" is a convolution of the original data stream with a time-wise weighting kernel. In other words, we cannot assume that the observations are point-wise evaluations of any function and so, in a spacewise approach, any averaging or interpolating operation to obtain gridded spatial data has little sense. The problem is therefore to model correctly the observational functionals, including the correlation along the orbit. This can be done by exploiting theWiener filter theory, using the prior knowledge of a geopotential model and the power spectral density (PSD) of the measurement error. A numerical simulation from the EGM96 model (degrees between 50 and 300) is performed, showing that the along track Wiener filter produces Trr spatialized observables with an error standard deviation of the order of 5 mE. A covariance function of the estimation error is also provided by the Wiener filter theory. The use of these filtered observables in a space-wise approach allows for the reconstruction of the gravity field in terms of spherical harmonics up to degree 200.Key words. Satellite gradiometry, space-wise approach, measurement bandwidth, Wiener filter
Globally covering a-priori regional gravity covariance models
Authors: Arabelos D. , Tscherning C. C.
Published: April 2010

Abstract. Gravity anomaly data generated using Wenzel’s GPM98A model complete to degree 1800, from which OSU91A has been subtracted, have been used to estimate covariance functions for a set of globally covering equal-area blocks of size 22.5° × 22.5° at Equator, having a 2.5° overlap. For each block an analytic covariance function model was determined. The models are based on 4 parameters: the depth to the Bjerhammar sphere (determines correlation), the free-air gravity anomaly variance, a scale factor of the OSU91A error degree-variances and a maximal summation index, N, of the error degree-variances. The depth of Bjerhammar-sphere varies from -134km to nearly zero, N varies from 360 to 40, the scale factor from 0.03 to 38.0 and the gravity variance from 1081 to 24(10µms-2)2. The parameters are interpreted in terms of the quality of the data used to construct OSU91A and GPM98A and general conditions such as the occurrence of mountain chains. The variation of the parameters show that it is necessary to use regional covariance models in order to obtain a realistic signal to noise ratio in global applications.Key words. GOCE mission, Covariance function, Spacewise approach`
Static and temporal gravity field recovery using grace potential difference observables
Authors: Han S.-C. , Jekeli C. , Shum C. K.
Published: April 2010

Abstract. The gravity field dedicated satellite missions like CHAMP, GRACE, and GOCE are supposed to map the Earth’s global gravity field with unprecedented accuracy and resolution. New models of Earth’s static and time-variable gravity field will be available every month as one of the science products from GRACE. Here we present an alternative method to estimate the gravity field efficiently using the in situ satellite-to-satellite observations at the altitude and show results on static as well as temporal gravity field recovery. Considering the energy relation between the kinetic energy of the satellite and the gravitational potential, the disturbing potential difference observations can be computed from the orbital parameter vectors in the inertial frame, using the high-low GPS-LEO GPS tracking data, the low-low satelliteto- satellite GRACE measurements, and data from 3-axis accelerometers (Jekeli, 1999). The disturbing potential observation also includes other potentials due to tides, atmosphere, other modeled signals (e.g. N-body) and the geophysical fluid signals (hydrological and oceanic mass variations), which should be recoverable from GRACE mission with a monthly resolution. The simulation results confirm that monthly geoid accuracy is expected to be a few cm with the 160 km resolution (up to degree and order 120) once other corrections are made accurately. The time-variable geoids (ocean and ground water mass) might be recovered with a noise-to-signal ratio of 0.1 with the resolution of 800 km every month assuming no temporal aliasing.Key words. GRACE mission, Energy integral, Geopotential, Satellite-to-satellite tracking, Temporal gravity field
Error assessment of GOCE SGG data using along track interpolation
Authors: Bouman J. , Koop R.
Published: April 2010

Abstract. GOCE will be the first satellite gravity mission measuring gravity gradients in space using a dedicated instrument called a gradiometer. High resolution gravity field recovery will be possible from these gradients. Such a recovery requires a proper description of the gravity gradient errors, where the a priori error model is for example based on end-to-end instrument simulations. One way to test the error model against real data, i.e. to see if the a priori model really describes the actual error, is to compare along track interpolated gradients with the measured gradients. The difference between the interpolated and measured gravity gradients is caused by, among others, the interpolation error and the measurement errors. The idea is that if the interpolation error is small enough, then the differences should be predicted reasonably well by the error model. This paper discusses a simulation study where the gravity gradient errors are generated with an end-to-end instrument simulator. The measurement error will be compared with the interpolation error and we will assess the latter as a function of the sampling interval.
Comparison of numerical solution strategies for gravity field recovery from GOCE SGG observations implemented on a parallel platform
Authors: Pail R. , Plank G.
Published: April 2010

