Presence Of Noctilucent Clouds Research Articles

Variations in the Polar Mesospheric Summer Echoes during the Appearance of Irregularities of Noctilucent Clouds

Variations in the amplitude of the ordinary wave from a received signal on a partial reflection radar at a short-wave range on the Kola Peninsula during the appearance of noctilucent clouds on August 12, 2016, are examined. Noctilucent clouds are registered by the all-sky camera located 100 km southward of the partial reflection radar. They extended over the entire celestial hemisphere observed by the all-sky camera; all of them moved in the southern direction, and the clouds had a tenuous structure and showed gravity waves with spatial periods of 15–100 km. During the presence of noctilucent clouds over the partial reflection radar, polar mesospheric summer echoes (PMSEs) were recorded at heights of 83–86 km. It was found that the presence of only noctilucent clouds in diagram of the antenna pattern of partial frequency radar is not sufficient for the appearance of PMSEs; noctilucent clouds must also have irregularities of several kilometers. The PMSE heights decreased with a velocity of 0.5 and 1.3 m/s. The issue of aerosols that cause the appearance of PMSEs and noctilucent clouds is discussed.

The lunar semidiurnal tide at the polar summer mesopause observed by SOFIE

The polar summer mesopause, particularly the presence of noctilucent clouds (NLCs), exhibits pronounced temporal variability. Parts of this variability are thought to be caused by lunar tidal influences. We extract the semidiurnal lunar tide in various NLC related parameters by applying the superposed epoch analysis method to the dataset of the SOFIE satellite instrument. Analyzing the NLC seasons from 2007 to 2015 in the northern and southern hemisphere we, first, confirm the influence of the lunar tide on ice water content (IWC) and temperature. For both parameters the lunar influence had already recently been demonstrated in satellite measurements. Second, we apply the analysis to the variety of parameters observed by SOFIE including trace gases (H2O, O3, CH4, and NO), NLC properties (e.g., NLC altitudes and ice mass density), microphysical properties (e.g., particle concentration and mean radius), and mesopause properties. In all of these parameters we find signatures of the semidiurnal lunar tide, which is the first demonstration of this effect for all of these parameters. We quantify the lunar influence in terms of amplitudes and phases. Whereas the focus of the present study is providing observational evidence for the existence of lunar tidal signatures in various parameters, we do not aim at investigating the underlying mechanisms in detail, which is only possible with the utilization of comprehensive modeling approaches. Nevertheless, we briefly discuss the relations to known processes of the NLC evolution where appropriate, e.g., the relevance of the freeze-drying effect for the signature in H2O and the relation of IWC and NLC altitudes.

PMSE dependence on aerosol charge number density and aerosol size

It is commonly accepted that the existence of polar mesosphere summer echoes (PMSEs) depends on the presence of charged aerosols since these are comparatively heavy and reduce the diffusion of free electrons due to ambipolar forces. Simple microphysical modeling suggests that this diffusivity reduction is proportional to rA2 (rA = aerosol radius) but only if a significant amount of charges is bound on the aerosols such that NA∣ZA∣/ne > 1.2 (NA = number of aerosols, ZA = aerosol charge, ne = number of free electrons). The fact that the background electron profile frequently shows large depletions (“biteouts”) at PMSE altitudes is taken as a support for this idea since within biteouts a major fraction of free electrons is missing, i.e., bound on aerosols. In this paper, we show from in situ measurements of electron densities and from radar and lidar observations that PMSEs can also exist in regions where only a minor fraction of free electrons is bound on aerosols, i.e., with no biteout and with NA∣ZA∣/ne ≪ 1. We show strong experimental evidence that it is instead the product NA∣ZA∣rA2 that is crucial for the existence of PMSEs. For example, small aerosol charge can be compensated by large aerosol radius. We show that this product replicates the main features of PMSEs, in particular the mean altitude distribution and the altitude of PMSEs in the presence of noctilucent clouds (NLCs). We therefore take this product as a “proxy” for PMSE. The agreement between this proxy and the main characteristics of PMSEs implies that simple microphysical models do not satisfactorily describe PMSE physics and need to be improved. The proxy can easily be used in models of the upper atmosphere to better understand seasonal and geographical variations of PMSEs, for example, the long debated difference between Northern and Southern hemisphere PMSEs.

