1  Background

The proposed ISO standard is a magnetic field model of the Earth's magnetosphere. It is intended to calculate the magnetic induction field generated from a variety of current systems located on the boundaries and within the boundaries of the Earth's magnetosphere under a wide range of environmental conditions, quiet and disturbed, affected by Solar-Terrestrial interactions simulated by Solar activity such as Solar Flares and related phenomena which induce terrestrial magnetic disturbances such as Magnetic Storms.

1.1  Purposes and scope

The goals of standardization of the Earth's magnetospheric magnetic field are:

• providing the unambiguous presentation of the geomagnetic field of currents flowing inside the Earth and the magnetic field of magnetospheric currents;
• providing comparability of results of interpretation and analysis of space experiments;
• providing less labour-consuming character of calculations of the magnetic field of magnetospheric currents in the space at geocentric distances of 1-6.6 Earth's radii (R_E);
• providing the most reliable calculations of all elements of the geomagnetic field in the space environment.

The main purposes of elaboration of the "Model of the Earth's Magnetospheric Magnetic Field" Standard are

• standardization of method of presentation of the magnetospheric magnetic field as a sum of magnetic fields induced by large-scale magnetospheric current systems;
• standardization of the set of physical parameters of magnetospheric current systems ("key model parameters");
• standardization of the methods of magnetospheric magnetic field calculations by temporal variations of the magnetospheric current systems parameters;
• elaboration of the quantitative model of the Earth's Magnetospheric Magnetic Field dependent on physical parameters.

Technique of calculation of the main parameters of the magnetospheric model using data of measurements in the Earth's environment is not the subject of standardization.

The model elaborated in the framework of standard will work in

• Data Analyzing
• Watching the space environment conditions
• Forecasting the space environment conditions
• Warning the expected extremal conditions
• Postcasting and case study

1.2  Identification of users

The model will be useful for user communities working with applications in Space Weather Forecasting, human health radiation hazards determination, the estimation of spacecraft and electronic devices integrity, and in pure and applied space physics environmental research.

1.3  Users requirements

The ultimate objective of space weather research is the development of quantitative forecasting models. The main requirements of the Space Weather community to magnetospheric model are

• Model reliability:

  1. the model of the magnetospheric currents magnetic field must describe a regular part of the magnetic field, its dependence on the interplanetary medium parameters and reflects such magnetospheric magnetic field features as depression of the Earth's magnetosphere on the dayside due to its interaction with the solar wind, day and seasonal variations of the magnetic field;
  2. the model takes into account the tilt angle between the geomagnetic dipole and plane orthogonal to the Earth-Sun line varying within a range from -35 to +35 degrees;
  3. the model describes dynamics of the magnetospheric large-scale current systems;
  4. the model takes into account the dependence of the magnetic field of the magnetospheric current systems on the conditions in the Earth's environment;
  5. the model enables description of the magnetosphere under disturbed conditions, without restrictions imposed on the values of interplanetary medium parameters;
  6. the model enables taking into account variations of the magnetopause form and location as well as IMF penetration into the magnetosphere in dependence on solar wind conditions.
• Algorithm simplicity allowing the real-time (near real-time) calculations.
• The model must be based on closed set of mathematical equations derived from well founded physical principles.

