Unlike other ground-based optical instruments that are affected by weather conditions, a meteor radar (MR) has the capability of monitoring mesospheric temperature continuously. However, to date, lack of reliable temperature measurements has limited the applicability of MR to its full usefulness. Following a recently developed theory of meteor height distribution, here we present a practical implementation of temperature measurement at the peak meteor heights ($89\pm 1$ km). For the first time, this technique rigorously takes into account the seasonal variability of the meteor mass function (i.e. sensitivity variation) to correct for the systematic biases in meteor radar temperatures. The precision of the measured temperature varies between 4 and 6 per cent. Comparison of SABER measurements on board the TIMED satellite showed that 85 per cent of all simultaneous MR/SABER observations agree within the limit of this precision. In addition, the MR temperature during the well-known Sudden Stratospheric Warming (SSW) in January 2010 has been analysed. The calibrated temperature is shown to correctly replicate the expected prolonged cooling effect in the mesosphere prior to the maximum warming in the stratosphere.

The EISCAT Scientific Association is currently building the most advanced 3-dimensional imaging radar for atmospheric, ionospheric and near-Earth space investigations. The fully steerable, tri-static, phased-array incoherent scatter radar is located in Skibotn (inland from Tromsø, Norway), Karesuvanto (Finland, north of Kiruna), and Kaiseniemi (Sweden, west of Kiruna). The transmit-receive array at Skibotn consists of about 10,000 aerials and ten 91-aerial outrigger receivers in the immediate vicinity. The receive-only arrays of Kaiseniemi and Karesuvanto consist of about 5,000 aerials each. Construction of the facility began after the project kick-off in September 2017. During 2024, EISCAT_3D will gradually begin operations, starting with a seven-element test system and expanding from that. EISCAT_3D will replace the EISCAT mainland radars, i.e. the mono-static, 930-MHz UHF radar at Tromsø and the tri-static, 224-MHz radar at Tromsø with additional receivers at Sodankylä (Finland) and Kiruna (Sweden). The EISCAT Svalbard Radar (ESR) and the Ionospheric Heating facility at Tromsø will not be affected by EISCAT_3D becoming operational. Here we give an status update of the new facility. EISCAT_3D is a European Strategy Forum for Research Infrastructures (ESFRI) Landmark in the Environment domain.

This study investigates the characteristics of medium scale traveling ionospheric disturbances (MSTIDs) relative amplitudes () in the ionospheric E to lower F regions, using the EISCAT VHF radar data measured from 41 daytime runs in years 2008-2024 carried out mostly between UT. Spectral analysis is applied to identify the dominant wave amplitudes and periods, while a cross-correlation method is used to determine the vertical wavelength, . It is observed that the dominant reveal both seasonal and height variations. The amplitudes of MSTIDs observed during winter () are approximately times larger compared to other seasons (2.5). Additionally, exhibit a general increase with height during winter, whereas during other seasons, they show mixed trends. The seasonal dependence of MSTID amplitudes may depend on the pattern of meridional wind direction and the prevailing conditions such as absence or presence of strong mesospheric wind shear for upward propagating gravity waves. The seasonal variation for the altitude behaviors may be subject to the competition between how the neutral density, ion-neutral friction, kinematic viscosity and thermal conductivity varies with altitude. Our estimates of show a gradual/faster increase during winter/summer, corresponding to colder/hotter ionosphere. This suggests that although atmospheric gravity wave-MSTIDs can reach higher altitudes in summer due to faster growth of , they can be less detectable due to lower amplitudes. Furthermore, waves with shorter that would reach the F2-region during winter are more likely to decay at lower altitudes in summer.

