• July 17, 1357. Locust plague in Tortosa (a)
  • February 2, 1373 . Earthquake in the Ebro valley
  • November 10, 1448. Flooding in Tortosa (a)
  • December 12, 1506. The Ebro River froze over in Tortosa. People crossed the Ebro River walking (a)
  • May 21, 1582. Flood of Ebro River. The level was 6 m above the low water level (c)
  • February 12, 1603. Due to the snow, some houses fell down in Barcelona, ​​Tortosa and Lleida (a)
  • 1932 Snow covered ground with a thickness of 6 cm
  • September 28, 1605.  In Tortosa the Ebro River overflowed. The water level was 5 meters height (a)
  • November 5, 1617. Flooding in Tortosa, one of largest known, as the waters reached an altitude of 8.53 meters (a)
  • December 30, 1624. The Ebro River froze over in Tortosa (a)
  • August 20, 1691. A whirlwind in Tortosa, at 8 am, took upstream the 10 boats bridge over the Ebro (a)
  • January 11, 1694.The Ebro River froze (e)
  • January 11, 1709. The Ebro River was frozen (e)
  • January 11, 1712. The Ebro River was frozen (e)
  • October 8, 1787. Flooding in Tortosa.  The water level was 8.73 meters height (a)
  • October 9, 1787. Flooding in Xerta, where the water level reached 16 meters. In Tortosa, there were 85 victims, with a water level of 8.73 meters (a)
  • December 29, 1788. The Ebro River froze over in Tortosa (e)
  • September 9, 1845. The level of the Ebro River increased more than 20 hands (4 m) it usual level. At 6 am the overflow of the Rastre’s ravine caused the fall of the Hospital. 7 people died (b)(e)
  • May 26, 1853. Flooding in Tortosa. The water reached 7.4 meters. The swollen river swept along the boat bridge (a)(d)
  • October 20, 1866. 4 inches of water in the Immaculate convent by overflow of Rastre ravine (b)
  • October 5, 1874. The Rastre’s ravine overflowed. More than 8 inches of water in the Immaculate convent. 7 gates and two walls knocked down. In the church, the water came up to the pulpit and the image of St. Mary Magdalene floated overnight. Two nuns were about to die (b)
  • January 18, 1891. The latest time that Ebro River froze over at Tortosa. Some authors mentioned temperatures of -9.5 C (c)
  • October 23 1907. Flooding in Xerta. The water reached the 15.65 meters. 29 people died and 110 houses fell. On the streets of Tortosa there were 3.5 meters of water (a)
  • February 24, 1916 Reported 3 cm of snow on the ground
  • August 5, 1916. At 14:25 hours a meteorite fall was sighted. A light in NS direction was visible, as well as a trail of smoke, and finally an explosion was felt. The fireball fallen into the sea near Peniscola
  • December 19, 1920. 13 cm of snow on the ground
  • January 14, 1926. Snow depth of 5 cm
  • November 11, 1932. Earthquake with epicentre near Aldover
  • January 1, 1937.  11 cm of snow was measured
  • January 22, 1940. 1.5 cm of snow covers the ground
  • January 25, 1941. The River Ebro reached 7.30 m above the level of low water
  • September 16, 1943. A total precipitation of 265 mm was recorded in 19 hours. It is the daily maximum precipitation never measured at the Observatory
  • January 12-13, 1945. 11 cm of snow on the ground
  • January 16-17, 1946. 13 cm of snow on the ground
  • January 25, 1947. 3 cm of snow on the ground
  • February 11, 1956. Minimum temperature never recorded at Ebro observatory. The value was -6.4 C
  • January 11, 1960. Snow depth of 6 cm on the ground
  • September 20, 1972. In Sant Carles de la Rapita the precipitation was 307 mm in 24 hours (a)
  • July 7, 1982. The maximum temperature was 43.0 ° C, which is the largest value recorded at the observatory
  • November 9, 1982. In Tortosa the river level was 7.5 m above the usual
  • March 26, 1983. The anemometer recorded a value of 158.8 Km/h NW at 07:26 (TU) which is the largest value recorded at the observatory
  • March1, 2005. 5 cm of snow on the ground
  • November 29, 2014. A total precipitation of 336.1 mm was recorded by an automatic weather station operated by the Servei Meteorològic de Catalunya at the P.N. del Ports (f)


(a) Agenda "El Tiempo 1995",  Ministerio de Obras Públicas, Transportes y Medio Ambiente. Instituto Nacional de Meteorología
(b) Historia del Real Monasterio de la Purísima Concepción Victoria de Tortosa. Rafael María López Melús. 1986
(c) Historia de Tortosa y su comarca. Enrique Bayerri.1933
(d) Anales ó historia de Tortosa: desde su fundación hasta nuestros días. Daniel Fernández y Domingo. 1867.
(e) Anales de Tortosa e Historia de la Santa Cinta. Ramón O'Callaghan. 1886
(f) Servei Meteorològic de Catalunya.

