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Post-equinox observations of Uranus: Berg’s evolution, vertical structure, and track towards the equator

de Pater, Imke and Sromovsky, L. A. and Hammel, Heidi B. and Fry, P. M. and LeBeau, R. P. and Rages, Kathy and Showalter, Mark and Matthews, Keith (2011) Post-equinox observations of Uranus: Berg’s evolution, vertical structure, and track towards the equator. Icarus, 215 (1). pp. 332-345. ISSN 0019-1035. http://resolver.caltech.edu/CaltechAUTHORS:20111011-141239766

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Abstract

We present observations of Uranus taken with the near-infrared camera NIRC2 on the 10-m W.M. Keck II telescope, the Wide Field Planetary Camera 2 (WFPC2) and the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) from July 2007 through November 2009. In this paper we focus on a bright southern feature, referred to as the “Berg.” In Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Hammel, H.B., Ahue, A.W., de Pater, I., Rages, K.A., Showalter, M.R., van Dam, M. [2009]. Icarus 203, 265–286), we reported that this feature, which oscillated between latitudes of −32° and −36° for several decades, suddenly started on a northward track in 2005. In this paper we show the complete record of observations of this feature’s track towards the equator, including its demise. After an initially slow linear drift, the feature’s drift rate accelerated at latitudes ∣θ∣ < 25°. By late 2009 the feature, very faint by then, was spotted at a latitude of −5° before disappearing from view. During its northward track, the feature’s morphology changed dramatically, and several small bright unresolved features were occasionally visible poleward of the main “streak.” These small features were sometimes visible at a wavelength of 2.2 μm, indicative that the clouds reached altitudes of ∼0.6 bar. The main part of the Berg, which is generally a long sometimes multipart streak, is estimated to be much deeper in the atmosphere, near 3.5 bars in 2004, but rising to 1.8–2.5 bars in 2007 after it began its northward drift. Through comparisons with Neptune’s Great Dark Spot and simulations of the latter, we discuss why the Berg may be tied to a vortex, an anticyclone deeper in the atmosphere that is visible only through orographic companion clouds.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.icarus.2011.06.022DOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/S0019103511002399PublisherUNSPECIFIED
Additional Information:© 2011 Elsevier Inc. Received 29 March 2011. Revised 14 June 2011. Accepted 15 June 2011. Available online 28 June 2011. We thank Marcos van Dam for trading an hour of Keck time in September 2007. The near-infrared data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The WFPC2 and the WFC3 845 nm wavelength data were obtained with the NASA/ESA Hubble Space Telescope as part of HST programs GO11156 (SNAP, WFPC2; PI: K. Rages) and GO11573 (WFC3; PI: L. Sromovsky), with support provided by NASA through grants from the Space Telescope Science Institute to the PIs by the Association of Universities for Research in Astronomy, Inc., under NASA Contract NAS 5-26555. This work was further supported in part by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement AST 98-76783. In addition, IdP. acknowledges support from NASA Grant NNX07AK70G; HBH from NASA Grants NNX06AD12G and NNX07AO43G; LAS from NASA Grant NNX08A051G; RPL from NASA Grant NNX11AC01G. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.
Funders:
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
NASA Space Telescope Science InstituteUNSPECIFIED
NASANAS 5-26555
NSF Science and Technology Center for Adaptive OpticsAST-98-76783
NASANNX07AK70G
NASANNX06AD12G
NASANNX07AO43G
NASANNX08A051G
NASANNX11AC01G
Subject Keywords:Uranus, Atmosphere; Infrared observations; Adaptive optics
Record Number:CaltechAUTHORS:20111011-141239766
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20111011-141239766
Official Citation:Imke de Pater, L.A. Sromovsky, Heidi B. Hammel, P.M. Fry, R.P. LeBeau, Kathy Rages, Mark Showalter, Keith Matthews, Post-equinox observations of Uranus: Berg’s evolution, vertical structure, and track towards the equator, Icarus, Volume 215, Issue 1, September 2011, Pages 332-345, ISSN 0019-1035, 10.1016/j.icarus.2011.06.022. (http://www.sciencedirect.com/science/article/pii/S0019103511002399)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:27167
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:11 Oct 2011 21:58
Last Modified:23 Aug 2016 10:06

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