International Association Of Geomagnetism And Aeronomy Research Articles

Rescue and quality control of historical geomagnetic measurement at Sheshan observatory, China

Abstract. The Sheshan Geomagnetic Observatory (International Association of Geomagnetism and Aeronomy (IAGA) code SSH), China was built in Xujiahui, Shanghai in 1874 and moved to Sheshan, Shanghai at the end of 1932. So far, the SSH has a history of nearly 150 years. It is one of the earliest geomagnetic observatories in China and one of the geomagnetic observatories with the longest history in the world. In this paper, we present the rescue and quality control (QC) of the historical data at the SSH from 1933 to 2019. The rescued data are the absolute hourly mean values (AHMVs) of declination (D), horizontal (H), and vertical (Z) components. Some of these data are paper-based records and some are stored in a floppy disk in BAS, DBF, MDB, and other file storage formats. After digitization and format transformation, we imported the data into the Toad database to achieve the unified data management. We performed statistics of completeness, visual analysis, outliers detects, and data correction on the stored data. We then conducted the consistency test of daily variation and secular variation (SV) by comparing the corrected data with the data of the reference observatory, and the computational data of the COV-OBS model, respectively. The consistency test reveals good agreement. However, the individual data should be used with caution because these data are suspicious values, but there is not any explanation or change registered in the available metadata and logbooks. Finally, we present examples of the datasets in discriminating geomagnetic jerks and study of storms. The digitized and quality-controlled AHMVs data are available at: https://doi.org/10.5281/zenodo.7005471 (Zhang et al., 2022).

The Use of Invalid Polar Cap South (PCS) Indices in Publications

AbstractPolar Cap (PC) indices, PCN North based on magnetic observations from Qaanaaq (THL) in Greenland and PCS South based on magnetic data from Vostok in Antarctica, are very useful indices for studies of solar wind‐magnetosphere interactions and for space weather monitoring and forecasts. PCN indices are issued from the Danish Space Research Institute (DTU Space) while PCS indices are issued from the Arctic and Antarctic Research Institute (AARI) in St Petersburg. Unfortunately, series of invalid PCS values have been provided from AARI and used in a number of publications issued since the PC index concept was endorsed by the International Association of Geomagnetism and Aeronomy (IAGA) in 2013. In spite of the disclosure of the failure in the PCS indices in 2018, publishing at the IAGA‐supported International Service of Geomagnetic Indices of the invalid indices has continued up to now (2022). The present contribution defines the invalidating features of the PCS indices in question, conveys examples, and discusses the applications in peer‐reviewed publications.

International Geomagnetic Reference Field: the thirteenth generation

In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

Bootstrapping Swarm and observatory data to generate candidates for the DGRF and IGRF-13

As posted by the Working Group V of the International Association of Geomagnetism and Aeronomy (IAGA), the 13th generation of the International Geomagnetic Reference Field (IGRF) has been released at the end of 2019. Following IAGA recommendations, in this work we present a candidate model for the IGRF-13, for which we have used the available Swarm satellite and geomagnetic observatory ground data for the last year. In order to provide the IGRF-13 candidate, we have extrapolated the Gauss coefficients of the main field and its secular variation to January 1st, 2020. In addition, we have generated a Definitive Geomagnetic Reference Field model for 2015.0 using the same modelling approach, but focussed on a 1-year time window of data centred on 2015.0. To jointly model both satellite and ground data, we have followed the classical protocols and data filters applied in geomagnetic field modelling. Novelty arrives from the application of bootstrap analysis to solve issues related to the inhomogeneity of the spatial and temporal data distributions. This new approach allows the estimation of not only the Gauss coefficients, but also their uncertainties.

