Cosmic ray and solar activity influences on long-term variations of cave climate systems

During the analysis of solar activity impact on climate, the emphasis is placed on temperature changes. Earth's atmosphere is a dynamical system with a complex variability in space and time. Due to the fact that caves in Karst preserve the long term environmental changes, the investigation of the in-caves’ atmospheric parameters and their variations with time becomes very important in the last quarter of century. In this paper we investigate the temporal evolution of the temperature and pressure of the ground atmospheric layer in the region of two Bulgarian caves: Snezhanka (Pazardjik region) and Uhlovitsa (Smolyan region), during the period 2005–2017. We show that thermal and mass exchange of the caves’ air with the environment has significant temporal variations. On annual basis the thermo-dynamical parameters of the observed caves behaves as a barotropic fluid, in which the air density depends only on atmospheric pressure. As a result, the temporal evolution of in-caves’ pressure and temperature change synchronously with time. The observed 11-year signal could be attributed to the heliospheric modulation of galactic cosmic ray (GCR) intensity, which modulates the ozone and humidity near the tropopause and correspondingly the strength of the atmospheric greenhouse effect. Our study helps to clarify the influence of helio-geophysical factors on the state of the lower atmosphere.