| 1. |
- Enell, Carl-Fredrik, et al.
(författare)
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The Hotel Payload 2 campaign : Overview of NO, O and electron density measurements in the upper mesosphere and lower thermosphere
- 2011
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 73:14-15, s. 2228-2236
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Tidskriftsartikel (refereegranskat)abstract
- The ALOMAR eARI Hotel Payload 2 (HotPay 2) rocket campaign took place at Andoya Rocket Range, Norway, in January 2008. The rocket was launched on January 31, 2008 at 19:14 UT, when auroral activity appeared after a long geomagnetically quiet period. In this paper we present an overview of the HotPay 2 measurements of upper mesospheric and lower thermospheric (UMLT) electron, atomic oxygen (O) and nitric oxide (NO) densities. [O] and [NO] were retrieved from a set of three photometers, Night-Time Emissions from the Mesosphere and Ionosphere (NEMI). Faraday rotation receivers on the rocket and the EISCAT UHF incoherent scatter radar provided simultaneous electron density profiles, whereas the ALOMAR Na lidar and meteor radar measured the temperature profile and wind. The aurora was also observed with ground-based imagers. The retrieved oxygen number density profile has a maximum at 89 km, some 10 km lower than expected from earlier measurements and modelled profiles based on climatological averages (such as the MSIS model), and the retrieved NO densities are also lower than the expected. Satellite measurements indicate that subsidence over the winter pole controlled the densities. Quantitative chemistry model results based on climatological average atmospheric density and temperature profiles were, therefore, not in good agreement with the measured profiles. The Hotel Payload 2 measurements thus confirm the importance of downward transport from the thermosphere into the winter polar vortex.
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| 2. |
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| 3. |
- Espy, P. J., et al.
(författare)
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The role of the QBO in the inter-hemispheric coupling of summer mesospheric temperatures
- 2011
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:2, s. 495-502
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Tidskriftsartikel (refereegranskat)abstract
- Inter-hemispheric coupling between the polar summer mesosphere and planetary-wave activity in the extra-tropical winter stratosphere has recently been inferred using Polar Mesospheric Cloud (PMC) properties as a proxy for mesospheric temperature (Karlsson et al., 2007). Here we confirm these results using a ten-year time series of July mesospheric temperatures near 60 degrees N derived from the hydroxyl (OH) nightglow. In addition, we show that the time-lagged correlation between these summer mesospheric temperatures and the ECMWF winter stratospheric temperatures displays a strong Quasi-Biennial Oscillation (QBO). The sign and phase of the correlation is consistent with the QBO modulation of the extra-tropical stratospheric dynamics in the Southern Hemisphere via the Holton-Tan mechanism (Holton and Tan, 1980). This lends strength to the identification of synoptic and planetary waves as the driver of the inter-hemispheric coupling, and results in a strong QBO modulation of the polar summer mesospheric temperatures.
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| 4. |
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| 5. |
- Gattinger, R. L., et al.
(författare)
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H Balmer lines in terrestrial aurora : Historical record and new observations by OSIRIS on Odin
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. A09306-
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Tidskriftsartikel (refereegranskat)abstract
- The H Balmer emissions were first identified in terrestrial aurora by Vegard (1939). The earliest photographic spectral observations are reviewed. In the subsequent decade, the intensity ratios for H alpha, H beta, and H gamma were measured, and the well-known line broadening and blue shift were established. Recently, the H alpha, H gamma, H delta, and H epsilon features have been measured by OSIRIS on Odin. The Balmer components are resolved from other auroral features using sets of synthetic spectra. The measured intensity ratios are in good agreement with an extensive set of published model calculations. The presented observations are in the polar region averaged over limb tangent altitudes from 100 to 105 km, approximately perpendicular to the terrestrial magnetic field lines, for this geometry showing Doppler broadening without obvious Doppler shifts. The OSIRIS-measured full-width at half-height of the Ha feature is 2.2 nm corresponding to an H atom velocity of 500 km s(-1) and energy approximately 1.3 keV.