The compass needle points magnetic North; not geographic North. However, the compass needle progresses over time. During the last centuries, magnetic North was deflected towards west in Roquetes. However, this has changed and now it points eastward. In this article we explain what magnetic declination is, and we monitor its change in real time using Ebre Observatory data.



The current direction the compass needle points at  Roquetes derived using the locally recorded value of the magnetic declination. Each small division corresponds to one minute of arc. Positive values ​​indicate the needle points eastward, while negative values ​​indicate that the compass needle points westward. A zero value indicates that the agonic line is above us, which means that the compass needle is pointing true north.


Record of the magnetic declination in Roquetes (updated every 12 minutes).




At the time of Columbus the compass needle in the Iberian Peninsula did not point towards Polaris (the geographic or true North), but it was always deflected towards east. However, as he crossed the Atlantic on one of his voyages to the New World, somewhere during the journey his compass pointed directly to Polaris, right in the direction of true North. He had crossed the agonic line, literally, the line without angle. This phenomenon, which might seem unusual, even radical for the people of that time, is now a well known fact and hides no mystery. Many of us may have heard that in the Iberian Peninsula the compass needle is deflected towards west; we might even say that it is an accepted truth. This is justified by the fact that it was the case for the last three centuries. The magnetic field of the Earth, however, changes slowly over time, and the agonic line that runs through Europe in a direction approximately north - south, has been progressing slowly from east to west since the mid-nineteenth century. Thus, the agonic line was centered on the eastern part of the Iberian Peninsula sometime between late 2009 and early 2010, and moved through the western part of the Terres de l’Ebre in late 2014, beginning of 2015. In short: magnetic declination becomes east. The compass needle points to the right; we will have to get used to it.


Declinació Colom

World Map of Magnetic Declination valid for the time of Columbus. It was computed from an archaeomagnetic model developed in close collaboration with Ebre Observatory. The red areas correspond to positive declinations; blue areas to negative declinations. The agonic line (represented by a thick black line) is observed in the Atlantic.


Declinació 2014

Declination map valid for the present time. The agonic line is observed to the east of the Iberian Peninsula, particularly at the Terres de l'Ebre. The agonic line has progressed erratically since the epoch of Columbus, but it has been drifting westward since the mid-nineteenth century.


Magnetic observatories are facilities devoted to measuring the changes of the Earth's magnetic field at their location. From their measurements, integrated in a worldwide network which includes the two stations managed by Ebre Observatory, one in Horta de Sant Joan and another in Livingston Island (Antarctica), scientists can infer the shape and intensity of this physical magnitude globally. It is precisely thanks to data from many observatories like ours around the world that models and maps can be developed to show how declination varies over time and space. Scientists in Ebre Observatory are also experts in developing models and maps of these features. Other methods of analysis, which include dating of old samples, have been developed in close collaboration with researchers from Ebre Observatory to allow a retrospective look of the magnetic field over thousands of years in the past (although with a greatest uncertainty), long before the advent of the first magnetic observatories. But it is precisely in these observatories, where measurements are much more accurate, that we substantiate that the agonic line passed through Ebre Observatory in Roquetes in April 2014, and through our station at Horta de Sant Joan in September 2014. Indeed, the line possesses an intrinsic oscillation due to the magnetic field produced by the ionospheric currents induced by solar radiation. This runs over tens of miles a day around an average position, relatively at rest, which is attained at night and that we use as a reference. In fact, this daily oscillation made the agonic line to come across Roquetes, for the first time, twice a day since January 2014, preferably during the early morning (see, on the top of this article, the compass direction and the record of the magnetic declination at present, or an animation for a whole day). And at some extent moves in an erratic manner during geomagnetic storms, these taking place when particles from a solar eruption hit the Earth (see an example in this other animation).

