Speaker
Description
The atmospheric dynamics of Venus's mesosphere (60–120 km) present a long-standing scientific challenge, characterized by complex interactions between meridional circulation and photochemistry. A recent, unexpected observation revealed a massive increase in the gas-phase deuterium-to-hydrogen (D/H) ratio in this layer, rising from 162 to 1,519 times Earth’s standard between 70 and 108 km in altitude, suggesting the existence of a powerful transport mechanism, possibly an aerosol-driven cycle and a meridional circulation (Mahieux et al., 2024).
To quantitatively test this hypothesis, this study employs the 2D KINETIC (Yung et al., 2009) and 1D VULCAN (Tsai et al., 2017; Dai et al., 2024) Chemical Transport Models (CTMs). Both models were updated to integrate the requisite physics, including a temperature-dependent frozen-reservoir switch, bimodal aerosol transport, altitude-dependent condensation fractionation, and differential photolysis.
Our simulations demonstrate that the theoretical pathways for upward transport and high-altitude release are numerically viable and capable of producing upper-atmosphere D/H anomalies. Both models correctly sequester deuterium into the condensed phase near the cold trap (80–95 km). However, when strictly enforcing physically realistic, mass-conserving co-transport of both H₂O and HDO, the extreme upper-mesospheric D/H enrichment collapses to a low-amplitude ceiling in our models. These results indicate that the fundamental bottleneck is not the atmospheric transport architecture itself, but rather the insufficient isotopic enrichment within the aerosol reservoir prior to its ascent. Ultimately, this structural limitation suggests that replicating the observed stratification requires either a stronger or repeated Rayleigh-like fractionation. This study provides critical new constraints for understanding Venus's atmospheric evolution and historical water loss (Donahue et al., 1982).
This presentation is dedicated to the memory of Professor Yuk L. Yung (1946-2026).
| Participate the oral/poster presentation award competition | Yes |
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