Abstract Typical ionosondes operate with >5 min time intervals, which is enough to obtain regular parameters of the ionosphere, but insufficient to observe short‐term processes in the Earth's ionosphere. The key point for this study is to increase the ionosondes data time resolution by automatization of ionogram scaling routine. In this study we show the results of implementation of deep learning approach for ionogram parameters scaling. We trained the model on 13 years ionogram data set of Sodankyla ionosonde at high latitude region (67°N). We tested our autoscaling program tool on 2021 years data set and evaluate errors between operator and automatic parameters scaling. The root mean square errors for critical frequencies foF2, foF1, foE, foEs, fmin, fbEs and virtual heights h′F, h′E, h′Es are estimated as 0.12 MHz (2 pixels), 0.07 MHz (1.16 pixels), 0.15 MHz (2.5 pixels), 0.33 MHz (5.5 pixels), 0.15 MHz (2.5 pixels), 0.17 MHz (2.83 pixels), 7.7 km (1.34 pixels), 7.0 km (1.22 pixels), 7.1 km (1.24 pixels), respectively.

We investigated the amplitude of medium scale traveling ionospheric disturbances (MSTIDs, with periods 25-100 min) and their dependence on the solar activity using 16 years data of the rapid run-ionosonde operating at high latitudes (67 degrees $67{}<^>{\circ}$N, Sodankyl & auml;, Finland). A deep learning neural network was applied to ionograms to extract critical frequency of the F2 region (foF2) with a 1 min time resolution. Then, we analyzed the relative amplitude of MSTIDs (i.e., 2 delta $2\delta $foF2/foF2), which corresponds to the amplitude of atmospheric gravity waves (AGWs) causing MSTIDs. The amplitude of AGWs propagating upward increases with height due to the decreasing density of the air, and hmF2 varies depending on local time, seasonal and solar activity conditions. To account for this effect, we calculated a corrected MSTID amplitude by normalizing the relative amplitude for the air density at the hmF2. The corrected amplitudes show no clear dependence on F10.7 during winter (0-12 UT), equinox (20-01 UT) and summer (19-01 UT), while a positive dependence of corrected amplitudes on F10.7 was observed during winter and equinox, in 14-22 UT and 15-19 UT, respectively. Corresponding to the dependence behaviors of corrected and relative amplitudes, two likely mechanisms of MSTIDs, AGWs from the lower atmosphere and auroral sources, are inferred. Their subsequent roles in the solar activity dependence of MSTID amplitudes were separately discussed, although in reality, the observed dependence is complex and often involves several mechanisms together.

The potential of deep learning for the investigation of medium scale traveling ionospheric disturbances (MSTIDs) has been exploited through the Sodankyl & auml; rapid-run ionosonde in this statistical study. The complementing observations of the Sodankyl & auml; ionosonde with those of the Sodankyl & auml; meteor radar reveals the diurnal and seasonal occurrence rate of high-latitude MSTIDs in the recent low solar activity period, 2018-2020. In our results, the daytime, nighttime and dusk MSTIDs are predominantly identified during winter, summer, and equinoctial months, respectively. The winter daytime higher (lower) occurrence rate is well correlated with the lower (higher) altitude of the height of the F2-layer peak (hmF2), and the low occurrence rate of the summer daytime is well correlated with the mesosphere-lower-thermosphere wind shear and higher gradient of temperature. Relatively high occurrence rate (>0.4) of summer nighttime MSTIDs has a general-but not one-to-one agreement-with post-noon to evening IU (eastward auroral current index) inferred ionospheric conductivity. Rather, we see a one-to-one relationship between the summer nighttime MSTIDs and zonal wind shear suggesting that the wind shear-induced electrodynamic processes could play significant roles for higher occurrence rate of MSTIDs. Furthermore, significant MSTIDs with similar to 0.4 occurrence rate are so far revealed during spring and autumn transition periods. The enhanced nighttime MSTID amplitudes during the equinox are observed to be well correlated with IL index (westward auroral current indicator) suggesting that the particle precipitation during substorms could be the primary cause.

