ST3.4

The aurora can have strong electric fields and currents associated with it, which deposit a significant amount of energy in the neutral upper atmosphere through heating. Such heating must be included in global atmospheric models used to study thermospheric dynamics, coupling between the atmospheric layers, climate, and drag on spacecraft and space debris in low Earth orbit. However, the heating rate is poorly quantified, and often spatial structure is not well represented. Heating is typically estimated by measuring the ionospheric electric field using radar, which is then combined with measurements or estimates of the neutral wind velocity and Pedersen conductivity to calculate a Joule heating rate. However, such measurements of the electric field necessarily neglect small scale spatial and temporal variability through their relatively coarse resolution and averaging. The Joule heating rate is proportional to the square of the electric field, and therefore the spatial and temporal averaging can lead to a significant underestimate of the Joule heating rate. As a step towards improving estimates of neutral heating, we have developed a technique to invert spectrographic measurements of aurora to observe the thermospheric neutral temperature altitude profile at high temporal resolution. Application of the technique to an auroral event shows substantial Joule heating adjacent to an arc where the E-field must be strong, as well as heating embedded within an auroral curl, which we associate with an intense field-aligned current.

How to cite: Whiter, D. and Price, D.: Optical observations of thermospheric neutral temperature in aurora, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12282, https://doi.org/10.5194/egusphere-egu22-12282, 2022.

Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval, at latitudes where auroras are less common, suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity above 12.5° colatitude, in two or more of the wavelengths/bands sensed by SSUSI.

Using the detection algorithm on observations from the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPA images suggest a seasonal dependence, with more TPAs observed in the winter hemisphere. The orbital plane of DMSP has been investigated as a possible explanation of the dependences in the results of the detection algorithm. It has been found that each DMSP spacecraft has a different bias due to its orbit. For the spacecraft of interest (F16, F17 and F18) this leads to a preferential observation of the northern hemisphere, with the detection algorithm missing TPAs in the southern hemisphere around 01 - 06 UT. No seasonal bias has been found for these spacecraft.

We also discover that the majority of TPAs occur in the dawn sector of the polar cap, which is unexpected in current TPA models. Comparing with previous statistical surveys, we note that the dawn-dusk asymmetry has been present but has not gained significant attention.  We suggest that field-aligned current polarity may play a role in the observed asymmetry.

We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms and suggest reasons for the seasonal dependence including it being a reflection of probability of seeing TPAs due to visibility.

How to cite: Bower, G., Milan, S., Paxton, L., and Imber, S.: Statistics of transpolar arcs identified by an automated detection algorithm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2360, https://doi.org/10.5194/egusphere-egu22-2360, 2022.

Solar, auroral, and radiation belt electrons enter the atmosphere at polar regions leading to ionization and affecting its chemistry. Climate models with interactive chemistry in the upper atmosphere, such as WACCM-X or EDITh, usually parametrize this ionization and calculate the related changes in chemistry based on satellite particle measurements. Precise measurements of the particle and energy influx into the upper atmosphere are difficult because they vary substantially in location and time. Widely used particle data are derived from the POES and GOES satellite measurements which provide electron and proton spectra. These satellites provide in-situ measurements of the particle populations at the satellite altitude, but require interpolation and modelling to infer the actual input into the upper atmosphere.

Here we use the electron energy and flux data products from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instruments on board the Defense Meteorological Satellite Program (DMSP) satellites. This formation of currently three operating satellites observes both auroral zones in the far UV from (115--180 nm) with a 3000 km wide swath and 10 x 10 km (nadir) pixel resolution during each orbit. From the N₂ LBH emissions, the precipitating electron energies and fluxes are inferred in the range from 2 keV to 20 keV. We use these observed electron energies and fluxes to calculate auroral ionization rates in the lower thermosphere (≈ 90–150 km), which have been validated previously against ground-based electron density measurements from EISCAT. We present an empirical model of these ionization rates derived for the entire satellite operating time and sorted according to magnetic local time and geomagnetic latitude and longitude. The model is based on geomagnetic and solar flux indices, and a sophisticated noise model is used to account for residual noise correlations. The model will be particularly targeted for use in climate models that include the upper atmosphere, such as the aforementioned WACCM-X or EDITh models. Further applications include the derived conductances in the auroral region, as well as modelling and forecasting E-region disturbances related to Space Weather.

