A. Brattli

Universitetet i Tromsø, Tromsø, Troms, Norway

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Publications (15)26.7 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The first sounding rocket of the European ECOMA-project (ECOMA, Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere) was launched on 8 September 2006. Measurements with a new particle detector described in the companion paper by Rapp and Strelnikova [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.06.002] clearly showed meteor smoke particle (MSP) signatures in both data channels. The data channels measure particles directly impacting on the detector electrode and photoelectrons from the particles actively created using ionization by the UV-photons of a xenon-flashlamp. Measured photoelectron currents resemble model expectations of the shape of the MSP layer almost perfectly, whereas derived number densities in the altitude range 60–90 km are larger than model results by about a factor of 5. Given the large uncertainties inherent to both model and the analysis of our measurements (e.g., the composition of the particles is not known and must be assumed) we consider this a satisfactory agreement and proof that MSPs do extend throughout the entire mesosphere as predicted by models. The measurements of direct particle impacts revealed a confined layer of negative charge between 80 and 90 km. This limited altitude range, however, is quantitatively shown to be the consequence of the aerodynamics of the rocket flight and does not have any geophysical origin. Measured charge signatures are consistent with expectations of particle charging given our own measurements of the background ionization. Unfortunately, however, a contamination of these measurements from triboelectric charging cannot be excluded at this stage.
    Journal of Atmospheric and Solar-Terrestrial Physics 01/2009; · 1.42 Impact Factor
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    ABSTRACT: The ECOMA series of rocket payloads use a set of aerosol particle, plasma, and optical instruments to study the properties of aerosol particles and their interaction with the ambient plasma environment in the polar mesopause region. In August 2007 the ECOMA-3 payload was launched into a region with Polar Mesosphere Summer Echoes (PMSE) and noctilucent clouds (NLC). An electron depletion was detected in a broad region between 83 and 88 km, coincident with enhanced density of negatively charged aerosol particles. We also find evidence for positive ion depletion in the same region. Charge neutrality requires that a population of positively charged particles smaller than 2 nm and with a density of at least 2×108 m−3 must also have been present in the layer, undetected by the instruments. A numerical model for the charging of aerosol particles and their interaction with the ambient plasma is used to analyse the results, showing that high aerosol particle densities are required in order to explain the observed ion density depletion. The model also shows that a very high photoionisation rate is required for the particles smaller than 2 nm to become positively charged, indicating that these may have a lower work function than pure water ice.
    Annales Geophysicae 01/2009; · 1.52 Impact Factor
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    ABSTRACT: In August 2007 the joint European-American ECOMA/MASS (Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere/Dust MASS Analyzer) sounding rocket and ground-based campaign took place at the Andøya Rocket Range (ARR) (69° N). This campaign was devoted to the investigation of mesospheric aerosol particles. During this campaign, three instrumented sounding rockets were launched under the PMSE and NLC conditions. All rockets were carrying instruments to characterize mesospheric aerosol particles and their environment. The ECOMA rocket was launched during the first salvo shortly (30 min) after the MASS payload. At that time, the EISCAT (69° N, 19° E) VHF and ALWIN radars observed a double layered PMSE. Also an NLC layer was detected by lidar and photometers onboard each rocket. The main instrument of the ECOMA payload is the "ECOMA particle detector". This instrument comprises a classical Faraday cup with a xenon-flash lamp for the active photoionization/photodetachment of mesospheric smoke particles (MSPs) and the subsequent detection of corresponding photoelectrons. Comparing direct Faraday cup measurements and photocurrents we are able to derive particle properties like number densities and particle radii. We present the results of these measurements that show the presence of aerosol particles inside the NLC and PMSE layer, but not below or above these layers. These results are consistent with model predictions, which account for global transport of meteoric smoke. This implies that ice nucleation in the polar summer needs to be reconsidered.
