**4. Conclusion**

38 Space Science

V/km creates. Here it should be noted that, by using a linear superposition, these data enable the computation of GIC due to any uniform horizontal geoelectric field impacting the network. For some additional details about the test model, Pirjola (2009) is referred to.

The Rauma 400 kV station discussed in Section 2.1 and especially in Figure 1 was not yet included in the Finnish 400 kV system in October 1978 to November 1979. It is located in the line between stations 4 and 7 quite near station 7. Note that geographic and geomagnetic latitudes are far from being parallel in Finland and that the former are higher. In North America, the geographic latitudes are lower than the geomagnetic since the north

Pirjola & Lehtinen (1985) present theoretical computations of GIC for the Finnish natural gas pipeline by using the matrix formalism discussed in Section 3.1 and appropriate to a discretely-earthed network, such as a power system. The assumption is included in the treatment by Pirjola & Lehtinen (1985) that the insulating coating of the pipeline is ideal and perfect with a zero conductivity and that the pipeline is earthed at the cathodic protection stations. This approximation should not be considered very good because the large surface area of the pipe makes the pipeline continuously earthed in practice even though the conductivity of the coating material is very small. Furthermore, the CP stations do not constitute normal earthings since the current can only go to the Earth there (to return from

Viljanen (1989) presents a GIC study about the Finnish natural gas pipeline based on the simplified assumption that the pipeline is an infinitely long multi-layered cylindrical structure in a homogeneous medium. The model is in agreement with the continuous earthing but it is otherwise too much idealised. According to this model, GIC flowing along the pipeline may reach values of hundreds of amps, which are clearly larger than those measured in Finland (Section 2.1). Although Viljanen (1989) also estimates the effects of a horizontal change of the Earth's conductivity, and of a bend of the pipeline, the treatment is not yet complete for a real pipeline network. A significant improvement in theoretical modelling is shown by Boteler (1997) by incorporating the distributed-source transmission line theory into pipeline-GIC calculations. In fact, the applicability of the DSTL theory is already considered by Boteler and Cookson (1986). An extension is provided by Pulkkinen et al. (2001b) as they also treat branches of a

In the DSTL theory, the pipeline is considered a transmission line containing a series impedance (or resistance due to the dc treatment) *Z* determined by the properties of the pipeline steel and a parallel admittance *Y* associated with the resistivity of the coating. The geoelectric field affecting the pipeline forms the distributed source. An important parameter, called the adjustment distance, is the inverse of the propagation constant

Typical values of the adjustment distance of a real pipeline are tens of kilometres. For the Finnish natural gas pipeline, *Z* = 5…9·10–3 km–1 and *Y* = 5·10–2…0.25 –1 km–1 with the

*ZY* (17)

geomagnetic pole is on the American side of the geographic pole.

**3.2 Pipelines** 

the ground to the pipe elsewhere).

pipeline network.

defined by

Geomagnetically induced currents (GIC) are ground effects of space weather, which is associated with a complex chain of phenomena extending from processes in the Sun to GIC in technological networks. In general, GIC are a possible source of problems to the network. Thus research of GIC is practically important, but it also has scientific significance because a ground-based network carrying GIC can be regarded as a huge antenna that collects information from processes in space and within the Earth.

The first GIC observations date back to early telegraph systems more than 150 years ago. Today power systems constitute the most important target of GIC research. The problems in power networks result from half-cycle saturation of transformers created by dc-like GIC. In the worst cases, large areas may experience a blackout due to GIC and transformers can be permanently damaged. The most significant GIC event so far is the blackout in Québec, Canada, for several hours during a large geomagnetic storm in March 1989. Another well-known GIC event caused a blackout in southern Sweden during the so-called "Halloween storm" at the end of October 2003. In 2011 to 2014, an EU-funded project is going on in which GIC in the entire European high-voltage system are considered.

In this paper, we discuss the techniques readily available for calculating GIC values in power networks and pipelines. Future research efforts should be focussed on the application

Geomagnetically Induced Currents as Ground Effects of Space Weather 41

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#### **5. Acknowledgment**

The author wishes to thank his colleagues for excellent collaboration in GIC research during many years. Special thanks go to Drs. David Boteler (Canada), Antti Pulkkinen (Finland & USA), Larisa Trichtchenko (Canada), Ari Viljanen (Finland) and Magnus Wik (Sweden) (in alphabetical order). The author also wants to acknowledge the interest and support that Finnish power and pipeline industry have shown to GIC investigations during more than thirty years.

#### **6. References**


40 Space Science

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**3** 

*USA* 

**Why Isn't the Earth Completely** 

*2Dept. of Earth and Planetary Sciences, MSC03-2040* 

*3University of Wisconsin at Green Bay, Green Bay* 

Joseph A. Nuth III1, Frans J. M. Rietmeijer2 and Cassandra L. Marnocha1,3 *1Astrochemistry Laboratory, Code 691 NASA's Goddard Space Flight Center, Greenbelt* 

There is considerable discussion about the origin of Earth's water and the possibility that much of it may have been delivered by comets either within the first several hundred million years or possibly over geologic time [Drake, 2005]. Typical models for the origin of the Earth begin by assuming the accumulation of some combination of chondritic meteorites (Javoy, 1995; Ringwood, 1979; Wanke, 1981), yet it is highly likely that the asteroids that went into the terrestrial planets are no longer represented to any significant extent in the present-day asteroid population (Nuth, 2008). The argument concerning the composition of the building blocks of the Earth is typically phrased in terms of the chemical composition of the terrestrial mantle as compared to that of primitive meteorites [Righter et al., 2006] or to the isotopic composition of the Earth's oceans as compared to that of cometary water [Righter, 2007]. Both of these considerations yield important constraints on the problem. However, we will demonstrate that a completely novel examination of the problem based on models of nebular accretion, terrestrial planet formation and the evolution of primitive bodies makes using any modern meteorite type as the basis for understanding the volatile content of the Earth inappropriate. Unfortunately, while this approach yields terrestrial planets with sufficient water to easily explain the Earth's oceans, it also introduces a new

problem: How do we get rid of the massive excess of water that this model predicts?

The mechanism for the formation of the terrestrial planets has been the subject of considerable debate. Gravitational instabilities in a dusty disk (Goldreich & Ward, 1973; Youdin and Shu, 2002) may have been responsible for planetesimal formation on very rapid timescales compared to the lifetime of the nebula. On the other hand, collisional accretion of larger aggregates starting from primitive interstellar dust grains should also occur in the nebula (Blum, 1990; Blum and Wurm, 2000), and these aggregates could continue to evolve into kilometer scale planetesimals or even into proto-planetary scale objects. While it is not clear if dust and gas can be concentrated sufficiently to trigger the gravitational accretion (Cuzzi and Weidenschilling, 2006) of planetesimals or proto-planets, it is clear that some level of collisional accretion must occur in proto-planetary nebulae in order to at least make chondrule precursors and probably to make components of meteorite parent bodies, meters

**1. Introduction** 

**Covered in Water?** 

*University of New Mexico, Albuquerque* 

induced currents on Swedish technical systems. *Annales Geophysicae*, Vol.27, No.4, pp. 1775-1787

Wik, M.; Viljanen, A.; Pirjola, R.; Pulkkinen, A.; Wintoft, P. & Lundstedt, H. (2008). Calculation of geomagnetically induced currents in the 400 kV power grid in southern Sweden. *Space Weather*, Vol.6, No.7, S07005, doi: 10.1029/2007SW000343, 11 pp.