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| 6. |
- Gattinger, R. L., et al.
(författare)
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Vibrational populations of near-ultraviolet O-2 band systems in the night airglow
- 2012
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Ingår i: Canadian journal of physics (Print). - : Canadian Science Publishing. - 0008-4204 .- 1208-6045. ; 90:8, s. 741-751
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Tidskriftsartikel (refereegranskat)abstract
- Observations of the limb night airglow spectrum from 250 to 475 nm, emitted from the upper mesosphere and lower thermosphere, are compared with model spectra. Data from the Arizona GLO-1 imaging spectrograph and the OSIRIS spectrograph are combined to form the observed mean airglow spectrum; a tabulated version of this spectrum is included. Model spectra of the individual O-2 Herzberg I, II, and III, Chamberlain, and Slanger band systems are combined to simulate the observed mean spectrum. Franck-Condon relative band intensities are used to form a series of basis functions for the upper vibrational levels in each band system. These functions are fitted to the observed airglow spectrum with a least-squares method, the relative vibrational populations are derived and discussed.
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| 7. |
- Gumbel, Jörg, et al.
(författare)
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Retrieval of global mesospheric sodium densities from the Odin satellite
- 2007
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 34:L04813
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Tidskriftsartikel (refereegranskat)abstract
- Satellite observations of the Na D dayglow at 589 nm provide a global database for the climatology of the mesospheric sodium layer. More than five years of Na D limb observations are available from the Optical Spectrograph and InfraRed Imager System onboard the Odin satellite. We describe a robust retrieval method that provides individual sodium density profiles with a typical accuracy of 20% and altitude resolution of 2 km. Retrieved column abundances and density profiles are validated against sodium resonance lidar measurements at mid- latitudes. Examples of the seasonal and latitudinal variation of the sodium layer illustrate Odin's potential for climatological studies of mesospheric metals.
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| 8. |
- Gumbel, Jörg, et al.
(författare)
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The MATS satellite mission - gravity wave studies by Mesospheric Airglow/Aerosol Tomography and Spectroscopy
- 2020
-
Ingår i: Atmospheric Chemistry And Physics. - : COPERNICUS GESELLSCHAFT MBH. - 1680-7316 .- 1680-7324. ; 20:1, s. 431-455
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Tidskriftsartikel (refereegranskat)abstract
- Global three-dimensional data are a key to understanding gravity waves in the mesosphere and lower thermosphere. MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a new Swedish satellite mission that addresses this need. It applies space-borne limb imaging in combination with tomographic and spectroscopic analysis to obtain gravity wave data on relevant spatial scales. Primary measurement targets are O-2 atmospheric band dayglow and nightglow in the near infrared, and sunlight scattered from noctilucent clouds in the ultraviolet. While tomography provides horizontally and vertically resolved data, spectroscopy allows analysis in terms of mesospheric temperature, composition, and cloud properties. Based on these dynamical tracers, MATS will produce a climatology on wave spectra during a 2-year mission. Major scientific objectives include a characterization of gravity waves and their interaction with larger-scale waves and mean flow in the mesosphere and lower thermosphere, as well as their relationship to dynamical conditions in the lower and upper atmosphere. MATS is currently being prepared to be ready for a launch in 2020. This paper provides an overview of scientific goals, measurement concepts, instruments, and analysis ideas.
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| 9. |
- Hedin, Jonas, 1976-, et al.
