Neutral Air Density Research Articles

Estimate of size distribution of charged MSPs measured in situ in winter during the WADIS-2 sounding rocket campaign

Abstract. We present results of in situ measurements of mesosphere–lower thermosphere dusty-plasma densities including electrons, positive ions and charged aerosols conducted during the WADIS-2 sounding rocket campaign. The neutral air density was also measured, allowing for robust derivation of turbulence energy dissipation rates. A unique feature of these measurements is that they were done in a true common volume and with high spatial resolution. This allows for a reliable derivation of mean sizes and a size distribution function for the charged meteor smoke particles (MSPs). The mean particle radius derived from Schmidt numbers obtained from electron density fluctuations was ∼ 0.56 nm. We assumed a lognormal size distribution of the charged meteor smoke particles and derived the distribution width of 1.66 based on in situ-measured densities of different plasma constituents. We found that layers of enhanced meteor smoke particles' density measured by the particle detector coincide with enhanced Schmidt numbers obtained from the electron and neutral density fluctuations. Thus, we found that large particles with sizes > 1 nm were stratified in layers of ∼ 1 km thickness and lying some kilometers apart from each other.

Neutral density variation from specular meteor echo observations spanning one solar cycle

AbstractSpecular meteor radars have provided essential information about the mesospheric/lower thermosphere (MLT) dynamics. The Canadian Meteor Orbit Radar has been conducting continuous meteor echo observations in a fixed, stable configuration since 2002. Here we present estimates of the neutral air density variations derived from observations of the meteor peak flux altitude. Using a simple model assuming a linear trend and a sinusoidal solar cycle we derived a trend of a decreasing neutral density of 5.8 ± 1.1% per decade at approximately 91 km altitude and an amplitude across the most recent solar cycle, the solar cycle of 2.4 ± 0.7% for solar cycle 23/24. The long‐term trend of decreasing neutral air density in the MLT is in good agreement with the model results from Akmaev et al. (2006).

Neutral air density variations during strong planetary wave activity in the mesopause region derived from meteor radar observations

Meteor radar observations of upper mesospheric/lower thermospheric winds and temperatures are suitable to investigate planetary waves in the mesosphere. Here we present a case study of the winter season 2009/2010 for two mid-latitude stations at the edge of the polar vortex and one station within the polar vortex on the island of Andøya. The selected interval begins with the build up of a long period oscillation at the end of November 2009 and ends in March 2010 after the January 2010 stratospheric warming. Planetary wave signature is visible in the temperature as well as the wind field derived from standard meteor radar and EOS MLS observations. Further, we infer neutral air density variations caused by this long period oscillation from meteor peak altitude variations of the sporadic meteor component. The results are compared with density variation computed from MLS temperature and pressure data.

Mesospheric inversion layer and sprites

The vertical structure of temperature observed by Sounding of Atmosphere using Broadband Emission Radiometry (SABER) aboard Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) and sprites observations made during the Eurosprite 2003–2007 observational campaign were analyzed. Sprite observations were made at two locations in France, namely Puy de Dôme (45°46′19.2″N; 02°57′44.64″E; 1.464 km altitude) in the French Massif Central and at the Pic du Midi (42°56′11″N; 00°08′34″E; 2.877 km altitude) in the French Pyrénées. It is observed that the vertical structure of temperature shows evidence for a Mesospheric Inversion Layer (MIL) on those days on which sprites were observed. A few events are also reported in which sprites were not recorded, although there is evidence of a MIL in the vertical structure of the temperature. It is proposed that breaking gravity waves produced by convective thunderstorms facilitate the production of (1) sprites by modulating the neutral air density and (2) MILs via the deposition of energy. The same proposition has been used to explain observations of lightings as well as both MILs and lightning arising out of deep convections.

