She was born during the summer of 2016 at La Herrería Forest (El Escorial), 40 km Northwest from the busy city of Madrid, and a few hundred meters from the quiet Royal Monastery of San Lorenzo de El Escorial – where many Spanish Kings from the last centuries rest. But the most important thing was that she was situated just at the foothills of the majestic Mount Abantos (1753 m), a prominent peak of the Guadarrama Mountain Range.

La Herrería Forest, with the Mount Abantos in the background and the Royal Monastery of San Lorenzo de El Escorial in the right side of the picture. The greenness still dominated during mid-June 2022.

With this beautiful environment, it is not strange that she started talking just a few days later after her birth, telling us details about how her day was. That was the 7th of June of 2016, but she has been doing the same during more than six years now. Indeed, her everyday life is sometimes quite cyclical, which is good for her, and for us. But, as everyone, she also has some days in which everything is different, which is also good for her, and for us.

The routine life of la torre was indeed scheduled by the Mount Abantos closeness, which causes recurrent and cyclical winds during fair-weather days, conditions that are relatively typical in the area. These winds – known as mountain breezes – are characterised by wind blowing down the slope during the nighttime (katabatic) and upslope during the daytime (anabatic) [3,4]. But she has also experienced periods characterised by extreme conditions: in summer after long periods without rain leading to dry soils [5] and in winter days under cold temperatures and snowy ground, as happened during the post-period of the famous Filomena storm [6], in January 2021.

Apart from the special and challenging environment where the tower is, her singularity also falls in her capability for measuring all the components that participate in the surface energy balance (SEB).

Firstly, the sensors located at the upper part of the 4-component radiometer measure the incoming shortwave (solar, SW) and longwave (atmospheric, LW) radiation that reaches the surface, while the sensors at the bottom part are oriented towards the ground to capture the outgoing amount of solar energy reflected by the surface and the terrestrial emission (LW). The sum of the incoming components minus the outgoing ones provides us with the radiative energy available at the surface, commonly known as the Net Radiation (Rnet):

From the measurements of HER, we can expect a positive Rnet during daytime, negative during nighttime, and positive during the whole diurnal cycle. This means that some energy is available, free, there…

This net radiation, which resulted from the play between the solar radiation, the surface, and the atmospheric and land surface radiative properties, is now employed by the surface turbulent fluxes to redistribute the heat in the lower atmosphere. Here, the term “heat” redistribution includes both the sensible and the latent heat fluxes (SH and Le, respectively). While the former is related to the vertical differences in temperature, the latter is due to vertical differences in water vapour concentration (which contains “latent” energy awaiting changes in phase).

All the components of the SEB, averaged for the month of July (2017-2021). From [7]. All the radiative components are shown in the left-side panel, summing up the net radiation (in green).

The right-side panel shows the surface fluxes that employ this available net radiation. And if that was not enough, she continues telling us histories about her life, also taking high-quality measurements of atmospheric variables at different heights: temperature, humidity, wind speed, wind direction, or atmospheric pressure. Besides, the IRGASON measures the CO2 concentration at a high frequency [4, 8], which is also used to calculate the CO2 flux by means of the EC technique. Last but not least, all these data are also complemented by continuous soil temperature and soil moisture measurements at different depths, the latter also telling us histories about the past rainfall, a variable that is also measured at the site.

The uniqueness of the commented measurements provided by La Herrería tower have fed numerous scientific studies aimed at investigating different topics. We hope she can continue telling us histories about her life in this awesome environment for several years, something needed to feed the scientific studies done by researchers interested in improving the knowledge of the land-atmosphere interactions in mountainous areas.