ABSTRACT A long-standing problem in meteor science has been the persistent presence of bias in the measured value of atmospheric scale heights obtained from radio meteor echoes. A common practice of fitting a linear function for bias correction follows the assumption that the systematic bias is devoid of seasonal asymmetry. This would be true if the mass and the velocity distribution of meteoroids remain invariant, both spatially and temporally. But so far no such convincing evidence has been published. On the contrary, fundamental arguments suggest that a universal mass function of radio meteoroids is counterintuitive. This parameter cannot remain invariant due to the intrinsic variability in the meteor response function resulting from the Earth’s motion on the plane of ecliptic. In this paper, we show that an inverse relation exists between the width of meteor height distribution, expressed in unit of atmospheric scale height, and the exponent of the mass function. The overall mean of this exponent for the Sodankylä radar is $1.91 \pm 0.02$, modulated by a seasonal variation from the mean of the order of $\sim \pm 0.1$. The stated inverse relation is applied to correct for the effect of mass distribution on the height distribution. Allowing for variable mass correction effectively removes the non-linear bias in the measured scale heights in the meteor ionization region.

Abstract Over 1500 balloons are launched every day, from every continent on Earth, to provide forecasting of tropospheric weather. Similar balloons, which can fly to the edge of space (>30 km), can be used for other science projects. Professional scientists, military users, commercial organisations, and interested amateurs, all fly payloads that provide a relatively low-cost means to reach the upper atmosphere. Weather ballooning is perfectly suited to student education and has been carried out for decades by groups of school, college, and university students. Here we report on one such a project. During March/April 2023 a series of balloons were launched from Sodankylä, Finland, in order to study the particle and radiation environment, along with ozone, in the stratosphere. Inexpensive off-the-shelf Geiger-counters were part of a payload flown to investigate how the radiation environment changed over time. Balloon payloads can be tracked with simple and inexpensive radio receivers. Similar projects to the one outlined here should be possible for any school, college, or university that has a reasonably well-equipped workshop, a group of interested and capable students, and a desire to investigate and learn something new about the planet we live on.

The EISCAT Scientific Association is currently building the most advanced 3-dimensional imaging radar for atmospheric, ionospheric and near-Earth space investigations. The fully steerable, tri-static, phased-array incoherent scatter radar is located in Skibotn (inland from Tromsø, Norway), Karesuvanto (Finland, north of Kiruna), and Kaiseniemi (Sweden, west of Kiruna). The transmit-receive array at Skibotn consists of about 10,000 aerials and ten 91-aerial outrigger receivers in the immediate vicinity. The receive-only arrays of Kaiseniemi and Karesuvanto consist of about 5,000 aerials each. Construction of the facility began after the project kick-off in September 2017. During 2024, EISCAT_3D will gradually begin operations, starting with a seven-element test system and expanding from that. EISCAT_3D will replace the EISCAT mainland radars, i.e. the mono-static, 930-MHz UHF radar at Tromsø and the tri-static, 224-MHz radar at Tromsø with additional receivers at Sodankylä (Finland) and Kiruna (Sweden). The EISCAT Svalbard Radar (ESR) and the Ionospheric Heating facility at Tromsø will not be affected by EISCAT_3D becoming operational. Here we give an status update of the new facility. EISCAT_3D is a European Strategy Forum for Research Infrastructures (ESFRI) Landmark in the Environment domain.

Ionosondes are most widely used instruments to obtain electron density profiles of ionosophere. Typically ionosondes operates with $\gt 15$ minutes time intervals that is enough to obtain regular parameters of the ionosphere, but insufficient to study small- and medium-scale traveling ionospheric disturbances and sporadic E layers. The key points for such studies are the increase of the ionosondes time resolution, as well as automation of ionogram scaling routine. In this study we show the results of implementation of deep learning for ionogram parameters scaling. We trained and tested a convolutional neural network on data of Sodankyla ionosonde at high latitude region. Our results show a close to human ability to recognise layers shape of F1, F2, E, 6 types of Es and scaling foF1, foF2, foE, foEs parameters.

Sodankylä's high latitude location serves an ideal ground for testing more comprehensive physics theory related to radio meteor data. The atmospheric scale height shows significant variation at this latitude. Also, the observational geometry towards the plane of ecliptic plane changes drastically with seasons. On theory, the reflected radio signal from the ablating meteor train can be used to continuously monitor atmospheric temperature at the 90 km altitudes. In practice, complication arises due to the selection effects in the system as well as the persistent effect of natural variability (size, mass, velocity, entry angle) in meteoroids property. The long-standing hypothesis that needs to be debated: Is the assumed equality between atmospheric scale height (H_KT) and the effective diffusion scale height (H_D) of meteor trails valid for these data? In this study, we argue that such an hypotheis can not be experimentally validated, and hence the need for subsequent calibration. Furthermore, long-term trend analysis showed that the discrepancy between H_KT and H_D has non-linear seasonal trends. Alternatively, we demonstrate an alternative method of scale-height measurement based on meteor height distribution. The technical and theoretical limits of this methodology are discussed and validated using 10 years of observational data.