On the validation of K-index values at Italian geomagnetic observatories

Abstract. The local K index and the consequent global Kp index are well-established 3 h range indices used to characterize geomagnetic activity. The K index is one of the parameters that INTERMAGNET observatories can provide, and it has been widely used for several decades, although many other activity indices have been proposed in the meanwhile. The method for determining the K values has to be the same for all observatories. The INTERMAGNET consortium recommends the use of one of the four methods endorsed by the International Service of Geomagnetic Indices (ISGI) in close cooperation and agreement with the ad hoc working group of the International Association of Geomagnetism and Aeronomy (IAGA). INTERMAGNET provides the software code KASM, designed for an automatic calculation of the K index according to the adaptive smoothed method. K values should be independent of the local dynamic response, and therefore for their determination each observatory has its own specific scale regulated by the L9 lower limit, which represents the main input parameter for KASM. The determination of an appropriate L9 value for any geomagnetic observatory is then fundamental. In this work we statistically analyze the K values estimated by means of KASM code for the Italian geomagnetic observatories of Duronia (corrected geomagnetic latitude λ∼36∘ N) and Lampedusa (λ∼28∘ N) by comparing them with the German observatories of Wingst and Niemegk. Our comparative analysis is finalized to establish the best estimation of the L9 lower limit for these two stations. A comparison of L9 lower limits found for the Italian observatories with results from a previous empirical method was also applied and used to verify the consistency and reliability of our outcomes.

Sydney Chapman: A Biographical Sketch Based on the Book “Chapman Eighty, From His Friends”

AbstractThis is a brief biographical sketch of Sydney Chapman, who was one of the greatest geophysicists in the world during the 20th century and also a pioneer in space physics. It is based on the book “Chapman eighty, from his friends,” together with a few notes by the author. In his early days, Chapman devoted his study on the transport property of gases and wrote “The Mathematical Theory of Non‐Uniform Gases” with T. G. Cowling. In the field of geophysics (geomagnetism, ionospheric physics, and auroral physics), Chapman made fundamental contributions in each field, on the basis of rigorous mathematical physics and deep insight. Chapman also wrote the book “Geomagnetism” with J. Bartels. These efforts helped establish the foundation of a new field, space physics. Chapman was instrumental and effective in coordinating various international scientific organizations, serving as presidents for the International Union of Geodesy and Geophysics (IUGG), the International Association of Geomagnetism and Aeronomy (IAGA), and the International Geophysical Year (IGY). Present advance in geophysical sciences owes greatly his devotion and accomplishments.

Analysis of Several Years of DI Magnetometer Comparison Results by the Geomagnetic Network of China and IAGA

The comparison of absolute geomagnetic instruments is an important component of geomagnetic observation. To promote high quality standards in geomagnetic data acquisition, the International Association of Geomagnetism and Aeronomy (IAGA) organizes an international comparison every two years. In China, this comparison is part of quality control process for geomagnetic observation data, and is organized by the Geomagnetic Network of China (GNC). In this paper, the comparison results from several years are analysed in detail, and some useful information is presented that will help to guide the observatory’s future observation work and improve data quality. In addition, the quality of the absolute observation data of GNC and IAGA is evaluated using a statistical method. This should aid scientists who use these data to understand their research results.

Construcción del Observatorio Geomagnético de Mérida, Venezuela

Un nuevo observatorio geomagnético se ha construido en Mérida, Venezuela (8° 33’ N, 71° 19’ O, 1755m), siendo este observatorio el primero en nuestro país. El emplazamiento del observatorio se encuentra alejado de las perturbaciones pro- vocadas por el hombre (ruido cultural), del mismo modo, se cuenta con un área apropiada para su correcto funcionamiento; obteniéndose un gradiente horizontal y vertical menor a 1nT/m, esto es excelente para la operatividad del mismo. Toda la construcción se ha llevado a cabo bajo las recomendaciones de la Asociación Inter- nacional de Geomagnetismo y Aeronomía (IAGA, por sus siglas en inglés) mediante el libro de Jankowski y Sucksdorff (1996). El observatorio está conformado por tres casas o pabellones de madera y dos pilares externos libres de materiales magnéticos. Estas casas son construidas para albergar los equipos de medición denomina- dos “magnetómetros”, los cuales están constituidos por equipos de alta sensibilidad para las mediciones del campo geomagnético.

The IAU and French women astronomers

AbstractThe research about women in astronomy began in 1988 following a request received from Wilfried Schröder, now deceased but, at that time, in charge of the Interdivision Commisssion on History, which was included in the International Association of Geomagnetism and Aeronomy (IAGA) attached to the IUGG International Union of Geodesy and Geophysics. The results obtained concerning “Astronomy, Geophysics and Women”, presented at the symposium “The history of geomagnetism and aeronomy”, were published (Débarbat 1989) in Advances in Geosciences in the form of a short paper. The IAU began to publish, in 1992, membership statistics in its Information Bulletin IB 68, including percentages of women and men, and several papers were published on the subject up to the last one Statistics on Women in IAU Membership (Débarbat 1989). Recent results are given including examples from the past.