(författare)
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Observations of NO in the upper mesosphere and lower thermosphere during ECOMA 2010
- 2012
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:11, s. 1611-1621
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Tidskriftsartikel (refereegranskat)abstract
- In December 2010 the last campaign of the German-Norwegian sounding rocket project ECOMA (Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere) was conducted from Andøya Rocket Range in northern Norway (69° N, 16° E) in connection with the Geminid meteor shower. The main instrument on board the rocket payloads was the ECOMA detector for studying meteoric smoke particles (MSPs) by active photoionization and subsequent detection of the produced charges (particles and photoelectrons). In addition to photoionizing MSPs, the energy of the emitted photons from the ECOMA flash-lamp is high enough to also photoionize nitric oxide (NO). Thus, around the peak of the NO layer, at and above the main MSP layer, photoelectrons produced by the photoionization of NO are expected to contribute to, or even dominate above the main MSP-layer, the total measured photoelectron current. Among the other instruments on board was a set of two photometers to study the O2(b1Σg+−X3Σg-) Atmospheric band and NO2 continuum nightglow emissions. In the absence of auroral emissions, these two nightglow features can be used together to infer NO number densities. This will provide a way to quantify the contribution of NO photoelectrons to the photoelectron current measured by the ECOMA instrument and, above the MSP layer, a simultaneous measurement of NO with two different and independent techniques. This work is still on-going due to the uncertainties, especially in the effort to quantitatively infer NO densities from the ECOMA photoelectron current, and the lack of simultaneous measurements of temperature and density for the photometric study. In this paper we describe these two techniques to infer NO densities and discuss the uncertainties. The peak NO number density inferred from the two photometers on ascent was 3.9 × 108 cm−3 at an altitude of about 99 km, while the concentration inferred from the ECOMA photoelectron measurement at this altitude was a factor of 5 smaller.
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| 10. |
- Hedin, Jonas, et al.
(författare)
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Optical studies of noctilucent clouds in the extreme ultraviolet
- 2008
-
Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26:5, s. 1109-1119
-
Tidskriftsartikel (refereegranskat)abstract
- In order to better understand noctilucent clouds (NLC) and their sensitivity to the variable environment of the polar mesosphere, more needs to be learned about the actual cloud particle population. Optical measurements are today the only means of obtaining information about the size of mesospheric ice particles. In order to efficiently access particle sizes, scattering experiments need to be performed in the Mie scattering regime, thus requiring wavelengths of the order of the particle size. Previous studies of NLC have been performed at wavelengths down to 355 nm from the ground and down to about 200 nm from rockets and satellites. However, from these measurements it is not possible to access the smaller particles in the mesospheric ice population. This current lack of knowledge is a major limitation when studying important questions about the nucleation and growth processes governing NLC and related particle phenomena in the mesosphere. We show that NLC measurements in the extreme ultraviolet, in particular using solar Lyman-α radiation at 121.57 nm, are an efficient way to further promote our understanding of NLC particle size distributions. This applies both to global measurements from satellites and to detailed in situ studies from sounding rockets. Here, we present examples from recent rocket-borne studies that demonstrate how ambiguities in the size retrieval at longer wavelengths can be removed by invoking Lyman-α. We discuss basic requirements and instrument concepts for future rocket-borne NLC missions. In order for Lyman-α radiation to reach NLC altitudes, high solar elevation and, hence, daytime conditions are needed. Considering the effects of Lyman-α on NLC in general, we argue that the traditional focus of rocket-borne NLC missions on twilight conditions has limited our ability to study the full complexity of the summer mesopause environment.
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| 11. |
- Hedin, Jonas, et al.