Abstract The Assimilative Canadian High Arctic Ionospheric Model (A‐CHAIM) is an operational ionospheric data assimilation model that provides a 3D representation of the high latitude ionosphere in Near‐Real‐Time (NRT). A‐CHAIM uses low‐latency observations of slant Total Electron Content (sTEC) from ground‐based Global Navigation Satellite System (GNSS) receivers, ionosondes, and vertical TEC from the JASON‐3 altimeter satellite to produce an updated electron density model above 45° geomagnetic latitude. A‐CHAIM is the first operational use of a particle filter data assimilation for space environment modeling, to account for the nonlinear nature of sTEC observations. The large number (>104) of simultaneous observations creates significant problems with particle weight degeneracy, which is addressed by combining measurements to form new composite observables. The performance of A‐CHAIM is assessed by comparing the model outputs to unassimilated ionosonde observations, as well as to in‐situ electron density observations from the SWARM and DMSP satellites. During moderately disturbed conditions from 21 September 2021 through 29 September 2021, A‐CHAIM demonstrates a 40%–50% reduction in error relative to the background model in the F2‐layer critical frequency (foF2) at midlatitude and auroral reference stations, and little change at higher latitudes. The height of the F2‐layer (hmF2) shows a small 5%–15% improvement at all latitudes. In the topside, A‐CHAIM demonstrates a 15%–20% reduction in error for the Swarm satellites, and a 23%–28% reduction in error for the DMSP satellites. The reduction in error is distributed evenly over the assimilation region, including in data‐sparse regions.

In this paper equatorward propagating large scale traveling ionospheric disturbance (LSTID) on 17 March 2015 were investigated using the Statistical Angle‐of‐Arrival and Doppler Method for GPS (SADM‐GPS) radio interferometry technique in data‐scarce East Africa. To apply the SADM‐GPS method, 5 GPS arrays each with 3 GPS receivers arranged in a triangular geometry were used. Our results show that during 15:00–18:00 UT on 17 March, TIDs with mean horizontal velocities between 161.9 and 464.4 m/s were observed. Using the wavelet analysis, the periods of TIDs in a range of 51–69 min that qualify to LSTIDs were revealed. The peak‐to‐peak phase shift of detrended total electron content (TEC) over latitudes in this study confirms the equatorward TID propagation, which was obtained by the SADM‐GPS technique. A pair of magnetometers were used to infer E × B drift and an adequate agreement was found with Swarm satellites derived plasma density that enabled us to explain the behaviour of ionospheric irregularity during the main phase of the geomagnetic storm. Moreover, significant TEC enhancement (reaching ∼20%–105%) were captured by GPS arrays during the period of TID propagation. Nevertheless, the rate of change of TEC (ROT) and ROT index (ROTI) show wavy structures that reflect TID effects over ionospheric modulations during the post noon to evening hours of 17 March 2015.

In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: ( A ) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? ( B ) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus.

