arXiv subjects

Oleg S. Ugolnikov

Publications and source records attributed to Oleg S. Ugolnikov.

At least 19 recordsLinked to original sources

arXiv2026

Three-Dimensional Velocity Analysis and Particle Size Dynamics from Multi-Site RGB-Photometry of Noctilucent Clouds

A method for measuring the altitude and particle size of noctilucent clouds, based on positioning and photometry from wide-angle three-color cameras, has been developed to determine the three velocity components, particle radius, and its derivative with respect to time for different cloud fragments. The updated method is applied to observational data of bright clouds during the summers of 2023-2025. Meridional motion of the cloud is found to be the principal factor driving the change in particle size. The effect of particle size evolution in the presence of a strong latitudinal temperature gradient is also studied.

physics.ao-ph↗

arXiv2025

Noctilucent Clouds Modulated by Strong 5-day Planetary Wave in 2025: Amplitudes, Phases and Altitudes Based on Ground-Based Observations and Satellite Temperature Data

During the summer season of 2025, noctilucent clouds (NLC) were observed at the latitudes 55-60N from the late May until the late August. A distinct 5-day periodicity in their occurrence emerged following the summer solstice. Analysis of EOS Aura/MLS satellite data revealed that this effect was driven by a westward 5-day planetary wave, the amplitude of which was twice that of any previous northern summer since the start of the EOS Aura measurements in 2005. This study details the evolution of this exceptional planetary wave throughout the summer. Furthermore, NLC altitudes were determined via triangulation and colorimetry and were compared with MLS temperature profiles, enabling the determination of a mean positive phase lag for NLC occurrence relative to the temperature minimum.

physics.ao-ph↗

arXiv2025

Multiple Scattering Effects in Noctilucent Clouds: Numerical Estimation and Application to Altitude and Particle Size Measurements

The simple 3-D radiative transfer model in the atmosphere of the Earth is built for numerical comparison of direct solar radiation and limb scattering background at the definite layer during the deep twilight period at the middle and upper atmosphere. This allows finding the contribution of multiple scattering in the field of high-altitude clouds such as polar stratospheric and noctilucent clouds. This is the factor that can influence the results of altitude and microphysical study of the particles based on the approximation of single scattering. The possible errors caused by this effect are estimated together with the contribution of multiple scattering for different altitudes of the clouds, wavelengths and solar zenith angles. The results are interpreted geometrically and optically, color effects observed for noctilucent clouds are described.

physics.ao-ph↗

arXiv2025

Winter Noctilucent Clouds Following Sudden Stratospheric Warming: First Observations

Mesospheric structures identical to summer noctilucent clouds were observed during the nights of December 17-19, 2024 in Siberian Russia. Basing on the available photo data, the mean altitude of the clouds 70.1+-1.5 km was measured by umbral colorimetric method. This coincided spatially and temporary with deep temperature minimum below 160K in mesosphere, followed the polar vortex displacement and warming of stratosphere below the clouds. The satellite data on temperature and water vapor is used to study the nature of this unexpected event.

physics.ao-ph↗

arXiv2024

Five-years Altitude Statistics of Noctilucent Clouds Based on Multi-Site Wide-Field Camera Survey

The results of simultaneous measurements of noctilucent clouds (NLC) position in a number of ground-based locations are presented. Observational data of 14 bright NLC events over 5 years is used for building the altitude maps of cloud fields using triangulation technique updated for multi-location case. Statistical distribution of NLC altitude and its change during the summer season is considered. Mean NLC altitudes are compared with colorimetric technique based on the same data and simple radiation transfer model. This can be used to check the model and estimate the accuracy of single-camera technique of NLC altitude measurements. Results and methods are suggested for net ground-based survey of noctilucent clouds.

physics.ao-ph↗

arXiv2023

Noctilucent Clouds Altitude and Particle Size Mapping Based on Spread Observations by Ground-based All-sky Cameras

We suggest the procedure of building the maps of noctilucent clouds (NLC) zonal and meridional velocity, mean altitude and particle size based on three-color photometry by identical all-sky RGB-cameras separated by 115 km in a close-meridional direction. The procedure is applied to the bright NLC event on July 3, 2023. The altitude is measured by precise triangulation technique, and effective particle radius is estimated by comparison of each definite NLC fragment intensity and colors at different scattering angles as it is registered from different observation sites. The results are compared with existing photometric methods for average altitude and particle size measurements. A significant difference in evening and morning twilight NLC parameters is found, which is discussed in comparison with existing analysis of diurnal NLC variations.

