The effect of near-surface winds on surface temperature and dust transport on Venus

TL;DR

This study applies the first mesoscale regional model of Venus to quantify near-surface slope winds and their diurnal cycle. Using the LMD Venus model with multiple nested domains and PCM boundary fields, it shows a diurnal reversal of slope winds—upslope winds at noon and downslope winds at night—strongly modulated by topography and leading to significant adiabatic heating/cooling of the surface. The work links these winds to surface temperature implications (4 K diurnal amplitude on plains, <1 K on mountains) and assesses the potential for saltation, indicating notable dust transport especially near mountain flanks and convergence zones, with thresholds for 75 μm particles met in substantial portions of the domain. These findings inform mission planning and interpretation of near-surface observations, while highlighting model simplifications and avenues for future refinement, including variable surface properties, CO$_2$ thermodynamics, and explicit dust tracers.

Abstract

The knowledge of the Venus near-surface atmosphere is sparse. Few spacecrafts landed on the surface and measured winds with amplitudes below 1 m/s. The diurnal cycle of the wind amplitude and orientation is not known. Recent numerical simulations showed that slope winds along topographic structures could strongly impact the direction of winds. This study presents the first mesoscale modelling of such winds on Venus. A change of direction is occurring during the day in the main slopes, with upslope winds at noon due to solar heating and downslope winds at night. This is due to efficient IR cooling of the surface during the night, being colder than its surroundings slope atmospheric environment and leading to displacement of air. The temperature is impacted by the adiabatic cooling/warming induced by those winds. A strong heating effect is occurring for the downslope winds, leading to an anti-correlation between the surface temperature diurnal amplitude and the topography. This diurnal amplitude reaches 4 K in the plains and below 1 K in the mountains. The saltation of sediment by those winds was also quantified, with a higher probability at night along the slopes on the western flanks.

Figures (11)

• Figure 1: Elevation map of the Equatorial (top-left) and Polar (top-right) and Alpha Regio (bottom) domains with the location of the seven VENERA spacecrafts landing sites and 5 other points of interest represented by red squares. The red ellipse represents the landing area of DAVINCI garvinRevealingMysteriesVenus2022.
• Figure 2: Sunflower wind chart of the 10 m horizontal wind for VENERA-8 (A), VENERA-9 (B), VENERA-10 (C), VENERA-11 (D), VENERA-12 (E), VENERA-13 (F) VENERA-14 (G) locations every 8 Venusian minutes (.i.e). H is a point in the Equatorial plain near Phoebe Regio, and I is a point in the East flank of Beta Regio. J and K are two points on Ishtar Terra. L is located in Meskhenet Tessera where a dune field was observed (See Fig \ref{['21']}). The cyan lines represent the surface wind amplitude measured range for the VENERA landers in the late morning/early afternoon (Table \ref{['22']}). No directions were estimated for VENERA observations, the Eastern direction is for illustration only.
• Figure 3: Snapshots maps of horizontal winds 10 m above the local surface (m s$^{-1}$) at midnight (left column) and midday (right column) in the centre of the domain above Phoebe Regio, Beta Regio, Ishtar Terra and Alpha Regio.
• Figure 4: Map of the surface temperature diurnal amplitude (K) for Equatorial (top-left), Polar domain (top-right) and Alpha Regio (bottom). White contours represent the topography (Fig \ref{['21']}), every kilometer for the Equatorial domain, two kilometers for the Polar domain and every 600 m for Alpha Regio.
• Figure 5: Top: Snapshots maps of the adiabatic heating rate of an atmospheric parcel with vertical wind velocity at 2 m above local surface $\jmath_{adiab}$ (K/s) at midnight (left) and midday (right) for the Equatorial (top) and Polar (centre) domains and Alpha Regio (bottom). Black contours represent the topography (Fig \ref{['21']}), every kilometer for the Equatorial domain, two kilometers for the Polar domain and every 600 m for Alpha Regio.