Indonesian Geomagnetic Maps for Epoch 2015.0 to cover of Indonesian Regions

In compliance with the resolutions of IAGA (International Association of Geomagnetism and Aeronomy), Since 1960’s, every five years BMKG or Meteorology, Climatology and Geophysics Agency of Indonesia made geomagnetic field maps based on actual measurements in 53 repeat stations. It’s the map for more accurate result of Geomagnetic maps Epoch 2015.0, the number of repeat stations has been increased to 68 locations. Analysis data was conducted by spatial analyses using collocated co-kriging and kriging with external drift to map the observation data in five components, such as Declination (D), Inclination (I), Vertical (Z), Horizontal (H), and Total Geomagnetic Field (F). The data reduction used one permanent observatory i.e., Kupang Geophysical Observatory, as a reference standard. The results of this Geomagnetic Maps, that the contour lines of Indonesian geomagnetic declination in range -1 to 4.5 degree, Inclination component are -5 to -37 degree, Vertical component are -4000 to -28000 nT, Horizontal component are 36000 to 42000 nT, and Total Geomagnetic Field are 39000 to 46000 nT. In conclusion, Indonesian Geomagnetic Maps for Epoch 2015.0 can be used to compute geomagnetic data around Indonesian regions until next 5 years.

A critical note on the IAGA-endorsed Polar Cap index procedure: effects of solar wind sector structure and reverse polar convection

Abstract. The International Association of Geomagnetism and Aeronomy (IAGA) has recently endorsed a new Polar Cap (PC) index version to supersede the previous seven different versions of the PCN (North) index and the five different PCS (South) index versions. However, the new PC index has some adverse features which should be known and taken into account by users of the index. It uses in its derivation procedure an "effective" quiet day level (QDC) composed of a "basic" QDC and an added solar wind sector term related to the azimuthal component (By) of the interplanetary magnetic field (IMF). The added IMF By-related terms may introduce unjustified contributions to the PC index of more than 2 index units (mV m−1). Furthermore, cases of reverse convection during strong northward IMF Bz (NBZ) conditions included in the database for calculation of index coefficients can cause unjustified index enhancements of 0.5–1 mV m−1 during calm conditions, reduction of index values by more than 20 % during disturbed conditions, and inconsistencies between index coefficients and index values for the northern and southern polar caps. The aim here is to specify these adverse features and quantify their effects, and to suggest alternative steps for future modifications of the index procedure.

Evaluation of candidate geomagnetic field models for IGRF-12

The 12th revision of the International Geomagnetic Reference Field (IGRF) was issued in December 2014 by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD ( http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html ). This revision comprises new spherical harmonic main field models for epochs 2010.0 (DGRF-2010) and 2015.0 (IGRF-2015) and predictive linear secular variation for the interval 2015.0-2020.0 (SV-2010-2015). The models were derived from weighted averages of candidate models submitted by ten international teams. Teams were led by the British Geological Survey (UK), DTU Space (Denmark), ISTerre (France), IZMIRAN (Russia), NOAA/NGDC (USA), GFZ Potsdam (Germany), NASA/GSFC (USA), IPGP (France), LPG Nantes (France), and ETH Zurich (Switzerland). Each candidate model was carefully evaluated and compared to all other models and a mean model using well-defined statistical criteria in the spectral domain and maps in the physical space. These analyses were made to pinpoint both troublesome coefficients and the geographical regions where the candidate models most significantly differ. Some models showed clear deviation from other candidate models. However, a majority of the task force members appointed by IAGA thought that the differences were not sufficient to exclude models that were well documented and based on different techniques. The task force thus voted for and applied an iterative robust estimation scheme in space. In this paper, we report on the evaluations of the candidate models and provide details of the algorithm that was used to derive the IGRF-12 product.

International Geomagnetic Reference Field: the 12th generation

The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth’s magnetic field.

