On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

The dust probe DUSTY, first launched during the summer of 1994 (flights ECT–02 and ECT–07) from Andøya Rocket Range, northern Norway, was the first probe to unambiguously detect heavy charged mesospheric aerosols, from hereon referred to as dust. In ECT–02 the probe detected negatively charged dust particles in the height interval of 83 to 88.5 km. In this flight, the lower grid in the detector (Grid 2) measures both positive and negative currents in various regions, and we find that the relationship between the current measurements of Grid 2 and the bottom plate can only be explained by influence from secondary charge production on Grid 2. In ECT–07, which had a large coning, positive currents reaching the top grid of the probe were interpreted as due to the impact of positively charged dust particles. We have now reanalyzed the data from ECT–07 and arrived at the conclusion that the measured positive currents to this grid must have been mainly due to secondary charging effects from the impacting dust particles. The grid consists of a set of parallel wires crossed with an identical set of wires on top of it, and we find that if the observed currents were created from the direct impact of charged dust particles, then they should be very weakly modulated at four times the rocket spin rate ω<sub><I>R</I></sub>. Observations show, however, that the observed currents are strongly modulated at 2ω<sub><I>R</I></sub>. We cannot reproduce the observed large modulations of the impact currents in the dust layer if the currents are due only to the transfer of the charges on the impacted dust particles. Based on the results of recent ice cluster impact secondary charging experiments by Tomsic (2003), which found that a small fraction of the ice clusters, when impacting with nearly grazing incidence, carried away one negative charge −1<I>e</I>, we have arrived at the conclusion that similar, but significantly more effective, charging effects must be predominantly responsible for the positive currents measured by the top grid in ECT–07 and their large rotational modulation at 2ω<sub><I>R</I></sub>. <br><br> Since the secondary effect is dependent on the size of the impacting dust, this opens up for the possibility of mapping the relative dust sizes throughout a dust layer by comparing the observed direct and secondary currents

CHARGING AND DETECTION OF MESOSPHERIC DUST WITH INSTRUMENT SPID ON G-CHASER ROCKET

The Smoke Particle Impact Detector (SPID) was flown on the G-Chaser student rocket that was launched from Andøya on 13 January 2019. SPID is a Faraday cup instrument with applied bias voltages to deflect the ambient plasma and a target area inside the probe designed to measure the dust particles by charge detection. The charging process of the dust particles in the detector is important for interpretation of the measurements and the influence of the charging models is discussed. Preliminary analysis of the SPID observations shows that ambient plasma and sunlight had an influence on the signals; further analysis is needed to retrieve information on impacting dust from the data

The red-sky enigma over Svalbard in December 2002

On 6 December 2002, during winter darkness, an extraordinary event occurred in the sky, as viewed from Longyearbyen (78° N, 15° E), Svalbard, Norway. At 07:30 UT the southeast sky was surprisingly lit up in a deep red colour. The light increased in intensity and spread out across the sky, and at 10:00 UT the illumination was observed to reach the zenith. The event died out at about 12:30 UT. Spectral measurements from the Auroral Station in Adventdalen confirm that the light was scattered sunlight. Even though the Sun was between 11.8 and 14.6deg below the horizon during the event, the measured intensities of scattered light on the southern horizon from the scanning photometers coincided with the rise and setting of the Sun. Calculations of actual heights, including refraction and atmospheric screening, indicate that the event most likely was scattered solar light from a target below the horizon. This is also confirmed by the OSIRIS instrument on board the Odin satellite. The deduced height profile indicates that the scattering target is located 18–23km up in the stratosphere at a latitude close to 73–75° N, southeast of Longyearbyen. The temperatures in this region were found to be low enough for Polar Stratospheric Clouds (PSC) to be formed. The target was also identified as PSC by the LIDAR systems at the Koldewey Station in Ny-Ålesund (79° N, 12° E). The event was most likely caused by solar illuminated type II Polar Stratospheric Clouds that scattered light towards Svalbard. Two types of scenarios are presented to explain how light is scattered.publishedVersio