    01/2008;
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    ABSTRACT: The ECOMA-project is dedicated to the study of the `Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere'. The project is led by the Leibniz Institute of Atmospheric Physics, Germany, and the Norwegian Defence Research Establishment, Norway, and utilizes rocket borne in situ measurements as well as ground based observations with radars and lidars to characterize meteor smoke particles and their atmospheric and ionospheric environment. The prime instrument of the ECOMA payload is a new particle detector which combines a classical Faraday cup-design with a xenon-flashlamp for the active photoionization of mesospheric aerosol particles and the subsequent detection of corresponding photoelectrons. Other instruments are a swept Langmuir probe, two fixed biased probes and a wave propagation experiment to measure plasma parameters. In addition, an ionization gauge and two simple Pirani gauges are used for neutral density measurements, and a particle sampler is applied for the in flight collection of meteor smoke particles and their return to the ground. Two campaigns have been conducted to date: the first in September 2006 comprising two rocket launches and one in August 2007 where one sounding rocket was launched under conditions of noctilucent clouds and polar mesosphere summer echoes. A third campaign is currently planned for early July 2008. In the present paper we will present results from these campaigns. We will show that the ECOMA particle detector allows to detect meteor smoke particles throughout the mesosphere and that our measurements in autumn 2006 basically confirm expectations regarding the abundance of meteor smoke particles in the mesosphere from microphysical models. We will further compare measurements from autumn and summer conditions, where the most striking finding is that significantly less particles were observed in summer 2007 as compared to autumn 2006. The latter result will be critically discussed with respect to its implications for ice particle nucleation at the polar summer mesopause.
    01/2008;
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    ABSTRACT: In the course of the European ECOMA project (ECOMA = Existence and Charge State of Meteoric Smoke Particles in the Middle Atmosphere) two sounding rocket campaigns were conducted in September 2006 and August 2007 from the North Norwegian Andoya Rocket Range (69N). The latter campaign was closely coordinated with the US-American MASS campaign which also focused on mesospheric aerosol particles and their plasma environment. A core instrument of the ECOMA payload is a Faraday-Cup-based particle detector which is combined with a Xenon-flashlight for the active photo-ionization of mesospheric aerosol particles. The first launch in September 2006 revealed evidence for meteor smoke particles in the entire altitude range from 60 - 110 km, as indicated by detected photo-emission signatures. In August 2007, however, when the ECOMA payload was launched into a weak event of polar mesosphere summer echoes and noctilucent clouds, particle signatures were confined to the altitude region of mesospheric ice layers identified by the ALWIN MST radar and the ALOMAR RMR lidar, i.e., roughly between 82 - 88 km altitude. These results will be discussed in the scope of our current understanding of the seasonal distribution of meteor smoke particles, corresponding implications for the nucleation of mesospheric ice clouds, and the physical mechanisms giving rise to polar mesosphere summer echoes.
    AGU Fall Meeting Abstracts. 12/2007;
  • Ove Havnes, Torsten Aslaksen, Alvin Brattli
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    ABSTRACT: We discuss the few existing in situ rocket observations of dust and plasma during the radar backscatter phenomenon Polar Mesospheric Summer Echoes (PMSE). We show from one recent observation, where the rocket flew directly through the radar beam during observation of a PMSE, that there is a very good correspondence between the charge density of dust layer and the PMSE. A surprising observation is that only a small amount of charged dust can be associated with a considerable PMSE signal strength. By estimating the relationship between radar backscatter and dust charge density for other rocket measurements we have found a total relationship between radar backscatter strength and dust charge density. This shows a rapid increase of radar backscatter strength at low NdZd, a more or less constant level for a considerable range in NdZd and a decrease to low values for large values of NdZd where most of the negative charge will be on the dust.