How to cite: Bender, S., Espy, P., and Paxton, L.: Empirical modelling of SSUSI derived auroral ionization rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3759, https://doi.org/10.5194/egusphere-egu22-3759, 2022.

Space weather is a system science in the sense that it includes a chain of complex phenomena coming from the Sun and going to the Earth mainly through the magnetosphere. Added to this, the effects on the Earth infrastructures and their vulnerability should be taken into account. All this chain is too poorly described to allow accurate nowcasting and forecasting of the space weather events and of their effects on Earth. In this chain, the upper atmosphere as well as its interface with the magnetosphere require improvements in their description.

Precipitations of auroral electrons along magnetic lines lead to auroras, which are one of the most striking manifestations of space weather. These phenomena characterize the relationship of the magnetosphere and the upper atmosphere, and their intensity and localization indicate the state of near-Earth space. The energy release in the region of the auroral oval, associated with precipitation of auroral electrons, is controlled by the solar wind parameters and is one of the important reasons leading to changes in space weather in the polar magnetosphere and ionosphere.

In this frame, one of the main gaps in both data and modelling is the monitoring of the precipitation of low-energy (0.02 − 30keV ) particles in the ionosphere and in the magnetosphere, especially electrons which are key contributors to ionospheric currents.

Numerous satellites observed the polar lights both in the UV and visible, however AMICal Sat is the first cubesat to be dedicated to the observation of the optical emissions of the auroras. It contains a sparse RGB imager and has been launched on board the VV16 flight, September 3rd 2020. It will be followed by a spectrometer ATISE planned to be launched in 2023.

In this presentation, we propose to present the first results of AMICal Sat, the data processing to extract the intensity of each lines and thus deduce the electron fluxes. Plans for ATISE developments and ground based tests will also be detailed.

How to cite: Barthelemy, M., Kalegaev, V., and Robert, E.: AMICal Sat, ATISE : From imagery to spectro-imagery for auroral studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11881, https://doi.org/10.5194/egusphere-egu22-11881, 2022.

When IMF By is dominant, which is the typical situation, a highly vortical convection pattern is seen inside the dayside polar cap in the summer hemisphere. In the winter hemisphere, however, the convection is mainly from noon to midnight with little vorticity inside the polar cap. Combined with the vastly different ionospheric conductance between summer and winter due to solar EUV irradiance, these differences in convection cause large summer/winter differences in the Birkeland currents in the dayside polar cap. Hence, the joule heating rates will be very different in the dayside polar cap between summer and winter during the IMF By dominant periods, which is typically associated with weak geomagnetic activity inside the auroral oval. This presentation will focus on the hemispheric differences in e.g. joule heating during such conditions, which will be quantified using the newly developed LOcal Mapping of Polar ionospheric Electrodynamics (Lompe) data assimilation technique. The Lompe technique is similar to the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique, but allows the electrodynamics to be described only in a limited region to reflect the observational coverage. The prescribed conductance will be provided from UV imaging of the aurora (in addition to EUV), allowing also the energy from precipitation to be estimated. While existing empirical models [e.g. Weimer 2005, doi:10.1029/2004JA010884] capture some aspects of the hemispheric asymmetries, this presentation will focus on how recent advances in data assimilation techniques allows us to quantify these asymmetries on an event basis, showing how these typical conditions can lead to vastly different energy input into the two hemispheres.

How to cite: Reistad, J. P., Laundal, K. M., Ohma, A., and Hatch, S.: Energy input in the dayside polar cap during IMF By dominated conditions: Summer vs. Winter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6396, https://doi.org/10.5194/egusphere-egu22-6396, 2022.

