Mapping polar atmospheric features on Titan with VIMS: From the dissipation of the northern cloud to the onset of a southern polar vortex

Research areas:
Year:
2018
Authors:
  • Stéphane Le Mouélic
  • S. Rodriguez
  • R. Robidel
  • B. Rousseau
  • B. Seignovert
  • Christophe Sotin
  • J. W. Barnes
  • R. H. Brown
  • K. H. Baines
  • B. J. Buratti
  • R. N. Clark
  • P. D. Nicholson
  • R. Rannou
  • Thomas Cornet
Journal:
ICARUS
Volume:
311
Pages:
371-383
Month:
SEP 1
ISSN:
0019-1035
Abstract:
We have analyzed the complete archive of the Visual and Infrared Mapping
Spectrometer (VIMS) data in order to monitor and analyze the evolution
of the clouds and haze coverage at both poles of Titan during the entire
Cassini mission. Our objective is to give a cartographic synopsis from a
VIMS perspective, to provide a global view of the seasonal evolution of
Titan's atmosphere over the poles. We leave the detailed comparison with
the Imaging Science Subsystem (ISS) and the Composite Infrared
Spectrometer (CIRS) data sets to further studies. We have computed
global hyperspectral mosaics for each of the 127 targeted flybys of
Titan to produce synthetic color maps emphasizing the main atmospheric
features. The north pole appears fully covered by a huge cloud as soon
as the first observations in 2004 and up to the equinox in 2009 (Le
Mouelic et al., 2012). The northern skies then became progressively
clearer, after the circulation turnover in 2009, revealing the
underlying lakes and seas to the optical instruments up to 2017. The
reverse situation is observed over the south pole, which was mostly
clear of such a high obscuring cloud during the first years of the
mission, but started to develop a polar cloud in 2012. This feature grew
up month after month until the end of the mission in 2017, with a
poleward latitudinal extent of 75 degrees S in 2013 up to 58 degrees S
in April 2017. Thanks to the spectral capabilities of VIMS, we have
detected HCN spectral signatures over the north pole in almost all
flybys between 2004 and 2008. These HCN signatures started then to show
up over the south pole in almost all flybys between 2012 and 2017, so
perfectly matching the timing and spatial extent of the northern and
southern polar atmospheric features. (C) 2018 Elsevier Inc. All rights
reserved.