The solar activity appears in the three obsesol08 588x476.pngrvable layers of the Sun: the photosphere, which is the lower layer and, in fact it is the Sun that we see, the chromospheres situated above the photosphere and typically observed by filtered light, removing the intense light from the photosphere, and finally in the corona, which is the most external layer and extends to a distance of many solar radii. From the Earth, the solar corona can only be seen with the naked eye during the brief period of totality of a total solar eclipse.

 

 

 

 

   

x010925 103635 0One of the most characteristic features of solar activity are the sunspots, which appear on the surface of the Sun. They vary from day to day and have an average life ranging between days and weeks. Approximately every eleven years the number of sunspots goes through a maximum. Sunspots are regions of the Sun with magnetic field intensities thousands of times greater than the Earth's magnetic field. Due to the rotation of the Sun on its axis, which has a period of 27 days, these sunspots appear on the East limb of the Sun, pass through its central meridian, which is on the direction of the Earth,  and finally disappear on the West side of the solar disc, if their life is long enough. Sunspots are dark areas on the surface of the Sun. The indoor area used to be darker and is called umbra, while the outside zone tends to be less dark and is called the penumbra. Temperature, in the dark centres of sunspots, decreases to about 3,700 ° K (compared to the 5700 ° K of the surrounding photosphere).

 

Solar activity has a periodicity of about 11 years, although it can vary between 8 and 15 years. The astronomer Heinrich Schwabe in 1843 determined for the first time the 11-year cycle. Schwabe cycles are numbered from the maximum of 1761.

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In Ebro Observatory, every day that the weathertelescopi conditions allow it, the solar photosphere is photographed using a Zeiss APQ 150/1200 telescope on equatorial mount , with a resolution of +0.7 arcseconds and a digital camera.In May 2017, the old DALSA CA D4 camera was replaced by a new IDS 2048x2048 pixels with a pixel size of 5.5 x 5.5 μm, and a total area of 11.26 mm2.  A photocompressor lent was also installed. Applying an algorithm of digital image processing developed in the Observatory (Curto et al. 2008), the number of sunspots and groups are determined. For each sunspot, among other parameters, the number of pixels it occupies, its area in millionths of hemisphere, and its intensity (grey level) are measured. For the groups, its heliographic longitude and latitude, its  area, the number of spots that compose it, as well as the type of group according to the Zurich classification system are determined. The quality of the solar image is described by a parameter which varies between 1 and 5.

 

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Finally, the index of solar activity known as Wolf number (W) is calculated based on the number of groups (G) and sunspots (t) according to the well known expression W = 10 G+ t. This formula indicates that the emergence of a coherent group of sunspots (an active region) is more important than to add some sunspots more to an already existing group. These data are send to the Solar Influences Data Analysis Center (SCID) in Brussels, and are published in the bulletins online. A detailed representation on the butterfly diagram of the groups’ latitude shows the fact that the groups do not appear in random positions on the solar surface, they are concentrated in two bands around the equator, and its latitude decreases as This fact could also be seen in this animation which shows the evolution of sunspots during the year 2013.

Seismology is a branch of geophysics that is responsible for the study of earthquakes and the propagation of mechanical waves (seismic) that are generated in the interior and the surface of the Earth. Seismology includes, among other phenomena, the study of the mechanisms that generate tsunamis and volcanic activity.

The majority of earthquakes, and especially those of greater magnitude, occur in plate boundary zones, although they also occur in the interior of the continents due to readjustments of forces through the movement of faults.

 

Most seismic events in the Iberian Peninsula occur in the south as a result of the interaction of the Eurasian and African plaques. Within the Peninsula stands out the seismicity that occurs in the Pyrenees, consequence of the push of Africa that makes towards the North and constrains us between Africa and the rest of Europe. (Source: IGN)

 

During an earthquake several seismic waves are generated, some traveling through the interior of the Earth: they are the primary P and secondary S, and others they do by the surface like the waves Rayleigh and Love. Internal Waves: The internal waves travel through the interior, they are the fastest. They follow curved paths due to the different density and composition of the interior of the Earth. This effect is similar to that of refraction of light waves. Surface waves: When the internal waves reach the surface, the L waves (longae), which propagate on the discontinuity surface of the interface of the Earth's surface (earth-air and earth-water), are generated. They are the cause of the damages produced by the earthquakes in the constructions.

 

Record of a hypothetical earthquake with the corresponding first arrivals of the Primary waves, then Secondary and finally surface waves

 

Earthquakes usually occur in the first kilometers of the earth's crust (although there are also very deep earthquakes associated with subduction zones). The point where the "rupture" occurs is called the focus or hypocenter, while the projected point on the surface is called the epicenter.

