Measuring Early-Morning Cloud and Haze Opacity on Mars with THEMIS-VIS on Mars Odyssey, Identifying Diurnal Changes by Reference to MRO's MARCI
Abstract
Martian water ice clouds and hazes are now well known to have significant feedbacks with atmospheric dynamics and climate [e.g. Navarro et al. 2014, JGR 119 p. 1479]. They have also been shown, not surprisingly, to have significant diurnal variability [e.g. Wilson et al. 2007, GRL 34 L02710], but current estimates of cloud/haze opacity are quite limited in their coverage of the diurnal cycle. The Mars Odyssey spacecraft is now in an orbit which crosses the equator at 07:30 local solar time, providing an opportunity to study the early morning portion of the cloud/haze diurnal cycle with its Thermal Emission Imaging System (THEMIS).
Since early morning observations of aerosols in the thermal infrared are challenging due to low thermal contrasts, we use THEMIS's visible light subsystem (THEMIS-VIS) [e.g. Christensen et al. 2004, Space Science Reviews 110 p. 85; McConnochie et al. 2006, JGR 111 p. 32] for this initial study. We focus in particular on making a systematic survey of the change in opacity from the relatively well-studied mid-afternoon hours to the 07:00 - 08:00 early morning hours. Rather than making questionable assumptions about lack of interannual variability and lack of spatial variability, we survey opacity changes by directly comparing THEMIS-VIS images with Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI) [Malin et al. 2008, Icarus 194 p. 501; Bell et al. 2009, JGR 114 E08S92] images of the same location acquired on the same or nearly the same sol. MARCI's visible-light filter passbands are very similar to those of THEMIS-VIS, its daily approximately-global coverage ensures a high probability of overlap with any given THEMIS-VIS frame, and MRO's 15:00 local-time orbit provides the necessary local-time reference. For each THEMIS-VIS frame, we solve for aerosol opacity using a discrete ordinates radiative transfer code, and then do the same with the corresponding MARCI pixels. We then use the resulting data set to establish spatial and seasonal trends in diurnal opacity changes.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P43K3893M
- Keywords:
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- 3346 Planetary meteorology;
- ATMOSPHERIC PROCESSESDE: 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5445 Meteorology;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS