Auroral Electrojet Research Articles

Latitudinal responses of the ionosphere over South America during HILDCAA intervals: Case studies

Aspects regarding the influence of High-Intensity Long-Duration Continuous Auroral Electrojet Activity (HILDCAA) intervals on ionospheric dynamics have been objecting to increasing interest in the last years. Notwithstanding, some key interconnections between the HILDCAA intervals impacts on the ionosphere over distinct latitudes, according to the solar cycle phase, remain to require further investigation. In this work, the F2 layer peak height and its critical frequency (hmF2 and foF2, respectively) from Digisonde data obtained over São Luís (2.60° S; 44.21° W), Cachoeira Paulista (22.70° S; 44.98° W), and Port Stanley (51.60° S, 57.9° W), were evaluated to unravel more details of the ionospheric responses to four HILDCAA intervals as case studies. Those are equatorial, low, and mid-latitude stations, respectively, and the main results over them presented a similar trend in terms of solar cycle dependence, with the greater impact on the ionospheric density along with solar maximum conditions, despite the higher frequency of HILDCAA occurrences in the descending and minimum phases. The variation of hmF2 due to HILDCAA effects in comparison to quiet time is about 20% in equatorial and mid-latitudes, while over the low latitude station the hmF2 ranges positively up to 40%. These results enhance our understanding of the HILDCAAs magnitude degree both regarding its solar cycle occurrence, and its effects in different ionospheric latitudinal sections.

Generation of Field‐Aligned Currents During Substorm Expansion: An Update

AbstractWe investigated generation processes of field‐aligned currents (FACs) that are abruptly intensified at the beginning of the substorm expansion phase by tracing a packet of the Alfvén wave backward in time from the onset position in the ionosphere in the global magnetohydrodynamics (MHD) simulation. The generation region is found in the near‐Earth plasma sheet, in which (a) azimuthally moving plasma pulls the magnetic field line, and performs negative work against the magnetic tension force to excite the Alfvén waves, (b) FACs are generated from the requirement of Ampère and Faraday laws, and (c) field‐perpendicular current is converted to FACs. We call this near‐Earth FAC dynamo. The plasma involved originates in the tail lobe region. When near‐Earth reconnection occurs in the plasma sheet, the plasma is accelerated earthward by the Lorentz force, and decelerated by the plasma pressure gradient force, followed by the Lorentz force. The flow is deflected to the west and east directions by the plasma pressure gradient force and the Lorentz force, resulting in the excitation of Alfvén waves and FACs. The Alfvén waves propagate along the magnetic field in the rest frame of the moving plasma. When it arrives at the ionosphere, the auroral electrojet starts developing and the substorm expansion phase begins. The near‐Earth FAC dynamo can be distinguished from the near‐Earth dynamo (J · E < 0, where J is the current density and E is the electric field). We suggest that the evolution of the substorm can be understood in terms of the development of FACs.

Newcomb–Benford Law as a generic flag for changes in the derivation of long-term solar terrestrial physics timeseries

Abstract The Newcomb–Benford Law (NBL) prescribes the probability distribution of the first digit of variables which explore a broad range under conditions including aggregation. Long-term space weather relevant observations and indices necessarily incorporate changes in the contributing number and types of observing instrumentation over time and we find that this can be detected solely by comparison with the NBL. It detects when upstream solar wind magnetic field high resolution OMNI interplanetary magnetic field incorporated new data from the WIND and Advanced Composition Explorer spacecraft after 1995. NBL comparison can detect underlying changes in the geomagnetic auroral electrojet index (activity-dependent background subtraction) and the SuperMAG electrojet index (different station types) that select individual stations showing the largest deflection, but not where station data are averaged, as in the SuperMAG ring-current index. As composite indices become more widespread across the geosciences, the NBL may provide a generic, data processing-independent flag indicating changes in the constituent raw data, calibration, or sampling method.

