bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meteor velocity determination with plasma physics
Authors: Dyrud L. P. , Denney K. , Close S. , Oppenheim M. , Ray L. , Chau J. 
Published: April 2010

Abstract. Understanding the global meteor flux at Earth requires the measurement of meteor velocities. While several radar methods exist for measuring meteor velocity, they may be biased by plasma reflection mechanisms. This paper presents a new method for deriving meteoroid velocity from the altitudinal extent of non-specular trails. This method employs our recent discoveries on meteor trail plasma instability. Dyrud et al. (2002) demonstrated that meteor trails are unstable over a limited altitude range, and that the precise altitudes of instability are dependent on the meteoroid velocity that generated the trail. Since meteor trail instability results in field aligned irregularities (FAI) that allow for radar reflection, non-specular trail observations may be used to derive velocity. We use ALTAIR radar data of combined head echos and non-specular trails to test non-specular trail derived velocity against head echo velocities. Meteor velocities derived from non-specular trail altitudinal width match to within 5 km/s when compared with head echo range rates from the same meteor. We apply this technique to Piura radar observations of hundreds of non-specular trails to produce histograms of occurrence of meteor velocity based solely on this non-specular trails width criterion. The results from this study show that the most probable velocity of meteors seen by the Piura radar is near 50 km/s which is comparable with modern head echo studies.
Quantification of the impact in mid-latitudes of chemical ozone depletion in the 1999/2000 Arctic polar vortex prior to the vortex breakup
Authors: Koch G. , Wernli H. , Buss S. , Staehelin J. , Peter T. , Liniger M. A. , Meilinger S. 
Published: April 2010

Abstract. For the winter 1999/2000 transport of air masses out of the vortex to mid-latitudes and ozone destruction inside and outside the northern polar vortex is studied to quantify the impact of earlier winter (before March) polar ozone destruction on mid-latitude ozone. Nearly 112 000 trajectories are started on 1 December 1999 on 6 different potential temperature levels between 500–600 K and for a subset of these trajectories photo-chemical box-model calculations are performed. We linked a decline of −0.9% of mid-latitude ozone in this layer occurring in January and February 2000 to ozone destruction inside the vortex and successive transport of these air masses to mid-latitudes. Further, the impact of denitrification, PSC-occurrence and anthropogenic chlorine loading on future stratospheric ozone is determined by applying various scenarios. Lower stratospheric temperatures and denitrification were found to play the most important role in the future evolution of polar ozone depletion.
A quantitative analysis of grid-related systematic errors in oxidising capacity and ozone production rates in chemistry transport models
Authors: Esler J. G. , Roelofs G. J. , Köhler M. O. , O’Connor F. M. 
Published: April 2010

Abstract. Limited resolution in chemistry transport models (CTMs) is necessarily associated with systematic errors in the calculated chemistry, due to the artificial mixing of species on the scale of the model grid (grid-averaging). Here, the errors in calculated hydroxyl radical (OH) concentrations and ozone production rates P(O3) are investigated quantitatively using both direct observations and model results. Photochemical steady-state models of radical chemistry are exploited in each case to examine the effect on both OH and P(O3) of averaging relatively long-lived precursor species, such as O3, NOx, CO, H2O, etc., over different spatial scales. Changes in modelled P(O3) are estimated, independently of other model errors, by calculating the systematic effect of spatial averaging on the ozone production efficiency εN, defined as the ratio of ozone molecules produced per NOx molecule destroyed. Firstly, an investigation of in-flight measurements suggests that, at least in the northern midlatitude upper-troposphere/lower stratosphere, averaging precursor species on the scale of a T42 grid (2.75°×2.75°) leads to a 15–20% increase in OH concentrations and a 5–10% increase in εN. Secondly, results from CTM model experiments are compared at different horizontal resolutions. Low resolution experiments are found to have significantly higher [OH] and P(O3) compared with high resolution experiments. The degree to which these differences may be explained by the systematic error associated with the model grid size is investigated by degrading the high resolution data onto a low resolution grid and then recalculating εN and [OH]. The change in calculated εN is found to be significant and can account for much of the difference in P(O3) between the high and low resolution experiments. The calculated change in [OH] is less than the difference in [OH] found between the experiments, although the shortfall is likely to be due to the indirect effect of the change in modelled NOx, which is not accounted for in the calculation. It is argued that systematic errors caused by limited resolution need to be considered when evaluating the relative impacts of different pollutant sources on tropospheric ozone.
Photolysis frequencies in water droplets: Mie calculations and geometrical optics limit
Authors: Mayer B. , Madronich S. 
Published: April 2010