Abstract. The recovery of a full set of gravity field parameters from satellite gravity gradiometry (SGG) is a huge numerical and computational task. In practice, parallel computing has to be applied to estimate the more than 90 000 harmonic coefficients parameterizing the Earth’s gravity field up to a maximum spherical harmonic degree of 300. Three independent solution strategies, i.e. two iterative methods (preconditioned conjugate gradient method, semi-analytic approach) and a strict solver (Distributed Non-approximative Adjustment), which are operational on a parallel platform (‘Graz Beowulf Cluster’), are assessed and compared both theoretically and on the basis of a realistic-as-possible numerical simulation, regarding the accuracy of the results, as well as the computational effort. Special concern is given to the correct treatment of the coloured noise characteristics of the gradiometer. The numerical simulations show that there are no significant discrepancies among the solutions of the three methods. The newly proposed Distributed Nonapproximative Adjustment approach, which is the only one of the three methods that solves the inverse problem in a strict sense, also turns out to be a feasible method for practical applications.Key words. Spherical harmonics – satellite gravity gradiometry – GOCE – parallel computing – Beowulf cluster
Integrated sensor analysis for GRACE – development and validation
Authors: Frommknecht B. , Oberndorfer H. , Flechtner F. , Schmidt R.
Published: April 2010

Abstract. The focus of this article is on the accelerometer on board the two GRACE (Gravity Recovery and Climate Experiment) satellites. In a first analysis the accelerometer system is studied. The behavior of the test mass and its capacitive feedback system is simulated in the time and the frequency domain for one degree of freedom. Only linear accelerations are considered so far. The second part of the analysis is about the practical implementation of the simulation model: Non-gravitational forces were derived from the GFZ (GeoForschungsZentrum) EPOS (Earth Parameter and Orbit System) software. In a closed loop the accelerometer measurements derived from these data in connection with simulated tracking data have been used for orbit recovery including the estimation of biases and scale factors for the accelerometer data. Details and results of this procedure are presented.Key words. GRACE – sensor analysis – accelerometer
The potential of ground gravity measurements to validate GRACE data
Authors: Crossley D. , Hinderer J. , Llubes M. , Florsch N.
Published: April 2010

Abstract. New satellite missions are returning high precision, time-varying, satellite measurements of the Earth’s gravity field. The GRACE mission is now in its calibration/- validation phase and first results of the gravity field solutions are imminent. We consider here the possibility of external validation using data from the superconducting gravimeters in the European sub-array of the Global Geodynamics Project (GGP) as ‘ground truth’ for comparison with GRACE. This is a pilot study in which we use 14 months of 1-hour data from the beginning of GGP (1 July 1997) to 30 August 1998, when the Potsdam instrument was relocated to South Africa. There are 7 stations clustered in west central Europe, and one station, Metsahovi in Finland. We remove local tides, polar motion, local and global air pressure, and instrument drift and then decimate to 6-hour samples. We see large variations in the time series of 5–10µgal between even some neighboring stations, but there are also common features that correlate well over the 427-day period. The 8 stations are used to interpolate a minimum curvature (gridded) surface that extends over the geographical region. This surface shows time and spatial coherency at the level of 2– 4µgal over the first half of the data and 1–2µgal over the latter half. The mean value of the surface clearly shows a rise in European gravity of about 3µgal over the first 150 days and a fairly constant value for the rest of the data. The accuracy of this mean is estimated at 1µgal, which compares favorably with GRACE predictions for wavelengths of 500 km or less. Preliminary studies of hydrology loading over Western Europe shows the difficulty of correlating the local hydrology, which can be highly variable, with large-scale gravity variations.Key words. GRACE, satellite gravity, superconducting gravimeter, GGP, ground truth
Noise variance estimation and optimal weight determination for GOCE gravity recovery­
Authors: Kusche J.
Published: April 2010

Abstract. In the course of level 2 data processing for the GOCE (Gravity Field and Steady–State Ocean Circulation Explorer) satellite mission different streams of level 1b data will be merged in a single solution providing the Earth’s gravity field, but also state-vector parameters and other quantities. A proper weighting of orbit tracking data, gravity gradiometry data and certain a priori information, usually considered as ‘solution constraints’, can be expected as crucial for the solution quality. But the a priori stochastic models, based on pre–mission assessment of the expected instrument behaviour, may be over–optimistic or even too pessimistic since they refer to an unprecedented mission with scientific payload never tested in space. One way to derive an optimal weighting scheme on a statistically sound basis while simultaneously validating the stochastic noise levels of the data is by including variance component estimation as a part of the level 1b to level 2 data analysis process. The idea is that by applying Monte-Carlo techniques this method can be extended to a large-scale problem like GOCE data analysis, using software modules that already exist or are currently under development. The proposed method has been tested using simulated GOCE orbit trajectories as well as gravity gradiometry data corrupted by colored random noise.Key words. GOCE, gravity field modelling, combination solutions, weight estimation, variance component estimation
On the joint inversion of SGG and SST data from the GOCE mission
Authors: Ditmar P. , Visser P. , Klees R.
Published: April 2010

