ARCHIVES OF TIME
ARCHIVES OF TIME
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The Earth's atmosphere is subject to continuous changes in its physical conditions. Air temperature, and relative humidity, vary following the daily cycle of solar radiation. Atmospheric pressure also changes, influenced by temperature variations that trigger ascending or descending air movements. Air masses of different origins move across the Earth's surface, driven by horizontal pressure gradients, bringing intense disturbances or periods of good weather.
The Earth's atmosphere is subject to continuous changes in its physical conditions. Air temperature, and relative humidity, vary following the daily cycle of solar radiation. Atmospheric pressure also changes, influenced by temperature variations that trigger ascending or descending air movements. Air masses of different origins move across the Earth's surface, driven by horizontal pressure gradients, bringing intense disturbances or periods of good weather.
As regards temperature, beyond the aforementioned daily cycle, the succession of seasons brings the annual alternation of cold (winter) and warm periods (summer). In addition to these regular cycles, there are others of longer duration linked to variations in solar activity, small changes in the characteristics of Earth's orbit or rotation about its own axis, or even complex processes of geological, biological or anthropogenic nature.
As regards temperature, beyond the aforementioned daily cycle, the succession of seasons brings the annual alternation of cold (winter) and warm periods (summer). In addition to these regular cycles, there are others of longer duration linked to variations in solar activity, small changes in the characteristics of Earth's orbit or rotation about its own axis, or even complex processes of geological, biological or anthropogenic nature.
Any variation in the atmospheric temperature near the ground influences the heat flux that rises incessantly from the depths of our planet. These variations, therefore, make their effects felt even in the subsoil, propagating as variations in rock temperature, progressively attenuating in function of depth, but theoretically never entirely disappearing.
Any variation in the atmospheric temperature near the ground influences the heat flux that rises incessantly from the depths of our planet. These variations, therefore, make their effects felt even in the subsoil, propagating as variations in rock temperature, progressively attenuating in function of depth, but theoretically never entirely disappearing.
Caves offer the possibility to "pursue" underground, and to measure within the limits of our instruments, the effects of temperature variations to which the atmosphere is, or has been, subject over time. Descending into a cave is therefore like undertaking a journey into the (recent) past of the atmospheric "weather".
Caves offer the possibility to "pursue" underground, and to measure within the limits of our instruments, the effects of temperature variations to which the atmosphere is, or has been, subject over time. Descending into a cave is therefore like undertaking a journey into the (recent) past of the atmospheric "weather".
Daily temperature variations propagate into the subsoil through cavities for distances that at most reach a few hundred metres, in cases where there is intense incoming air circulation that transports the external thermal signal with a delay that can vary from a few minutes to a few hours, depending on air velocity.
Daily temperature variations propagate into the subsoil through cavities for distances that at most reach a few hundred metres, in cases where there is intense incoming air circulation that transports the external thermal signal with a delay that can vary from a few minutes to a few hours, depending on air velocity.
Seasonal temperature variations, however, can penetrate deeper with a delay that can reach several months. The seasonal thermal wave also propagates through the rock mass but for much shorter distances, a few tens of metres at most, and it is possible to monitor it by measuring temperature in boreholes in the rock in karst cavities that extend into the heart of mountains.
Seasonal temperature variations, however, can penetrate deeper with a delay that can reach several months. The seasonal thermal wave also propagates through the rock mass but for much shorter distances, a few tens of metres at most, and it is possible to monitor it by measuring temperature in boreholes in the rock in karst cavities that extend into the heart of mountains.
Even deeper, at several hundred metres distance from the surface, only variations of longer period, from decadal to centennial, are detectable with our instruments. It is not excluded that somewhere, in the depths of a mountain, today the rock may still be cooling, perhaps imperceptibly, as a consequence of the cold phase that characterised the centuries of the so-called "Little Ice Age", spanning from the 15th to the end of the 19th century of the second millennium.
Even deeper, at several hundred metres distance from the surface, only variations of longer period, from decadal to centennial, are detectable with our instruments. It is not excluded that somewhere, in the depths of a mountain, today the rock may still be cooling, perhaps imperceptibly, as a consequence of the cold phase that characterised the centuries of the so-called "Little Ice Age", spanning from the 15th to the end of the 19th century of the second millennium.
Caves, therefore, offer the possibility to monitor terrestrial climate changes filtered from short-period variations, such as daily and seasonal ones, providing us with a dampened signal that is much "cleaner" and indicative of longer-term trends.
Caves, therefore, offer the possibility to monitor terrestrial climate changes filtered from short-period variations, such as daily and seasonal ones, providing us with a dampened signal that is much "cleaner" and indicative of longer-term trends.
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