A. A. Pulkkinen

Ionospheric equivalent current distributions determined with the method of spherical elementary current systems

[1]xa0The ground magnetic field disturbance caused by ionospheric currents can be represented by equivalent currents placed to the ionospheric plane. Equivalent currents provide valuable information about the ionospheric electrodynamics, and thus they can be used, for example, in studies of space weather, ionosphere-magnetosphere coupling, and the magnetotelluric source effect. We derive equivalent currents by using the spherical elementary current system method. The applicability of the method for the Baltic Electromagnetic Array Research (BEAR) magnetometer array is validated by means of synthetic ionospheric current models and by investigating the goodness of the fit between the modeled and measured ground magnetic field. The applicability of the method for the sparser International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network is also proved. In addition, the combination of the elementary current system method and the complex image method, used for the calculation of the induced electromagnetic fields on ground, is introduced, and the combination of the methods is tested by using geoelectric field data from the BEAR project. Our special interest is in the effects that rapidly varying ionospheric currents have on technological conductor systems at the surface of the Earth due to geomagnetically induced currents. Comparison between equivalent currents and the time derivative vector of the horizontal magnetic field emphasizes the importance of small-scale structures.

At substorm onset, 40% of AL comes from underground

Magnetic variations observed at the Earths surface are caused by external and internal sources. External variations arise from currents in the ionosphere and magnetosphere, and internal variations arise from currents induced in the solid Earth. In this paper we examine how large the internal contribution is to magnetic variations measured at the Earths surface. We use IMAGE magnetometer measurements to analyze 77 substorms during 1997. For each event we evaluate the internal and external parts of a locally derived auroral electrojet index (IL index). The magnetic field separation is performed using the Siebert-Kertz equations. A superposed epoch analysis of all events clearly shows that the internal contribution peaks strongly at substorm onset, when the internal contribution is ∼ 40% of the total field. After the substorm peak intensity, the internal contribution decreases almost linearly to the quiet time value of 10-20%. The induction effects are largest during the times of rapid changes and at stations located over the Arctic Ocean.

April 2000 magnetic storm: Solar wind driver and magnetospheric response

[1]xa0On 4 April 2000, a coronal mass ejection (CME) took place close to the western limb of the Sun. The shock front of the CME hit the Earths magnetosphere on 6 April. A strong interplanetary southward BZ event in the sheath region caused a magnetic storm that was the second strongest in the year 2000 if quantified by the peak of the Dst index. We have analyzed this sequence of events using observations of several spacecraft in the solar wind and at geostationary orbit as well as recordings from more than 80 magnetometer stations at latitudes higher than 40°N. In the sheath region behind the shock, the interplanetary magnetic field had an intense and long-sustained southward magnetic field orientation, and the solar wind magnetic pressure was very large, which compressed the dayside magnetopause inside geostationary orbit for a period of more than 6 hours. We conclude that it was the fluctuating but strongly southward field accompanied by the high pressure that allowed for the exceptionally strong driving of magnetospheric activity. During the main phase of the storm, the magnetosphere and ionosphere were in highly perturbed states, with several activations all around the auroral region. Detailed analysis shows that many of these activations were not substorms, in the sense that they were not associated with poleward and westward electrojet/auroral enhancement or geostationary particle injections, but were directly driven perturbations due to variations in the solar wind features. In fact, it was found that the development of the entire storm was quite independent of substorm activations and injections. Instead, the ring current development was driven by the strong convection enhancements. During the storm, the geomagnetically induced currents were strongly enhanced during several periods. While some activations were associated with substorm onsets or electrojet enhancements, others were caused by extremely localized and short-lived electrojet activations.

Recordings and occurrence of geomagnetically induced currents in the Finnish natural gas pipeline network

Abstract A project implemented to study the effects of space weather on the Finnish natural gas pipeline was started in August 1998. The aims of the project were (1) to derive a model for calculating geomagnetically induced currents (GIC) and pipe-to-soil (P/S) voltages in the Finnish natural gas pipeline, (2) to perform measurements of GIC and P/S voltages in the pipeline and (3) to derive statistical predictions for the occurrences of GIC and P/S voltages at different locations in the pipeline network. GIC and P/S voltage were recorded at a compressor station. The GIC measurement was made with two magnetometers, one right above the pipe, and another at the Nurmijarvi Geophysical Observatory about 30 km southwest. The largest GIC since November 1998 has been 30 A. The P/S voltage recording was stopped in May 1999, but GIC is still measured. GIC statistics were derived based on the recordings of the geomagnetic field at Nurmijarvi. The geoelectric field was calculated by using the plane wave model. This field was input to the general pipeline model resulting in the distribution of currents and P/S voltages at selected points in the pipeline. As could be expected, the largest P/S voltage variations occur at the ends of the pipeline network, while the largest GIC flow in the middle parts.

Modelling of space weather effects on pipelines

Abstract The interaction between the solar wind and the Earths magnetic field produces time varying currents in the ionosphere and magnetosphere. The currents cause variations of the geomagnetic field at the surface of the earth and induce an electric field which drives currents in oil and gas pipelines and other long conductors. Geomagnetically induced currents (GIC) interfere with electrical surveys of pipelines and possibly contribute to pipeline corrosion. In this paper, we introduce a general method which can be used to determine voltage and current profiles for buried pipelines, when the external geoelectric field and the geometry and electromagnetic properties of the pipeline are known. The method is based on the analogy between pipelines and transmission lines, which makes it possible to use the distributed source transmission line (DSTL) theory. The general equations derived for the current and voltage profiles are applied in special cases. A particular attention is paid to the Finnish natural gas pipeline network. This paper, related to a project about GIC in the Finnish pipeline, thus provides a tool for understanding space weather effects on pipelines. Combined with methods of calculating the geoelectric field during magnetic storms, the results are applicable to forecasting of geomagnetically induced currents and voltages on pipelines in the future.

