A Caltech Library Service

Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus

Gao, Peter and Zhang, Xi and Crisp, David and Bardeen, Charles G. and Yung, Yuk L. (2014) Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus. Icarus, 231 . pp. 83-98. ISSN 0019-1035. doi:10.1016/j.icarus.2013.10.013.

PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Observations by the SPICAV/SOIR instruments aboard Venus Express have revealed that the upper haze (UH) of Venus, between 70 and 90 km, is variable on the order of days and that it is populated by two particle modes. We use a one-dimensional microphysics and vertical transport model based on the Community Aerosol and Radiation Model for Atmospheres to evaluate whether interaction of upwelled cloud particles and sulfuric acid particles nucleated in situ on meteoric dust are able to generate the two observed modes, and whether their observed variability are due in part to the action of vertical transient winds at the cloud tops. Nucleation of photochemically produced sulfuric acid onto polysulfur condensation nuclei generates mode 1 cloud droplets, which then diffuse upwards into the UH. Droplets generated in the UH from nucleation of sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles and therefore cannot reproduce the observed bimodal size distribution. By comparison, the mass transport enabled by transient winds at the cloud tops, possibly caused by sustained subsolar cloud top convection, are able to generate a bimodal size distribution in a time scale consistent with Venus Express observations. Below the altitude where the cloud particles are generated, sedimentation and vigorous convection causes the formation of large mode 2 and mode 3 particles in the middle and lower clouds. Evaporation of the particles below the clouds causes a local sulfuric acid vapor maximum that results in upwelling of sulfuric acid back into the clouds. In the case where the polysulfur condensation nuclei are small and their production rate is high, coagulation of small droplets onto larger droplets in the middle cloud may set up an oscillation in the size modes of the particles such that precipitation of sulfuric acid “rain” may be possible immediately below the clouds once every few Earth months. Reduction of the polysulfur condensation nuclei production rate destroys this oscillation and reduces the mode 1 particle abundance in the middle cloud by two orders of magnitude. However, it better reproduces the sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets as constrained by fits to UV reflectivity data. In general we find satisfactory agreement between our nominal and transient wind results and observations from Pioneer Venus, Venus Express, and Magellan, though improvements could be made by incorporating sulfur microphysics.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gao, Peter0000-0002-8518-9601
Crisp, David0000-0002-4573-9998
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2013 Elsevier Inc. Received 5 March 2013; Revised 10 October 2013; Accepted 11 October 2013; Available online 29 October 2013. We thank S. Garimella and R.L. Shia for assistance with the setting up and running of the CARMA code. We thank R.W. Carlson and C. Parkinson for their valuable inputs. We thank C. Li for his help in speeding up our model runs by more than a factor of 10. This research was supported in part by the Venus Express program via NASA NNX10AP80G grant to the California Institute of Technology, and in part by an NAI Virtual Planetary Laboratory grant from the University of Washington to the Jet Propulsion Laboratory and California Institute of Technology. Part of the research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
NASA Venus Express programNNX10AP80G
University of Washington NAI Virtual Planetary Laboratory grantUNSPECIFIED
Subject Keywords:Atmospheres, composition; Atmospheres, structure; Atmospheres, dynamics; Venus; Venus, atmosphere
Record Number:CaltechAUTHORS:20140107-152003222
Persistent URL:
Official Citation:Peter Gao, Xi Zhang, David Crisp, Charles G. Bardeen, Yuk L. Yung, Bimodal distribution of sulfuric acid aerosols in the upper haze of Venus, Icarus, Volume 231, 1 March 2014, Pages 83-98, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43253
Deposited By: Ruth Sustaita
Deposited On:07 Jan 2014 23:41
Last Modified:10 Nov 2021 16:35

Repository Staff Only: item control page