Santiago Marsal

Evidence for a new geomagnetic jerk in 2014

The production of quasi-definitive data at Ebre observatory has enabled us to detect a new geomagnetic jerk in early 2014. This has been confirmed by analyzing data at several observatories in the European-African and Western Pacific-Australian sectors in the classical fashion of looking for the characteristic V shape of the geomagnetic secular variation trend. A global model produced with the latest available satellite and observatory data supports these findings, giving a global perspective on both the jerk and a related secular acceleration pulse at the core-mantle boundary. We conclude that the jerk was most visible in the Atlantic and European sectors.

Remote Geophysical Observatory in Antarctica with HF Data Transmission: A Review

The geophysical observatory in the Antarctic Spanish Station, Juan Carlos I (ASJI), on Livingston Island, has been monitoring the magnetic field in the Antarctic region for more than fifteen years. In 2004, a vertical incidence ionospheric sounder completed the observatory, which brings a significant added value in a region with low density of geophysical data. Although the ASJI is only operative during the austral summer, the geomagnetic station records the data throughout the year. A High Frequency (HF) transmission system was installed in 2004 in order to have the geomagnetic data available during the whole year. As the power supply is very limited when the station is not operative, we had to design a low-power HF transceiver with a very simple antenna, due to environmental aspects. Moreover, the flow of information was unidirectional, so the modulation had to be extremely robust since there is no retransmission in case of error. This led us to study the main parameters of the ionospheric channel and to design new modulations specially adapted to very low signal to noise scenarios with high levels of interference. In this paper, a review of the results of our remote geophysical observatory and associated transmission system in Antarctica during the last decade is presented.

Remote sensing and skywave digital communication from antarctica.

This paper presents an overview of the research activities undertaken by La Salle and the Ebro Observatory in the field of remote sensing. On 2003 we started a research project with two main objectives: implement a long-haul oblique ionospheric sounder and transmit the data from remote sensors located at the Spanish Antarctic station Juan Carlos I to Spain. The paper focuses on a study of feasibility of two possible physical layer candidates for the skywave link between both points. A DS-SS based solution and an OFDM based solution are considered to achieve a reliable low-power low-rate communication system between Antarctica and Spain.

An evaluation of the uncertainty associated with the measurement of the geomagnetic field with a D/I fluxgate theodolite

An analysis of the sources of uncertainty in measuring the angular elements of the geomagnetic field with the D/I fluxgate theodolite on the basis of the Guide to the Expression of Uncertainty in Measurement published by the International Organization for Standardization is presented. Along with the uncertainty associated with random effects, the habitual measurement procedure evidences the existence of systematic effects that are often ignored in the daily observatory practice. Special emphasis has been put on the development of a plausible theoretical scheme to explain the origin of such effects, and a series of procedures are proposed to find their actual sources as well as several recommendations with the final aim to improve the accuracy of the observations. Other effects, which strictly do not seem to suit the traditional classification into either systematic or random, are also analysed. Some of the results obtained have been applied to the absolute instruments in use at the Livingston Island Geomagnetic Observatory and at certain European observatories. Systematic contributions to uncertainty are difficult to outline in a general case, since they depend on each particular instrument. On the other hand, an accurate estimation of the uncertainty associated with random effects has been obtained, concluding that their magnitude does not generally exceed 0.1 arcmin for an experienced observer, for either declination or inclination.

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.

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.