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Saturn’s thermal emission at 2.2-cm wavelength as imaged by the Cassini RADAR radiometer

Janssen, M. A. and Ingersoll, A. P. and Allison, M. D. and Gulkis, S. and Laraia, A. L. and Baines, K. H. and Edgington, S. G. and Anderson, Y. Z. and Kelleher, K. and Oyafuso, F. A. (2013) Saturn’s thermal emission at 2.2-cm wavelength as imaged by the Cassini RADAR radiometer. Icarus, 226 (1). pp. 522-535. ISSN 0019-1035. https://resolver.caltech.edu/CaltechAUTHORS:20131101-144840642

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Abstract

We present well-calibrated, high-resolution maps of Saturn’s thermal emission at 2.2-cm wavelength obtained by the Cassini RADAR radiometer through the Prime and Equinox Cassini missions, a period covering approximately 6 years. The absolute brightness temperature calibration of 2% achieved is more than twice better than for all previous microwave observations reported for Saturn, and the spatial resolution and sensitivity achieved each represent nearly an order of magnitude improvement. The brightness temperature of Saturn in the microwave region depends on the distribution of ammonia, which our radiative transfer modeling shows is the only significant source of absorption in Saturn’s atmosphere at 2.2-cm wavelength. At this wavelength the thermal emission comes from just below and within the ammonia cloud-forming region, and yields information about atmospheric circulations and ammonia cloud-forming processes. The maps are presented as residuals compared to a fully saturated model atmosphere in hydrostatic equilibrium. Bright regions in these maps are readily interpreted as due to depletion of ammonia vapor in, and, for very bright regions, below the ammonia saturation region. Features seen include the following: a narrow equatorial band near full saturation surrounded by bands out to about 10° planetographic latitude that demonstrate highly variable ammonia depletion in longitude; narrow bands of depletion at −35° latitude; occasional large oval features with depleted ammonia around −45° latitude; and the 2010–2011 storm, with extensive saturated and depleted areas as it stretched halfway around the planet in the northern hemisphere. Comparison of the maps over time indicates a high degree of stability outside a few latitudes that contain active regions.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.icarus.2013.06.008DOIArticle
http://www.sciencedirect.com/science/article/pii/S0019103513002649PublisherArticle
ORCID:
AuthorORCID
Janssen, M. A.0000-0001-5476-731X
Ingersoll, A. P.0000-0002-2035-9198
Oyafuso, F. A.0000-0002-8862-8737
Additional Information:© 2013 Elsevier Inc. Available online 21 June 2013. This research was conducted at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). It is partly based upon work supported by NASA under Grant No. 10-CDAP10-0051 issued through the Cassini Data Analysis and Participating Scientist (CDAPS) Program. We acknowledge Sushil Atreya, Lena Adams, and Virgil Adumantroi for their invaluable contributions to the Juno Atmospheric Microwave Radiative Transfer (JAMRT) program, P. Steffes for discussions on the microwave absorption of ammonia in the Saturn atmosphere, Scott Bolton, Steve Levin, and the Juno project for their encouragement of this work, Alice Le Gall for her contributions to the calibration, Bryan Butler for discussion of the capabilities of ground-based interferometers, and Glenn Orton for useful discussions on sources of microwave absorption as well as related visual and infrared observations of giant planet atmospheres. We also gratefully acknowledge the Cassini RADAR team in general for their support, along with those who designed, developed and operate the Cassini/Huygens mission, which is a joint endeavor of NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) and is managed by JPL/Caltech under a contract with NASA.
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
NASA10-CDAP10-0051
Subject Keywords: Saturn, Atmosphere; Atmospheres, Structure; Atmospheres, Composition; Radiative transfer; Radio observations
Issue or Number:1
Record Number:CaltechAUTHORS:20131101-144840642
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20131101-144840642
Official Citation:M.A. Janssen, A.P. Ingersoll, M.D. Allison, S. Gulkis, A.L. Laraia, K.H. Baines, S.G. Edgington, Y.Z. Anderson, K. Kelleher, F.A. Oyafuso, Saturn’s thermal emission at 2.2-cm wavelength as imaged by the Cassini RADAR radiometer, Icarus, Volume 226, Issue 1, September–October 2013, Pages 522-535, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2013.06.008. (http://www.sciencedirect.com/science/article/pii/S0019103513002649)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42201
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:01 Nov 2013 22:01
Last Modified:03 Oct 2019 05:56

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