Description and validation of a limb scatter retrieval method for Odin/OSIRIS

In this paper we present the Modified Onion Peeling (MOP) inversion method, which is for the first time used to retrieve vertical profiles of stratospheric trace gases from Odin/OSIRIS limb scatter measurements. Since the original publication of the method in 2002, the method has undergone major modifications discussed here. The MOP method now uses a spectral microwindow for the NO2 retrieval, instead of the wide UV‐visible band used for the ozone, air, and aerosol retrievals. We give a brief description of the algorithm itself and show its performance with both simulated and real data. Retrieved ozone and NO2 profiles from the OSIRIS measurements were compared with data from the GOMOS and HALOE instruments. No more than 5% difference was found between OSIRIS daytime and GOMOS nighttime ozone profiles between 21 and 45 km. The difference between OSIRIS and HALOE sunset NO2 mixing ratio profiles was at most 25% between 20 and 40 km. The neutral air density was compared with the ECMWF analyzed data and around 5% difference was found at altitudes from 20 to 55 km. However, OSIRIS observations yield as much as 80% greater aerosols number density than GOMOS observations between 15 and 35 km. These validation results indicate that the quality of MOP ozone, NO2, and neutral air is good. The new version of the method introduced here is also easily expanded to retrieve additional species of interest.

Parameterization of Temporal Structure in the Single-Dielectric-Barrier Aerodynamic Plasma Actuator

We present the results of two measurements that describe the interaction of an aerodynamic plasma actuator (a dielectric barrier discharge plasma in which an asymmetric arrangement of electrodes leads to momentum coupling into neutral air) with the surrounding atmosphere. We show that the presence of oxygen in the Earth's atmosphere plays a substantial role in the efficiency of the actuator. We measure the time-resolved neutral air density in the vicinity of the actuator using a laser beam probe. We show that the effect of the actuator is to establish a region of increased neutral density in the vicinity of its exposed electrode's edge, and we show that the actuator couples directed momentum into the air by pulling air up this density gradient, against the corresponding pressure, and releasing it in the downstream direction when the plasma quenches, replacing it with air from the volume above the actuator. These measurements harmonize previously contradictory measurements of the actuator's behavior.

In situ observations of small scale neutral and plasma dynamics in the mesosphere/lower thermosphere at 79°N

From June 29 to July 6 2003, the German-Norwegian ROMA-SvalRak campaign (ROMA = Rocket borne Observations in the Middle Atmosphere) took place at the SvalRak rocket range, Ny-Ålesund (78.9°N, 11.9°E; Spitzbergen). The main scientific aim of this campaign was to study polar mesosphere summer echoes (PMSE) and mesospheric turbulence. During this campaign a total of three instrumented sounding rockets was launched. In addition, ground based observations with a VHF radar and a potassium lidar at Longyearbyen complemented the in situ measurements. All three sounding rockets were equipped with the CONE (COmbined sensor for Neutrals and Electrons) instrument to measure small scale structure of neutral air and electron density, and neutral temperature. The PIP (positive ion probe) instrument was used to measure small scale structure of the positive ion density. Furthermore, two cold plasma probes were flown to measure electron temperature, and a particle detector was employed to detect signatures of charged aerosols. During the first launch, an electric field experiment was also incorporated, while during the other two launches, Faraday rotation experiments yielded absolute electron number densities. During all three rocket flights a PMSE was observed by the VHF radar, whereas the potassium lidar detected a noctilucent cloud (NLC) only during the second launch. Signatures of charged particles forming the PMSE and NLC layers were recorded by the onboard particle detectors.

A new technique for the analysis of neutral air density fluctuations measured in situ in the middle atmosphere

We consider the analysis of mesospheric neutral air density fluctuations caused by turbulent eddy motions as measured by rocket borne ionization gauges. After shortly reviewing the so far standard Fourier‐approach we introduce wavelets as a suitable tool to derive spectral information of the data both as a function of spatial scale and altitude. Applying both techniques to a data set obtained during a recent sounding rocket campaign we show that both methods yield consistent results, however, the wavelet technique yields additional information on the actual vertical extent of the observed turbulent structures.