Determining the Timing of Driver Influences on 1.8–3.5 MeV Electron Flux at Geosynchronous Orbit Using ARMAX Methodology and Stepwise Regression

AbstractAlthough lagged correlations have suggested influences of solar wind velocity (V) and number density (N), Bz, ultralow frequency (ULF) wave power, and substorms (as measured by the auroral electrojet (AE) index) on MeV electron flux at geosynchronous orbit over an impressive number of hours and days, a satellite's diurnal cycle can inflate correlations, associations between drivers may produce spurious effects, and correlations between all previous time steps may create an appearance of additive influence over many hours. Autoregressive‐moving average transfer function (ARMAX) multiple regressions incorporating previous hours simultaneously can eliminate cycles and assess the impact of parameters, at each hour, while others are controlled. ARMAX influences are an order of magnitude lower than correlations uncorrected for time behavior. Most influence occurs within a few hours, not the many hours suggested by correlation. A log transformation accounts for nonlinearities. Over all hours, solar wind velocity (V) and number density (N) show an initial negative impact, with longer term positive influences over the 9 (V) or 27 (N) hr. Bz is initially a positive influence, with a longer term (6 hr) negative effect. ULF waves impact flux in the first (positive) and second (negative) hour before the flux measurement, with further negative influences in the 12–24 hr before. AE (representing electron injection by substorms) shows only a short term (1 hr) positive influence. However, when only recovery and after‐recovery storm periods are considered (using stepwise regression), there are positive influences of ULF waves, AE, and V, with negative influences of N and Bz.

DETERMINATION OF THE OCCURRENCE RATES OF THE GEOMAGNETIC DISTURBANCES AT EUROPEAN AURORAL AND HIGH LATITUDES

Statistical studies allow probability statements about the frequency of certain events. The occurrence of magnetic substorms and their activity have been described with the help of extreme value distributions in the last few decades using the auroral electrojet indices AE, AL and AU. In this work we examined the distribution of the IL index, derived from observations at stations of the IMAGE magnetometer network. The distributions of magnetic disturbances, based on IL, were studied separately in the morning (3-9 MLT), day (9-15 MLT), evening (15-21 MLT), and night (21-3 MLT) sectors. In addition, we used the values of the IL index calculated from the meridional chains in the auroral zone (PPN-SOR) and from the chain of stations at high latitudes (BJN-NAL). By help of the histograms and the empirical cumulative distributions, the occurrence rates were computed. It was shown that the empirical distributions could be well approximated with exponential distributions. The distribution parameters were determined from the occurrence rates. Three classes were discovered, which differ significantly by the respective distribution parameters. Structure changes in the distributions were found in the morning sector at both auroral and high latitudes.

Formation of Beading Auroral Arcs at Substorm Onset: Implications of Its Variability Into the Generation Process

AbstractThe formation of auroral beads, wavy onset arcs, is often discussed in terms of substorm initiation. The present study addresses several aspects of their development and propagation by examining ground all‐sky images for representative events for each aspect. The results are summarized as follows: (a) the expansion and propagation of auroral beads do not depend on whether they form east or west of a preceding equatorward flow; (b) Auroral beads propagate either eastward or westward when the westward auroral electrojet intensifies apparently not preceded by the approach of an equatorward flow in neighboring sectors; (c) A nearby arc does not seem to be affected even if auroral beads form only a few tenths of degree apart in latitude; (d) two wavy arcs occasionally form next to each other and propagate in different directions; (e) the evolution of beading arcs is not always conjugate in two hemispheres. Results (a) and (b) suggest that meso‐ or large‐scale ionospheric convection as inferred from ground magnetic disturbances does not regulate the development and propagation of auroral beads. Results (c) and (d) imply that the development of auroral beads can be attributed to a small‐scale process, possibly a convection flow, at a latitudinal scale of a few tenths of degree or less. Such a small‐scale process may not be conjugate in two hemispheres, which potentially explains Result (e). These results do not necessarily mean that the cause of auroral beads is ionospheric, but suggest that the magnetosphere‐ionosphere coupling plays an important role in their development.

Modeling of Auroral Electrojet Index with Ultraviolet Aurora Image

极光电集流指数<i>AE</i>是描述地磁亚暴强弱的重要指标，且与极区磁层扰动及极光粒子沉降过程密切相关。因此，建立更加准确的极光电集流指数模型对空间天气的研究具有重要意义。利用1997年POLAR卫星紫外极光图像数据探究了紫外极光图像中极光强度<i>I</i>_AP的空间分布与<i>AE</i>指数在不同季节的相关性，并在此基础上提出了基于紫外极光图像的<i>AE</i>指数模型。以网格化方法提取极光强度空间分布特征，采用广义回归神经网络，通过相关系数法和方差选择法构建Cor-GRNN和Var-GRNN两种<i>AE</i>指数模型，并针对冬至月份、夏至月份、分点月份3个季节分别进行训练。研究结果表明，<i>AE</i>指数与<i>I</i>_AP具有相似的半年变化趋势，其相关性在不同季节差异较大。相比于太阳风驱动下的<i>AE</i>指数神经网络预测模型，基于极光图像的<i>AE</i>指数模型在<i>E</i>_RMS和<i>R</i>²标准上均优于其他模型，其中归一化<i>E</i>_RMS小于0.1，模型对于<i>AE</i>指数变化的可解释度提升了10%左右。