    Physica Scripta 10/2006; 2001(T89):133. · 1.03 Impact Factor
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    ABSTRACT: In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N) into strong VHF radar echoes called 'Polar Mesosphere Winter Echoes' (PMWE). The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE occur much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively). Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km): viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the radar backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar proton events. We have studied the sensitivity of the radar echo strength on various parameters, most important electron number density and turbulence intensity. Our observational and theoretical considerations do not provide any evidence that charged aerosol particles are needed to explain PMWE, in contrast to the summer echoes which owe their existence to charged ice particles.
    Atmospheric Chemistry and Physics 01/2006; · 4.88 Impact Factor
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    ABSTRACT: On 18 January 2005, two small, instrumented rockets were launched from Andøya Rocket Range (69.3° N, 16° E) during conditions with Polar Mesosphere Winter Echoes (PMWE). Each of the rockets was equipped with a Positive Ion Probe (PIP) and a Faraday rotation/differential absorption experiment, and was launched as part of a salvo of meteorological rockets measuring temperature and wind using falling spheres and chaff. Layers of PMWE were detected between 55 and 77 km by the 53.5 MHz ALWIN radar. The rockets were launched during a solar proton event, and measured extremely high ion densities, of order 10<sup>10</sup> m<sup>−3</sup>, in the region where PMWE were observed. The density measurements were analyzed with the wavelet transform technique. At large length scales, ~10<sup>3</sup> m, the power spectral density can be fitted with a k <sup>−3</sup> wave number dependence, consistent with saturated gravity waves. Outside the PMWE layers the k <sup>−3</sup> spectrum extends down to approximately 10<sup>2</sup> m where the fluctuations are quickly damped and disappear into the instrumental noise. Inside the PMWE layers the spectrum at smaller length scales is well fitted with a k <sup>−5/3</sup> dependence over two decades of scales. The PMWE are therefore clearly indicative of turbulence, and the data are consistent with the turbulent dissipation of breaking gravity waves. We estimate a lower limit for the turbulent energy dissipation rate of about 10<sup>−2</sup> W/kg in the upper (72 km) layer.
    Atmospheric Chemistry and Physics 01/2006; · 4.88 Impact Factor
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    ABSTRACT: On Janurary 18, 2005, two instrumented miniaturised rocket payloads, each with a Positive Ion Probe (PIP) and a Faraday rotation/differential absorption experiment, were launched from Andøya Rocket Range (69°N). The instrumented payloads were launched into conditions with Polar Mesosphere Winter Echoes (PMWE) as part of a salvo of meteorological rockets measuring temperature and wind using falling spheres and chaff. Layers of PMWE were detected in the altitude range 55-77 km by the 53.5 MHz ALWIN radar. Fluctuations in the ion density, as measured in situ by the instrumented payloads, show that there was turbulence inside the PMWE layers, but not above/below and between. Data from the PIPs are analysed and related to the geophysical conditions, as observed with the ALWIN radar and meteorological rockets.
    07/2005; 590:109-114.
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    ABSTRACT: We demonstrate how the observation of dynamic Mach cones in dusty plasma experiments allows one to follow the evolution of the dust acoustic wave velocity as charges on dust particles change, or as their mass changes. In experiments in which only the charge is changing due to, e.g., the application of a thin coating on UV-illuminated dust particles, the coating rate may be inferred through the analysis of the Mach cone pattern. In other experiments where the dust sizes are changing, also leading to some change in charge, the growth rate can be followed.
    Physical Review E 05/2002; 65(4 Pt 2A):045403. · 2.31 Impact Factor
  • A. Brattli, O. Havnes, F. Melandsø
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    ABSTRACT: The flow of charged dust around an electrically charged boulder moving through an environment thought to be typical of planatery rings is studied. As the boulder moves through the ring dust it will excite a V-shaped Mach cone pattern of a form and complexity which varies significantly with boulder size, relative velocity between the boulder and the dust, and with dust plasma conditions. Parameters relevant to the Saturnian ring system are used to compute examples which demonstrate the change in Mach cone patterns with the relevant parameters. Shortcomings of the model are discussed and ways to improve the calculations of Mach cone patterns are pointed out. © 2002 American Institute of Physics.