(författare)
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The MAGIC meteoric smoke particle sampler
- 2014
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 118, s. 127-144
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Tidskriftsartikel (refereegranskat)abstract
- Between a few tons to several hundred tons of meteoric material enters the Earth's atmosphere each day, and most of this material is ablated and vaporized in the 70-120 km altitude region. The subsequent chemical conversion, re-condensation and coagulation of this evaporated material are thought to form nanometre sized meteoric smoke particles (MSPs). These smoke particles are then subject to further coagulation, sedimentation and global transport by the mesospheric circulation. MSPs have been proposed as a key player in the formation and evolution of ice particle layers around the mesopause region, i.e. noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). MSPs have also been implicated in mesospheric heterogeneous chemistry to influence the mesospheric odd oxygen/odd hydrogen (O-x/HOx) chemistry, to play an important role in the mesospheric charge balance, and to be a significant component of stratospheric aerosol and enhance the depletion of O-3. Despite their apparent importance, little is known about the properties of MSPs and none of the hypotheses can be verified without direct evidence of the existence, altitude and size distribution, shape and elemental composition. The aim of the MAGIC project (Mesospheric Aerosol - Genesis, Interaction and Composition) was to develop an instrument and analysis techniques to sample for the first time MSPs in the mesosphere and return them to the ground for detailed analysis in the laboratory. MAGIC meteoric smoke particle samplers have been flown on several sounding rocket payloads between 2005 and 2011. Several of these flights concerned non-summer mesosphere conditions when pure MSP populations can be expected. Other flights concerned high latitude summer conditions when MSPs are expected to be contained in ice particles in the upper mesosphere. In this paper we present the MAGIC project and describe the MAGIC MSP sampler, the measurement procedure and laboratory analysis. We also present the attempts to retrieve MSPs from these flights, the challenges inherent to the sampling of nanometre sized particles and the subsequent analysis of the sampled material, and thoughts for the future. Despite substantial experimental efforts, the MAGIC project has so far failed to provide conclusive results. While particles with elemental composition similar to what is to be expected from MSPs have been found, the analysis has been compromised by challenges with different types of contamination and uncertainties in the sticking efficiency of the particles on the sampling surfaces.
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| 12. |
- Hedin, Jonas, et al.
(författare)
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Use of O2 airglow for calibrating direct atomic oxygen measurements from sounding rockets
- 2009
-
Ingår i: Atmospheric Measurement Techniques. - 1867-1381. ; 2, s. 801-812
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Tidskriftsartikel (refereegranskat)abstract
- Accurate knowledge about the distribution of atomic oxygen is crucial for many studies of the mesosphere and lower thermosphere. Direct measurements of atomic oxygen by the resonance fluorescence technique at 130 nm have been made from many sounding rocket payloads in the past. This measurement technique yields atomic oxygen profiles with good sensitivity and altitude resolution. However, accuracy is a problem as calibration and aerodynamics make the quantitative analysis challenging. Most often, accuracies better than a factor 2 are not to be expected from direct atomic oxygen measurements. As an example, we present results from the NLTE (Non Local Thermodynamic Equilibrium) sounding rocket campaign at Esrange, Sweden, in 1998, with simultaneous O2 airglow and O resonance fluorescence measurements. O number densities are found to be consistent with the nightglow analysis, but only within the uncertainty limits of the resonance fluorescence technique. Based on these results, we here describe how better atomic oxygen number densities can be obtained by calibrating direct techniques with complementary airglow photometer measurements and detailed aerodynamic analysis. Night-time direct O measurements can be complemented by photometric detection of the O2 (b1∑g+−X3∑g-) Atmospheric Band at 762 nm, while during daytime the O2 (a1Δg−X3∑g-) Infrared Atmospheric Band at 1.27 μm can be used. The combination of a photometer and a rather simple resonance fluorescence probe can provide atomic oxygen profiles with both good accuracy and good height resolution.
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| 13. |
- Hultgren, Kristoffer, et al.
(författare)
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First simultaneous retrievals of horizontal and vertical structures of Polar Mesospheric Clouds from Odin/OSIRIS tomography
- 2013
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 104, s. 213-223
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Tidskriftsartikel (refereegranskat)abstract
- Limb-scanning satellites can provide global information about the vertical structure of Polar Mesospheric Clouds. However, information about horizontal structures usually remains limited. In eighteen days during the northern hemisphere summers of 2010 and 2011, the Odin satellite was operated in a special mesospheric mode with short limb scans limited to the altitude range of Polar Mesospheric Clouds. For Odin's Optical Spectrograph and InfraRed Imager System (OSIRIS) this provides multiple views through a given cloud volume, which forms a basis for tomographic analyses of the vertical/horizontal cloud structures. Here we present an algorithm for a tomographic analysis of mesospheric clouds based on maximum probability techniques. We also present the first simultaneously retrieved vertical and horizontal Polar Mesospheric Cloud structures. The findings show that the tomographic algorithm is able to locate detailed structures such as tilts, stratifications, or holes that cannot be analyzed by other limb, nadir, or ground-based measurements. We find a mean peak altitude of the clouds to be 83.6 km. We identify horizontal patches down to sizes of 300 km, which corresponds to a horizontal resolution that is limited by the available number of limb scans.