Evaluation of candidate geomagnetic field models for IGRF-11

The eleventh generation of the International Geomagnetic Reference Field (IGRF) was agreed in December 2009 by a task force appointed by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD. New spherical harmonic main field models for epochs 2005.0 (DGRF-2005) and 2010.0 (IGRF-2010), and predictive linear secular variation for the interval 2010.0–2015.0 (SV-2010-2015) were derived from weighted averages of candidate models submitted by teams led by DTU Space, Denmark (team A); NOAA/NGDC, U.S.A. (team B); BGS, U.K. (team C); IZMIRAN, Russia (team D); EOST, France (team E); IPGP, France (team F); GFZ, Germany (team G) and NASA-GSFC, U.S.A. (team H). Here, we report the evaluations of candidate models carried out by the IGRF-11 task force during October/November 2009 and describe the weightings used to derive the new IGRF-11 model. The evaluations include calculations of root mean square vector field differences between the candidates, comparisons of the power spectra, and degree correlations between the candidates and a mean model. Coefficient by coefficient analysis including determination of weighting factors used in a robust estimation of mean coefficients is also reported. Maps of differences in the vertical field intensity at Earth’s surface between the candidates and weighted mean models are presented. Candidates with anomalous aspects are identified and efforts made to pinpoint both troublesome coefficients and geographical regions where large variations between candidates originate. A retrospective analysis of IGRF-10 main field candidates for epoch 2005.0 and predictive secular variation candidates for 2005.0–2010.0 using the new IGRF-11 models as a reference is also reported. The high quality and consistency of main field models derived using vector satellite data is demonstrated; based on internal consistency DGRF-2005 has a formal root mean square vector field error over Earth’s surface of 1.0 nT. Difficulties nevertheless remain in accurately forecasting field evolution only five years into the future.

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

Abstract We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm2which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a ‘Proterozoic dipole low’ period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth’s history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

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

Abstract 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.

Classification of Geomagnetic Micropulsations

The notation and classification of geomagnetic micropulsations have been discussed in two recent letters in this Journal [Matsushita, 1963; Jacobs et al., 1963]. At the 13th General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Berkeley, California, August 1963, the question was considered in some detail by Committee 10 of the International Association of Geomagnetism and Aeronomy (IAGA). A small subcommittee, consisting of the four authors of this note, was set up to submit the recommendations which are presented below. From experimental knowledge, particularly that obtained since the IGY, it has been recognized that micropulsations can be divided into two main classes: those of a regular and mainly continuous character, and those with an irregular pattern. The first class covers the whole range of micropulsations with periods from about 0.2 to 600 sec. They can be divided into subgroups depending on their period, but it is extremely difficult to decide where the boundaries should be drawn. A purely mathematical division can be made, based perhaps on a logarithmic scale, or a division can be based on their physical and morphological properties. The second approach was adopted, and Table 1 gives the proposed classification and notation.

International Geomagnetic Reference Field—the tenth generation

Abstract The International Geomagnetic Reference Field (IGRF) 10th Generation was adopted in 2004 by the International Association of Geomagnetism and Aeronomy (IAGA) Working Group V-MOD. It is the latest version of a standard mathematical description of the Earth’s main magnetic field and is used widely in studies of the Earth’s deep interior, its crust and its ionosphere and magnetosphere. This generation differs from the previous generation with the replacement of the secular-variation model for 2000.0–2005.0 with a main-field model at 2005.0 and a secular-variation model for 2005.0–2010.0. The IGRF is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world. This paper lists the new coefficients and includes contour maps and pole positions.

The 10th generation international geomagnetic reference field

The International Association of Geomagnetism and Aeronomy (IAGA) on 12 December 2004 released the 10th generation International Geomagnetic Reference Field (IGRF)—the latest version of a standard mathematical description of the Earth's main magnetic field and used widely in studies of the Earth's deep interior, its crust, ionosphere and magnetosphere. The coefficients were finalised by a task force of IAGA. The IGRF is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world.

10th Generation International Geomagnetic Reference Field

The International Association of Geomagnetism and Aeronomy (IAGA) released the 10th Generation International Geomagnetic Reference Field (IGRF) on 12 December 2004. This is the latest version of a standard mathematical description of the Earth's main magnetic field, and is used widely in studies of the Earth's deep interior, crust, ionosphere, and magnetosphere. The coefficients were finalized by a task force of IAGA, Division V, Working Group V‐MOD: Geomagnetic Field Modeling. The IGRF is the product of a large collaborative effort between magnetic field modelers and the institutes around the world involved in collecting and disseminating magnetic field data from satellites and observatories.