J/A+A/664/A153 APEX atmospheric profiles (Pardo+, 2022)
Extremely high spectral resolution measurements of the 450 um atmospheric
window at Chajnantor with APEX.
Pardo J.R., De Breuck C., Muders D., Gonzalez J., Montenegro-Montes F.M.,
Perez-Beaupuits J.P., Cernicharo J., Prigent C., Serabyn E., Mroczkowski T.,
Phillips N.
<Astron. Astrophys. 664, A153 (2022)>
=2022A&A...664A.153P 2022A&A...664A.153P (SIMBAD/NED BibCode)
ADC_Keywords: Earth ; Spectroscopy
Keywords: atmospheric effects - techniques: spectroscopic - molecular data -
line: profiles - opacity
Abstract:
Ground-based telescopes observing at millimeter (mm) and submillimeter
(submm) wavelengths have to deal with a line-rich and highly variable
atmospheric spectrum, both in space and time. Models of this spectrum
play an important role in planning observations that are appropriate
for the weather conditions and also calibrating those observations.
Through magnetic dipolar (M1) rotational transitions and electric
dipolar (E1) transitions O2 and H2O, respectively, dominate the
atmospheric opacity in this part of the electromagnetic spectrum.
Although O2 lines, and more generally the so-called dry opacity, are
relatively constant, the absorption related to H2O can change by
several orders of magnitude leading from a totally opaque atmosphere
near sea level with high H2O columns to frequency windows with good
transmission from high and dry mountain sites. Other minor atmospheric
gases, such as O3 and N2O among others, are present in the
atmospheric spectrum which also includes nonresonant collision-induced
absorption due to several mechanisms. The aim of our research is to
improve the characterization of the mm/submm atmospheric spectrum
using very stable heterodyne receivers with excellent sideband
separation and extremely high (kHz) spectral resolutions at the 5000m
altitude Chajnantor site in northern Chile. This last aspect (spectral
resolution) is the main improvement (by more than three orders of
magnitude) in the presented data with respect to our previous work
conducted ∼20 years ago from Mauna Kea in Hawai'i. These new
measurements have enabled us to identify slight modifications needed
in the Atmospheric Transmission at Microwaves (ATM) model to better
take into account minor constituent vertical profiles, include a few
missing lines, and adjust some high-energy O3 line frequencies.
After these updates, the ATM model is highly consistent with all data
sets presented in this work (within ∼2 % at 1GHz resolution).
Description:
We obtained the first kilohertz-resolution atmospheric spectra in the
450um atmospheric window from a ground-based submm observatory. The
conditions during the observations were relatively dry and stable. The
performance of the receiver in terms of stability and sensitivity has
produced data suitable for comparison with the atmospheric model
currently implemented at ALMA, APEX, and other observatories, allowing
us to check its overall validity, and also verify how well the weakest
features of the atmospheric spectrum are reproduced.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
atm.dat 80 82484 Smoothed atmospheric spectra and ATM model
simulations for three different air masses
list.dat 34 167 List of atmospheric profile files
profiles/* . 167 *Individual atmospheric profile files
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Note on profiles/* : File names: ATMOSPHEREXXXYYY_GHz.DAT.
Atmospheric profiles used by the ATM code to generate the model simulations
(columns 5,6,7 of file atm.dat) between frequencies XXX and YYY GHz). As the
atmospheric conditions were changing slightly during the observations, it was
necessary to adapt the input to the ATM model in this way (see paper for
more information on this).
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Byte-by-byte Description of file: atm.dat
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Bytes Format Units Label Explanations
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3- 13 F11.4 MHz Freq Frequency
16- 22 F7.3 K TEBBrAM10 Equivalent Blackbody Temperature (TEBB) after
recalibration for air mass AM=1.00 (1)
25- 31 F7.3 K TEBBrAM15 Equivalent Blackbody Temperature (TEBB) after
recalibration for air mass AM=1.50 (1)
34- 40 F7.3 K TEBBrAM20 Equivalent Blackbody Temperature (TEBB) after
recalibration for air mass AM=2.00 (1)
43- 49 F7.3 K TEBBMAM10 Equivalent Blackbody Temperature (TEBB) from
Atmospheric Transmission at Microwaves (ATM)
model simulations for air mass AM=1.00
52- 58 F7.3 K TEBBMAM15 Equivalent Blackbody Temperature (TEBB) from
Atmospheric Transmission at Microwaves (ATM)
model simulations for air mass AM=1.50
61- 67 F7.3 K TEBBMAM20 Equivalent Blackbody Temperature (TEBB) from
Atmospheric Transmission at Microwaves (ATM)
model simulations for air mass AM=2.00
71- 80 F10.8 % Diff Quadratic residuals between data and model
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Note (1): smoothed atmospheric spectra (after recalibration discussed in the
paper) for three different air masses (AM) corresponding to
Dec. 6th 2020 APEX observations.
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 3 I3 GHz bFreq Lower value of frequency interval
4 A1 --- --- [-]
5- 7 I3 GHz BFreq Upper value of frequency interval
9- 34 A26 --- FileName Name of the file in subdirectory profiles
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Byte-by-byte Description of file (!): profiles/*
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Bytes Format Units Label Explanations
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1- 7 F7.3 km h0 Altitude at bottom of atmospheric layer
10- 15 F6.3 km h1 Altitude at top of atmospheric layer
17- 26 E10.5 hPa Pavg Average pressure in atmospheric layer
28- 37 E10.5 K Tavg Average temperature in atmospheric layer
39- 47 E9.4 g/m3 rho Average density
49- 57 E9.4 --- O2-Mix.r O2 mixing ratio
59- 67 E9.4 % r.hum Relative humidity
69- 78 E10.5 K DewPt Dew point temperature
80- 89 E10.5 mbar pH2O Partial pressure of H2O pressure
91-100 E10.5 g/m3 H2O H2O mass density
102-111 E10.5 g/m2 H2OT H2O accumulated column density
113-122 E10.5 cm-3 O3 Ozone number density
124-133 E10.5 cm-3 NNO NNO number density
135-144 E10.5 cm-3 HCL HCL number density
146-155 E10.5 cm-3 CO CO number density
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Acknowledgements:
Juan R. Pardo, jr.pardo(at)csic.es
(End) Patricia Vannier [CDS] 23-Jun-2022