Irina Strelnikova

Rocket-borne in situ measurements of meteor smoke: Charging properties and implications for seasonal variation

Rocket-borne observations of meteoric smoke particles (MSPs) are presented from three campaigns at polar latitudes (69 degrees N) in September 2006, and in the summers of 2007 and 2008. MSPs are detected using a novel technique based on photoelectron emission from the particles after stimulation by UV photons emitted by a xenon flashlamp. Resulting photoelectron currents are shown to be proportional to particle volume density. September results match model predictions qualitatively at altitudes from 65 to 85 km while measurements at higher altitudes are contaminated by photoelectrons from NO and O-2((1)Delta(g)). Contamination below this altitude can be excluded based on concurrent satellite observations. The observations show a large variability from flight to flight. Part of this variability can be attributed to differences in the charging of MSPs during day and night. Finally we find that MSP volume density in summer can exceed that during September. Analyzing model simulations of the global transport and microphysics of these particles, we show that our observations are in agreement with the model predictions, even though number densities of particles with radii >1 nm, which have long been thought to be suitable condensation nuclei for mesospheric ice particles, show the opposite behavior. It is shown that this discrepancy is caused by the fact that even larger particles (similar to 3 nm) dominate the volume density and that transport affects these different particle sizes in different ways. These results reinforce previous model findings according to which seasonal MSP variability is mainly driven by the global circulation and corresponding transport.

Nonspecular meteor trails from non‐field‐aligned irregularities: Can they be explained by presence of charged meteor dust?

Nonspecular meteor echoes have been associated with field-aligned irregularities and have been observed at low-latitude and midlatitude sites. We present observations obtained at high latitudes with range-time features that resemble those at lower latitudes. However, these echoes cannot come from field-aligned irregularities, since the radar-pointing angles are almost parallel to the magnetic field. Using interferometry, we have been able to discriminate space and time features. Our echoes could be qualitatively explained by the presence of charged dust forming from the meteoric material immersed in a turbulent flow. This can lead to a high Schmidt number plasma that can sustain meter-scale turbulence just as it does for the polar mesospheric summer echoes. These rare events require relatively large meteoroids. The result emphasizes the importance of charged dust in understanding all long-duration nonspecular meteor echoes. This dust will extend their diffusion times and will affect temperature estimations from specular echoes.

Extended observations of polar mesosphere winter echoes over Andøya (69°N) using MAARSY

Continuous observations of Polar Mesosphere Winter Echoes (PMWE) have been conducted at the Norwegian island Andoya (69.30°N, 16.04°E) since autumn 2004 using the ALWIN VHF radar (until 2008) and the Middle Atmosphere Alomar Radar System (MAARSY) (since 2011). Using the more sensitive MAARSY compared to the ALWIN radar results in more detections characterized by smaller volume reflectivity values down to 4·10−18m−1 and a greater altitudinal coverage, 50–88 km compared to previous observations between 65 and 75 km. The results obtained by MAARSY show that the PMWE season starts clearly at the beginning of September with a mean seasonal occurrence rate of about 16%, but a strong seasonal variability with maxima up to 70% in the seasonal variation of the individual years. The end of the winter season is hard to determine since mesospheric echoes have also been observed below altitudes of 80km during nonwinter months, particularly around the end of May, i.e., the beginning of the polar mesospheric summer echo season, indicating that the physical mechanism for creating the lower mesospheric echoes is present during the early summer months as well.

Microphysical Properties of Mesospheric Aerosols: An Overview of In Situ-Results from the ECOMA Project

Six sounding rockets were launched within the ECOMA (=“Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere”) project to study the characteristics of meteoric smoke particles (MSPs) and mesospheric ice particles, as well as their possible microphysical relation. The launches were conducted during three campaigns from the Andoya Rocket Range (69°N, 16°E), one in September 2006, and the other two in the summers of 2007 and 2008. This chapter provides an overview of these observations and presents the corresponding geophysical results with special emphasis on our understanding of the micropyhsics of mesospheric ice particles. Most notably, we are able to confirm the existence of MSPs at all altitudes between 60 and 85 km in September, and a seasonal variation that is consistent with previous model studies in which MSP-variability is mainly driven by the global circulation. Together with these model studies as well as recent satellite observations of MSPs our results hence cast some doubt on a standard assumption of state-of-the-art microphysical models of mesospheric ice clouds, namely that ice nucleation mainly occurs heterogeneously on MSPs.

D region meteoric smoke and neutral temperature retrieval using the poker flat incoherent scatter radar

Summary form only given. This presentation describes the first measurement of the microphysical properties and variability of meteoric smoke particles (MSPs) at high latitude using the Poker Flat ISR (65.1N, 147.5W). In addition, we present a novel technique for determining height resolved daytime D region neutral temperatures, which takes into account the presence of charged dust. We discuss the temporal/spatial variability and the relation to meteoric input observed and MSP microphysical properties in the polar mesopause region. Further investigation and multi-site measurements in conjunction with global models and neutral wind measurements are required to assess the relative contribution from transport versus local production. This work provides a template for potential use at many other radar sites for the determination of microphysical properties of MSPs and day-time neutral temperature in the D region that show good general agreement with other temperature data during the observing period.

Charged Aerosol Effects on the Scattering of Radar Waves from the D-Region

Charged aerosol particles are an important contributor to the D-region charge balance and affect the scattering of radar waves. Among these particles are meteoric smoke particles (MSP) which occur at all D-region altitudes and all seasons, and mesospheric ice particles whose occurrence is confined to altitudes of ∼80–90 km at polar latitudes during summer. We argue that it is the modification of electron diffusion by the heavy charged aerosol particles which is the prime effect leading to clearly detectable signatures in both incoherent and coherent radar backscatter. In the case of incoherent scatter, it is shown that the presence of charged aerosol particles modifies the incoherent scatter spectrum. Corresponding observations with the EISCAT UHF radar and the Arecibo radar have been used to detect both MSP and ice particles at D-region altitudes and characterize their radii and number densities. In the case of coherent scatter, it is argued that the modified diffusion properties of the D-region electrons lead to small scale structures at the radar Bragg wavelength due to turbulent mixing in combination with a large Schmidt number. To test this theory, calibrated echo strengths of polar mesosphere summer echoes have been measured with the EISCAT radars at Tromso (69°N) and Svalbard (78°N) and collocated 53 MHz radars, thus covering frequencies of 53 MHz, 224 MHz, 500 MHz, and 933 MHz. Importantly, the vast majority of these observations show excellent agreement with the corresponding theoretical predictions thus providing strong support for this theory. This theory was subsequently applied to the same data sets in order to derive ice particle radii. Corresponding results are in excellent agreement with independent data sets from satellite-borne and ground-based optical observations. Finally, some suggestions for future investigations are given.