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<jats:title>Abstract</jats:title> <jats:p>Recent observations of molecular clouds show that dense filaments are the sites of present-day star formation. Thus, it is necessary to understand the filament formation process because these filaments provide the initial condition for star formation. Theoretical research suggests that shock waves in molecular clouds trigger filament formation. Since several different mechanisms have been proposed for filament formation, the formation mechanism of the observed star-forming filaments requires clarification. In the present study, we perform a series of isothermal magnetohydrodynamics simulations of filament formation. We focus on the influences of shock velocity and turbulence on the formation mechanism and identified three different mechanisms for the filament formation. The results indicate that when the shock is fast, at shock velocity <jats:italic>v</jats:italic> <jats:sub>sh</jats:sub> ≃ 7 km s<jats:sup>−1</jats:sup>, the gas flows driven by the curved shock wave create filaments irrespective of the presence of turbulence and self-gravity. However, at a slow shock velocity <jats:italic>v</jats:italic> <jats:sub>sh</jats:sub> ≃ 2.5 km s<jats:sup>−1</jats:sup>, the compressive flow component involved in the initial turbulence induces filament formation. When both the shock velocities and turbulence are low, the self-gravity in the shock-compressed sheet becomes important for filament formation. Moreover, we analyzed the line-mass distribution of the filaments and showed that strong shock waves can naturally create high-line-mass filaments such as those observed in the massive star-forming regions in a short time. We conclude that the dominant filament formation mode changes with the velocity of the shock wave triggering the filament formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Sun is the primary source of energy for the Earth. The small changes in total solar irradiance (TSI) can affect our climate on the longer timescale. In the evolutionary timescale, the TSI varies by a large amount and hence its influence on the Earth’s mean surface temperature (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>) also increases significantly. We develop a mass loss dependent analytical model of TSI in the evolutionary timescale and evaluated its influence on the <jats:italic>T</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub>. We determined the numerical solution of TSI for the next 8.23 Gyr to be used as an input to evaluate the <jats:italic>T</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> which formulated based on a zero-dimensional energy balance model. We used the present-day albedo and bulk atmospheric emissivity of the Earth and Mars as initial and final boundary conditions, respectively. We found that the TSI increases by 10% in 1.42 Gyr, by 40% in about 3.4 Gyr, and by 120% in about 5.229 Gyr from now, while the <jats:italic>T</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> shows an insignificant change in 1.644 Gyr and increases to 298.86 K in about 3.4 Gyr. The <jats:italic>T</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> attains the peak value of 2319.2 K as the Sun evolves to the red giant and emits the enormous TSI of 7.93 × 10<jats:sup>6</jats:sup> W m<jats:sup>−2</jats:sup> in 7.676 Gys. At this temperature Earth likely evolves to be a liquid planet. In our finding, the absorbed and emitted flux equally increases and approaches the surface flux in the main sequence, and they are nearly equal beyond the main sequence, while the flux absorbed by the cloud shows the opposite trend.</jats:p>