Alexander E. Kozlovsky

University of Oulu · Sodankylä Geophysical Observatory

Atmospheric gravity waves and traveling ionospheric disturbances can be observed in the neutral atmosphere and the ionosphere at a wide range of spatial and temporal scales. Especially at medium scales, these oscillations are often not resolved in general circulation models and are parameterized. We show that ionospheric disturbances forced by upwa...

We investigated statistically the orientation of about 10,000 auroral arcs observed during 2016–2021 in Abisko (68.36°N, 18.81°E, Sweden) in the equatorward part of the nightside auroral oval. The observations were made between 19 and 06 magnetic local time (MLT). On average, the orientation of the arcs, that is, the angle between an arc and the We...

The potential of deep learning for the investigation of medium scale traveling ionospheric disturbances (MSTIDs) have been exploited through the Sodankylä rapid-run ionosonde in this statistical study. The complementing observations of the Sodankylä ionosonde with those of the Sodankylä meteor radar reveals the diurnal and seasonal occurrence ra...

Atmospheric Gravity Waves (AGWs) forced in the lower atmosphere are known to have a significant impact on the mesosphere and lower thermosphere (MLT) region. In the ionosphere, they can generate Medium-Scale Traveling Ionospheric Disturbances (MSTIDs). These disturbances roughly occur on time scales of 15−80 min and are therefore often parametrized...

The Hunga Tonga–Hunga Ha′apai volcano eruption was a unique event that caused many atmospheric phenomena around the globe. In this study, we investigate the atmospheric gravity waves in the mesosphere/lower-thermosphere (MLT) launched by the volcanic explosion in the Pacific, leveraging multistatic meteor radar observations from the Chilean Observa...

Atmospheric Gravity Waves and Traveling Ionospheric Disturbances can be observed in the neutral atmosphere and the ionosphere at a wide range of spatial and temporal scales. Especially at medium scales, these oscillations are often not resolved in general circulation models and are parameterized. We show that ionospheric disturbances forced by upwa...

Plain Language Summary High up in our atmosphere lies the mesosphere/lower thermosphere region (80–100 km); an important transition zone between the atmosphere below and space above. Existing studies indicate that this region is changing (cooling and contracting) in response to increasing greenhouse gas emissions, quite unlike the net warming we se...

The Hunga Tonga-Hunga Ha‘apai volcano eruption was a unique event that caused many atmospheric phenomena around the globe. In this study, we investigate the atmospheric gravity waves in the mesosphere/lower thermosphere (MLT) launched by the volcanic explosion in the Pacific leveraging multistatic meteor radar observations from the Chilean Observat...

Meteor radars have become widely used instruments to study atmospheric dynamics, particularly in the 70 to 110 km altitude region. These systems have been proven to provide reliable and continuous measurements of horizontal winds in the mesosphere and lower thermosphere. Recently, there have been many attempts to utilize specular and/or transverse...

In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochro...

Meteor radars have become a widely used instrument to study atmospheric dynamics, in particular in the 70 to 110 km altitude region. These systems have been proven to provide reliable and continuous measurements of horizontal winds in the mesosphere and lower thermosphere. Recently, there have been many attempts to utilize specular/transverse scatt...

In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras such as pulsating auroras (PsAs) to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochroma...

Meteor radars have been proven to be valuable assets in investigating and monitoring mesosphere/lower thermosphere winds for the last two decades. In this study we present a comparison of almost continuous meteor radar measurements obtained from six meteor radars located at mid- and polar conjugate latitudes in both hemispheres. For this purpose we...

Using data of the all‐sky interferometric meteor radar (SKiYMET, 36.9 MHz) operating in the Sodankylä Geophysical Observatory (67°22′N, 26°38′E, Finland) we found a specific type of polar mesosphere summer echo (PMSE), the power of which exhibits irregular variations at a frequency of the order of a few Hz. We classified such radar echoes as pulsat...

Ground-based remote sensing of atmospheric parameters is often limited to single station observations by vertical profiles at a certain geographic location. This is a limiting factor for investigating gravity wave dynamics as the spatial information is often missing, e.g., horizontal wavelength, propagation direction or intrinsic frequency. In this...

Thermal and dynamic perturbations in the polar upper stratospheric/mesosphere‐lower thermosphere in the Arctic winter of 2019–2020 as measured by a meteor radar at 67°N, Aura Microwave Limb Sounder and reanalysis are presented. The most severe disturbances occur from late December to mid‐January, while the rest of the winter is relatively stable. M...