1.4   Specification of the usefulness of the proposed standard

The model is used for instance to harden both spacecraft and the sensitive electronic devices carried by them from the effects of high-energy cosmic radiation. Space Weather Forecasting has value to the electrical utility community which can loose of millions of dollars in equipment such as transformers and in downtime due to magnetic storm induction effects at the Earth's surface. For example, during the March 1989 magnetic storm the Quebec Hydroelectric Utility grid failed costing on the order of 8600 million. Other utility grids around the world were also adversely affected by this storm. Transcontinental oil and gas pipelines are also susceptible to electromagnetic induction due to Space Weather, which causes corrosion and high-voltage hazards. Similar problems occur with spacecraft such as communications and weather satellites. These satellites are often in geostationary orbits. During a magnetic storm, the magnetospheric boundary, called the magnetopause, which ordinary acts as a deflecting shield against the Solar Wind is compressed inside the orbits of these satellites, leaving them exposed to the full impact of the Solar Wind's radiation. Often the orientation of the satellites is determined by sensing the geomagnetic field. During a magnetic storm, when the magnetopause is compressed inside a satellite's orbit, the magnetic field orientation is suddenly reversed causing the satellite to abruptly rotate, which inturn causes extended booms (e.g. gravity gradient stabilization booms and others carrying electronic sensors) to snap off, leaving the satellite dysfunctional. The strong increase of the relativistic electron fluxes in the inner magnetosphere during magnetic storm main and recovery phases is the factor which can also be responsible for the satellite dysfunction and even losses. With sufficient warning through Space Weather forecasting, such damage can be minimized or eliminated.

Noting that over the past century the degree of Solar activity in terms of the number of sunspots occurring during the maximum of the 11-year Solar Cycle has generally been increasing from one cycle to the next, with some exceptions, and noting that the Earth's dipole magnetic field strength, which accounts for approximately 90% of the Earth's total magnetic field, is currently decreasing by approximately 7.14% per century, and further noting that Earth's dipole field strength has decreased by 50% in the passed 2000 years, it is clear that the degree of penetration of energetic cosmic radiation to lower altitudes is correspondingly increasing. This in turn heats the upper atmosphere, which eventually affects the lower atmosphere and subsequently the daily weather and storm patterns at Earth's surface as well as posing human health hazards such as increased cancer risk due to increased radiation at the Earth's surface. The more energy penetrating into the Earth's atmosphere, the more active atmospheric weather patterns tend to be and the more severe are the solar related health hazards likely to be. These facts, plus our increased use of the space environment, mean substantially increased hazards related to Space Weather over the next century. Knowledge through modeling of the magnetospheric environment and the resulting ability to predict its behavior are therefore becoming critical from the points of view of space mission accomplishment, health, economics, and natural disaster mitigation. Space Weather is clearly a global phenomenon, for which it is desirable to have an internationally accepted magnetospheric model.

1.5   Short review of relevant existing models

At present a lot of the models are used to calculate the magnetic field in the magnetosphere. The empirical models based on averaging of spacecraft experimental data (the OP-74, MF-73, T-87, T-89 models) allowing the real-time calculations and satisfactory describe the main magnetospheric magnetic field features during quite times but can not represent the magnetic field dynamics especially during disturbances. Their parameters are often non-physical and can not be changed according to magnetospheric conditions.

Version of the Tsyganenko model, T96 [Tsyganenko, 1995], uses the observed values of Dst, Bz_IMF, and the solar wind dynamic pressure to parameterize the intensity of the magnetospheric current systems. In the T96 model these parameters are replaced with the Kp index which has been used in the earlier versions of the Tsyganenko models. The T96 (as the earlier Tsyganenko models) was constructed using the minimization of the deviation from a data set of the magnetospheric magnetic field measurements gathered by several spacecrafts during many years. The disturbed periods are relatively rare events during the observation time, so their influence on the model coefficients is negligibly small. That is why the T96 model's applicability is limited by Dst, Bz_IMF, and the solar wind dynamic pressure low values.

So-called dynamical models are based on mathematical equations derived from physical lows and allow calculations of magnetospheric magnetic field for any level of disturbance. The investigation of the magnetospheric current systems during magnetic storm is possible in terms of the modern dynamic models of the magnetospheric magnetic field (OP-88, HV-95, A96). An important advantage of the paraboloid model A96 [Alexeev et al., 1996] is that it can describe the magnetic field of each magnetospheric current system as a function of its own time-dependent input parameters. A functional dependence of the model input parameters on the empirical data obtained by the satellites and on-ground observatories is determined by a set of submodels. The term ``submodel'' is used for the analytical definition of each model input parameter as a function of the empirical data.