Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling
Ice clouds in Titan’s polar stratosphere are implicated in radiative heating and cooling and in transporting volatile organic compounds from where they form in the upper atmosphere to the surface of the moon. In early southern fall, Cassini detected a large, unexpected cloud at an altitude of 300 km...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2023-01-01
|
| Series: | The Planetary Science Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/PSJ/ad0837 |
| _version_ | 1797393674684858368 |
|---|---|
| author | Lavender E. Hanson Darryn Waugh Erika Barth Carrie M. Anderson |
| author_facet | Lavender E. Hanson Darryn Waugh Erika Barth Carrie M. Anderson |
| author_sort | Lavender E. Hanson |
| collection | DOAJ |
| description | Ice clouds in Titan’s polar stratosphere are implicated in radiative heating and cooling and in transporting volatile organic compounds from where they form in the upper atmosphere to the surface of the moon. In early southern fall, Cassini detected a large, unexpected cloud at an altitude of 300 km over Titan’s south pole. The cloud, which was found to contain HCN ice, was inconsistent with the most recent measurements of temperature in the same location and suggested that the atmosphere had to be 100 K cooler than expected. However, changes to Cassini’s orbit shortly after the cloud’s appearance precluded further observations, and, consequently, the atmospheric conditions and the details of the formation and evolution of the cloud remain unknown. We address this gap in the observational record by using microphysical cloud modeling to estimate the parameter space consistent with published measurements. Based on the nearest available temperature profile retrievals and other observations, we hypothesize that the cloud forms around 300 km and then descends until it reaches the cold lower stratosphere by late southern fall. The observations can be simulated using a cloud microphysical model by introducing a descending cold layer with temperatures near 100 K. In simulations of this scenario, the precipitation from this cloud rapidly removes over 70% of the HCN vapor from the stratosphere. This result suggests that vapor descending into the polar stratosphere during early fall is mostly removed from the stratosphere before the onset of winter and does not circulate to lower latitudes. |
| first_indexed | 2024-03-09T00:06:16Z |
| format | Article |
| id | doaj.art-723f12265dba4533862b905b33732cbd |
| institution | Directory Open Access Journal |
| issn | 2632-3338 |
| language | English |
| last_indexed | 2024-03-09T00:06:16Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Planetary Science Journal |
| spelling | doaj.art-723f12265dba4533862b905b33732cbd2023-12-12T13:15:30ZengIOP PublishingThe Planetary Science Journal2632-33382023-01-0141223710.3847/PSJ/ad0837Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical ModelingLavender E. Hanson0https://orcid.org/0000-0003-2298-8382Darryn Waugh1https://orcid.org/0000-0001-7692-2798Erika Barth2https://orcid.org/0000-0002-5034-1300Carrie M. Anderson3https://orcid.org/0000-0003-2175-3709Department of Earth and Planetary Sciences, Johns Hopkins University , Baltimore, MD 21218, USA ; lhanso14@jh.eduDepartment of Earth and Planetary Sciences, Johns Hopkins University , Baltimore, MD 21218, USA ; lhanso14@jh.eduSouthwest Research Institute , Boulder, CO 80302, USAPlanetary Systems Laboratory, NASA Goddard Space Flight Center , 8800 Greenbelt Road, Greenbelt, MD 20771, USAIce clouds in Titan’s polar stratosphere are implicated in radiative heating and cooling and in transporting volatile organic compounds from where they form in the upper atmosphere to the surface of the moon. In early southern fall, Cassini detected a large, unexpected cloud at an altitude of 300 km over Titan’s south pole. The cloud, which was found to contain HCN ice, was inconsistent with the most recent measurements of temperature in the same location and suggested that the atmosphere had to be 100 K cooler than expected. However, changes to Cassini’s orbit shortly after the cloud’s appearance precluded further observations, and, consequently, the atmospheric conditions and the details of the formation and evolution of the cloud remain unknown. We address this gap in the observational record by using microphysical cloud modeling to estimate the parameter space consistent with published measurements. Based on the nearest available temperature profile retrievals and other observations, we hypothesize that the cloud forms around 300 km and then descends until it reaches the cold lower stratosphere by late southern fall. The observations can be simulated using a cloud microphysical model by introducing a descending cold layer with temperatures near 100 K. In simulations of this scenario, the precipitation from this cloud rapidly removes over 70% of the HCN vapor from the stratosphere. This result suggests that vapor descending into the polar stratosphere during early fall is mostly removed from the stratosphere before the onset of winter and does not circulate to lower latitudes.https://doi.org/10.3847/PSJ/ad0837TitanAtmospheric cloudsPlanetary atmospheres |
| spellingShingle | Lavender E. Hanson Darryn Waugh Erika Barth Carrie M. Anderson Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling The Planetary Science Journal Titan Atmospheric clouds Planetary atmospheres |
| title | Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling |
| title_full | Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling |
| title_fullStr | Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling |
| title_full_unstemmed | Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling |
| title_short | Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling |
| title_sort | investigation of titan s south polar hcn cloud during southern fall using microphysical modeling |
| topic | Titan Atmospheric clouds Planetary atmospheres |
| url | https://doi.org/10.3847/PSJ/ad0837 |
| work_keys_str_mv | AT lavenderehanson investigationoftitanssouthpolarhcncloudduringsouthernfallusingmicrophysicalmodeling AT darrynwaugh investigationoftitanssouthpolarhcncloudduringsouthernfallusingmicrophysicalmodeling AT erikabarth investigationoftitanssouthpolarhcncloudduringsouthernfallusingmicrophysicalmodeling AT carriemanderson investigationoftitanssouthpolarhcncloudduringsouthernfallusingmicrophysicalmodeling |