  MOSAIC 3 agulles

Detail of the mosaic on the floor of the Landerer Pavilion at Ebre Observatory, where a compass is displayed with its changes of direction along the first one hundred years of its history (particularly for 1904, 1949 and 2004). While the current declination is close to 0˚, the measurements made in the early times of this institution established a compass deflection of about 14˚ west from true North.


All this is anecdotal for mostof us: nothing will stop working because of this change; even "classic" hikers can continue to use the compass as a good indicator of true North in our country, now and for the rest of their lives.Of course, those who come after us, and even today systems that need higher precision, will have to correct the difference between magnetic (compass direction) and geographic (true) North. But all this is certainly a story that illustrates to what extent we have a detailed understanding of the internal dynamics of our planet and of the scientific issues surrounding this,and of how our institution is represented at the highest international level.


The observation and monitoring of the state of the ionosphere in the Observatori de l’Ebre began on 26 March 1955, when the first ionospheric sounder in Spain was inaugurated.

The ionosphere is the part of the upper atmosphere, situated roughly between 60 and 1000 Km of height, which is weakly ionised. This means that there are free electrons and positive ions which can move freely. This endows the atmosphere of interesting electrical properties. At middle and low latitudes, i.e., far from the poles, the upper atmosphere is basically ionised by the solar radiation (in the bands of Ultraviolet and X-rays, that are absorbed by the highest layers of the atmosphere). At high latitudes, i.e., near from the poles, the ionisation of the atmosphere is basically due to the corpuscular radiation (particles) transported by the solar wind by effect of the geomagnetic field. This fact makes the ionosphere to behave as an electrical conductor, which is able to modify the propagation of the radioelectric waves, by diverting them from its straight line path. So much so that it can reflect some radio waves, of until some 30 - 40 MHz, which allows the communication between two far places of the Earth, by saving either its curvature or its orography. The ionosphere can also affect significantly the signals sent from the satellites, by causing strong interferences. These reasons, among others, make its knowledge to be important, since it has a lot of applications, both scientific and technical.

Thus, although some theoretical studies was claiming that it could exist a conductive layer in the upper atmosphere, the interest in this region increased after Marconi, in 1901, achieved transmitting radio signals from Cornwall (England) until Newfouland (Canada), with the consistent hypotheses that Kennelly and Heaviside independently formulated. These two researchers claimed that because of the curvature of the Earth, the radio waves had unavoidably been reflected in an ionized layer, the ionosphere.

The observation of the terrestrial ionosphere is based, predominantly, on indirect measurement techniques, by taking advantage of the fact that the electromagnetic waves, in the presence of a magnetic field, are modified during their propagation when they cross an ionized medium.


figura1 Basically, at middle latitudes, the vertical structure of the ionosphere shows three regions, which in ascending order are named D, E and F. The D region (at 60-90 Km roughly) is the most complex part of the ionosphere from the chemical point of view. It is highly controlled by solar radiation and it vanishes at night. It is the region which absorbs most of the radio waves, and this the reason why it is easier to listen remote broadcasting stations during the night. The following region is the E region (at 90-120 km approximately), which is also strongly controlled by solar radiation. It reaches its maximum at local noon, and it remains quite weak at night. In certain circumstances it appears a second layer, called sporadic E (Es), which is related with the neutral wind shear. Above these two regions, there is the F region (at 150-1000 Km approximately), which in turn, presents two layers called F1 and F2 layers during daytime, and mainly during the summer. At night time, only the F2 layer remains, which has the greatest concentration of electrons, and in general, thanks to it we can communicate via radio to long distances.




At present, the study of the ionosphere at the Observatori de l’Ebre is done by the use of the well known technique of the vertical ionospheric sounding. This is based, in a summarized form, on the transmission of a radio pulse vertically and on the measurement of the time which elapses before the echo is received. Assuming, at first instance, that the pulse runs at the speed of the light, the virtual height to which the reflection has taken place is calculated. This principle can be recognized as that of the radar, but it should be noted that the radar for aircrafts detection was developed from the techniques of the ionospheric sounding.





