Observations Of Noctilucent Clouds Research Articles

Analysis of noctilucent clouds’ fields according to ground-based network and airborne photography data

The article analyzes the fields of noctilucent clouds over the territory of the Russian Federation, recorded by a ground-based network of cameras using also aircraft photography, over the two nights in June 2021. It is demonstrated that aircraft photography can significantly improve the coverage of the territory of noctilucent clouds’ probable appearance. The detected noctilucent cloud fields are compared with model regions of water vapor condensation derived from satellite measurements of temperature and water vapor mixing ratio. Practical steps are proposed for the development of aircraft observations of noctilucent clouds.

Version 8 IMK–IAA MIPAS temperatures from 12–15 µm spectra: Middle and Upper Atmosphere modes

Abstract. Motivated by an improved European Space Agency (ESA) version of calibrated Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) spectra (version 8.03), we have released version 8 of MIPAS temperatures and pointing information retrieved from 2005–2012 MIPAS measurements at 12–15 µm in the Middle Atmosphere (MA), Upper Atmosphere (UA) and Noctilucent Cloud (NLC) measurement modes. The Institute of Meteorology and Climate Research–Instituto de Astrofisica de Andalucia (IMK–IAA) retrieval processor in use considers non-local thermodynamic equilibrium (non-LTE) emission explicitly for each limb scan. This non-LTE treatment is essential to obtain accurate temperatures above the mid-mesosphere because at the altitudes covered, up to 115 km, the simplified climatology-based non-LTE treatment employed for the Nominal (NOM) measurements is insufficient. Other updates in MA/UA/NLC version 8 non-LTE temperature retrievals from previous data releases include more realistic atomic oxygen and carbon dioxide abundances, an updated set of spectroscopic data, an improved spectral shift retrieval, a continuum retrieval extended to altitudes up to 58 km, consideration of an altitude-dependent radiance offset retrieval, the use of wider microwindows above 85 km to capture the offset, an improved accuracy in forward model calculations, new a priori temperature information, improved temperature horizontal gradient retrievals and the use of MIPAS version 5 interfering species where available. The resulting MIPAS MA/UA/NLC IMK–IAA temperature dataset is reliable for scientific analysis in the full measurement vertical range for the MA (18–102 km) and the NLC (39–102 km) observations and from 42 to 115 km for the UA observations. The random temperature errors, dominated by the instrumental noise, are typically less than 1 K below 60 km, 1–3 K at 60–70 km, 3–5 K at 70–90 km, 6–8 K at 90–100 km, 8–12 K at 100–105 km and 12–20 K at 105–115 km. Random pointing correction errors, also mainly arising from instrumental noise, are on average 50 m for tangent altitudes up to 60 km and decrease linearly to values smaller than 20 m for altitudes above 95 km. The vertical resolution is 3 km at altitudes below 50 km, 3–5 km at 50–70 km, 4–6 km at 70–90 km, 6–10 km at 90–100 km and 8–11 km at 100–115 km. The systematic errors in retrieved temperatures below 75 km are driven by uncertainties in the CO2 spectroscopic data and, above 80 km, by uncertainties in the non-LTE model parameters (including collisional rates and atomic oxygen abundance) and the CO2 abundance. These lead to systematic temperature errors of less than 0.7 K below 55 km, 1 K at 60–80 km, 1–2 K at 80–90 km, 3 K at 95 km, 6–8 K at 100 km, 10–20 K at 105 km and 20–30 K at 115 km. Systematic errors in the tangent altitude correction, mainly arising from CO2 spectroscopic uncertainties, are 250 m at 20 km, 200 m at 40–60 km, 100 m at 80 km and smaller than 50 m above 90 km. The consistency between the MA/UA/NLC and the NOM IMK–IAA datasets is excellent below 70 km (typical 0.5–1 K differences). The comparison of this temperature dataset with co-located Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements shows excellent agreement, with differences typically within 1.5 K below 90 km, 1–3 K at 90–95 km, 1–5 K at 95–100 km, 1–8 K at 100–105 km and 1–10 K above. The agreement with SABER improves with respect to previous MIPAS IMK–IAA data versions.