Long-term and continuous observations of mesospheric–lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on timescales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere–lower thermosphere climate, and they are valuable t...

The Draconid meteor shower shows strong bursts of activity at irregular intervals, with nearly no activity in intervening years. Five outbursts of the Draconid meteor shower were observed with specular meteor radars in Canada and Europe between 1999 and 2018. The outbursts generally lasted between 6 and 8 hours, and most were not fully visible at a...

The Draconid meteor shower shows strong bursts of activity at irregular intervals, with nearly no activity in intervening years. Five outbursts of the Draconid meteor shower were observed with specular meteor radars in Canada and Europe between 1999 and 2018. The outbursts generally lasted between 6 and 8 hours, and most were not fully visible at a...

The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67∘ N, 27∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic...

For 2 decades, meteor radars have been routinely used to monitor atmospheric temperature around 90 km altitude. A common method, based on a temperature gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by fitting a linear regression mode...

Meteor phenomena cause ionized plasmas that can be roughly divided into two distinctly different regimes: a dense and transient plasma region co-moving with the ablating meteoroid and a trail of diffusing plasma left in the atmosphere and moving with the neutral wind. Interferometric radar systems are used to observe the meteor trails and determine...

Ground-based remote sensing of atmospheric parameters is often limited to single station observations of vertical profiles at a certain geographic location. This can be a limiting factor to investigating gravity wave dynamics. In this study we present a new retrieval algorithm for multi-static meteor radar networks to obtain tomographic 3D wind fie...

In the middle atmosphere, spring transition is the time period where the zonal circulation reverses from winter westerly to summer easterly which has a strong impact on the vertical wave propagation influencing the ionospheric variability. The spring transition can be rapid in form of a final sudden stratospheric warming (SSW, mainly dynamically dr...

In the middle atmosphere, spanning the stratosphere and mesosphere, spring transition is the time period where the zonal circulation reverses from winter westerly to summer easterly which has a strong impact on the vertical wave propagation influencing the tropospheric and ionospheric variability. The spring transition can be rapid in form of a fin...

In this study, we cross-compare the nudged models Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) and Whole Atmosphere Community Climate Model Extended Version (Specified dynamics) ( WACCM-X(SD)), a free-running version of Upper Atmosphere ICOsahedral Non-hydrostatic (ICON-UA) with six meteor radars located at conjugate pol...

Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable...

In the middle atmosphere, spring transition is the time period where the zonal circulation reverses from westerly in winter to easterly in summer which has a strong impact on the vertical wave propagation influencing the variability of the ionosphere. The spring transition itself can be rapid in form of a final sudden stratospheric warming (SSW, ma...

For two decades meteor radars have been routinely used to monitor temperatures around the 90 km altitude. A common method, based on a temperature-gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by fitting a linear regression model in t...

This paper characterizes the impacts of sudden stratospheric warmings (SSWs) and mesospheric coolings (MCs) on the light species distribution (i.e., helium [He], and atomic hydrogen [H]) of the thermosphere using a combined data‐modeling approach. Performing a set of numerical experiments with a general circulation model whose middle atmospheric dy...

Meteor phenomena cause ionized plasmas that can be roughly divided into two distinctly different regimes: a dense and transient plasma region co-moving with the ablating meteoroid and a trail of diffusing plasma left in the atmosphere and moving with the neutral wind. Interferometric radar systems are used to observe the meteor trails and determine...

Meteoroids entering the Earth's atmosphere produce ionized trails, which are detectable by radio sounding. Cylindrical underdense (and partly overdense) trails form a great majority of meteor echoes received by meteor radars (MRs). Additionally, the long‐lived nonspecular (LLNS) meteor echoes are received from irregularities of ionization generated...

Comprehensive analysis of a moderate 600 nT substorm was performed using simultaneous optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. The substorm o...

We study the properties and geoeffectiveness of solar wind high-speed streams (HSSs) emanating from coronal holes and associated with stream interaction regions (SIRs). This paper presents a statistical study of 588 SIR/HSS events with solar wind speed at 1 AU exceeding 500 km/s during 1995-2017, encompassing the decline of solar cycle 22 to the de...

Abstract. Using data of the ionosonde in Sodankyla, (SOD, 67° N, 27° E, Finland), variations of the critical frequency of o-mode radiowave reflected from ionospheric F2 layer (foF2) in 1–5 mHz frequency range and their possible association with long period (Pc5/Pi3) geomagnetic pulsations are studied. For that, a technique of automatic detection of...

