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Juan R. Pardo-Carrion
Abstract N. 21
- J. R. Pardo, E. Serabyn, ,
and
J. Cernicharo.
"Submillimeter atmospheric transmission
measurements on Mauna Kea during extremely dry El Niño conditions:
Implications for broadband opacity contributions"
J. Quant. Spectr. and Radiat. Transfer, Accepted, (2000).
We present broadband atmospheric transmission spectra
obtained on Mauna Kea, Hawaii (4100 m. above sea level)
on UT April 1st 1998 and July 1st 1999 under
very similar pressure and temperature conditions. The
1998 measurements occurred under conditions of
extremely low atmospheric water vapor, with a ground-level
relative humidity of ~2 %. As a result of its dryness
the Mauna Kea site allows access to a partially
transparent atmosphere up to
frequencies exceeding 1000 GHz, where the relative
importance of atmospheric continuum-like absorption is much
larger than at millimeter
wavelengths, and hence easier to measure. As shown in
this paper, these conditions have allowed us to measure
and separate the submillimeter absorption spectrum into three
terms: resonant lines, non-resonant absorption of the dry
atmosphere due to collision-induced mechanisms involving
electric multipoles, and continuum-like water vapor opacity.
The spectra presented here
were obtained with a Fourier Transform Spectrometer (FTS)
at the Caltech Submillimeter Observatory and cover a continuous
frequency range from 350 GHz to 1100 GHz, with a finest
spectral resolution of 200 MHz. The 1998 conditions were
so exceptionally dry that
an atmospheric window centered
at 1035 GHz showed
up to 35 % zenith transmission. The calibration
of our data is especially careful and includes
corrections for differences between the ground atmospheric
temperature and
the calibrator temperature, as well as for the tropospheric
temperature lapse rate, and the water vapor scale height. This
procedure is able to yield transmission spectra calibrated
to within 1-2 %. A multilayer atmospheric radiative
transfer model has been used for data analysis.
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