Studies of noctilucent clouds from the stratosphere during the SONC balloon-borne experiment in 2021

On the night 16–17 August 2021, a balloon-borne experiment called Stratospheric Observations of Noctilucent Clouds (SONC) was successfully performed. A big scientific balloon, having onboard three automated cameras for studies of noctilucent clouds (NLC), was launched to 32.7 km altitude from Esrange (northern Sweden). All three NLC cameras and electronics were completely operational in the stratosphere for more than 10 h at low temperatures of about −30 °C. Two wide angle cameras registered an extended NLC field of about 1700 km long in the twilight sky sector from the north-west to the north-east of Esrange. NLC were of a moderate brightness and were located at high latitudes between 68° and 71°N. The NLC field was located in a cold area (138–142 K) below the frost point temperature (145–148 K) in the mesopause region that was confirmed by Aura/MLS satellite and Esrange lidar measurements. The balloon-borne NLC measurements were accompanied by ground-based lidar and radar measurements. The latter have registered Polar Mesosphere Summer Echoes (PMSE) in the same volume of the summer mesopause along with NLC observed from the stratosphere that has been performed for the first time above northern Scandinavia. We describe the technique and method of the NLC observation from the stratosphere as well as present the first scientific results of the SONC experiment.

Capability of airline jets as an observation platform for noctilucent clouds at middle latitudes

The exact occurrence frequency of noctilucent clouds (NLCs) in middle latitudes is significant information because it is thought to be sensitive to long-term atmospheric change. We conducted NLC observation from airline jets in the Northern Hemisphere during the summer 2019 to evaluate the effectiveness of NLC observation from airborne platforms. By cooperating with the Japanese airline All Nippon Airways (ANA), imaging observations of NLCs were conducted on 13 flights from Jun 8 to Jul 12. As a result of careful analysis, 8 of these 13 flights were found to successfully detect NLCs from middle latitudes (lower than 55° N) during their cruising phase. Based on the results of these test observations, it is shown that an airline jet is a powerful tool to continuously monitor the occurrence frequency of NLCs at midlatitudes which is generally difficult with a polar orbiting satellite due to sparse sampling in both temporal and spatial domain. The advantages and merits of NLC observation from jets over satellite observation from a point of view of imaging geometry are also presented.

Corrigendum to the Reply to ‘Critical review on the paper: The earliest datable noctilucent cloud observation (Parma, Italy AD 1840)’

The first aim of this corrigendum is to point out and correct calculation errors on solar depression angle and azimuth angle in Bertolin and Domínguez-Castro (2020a, 2020b). The second aim is to recognize that these calculations are correct in Dalin (2020). The third aim is to analyze the chances of Antonio Colla to observe the noctilucent cloud (NLC) taking into account the correct calculations of the twilight sky arc determining the illuminated area of an NLC and the uncertainties in the Colla’s observation report.

Reply to the ‘Critical review on the paper: The earliest datable noctilucent cloud observation (Parma, Italy AD 1840)’

In this reply, the aim of the authors is to correct the calculation errors on solar depression angle and azimuth angle as recognized by Dr. Dalin in his critical review. However, these updated and corrected calculations do not affect the possibility for Antonio Colla of having observed the Noctilucent Cloud (NLC) plausible both in the direction and for the duration he described in his observations. In this reply, the authors offer two different interpretations in this regard.

A critical review of the paper ‘The earliest datable noctilucent cloud observation (Parma, Italy, AD 1840)’

In the present critical review, my aim is to address serious calculation mistakes made by the authors. I do not want to review their interpretation of a given observation on 18 June 1840 made by Antonio Colla, who was a professor of Astronomy and Meteorology at the University of Parma. There is no sense interpreting Colla’s observation since the basic astronomical calculations have been made incorrectly by the authors Chiara Bertolin and Fernando Domínguez-Castro. Summarizing, in theory and practice, astronomer Antonio Colla could not have observed noctilucent clouds (NLC) at Parma on 18 June 1840. That is why the conclusions of the present paper are not valid.