We track the progression of height-integrated conductances over the course of an average substorm in a narrow local time sector of the nightside polar cap. These conductances are calculated from the mean energy flux and energy flux of precipitation, as estimated from a ratio of auroral emissions of the Lyman-Birge-Hopfield long and short band obtained by multiple polar region crossings of the Defence Meteorological Satellite Program F16, F17, and F18 spacecraft. Contributing auroral emission data span 1 January 2005 to 31 December 2017. Both Pedersen and Hall conductances are considered, as well as the influence of the magnetic latitude of substorm onset. Substorm onset times and magnitudes are provided by the SuperMAG network and SOPHIE substorm lists. We compare superimposed epoch ordered conductances with similarly averaged field aligned currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Shortly before onset, conductances increase in a low latitude region, before an increase in conductance seen at all latitudes at the time of onset. The energy flux is shown to peak quickly after substorm onset, followed by mean energy. The conductances, energy flux, and mean energy are ordered by magnetic latitude of substorm onset, so that the lowest onset latitudes correspond to the highest value of any given parameter. Conductances recover quicker to pre-substorm levels for those substorms with higher onset magnetic latitudes.

How to cite: Carter, J. A., Milan, S., Lester, M., Forsyth, C., Paxton, L., Gjerloev, J., and Anderson, B.: Height-integrated polar cap conductances during an average substorm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9261, https://doi.org/10.5194/egusphere-egu22-9261, 2022.

The ionosphere-thermosphere research community has clearly expressed a need for improved, observation-based estimates of key ionosphere-thermosphere parameters such as Joule dissipation, Poynting flux, and ionospheric conductances. While global estimates of these key parameters can be obtained by combining existing empirical models, one often encounters some frustrating sources of uncertainty: the models to be combined often use different input parameters, different assumptions about hemispheric symmetry, and/or different coordinate systems. We eliminate these sources of uncertainty by deriving a new model of high-latitude ionospheric potential that can be combined with the Average Magnetic Field and Polar Current System (AMPS) model to obtain empirical estimates of Joule dissipation, Poynting flux, and ionospheric conductances. These models treat the two hemispheres independently, are derived in a mutually consistent fashion, and are based entirely on electric and magnetic field measurements made by the Swarm satellites.

How to cite: Hatch, S., Laundal, K. M., Reistad, J. P., and Ohma, A.: A consistently derived set of empirical models for high-latitude electrodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8283, https://doi.org/10.5194/egusphere-egu22-8283, 2022.

Modern high latitude ionospheric electric field models have been developed to incorporate advances in data availability, however the use of older spacecraft-based models is still widespread.  AENeAS (Advanced Ensemble electron density [Ne] Assimilation System) is a physics-based, thermosphere-ionosphere, coupled, assimilative model, which makes possible thermospheric forecasts. Currently AENeAS uses the Heelis and Weimer electric field spacecraft climatology models but it is possible a more recent electric field model could improve its functionality.  Two such models are calculated using line-of-sight velocity measurements from the Super Dual Auroral Radar Network (SuperDARN): the Thomas and Shepherd model (TS18), and the Time-Variable Ionospheric Electric Field model (TiVIE) . Here we compare the electric field models during the September 2017 storm, covering a range of solar wind and interplanetary magnetic field (IMF) conditions. We explore the relationships between the IMF conditions and model output parameters such as transpolar voltage, the polar cap size and the lower latitude boundary. We find the spacecraft-based model electric potential and field parameters to have a significantly higher magnitude than the SuperDARN-based models. We will discuss the similarities and differences in topology and magnitude for each model.

How to cite: Orr, L., Grocott, A., Walach, M., Lam, M. M., Freeman, M., Chisham, G., and Shore, R.: High latitude ionospheric electric field models comparison, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8135, https://doi.org/10.5194/egusphere-egu22-8135, 2022.