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| 14. |
- Karlsson, Bodil, 1976-
(författare)
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Noctilucent clouds in a coupled atmosphere
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Noctilucent clouds (NLC) at altitudes around 80 km are the highest clouds in our atmosphere. They have been a subject of research ever since their discovery in the late 19th century. This thesis takes an important step towards using NLC as a tool for studying dynamic coupling processes in the atmosphere on a global scale.Six years of NLC observations by the Odin satellite have provided information on global distribution, seasonal variation and hemispheric differences in cloud properties. Spectroscopic measurements by the OSIRIS instrument onboard Odin are used to retrieve cloud particle sizes. The ideas and challenges behind these retrievals are discussed in detail. A study of the latitudinal dependence of NLC shows a general increase of cloud occurrence, brightness, and particle sizes towards the pole. Microphysical modelling suggests that the particles grow larger near the pole because of a combined effect of colder temperature, availability of water vapour, and meridional transport times.To investigate the relationship between the cold summer mesopause region and the dynamics in the stratosphere, NLC properties derived from Odin have been used as a proxy for the state of the summer mesosphere. These data have been co-analysed with ECMWF temperatures as a proxy for the residual circulation in the stratosphere. The results of this study reveal a surprising coupling between the winter stratosphere and the summer mesopause. This interhemispheric link is suggested to be the principal cause for both year-to-year variability and hemispheric differences in summer mesosphere conditions. Further studies of the underlying dynamic coupling mechanisms were carried out using a comprehensive middle atmospheric model. As a conclusion from this study, the interannual variability in the summer polar mesopause region can be traced back to the planetary wave flux entering the winter stratosphere from the troposphere.
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| 15. |
- Lossow, Stefan, et al.
(författare)
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Middle atmospheric water vapour and dynamics in the vicinity of the polar vortex during the Hygrosonde-2 campaign
- 2009
-
Ingår i: Atmospheric Chemistry And Physics. - 1680-7316 .- 1680-7324. ; 9, s. 4407-4417
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Tidskriftsartikel (refereegranskat)abstract
- The Hygrosonde-2 campaign took place on 16 December 2001 at Esrange/Sweden (68° N, 21° E) with the aim to investigate the small scale distribution of water vapour in the middle atmosphere in the vicinity of the Arctic polar vortex. In situ balloon and rocket-borne measurements of water vapour were performed by means of OH fluorescence hygrometry. The combined measurements yielded a high resolution water vapour profile up to an altitude of 75 km. Using the characteristic of water vapour being a dynamical tracer it was possible to directly relate the water vapour data to the location of the polar vortex edge, which separates air masses of different character inside and outside the polar vortex. The measurements probed extra-vortex air in the altitude range between 45 km and 60 km and vortex air elsewhere. Transitions between vortex and extra-vortex usually coincided with wind shears caused by gravity waves which advect air masses with different water vapour volume mixing ratios. From the combination of the results from the Hygrosonde-2 campaign and the first flight of the optical hygrometer in 1994 (Hygrosonde-1) a clear picture of the characteristic water vapour distribution inside and outside the polar vortex can be drawn. Systematic differences in the water vapour concentration between the inside and outside of the polar vortex can be observed all the way up into the mesosphere. It is also evident that in situ measurements with high spatial resolution are needed to fully account for the small-scale exchange processes in the polar winter middle atmosphere.