Meteor observations provide information about Solar System constituents and their influx onto Earth, their interaction processes in the atmosphere, as well as the neutral dynamics of the upper atmosphere. This study presents optical, radar, and infrasound measurements of a daytime fireball that occurred on 4 December 2020 at 13:30 UTC over Northeast Sweden. The fireball was recorded with two video cameras, allowing a trajectory determination to be made. The orbital parameters are compatible with the Northern Taurid meteor shower. The dynamic mass estimate based on the optical trajectory was found to be 0.6–1.7 kg, but this estimate can greatly vary from the true entry mass significantly due to the assumptions made. The meteor trail plasma was observed with an ionosonde as a sporadic E-like ionogram trace that lasted for 30 min. Infrasound emissions were detected at two sites, having propagation times consistent with a source location at an altitude of 80–90 km. Two VHF specular meteor radars observed a 6 minute long non-specular range spread trail echo as well as a faint head echo. Combined interferometric range-Doppler analysis of the meteor trail echoes at the two radars, allowed estimation of the mesospheric horizontal wind altitude profile, as well as tracking of the gradual deformation of the trail over time due to a prevailing neutral wind shear. This combined analysis indicates that the radar measurements of long-lived non-specular range-spread meteor trails produced by larger meteoroids can be used to measure the meteor radiant by observing the line traveled by the meteor. Furthermore, a multistatic meteor radar observation of these types of events can be used to estimate mesospheric neutral wind altitude profiles.

Abstract. Energetic particle precipitation leads to ionization in the Earth's atmosphere, initiating the formation of active chemical species which destroy ozone and have the potential to impact atmospheric composition and dynamics down to the troposphere. We report on one exceptionally strong high-energy electron precipitation event detected by balloon measurements in middle latitudes on 14 December 2009 with ionization rates locally comparable to strong solar proton events. This electron precipitation was likely caused by wave-particle interactions in the slot region between the inner and outer radiation belts, connected with still not well understood natural phenomena in the magnetosphere. Satellite observations of odd nitrogen and nitric acid are consistent with wide-spread electron precipitation into magnetic midlatitudes. Simulations with a 3D chemistry-climate model indicate almost complete destruction of ozone in the upper mesosphere over the region where high-energy electron precipitation occurred. Such an extraordinary type of energetic particle precipitation can have major implications for the atmosphere, and their frequency and strength should be carefully studied.

For two decades meteor radars have been routinely used to monitor atmospheric 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 the scattered plot of log10(1/tau) and height, where ’tau’ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such bias is that it produces a systematic offset in the estimated temperature, and thus requiring calibration with other colocated measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in decay time or the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. We demonstrate an alternative regression method that incorporates various error terms in the statistical model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log10(1/tau). This solution is found to be a good prior solution for the core of this bivariate distribution. However, depending on the data selection process the error variances may not be exactly equal. A first-order correction is then carried out to address the biasing effect due to asymmetric error variances. This allows to construct an analytic solution for the bias-corrected slope coefficient for this data. With this solution, meteor radar temperatures can be obtained independently without using any external calibration procedure. When compared with colocated lidar measurements, the temperature estimated using this method is found to be accurate within 7% or better and without any systematic offset.

Meteoroids entering the Earth's atmosphere are associated with a number of phenomena including ablation, ambipolar diffusion, plasma transport, chemical reactions, shock waves, and plasma turbulence. A bright daylight fireball observed on 2020-12-04 13:30 UTC with two meteor cameras located in Skibotn and Sørreisa allowed the precise entry trajectory of the fireball to be determined. The path of the entering object is approximately between Angeli Finland and Pajala Sweden. Based on the brightness and entry trajectory, it is possible to estimate the approximate mass of the object, and associate it with a meteor shower (Northern Taurids). The effects of the fireball on the atmosphere were detected with a number of radar and radio instruments within the region, including ionosondes, meteor radars, an all-sky VHF imaging system, and an infrasound sensor. These observations allow a detailed study of the atmospheric interaction of a large meteoric body with the Earth's atmosphere to be made. In this talk, we will describe the observations of this fireball and discuss preliminary findings.

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 model in the scattered plot of log⁡10(1/τ) and height, where τ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such a bias is that it produces a systematic offset in the estimated temperature, thus requiring calibration with other co-located measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in τ and the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. To incorporate various error terms in the statistical model, an appropriate regression analysis for these data is the errors-in-variables model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log⁡10(1/τ). This solution is found to be a good prior estimate for the core of this bivariate distribution. Further improvement is achieved by defining density contours of this bivariate distribution and restricting the data selection process within higher contour levels. With this solution, meteor radar temperatures can be obtained independently without needing any external calibration procedure. When compared with co-located lidar measurements, the systematic offset in the estimated temperature is shown to have reduced to 5 % or better on average.