 

When an earthquake is recorded, seismic waves propagate in all directions from the hypocenter. The study of the waves that are registered allows to locate the epicenter and the depth to which the earthquake has originated

 

The study of seismograms allows us to know the distance to which a given earthquake has occurred. The difference in time between the arrival of the P and S wave tells us how far or near the earthquake has been. So, to better define the epicenter of an earthquake it is necessary, at least, 3 seismic stations to record it.

The first seismic station in Catalonia was installed in the Ebre Observatory in 1904.  As the technology has progressed, the instruments have been updated and today it is still in operation thanks to the collaboration with the ICGC.

Although initially was thought that the seismic movements were related to the solar activity, soon the scientific community understood that it was the consequence of the own dynamics of the Earth crust. Much has changed the seismic detection equipment. In origin, they were based on a series of large masses suspended in a column anchored to the rocky substrate, which in the event of an earthquake oscillated in certain directions or components (NS, EW and vertical), thus characterizing any movement was registered.

 

Seismometer Mainka modified, that was operative between 1942 and 1965 in the Observatory. Both the N-S and E-W sensors have a weight of 1500kg, however the sensor of the vertical component (bottom left) weighs only 635kg.

 

Fortunately today, advances in technology have led to a considerable reduction in the size of equipment, although in essence, the physical basis of a mass that oscillates when receiving a seismic wave is still valid.

 

Seismometer with the three components of registration in the station of the Ebro Observatory located at Alcalà de Xivert (Castellón)

 

Likewise, the way earthquakes are recorded has also changed a great deal over time.

 

Left: system of acquisition through a pen that recorded on paper. Right: seismic record of the earthquake of San Francisco of magnitude 7.8 the 18 of April of 1906 detected in the Observatory on band of paper smoked.

 

Through the use of computers, seismic events are much better characterized and thanks to the use of specialized software, the different types of waves are better identified and cataloged.

 

M6.8 earthquake occurred in Hoshu, Japan on February 16, 2015. The stations that registered it in descending order were: Poblet, Horta de Sant Joan, Escorca (Mallorca), Ebro and Mosqueruela (Teruel).

 

Currently, the Seismic Observation Service of the Observatory of the Ebro maintains the historical stations of the center, among them EBR with the collaboration of the ICGC. In addition, it also maintains a newly created network, which was initially dedicated to seismic monitoring in the surroundings of the underground natural gas reservoir CASTOR. To this end, a local seismic network was established in 2009, consisting of different stations belonging to the Observatory itself and to the national network IGN and regional ICGC.

 

Detail of the geographic position of the Ebre seismic network stations ALCN and ALCX are stations from the Observatory, EBR is a station that is jointly managed by the OE, which owns the sensors and the system of data transmission, and the ICGC, which provided the digitizer, CMAS is an ICGC station and the rest are IGN stations

The earth's magnetic field is generated by an internal molten layer in the Earth. This layer, rich in iron and nickel, constitutes the outer core, whose dynamics (the so-called geodynamo) causes the field. Broadly speaking, it could be approximated by a magnetic dipole tilted some 10 degrees from the axis of rotation of the Earth and slightly displaced from its center. This internal field does not remain invariant in time or in space. Its poles move several hundred kilometers a year, and it also varies in intensity and polarity, being reversals relatively frequent in the geological past. Although it was established that the magnetic N Pole was the one near the geographic N Pole, later it was found that it was not. The field lines of the Earth's dipole come from the South and enter the North, so strictly, a compass points the magnetic south (located near the geographical N Pole at present), but the original nomenclature has prevailed.

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Left: observed and modelled drift of the magnetic North Pole. Top: actual position of the dipole, where the field lines enter the geographic N (South of the magnetic dipole which approximates the geomagnetic field) and vice versa. 

 

 

 

 

The field generated within the Earth has a number of observable variations in scales of months and years, known as the secular variation, such as the drift of the magnetic poles. However, when geomagnetic measurements started, a series of daily variations were observed which could not be attributed to the internal field. These daily fluctuations are actually part of the so-called external field, which is much weaker, but has interesting consequences. A series of magnetic disturbances are detected and studied in different geomagnetic observatories in the world. Its sources are diverse: a system of electrical currents in the ionosphere due to the ionization produced by the Sun in the conductive layer of the atmosphere, the solar wind interaction with the magnetosphere (the region where the geomagnetic field is confined, which protects us from the solar wind) and the ionosphere itself, together with the conductive nature of the earth's crust and mantle. The knowledge of these variations over time allows a better modeling of the geomagnetic field behavior, and is a fundamental tool in disciplines recently created as space weather, whose relevance is increasing gradually.

