Meteorology, climate and solar activity section

Aims and goals

The meteorological part of the Section, in collaboration with the Instituto Nacional de Meteorología, is basically devoted to observe and record the different meteorological parameters. Continuously, the most typical variables are recorded: temperatu re, pressure, humidity, rain, direction and wind speed. In addition, daily observations at 6, 7, 9, 12, 13, 15 and 18 hours UT are done for these and others parameters like cloudiness, type of clouds, etc. This section has got the longest series of observations of the Observatory, with continuos measurements of the most important meteorological parameters since 1904.

To carry out these works the Instituto Nacional de Meteorología installed a standard station (which belongs to the National Meteorological Network), solar radiation meters, and a station for the measurement of pollution, which is integrated in the BAPMON-EMEP Network. This is one of the six stations that are operating in Spain, in order to quantify the background pollution and evaluate the transport, transformation and deposit of some contaminants, which cause the acid rain. The measured parameters correspond to samples taken from the air, rain and solid particles drifted by the wind and deposited on special filters. Due to its importance for the acid rain we underline the measure of SO2 and NO2 contaminants.

This section is devoted to study the solar activity, too. This activity propagates towards the Earth as radiation and particles, as the so-called "Solar Wind". The solar activity appears in several layers of the Sun:

The "PHOTOSPHERE" is the layer from which practically all the Sun's visible light is emitted, and as such represents what is called the "surface" of the Sun. The most obvious signs of activity on the photosphere are the sunspots. They change from a day to another. Seen from the Earth, the Sun rotates on its axis with a synodic period of 27 days. So the sunspots can appear in the East Limb of the Sun, cross the central meridian and disappear in the West Limb if their life lasts enough. The number of sunspots varies with an 11 years period called "Solar Cycle". The level of sunspot activity is assessed by the Zurich (or "Wolf") relative sunspot number, R, which can be computed with the total number of spots and the number of groups. We photograph the Solar Photosphere with a telescope on an equatorial mount. With this photograph we determine the area and the position of the sunspots and we compute the solar activity index R (Wolf number) taking into account the total number of spots and the number of groups. These data are daily communicated to the International Data Centre located in Brussels where the International Wolf Number is elaborated considering our data jointly with data from other solar observatories. Following the recommendation of the "Workshop on Solar-Terrestrial Prediction" held in Ottawa, May 1992, we study the hemispheric evolution of this index.

Associated with sunspots, there are "faculae". They are patches of light (brighter than average) in the upper region of the photosphere which usually appear in the vicinity of a sunspot group before the sunspots themselves emerge, and which usually persist for several weeks after the disappearance of the spots.

Above the photosphere, there is a tenuous layer of gas, called "CHROMOSPHERE" far too faint to be seen against the brilliance of the photosphere. It can be studied with the aid of a spectroheliograph or a monochromatic filter (as our LYOT FILTER) which remove the photospheric emissions and allow observing the lines of the chromospheric spectrum. Line alpha of Hidrogen at a wavelength of 656.3 nm in the red part of the spectrum is particularly prominent, and gives the Chromosphere its characteristic colour. The chromosfere exhibits some large-scale phenomena:

Plages - They are areas of intensified brightness visible in various monochromatic lines. They look, in a way, like bright, sandy beaches against the background of the chromosphere. Plages coincide approximately in position with the photospheric faculae and represent regions of enhanced density and temperature. They delineate the area of enhanced magnetic field, which constitutes a complete active region. Formerly they were known as "flocculi" and sometimes the term "chromospheric faculae" is used to describe them.

Prominences - They appear at the limb of the Sun as huge flare-like clouds of luminous gas in the upper Chromosphere and inner Corona, and consist of clouds of material at lower temperatures but higher densities than their surroundings erupting violently to the space at heights of several hundred thousand kilometres and dispersing. However, when seen against the bright background of the disc the absorption produced by these clouds predominates, and they are seen as dark Filaments (formerly known as "dark floculi").

Flares - They are sudden releases of energy that occur in the vicinity of active regions. They eject particles and emit radiation across the entire range of the electromagnetic spectrum form gamma rays and hard X-rays to radio wavelengths of several kilometres. Flares reach maximum brightness within and few minutes and decline more slowly thereafter.

Finally, above the chromosphere there is a layer called "CORONA" that extends outward to a distance a several solar radii, as an atmosphere of the Sun. Under normal circumstances, the chromosphere and the corona cannot be seen without the aid of specialised instrumentation, but when a total eclipse occurs these layers may be seen directly.