Computer Science – Sound
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.4609c&link_type=abstract
American Astronomical Society, DPS meeting #41, #46.09
Computer Science
Sound
Scientific paper
The sub-millimetre wave spectra of the outer planets are rich in absorption line features that can be measured with extremely high spectral resolution with sub-millimetre wave heterodyne technology to determine temperature, winds and composition in the stratosphere. To measure stratospheric temperature requires the observation of the absorption of a well-mixed gas such as methane and while there is a methane absorption feature near 1.2 THz that is measurable with current solid-state receiver technology, this feature is relatively weak. Methane absorption lines become stronger at increasing frequency and the feature at 2.2 THz is particularly attractive as there is a strong water line lying 2GHz from the line centre that could be measured simultaneously with the methane absorption line.
Sub-millimetre wave spectroscopy at this frequency is advancing rapidly and we believe that observation of this feature will be technically feasible within the timeframe of EJSM. The advantages over lower frequency measurements include: 1) the methane absorption line is stronger, allowing sounding to higher altitudes; 2) the field-of-view is smaller for the same antenna size allowing easier limb-sounding; 3) the Doppler shifting of lines due to winds is larger; and 4) the instrument payload is more compact.
A sub-millimetre wave device would provide valuable information Jupiter's stratosphere, but the radiance away from the line centres is governed by both the temperature in the upper troposphere and also the ammonia abundance. We propose to combine the sub-millimetre wavelength device with an infrared spectrometer, which would be able to measure the upper tropospheric temperatures in the H2-H2, H2-He collision induced continuum (200 - 650 cm-1), not affected by ammonia, simply extending the vertical coverage of temperature of the combined instrument right down to the cloud tops. The combined device would also return the tropospheric para-H2 fraction and ammonia abundance and also stratospheric hydrocarbon abundances.
Alderman Byron
Bowles Neil E.
Calcutt Simon
Ellison Brian N.
Irwin Patrick G. J.
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