International audienceThe eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined

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The 3‐hour K index was the first to provide an objective and quantitative monitoring of the irregular variations of the transient geomagnetic field observed in a given place. The use of K indices from a network of observatories to derive a planetary index of geomagnetic activity was suggested by Bartels when defining these indices. Then, Kp, am, Km, an, as, and aa were successively designed and accepted as International Association of Geomagnetism and Aeronomy indices. At present these K‐derived planetary indices are routinely computed and circulated. They make long homogeneous data sets and are widely used for long‐term and statistical studies in geomagnetism and solar‐terrestrial physics. After a short description of the main features of transient geomagnetic activity a definition of the K index as a measure of the irregular activity is given with a summary of its basic characteristics. The derivation of K‐derived planetary indices is described and discussed, and updated indications concerning their availability are presented. This short review provides users with the minimum required knowledge about these indices and may serve as an introduction to the Mayaud (1980) monograph.

[1] On 15 May 2005, a huge interplanetary coronal mass ejection (ICME) was observed near Earth. It triggered one of the most intense geomagnetic storms of solar cycle 23 (Dst peak = À263 nT). This structure has been associated with the two-ribbon flare, filament eruption, and coronal mass ejection originating in active region 10759 (NOAA number). We analyze here the sequence of events, from solar wind measurements (at 1 AU) and back to the Sun, to understand the origin and evolution of this geoeffective ICME. From a detailed observational study of in situ magnetic field observations and plasma parameters in the interplanetary (IP) medium and the use of appropriate models we propose an alternative interpretation of the IP observations, different to those discussed in previous studies. In our view, the IP structure is formed by two extremely close consecutive magnetic clouds (MCs) that preserve their identity during their propagation through the interplanetary medium. Consequently, we identify two solar events in Ha and EUV which occurred in the source region of the MCs. The timing between solar and IP events, as well as the orientation of the MC axes and their associated solar arcades are in good agreement. Additionally, interplanetary radio type II observations allow the tracking of the multiple structures through inner heliosphere and pin down the interaction region to be located midway between the Sun and the Earth. The chain of observations from the photosphere to interplanetary space is in agreement with this scenario. Our analysis allows the detection of the solar sources of the transients and explains the extremely fast changes of the solar wind due to the transport of two attached (though nonmerging) MCs which affect the magnetosphere.