    Physics of Plasmas 02/2002; 9(3):958-963. · 2.38 Impact Factor
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    ABSTRACT: We have discussed in more detail the possibilities of extracting information on the dusty plasma conditions in planetary rings and in laboratories by observing the V-shaped Mach cone pattern around a charged body moving through or close to a layer of dusty plasma. Based on the existing theories for dust acoustic waves and accelerations of dust orbits at the front of the body we find that, if the normal plasma parameters are known, we should be able to extract information on the dust average sizes and size distribution, the dust number density and material density. With more refined theories for the dust acoustic wave and dust bow shocks, including a dust size distribution it should be possible to find additional and more accurate information on the total plasma conditions.
    Planetary and Space Science 01/2001; 49(2):223-229. · 2.11 Impact Factor
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    ABSTRACT: We report the results from simultaneous radar and rocket measurements of a PMSE event where for the first time the rocket measured dust and plasma within the radar beam. We find very clear correspondence between the measured dust charge density profile and the radar backscater profile as a function of height. We find that even very small amounts of charged dust is associated with an appreciable PMSE radar backscatter. Although we find it likely that the dust layer corresponds fully with the PMSE layer there is a possibility that the upper part of the PMSE layer may be influenced by ion clusters which are too small to be detected by the rocket dust probe.
    Geophysical Research Letters 01/2001; 28(8):1419-1422. · 3.98 Impact Factor
  • A.  BRATTLI , O.  HAVNES , F.  MELANDSØ 
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    ABSTRACT: Using a kinetic model for low-frequency dust acoustic waves (DAW) in a dusty plasma, we have examined the effects of a dust-size distribution on their propagation and damping. Both Landau damping and damping due to dust-charge variation are included. We consider Gaussian and power-law dust-size distributions. In accordance with earlier results of Melandsø et al., we find that the dust Landau damping dominates at short wavelengths. At wavelengths longer than the Debye length λD0, the dust-charge variation is generally dominant. It is always dominant for the power-law size distributions that we have studied. We also find that if the upper and lower size limits of the dust are chosen so that the average dust size remains constant, regardless of the power-law exponent γ, the wave properties are practically identical to those of a monosize distribution of the average dust size. For a Gaussian dust-size distribution, Landau damping may be the dominant damping mechanism if the dust plasma is tenuous (P[double less-than sign]1) and the width of the distribution is large.
    Journal of Plasma Physics 11/1997; 58(04):691 - 704. · 0.76 Impact Factor
  • A. Brattli, O. Havnes
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    ABSTRACT: The thermophoretic force on dust particles is caused by a temperature gradient in the background gas. This force can be important in experiments or production processes and in other environments where dust occurs. We discuss the local cooling of the neutral gas by levitated dust clouds and how this affects the temperature gradient and the equilibrium dust density profile. Dust is heated through neutral gas particle impacts while it loses energy by either reemitting impacting particles or by thermal radiation at the particle temperature. The dust particle temperature can be considerably lower than that of the ambient gas and can therefore lead to a local cooling of the gas. Changes in the temperature gradient and the thermophoretic force can be large enough to affect the equilibrium density profile of levitated dust. We find that the equilibrium profile with the thermophoretic force calculated from the temperature profile without dust cooling is closer to the electrode but with much the same shape as the profile calculated without the thermophoretic force. The profile where local cooling is included in the thermophoretic force is more compressed compared to the profile without local cooling and it often has a pronounced peak closest to the electrode. Since radiation cooling of a dust particle is proportional to the fourth power of its temperature, the cooling effect is largest at comparatively high gas (and dust) temperatures. We show examples of levitated dust layer profiles with and without the dust cooling effect. © 1996 American Vacuum Society
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/1996; · 1.43 Impact Factor