Stratospheric observations of noctilucent clouds: a new approach in studying middle- and large-scale mesospheric dynamics

Abstract. The Stratospheric Observations of Noctilucent Clouds (SONC) experimental campaign was conducted on the night of 5–6 July 2018 with the aim of photographing noctilucent clouds (NLCs) and studying their large-scale spatial dynamics at scales of 100–1450 km. An automated high-resolution camera (equipped with a wide-angle lens) was lifted by a stratospheric sounding balloon to 20.4 km altitude above the Moscow region in Russia (∼56∘ N, 41∘ E), taking several hundreds of NLC images during the flight that lasted 1.7 h. The combination of a high-resolution camera and large geographic coverage (∼1500 km) has provided a unique technique of NLC observations from the stratosphere, which is impossible to currently achieve from either the ground or space. We have estimated that a horizontal extension of the NLC field as seen from the balloon was about 1450×750 km, whereas it was about 800×550 km as seen from the ground. The NLC field was located in a cold area of the mesopause (136–146 K), which was confirmed by satellite measurements. The southernmost edge of the NLC field was modulated by partial ice voids of 150–250 km in diameter. A medium-scale gravity wave had a wavelength of 49.4±2.2 km and an amplitude of 1.9±0.1 km. The final state of the NLC evolution was represented by thin parallel gravity wave stripes. Balloon-borne observations provide new horizons in studies of NLCs at various scales from metres to thousands of kilometres. Here we present a review paper on our experiment describing the initial results. Detailed studies on the time evolution of the cloud movements will be done in the future.

The earliest datable noctilucent cloud observation (Parma, Italy, AD 1840)

Noctilucent clouds (NLCs) are an uncommon phenomenon that provides information about the conditions and dynamics of the mesosphere. The first observation of NLCs was recorded in 1884/1885, following Krakatoa’s eruption in 1883. The literature speculates that this observation was trigged by the injection of millions of tons of H2O by the Krakatoa into the stratosphere. We have discovered that 43 years before Krakatoa, Antonio Colla observed an NLC in Parma. He was a meticulous astronomer and meteorologist with special interest in astronomical and atmospheric phenomena occurring during twilight. On 18 June 1840, from 21:00 to 22:15 (Local Mean Sideral Time), Antonio Colla observed a ‘ phosphoric cloud’. Analysis of the Colla’s description, the local sky and the condition of the observation proves that he was recording an NLC. This finding forces to develop a new hypothesis to explain the early NLC observations and encourages the rescue of NLC observations from documentary sources.

Simultaneous observations of NLCs and MSEs at midlatitudes: implications for formation and advection of ice particles

Abstract. We combined ground-based lidar observations of noctilucent clouds (NLCs) with collocated, simultaneous radar observations of mesospheric summer echoes (MSEs) in order to compare ice cloud altitudes at a midlatitude site (Kühlungsborn, Germany, 54∘ N, 12∘ E). Lidar observations are limited to larger particles (>10 nm), while radars are also sensitive to small particles (<10 nm), but require sufficient ionization and turbulence at the ice cloud altitudes. The combined lidar and radar data set thus includes some information on the size distribution within the cloud and through this on the “history” of the cloud. The soundings for this study are carried out by the IAP Rayleigh–Mie–Raman (RMR) lidar and the OSWIN VHF radar. On average, there is no difference between the lower edges (zNLClow and zMSElow). The mean difference of the upper edges zNLCup and zMSEup is ∼500 m, which is much less than expected from observations at higher latitudes. In contrast to high latitudes, the MSEs above our location typically do not reach much higher than the NLCs. In addition to earlier studies from our site, this gives additional evidence for the supposition that clouds containing large enough particles to be observed by lidar are not formed locally but are advected from higher latitudes. During the advection process, the smaller particles in the upper part of the cloud either grow and sediment, or they sublimate. Both processes result in a thinning of the layer. High-altitude MSEs, usually indicating nucleation of ice particles, are rarely observed in conjunction with lidar observations of NLCs at Kühlungsborn.