physics.ao-ph↗

arXiv2022

Cross-Wave Profiles of Altitude and Particle Size of Noctilucent Clouds in the Case of One-Dimensional Small-Scale Gravity Wave Pattern

This paper describes the wide-field three-color observations of an expanded field of noctilucent clouds modulated by a one-dimensional gravity wave. Long wave crests were aligned by a small angle to the solar vertical in the sky. This made possible separate determination of altitude and particle size at different wave phases based on three-color photometry of noctilucent clouds. Thereby, it is possible to use simple optical imaging to record the changes in the parameters of noctilucent clouds when a short-period gravity wave passes by.

physics.ao-ph↗

arXiv2021

Altitude and Particle Size Measurements of Noctilucent Clouds by RGB Photometry: Radiative Transfer and Correlation Analysis

Noctilucent or polar mesospheric clouds have become visually brighter and occurred more frequently during the recent years and decades. The study of possible reasons and relations with climate changes requires data on long-time trends of mean particle size and altitude. Extended worldwide observational data is a good tool for this, and it can be provided by simple RGB-photometry using widely distributed all-sky cameras. Based on observations of bright expanded clouds in summer 2020 and 2021, the method of mean particle size determination is developed, results are validated using the radiative transfer model. The procedure also allows finding the effective 'umbral' altitude of clouds. The correlation of size and altitude of particles is compared with existing lidar data and models of particle growth.

physics.ao-ph↗

arXiv2020

Retrieval of Particle Size Distribution of Polar Stratospheric Clouds Based on Wide-Angle Color and Polarization Analysis

The intensive polar stratospheric vortex in the Arctic that shifted to northern Europe in the winter of 2019-2020 caused low temperatures and the frequent occurrence of polar stratospheric clouds followed by a significant decrease in the total ozone content. Polarimetry and multi-color photometry using all-sky cameras in Lovozero (Murmansk Region, Russia, 68.0 deg N, 35.1 deg E) together with a new method of cloud field separation against the twilight background allowed for finding the light scattering characteristics related to the particle size distribution of polar stratospheric clouds. The results are compared with lidar and balloon experiments. The conditions of the appearance of visually bright polar stratospheric clouds of type I are discussed.

astro-ph.EP↗

arXiv2020

Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry

Measurements of the background intensity and polarization of the twilight sky were conducted during the "purple lights" epoch that was potentially caused by the Raikoke volcano eruption in the summer of 2019. An increase in sky brightness paired with a decrease in polarization was registered, especially noticeable in the dusk segment. Using techniques developed in previous works, altitude distribution and the mean particle size of additional aerosol was found. The mean radius of (0.11 micrometers) is typical for background or moderate eruption conditions, however, aerosols were mostly observed in the upper troposphere and near the tropopause rather than in the stratosphere. A comparison with existing aerosol data after mid-latitude eruptions like the Kasatochi volcano eruption one decade ago showed similar properties, which can be used as confirmation that the "purple lights" event in 2019 was of volcanic nature.

physics.ao-ph↗

arXiv2018

Polarization Analysis and Probable Origin of Bright Noctilucent Clouds with Large Particles in June 2018

A sequence of very bright noctilucent clouds (NLC) was observed in central Russia during the last decade of June, 2018. It followed the meteorite impact 300 km southwards from Moscow in the morning of June 21. Polarization measurements of NLC in a wide range of scattering angles allowed finding the effective size of ice particles forming the clouds. These estimations together with satellite data on gravity waves, temperature, and water vapor mixing ratio during these days help to understand the basic causes of the observed NLC brightness and particle size anomaly.

physics.ao-ph↗

arXiv2018

Optical Depth and Vertical Profile of Stratospheric Aerosol based on Multi-Year Polarization Measurements of the Twilight Sky

The method of detection of light scattering on stratospheric aerosol particles on the twilight sky background is considered. It is based on the data on sky intensity and polarization in the solar vertical at zenith distances of up to 50 deg from the sunset till the moment of the Sun depression to 8 deg below the horizon. The measurements conducted in central Russia since 2011 had shown the negative trend of stratospheric aerosol content, this can be related with the relaxation of the stratosphere after the number of volcanic eruptions during the first decade of XXI century.