Odd oxygen measurements during the Noctilucent Cloud 93 rocket campaign

The NLC‐93 campaign at Esrange, Sweden, addressed the chemical, dynamical and electrical environment of the summer mesopause in the presence of noctilucent clouds (NLC). A major topic was the detailed investigation of odd oxygen abundances and their structure in the vicinity of the cloud layer. Applying independent in situ measurements, we have obtained consistent profiles of atomic oxygen, ozone, and mesospheric total density. Atomic oxygen was measured on two rocket flights by means of a newly developed probe utilizing the 1304 Å resonance fluorescence / absorption technique. Detailed Monte Carlo simulations of the radiative transfer and the instrument aerodynamics are included in the data analysis. We find relatively low atomic oxygen densities with a peak of 2 × 1011 cm−3 at 96 km. An airglow radiometer recorded the O2 IR‐atmospheric band emission, allowing the retrieval of ozone densities by means of an inversion model that considers both direct and indirect sources of O2 (a1Δg). The odd oxygen measurements are compared to a steady state photochemical model. While good agreement is found in the mesosphere, the results deviate close to the cold mesopause. Significant vertical structures are found in the atomic oxygen profiles; sharp gradients and distinct minima coincide with the observed NLC layer. Possible influences of heterogeneous chemistry on the odd oxygen abundance are discussed.

Hydroxyl temperature and intensity measurements during noctilucent cloud displays

Abstract. Two Fourier transform spectrometers have been used to investigate the properties of the near-infrared hydroxyl (OH) nightglow emission under high-latitude summertime conditions and any association with noctilucent clouds (NLCs). The measurements were made from Poker Flat Research Range, Alaska (65.1°N, 147.5°W), during August 1986. Simultaneous photographic observations of the northern twilight sky were made from Gulkana, Alaska (62.2°N, 145.5°W), approximately 340 km to the south to establish the presence of NLCs over the spectrometer site. Data exhibiting significant short-term variations in the relative intensity (as much as 50–100%) and rotational temperature (typically 5–15 K) were recorded on six occasions when NLCs were observed. Joint measurements were also obtained on several "cloud-free" nights. No obvious relationship was found linking the mean OH intensity or its variation with the occurrence of NLCs. However, a clear tendency was found for the mean OH temperature to be lower on NLC nights than on cloud-free nights. In particular, a significant fraction of the OH(3–1) band spectra recorded by each instrument (16–57%) exhibited temperatures below ~154 K on NLC nights compared with <3% on cloud-free nights. This result is qualitatively consistent with current models for ice particle nucleation and growth, but the mean OH temperature on NLC nights (~156 K) was significantly higher than would be expected for long-term particle growth in this region. These observations raise questions concerning the expected proximity of the high-latitude, summertime OH layer and the NLC growth region.

Large‐scale, persistent latitude structures in the mesospheric temperature during ANLC‐93

Michelson interferometer measurements of the hydroxyl (OH) Meinel night‐airglow emissions were made from the NCAR aircraft during the ANLC‐93 Campaign. The spectra have been analysed to give the OH band radiance and rotational temperature, which is taken to be the neutral temperature at the peak of the OH emissions near 87 km. On two occasions, once in the presence of Noctilucent Clouds (NLC), the research flights spanned ∼10° of latitude and reached as high as 66°N. The mean latitudinal structure of the measured mesospheric temperature field is in good agreement with the CIRA‐86 model. In addition, both measurements show large‐amplitude (∼15 K), large‐scale (2–4° of latitude), quasi‐periodic oscillations about the model mean. Finally, the data support the hypothesis that these oscillations are temporally stable, and that they, along with the air mass characterized by the mean temperature field, can be advected with the tidal winds, and play a role in NLC formation.

Mass spectrometric detection of precondensation nuclei at the Artic summer mesopause

A positive ion composition measurement at the summer, high latitude mesopause in the presence of noctilucent clouds has revealed the existence of very massive positive ionospheric ions. The ions were assigned to be proton hydrates of which the heaviest ones contained up to 20 water molecules. These most massive ions were concentrated in a thin layer at an altitude of 90 km. A likely explantation of the existence of so heavy ionospheric ions is a strong local cooling within the layer in combination with a very low electron concentration. In spite of the high altitude of detection of these ions it is conceivable that they represented condensation nuclei eventually leading to the formation of visible notilucent clouds.