Studies of space weather effects on the finnish natural gas pipeline and on the finnish high-voltage power system

Abstract Geomagnetically induced currents (GIC) in technological systems are the ground end of the complicated space weather chain. GIC are a possible source of problems to the systems. In power networks, GIC cause saturation of transformers, which may even result in a collapse of the whole system and in damage of transformers. Pipelines can suffer from problems associated with corrosion and its control. The Finnish high-voltage power grid and the Finnish natural gas pipeline have not encountered GIC harm but due to the high-latitude location of the country and to a general interest in phenomena in the auroral region, an active research of the occurrence of GIC in these systems has been continued for about twenty years. The studies carried out have contained both GIC measurements and theoretical modelling, partly based on geomagnetic data. Estimates of expectable GIC magnitudes at different sites of the systems have been derived. However, GIC values greatly depend on the network configuration, so GIC estimates need not be valid after changes in the configuration. The electric field at the Earths surface is the key parameter when calculating GIC in a network as it is not affected by network configuration changes. Future efforts in investigations of GIC will be focused on understanding ionospheric and magnetospheric processes responsible for large GIC events.

Space weather risk in power systems and pipelines

Abstract Geomagnetically induced currents (GIC) in technological systems, such as electric power transmission grids, oil and gas pipelines, telecommunication cables and railway equipment, are a harmful space weather effect at the earths surface. In power systems GIC cause saturation of transformers, which may lead to serious problems and even to a collapse of the whole system, as occurred in Quebec in March 1989, or to permanent damage of transformers. In buried pipelines GIC give rise to corrosion problems. GIC are driven by the geoelectric field induced by a geomagnetic disturbance. The electric and magnetic fields primarily depend on ionospheric currents and secondarily on currents induced in the earth. GIC risk in a technological system can be decreased by help of forecasting methods. This requires predictions of ionospheric currents to be used as an input for the calculation of the geoelectric field and GIC. Recent developments in the calculation techniques based on the Complex Image Method (CIM) permit fast and accurate computations suitable for a time-critical application like GIC forecasting.

Study explores space weather risk to natural gas pipeline in Finland

Data being collected on the Finnish natural gas pipeline are providing a basis for estimating the space weather risk for the pipeline and for designing possible countermeasures. Finlands high latitude location makes such systems prone to problems caused by geomagnetically induced currents (GICs),but so far no harm has been detected. n nThe statistical GIC risk in the Finnish high-voltage power system has already been estimated [Viljanen and Pirjola, 1989semi;Makinen, 1993],and the recent 8-month project in 1998 to 1999, involving the Gasum Oy Company and the Finnish Meteorological Institute, has been gathering similar statistics on the pipeline. The work is based on theoretical model calculations of the geoelectric field, on observatory recordings of magnetic variations, on measurements of GICs in the pipeline, and on an extension of distributed-source transmission line (DSTL) theory.

Breakdown caused by a geomagnetically induced current in the Finnish telesystem in 1958

Abstract At the Earths surface, a “space weather” event is seen as a geomagnetic storm, accompanied by a geoelectric field, and “geomagnetically induced currents” (GIC) in technological systems, like electric power transmission grids, pipelines, telecommunication networks and railway equipment. In general, GIC are a potential source of problems to the system. Although Finland is located at high latitudes with intense geomagnetic storms the country has not suffered from major GIC harm. This paper presents the only event with noticeable GIC consequences in Finland, namely a sudden interruption of two coaxial phone cable systems in the southern part of the country during the great magnetic storm of February 11, 1958. Blown fuses associated with the ac power feed at the repeaters were the reason for the problems. As inferred from analogue magnetograms of the Nurmijarvi Geophysical Observatory in southern Finland, the largest time derivatives of the magnetic field were about 6.5 nT / s . A rough estimation indicates a strength of the GIC of about 0.5 A , which would not be a high value in power lines, but obviously critical in a telecommunication system.

Ground Effects of Space Weather

Space storms produce geomagnetically induced currents (GIC) in technological systems at the Earth’s surface, such as electric power transmission grids, pipelines, communication cables and railways. Thus GIC are the ground end of the space weather chain originating from the Sun. The first GIC observations were already made in early telegraph equipment about 150 years ago, and since then several different systems have experienced problems during large magnetic storms. Physically, GIC are driven by the geoelectric field induced by a geomagnetic variation. The electric and magnetic fields are primarily created by magnetospheric-ionospheric currents and secondarily influenced by currents induced in the Earth that are affected by the ground conductivity. The most violent magnetic variations occur in auroral regions, which indicates that GIC are a particular high-latitude problem but lower-latitude systems can also experience GIC problems. In power networks, GIC may cause saturation of transformers with harmful consequences extending from harmonics in the electricity to large reactive power consumption and even to a collapse of the system or to permanent damage of transformers. In pipelines, GIC and the associated pipe-to-soil voltages can enhance corrosion and disturb corrosion control measurements and protection. Modelling techniques of GIC are discussed in this paper. Having information about the Earth’s conductivity and about space currents o the ground magnetic field, a GIC calculation contains two steps: the determination of the geoelectric field and the computation of GIC in the