The SKYiMET meteor radar is capable of measuring the height distribution of ionized meteor trails. Observations of the Sodankyla radar (67°N, 23°E) in 2008–2019 are analyzed. A method is applied, based on the median and quartiles of meteor heights, for distinguishing meteor showers from much more intense background sporadic meteors. Since the showe...

Plain Language Summary Auroral hiss is a well‐known type of nighttime natural VLF emission with a noise‐like structure generated by the Cherenkov instability of precipitating soft electrons above the ionosphere. Auroral hiss occurrence up to 39 kHz was studied in the equatorward region of the auroral oval at the Finnish station Kannuslehto (KAN, ML...

Describing the current ionospheric conditions is crucial to solving problems of radio communication, radar, and navigation. Techniques to update ionospheric models using current measurements found a wide application to improve the ionosphere description. We present the results of updating the NeQuick and IRI-Plas empirical ionosphere models using t...

Abstract. Using data of the ionosonde in Sodankyla, (SOD, 67° N, 27° E, Finland), parameters of variations of foF2 critical frequency in the Pc5/Pi3 (1–5 mHz) frequency range are studied. For that, a technique of automatic detection of critical frequency from an ionogram is developed. The variations of foF2 are compared with the Pc5/Pi3 geomagnetic...

We analyse gravity waves in the upper-mesosphere, lower-thermosphere region from high-resolution temperature variations measured by the Rayleigh lidar and OH temperature mapper. From this combination of instruments, aided by meteor radar wind data, the full set of ground-relative and intrinsic gravity wave parameters are derived by means of the nov...

Multi‐instrument observations by a meteor radar (MR), auroral cameras, ionosondes, and ground magnetometers were made in Northern Europe at auroral latitudes (between 64° and 72° corrected geomagnetic latitude) at 22–24 magnetic local time in the substorm growth phase. The southward drifting growth phase auroral arc was associated with enhanced ele...

Comprehensive analysis of a moderate 600-nT substorm was performed with using simultaneous optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. The subst...

We study the properties and geoeffectiveness of solar wind high‐speed streams (HSSs) emanating from coronal holes and associated with stream interaction regions (SIRs). This paper presents a statistical study of 588 SIR/HSS events with solar wind speed at 1 AU exceeding 500 km/s during 1995–2017, encompassing the decline of solar cycle 22 to the de...

We analyze gravity waves in the mesosphere, lower thermosphere region from high-resolution temperature variation measured by Rayleigh lidar and OH temperature mapper. From this combination of instruments, aided by meteor radar wind data, the full set of ground-relative and intrinsic gravity wave parameters are derived by means of the novel WAPITI m...

The study is based on the data of the rapid-run ionosonde at the Sodankylä Geophysical Observatory at auroral latitude (L = 5.25) which routinely performs one-minute sounding since 2007. This dataset allows a unique opportunity for investigating possible effects of ultra-low frequency (ULF, 1–7 mHz) waves in the auroral ionosphere. Suitable observa...

A comprehensive analysis of the polar substorm registered by IMAGE network stations close to the poleward boundary of the auroral oval has been carried out with THEMIS, CLUSTER, and GEOTAIL satellites in favorable positions for analysis. The observation interval is characterized by a low level of geomagnetic activity. The polar substorm looked like...

Meteoroids constantly enter the Earth's atmosphere, collide with atmospheric molecules, and heat and ablate in the sufficiently dense atmospheric layers at heights between 70 and 110 km. It is still a problem to recognize properties of the meteor streams among the sporadic background. The meteor radar observations at Sodankylä Geophysical Observato...

Our aim is to understand the effect of high-speed stream events on the high-latitude ionosphere and more specifically the decrease of the foF2 frequency during the entire day following the impact. First, we have selected one summertime event, for which a large data set was available: Super Dual Auroral Radar Network (SuperDARN) and European Incoher...

Using data from the Sodankylä Geophysical Observatory (67°22'N, 26°38'E, Finland) meteor camera from the whole year 2015, we identified and investigated 28 optical meteors with accompanying ionization trails unambiguously detected by the Sodankylä Geophysical Observatory ionosonde, which sounded the ionosphere once per minute with frequency rising...

Geomagnetic storms and substorms are the principal elements of the disturbed Space Weather conditions. The aim of the study was to reveal the ionospheric precursors that can be used to forecast geomagnetic disturbance beginning. To study the ionospheric processes before, during and after magnetic storms and substorms data from Sodankylä Geophysical...

This study investigates the contribution of energetic (E > 30 keV) particle precipitation during a pulsating aurora event over Kilpisjärvi (L = 6.2) on 26 February 2014. It is based on the comparison of auroral blue-line emission (427.8 nm) data from an all-sky camera and cosmic noise absorption (CNA) data obtained from a multibeam experiment of th...

