Caves as observatories for atmospheric thermal tides: an example from Ascunsă Cave, Romania

Abstract

Abstract:As part of a microclimate study at Ascunsă Cave, Romania, we used Gemini Tinytag Plus 2 data loggers to record cave air temperature variability. At one of the monitoring points we recognized the presence of semidiurnal cycles on the order of a few thousands of a degree Celsius that could be produced under the influence of the semidiurnal tidal components of the Sun (S 2 ) or the Moon (M 2 ). Using a Gemini Tinytag Plus 2 data logger with an external probe we measured core rock temperature and showed that it does not influence the cave air temperature on such short time scales. We thus rejected the possibility that Earth tides, mostly produced by the lunar tidal influence on the Earth's crust, would have had a semidiurnal influence on cave air temperature. Moreover, time series analysis revealed a 12.00-hour periodicity in temperature data, specific for the S 2 , allowing us to assign these variations to the influence of the thermo-tidal action of the Sun. Using the Ideal Gas Law and assuming a constant volume and amount of air, we calculated that a theoretical change in atmospheric pressure of around 40 Pa was needed to produce the temperature changes we observed. This agrees with published values of atmospheric pressure changes induced by the semidiurnal solar component of the thermal tides (S 2(t) ). We thus can assign the observed temperature changes to semidiurnal atmospheric pressure changes (S 2(p) ) induced by the thermal excitation of the Sun. Our study signals the possibility that readily available data from cave monitoring studies around the world could be used in the study of atmospheric tides.Moreover, it appears that Ascunsă Cave acts as a natural meteorological filter on a short time scale, removing the direct thermal influences of the Sun (especially night and day differences) and preserving only the barometric information from the surface.cave atmosphere, thermal tide, semidiurnal, S 2(t) , Romania

Temperature fluctuations and ventilation dynamics induced by atmospheric pressure variations in Lamalunga Cave (Apulia, Italy) and their influences on speleothem growth

“…Perturbations and daily to sub-daily cycles in the cave microclimate parameters are well known in the literature, and can affect air temperature, relative humidity, dripwater flow rate, radon-222, CO 2 concentration, and barometric air pressure (Genty and Deflandre, 1998;Perrier et al, 2001Perrier et al, , 2004Perrier et al, , 2023Sondag et al, 2003;Bourges et al, 2006;Richon et al, 2009;Drăgușin et al, 2018;Sekhon et al, 2021;Gomell and Pflitsch, 2022). In underground environments and, particularly, in barometric caves, daily to sub-daily cycles are induced by atmospheric pressure variations (APV), which are characterized by strong 24-hour (S1 = 1.0 cpd) and 12-hour (S2 = 2.0 cpd) solar harmonic frequencies (Perrier et al, 2001;Sondag et al, 2003;Richon et al, 2009;Mentes, 2018).…”