Abstract. The computation of spherical harmonic coefficients of the Earth’s gravity field from satellite-to-satellite tracking (SST) data and satellite gravity gradiometry (SGG) data is considered. As long as the functional model related to SST data contains nuisance parameters (e.g. unknown initial state vectors), assembling of the corresponding normal matrix must be supplied with the back-substitution operation, so that the nuisance parameters are excluded from consideration. The traditional back-substitution algorithm, however, may result in large round-off errors. Hence an alternative approach, back-substitution at the level of the design matrix, is implemented. Both a stand-alone inversion of either type of data and a joint inversion of both types are considered. The conclusion drawn is that the joint inversion results in a much better model of the Earth’s gravity field than a standalone inversion. Furthermore, two numerical techniques for solving the joint system of normal equations are compared: (i) the Cholesky method based on an explicit computation of the normal matrix, and (ii) the pre-conditioned conjugate gradient method (PCCG), for which an explicit computation of the entire normal matrix is not needed. The comparison shows that the PCCG method is much faster than the Cholesky method.Key words. Earth’s gravity field, GOCE, satellite-tosatellite tracking, satellite gravity gradiometry, backsubstitution
A first analysis of the mean motion of CHAMP
Authors: Deleflie F. , Exertier P. , Berio P. , Metris G. , Laurain O. , Lemoine J.-M. , Loyer S.
Published: April 2010

Abstract. The present study consists in studying the mean orbital motion of the CHAMP satellite, through a single long arc on a period of time of 200 days in 2001. We actually investigate the sensibility of its mean motion to its accelerometric data, as measures of the surface forces, over that period. In order to accurately determine the mean motion of CHAMP, we use “observed" mean orbital elements computed, by filtering, from 1-day GPS orbits. On the other hand, we use a semi-analytical model to compute the arc. It consists in numerically integrating the effects of the mean potentials (due to the Earth and the Moon and Sun), and the effects of mean surfaces forces acting on the satellite. These later are, in case of CHAMP, provided by an averaging of the Gauss system of equations. Results of the fit of the long arc give a relative sensibility of about 10-3, although our gravitational mean model is not well suited to describe very low altitude orbits. This technique, which is purely dynamical, enables us to control the decreasing of the trajectory altitude, as a possibility to validate accelerometric data on a long term basis.Key words. Mean orbital motion, accelerometric data
Spatial correlation of radar and gauge precipitation data in high temporal resolution
Authors: Brommundt J. , Bárdossy A.
Published: April 2010

Abstract. A multi-sites precipitation time series generator for engineering designs is currently being developed. The objective is to generate several time series' simultaneously with correct inter-station relationships. Therefore, a model to estimate correlation between stations for arbitrary points in a project area is needed, using rain gauge data as well as radar data. Two methods are applied to compare the spatial behaviour of precipitation in both the rain gauge data and the radar data. The first approach is to calculate precipitation intensities from radar reflectivity and use it as gauge data. The results show that the spatial structure in both data sets is similar, but cross correlation varies too much to use radar derived spatial correlation to describe gauge inter-station relationship. Thus, a second approach was tested to account for the differences in the spatial correlation associated to the distribution. Using the indicator time series, cross correlations for different quantiles were calculated from both the rain gauge and radar data. This approach shows that cross correlation varies depending on the chosen quantile. In the lower quantiles, the correlation is very similar in rain gauge and radar data, hence a transfer is possible. This insight is useful to derive cross correlations of rain gauges from radar images. Correlation data for rain gauges thus obtained contains all the information about heterogeneity and anisotropy of the spatial structure of rainfall, which is in the radar data.
Precipitation rate spectra as dependent on dynamic forcing: application to probabilistic forecasting
Authors: Chakina N. P. , Skriptunova E. N. , Ivanova A. R.
Published: April 2010

Abstract. Occurrence frequencies, OF, of 12-h precipitation amounts, P, at stations in the former European USSR are displayed as dependent on dynamic forcing of vertical motions. The dynamic forcing is described by a "frontal parameter", F (calculated in the points of objective analysis grid), which depends on the surface pressure field curvature and on the baroclinicity in the lower half of the troposphere. The precipitation rate spectra for 4 seasons, calculated from a large sample of data (7 years, about 650 000 values of P for one season), show a monotonous OF growth of all ranges of P>1 mm/12 h with F increase. The growth is especially significant for heavy precipitation. As a result, F is shown to be an informative predictor of P spectrum or of probability of any given range of P. As a next step, two-dimensional spectra of precipitation occurrence frequency, as a function of F and LNB, that is, OF (F, LNB), are calculated, LNB being the level of neutral buoyancy at the gridpoint, an estimate of grid-scale convective instability. On this basis, an approach to probabilistic forecasting is suggested.