Abstract. Photolysis of water-soluble components inside cloud droplets by ultraviolet/visible radiation may play an important role in atmospheric chemistry. Two earlier studies have suggested that the the actinic flux and hence the photolysis frequency within spherical droplets is enhanced relative to that in the surrounding air, but have given different values for this enhancement. Here, we reconcile these discrepancies by noting slight errors in both studies that, when corrected, lead to consistent results. Madronich (1987) examined the geometric (large droplet) limit and concluded that refraction leads to an enhancement factor, averaged over all incident directions, of 1.56. However, the physically relevant quantity is the enhancement of the average actinic flux (rather than the average enhancement factor) which we show here to be 1.26 in the geometric limit. Ruggaber et al. (1997) used Mie theory to derive energy density enhancements slightly larger than 2 for typical droplet sizes, and applied these directly to the calculation of photolysis rates. However, the physically relevant quantity is the actinic flux (rather than the energy density) which is obtained by dividing the energy density by the index of refraction of water, 1.33. Thus, the Mie-predicted enhancement for typical cloud droplet sizes is in the range 1.5, only coincidentally in agreement with the value originally given by Madronich. We also investigated the influence of resonances in the actinic flux enhancement. These narrow spikes which are resolved only by very high resolution calculations are orders of magnitude higher than the intermediate values but contribute only little to the actinic flux enhancement when averaged over droplet size distributions.
Polar mesosphere summer echoes (PMSE): review of observations and current understanding
Authors: Rapp M. , Lübken F.-J. 
Published: April 2010

Abstract. Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is solely determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e. 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.
Using photochemical models for the validation of NO2 satellite measurements at different solar zenith angles
Authors: Bracher A. , Sinnhuber M. , Rozanov A. , Burrows J. P. 
Published: April 2010

Abstract. SCIAMACHY (Scanning Imaging Spectrometer for Atmospheric Chartography) aboard the recently launched Environmental Satellite (ENVISAT) of ESA is measuring solar radiance upwelling from the atmosphere and the extraterrestrial irradiance. Appropriate inversion of the ultraviolet and visible radiance measurements, observed from the atmospheric limb, yields profiles of nitrogen dioxide, NO2, in the stratosphere. In order to assess their accuracy, the resulting NO2 profiles have been compared with those retrieved from the space borne occultation instruments Halogen Occultation Experiment (HALOE, data version v19) and Stratospheric Aerosol and Gas Experiment II (SAGE II, data version 6.20). As the HALOE and SAGE II measurements are performed during local sunrise or sunset and because NO2 has a significant diurnal variability, the NO2 profiles derived from HALOE and SAGE II have been transformed to those predicted for the solar zenith angles of the SCIAMACHY measurement by using a 1-D photochemical model. The model used to facilitate the comparison of the NO2 profiles from the different satellite sensors is described and an error assessment provided. Comparisons between NO2 profiles from SCIAMACHY and those from HALOE NO2 but transformed to the SCIAMACHY solar zenith angle, for collocations from July to October 2002, show good agreement (within +/−15%) between the altitude range from 22 to 33 km. The results from the comparison of all collocated NO2 profiles from SCIAMACHY and those from SAGE II transformed to the SCIAMACHY solar zenith angle show a systematic negative bias of 10 to 35% between 20 km to 38 km with a small standard deviation between 5 to 14%. These results agree with those of Newchurch and Ayoub (2004), implying that above 20 km NO2 profiles from SAGE II sunset are probably somewhat high.
Flux measurements of biogenic VOCs during ECHO 2003
Authors: Spirig C. , Neftel A. , Ammann C. , Dommen J. , Grabmer W. , Thielmann A. , Schaub A. , Beauchamp J. , Wisthaler A. , Hansel A. 
Published: April 2010