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Animation showing how the magnetosphere is deformed when hitting the solar wind on it. As it can be seen, there are two areas in the North and in the South where the geomagnetic field is weaker, so that the solar wind can penetrate more easily. As a result of the interaction of these charged particles from the Sun with the atmosphere, auroras borealis and australis are generated.

 

 

The mission of the Observation Service of Ebro Observatory in relation tomagnet01
terrestrial magnetism is the management of the Ebro geomagnetic observatory. On the other hand, through the granting of various projects of the National Antarctic Research Program, the Ebro Observatory also installed and operates the Livingston Island Observatory, in Antarctica. These two stations are part of the global network of geomagnetic observatories and contribute to the development of models such as the International Geomagnetic Reference Field (IGRF) and other studies of various kinds, such as those dealing with the Sun-Earth relationship, framed within the modern discipline known as Space Weather.

The main objective of a geomagnetic observatory is to determine the temporal evolution of the Earth's magnetic field vector at the point where it is located. Data from observatories reveal the magnetic field variations in a wide range of time scales, from seconds to centuries, and this is important for understanding processes both inside and outside the Earth.

P1090359The records of the Ebro geomagnetic observatory, at Roquetes (40.8 °N, 0.5 °E), have more than 100 years of history. They are kept since 1910, except for the period covering April 1938 to December 1941. The data were collected in analog format until 2000 and in digital format since. However, many of the classic records of the three magnetic field elements have been digitized using a system developed at the Centre. Disturbances due to railway electrification reaching the city of Tortosa forced us to place a few years ago another variometric station in the town of Horta de Sant Joan (41.0 °N, 0.3 °E), at the foot of the mountain of Santa Barbara, in the Sant Onofre chapel, near the convent of San Salvador. This is done in collaboration with the Instituto Geográfico Nacional. Currently, the observatory has a FGE Fluxgate Magnetometer with suspended sensor (manufactured by the Danish Meteorological Institute) and a GSM19 proton precession magnetometer in Horta, and a magnetometer Geomag M390, also equipped with an Overhauser effect magnetometer GSM90 in Roquetes. The recording equipment of this latter station is completed by a proton vector magnetometer (dIdD equipment) designed by the British Geological Survey. The absolute observing program is done on a daily basis with a declinometer-inclinometer (DI-flux) Zeiss 010B with an 810 Elsec fluxgate probe. Observatory data are referred to a single point on the main pillar of observations which, since Januray 1, 2012, is that of Horta de Sant Joan, remaining those of Ebro as a backup station. The Ebro Observatory is an INTERMAGNET magnetic observatory, sending data daily to the Edinburgh GIN.

The Livingston Island geomagnetic observatory (62.7 °S, 60.4 °W) is located in the Spanish Antarctic Base Juan Carlos I, in the South Shetlands, north of the Antarctic Peninsula. Its installation took place during 1995-1996 and 1996-1997 Antarctic Surveys and it has records since December 1996. This is an observatory manned during the austral summer months, typically from November to February, being in automatic operation without human intervention the rest of the year. In terms of measuring instruments, currently it has three variometric magnetometers: a proton vector magnetometer in dIdD configuration (BGS), an FGE triaxial fluxgate magnetometer (DMI), and a GEM Systems scalar magnetometer. As for absolute instruments, it has a DI-flux with Carl Zeiss THEO 015B theodolite and 810 Elsec Fluxgate probe and another GEM Systems proton magnetometer.

In both cases, the instrumentation allows to sample the magnetic field avectors Santi
ccurately at a rate of once per second. The way the magnetic field measurements is expressed depends on the coordinate system used to characterize this vector. The two most commonly used coordinate systems are Cartesian and cylindrical. Thus, one can measure the components X, Y and Z in a geographic reference system, or equivalently, the elements H (intensity horizontal), D (declination) and Z (vertical intensity). The total intensity (F) and the inclination (I) are also often given.

You can get more information on the measuring instruments and data processing of both observatories in online bulletins. For the data, please consult the World Data Centres (eg WDC Edinburgh), our catalogues (Ebro data catalogues, Livingston data catalogues) or view the current and secular variations, or previous magnetograms (Ebro/Horta SJ magnetograms, Livingston magnetograms).

K-index of geomagnetic activity calculated from our data. (Unrevised automatic process)
07-08-22
10-08-22
Photographs of the solar photosphere taken with our own telescope
The compass is oriented according to the magnetic north, not the true one. The magnetic north varies with time. Over the past centuries, in Roquetes, compasses were deviated westward. But this has changed and now they are deviated eastward More information.

19/08/2022 09:50
Temperature Humidity Atmospheric pressure
24.7 ºC 46.2 % 1014.1 hPa
Accumulated rain Wind speed Wind bearing
0 mm 10 km/h N (350º)
Information from the automatic station of AEMET located at Ebro Observatory. These data are provisional and subject to revision.