The inter-annual variability, climatological mean wind and tide fields in the northern polar mesosphere/lower thermosphere region of 82–98 km height are studied using observations by the meteor radar which has operated continuously during solar cycle 24 (from December 2008 onward) at the Sodankylä Geophysical Observatory (67N, 26E). Summer mean zon...

On 9 December 2009 at about 07 UT a solid propellant 36.8 t ballistic rocket was self-destroyed at an altitude of 170–260 km, at a distance of about 500 km to the east of Sodankylä Geophysical Observatory (SGO, 67°22′N, 26°38′E, Finland). After 2–3 h the SGO meteor radar (operating at a frequency 36.9 MHz) received unusual echoes, which indicate tu...

The effect of solar wind high-speed streams (HSSs) on energetic particle precipitation at auroral and subauroral latitudes (L = 3.8–5.7) is studied by using cosmic noise absorption (CNA) data measured by the Finnish riometer chain during 95 HSS events occurring between 2006 and 2008. The data are divided into “long” and “short” HSS events, dependin...

Two Rayleigh lidars were employed at a southern-hemisphere mid-latitude site in New Zealand (45 °S) and a northern-hemisphere high-latitude site in Finland (67 °N) in order to observe gravity waves between 30 and 85 km altitude under wintertime conditions. Two-dimensional wavelet analysis is used to analyze temperature perturbations caused by gravi...

Earlier studies demonstrated that the monitoring of the ionospheric total electron content (TEC) by global satellite navigation systems is a powerful method to study the propagation of transient disturbances in the ionosphere, induced by internal gravity waves. This technique has turned out to be sensitive enough to detect ionospheric signatures of...

This paper presents a comparison between standard ionospheric parameters manually and automatically scaled from ionograms recorded at the high-latitude Sodankylä Geophysical Observatory (SGO, ionosonde SO166, 64.1° geomagnetic latitude), located in the vicinity of the auroral oval. The study is based on 2610 ionograms recorded during the period Jun...

Meteor radar observations at the Sodankylä Geophysical Observatory (67° 22' N, 26° 38' E, Finland) indicate that the mesospheric temperature derived from meteor decay times is systematically underestimated by 20 – 50 K during the Geminids meteor shower which has peak on 13 December. A very good coincidence of the minimum of routinely calculated tem...

We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and di...

Solar wind high-speed streams (HSSs) are the most important source of geomagnetic disturbances during the declining phase of the solar cycle. Their ionospheric response, especially at high latitudes, is not fully understood yet. We carried out a phase-locked superposed epoch analysis to study the effects of HSSs on the high-latitude ionospheric F r...

We investigate a non-typical very low frequency (VLF) 1–4 kHz hiss representing a sequence of separated noise bursts with a strange " mushroom-like " shape in the frequency–time domain, each one lasting several minutes. These strange afternoon VLF emissions were recorded at Kannuslehto (KAN, ϕ = 67.74 • N, λ = 26.27 • E; L ∼ 5.5) in northern Finlan...

According to results of sounding of the lower ionosphere at altitudes of about 100 km, the duration of radio reflections from sufficiently dense ionized meteor trails, which characterizes their lifetime, can reach a few tens of seconds to several tens of minutes. This is much longer than the characteristic spreading time (on the order of fractions...

The upper mesospheric neutral winds and temperatures have been derived from continuous meteor radar (MR) measurements over Sodankyla, Finland in 2008–2014. Under conditions of low solar activity pronounced sudden mesospheric coolings linked to the major stratospheric warming (SSW) in 2009 and a medium SSW in 2010 are observed while there is no obse...

A total solar eclipse is a spectacular natural phenomenon whose consequences over the underlying ionosphere and thermosphere remain complex and not fully explained. On 20 March 2015, a total solar eclipse lasting almost 2 hours passed over the Atlantic Ocean, then over Svalbard. These specific regions are extremely interesting as they are covered b...

We compare simultaneous observations of long-period ultra-low-frequency (ULF) wave activity from a Svalbard/IMAGE fluxgate magnetometer latitudinal profile covering the expected cusp geomagnetic latitudes. Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband Pc5 waves are found to be a ubiquitous element of ULF activity in the dayside high-...

We present SKiYMET meteor radar (MR), VHF (36.9 MHz), observations from Sodankylä Geophysical Observatory, and report on the unusual echoes, which were detected at low elevation on the northern horizon, typically during substorms. These echoes have a near-zero Doppler shift, relatively low power, but with a sharp rise to the power peak, short lifet...