sondejadorThe instrument currently installed at the Observatori de l’Ebre is a DPS-4D ionospheric sounder, which was developed and built by Lowell Digisonde International in collaboration with UMass Lowell Center for Atmospheric Research. Routinely, it performs an ionospheric sounding every 15 minutes, but we are able to modify this cadence during specific campaigns. The instrument has a transmitter antenna, an integrated transceiver package (control unit), and a network of receiver antennas formed by four crossed magnetic dipole antennas. This station, which is singular in the Iberian Peninsula, belongs to the world-wide ionospheric observation network GIRO, and provides information for the products of the European network DIAS.


antena iono


The system has complementary cards of codifying phase and it benefits of advanced technology of radar in HF, like compression of pulses and coherent integration of phase, which makes it able to be used also as a spectrum analyser in HF. Thus, it allows obtaining the phase of the signal in each one of the four receiver antennas, by each spectral component, and identifying the angle from where the reflected pulses in the ionosphere come from (azimuth and elevation), its polarisation, the Doppler shift, and the time of flight, from the transmission until the reception.



ionograma 1Among the records provided by system, the ionogram is the most classical. The system performs a frequency sweep and it obtains a representation of the sounding frequency in function of the virtual height (time of flight). The virtual height is greater that the real height, due to the fact that the ionosphere behaves as a dispersive medium and radio pulses travel slower than light. Nevertheless, by applying inversion ionogram algorithms it is possible to calculate a profile of the electronic density in real height. Besides, the Total Electron Content (TEC) could be estimated by means of the integration of the electron density profile.




skymapThe skymap is another type of record provided by the system. It collects, for both a certain band of frequencies and a certain rank of reflection heights, the angle from where  the reflected pulses in the ionosphere come from (azimuth and elevation), and the Doppler shift. This information indicates the place on the vertical where the radio pulses have been reflected (if the reflective layer is tilted or if it presents irregularities), and if these reflection points move respect to the transmitting source (if the reflective layer is dynamic), providing us the apparent drift speed of the reflective layer. In the ideal case of an ionosphere in calm, it would be expected that all the reflections rebounded on the vertical (centre of the map) with a zero Doppler shift.



From an ionogram, we basically measure the critical frequencies of each layer, the virtual heights, and some parameters of propagation as for example the M(3000)F2, and we are able to derive the electronic density profile in function of the height. We reduce hourly ionograms every dat, and we calculate the day to day variability of the plasma frequency with height.




The ionospheric database of the Observatori de l’Ebre contains all digitized ionospheric parameters from the beginning in 1955. Every year, we produce an ionospheric butlletin, which, from the one corresponding to 2004, can be downloaded from our web page. The catalogue of the available data may also be consulted. This large quantity of data, together with data from other observatories, allows us to both analyze and know the state of the ionosphere either on quiet intervals or on disturbed periods due to the effects of the geomagnetic storms in the ionosphere.

In 2004, the Observatori de l’Ebre installed an ionospheric sounder in the Livingston Island, in the Antarctica, in order to study the state of the ionosphere in such remote location. Due to technical requirements of the device, this sounder only operates during the austral summer, when the Spanish Antartic station is open. The instrument is an Advanced Ionspheric Sounder developed by the Italian Istituto Nacionale de Geofisica e Vulcanologia (AIS_IGNV) and provides hourly ionograms that are analysed in the observatory.

GPSDuring the history of the ionospheric observation in the Observatori de l’Ebre, other systems, in addition to the ionospheric sounder, have been employed, as for example the A3 absorption method, that served for the study of the D region, and the calculation of the TEC by means of the calculation of the Faraday rotation. At present, the technique for measuring the TEC is based on the analysis of the signals emitted by the constellation of GPS, GLONASS, GALILEO, satellites …, known as GNSS (Global Navigation Satellite Systems). These emit, at least, two frequencies, and it is necessary to have suitable GNSS receivers, with which it is possible to differentiate the two phases associated to the above mentioned frequencies. This allows the determination of the phase delays due to the propagation of the signals through the ionosphere. These delays are proportional, except instrumental terms, to the integrated electronic density in the entire ray path, and enable to obtain the TEC. From 1996, l’Institut Cartogràfic i Geològic de Catalunya maintains an operative GPS receiver in the observatory.

K-index of geomagnetic activity calculated from our data. (Unrevised automatic process)
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 10:55
Temperature Humidity Atmospheric pressure
26.8 ºC 42.4 % 1014.2 hPa
Accumulated rain Wind speed Wind bearing
0 mm 5 km/h W (270º)
Information from the automatic station of AEMET located at Ebro Observatory. These data are provisional and subject to revision.