Improvement of ERS-1 orbits using along-track accelerations from DORIS data on SPOT2

Abstract. In long-arc precise orbit determinations of altimetric satellites such as ERS-1, large errors may occur from mismodelling of aerodynamic drag and solar radiation pressure. Such surface forces for non-spherical satellites require accurate modelling of the effective area and particle-surface interactions, but the dominant source of error is neutral air density as derived from thermospheric models for aerodynamic drag. Several techniques can be employed to alleviate air-drag mismodelling but all require the solution of additional parameters from the tracking data. However, for ERS-1 the sparsity of laser range data limits the application of such empirical techniques. To overcome this, use can be made of the dense DORIS Doppler tracking for SPOT2 which is in a similar orbit to ERS-1. A recent investigation by CNES examined the use of drag scale factors from SPOT2 to constrain the ERS-1 orbit. An improvement to that methodology is to consider along-track mismodelling as observed by timing errors in the Doppler data for each pass of SPOT2. The along-track correction to the acceleration as derived from SPOT2 can then be applied to ERS-1 orbits, solving for a scale factor to absorb systematic errors - particularly that arising from the 50 km altitude difference. Results are presented of the associated improvement in ERS-1 orbits as derived from concurrent SPOT2 arcs. It will be seen that the procedure not only improves the laser range fit, but more importantly, leads to more precise radial positioning as evident in the altimeter and crossover residuals.

Improvement of ERS-1 orbits using along-track accelerations from DORIS data on SPOT2

<strong class="journal-contentHeaderColor">Abstract.</strong> In long-arc precise orbit determinations of altimetric satellites such as ERS-1, large errors may occur from mismodelling of aerodynamic drag and solar radiation pressure. Such surface forces for non-spherical satellites require accurate modelling of the effective area and particle-surface interactions, but the dominant source of error is neutral air density as derived from thermospheric models for aerodynamic drag. Several techniques can be employed to alleviate air-drag mismodelling but all require the solution of additional parameters from the tracking data. However, for ERS-1 the sparsity of laser range data limits the application of such empirical techniques. To overcome this, use can be made of the dense DORIS Doppler tracking for SPOT2 which is in a similar orbit to ERS-1. A recent investigation by CNES examined the use of drag scale factors from SPOT2 to constrain the ERS-1 orbit. An improvement to that methodology is to consider along-track mismodelling as observed by timing errors in the Doppler data for each pass of SPOT2. The along-track correction to the acceleration as derived from SPOT2 can then be applied to ERS-1 orbits, solving for a scale factor to absorb systematic errors - particularly that arising from the 50 km altitude difference. Results are presented of the associated improvement in ERS-1 orbits as derived from concurrent SPOT2 arcs. It will be seen that the procedure not only improves the laser range fit, but more importantly, leads to more precise radial positioning as evident in the altimeter and crossover residuals.

Small‐scale structure of O2+ and proton hydrates in a noctilucent cloud and polar mesospheric summer echo of August 9/10 1991 above Kiruna

A novel mass spectrometer designed to measure simultaneously positive ion composition in the mesosphere, was successfully launched during the NLC‐91 project. Instruments supporting the mass spectrometer were a probe to measure both electrons and positive ions as well as a wave propagation experiment. The location of the Noctilucent Clouds (NLC) was determined by a particle impact sensor to detect secondary electrons and ions from the impact of NLC particle. The density of proton hydrates and of the related total ions is depleted in the NLC region at 83 km. An improved detection limit of 5 × 104 m−3 for positive ions and improved height resolution revealed for the first time large gradients in the O2+, H+(H2O)2 and H+(H2O)6 densities within a small height range of the order of 50 m. Such gradients at the altitude of NLC and Polar Mesospheric Summer Echoes (PMSE) are associated with strong variability of mesospheric water vapor, temperature and neutral air density.

Neutral air density and temperature measurements by the TOTAL instrument aboard the ROSE payloads

Four ROSE payloads, launched from November 1988 to February 1989 from northern Scandinavia, carried ionization gauges (‘TOTAL’ instruments) for neutral air density measurements in the altitude range 90–105 km. Temperature profiles are derived by integrating the number density profiles. Density and temperature data are presented. The limitations of the measurement technique as well as instrumental errors are discussed. In one of the flights (F1) a significant temperature enhancement was observed at an altitude where plasma instabilities were detected by independent measurements.

