Effects of variation in coagulation and photochemistry parameters on the particle size distributions in the Venus clouds

Abstract

This paper explores the effects that variation in the coalescence efficiency of the Venus cloud particles can have on the structure of the Venus cloud. It is motivated by the acknowledgment of uncertainties in the measured parameters-and the assumptions made to account for them-that define our present knowledge of the particle characteristics. Specifically, we explore the consequence of allowing the coalescence efficiency of supercooled sulfuric acid in the upper clouds to tend to zero. This produces a cloud that occasionally exhibits an enhancement of small particles at altitude (similar to the upper hazes observed by Pioneer Venus and subsequently shown to be somewhat transient). This simulated cloud occasionally exhibits a rapid growth of particle size near cloud base, exhibiting characteristics similar to those seen in the controversial Mode 3 particles. These results demonstrate that a subset of the variations observed as near-infrared opacity variations in the lower and middle clouds of Venus can be explained by microphysical, in addition to dynamical, variations. Furthermore, the existence of a population of particles exhibiting less efficient coalescence efficiencies would support the likelihood of conditions suitable for charge exchange, hence lightning, in the Venus clouds. We recommend future laboratory studies on the coalescence properties of sulfuric acid under the range of conditions experienced in the Venus clouds. We also recommend future in situ measurements to better characterize the properties of the cloud particles themselves, especially composition and particle habits (shapes).

Clouds and Hazes of Venus

“…For comparison, typical Earth Stratospheric conditions are indicated by the diagonal hatching on the lower left of the diagram. A similar version of this figure appeared in charging are best in the vicinity of the lower clouds (due to the higher temperatures), supersaturations can become very large indeed in the upper clouds and hazes (Gao et al 2014;McGouldrick 2017). It may be possible that these large supersaturations may overcome the temperature effect to encourage ion-induced charging in the upper clouds of Venus.…”

Venus Orbital Mission Concept: Kythiran Eolian dYnamics from the Surface to the Thermosphere from an Orbital NEtwork (KEYSTONE)

“…Significant variations in the cloud particle size distributions were identified by multiple in situ probes [24,17], as well as via remote sensing [4]. Variations in the upper clouds and hazes are also seen both in observations [41] and cloud models [14,34,26]. Further complicating the picture is the coupled nature of the clouds, absorbers, and governing chemistry.…”

Phosphorus in the Clouds of Venus: Potential for Bioavailability

“…The Venus International Reference Model (Kliore et al, 1985) includes a description of the venusian clouds based primarily on the Pioneer Venus Multiprobe results (Ragent et al, 1985), the essential characteristics validated by the subsequent Venera and VeGa missions (Ekonomov et al, 1984;Gnedykh et al, 1987;Zhulanov et al, 1987b). McGouldrick (2017) modeled variations in the cloud particle size distribution and considered the effects of coagulation and photochemistry.…”