Abstract. Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany using the eddy covariance (EC) technique. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. As a consequence, a considerable fraction of the measurements did not qualify for flux calculations by EC and had to be discarded. The validated results show light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average emissions (normalised to 30°C and 1000 µmoles m−2 s−1 PAR) of 1.5 and 0.39 µg m−2 s−1, respectively. Emissions of methanol reached on average 0.087 µg m−2 s−1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. The observed fluxes are consistent with upscalings from leaf-level emission measurements of representative tree species in this forest and, in the case of MVK and MACR, can plausibly be explained by chemical production through oxidation of isoprene within the canopy. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.
Transfer of organic Br and Cl from the Biosphere to the Atmosphere during the Cretaceous/Tertiary Impact: Implications for the stratospheric Ozone Layer
Authors: Kourtidis K. 
Published: April 2010

Abstract. Following the Cretaceous/Tertiary (K/T) meteoritic impact some 65 Myr ago, large portions of aboveground terrestrial biomass were burned. As a result, large amounts of various trace gases were injected to the atmosphere, inducing a wide range of effects on climate and ecosystems. Here, it is commented on the previously unaccounted emission to the atmosphere of methyl bromide (CH3Br) and methyl chloride (CH3Cl) from extensive biomass burning that followed the impact. Based on reported biomass burning emission rates of the above organohalogens relative to CO2, it is estimated that their emissions from global fires resulted in tropospheric mixing ratios of around 20–65.8 ppbv organic Cl and 110–390 pptv organic Br. The above calculated mixing ratios of active chlorine and bromine are more than an order of magnitude their present, anthropogenically perturbed level and, although the ocean ultimately might absorb them, we argue here that they could still remain in the stratosphere for many years, substantially affecting the ozone layer. This would have lead to very serious increases in short wavelength UV radiation reaching the lowermost atmosphere.
On the growth of nucleation mode particles: source rates of condensable vapor in polluted and clean environments
Authors: Kulmala M. , Petäjä T. , Mönkkönen P. , Koponen I. K. , Dal Maso M. , Aalto P. P. , Lehtinen K. E. J. , Kerminen V.-M. 
Published: April 2010

Abstract. The growth properties of nucleation mode particles were investigated. The variation of source rates of condensable vapors in different locations and environmental conditions was analyzed. The measurements were performed in background stations in Antarctica and in Finnish Lapland and Boreal Forest stations (SMEAR I and SMEAR II) as well as in polluted urban sites in Athens, Marseille and New Delhi. Taking advantage of only the measured aerosol particles spectral evolution as a function of time the formation and growth properties of nucleation mode aerosols have been evaluated. The diameter growth-rate and condensation sink have been obtained from the measured size distribution dynamics. Using this growth rate and condensation sink, the concentration of condensable vapours and their source rate have been estimated. The growth rates and condensation sinks were between 0.3–20 nm h−1 and 10−4–0.07 s−1, respectively. The corresponding source rate of condensable vapors varied more than 4 orders of magnitude from 103 to over 107 cm−1 s−1. The highest condensation sink and source rate values were observed in New Delhi and the smallest values in Antarctica.
Ozone loss derived from balloon-borne tracer measurements and the SLIMCAT CTM
Authors: Robinson A. D. , Millard G. A. , Danis F. , Guirlet M. , Harris N. R. P. , Lee A. M. , McIntyre J. D. , Pyle J. A. , Arvelius J. , Dagnesjo S. , Kirkwood S. , Nilsson H. , Toohey D. W. , Deshler T. , Goutail F. , Pommereau J.-P. , Elkins J. W. , Moore F. , Ray E. , Schmidt U. , Engel A. , Mueller M. 
Published: April 2010

Abstract. Balloon-borne measurements of CFC-11 (on flights of the DIRAC in situ gas chromatograph and the DESCARTES grab sampler), ClO and O3 were made during the 1999/2000 winter as part of the SOLVE-THESEO 2000 campaign. Here we present the CFC-11 data from nine flights and compare them first with data from other instruments which flew during the campaign and then with the vertical distributions calculated by the SLIMCAT 3-D CTM. We calculate ozone loss inside the Arctic vortex between late January and early March using the relation between CFC-11 and O3 measured on the flights, the peak ozone loss (1200 ppbv) occurs in the 440–470 K region in early March in reasonable agreement with other published empirical estimates. There is also a good agreement between ozone losses derived from three independent balloon tracer data sets used here. The magnitude and vertical distribution of the loss derived from the measurements is in good agreement with the loss calculated from SLIMCAT over Kiruna for the same days.
Nitric acid trihydrate (NAT) formation at low NAT supersaturations
Authors: Voigt C. , Schlager H. , Luo B. P. , Dörnbrack A. , Roiger A. , Stock P. , Curtius J. , Vössing H. , Borrmann S. , Davies S. , Konopka P. , Schiller C. , Shur G. , Peter T. 
Published: April 2010