Statistical Temporal Variations in the Auroral Electrojet Estimated With Ground Magnetometers in Fennoscandia

AbstractWe present the implementation of an improved technique to coherently model the high‐latitude ionospheric equivalent current. Using a fixed selection of 20 ground magnetometers in Fennoscandia, we present a method based on Spherical Elementary Current Systems (SECS) to model the currents coherently during 2000–2020. Due to the north‐south extent of the magnetometers, we focus on the model output along the 105° magnetic meridian. Our improvements involve fixed data locations and SECS analysis grid and using a priori knowledge of the large‐scale currents improving the robustness of the inverse problem solution. We account for contributions from ground induced currents assuming so‐called mirror currents. This study produces a new data set of divergence‐free (DF) currents and magnetic field perturbations along the 105° magnetic meridian with 1‐min resolution. By comparing averages of the data set with an empirical model of the ionosphere we demonstrate the validity of the data set. We show how our data set, in particular its temporal nature, is distinct from empirical models and other studies. Not only can the temporal evolution of the DF currents and magnetic field perturbations be investigated, but the time derivative of said quantities can be analyzed. For application in ground induced currents, we present the statistical properties of where (in magnetic latitude and local time) and at what rate (∂Br/∂t) the radial magnetic field component fluctuates, a temporal derivative that has received very little attention. We show that ∂Br/∂t is dependent on latitude, local time, and solar cycle. We present other applications such as Ultra Low Frequency Waves monitoring.

Models for magnetospheric mass density and average ion mass including radial dependence

Analytical models for magnetospheric mass density, ρm, and average ion mass, M, were created from a database of ρm and electron density, ne, values from six spacecraft missions by making use of the Eureqa nonlinear genetic regression algorithm. All values of ρm were determined from Alfvén frequencies, and the values of ne were determined from plasma wave or spacecraft potential data. Models of varying complexity are listed. The most complex models appearing in this paper are capable of modeling ρm within a factor of 1.81, and M within a factor of 1.34 if ne is used as an input parameter, or within a factor of 1.45 if ne is not used. The most important parameters for modeling ρm are L, the solar EUV index F10.7, magnetic local time, MLT, the geomagnetic activity index Kp, and the solar wind dynamic pressure, Pdyn. The very simplest model for M depends on Kp. In more complex models for M including ne, the most important parameters are ne with L, F10.7, and Pdyn or Kp. In more complex models for M not including ne, the most important parameters are Kp, MLT, F10.7, L, and the auroral electrojet index, AE. Explanations for most of the dependencies are given. We also demonstrate the danger of calculating spatial dependence without taking account of different conditions sampled in different regions. Here we avoid that problem by using multivariant models.

Longitudinal Evolution of Storm-Enhanced Densities: A Case Study

Due to the limitations on observational data, most storm-enhanced density (SED) studies have focused on the North American sector. The complete picture of the longitudinal evolution of SEDs is still not clear. In this study, we investigated the dynamic evolution of SEDs from the European sector to the North American sector during a geomagnetic storm that occurred on the 15 July 2012, the main phase of which lasted nearly 30 h, maintaining the stable interplanetary magnetic field (IMF) and solar wind input conditions. Multiple data sets were analyzed, including convection data from the Super Dual Auroral Radar Network (SuperDARN), total electron contents (TECs) from the Madrigal database, plasma data from the Millstone Hill incoherent scatter radar (MHISR), solar wind and geomagnetic indices from OMNIWeb, and regional auroral electrojet indices from SuperMAG. The observations showed that the positions of SEDs shifted from local noon over the European sector towards dusk over the American sector and simultaneously moved to lower latitudes. The peak values of SED TECs were found to be greater in the European sector and to decrease with universal time. A double SED phenomenon appeared in the North American sector, which is the first of its kind to be reported. Further analysis showed that the temporal and spatial changes in the SEDs were associated with the eastward auroral electrojet.