We present observations of a new type of small-scale aurora-like feature, which is further referred to as fragmented aurora-like emission(s) (FAEs).

They seem to appear in two categories – randomly occurring individual FAEs and wave-like structures with regular spacing between FAEs alongside auroral arcs. FAEs show horizontal sizes typically below 20 km, a lack of field-aligned emission extent, and short lifetimes of less than a minute. Emissions were observed at the 557.7 nm line of atomic oxygen and at 673.0 nm (N₂; first positive band system) but not at the 427.8 nm emission of N₂⁺ or the 777.4 nm line of atomic oxygen. This suggests an upper limit to the energy that can be produced by the generating mechanism. Their lack of field-aligned extent and 777.4 nm emissions indicates a different generation mechanism than for aurorae, which are caused by particle precipitation. Possible sources are Farley–Buneman instabilities or electrostatic ion cyclotron waves.

How to cite: Dreyer, J., Partamies, N., Whiter, D., Ellingsen, P. G., Baddeley, L., and Buchert, S. C.: Characteristics of Fragmented Aurora-like Emissions (FAEs), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5686, https://doi.org/10.5194/egusphere-egu22-5686, 2022.

Energetic Electron Precipitation (EEP) from the plasma sheet and the radiation belts ionize the polar lower thermosphere and mesosphere. EEP increase the production of NOx and HOx, which will catalytically destroy stratospheric ozone, an important element of atmospheric dynamics. Therefore, measurement of the latitudinal extent of the precipitation boundaries is important in quantifying atmospheric effects of Sun-Earth interaction.
This study uses measurements by Medium Energy Proton Electron Detector (MEPED) of six NOAA/POES and EUMETSAT/METOP satellites from 2004 to 2014 to determine the latitudinal boundaries of EEP and its variability with geomagnetic activity and solar wind drivers. Variation of the boundaries with respect to different particle energies and magnetic local time is studied. Regression analyses are applied to determine the best predictor variable based on solar wind parameters and geomagnetic indices. The highest correlation was found for pressure-corrected Dst index through linear regression. Although, the model has an error estimate of ±2.2° cgmlat and exhibits a solar cycle bias, it performs well in predicting the precipitation boundaries. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.

How to cite: Babu, E. M., Tyssøy, H. N., Smith-Johnsen, C., Maliniemi, V., Salice, J. A., and Millan, R.: Determining latitudinal extent of energetic electron precipitation  using MEPED on-board NOAA POES, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1322, https://doi.org/10.5194/egusphere-egu22-1322, 2022.

The ESA Swarm constellation of satellites have been measuring the ionospheric electric and perturbation magnetic fields since 2013. Recently, the entire dataset of Swarm electric fields has been reprocessed into a 16Hz data product, allowing the analysis of ionospheric dynamics on sub-kilometre scales.

In combination with the on-board magnetometer data, the Swarm satellites can use the electric field measurements to determine the total electromagnetic energy into and out of the ionosphere, the Poynting flux. The 16Hz dataset allows for the capturing of much smaller scale sizes than previously considered, thus presenting the opportunity to study how much Poynting flux is missed when utilizing data across typically monitored scales (usually on the order of tens to hundreds of kilometres).

We present a statistical analysis of the Swarm A and B derived 16Hz Poynting flux, utilising various low-pass filters on the electric and magnetic field data to simulate smoothing the data to larger scale sizes. We find that by increasing the width of the low-pass filters, measured Poynting flux decreases significantly and quickly. Our results show that there is an over 50% underestimation in the total hemisphere integrated Poynting flux when observing it on scale sizes of a few hundred kilometres, compared to the raw 16Hz measurements that correspond to scales of around 0.5km. Under certain circumstances, as much as a 10% underestimation in the Poynting flux is observed by increasing scale size to only 5km. These results stress the importance observing small-scale electric and magnetic fields, as they may account for a large proportion of the ionosphere-thermosphere energy budget.