Response of noctilucent cloud brightness to daily solar variations

For the first time, long-term data sets of ground-based observations of noctilucent clouds (NLC) around the globe have been analyzed in order to investigate a response of NLC to solar UV irradiance variability on a day-to-day scale. NLC brightness has been considered versus variations of solar Lyman-alpha flux. We have found that day-to-day solar variability, whose effect is generally masked in the natural NLC variability, has a statistically significant effect when considering large statistics for more than ten years. Average increase in day-to-day solar Lyman-α flux results in average decrease in day-to-day NLC brightness that can be explained by robust physical mechanisms taking place in the summer mesosphere. Average time lags between variations of Lyman-α flux and NLC brightness are short (0–3 days), suggesting a dominant role of direct solar heating and of the dynamical mechanism compared to photodissociation of water vapor by solar Lyman-α flux. All found regularities are consistent between various ground-based NLC data sets collected at different locations around the globe and for various time intervals. Signatures of a 27-day periodicity seem to be present in the NLC brightness for individual summertime intervals; however, this oscillation cannot be unambiguously retrieved due to inevitable periods of tropospheric cloudiness.

Analysis of small-scale structures in lidar observations of noctilucent clouds using a pattern recognition method

Noctilucent clouds (NLC) have been observed with the ALOMAR Rayleigh/Mie/Raman lidar at 69° N using a temporal resolution of 30s since 2008. We present an approach to identify and analyze the localized small scale wave structures of the varying altitude of the NLC layers in the range of 5–30min that may be caused by gravity waves. Small scale gravity waves breaking in the mesopause region contribute notably to the momentum flux but are difficult to observe and to characterize. The approach is based on a template matching method using generalized structures to be identified in the NLC observations. The new method permits the identification of structures that are present in NLC only for a time too short to appear in a Fourier or wavelet spectrum. Without the need for a continuous time series the method can handle multiple NLC layers and data gaps. In the 2000h of NLC data from the years 2008–2015, we find almost 5000 single wave structures with a total length of 738h. The structures are found on average 400m below the NLC centroid altitude and a large number of the structures has a length at the lower limit of 5min. With the background wind from the meteor radar near ALOMAR a horizontal scale is estimated based on the length of the individual structures. The distribution of horizontal scales shows a peak of wave structures at 15–20km in accordance with the horizontal wavelengths found by ground-based camera observations of NLC.

Mid-latitude mesospheric clouds and their environment from SOFIE observations

Observations from the Solar Occultation For Ice Experiment (SOFIE) on the Aeronomy of Ice in the Mesosphere (AIM) satellite are used to examine noctilucent clouds (NLC) and their environment at middle latitudes (~56°N and ~52°S). Because SOFIE is uniquely capable of measuring NLC, water vapor, and temperature simultaneously, the local cloud environment can be specified to examine what controls their formation at mid-latitudes. Compared to higher latitudes, mid-latitude NLCs are less frequent and have lower ice mass density, by roughly a factor of five. Compared to higher latitudes at NLC heights, mid-latitude water vapor is only ~12% lower while temperatures are more than 10K higher. As a result the reduced NLC mass and frequency at mid-latitudes can be attributed primarily to temperature. Middle and high latitude NLCs contain a similar amount of meteoric smoke, which was not anticipated because smoke abundance increases towards the equator in summer. SOFIE indicates that mid-latitude NLCs may or may not be associated with supersaturation with respect to ice. It is speculated that this situation is due in part to SOFIE uncertainties related to the limb measurement geometry combined with the non-uniform nature of NLCs. SOFIE is compared with concurrent NLC, temperature, and wind observations from Kühlungsborn, Germany (54°N) during the 2015 summer. The results indicate good agreement in temperature and NLC occurrence frequency, backscatter, and height. SOFIE indicates that NLCs were less frequent over Europe during 2015 compared to other longitudes, in contrast to previous years at higher latitudes that showed no clear longitude dependence. Comparisons of SOFIE and the Solar Backscatter Ultraviolet (SBUV) indicate good agreement in average ice water column (IWC), although differences in occurrence frequency were often large.

