Juan José Curto

Evolution of the concept of Sudden Storm Commencements and their operative identification

In this paper, we review the evolution of both, the concept and the operative methods of detection of Storm Commencements (SC’s) and we introduce suggestions for future improvements. Finally, a more precise definition of the events with consequences in terminology and detection is proposed.

Milestones of the IAGA International Service of Rapid Magnetic Variations and its contribution to geomagnetic field knowledge

The Service of Rapid Magnetic Variations (RMV) was created by the International Association of Geomagnetism and Aeronomy (IAGA) with the aim of obtaining an overall view of the temporal and spatial distribution of RMV as a base for further study of these phenomena. The Ebro Observatory participated in the creation of this service and has been administering it from the beginning; consequently, the histories of these two organizations are intertwined.

Automatic detection of sudden commencements using neural networks

The aim of this work is to develop an automatic system to detect sudden commencements (SCs). SCs are produced by a sudden increase of solar wind dynamic pressure and are detected simultaneously everywhere on the ground (Araki, 1994). Since 1975, Ebro Observatory is responsible to elaborate the list of SC, following the morphological rules given by Mayaud (1973). Nowadays, this task is still done manually and presents some difficulties; the most worrying one is the decreasing number of observatories who collaborate with this task because most of them opted for the installation of unattended observatories. Hence, the necessity of an alternative method to continue the service becomes a urgency. The automatic method presented in this work is based on neural network analysis. To succeed with neural networks, we did a previous work of characterization and parameterization of SCs by statistical analysis. In this way, we focused on the determination of the appropriate parameters to be used as the inputs of the network which resulted to be: slope, change of magnetic activity and difference of the levels before and after the jump. We worked with X component and also with Y component. An important criteria introduced in this work is the necessary coherence of the results obtained with this new automatic method with those obtained with the manual method and reported in the old list of SC. Finally, the neural network is able to recognize the SC pattern successfully, but now this is achieved in a non-manned way. A robust quasi-real-time detection can be undertaken in the future.

A new approach to the hourly mean computation problem when dealing with missing data

Geomagnetic observatory records are unavoidably affected by primary data interruptions which, in turn, may have possible effects on the accuracy of the definitive data derived from them. One of the products most widely used by the scientific community is the mean hourly values, immediately obtained from the primary minute values of the geomagnetic field. Although some precepts have already been proposed and used, a definitive criterion regarding the procedure to follow when dealing with missing data has not yet been established. This could be seen in the last IAGA meetings and workshops, where several constructive opinions were put forward in this respect. The present discussion is devoted to analyzing the effects that different amounts of missing data have upon the accuracy of the means, a necessary step before establishing a definitive rule as to how to deal with these situations. In this statistical approach, we propose a new criterion based on the relative value of the root mean square error (between actual and computed means) with respect to the natural magnetic field variations of the original hourly interval.

Geomagnetic secular variation over Spain 1970-1988 by means of spherical cap harmonic analysis

Abstract A spherical cap harmonic analysis was applied to Spain and neighbouring areas, covering a region with a cap halfangle of 16°. The technique, due to Haines, has allowed us to obtain a model of secular variation (SV) for a time interval of 18 years reduced to the epoch 1987.5. The total number of selected data points was 1581 provided from ten observatories and 60 repeat stations. The SV model has a maximum spatial index of four and temporal degree of two. The coefficients were tested and the statistically non-significant terms removed. Another model covering a smaller region with greater density of data has been developed and both results compared. The average secular variations derived from the definitive geomagnetic reference field (DGRF) and the international geomagnetic reference field (IGRF) were compared with these models and maps plotting the calculated first field derivatives are presented. The integration of the final model will serve to update satellite data in order to produce a regional main field model.

Automatic measurement of magnetic records on photographic paper

Abstract Measuring and storing magnetometer data recorded photographically is a difficult problem for a geomagnetic observatory. In the Ebre Observatory, to overcome the problem, we have developed a system using modern computing advances which include electronic scanning, storage on CD-ROM media, and image analysis. This paper describes the main processes performed by this system. In particular, it describes the main difficulties found in the process of digitization (intersections, gaps,…) and how they were solved.

Quality control of Ebro magnetic observatory using momentary values

Intercomparison of momentary values from observatories across Europe can be used as a test of reliability for a particular magnetic station in this area, as well as the whole network. The method presented by Voppel at the IAGA Assembly of Grenoble (1975) and developed by Schulz and Voppel at the IAGA Assembly of Edinburgh (1981) is based on simultaneous measurements taken at 02:00 UT, which coincides with the period least disturbed by Sq associated currents on central European longitudes. A selected list of ten least disturbed days per month is provided by the Niemegk (initially Wingst) Geomagnetic Observatory which gathers the corresponding momentary values from the collaborating institutions. This method can be applied to detect fluctuations or jumps in geomagnetic standards. Independent techniques, like linear regression and axial intercept of the standard deviation of the mutual differences of monthly mean values, have been applied to the magnetic elements of Ebro Observatory (EBR) for the period 1997–2001. These tools give results in good agreement amongst them, and most of the coefficients are similar to those obtained for the most significant observatories of the network. No jumps or trends in data are observed, indicating excellent performance of EBR.