How to cite: Billett, D. and McWilliams, K.: High-resolution Poynting fluxes derived from the ESA Swarm mission: How much are we underestimating?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6535, https://doi.org/10.5194/egusphere-egu22-6535, 2022.

The IRAP Plasmasphere Ionosphere Model (IPIM) is an ionospheric model which describes the transport equations of ionospheric plasma species along magnetic closed field lines. The development of a new operational version of IPIM as part of the EUHFORIA project to monitor and forecast space weather conditions and hazards includes using in-situ solar wind observations from the OMNI data set, ionospheric radar data of plasma motions from the Super Dual Auroral Radar Network (SuperDARN), and precipitation data from the Ovation model, as inputs to the model. A new conductivity module has also been developed for help in the simulation of geomagnetically induced currents based on a simplified version of IPIM. This model uses the photochemical module of IPIM in place of the fluid module and the full kinetic module, so that inter-hemispheric transport of suprathermal electrons is accounted for in the ion production term. As the main contribution to the conductivities comes from the lower ionosphere (typically below 150km) where the chemistry dominates, neglecting the field-aligned transport contribution in the fluid module does not alter significantly the conductivities. Based on the conductivities, the neutral wind and the electric field, ionospheric horizontal currents are computed. The ionospheric currents are used as an input for the Biot and Savart module to compute the resulting magnetic perturbations at the ground. We present the first results from this version which explores the ionosphere's response to different conditions in different regions in mid and high latitudes.

How to cite: Eisenbeis, J., Blelly, P.-L., Thomas, S., and Marchaudon, A.: Modeling horizontal currents and magnetic ground perturbations with the IPIM model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1660, https://doi.org/10.5194/egusphere-egu22-1660, 2022.

Ionospheric Alfvén Resonances (IAR) are observed in the British Geological Survey's ground based induction coil magnetometer data at Eskdalemuir. IAR are caused when Alfvén waves are partially reflected at boundaries of changing plasma density in the ionosphere. At the boundaries, the Alfvén velocity reaches a maximum and the IAR occurs in the cavity which is in the F region. In the data we observed some unusual variations in the frequency of the harmonics and so created a model to investigate this. We have modelled the harmonic frequency separation of the IAR using the magnetic field strength from the International Geomagnetic Reference Field, and the electron density and ion composition from the International Reference Ionosphere. We found the Alfvén velocity and calculated the time of flight for the Alfvén wave to travel up and down the cavity, and hence we found the frequency. The model shows that the frequency is highest in the winter, and often shows a double peak each day in the winter months. We then compared the model of the harmonic frequency separations to the harmonic frequency separations from the data, determined from an autocorrelation analysis of the observed spectra.

How to cite: Hodnett, R., Yeoman, T., Wright, D., and Beggan, C.: The Ionospheric Alfvén Resonator observed at Eskdalemuir magnetic observatory , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4829, https://doi.org/10.5194/egusphere-egu22-4829, 2022.

To model ionospheric climate and to study its long-term changes and trends we need solar activity proxies, because long and homogeneous data series of solar ionizing flux are not available. To select the optimum solar activity proxies, we use yearly average foF2 data of eleven ionospheric stations from middle and low/equatorial latitudes of four continents over 1976-2014 and six solar activity proxies, F10.7, sunspot numbers, F30, Mg II, He II and solar Lyman-α flux. For middle latitudes and higher low latitudes down to about 20-24^oN, Mg II and F30 are found to be the optimum solar proxies, not the usually used F10.7 or sunspot numbers. At lower and particularly equatorial latitudes the situation is different; the optimum proxy for Jicamarca is sunspot number and He II, and for Vanimo He II. Solar activity describes 99% of the total variance of yearly foF2 at midlatitudes and its dependence on solar proxies is highly linear. Long-term trends in foF2 are found to depend to some extent on solar proxy used

How to cite: Laštovička, J.: Different optimum solar activity proxies for foF2 at middle and low latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1593, https://doi.org/10.5194/egusphere-egu22-1593, 2022.