Computer Science – Sound
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....3985c&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #3985
Computer Science
Sound
Scientific paper
We have acquired new images of Titan using the adaptive optics system PUEO located at the CFHT in Hawaii. Combined with the infrared camera KIR, we have covered the near-infrared range on Titan using several new narrow-band filters covering the methane bands (pertaining to the atmosphere) and the so-called methane "windows" (containing both atmospheric and surface contribution) between 0.8 and 2.5 micron. Thus, we have observed Titan in 2001, on 7-8 March and 5 December, resolving Titan's disk during GEE and GEE+ 1 day, and during the nights of the 13th, 14th, 20th and 21st November 2002 (covering both the GEE and the GWE with seeing between 0.4 and 0.6"). These images allow us to achieve a very good resolution on Titan's disk. Our data were reduced and deconvolved, according the procedures described in Coustenis et al. (2001). Our March 2001 atmospheric images are all at wavelengths in the J band and show the north-south asymmetry observed usually with the South brighter than the North. The December 2001 atmospheric images, however, covering longer wavelengths, show some interesting phenomena: besides the well-known Titan "smile" observed at wavelengths between 1 and 1.3 micron, we find the situation to be currently changing, with a clear reversion of the asymmetry found in our FeII (1.64 micron) and Kcont (2.26 micron) filters, sounding higher atmospheric levels (in the stratosphere). We believe this is a seasonal phenomenon, following the previously reported "loss of the smile" (Lorenz, 2001). This inversion is progressing and we are founding its signature in our new images of 2002 at wavelengths of : 2.16 (BrGamma), 1.64 (FeII), 2.06 (J2). Another atmospheric phenomenon, the limb brightening reported in our 1998 images -- interpreted as a first detection of possible diurnal effects in Titan's atmosphere : something like a morning fog, observed after condensation processes have enhanced in condensates the atmospheric levels between 70 and 100 km (Coustenis et al., 2001) --, could not be firmly confirmed in our new data (although there is some indication for it) because the 2001 images were acquired in mediocre conditions (seeing of 0.5-1 arcsec). A third new feature is observed at wavelengths probing the atmosphere around 2 micron: a bright feature spanning about 2 by 4 pixels in latitude and longitude respectively (0.07x0.14 arcsec or roughly 9x18% of the projected disk) is seen attached to the Southern Pole of Titan and appears stable. This feature could be indicative of an atmospheric (cloud or more likely a vortex) phenomenon or a surface feature (polar cap?). After subtracting the atmosphere from the images sounding the CH4 windows, we recover information on the surface of Titan. We find the equatorial spot to be bright again in all the filters investigated from 1 to 2 micron and at the position expected with respect to the orbital phase. A preliminary study of the 2002 images already show pieces of evidence that the asymmetry inversion is still at work, furthermore at deeper altitudes than detected in 2001. Since we have observed at consequent nights around the GEE and the GWE, we expect to be able to trace the location (and the displacement) of the features observed and to check the bright zones found in the trailing hemisphere images of Titan (Combes et al., 1997). References: Combes et al (1997), Icarus 129, 482; Coustenis et al. (2001) Icarus 154, 501; Lorenz et al (2001), Geoph. Res. Letters 28, 4453.
Bratsolis Emmanuel
Combes Michel
Coustenis Athena
Fusco Th.
Gendron Eric
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