Dew Point Anchoring of Planetary Atmospheres: An Alternative Boundary Condition Framework

This short technical note examines atmospheric structure from a thermodynamic boundary‑condition perspective. Rather than treating climate primarily as a forward radiative problem starting at the top of the atmosphere, it explores an inverse approach anchored at the lifting condensation level (LCL).
The central hypothesis is that the dew‑point temperature of a planet’s dominant condensing volatile (e.g. water on Earth, sulfuric acid on Venus, methane on Titan) provides a physically fixed phase boundary that constrains the vertical temperature–pressure structure of the troposphere via the adiabatic lapse rate. In this framework, surface temperature and pressure emerge as co‑dependent variables governed by phase equilibrium and gravity, rather than independent outcomes of radiative forcing.
The approach highlights the observable role of cloud‑base formation as a thermodynamic constraint and suggests that radiative transfer processes operate within limits set by phase equilibrium, rather than defining them. The same structure is shown to apply across a range of planetary atmospheres, indicating a potentially general physical principle.
The note is intended as a concise conceptual contribution to discussions of atmospheric modelling and planetary climate, with an emphasis on first‑principles thermodynamics.