Variation of Total Electron Content in the Quiet and Disturbed Period and Their Correlation with Solar Wind Parameters

Total electron content and electron density are the fundamental parameters that determine the main properties of the ionosphere. We have observed variation of Global Positioning System (GPS) derived Vertical Total Electron Content (VTEC) on three different geomagnetic events. The observed VTEC data is recorded from four GPS stations at different locations (87.26°E, 26.48°N); (85.79°E, 27.87°N); (84.57°E, 28.17°N), and (86.70°E, 27.81°N). To determine the severity of storms, we analysed the north-south component of interplanetary magnetic field (IMF-Bz), solar wind parameters- solar wind speed (Vsw) and solar wind dynamic pressure (Psw) ,and geomagnetic indices- Dst index, Kp index and Auroral Electrojet (AE). For all the studied event days, we observed intensified VTEC on geomagnetically disturbed days over quiet days. The VTEC enhancement was significantly high on the severely disturbed day, followed by the moderate storm and the minor storm.The study made to observe association of VTEC with different interplanetary and geomagnetic indices shows that during all studied event days, VTEC enhancement is positively correlated with Vsw, Psw, AE and Kp with cross-correlation coefficient above 0.8 at zero time lag and strong negative correlation with Dst index. In contrast, the correlation of IMF-Bz vary with the intensity of storm. Our finding show a significant variation in VTEC during the geomagnetic disturbances, supporting previous studies on ionospheric responses to geomagnetic storms as well as theoretical assumptions.

How Energy Enters the Magnetosphere During a Substorm: A Perspective After 60 Years of Working in the Field

AbstractThis paper begins with a summary of my path into space physics and the following four decades of active research in ionosphere and magnetosphere. The following perspective part addresses the main subject in four steps, from flow braking and diversions prior to substorm onset, via the attachment of the magnetic field carried by the flow bursts, to the transformation of the incoming momentum and energy and their earthward propagation, and finally, the generation of the poleward arcs, auroral electrojet, and substorm current wedge. This is done mostly by a critical assessment of results and concepts from the author's research from 1992 to 2021. The outcome is a new scenario of the origin of the breakup arcs, auroral electrojet, and substorm current wedge.

Development of the Total Westward Auroral Electrojet Current Estimates during Intense Substorms

Development of the Total Westward Auroral Electrojet Current Estimates during Intense Substorms

Power-law dependence of the wavelet spectrum of ground magnetic variations during magnetic storms

We show that time variations in the ring current and auroral electrojets in 2015, during which three major magnetic storms (MSs) occurred, are recorded in several specific ways by ground magnetometers. Specifically, we show that the time variations in magnetic field intensity have power-law wavelet spectra. The variations in ring current intensity are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes between λ=-50° and +50°. We confirmed the results of Balasis et al. (2006), who had shown that the Dst index wavelet spectrum follows a power law of the form f-β, where f is the frequency, and β is the exponent of the power law, by applying the same wavelet analysis to the SYM-H index version of the Dst index, and also to ground magnetic field measurements. Balasis et al. (2006) also showed that the critical exponent β of the power law, obtains values greater than 2 (or equivalently that the Hurst exponent H>0.5), shortly before the onset and during the main phase of the storms. Here, using wavelet transforms on the Earth’s magnetic field as measured at different magnetic latitudes (MLAT), we showed that at mid-geomagnetic latitudes, where the Earth’s magnetic field is determined mainly by the ring current, the resulting Hurst exponent is greater than 0.5 several hours before and during magnetic storms. Geomagnetic field variation at higher magnetic latitudes between λ=+50° and +73°, also show power-law wavelet spectra. However, here we find a more complex dependence with two power-law exponents. We interpret this double power law as the effect of both the ring current and the auroral electrojets. Finally, for polar latitudes, between λ=+73° and +85°, we find the same complex dependence with two power-law exponents. Our results show that the geomagnetic field at auroral latitudes has much lower power and very different wavelet spectra compared to the geomagnetic field at ranges of lower magnetic latitude. Our results show how wavelet-based measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems.

Multi-instrument observations of polar cap patches and traveling ionospheric disturbances generated by solar wind Alfvén waves coupling to the dayside magnetosphere

Abstract. During minor to moderate geomagnetic storms, caused by corotating interaction regions (CIRs) at the leading edge of high-speed streams (HSSs), solar wind Alfvén waves modulated the magnetic reconnection at the dayside magnetopause. The Resolute Bay Incoherent Scatter Radars (RISR-C and RISR-N), measuring plasma parameters in the cusp and polar cap, observed ionospheric signatures of flux transfer events (FTEs) that resulted in the formation of polar cap patches. The patches were observed as they moved over the RISR, and the Canadian High-Arctic Ionospheric Network (CHAIN) ionosondes and GPS receivers. The coupling process modulated the ionospheric convection and the intensity of ionospheric currents, including the auroral electrojets. The horizontal equivalent ionospheric currents (EICs) are estimated from ground-based magnetometer data using an inversion technique. Pulses of ionospheric currents that are a source of Joule heating in the lower thermosphere launched atmospheric gravity waves, causing traveling ionospheric disturbances (TIDs) that propagated equatorward. The TIDs were observed in the SuperDual Auroral Radar Network (SuperDARN) high-frequency (HF) radar ground scatter and the detrended total electron content (TEC) measured by globally distributed Global Navigation Satellite System (GNSS) receivers.