physics.ao-ph↗

arXiv2017

Detection of Molecular Scattering Field by Polarization Analysis of Sky Background During the Transitive Twilight and Temperature Measurements near the Stratopause

The simplest version of the method of detection of single molecular scattering basing on the polarization measurements of the twilight sky background by all-sky cameras is considered. The method can be used during the transitive twilight (solar zenith angles 94-98 degrees), when effective single scattering takes place in upper stratosphere and lower mesosphere. The application of the method to the multi-year measurements in the vicinity of Moscow and Apatity allows determination of temperature of these atmospheric layers and estimation of contribution and properties of multiple scattering during the transitive twilight period.

physics.ao-ph↗

arXiv2017

Noctilucent Cloud Particle Size Determination based on Multi-Wavelength All-Sky Analysis

The article deals with the analysis of color distribution in noctilucent clouds (NLC) in the sky based on multi-wavelength (RGB) CCD-photometry provided with the all-sky camera in Lovozero in the north of Russia (68.0 deg N, 35.1 deg E) during the bright expanded NLC performance in the night of August 12, 2016. Small changes in the NLC color across the sky are interpreted as the atmospheric absorption and extinction effects combined with the difference in the Mie scattering functions of NLC particles for the three color channels of the camera. The method described in this paper is used to find the effective monodisperse radius of particles about 55 nm. The result of these simple and cost-effective measurements is in good agreement with previous estimations of comparable accuracy. Non-spherical particles, Gaussian and lognormal distribution of the particle size are also considered.

physics.ao-ph↗

arXiv2017

Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky

Polarization measurements of the twilight background with Wide-Angle Polarization Camera (WAPC) are used to detect the depolarization effect caused by stratospheric aerosol near the altitude of 20 km. Based on a number of observations in central Russia in spring and summer 2016, we found the parameters of lognormal size distribution of aerosol particles. This confirmed the previously published results of the colorimetric method as applied to the same twilights. The mean particle radius (about 0.1 micrometers) and size distribution are also in agreement with the recent data of in situ and space-based remote sensing of stratospheric aerosol. Methods considered here provide two independent techniques of the stratospheric aerosol study based on the twilight sky analysis.

physics.ao-ph↗

arXiv2017

Background Stratospheric Aerosol Investigations Using Multi-Color Wide-Field Measurements of the Twilight Sky

First results of multi-wavelength measurements of the twilight sky background using all-sky camera with RGB-color CCD conducted in spring and summer of 2016 in central Russia (55.2 deg N, 37.5 deg E) are discussed. They show the effect of aerosol scattering at altitudes up to 35 km which significantly increases to the long-wave range (624 nm, R channel). Analysis of sky color behavior during the light period of twilight with account of ozone Chappuis absorption allows retrieving the angle dependencies of scattering on the stratospheric aerosol particles. This is used to find the parameters of lognormal size distribution: median radius about 0.08 microns and width 1.5-1.6 for stratospheric altitude range.

physics.ao-ph↗

arXiv2015

Noctilucent Clouds Polarimetry: Twilight Measurements in a Wide Range of Scattering Angles

Wide-field polarization measurements of the twilight sky background during the several nights with bright and extended noctilucent clouds in central and northern Russia in 2014 and 2015 are used to build the phase dependence of degree of polarization of sunlight scattered by clouds particles in a wide range of scattering angles (from 40 to 130 degrees). This range covers the linear polarization maximum near 90 degrees and large-angle slope of the curve which are most sensitive to the particle size. The method of separation of scattering on clouds particles on the twilight background is presented. Results are compared with T-matrix simulations for different sizes and shapes of ice particles, the best-fit model radius of particles (0.06 microns) and maximum radius (about 0.1 microns) are estimated.

physics.ao-ph↗

arXiv2015

Mesosphere Study by Wide-Field Twilight Polarization Measurements: First Results beyond the Polar Circle

The paper describes the observations and first results of studying the mesosphere temperature and dust based on twilight wide-field polarization analysis using original all-sky camera started in 2015 in Apatity, northern Russia (67.6 deg N, 33.4 deg E). It is the first twilight polarization measurements session conducted in the polar region and the first measurements during the winter and early spring season. The general polarization properties of twilight sky and the separation procedure of single scattering are described. The Boltzmann temperature decrease above 70 km and lack of mesosphere dust that is typical for this season are the key results of the study.

physics.ao-ph↗