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| 16. |
- Lossow, Stefan, 1977-
(författare)
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Observations of water vapour in the middle atmosphere
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water vapour is the most important greenhouse gas and plays a fundamental role in the climate system and for the chemistry of the Earth's atmosphere. This thesis presents observations of water vapour in the middle atmosphere with a particular focus on the mesosphere. The majority of these observations presented in this thesis have been performed by the Swedish satellite Odin, providing global observations since 2001. Further observations come from the Hygrosonde-2 campaign in December 2001 based on balloon and rocket-borne measurements. A general overview of Odin's water vapour measurements in the middle atmosphere is given. The optimisation of the mesospheric water vapour retrieval is presented in detail.The analysis of the observations has focused mainly on different dynamical aspects utilising the characteristic of water vapour as a dynamical tracer in the middle atmosphere. One application is the mesospheric part of the semi-annual oscillation (SAO). The observations reveal that this oscillation is the dominant pattern of variability between 30°S and 10°N in the mesosphere up to an altitude of 80 km. Above 90 km the SAO is dominating at all latitudes in the tropics and subtropics. It is shown that the SAO exhibits a distinct phase change between 75 km and 80 km in the tropical region.This thesis also presents the first satellite observations of water vapour in the altitude range between 90 km and 110 km, extending the observational database up into the lower thermosphere. In the polar regions water vapour exhibits the annual maximum during winter time above 95 km, mainly caused by upwelling during this season. This behaviour is different from that observed in the subjacent part of the mesosphere where the annual maximum occurs during summer time.The Hygrosonde-2 campaign provided a high resolution measurement of water vapour in the vicinity of the polar vortex edge. This edge prevents horizontal transport causing different water vapour characteristics inside and outside the polar vortex. The observations show that this separating behaviour extends high up into the mesosphere. Small scale transitions in the Hygrosonde-2 profile between conditions inside and outside the vortex coincided with wind shears caused by gravity waves.
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| 17. |
- Megner, Linda, et al.
(författare)
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First Observed Temporal Development of a Noctilucent Cloud Ice Void
- 2018
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 45:18, s. 10003-10010
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Tidskriftsartikel (refereegranskat)abstract
- Noctilucent clouds are thin ice clouds that appear around the summer polar mesopause. Recently, the Cloud Imaging and Particle Size instrument on the AIM satellite discovered nearly circular ice free regions within the clouds-denoted as ice voids. The origin of these ice voids is not known. Their existence has so far only been reported by Cloud Imaging and Particle Size, which only can give very limited information of the time scales involved. On 4 July 2010, such an ice void was registered by our ground-based camera taking images with 30-s time interval. We thus here present the first full temporal development of an ice void. Surprisingly, the void did not drift with the prevailing wind as cloud features around it, but instead remained notably stationary for its entire existence of approximately 1 hr. This indicates that that the origin is of stationary character, rather than a rapid change of the local atmosphere. Plain Language Summary Noctilucent clouds are ice clouds that appear high in the atmosphere, about 80 km above the summer pole. By observing them we have learned a lot about the remote and inaccessible region where they form. Recently, a satellite borne instrument discovered nearly circular ice-free regions within the clouds, denoted as ice voids. The origin of these voids is a mystery-we do not know what causes the clouds to disappear in large circular areas. So far these voids have only been observed from satellites, which only can take pictures of the clouds when they pass above once every 1.5 hr-longer than most ice voids exist. This means that until now we completely lack observations of the development and disappearance of the voids. Here we therefore present the first full temporal development of a void, as observed by our ground-based camera taking images every 30 s. Surprisingly, the void did not drift with the wind as cloud features around it, but it remained notably stationary for approximately 1 hr. These observations give important clues to help us solve the mystery of the origin of these voids-they suggest a steady local heating of the atmosphere as the cause.
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| 18. |
- Megner, Linda, et al.
