Geomagnetically induced currents in a Norwegian transformer station

This report considers measurements of geomagnetically induced current (GIC) and comparison to recorded variations in the geomagnetic field (dB/dt). The GIC-sensors were installed in the neutral point of a 420 kV transformer located in Mid-Norway in 2019. The magnetometers (for dB/dt) are also located in Mid-Norway, but at another location. Recordings up to December 2021 are presented in this report. The maximum recorded GIC and dB/dt was about +/- 60 A and 14 nT/s, respectively. From linear regression, GIC is approximated to 3 times dB/dt, where GIC is measured in amps and dB/dt in nT/s. GIC is always lower than 7 times dB/dt based on the dataset with day-max values (699 points).Geomagnetically induced currents in a Norwegian transformer stationpublishedVersio

A-CHAIM: Near-Real-Time Data Assimilation of the High Latitude Ionosphere With a Particle Filter

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

An automated auroral detection system using deep learning: real-time operation in Tromsø, Norway

The activity of citizen scientists who capture images of aurora borealis using digital cameras has recently been contributing to research regarding space physics by professional scientists. Auroral images captured using digital cameras not only fascinate us, but may also provide information about the energy of precipitating auroral electrons from space; this ability makes the use of digital cameras more meaningful. To support the application of digital cameras, we have developed artificial intelligence that monitors the auroral appearance in Tromsø, Norway, instead of relying on the human eye, and implemented a web application, “Tromsø AI”, which notifies the scientists of the appearance of auroras in real-time. This “AI” has a double meaning: artificial intelligence and eyes (instead of human eyes). Utilizing the Tromsø AI, we also classified large-scale optical data to derive annual, monthly, and UT variations of the auroral occurrence rate for the first time. The derived occurrence characteristics are fairly consistent with the results obtained using the naked eye, and the evaluation using the validation data also showed a high F1 score of over 93%, indicating that the classifier has a performance comparable to that of the human eye classifying observed images

A statistical study of convective and dynamic instabilities in the polar upper mesosphere above Tromsø

We have studied the convective (or static) and dynamic instabilities between 80 and 100 km above Tromsø (69.6° N, 19.2° E) using temperature and wind data of 6 min and 1 km resolutions primarily almost over a solar cycle obtained with the sodium lidar at Tromsø. First, we have calculated Brunt–Väisälä frequency (N) for 339 nights obtained from October 2010 to December 2019, and the Richardson number (Ri) for 210 nights obtained between October 2012 to December 2019. Second, using those values (N and Ri), we have calculated probabilities of the convective instability (N2<0) and the dynamic instability (0≤Ri<0.25) that can be used for proxies for evaluating the atmospheric stability. The probability of the convective instability varies from about 1% to 24% with a mean value of 9%, and that of the dynamic instability varies from 4 to 20% with a mean value of 10%. Third, we have compared these probabilities with the F10.7 index and local K-index. The probability of the convective instability shows a dependence (its correlation coefcient of 0.45) of the geomagnetic activity (local K-index) between 94 and 100 km, suggesting an auroral infuence on the atmospheric stability. The probability of the dynamic instability shows a solar cycle dependence (its correlation coefcient being 0.54). The probability of the dynamic instability shows the dependence of the 12 h wave amplitude (meridional and zonal wind components) (C.C.=0.52). The averaged potential energy of gravity waves shows decrease with height between 81 and 89 km, suggesting that dissipation of gravity waves plays an important role (at least partly) in causing the convective instability below 89 km. The probability of the convective instability at Tromsø appears to be higher than that at middle/low latitudes, while the probability of the dynamic instability is similar to that at middle/low latitudes

The Dayside Open/Closed Field line Boundary -Ground-based optical determination and examination

The Open/Closed eld line Boundary (OCB) is the most important boundary in the magnetospheric system. On the dayside, the equatorward edge of the 6300 Å[OI] cusp aurora can be used as a proxy for the OCB. This work, which is a dissertation for the degree of philosophiæ Doctor consists of three scienti c papers focusing on the latitude of the optical cusp OCB and one paper focusing on polar cap patch generation mechanisms in the vicinity of the OCB. In Paper I we use modeling to demonstrate the variability of the cusp aurora with respect to vertical volume emission rate pro les and horizontal modulation owing to neutral wind. A meridian scanning photometer (MSP) simulator has been developed in order to study the manifestation of the cusp aurora in the MSP data from Svalbard. A method for obtaining the OCB location and nding the correct mapping altitude in order to transform the OCB location from MSP scan angle to magnetic latitude is found by simulating the horizontal movement of a reference cusp aurora. The reference cusp aurora, which is based on expected ionospheric and atmospheric conditions and electron precipitation characteristics, is de ned from the modeling results. Uncertainties in the scan angle to magnetic latitude transformation are found by simulating a wide range of realistic cusp auroras deviating from the reference cusp aurora. In Paper II the method of Paper I for finding the OCB is tested on real MSP data and compared with the OCB as obtained by satellite energetic particle measurements with very successful results. In Paper III the method of Paper I is used on 15 years of MSP data from Svalbard in order to study the statistical behavior of the cusp OCB. A possible relationship between the OCB latitude in the cusp and the solar cycle is revealed, and a possible expansion is brie y discussed. By comparing the OCB latitude with solar wind parameters, solar wind-magnetosphere coupling functions and geomagnetic indices, good correlations are found, which are in concurrence with previous satellite based, statistical studies. We nd a relationship between the OCB latitude and the ring current density (SYM/H), demonstrating great complexity in the physics behind the OCB location. We argue that the balance between reconnection dynamics on the dayside and nightside as well as the history or integral of previous events in the magnetospheric system are important factors for governing the cusp OCB latitude. Paper IV gives an overview of the solar wind and ionospheric conditions as measured during the Investigation of Cusp Irregularities 2 sounding rocket campaign. The rocket was launched through a newly produced polar cap patch. Based on the measurements performed in-situ by the rocket instrumentation and with groundbased optics and radars, a new creation mechanism, which partly involves ionization by both particle precipitation and solar irradiation and upwelling from sub F-layer altitudes, is suggested