Rapid-run ionosonde installed in the high-latitude Sodankylä Geophysical Observatory enable us to observe for the first time extraordinary details of E-F region coupling process in high latitude ionosphere during geomagnetically quiet period. We present an example on August, 15, 2009 when a dense, patchy sporadic E layer was detected. Associated wi...

We report on ionosonde and meteor radar observations made in Sodankylä Geophysical Observatory (SGO, 67° 22' N, 26° 38' E, Finland) on December 9, 2009, during a test launch of the Russian solid propellant military missile. Due to a technical problem the missile was self-destroyed around 07 UT at an ionospheric height (near 200 km altitude) over th...

We study properties of quasiperiodic (QP) VLF emissions recorded on December 24, 2011 during the VLF campaign in Northern Finland. The main attention is paid to interrelationships between different characteristic periods in the QP spectra. In particular, we analyze regular variations in the QP repetition intervals (1 – 10 min) during the event from...

2007, the Sodankylä Geophysical Observatory routinely performs vertical ionosphere soundings once per minute, using a frequency-modulated continuous-wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. We used these data to study traveling ionospheric disturbances (TIDs) during 10-16 local time. The observations were made between April 2007...

Non-typical long lasting quasi-periodic (QP) VLF emissions have been recorded in Northern Finland at L∼5.3 during the recent Finnish VLF campaign held in December 2011. Contrary to the typical daytime QP emissions, the night-time and early morning (00–05 UT) event reported here for the first time is a sequence of 1.5–3.5 kHz noise bursts lasting fo...

Based on a new database on positions of the auroral oval boundaries including measurements made by the IMAGE satellite in 2000–2002 with correct determination of the glow boundaries, statistical estimations of the latitudinal position of the polar cap boundary (PCB) are obtained depending on the IMF B y and B z , and the PCB evolution during a magn...

Structures controlled by the IMF By sign and season of the year have been detected based on the decomposition of field-aligned current maps constructed using magnetic field measurements on polar low-orbiting satellites. It has been indicated that field-aligned currents have identical structures, composed of the main polar circular current and the r...

Since April 2007 the Sodankyla Geophysical Observatory in Northern Finland (geomagnetic latitude 64 deg.) routinely performs vertical ionosphere sounding ones per minute, with using frequency-modulated continuous-wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. This allows studies of rapid variations in the auroral ionosphere. In particu...

To identify the physical nature of Pc5 pulsations and to determine relative contributions of different MHD modes into their structure, we introduce the method of apparent impedance. An approximate analytical relationship from the theory of ULF wave transmission through a thin ionosphere can be compared with the measured ratio between simultaneous i...

Seismic broad-band sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of hi...

The exceptionally high solar wind stream activity in 2003 caused a record intensity in the auroral electrojet currents, leading to a major reduction of the horizontal field at auroral latitudes and to a notable strengthening of the vertical geomagnetic field in the polar cap. This strengthening is clearly visible in the observatory annual values as...

We used the dataset obtained from the EISCAT Svalbard Radar during 2000–2008 to study statistically the ionospheric convection in a vicinity of the polar cap boundary as related to IMF By conditions separately for northward and southward IMF. The effect of IMF By is manifested in the intensity and direction of the azimuthal component of ionospheric...

The EISCAT Svalbard radar (ESR) monitors plasma parameters in the ionospheric region that is frequently located near the polar cap boundary. The SuperDARN radar at Hankasalmi, Finland, detects coherent echoes from this region, and these echoes typically show increased spectral width. We consider data of joint ESR and SuperDARN observations to show...

Seismic broad-band sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of hi...

The EISCAT Svalbard Radar (ESR) monitors plasma parameters in the ionospheric region that is frequently located near the polar cap boundary. The SuperDARN radar at Hankasalmi, Finland detects coherent echoes from this region and these echoes typically show increased spectral width. We consider data of joint ESR and SuperDARN observations to show th...

We present an overview of the Finnish experiments with European Incoherent Scatter (EISCAT) radar on Svalbard, which were performed during 2004 - 2009 to study ionospheric electric fields and currents in a vicinity of high-latitude (around 75 deg. MLAT) auroral arcs. The most important parameter is the electric field component perpendicular to an a...

We present the results of using the statistical model of field-aligned currents (FACs) based on satellite data and the numerical model of the electric potential distribution in order to detect the asymmetric part in FAC structures and ionospheric plasma convection controlled by the IMF azimuthal (B y ) component at different seasons of the year. Th...