(författare)
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Large mesospheric ice particles at exceptionally high altitudes
- 2009
-
Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 27, s. 943-951
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Tidskriftsartikel (refereegranskat)abstract
- We here report on the characteristics of exceptionally high Noctilucent clouds (NLC) that were detected with rocket photometers during the ECOMA/MASS campaign at Andøya, Norway 2007. The results from three separate flights are shown and discussed in connection to lidar measurements. Both the lidar measurements and the large difference between various rocket passages through the NLC show that the cloud layer was inhomogeneous on large scales. Two passages showed a particularly high, bright and vertically extended cloud, reaching to approximately 88 km. Long time series of lidar measurements show that NLC this high are very rare, only one NLC measurement out of thousand reaches above 87 km. The NLC is found to consist of three distinct layers. All three were bright enough to allow for particle size retrieval by phase function analysis, even though the lowest layer proved too horizontally inhomogeneous to obtain a trustworthy result. Large particles, corresponding to an effective radius of 50 nm, were observed both in the middle and top of the NLC. The present cloud does not comply with the conventional picture that NLC ice particles nucleate near the temperature minimum and grow to larger sizes as they sediment to lower altitudes. Strong up-welling, likely caused by gravity wave activity, is required to explain its characteristics.
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| 19. |
- Pautet, P. -D, et al.
(författare)
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Analysis of gravity waves structures visible in noctilucent cloud images
- 2011
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 73:14-15, s. 2082-2090
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Tidskriftsartikel (refereegranskat)abstract
- The noctilucent clouds (NLC) are high-altitude bright cloud formations visible under certain conditions from high-latitude places during the summer months. Even if the exact nature of these clouds still remains a mystery, they are an efficient tracer of the dynamic processes at their level, particularly the gravity waves propagating from the stratosphere through the mesopause layer. In this paper, we describe a technique developed to analyze the structures visible in the NLC images taken every summer night since 2004 from Stockholm, Sweden (59.4 degrees N). The parameters of 30 short-period gravity wave events have been measured and compared with older datasets obtained mostly from low and mid-latitude sites, using airglow imaging techniques. The horizontal wavelengths are in good agreement with previous results while the observed horizontal phase speeds exhibit smaller values than for other sites. The directionality of the waves presents strong poleward preference, traditionally observed during the summer season. This anisotropy and the difference in the phase speed distribution cannot be explained by the filtering due to the background wind field but more probably by the position of the gravity waves sources, located to the south of the observation site.
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| 20. |
- Plane, John M. C., et al.
(författare)
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A combined rocket-borne and ground-based study of the sodium layer and charged dust in the upper mesosphere
- 2014
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 118, s. 151-160
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Tidskriftsartikel (refereegranskat)abstract
- The Hotel Payload 2 rocket was launched on January 31st 2008 at 20.14 LT from the Andoya Rocket Range in northern Norway (69.31 degrees N, 16.01 degrees E). Measurements in the 75-105 km region of atomic O, negatively-charged dust, positive ions and electrons with a suite of instruments on the payload were complemented by lidar measurements of atomic Na and temperature from the nearby ALOMAR observatory. The payload passed within 2.58 km of the lidar at an altitude of 90 km. A series of coupled models is used to explore the observations, leading to two significant conclusions. First, the atomic Na layer and the vertical profiles of negatively-charged dust (assumed to be meteoric smoke particles), electrons and positive ions, can be modelled using a self-consistent meteoric input flux. Second, electronic structure calculations and Rice-Ramsperger-Kassel-Markus theory are used to show that even small Fe-Mg-silicates are able to attach electrons rapidly and form stable negatively-charged particles, compared with electron attachment to O-2 and O-3. This explains the substantial electron depletion between 80 and 90 km, where the presence of atomic O at concentrations in excess of 10(10) cm(-3) prevents the formation of stable negative ions.
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| 21. |
- Reisin, E. R., et al.