Real-time determination and monitoring of the auroral electrojet boundaries

A method for nowcasting of the auroral electrojet location from real-time geomagnetic data in the European sector is presented. Along the auroral ovals strong electrojet currents are flowing. The variation in the geomagnetic field caused by these auroral electrojets is observed on a routine basis at high latitudes using ground-based magnetometers. From latitude profiles of the vertical component of these variations it is possible to identify the boundaries of the electrojets. Using realtime data from ground magnetometer chains is the only existing method for continuous monitoring and nowcasting of the location and strength of the auroral electrojets in a given sector. This is an important aspect of any space weather programme. The method for obtaining the electrojet boundaries is described and assessed in a controlled environment using modelling. Furthermore a provisional, real-time electrojet tracker for the European sector based on data from the Tromsø Geophyiscal Observatory magnetometer chain is presented. The relationship between the electrojet and the diffuse auroral oval is discussed, and it is concluded that although there may exist time-dependent differences in boundary locations, there exists a general coincidence. Furthermore, it is pointed out that knowledge about the latitudinal location of the geomagnetic activity, that is the electrojets, is more critical for space weather sensitive, ground-based technology than the location of the aurora

Geomagnetic induced currents in long subsea power cables

Source at https://www.sintef.no/.This report focuses on geomagnetically induced currents (GIC) that can be induced in long subsea power cables. Literature indicates that the water depth itself, in which the cable will be laid, will not contribute to an attenuation of the geoelectric field for those water depths relevant for the Krafla power cable. However, the presence of a coast will introduce a strong enhancement. Even minor (<20 years) and moderate (~20-100 years) geomagnetic events can potentially cause considerable operational difficulty if sufficient mitigations are not in place. A close cooperation with Statnett (transmission system operator) is essential to limit any unintentional disconnection of the Krafla subsea cable

Geomagnetic induced currents in long subsea power cables

This report focuses on geomagnetically induced currents (GIC) that can be induced in long subsea power cables. Literature indicates that the water depth itself, in which the cable will be laid, will not contribute to an attenuation of the geoelectric field for those water depths relevant for the Krafla power cable. However, the presence of a coast will introduce a strong enhancement. Even minor (<20 years) and moderate (~20-100 years) geomagnetic events can potentially cause considerable operational difficulty if sufficient mitigations are not in place. A close cooperation with Statnett (transmission system operator) is essential to limit any unintentional disconnection of the Krafla subsea cable.Geomagnetic induced currents in long subsea power cablespublishedVersio

On the relation between ionospheric parameters and sunspot number

In a recent study, mid-latitude ionospheric parameters were compared with solar activity; it was suggested that the relationship between these, earlier assumed stable, might be changing with time (Lastovicka, 2019). Here, the information is extended to higher latitude (69.6°N, 19.2E) and further back in time. For the ionospheric F-region (viz. the critical frequency, FoF2) the same behaviour is seen with a change-point around 1996. For the ionospheric E-region (viz. the critical frequency, foE), change-points are less obvious than in the mid-latitude study, presumably owing to the observation site lying under the auroral oval

On the correction of temperatures derived from meteor wind radars due to geomagnetic activity

Radars used to observe meteor trails in the mesosphere deliver information on winds and temperature. Use of these radars is becoming a standard method for determining mesospheric dynamics and temperatures worldwide due to relatively low costs and ease of deployment. However, recent studies have revealed that temperatures may be overestimated in conditions such as high geomagnetic activity. The effect is thought to be most prevalent at high latitude, although this is not yet proven. Here, we demonstrate how temperatures might be corrected for geomagnetic effects; the demonstration is for a particular geographic location (Svalbard, 78°N, 16°E) because it is local geomagnetic disturbances that affects local temperature measurements, therefore requiring co-located instruments. We see that summer temperatures require a correction (reduction) of a few Kelvin, but winter estimates are more accurate