Rocket Mission Conjures a Ghostly Noctilucent Cloud

Night-shining clouds can be diagnostic tools to better understand how human activity is changing the meteorology of the mesosphere.

Waves at the edge of space revealed by noctilucent cloud observations using camera and lidar

<p>Noctilucent clouds (NLC) exist at an altitude of about 83 km during the summer season at middle and polar latitudes. They consist of icy particles that exist in the polar summer mesopause region where the atmosphere is about 100 K colder than expected from pure radiative forcing. Dynamical effects, for example the dissipation of gravity waves, play an important role in the global circulation finally leading to the cold summer mesopause region. Ever since the first reports on the occurrence of NLC in 1885 the observers noticed distinct structures in the clouds that are most often wave-like. However at times the wave field becomes seemingly chaotic. <br><br>State of the art lidar and camera observations of NLC allow studying small-scale structures of tens of meters in the vertical and horizontal direction. Given a high time resolution (about one second), the development of these structures is measured on temporal scales spanning the range from inertia gravity waves to acoustic gravity waves. We will show observations with the RMR-lidars at ALOMAR (Northern Norway at 69°N) and Kühlungsborn (54°N) as well as cameras located nearby these stations. Using these combined observations we study waves and their transition to turbulence.</p>

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.

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.

Towards a Framework for Noctilucent Cloud Analysis

In this paper, we present a framework to study the spatial structure of noctilucent clouds formed by ice particles in the upper atmosphere at mid and high latitudes during summer. We studied noctilucent cloud activity in optical images taken from three different locations and under different atmospheric conditions. In order to identify and distinguish noctilucent cloud activity from other objects in the scene, we employed linear discriminant analysis (LDA) with feature vectors ranging from simple metrics to higher-order local autocorrelation (HLAC), and histogram of oriented gradients (HOG). Finally, we propose a convolutional neural networks (CNN)-based method for the detection of noctilucent clouds. The results clearly indicate that the CNN-based approach outperforms the LDA-based methods used in this article. Furthermore, we outline suggestions for future research directions to establish a framework that can be used for synchronizing the optical observations from ground-based camera systems with echoes measured with radar systems like EISCAT in order to obtain independent additional information on the ice clouds.

Towards a framework for Noctilucent Cloud Analysis

In this paper, we present a framework to study the spatial structure of noctilucent clouds formed by ice particles in the upper atmosphere at mid and high latitude during summer. We study noctilucent cloud activity in optical images taken from three different locations and under different atmospheric conditions. In order to identify and distinguish noctilucent cloud activity from other objects in the scene, we employ linear discriminant analysis (LDA) with feature vectors ranging from simple metrics to higher-order local autocorrelation (HLAC), and histogram of oriented gradients (HOG). Finally, we propose a Convolutional Neural Networks (CNN) based method for the detection of noctilucent clouds. The results clearly indicate that the CNN based approach outperforms LDA based methods used in this article. Furthermore, we outline suggestions for future research directions to establish a framework that can be used for synchronizing the optical observations from ground based camera systems with echoes measured with radar systems like EISCAT in order to obtain independent additional information on the ice clouds.

Mesospheric anomalous diffusion during noctilucent cloud scenarios

The Andenes specular meteor radar shows meteor trail diffusion rates increasing on average by about 10 % at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC after exploring possible contributions from thermal tides. To make this claim, the current study evaluates data from three stations at high, middle, and low latitudes for the years 2012 to 2016 to show that NLC influence on the meteor trail diffusion is independent of thermal tides. The observations also show that the meteor trail diffusion enhancement during NLC cover exists only at high latitudes and near the peaks of NLC layers. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that the relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars at high latitudes.