First identification of lunar tides in satellite observations of noctilucent clouds

Noctilucent clouds (NLCs) are optically thin ice clouds occurring near the polar summer mesopause. NLCs are a highly variable phenomenon subject to different sources of variability. Here we report on a poorly understood mechanism affecting NLCs, i.e., the lunar gravitational tide. We extract remarkably clear and statistically highly significant lunar semidiurnal tidal signatures in NLC occurrence frequency, NLC albedo and NLC ice water content from observations with the Solar Backscatter Ultraviolet (SBUV) satellite instruments using the superposed epoch analysis method applied to a data set covering more than 3 decades. The lunar semidiurnal tide is identified in NLC measurements in both hemispheres. In addition, lunar semidiurnal tidal signatures in polar summer mesopause temperature were extracted from space borne observations with the Microwave Limb Sounder (MLS) and the phases of the lunar tidal signatures in NLC parameters and temperature are demonstrated to be consistent. To our best knowledge these results constitute the first identification of the lunar tide in non-visual NLC observations.

Noctilucent clouds observed from the ground: sensitivity to mesospheric parameters and long-term time series

Long-term systematic observations of noctilucent clouds in the regions of Moscow (Russia), Vilnius (Lithuania), and La Ronge (Canada) are considered. Variables, describing the seasonal activity of noctilucent clouds, are discussed. It is shown that there are no statistically significant trends within time intervals of several recent decades. This result is compared to other known findings on trends in mesospheric clouds. Based on the data of the modern ground-based noctilucent cloud observing network in the northern hemisphere and simultaneous satellite data on mesospheric temperature and humidity, we estimate sensitivity of noctilucent clouds to the relative humidity of the upper mesosphere. Such an approach allows us to discuss possible changes of the upper-mesospheric relative humidity, which are consistent with a zero secular trend in noctilucent cloud activity.

Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes

Abstract. We present small-scale structures and waves observed in noctilucent clouds (NLC) by lidar at an unprecedented temporal resolution of 30 s or less. The measurements were taken with the Rayleigh/Mie/Raman lidar at the ALOMAR observatory in northern Norway (69° N) in the years 2008–2011. We find multiple layer NLC in 7.9% of the time for a brightness threshold of δ β = 12 × 10−10 m−1 sr−1. In comparison to 10 min averaged data, the 30 s dataset shows considerably more structure. For limited periods, quasi-monochromatic waves in NLC altitude variations are common, in accord with ground-based NLC imagery. For the combined dataset, on the other hand, we do not find preferred periods but rather significant periods at all timescales observed (1 min to 1 h). Typical wave amplitudes in the layer vertical displacements are 0.2 km with maximum amplitudes up to 2.3 km. Average spectral slopes of temporal altitude and brightness variations are −2.01 ± 0.25 for centroid altitude, −1.41 ± 0.24 for peak brightness and −1.73 ± 0.25 for integrated brightness. Evaluating a new single-pulse detection system, we observe altitude variations of 70 s period and spectral slopes down to a scale of 10 s. We evaluate the suitability of NLC parameters as tracers for gravity waves.

Small scale structures of NLC observed by lidar at 69°N/69°S and their possible relation to gravity waves

Lidar measurements of noctilucent clouds (NLC) were conducted by the Davis Rayleigh-/Raman-lidar in Antarctica (68.58°S, 77.97°E) and by the Rayleigh-/Mie-/Raman-lidar at the ALOMAR observatory in northern Norway (69.28°N, 16.01°E). We compare southern and northern hemisphere NLC at time scales of 10min to several hours using multi-year datasets (four seasons at ALOMAR, 2008–2011, and nine seasons at Davis, 2001/2002 to 2009/2010). NLC characteristics studied include the vertical structure of NLC layers, the duration of NLC layers as well as the apparent downward motion of NLC layers with time. We find multiple layers during 9% of all NLC observations with vertical separations of double layers between 1.5 and 3km. The mean downward progression of NLC with measurement time is −0.3km/h and comparable at Davis and ALOMAR. We find no general spatial tilt of the layer at ALOMAR but individual layers show up to 2km altitude difference at 40km horizontal separation. Typical NLC observations at both stations last about 5 hours, hinting at horizontal extents of about 700km, and reoccur after approximately 10 hours. This is in the range of mid-frequency gravity waves (GW). On short-time scales NLC characteristics are presumably impacted by small scale processes in the vicinity of the clouds, generated by e.g. breaking GW. In addition, we discuss a possible relation to GW by looking at the influence of stratospheric wind conditions on NLC layer characteristics at 69°S.