Nordlys i verdensrommet

Vi vil ikke her gå inn i nordlyset som vi kjenner det fra jorden, men kort omtale andre steder i verdensrommet hvor vi har observert nordlyslignende fenomen eller hvor vi kan vente å finne beslektede fenomen

Nordlys i verdensrommet

This article is part of Ottar (1980), nr 121-122, "Nordlysobservatoriet 50 år", available in Munin at http://hdl.handle.net/10037/5177Vi vil ikke her gå inn i nordlyset som vi kjenner det fra jorden, men kort omtale andre steder i verdensrommet hvor vi har observert nordlyslignende fenomen eller hvor vi kan vente å finne beslektede fenomen

On the Relationship between PMSE Strength and Particle Precipitation

We have studied the relationship between particle precipitation and PMSE strength on days where we observe PMSE layers both with the EISCAT VHF and UHF radars. The UHF observations of the ionization and its variation, above the PMSE layer, is used as a measure of precipitation. Variations of the precipitation is compared with variations of the PMSE strengths observed with both radars. Although many cases apparently show a clear connection between precipitation and PMSE, where an increased precipitation leads to a strengthening of the PMSE, our findings confirm that there is no general and simple proportionality between the two. For the weakest PMSE there appears to be no correlation between precipitation and PMSE strength. For PMSEs around average strength of our observations there appears to be a weak positive correlation, which can be predicted by a timedependent dust cloud charge model. On some occasions an increased precipitation can, apparently, initially lead to an increase of PMSE strength which at some point starts to decline even if the precipitation continue to increase. This feature can also be seen in the results from the statistical analysis, however the number of occurrences is too low to conclude with significance and the time-dependent charge model described here does not reproduce such features. We have studied to what degree models for the PMSE scattering can explain the various cases of reaction of PMSE to changes in precipitatio

Mesospheric dust and its secondary effects as observed by the ESPRIT payload

The dust detector on the ESPRIT rocket detected two extended dust/aerosol layers during the launch on 1 July 2006. The lower layer at height ~81.5–83 km coincided with a strong NLC and PMSE layer. The maximum dust charge density was ~−3.5×10<sup>9</sup> e m<sup>−3</sup> and the dust layer was characterized by a few strong dust layers where the dust charge density at the upper edges changed by factors 2–3 over a distance of ≲10 m, while the same change at their lower edges were much more gradual. The upper edge of this layer is also sharp, with a change in the probe current from zero to <I>I</I><sub>DC</sub>=−10<sup>−11</sup> A over ~10 m, while the same change at the low edge occurs over ~500 m. The second dust layer at ~85–92 km was in the height range of a comparatively weak PMSE layer and the maximum dust charge density was ~−10<sup>8</sup> e m<sup>−3</sup>. This demonstrates that PMSE can be formed even if the ratio of the dust charge density to the electron density <I>P</I>=<I>N<sub>d</sub>Z<sub>d</sub> /n_e</I>≲0.01. <br><br> In spite of the dust detector being constructed to reduce possible secondary charging effects from dust impacts, it was found that they were clearly present during the passage through both layers. The measured secondary charging effects confirm recent results that dust in the NLC and PMSE layers can be very effective in producing secondary charges with up to ~50 to 100 electron charges being rubbed off by one impacting large dust particle, if the impact angle is θ<sub><I>i</I></sub>≳20–35°. This again lends support to the suggested model for NLC and PMSE dust particles (Havnes and Næsheim, 2007) as a loosely bound water-ice clump interspersed with a considerable number of sub-nanometer-sized meteoric smoke particles, possibly also contaminated with meteoric atomic species

A Dust-Driven Flux Tube Interchange Instability

We describe, formulate, and investigate quantitatively a physical process which will lead to radial plasma transport in dusty planetary magnetospheres. The process depends on plasma inhomogeneities (in,particular electron temperature fluctuations) interacting with distributed fine-grained ring material to drive currents along the magnetic field lines, which close through the ionosphere. Azimuthal electric fields generated in this way will then lead to radial plasma flows via the E x B drift. The process is investigated both for Saturn's oxygen torus and for the Io torus in Jupiter's magnetosphere