(författare)
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Traveling planetary wave activity from mesopause region airglow temperatures determined by the Network for the Detection of Mesospheric Change (NDMC)
- 2014
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 119, s. 71-82
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Tidskriftsartikel (refereegranskat)abstract
- The global distribution of traveling planetary wave (PW) activity in the mesopause region is estimated for the first time from ground-based airglow measurements. Monthly and total mean climatologies of PW power are determined from rotational temperatures measured at 19 sites from 78 degrees N to 76 degrees S which contribute to the Network for the Detection of Mesospheric Change (NDMC). Wave power is expressed as the standard deviation of nocturnal mean temperature around the seasonal temperature variation. The results from 20 degrees N confirm the SABER traveling PW proxy by Offermann et al. (2009, J. Geophys. Res. 114, D06110) at two altitudes. Most sites between 69 degrees S and 69 degrees N show total mean traveling PW activity of about 6 K, and only some high latitude sites have considerably higher activity levels. At the two tropical sites, there is practically no seasonal variation of PW activity. At 70% of the midlatitude sites, the seasonal variation is moderate for most of the year, but it is quite appreciable at all high latitude sites. Results about traveling PW activity at 87 km and 95 km available from several sites signal similar behavior at both altitudes. The total mean climatological results here obtained have further been used to separate the traveling PW contribution from the superposition of wave types contained in OH rotational temperature fluctuations measured by the SCIAMACHY instrument on Envisat. A narrow equatorial wave activity maximum is probably caused by gravity waves, while a tendency towards greater activity at higher northern latitudes may be due to stationary planetary waves.
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| 22. |
- Stegman, Jacek, 1944-
(författare)
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Spectroscopic and kinetic studies of atmospheric oxygen emissions
- 1991
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The terrestrial night sky spectrum Is dominated by emission features related to oxygen photochemistry. Photodissociation of molecular oxygen, the second most abundant atmospheric constituent Is the most efficient channel for converting solar electromagnetic radiation into chemical energy. This energy, deposited in the atmosphere during the day is carried by atomic oxygen that eventually initiates a number of chemical reactions leading to the emission of radiation. These processes continue throughout the night and are responsible for the production of the terrestrial nightglow.A systematic study of the thermospheric oxygen atom distribution and of related optical emission features was conducted with the specific aim of providing the link between the abundance of atomic oxygen and the intensity of nightglow. For this purpose the exact pathways of populating and de-populating the emitting states as well as the excitation and quenching processes have to be known. An attempt to determine these pathways and to understand the basic physics governing the process of the termolecular association of oxygen atoms have been the main objective of the works collected in this thesis.Within this study a series of rocket experiments, distributed over the years 1975 to 1983, three different geographical sites and varying geophysical conditions have been carried out. These rocket experiments provided an unique set of simultaneous measurements of the oxygen related airglow features and concurrent measurements of atomic oxygen. The first measurement of the 02 Chamberlain system (A'^AU -> a^Ag) altitude profile in the mesopause layer was secured and modelled according to an excitation scheme involving the direct production of the A'^AU (as well as A^SU+) in the termolecular association of oxygen atoms.Filter photometry alone cannot provide sulficiently detailed spectral information for the unambiguous Interpretation of the rocket-borne airglow measurements. As a continuation and as a necessary complement to the rocket work a ground-based high-resolution spectrometric study of the O2 UV airglow has also been conducted. For the qualitative interpretation of the Oo UV airglow spectra a powerful spectral analysis technique was developed. This method, involving a non-linear least-squares fitting of synthetic spectra to the observations, allows separation of individual bands and the measurement of their column integrated intensity. An exceptional data base of high resolution spectra (0.13 nm|, extending now over half a solar cycle, has been created. From these measurements the vibrational population distribution of the A'JIjj'1' state was obtained and the vibrational population distributions of the two other states (A’^AU and c^£u") were infered. Based on the co-variation studies of the Herzberg I and Herzberg II systems with simultaneously measured green line intensities a set of quenching parameters for 02(c1£u') was obtained. These results Imply that the Herzberg II emission should peak considerably below the Herzberg I and Chamberlain emissions which may explain earlier difficulties in interpreting rocket experiments.
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