Forecasting GIC Activity Associated With Solar Wind Shocks for the Australian Region Power Network

AbstractsSpace weather induced Geomagnetically Induced Currents (GICs) that are hazardous to power networks at high latitudes are often the result of rapid changes in near‐Earth space current systems such as the auroral electrojets and field‐aligned currents. GIC activity at low‐middle latitudes may be driven by currents that are more relevant to these regions such as the ring or magnetopause current systems. Solar wind shocks create rapid changes in the magnetopause current that manifest as large step changes in the geomagnetic field at the Earth's surface, often referred to as geomagnetic sudden impulses (SIs), that are effective drivers of GIC activity in power networks at low‐middle latitudes. This paper describes the results of a study into the relationship between the driver of SIs, solar wind shocks, and their potential impact on power systems in the Australian region, as quantified by a GIC‐index. The initial data set for analysis was produced by programmatically scanning solar wind data obtained from the ACE satellite spanning the period 1998–2008 for solar wind shocks. For each identified solar wind shock, geomagnetic field data from the Australian region were analyzed to determine the corresponding SI and GIC‐index. Statistical analyses of GIC‐indices and various solar wind parameters associated with the shocks resulted in an empirical model that is a function of solar wind dynamic pressure, geomagnetic latitude, and change in solar wind speed with good operational predictive capability. This model was further assessed using online catalogs of solar wind shock events.

Over 20‐Year Global Magnetohydrodynamic Simulation of Earth's Magnetosphere

AbstractWe present our approach to modeling over 20 years of the solar wind‐magnetosphere‐ionosphere system using version 5 of the Grand Unified Magnetosphere‐Ionosphere Coupling Simulation (GUMICS‐5). As input we use 16‐s resolution magnetic field and 1‐min plasma measurements by Advanced Composition Explorer satellite from 1998 to 2020. The modeled interval is divided into 28 hr simulations including 4 hr overlap. We use maximum magnetospheric resolution of 0.5 Earth radii (RE) up to about 15 RE from Earth and decreasing resolution further away. In the ionosphere we use a maximum resolution of approximately 100 km poleward of ±58° magnetic latitude and decreasing resolution toward equator. With respect to previous version GUMICS‐4, we have parallelized the magnetosphere of GUMICS‐5 using the Message Passing Interface and have made several improvements which have for example, decreased its numerical diffusion. In total we have performed over 8,000 simulations which have produced over 10,000,000 ionospheric files and 2,000,000 magnetospheric files requiring over 100 TB of disk space. We compare these results to several empirical models and geomagnetic indices derived from ground magnetic field measurements. GUMICS‐5 reproduces observed solar cycle trends in magnetopause stand‐off distance and magnetospheric lobe field strength but consistency in plasma sheet pressure and ionospheric cross‐polar cap potential is lower. Comparisons with geomagnetic indices show better results for Kp index than for auroral electrojet index. Our extensive results can serve, for example, as a foundation for combined physics‐based and black‐box approach to real‐time prediction of near‐Earth space, or as input to other physics‐based models of the inner magnetosphere, upper and middle atmosphere, etc.

