Search for: All records

Venus is an exceptional natural experiment to test our understanding of atmospheric sulfur chemistry. Previous modeling efforts have focused on understanding either the middle or lower atmosphere. In this work, we performed the first full atmosphere analysis of the chemical transport processes on Venus from the surface to 110 km using a 1‐D diffusion model with photochemistry. We focused on the cycling of chemical species between the upper and lower atmospheres and interactions between distinct species groups including SO, CO + OCS, chlorides, NO, O, and S. We tested different eddy diffusivity profiles and investigated their influences on the vertical profiles of important species. We find that the assumed boundary conditions in previous models strongly impacted their simulation results. This has a particularly large effect for SO. We find the high SOabundance in the lower atmosphere is readily transported into the middle atmosphere, far exceeding observed values. This implies some yet unknown chemistry or process limiting SOmixing. We summarize outstanding questions raised by this work and note chemical reactions that should be the highest priority for future laboratory studies and ab initio calculations.

 

Large eddy simulation (LES) of the Martian convective boundary layer (CBL) with a Mars‐adapted version of the Weather Research and Forecasting model is used to examine the impact of aerosol dust radiative‐dynamical feedbacks on turbulent mixing. The LES is validated against spacecraft observations and prior modeling. To study dust redistribution by coherent dynamical structures within the CBL, two radiatively active dust distribution scenarios are used: one in which the dust distribution remains fixed and another in which dust is freely transported by CBL motions. In the fixed dust scenario, increasing atmospheric dust loading shades the surface from sunlight and weakens convection. However, a competing effect emerges in the free dust scenario, resulting from the lateral concentration of dust in updrafts. The resulting enhancement of dust radiative heating in upwelling plumes both generates horizontal thermal contrasts in the CBL and increases buoyancy production, jointly enhancing CBL convection. We define a dust inhomogeneity index (DII) to quantify how much dust is concentrated in upwelling plumes. If the DII is large enough, the destabilizing effect of lateral heating contrasts can exceed the stabilizing effect of surface shading such that the CBL depth increases with increasing dust optical depth. Thus, under certain combinations of total dust optical depth and the lateral inhomogeneity of dust, a positive feedback exists between dust optical depth, the vigor and depth of CBL mixing, and—to the extent that dust lifting is controlled by the depth and vigor of CBL mixing—the further lifting of dust from the surface.

 

Sulfur‐water chemistry plays an important role in the middle atmosphere of Venus. Ground‐based observations have found that simultaneously observed SO₂and H₂O at ~64 km vary with time and are temporally anticorrelated. To understand these observations, we explore the sulfur‐water chemical system using a one‐dimensional chemistry‐diffusion model. We find that SO₂and H₂O mixing ratios above the clouds are highly dependent on mixing ratios of the two species at the middle cloud top (58 km). The behavior of sulfur‐water chemical system can be classified into three regimes, but there is no abrupt transition among these regimes. In particular, there is no bifurcation behavior as previously claimed. We also find that the SO₂self‐shielding effect causes H₂O above the clouds to respond to the middle cloud top in a nonmonotonic fashion. Through comparison with observations, we find that mixing ratio variations at the middle cloud top can explain the observed variability of SO₂and H₂O. The sulfur‐water chemistry in the middle atmosphere is responsible for the H₂O‐SO₂anticorrelation at 64 km. Eddy transport change alone cannot explain the variations of both species. These results imply that variations of species abundance in the middle atmosphere are significantly influenced by the lower atmospheric processes. Continued ground‐based measurements of the coevolution of SO₂and H₂O above the clouds and new spacecraft missions will be crucial for uncovering the complicated processes underlying the interaction among the lower atmosphere, the clouds, and the middle atmosphere of Venus.

 

Since January 2012, we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). Here, we present new data recorded in February and April 2019 in the 1345 cm −1 (7.4 μ m) spectral range, where SO 2 , CO 2 , and HDO (used as a proxy for H 2 O) transitions were observed. The cloud top of Venus was probed at an altitude of about 64 km. As in our previous studies, the volume mixing ratio (vmr) of SO 2 was estimated using the SO 2 /CO 2 line depth ratio of weak transitions; the H 2 O volume mixing ratio was derived from the HDO/CO 2 line depth ratio, assuming a D/H ratio of 200 times the Vienna standard mean ocean water. As reported in our previous analyses, the SO 2 mixing ratio shows strong variations with time and also over the disk, showing evidence for the formation of SO 2 plumes with a lifetime of a few hours; in contrast, the H 2 O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We have used the 2019 data in addition to our previous dataset to study the long-term variations of SO 2 and H 2 O. The data reveal a long-term anti-correlation with a correlation coefficient of −0.80; this coefficient becomes −0.90 if the analysis is restricted to the 2014–2019 time period. The statistical analysis of the SO 2 plumes as a function of local time confirms our previous result with a minimum around 10:00 and two maxima near the terminators. The dependence of the SO 2 vmr with respect to local time shows a higher abundance at the evening terminator with respect to the morning. The dependence of the SO 2 vmr with respect to longitude exhibits a broad maximum at 120–200° east longitudes, near the region of Aphrodite Terra. However, this trend has not been observed by other measurements and has yet to be confirmed.