Luehr, H; (2008) Ionospheric Current Quantification and Modelling for Improved Magnetic and Electric Field Analyses for Swarm (SWIO-SST-FR(2) ). ESTEC

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Abstract

This report describes the results of activities performed during the Science Study “Ionospheric Current Quantification and Modelling for Improved Magnetic and Electric Field Analyses” (ESTEC Contract No. 20943/07/NL/JA). This study intends to evaluate magnetic field recovery approaches for single component current systems in the night side ionosphere. The determination of ionospheric magnetic fields is especially important for main and crustal magnetic field modellers in order to avoid spurious effects in their results. These corrections are particularly important when field gradients (differences between two satellites) are employed in field modelling efforts. The gradient approach is considered as being a dedicated analysis tool for Swarm. The assessment of the single component current recovery is achieved by comparing the retrieved magnetic fields with results derived from the integration of current elements on the entire low and mid latitude night side. The requested test environment is provided by a physics-based ionosphere/thermosphere model. At the beginning, section 2 introduces dominant night side ionospheric currents and their significance for main and crustal field modelling. It also includes methods for the single component current recovery and reveals their limitations. Section 3 describes the physics based model in use, the Coupled Ionosphere-Thermosphere-Plasmasphere (CTIP) model pointing out its advantages and limitations. Section 4 describes the process of creating the modelled ionospheres and the resulting CTIP synthetic data base. The verification of the model output (the synthetic data base) against independent observations is performed in section 5. Methods of magnetic field recovery from modelled ionospheres and its applicability to the CTIP data base are discussed in section 6. Section 7 assesses the magnetic field derived from single component current recovery in comparison with the Biot-Savart method of currents calculated from the modelled data. The GPS measurements of total electron content (TEC) on board satellites are crucial ingredients to develop ionospheric models which in turn will help to interpret ionospheric current systems. Swarm will provide TEC observations, and section 8 describes our TEC retrieval approach. It also includes the justification for the product and mentions anticipated users. Small-scale but significant magnetic field deflections arise from ionospheric plasma irregularities in the post-sunset ionosphere (bubbles). The method of identifying bubbles in satellite magnetic field observations is given in section 9. Section 10 summarizes the important results obtained in this study.

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