Geomagnetic variation consists of quiet variation, which is regular in appearance and mostly of solar electromagnetic radiation origin, and geomagnetic disturbance, which is irregular in appearance and mostly driven by the solar wind. The purpose of the Kp index, or Kp for short, is to monitor subauroral geomagnetic disturbance on a global scale. Bartels (1949) introduced the standardized Ks and the planetary Kp indices (see also Bartels, 1957aBartels, , 1957bSiebert & Meyer, 1996), which are derived from observatory-specific three-hourly K indices (Bartels, 1938(Bartels, , 1939Bartels et al., , 1940. The methodology to determine Ks and Kp indices is based on earlier indices, namely the global Km index and the reduced Kr and global Kw indices (Bartels et al., 1940). The K index, for which is an early and excellent description in English, is defined as a quasi-logarithmic measure, ranging in steps of 1 from 0 to 9, of the range of geomagnetic disturbance at a geomagnetic observatory in a three-hourly UT interval (00-03, 03-06, …, 21-24). Geomagnetic disturbance is also denoted as K-variation. The concept of K-variation, also referred to as geomagnetic activity or disturbance, predates the discovery of the solar wind and historically, K-variation was seen as the effect of 'solar particle radiation' (e.g. Bartels, 1957a). Siebert (1971) and Siebert and Meyer (1996) use this definition: "K-variations are all irregular disturbances of the geomagnetic field caused by solar particle radiation within the 3 h interval concerned. All other regular and irregular disturbances are non-K-variations. Geomagnetic activity is the occurrence of K-variations." We regard geomagnetic disturbance that is instantaneously driven by the solar wind as K-variation.The sum of the K-variation and its counterpart, the non-K-variation, equals the measured geomagnetic field variation at a geomagnetic observatory. K-variation includes geomagnetic pulsations, bays or substorms, sudden commencements, geomagnetic storms (with the exception of the recovery phase, see below) and other geomagnetic disturbance from fast changes in the ring-current and other magnetospheric and ionospheric currents. The non-K-variation includes phenomena related to energetic electromagnetic solar radiation (EUV, X-ray) like the daily solar and lunar quiet variation Yamazaki & Maute, 2017) and the rare solar flare effects (SFE;Curto & Gaya-Piqué, 2009;Veldkamp & van Sabben, 1960). However, some phenomena that are related to the solar wind also contribute to the non-K-variation because of their regular appearance. Examples are the quiet-time magnetospheric fields of the tail current, the magnetopause current and the ring current that appear as diurnal variation of the geomagnetic field at a point rotating with the Earth (e.g., Maus & Lühr, 2005). Another example is the slow decay of the ring current field in the recovery phase of a geomagnetic storm (e.g., Kamide & Maltsev, 2007). While the ring current field is driven by the solar wind, its decay in the recovery phase i...

Stable adsorption configurations of several amino acid monomers on anatase (101) and (001) and rutile (110) as well as (100) were found in Car-Parrinello simulations of aqueous solutions. Adsorption energies were calculated by averaging over trajectories of the adsorbed and desorbed configuration, taking into account thermal fluctuations of the potential energy. The small adsorption energy of the cysteine on the stoichiometric (110) rutile surface is largely enhanced by inserting the S into an oxygen vacancy. Values for glutamic acid and lysine were significantly higher in the previously identified hydroxyl contact points (160 and 110 kJ/mol, respectively) than on the stoichiometric rutile surfaces (70 and 40 kJ/mol). Adsorption of histidine and glutamic acid on anatase largely depended on the surface orientation. Glutamic acid binds strongly to (101), whereas histidine on (001) was so stably bound that no molecular desorption was achieved. These results coincide with recent experiments on the crystallization of anatase in amino acid solutions [

Variations in the solar wind cause changes in electric currents that flow in the magnetosphere and ionosphere. The associated changes in the magnetic field can be observed using magnetometers on the ground. There exist various types of geomagnetic indices to monitor the intensity of geomagnetic disturbance associated with solar wind variations (Mayaud, 1980). The Kp index is one of the most widely used indices of geomagnetic activity. The derivation, application and historical background of Kp are detailed in , and thus are described here only briefly.Kp is derived from K indices (Bartels et al., 1939) evaluated at 13 subauroral observatories from both northern and southern hemispheres. A K index expresses geomagnetic activity on a scale of 0-9 at each observatory for a given 3-hourly interval of the UT day (00-03, 03-06, …, 21-24 UT). It is based on the range of geomagnetic disturbance over the 3-hourly interval, which may contain geomagnetic pulsations (McPherron, 2005;Saito, 1969), bays associated with substorms (McPherron, 1970;Lyons, 1996), sudden storm commencements and sudden impulses (Araki, 1994), geomagnetic storm main phase (Gonzalez et al., 1994) and solar-flare and eclipse effects (Yamazaki & Maute, 2017). K is designed to have a similar frequency distribution regardless of observatory, and thus it does not depend on latitude. K indices are converted to standardized Ks indices, which take into account the influence of seasonal and UT biases. Kp is the average of the 13 Ks indices expressed in units of thirds (0o, 0+, 1−, 1o, 1+, 2−, …, 9o), thus it represents planetary, rather than local, geomagnetic activity. The complete time series of the definitive Kp index since 1932 and nowcast indices for the most recent hours

Abstract. The Tatuoca magnetic observatory (IAGA code: TTB) is located on a small island in the Amazonian delta in the state of Pará, Brazil. Its location close to the geomagnetic equator and within the South Atlantic Anomaly offers a high scientific return of the observatory's data. A joint effort by the National Observatory of Brazil (ON) and the GFZ German Research Centre for Geosciences (GFZ) was undertaken, starting from 2015 in order to modernise the observatory with the goal of joining the INTERMAGNET network and to provide real-time data access. In this paper, we will describe the history of the observatory, recent improvements, and plans for the near future. In addition, we will give some comments on absolute observations of the geomagnetic field near the geomagnetic equator.

Abstract. The Tatuoca magnetic observatory (IAGA code: TTB) is located on a small island in the Amazonian delta in the state Pará of Brazil. Its location close to the geomagnetic equator and within the South Atlantic Magnetic Anomaly offers a high scientific return of the observatory's data. A joint effort by Observatorio Nacional, Brazil (ON) and the GFZ German Research Centre for Geosciences (GFZ) was undertaken starting from 2015 in order to modernize the observatory with the goal to join the INTERMAGNET network and to provide real-time data access. In this paper, we will describe the history of the observatory, recent improvements, and plans for the near future. In addition, we will give some comments on absolute observations of the geomagnetic field near the geomagnetic equator.