Abstract. A polar stratospheric cloud (PSC) was observed on 6 February 2003 in the Arctic stratosphere by in-situ measurements onboard the high-altitude research aircraft Geophysica. Low number densities (~10−4 cm−3) of nitric acid (HNO3) containing particles – probably NAT – with diameters up to 6 µm were measured at altitudes between 18 and 20 km. These particles have the potential to grow further and to remove HNO3 from the stratosphere, thereby enhancing polar ozone loss. Interestingly, the NAT particles formed in less than a day at temperatures T>TNAT−3.5 K, just slightly below the NAT equilibrium temperature TNAT. This unique measurement of PSC formation at extremely low NAT saturation ratios (SNAT≤11) constrains current NAT nucleation theories. In particular, NAT formation on ice can for certain be excluded. Conversely, we suggest that meteoritic particles may be favorable candidates for triggering nucleation of NAT at the observed low number densities.
The observation of nitric acid-containing particles in the tropical lower stratosphere
Authors: Popp P. J. , Marcy T. P. , Jensen E. J. , Kärcher B. , Fahey D. W. , Gao R. S. , Thompson T. L. , Rosenlof K. H. , Richard E. C. , Herman R. L. , Weinstock E. M. , Smith J. B. , May R. D. , Vömel H. , Wilson J. C. , Heymsfield A. J. , Mahoney M. J. , Thompson A. M. 
Published: April 2010

Abstract. Airborne in situ measurements over the eastern Pacific Ocean in January 2004 have revealed a new category of nitric acid (HNO3)-containing particles in the tropical lower stratosphere. These particles are most likely composed of nitric acid trihydrate (NAT). They were intermittently observed in a narrow layer above the tropopause (18±0.1 km) and over a broad geographic extent (>1100 km). In contrast to the background liquid sulfate aerosol, these particles are solid, much larger (1.7–4.7 µm vs. 0.1 µm in diameter), and significantly less abundant (<10-4 cm-3 vs. 10 cm-3). Microphysical trajectory models suggest that the NAT particles grow over a 6–14 day period in supersaturated air that remains close to the tropical tropopause and might be a common feature in the tropics. The small number density of these particles implies a highly selective or slow nucleation process. Understanding the formation of solid NAT particles in the tropics could improve our understanding of stratospheric nucleation processes and, therefore, dehydration and denitrification.
Deep stratosphere-to-troposphere transport (STT) over SE Europe: a complex case study captured by enhanced &lt;sup&gt;7&lt;/sup&gt;Be concentrations at the surface of a low topography region
Authors: Gerasopoulos E. , Zanis P. , Papastefanou C. , Zerefos C. S. , Ioannidou A. , Wernli H. 
Published: April 2010

Abstract. In this study we present a complex case study of a Stratosphere-to-Troposphere Transport (STT) event down to the surface of a low topography region in Northern Greece, during the second fortnight of March 2000. During this event our surface station at Livadi (23°15 E/40°32 N, 850 m a.s.l.), was influenced by very different synoptic systems developing over Eastern Europe, N. America and the N. Atlantic, the last one evolving to a cut-off low over France/Spain. This is the first study, to our knowledge, that presents a down to the surface STT event in the eastern Mediterranean. The intrusion is primarily captured with the use of the cosmogenic radionuclide 7Be, which increased to 9.07 mBq m-3 and 9.37 mBq m-3 on 30 and 31 March 2000, respectively. A 7Be concentration of around 8 mBq m-3 recorded during parallel measurements at Thessaloniki (20 m a.s.l.) gives strong evidence that air of stratospheric origins has even gone down to sea level. A rapid increase of 10–15 ppb is also observed in the surface ozone concentration on 31 March 2000. The relative increase of both tracers is consistent with a volume fraction of stratospheric air at the surface of about 5%, but the substantial increase in 7Be flags more clearly the event. Trajectory analyses, in conjunction with the evolution of the synoptic situation described by potential vorticity maps, are used for the exact identification of the different intrusions and the attribution of each intruding parcel of stratospheric air to a certain filament of high PV. Finally, the persistency of the stratospheric layers in the troposphere is another interesting point of this case study. The vast majority of the trajectories spent 7–10 days in the troposphere before reaching the surface at Livadi station.