Techniques for rocket sampling of noctilucent cloud particles

Particle sampling experiments utilizing sounding rockets were conducted in northern Sweden during August of 1962. Two successful flights were achieved, one in the presence of noctilucent clouds and one when no such clouds could be visually observed from the ground or from aircraft. The collecting surfaces were exposed between the altitudes of approximately 75 and 98 kilometers during ascent only. The instrumentation and performance of the rockets is discussed. DOI: 10.1111/j.2153-3490.1964.tb00147.x

Condensation products of meteor vapors and their connection with noctilucent clouds and rainfall anomalies

The presence of noctilucent clouds and world-wide rainfall anomalies is attributed to the formation of secondary particles from meteor vapors. These particles are formed by coagulation of meteor vapors and are subject to horizontal and vertical displacement by a Lorentz force and the gravitational force of the earth. Adsorption of water vapor by the surfaces of anhydrous secondary particles followed by adsorption of nitrogen (II) oxide in the D-layer is assumed to be the primary mechanism of production of positively charged particles. The increase of the residence time of the secondary particles in the vicinity of 80 km, due to rapid decrease in particle settling velocity and the consequent increase in particle concentration and the action of the Lorentz force on positively charged particles are assumed to cause formation of noctilucent clouds. The variable time lag between the appearance of meteor showers and corresponding rainfall anomalies is attributed, primarily, to the time of settling of sharply defined concentration profiles of coagulating particles through the 80-40 km layer.

Sampling of noctilucent cloud particles

Sampling of noctilucent cloud particles by means of sounding rockets has been successfully carried out from northern Sweden in the Summer of 1962. Two successful flights were achieved, one in the presence of noctilucent clouds and one when no such clouds could be visually observed from the ground or from aircraft. The collecting surfaces were exposed between the altitudes of approximately 75 and 98 kilometers during ascent only. The particle concentration in a vertical column through the noctilucent cloud display is found to be greater than 8 × 1010 particles per square meter which is at least one thousand times greater than in the case when no clouds were observed. The integral size distribution of the cloud particles is of the form N = Ad-p where 3 < p < 4. A significant fraction of the collected cloud particles had a volatile coating prior to collection. The particles were analyzed by electron diffraction, neutron activation, and electron beam microprobe techniques. Electron-beam microprobe analysis has given evidence for iron particles with high nickel content. Calcium films were used as indicators of moisture associated with the collected particles. Study of the exposed and unexposed films flown in the sampling experiments has revealed evidence for moisture. Laboratory simulation of a ring- or halo-patterns found in the electron microscopic examination of the noctilucent cloud particles has been attempted. This was done by impacting ice-coated nickel particles on collecting surfaces similar to those used in the sampling experiment. Ring patterns similar to those observed on the rocket sampling surfaces have been produced. The primary conclusions are that the cloud particles are probably of extraterrestrial origin and that a significant fraction appears to have been coated with terrestrial ice. Plans for future experiments are briefly outlined.

Techniques for rocket sampling of noctilucent cloud particles

Particle sampling experiments utilizing sounding rockets were conducted in northern Sweden during August of 1962. Two successful flights were achieved, one in the presence of noctilucent clouds and one when no such clouds could be visually observed from the ground or from aircraft. The collecting surfaces were exposed between the altitudes of approximately 75 and 98 kilometers during ascent only. The instrumentation and performance of the rockets is discussed.

Particle Sampling from Noctilucent Clouds

PARTICLE sampling experiments have been conducted at the mesopause region of the atmosphere. The experiments utilized sounding rockets which were fired from the Kronogard range (66° N, 19° E) in northern Sweden, during the summer of 1962. Two successful flights out of a total of four firings were achieved: one (August 11, 0140 G.M.T.) in the presence of noctilucent clouds and one (August 7, 0047 G.M.T.) when no such clouds could be visually observed from the ground and from aircraft. The Nike-Cajun rockets carried identical instruments and in so far as can at present be determined the experimental conditions of the two successful flights were similar.