Auroral Oval Boundary Dynamics on the Nature of Geomagnetic Storm

During emergency events, we could significantly depend on the stable operation of radio communication, navigation, and radars. The ionosphere, especially its auroral regions, significantly influences radio systems, which is why scientists and engineers create systems to monitor these regions. Using data from the global GNSS network, we analyzed the 10 strongest magnetic storms of solar cycle 24: five coronal mass ejection-driven (CME-driven) and five high-speed stream-driven (HSS-driven) storms. The analysis was based on the calculation of the standard deviation of the total electron content (TEC) derivative (rate of TEC index, ROTI). Under all the storms, the ROTI featured similar dynamics: the average ROTI reaches the highest values during the main phase, and the higher the intensity is, the more intense and equatorward the average ROTI registered. The highest cross-correlations are observed with a lag of 1 h, between the IMF z-component Bz and the magnetic latitude where the highest ROTI values appear. The auroral electrojet (SME index) shows the highest impact on the ROTI dynamics. An increase in the space weather indices (in absolute value) is accompanied by a decrease in the latitude where the maximal ROTI occurs. We found that the peculiarities of a storm affect the ROTI dynamics: all the CME-driven storms feature a high cross-correlation (&gt;0.75) between the IMF z-component Bz and the magnetic latitude where the highest ROTI appears, while the HSS-driven storms feature a lower cross-correlation (&lt;0.75) between them. The difference in duration of similar (by maximal values of geomagnetic indices) HSS- and CME-driven storms could produce differences in the highest ROTI values. Correlations show that compared to HSS-driven storms, CME-driven ones more directly impact the ROTI values and locations of regions with a high ROTI.

Using mutual information to investigate non-linear correlation between AE index, ULF Pc5 wave activity and electron precipitation

In this study, we use mutual information from information theory to investigate non-linear correlation between geomagnetic activity indicated by auroral electrojet (AE) index with both the global ultra low frequency (ULF) Pc5 wave power and medium energy (≥30 keV) electron precipitation at the central outer radiation belt. To investigate the energy and magnetic local time (MLT) dependence of the non-linearity, we calculate the mutual information and Pearson correlation coefficient separately for three different energy ranges (30–100 keV, 100–300 keV and ≥300 keV) and four different MLT sectors (0–6, 6–12, 12–18, 18–24). We compare results from 2 years 2004 and 2007 representing geomagnetically more active and less active years, respectively. The correlation analysis between the AE index and electron precipitation shows a clear MLT and energy dependence in both active and quiet conditions. In the two lowest energy ranges of the medium energy electrons (30–100 keV and 100–300 keV) both non-linear correlation and Pearson correlation indicate strong dependence with the AE index in the dawn sector. The linear dependence indicated by the Pearson correlation coefficient decreases from dawn to dusk while the change in the non-linear correlation is smaller indicating an increase in the non-linearity from dawn to dusk. The non-linearity between the AE index and electron precipitation is larger at all MLT sectors except MLTs 6–12 during geomagnetically more active year when larger amount of the activity is driven by interplanetary coronal mass ejections (ICMEs) compared to lower activity year with high speed stream (HSS) and stream interaction region (SIR) driven activity. These results indicate that the processes leading to electron precipitation become more non-linear in the dusk and during geomagnetically more active times when the activity is driven by ICMEs. The non-linearity between the AE index and global ULF Pc5 activity is relatively low and seems not to be affected by the difference in the geomagnetic activity during the 2 years studied.

Magnetic local time (MLT) dependence of auroral peak emission height and morphology

Abstract. We investigate the bulk behaviour of auroral structures and peak emission height as a function of magnetic local time (MLT). These data are collected from the Fennoscandian Lapland and Svalbard latitudes from seven identical auroral all-sky cameras (ASC) over about one solar cycle. The analysis focusses on green auroral emission, which is where the morphology is most clearly visible and the number of images is the highest. The typical peak emission height of the green and blue aurora varies from 110 km on the nightside to about 118 km in the morning MLT over the Lapland region. It stays systematically higher (at 118–120 km) at high latitudes (Svalbard) during the nighttime and reaches 140 km at around magnetic noon. During high solar wind speed (above 500 km s−1), nightside emission heights appear about 5 km lower than during slow solar wind speed (below 400 km s−1). The sign of the interplanetary magnetic field (IMF) has nearly no effect on the emission heights in the night sector, but the northward IMF causes lower emission heights at dawn over Lapland and during the noon hours over Svalbard. While the former is interpreted as a change in the particle population within the field-of-view (FoV), the latter is rather due to the movement of the cusp location due to the IMF orientation. The morning sector heights also show a pronounced difference when previously detected pulsating aurora (PsA) events have been excluded/included in the dataset, suggesting that this type of aurora is a dominant phenomenon in the morning and an important dissipation mechanism. An increase of complex auroral structures in the midnight hours agrees with the average substorm occurrence. This increase is amplified during stronger solar wind driving and during higher geomagnetic activity (as measured by auroral electrojet index, AL). During high solar wind speed, the high latitude auroral evolution shows particularly complex morphology, which is not limited to the nightside but rather only excludes the magnetic noon hours. An increase in the geomagnetic activity further enhances the structural complexity of the aurora in the morning sector.