Morphology of polar mesospheric clouds as seen from space

The Aeronomy of Ice in the Mesosphere (AIM) mission was launched in April 2007 and has completed observation of five northern hemisphere and four southern hemisphere seasons. One of the instruments aboard AIM, the Cloud Imaging and Particle Size (CIPS) Experiment produces high resolution images of Polar Mesospheric Clouds (PMCs) from space that reveal several interesting cloud structures in finer detail compared to previous space-based observations and on a larger scale than is commonly seen from ground based observations. We present the first classification of PMC structures as seen from space. Apart from Veils, Bands, and Whirls (Type I, II, and IV structures as identified in ground-based observations of noctilucent clouds (NLCs)) we also identify several structures that we denote as “Voids”, “Ice Rings”, “Fronts”, and “Vortex-like structures”. These structures are larger in scale compared to similar structures observed in ground-based NLC images. The structural similarity of several of the identified features in these space-based PMC images to those seen in tropospheric clouds and wintertime mesospheric airglow images suggests that similar processes (e.g., gravity waves, convective instability, Kelvin Helmholtz instability, turbulence etc.) influence the summer mesosphere.

Notes on historical aspects on the earliest known observations of noctilucent clouds

Abstract. The present paper considers historical aspects of the earliest known observations of noctilucent clouds (NLCs). The 1884 and 1885 are discussed by considering important historical citations by the pioneers of the earliest known observations of noctilucent clouds. For the first time in NLC studies, we consider seven major volcanic eruptions: Laki in 1783, Mount St. Helens in 1800, Tambora in 1815, Galunggung in 1822, Cosigüina in 1835, Shiveluch in 1854 and Askja in 1875. These all preceded the catastrophic 1883 eruption of Krakatoa, which despite having a lesser magnitude than Tambora in 1815, had pronounced effects on the atmosphere. These eruptions represent possible triggers for the appearance of NLCs. For the first time, we publish an unknown, in English-speaking literature, historical fact on the first determinations of the altitude of noctilucent clouds made by two Russian astronomers V. K. Tseraskii and A. A. Belopolskii on 26 June 1885, who managed to infer the altitude of the clouds in the range of 73–83 km, that is, for the first time, demonstrating the possible existence of the clouds at great altitudes in the Earth's atmosphere. Moreover, V. K. Tseraskii was the first observer to photograph noctilucent clouds in 1885 or 1886, which is 1–2 yr before the German astronomer O. Jesse, who owns the first published images of noctilucent clouds. The photographs made by V. K. Tseraskii, unfortunately, did not reach us.

On the horizontal and temporal structure of noctilucent clouds as observed by satellite and lidar at ALOMAR (69N)

Simultaneous and common volume observations of Noctilucent Clouds (NLC) and Polar Mesospheric Clouds (PMC) have been performed above the ALOMAR research station in Northern Norway (69°N, 16°E) from ground and space, respectively. A detailed case study on August 5, 2008 shows that the measured particle sizes and T‐matrix simulations of the optical properties allow to combine the two observation techniques. From the ground, the observations were performed by lidar sounding of the temporal evolution of the cloud at two locations separated by about 40 km, before, during and after the coincidence. From space, the CIPS instrument onboard the AIM satellite observed the horizontal structure of the cloud. Using mesospheric radar wind measurements at ALOMAR the advection of the cloud particles is calculated and the temporal evolution of the cloud as seen from ground is compared with the horizontal structure observed from satellite. This comparison allows estimation of the timescales during which the clouds behave as passive tracers. We find that during this case study cloud structures larger than about 5 km × 5 km and oscillations slower than about one minute behaved like a passive tracer for up to one hour corresponding to horizontal scales of about 300 km. However, if the cloud shows wave structures with brightness modulations of 20% microphysical changes might take place on scales of minutes and kilometers.