Some aspects of a global thermospheric density model deduced from the analysis of the orbit of Intercosmos 13 rocket (1975-22B)

An empirical density formula is explored as a practical model for atmospheric variations and satellite drag analyses. Expanding neutral air density as a series of spherical harmonics and normalizing to a fixed height, an analytical expression for the rate of change of the mean motion is developed for an oblate atmosphere with density scale height varying linearly with altitude. A subset of the coefficients in the density expansion is determined by least-squares adjustment to the observed orbital decay rate of Intercosmos 13 rocket (1975-22B) for the period May 1975–December 1979. Comparisons against four thermospheric models are undertaken for the solar activity effect and the diurnal and semi-annual variations. Given the even spread of data and the increase in solar activity from low to moderate, the air density variation with solar activity is particularly well determined. The results support the “J77” model revealing a greater increase in density with the daily solar index than either the “MSIS” or “DTM” thermospheric models near the solar minimum. Analyses of the diurnal and semi-annual variations are less exact.

II. Combined numerical model of ion and neutral composition above 120 km

A coupled neutral-ionic photochemical model has been used to interpret the ionic composition of the Venusian dayside ionosphere measured by the orbiter retarding potential analyser (ORPA) experiment on board the NASA Pioneer-Venus orbiter spacecraft. The electron and ion temperatures also measured by the ORPA are used for calculating the plasma-diffusion coefficients and scale heights for ions. The neutral temperature profiles and the densities of neutral constituents, particularly CO2 and O, play key roles in the determination of the height profiles of the ionic constituents. All these quantities vary substantially in the Venusian thermosphere near the terminator; the models presented are representatives of the solar zenith angle ∼65°. The predicted O2+ densities below ∼200km agree particularly well with observations by the ORPA, but the model values are significantly less than those measured by the orbiter ion mass spectrometer (OIMS). Models predict much smaller densities than observed values for all molecular ions above ∼200km. The reason for the turn-up trend of the concentration gradient of molecular ions observed at these heights by both ORPA and OIMS is unknown. One of the models can predict O+ ion densities above ∼200km compatible with observations, if an effective vertical escape flux (φ108cm−2sec−1) is assumed at the ionopause. The neutral air density required to explain the observed ion composition is about 1.4 times larger than the values measured by the orbiter neutral mass spectrometer (ONMS).

Results of air temperature, density and pressure measurements obtained with the aid of foil cloud sensors in the height region between 80 and 95 km

Results of neutral air density, temperature and pressure measurements obtained between November 1968 and June 1972 in the height range between 80 and 95 km over Arenosillo, Spain are given. A simple foil cloud payload, primarily designed for wind finding purposes, was used. The results obtained are compared with CIRA Standard Atmosphere data and ground based radio wave absorption measurements. An estimate of the accuracy of the method is given.

Neutral air density and composition at 150 kilometers

Mass densities derived from drag data are compared with densities determined by mass spectrometers, EUV extinction measurements, and observations of the growth of chemiluminescent clouds for an altitude of 150 km. Drag densities fall very close to the Cira 1965 mean atmosphere and are 10 to 20% higher than the average for all rocket measurements discussed. Mass spectrometric and EUV extinction measurements agree quite well for n(N2) and n(O2) but differ significantly for n(O). In order to derive an improved set of parameters of thermospheric density and composition, it is proposed that the Cira 1965 mean density be lowered by 10%, that the measured n(N2) and n(O2) number densities be maintained, and that n(O) be chosen such that the number densities become consistent with the mass density p. This results in the following reference set for 150-km altitude: ρ = 1.96 × 10−12 g cm−3; n(N2) = 2.6 × 1010 cm−3; n(O) = 2.3 × 1010 cm−3; n(O2) = 2.5 × 109 cm−3; n(Ar) = 5 × 107 cm−3; mean molecular weight M = 22.9 g mole−1.

A note on the features and cause of the diurnal variation of neutral air density at 205 km

The diurnal variation of air density at 205 km, deduced from changes in the orbit of Sputnik 3 satellite, is shown to have different characteristics in the low and high latitude regions of the southern hemisphere. At lower latitudes the maximum density occurs at 1400 hours L.T. and is 17 per cent greater than the minimum density, while at higher latitudes the maximum density occurs at 1700 hours and is 12 per cent greater than the minimum.