Analysis of the distribution of precipitable water vapor in the Chajnantor area

Cortés, Fernando; Reeves, R.; Bustos, R.

doi:10.1002/2015rs005929

Cited by 10 publications

(22 citation statements)

References 12 publications

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“…The PWV scale height derived from MERRA-2 (1,475 m at the median) agrees well with [24], which reported an exponential scale height of 1,379 m at the median using two identical radiometers, but is somewhat larger than the value given in [23] of 1,080 m.…”

Section: Atacama Desertsupporting

confidence: 82%

Assessments of Ali, Dome A, and Summit Camp for mm-wave Observations Using MERRA-2 Reanalysis

Kuo

2017

ApJ

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NASA's latest MERRA-2 reanalysis of the modern satellite measurements provides unprecedented uniformity and fidelity for the atmospheric data. In this paper, these data are used to evaluate five sites for millimeter-wave (mm-wave) observations. These include two established sites (South Pole and Chajnantor, Atacama), and three new sites (Ali, Tibet; Dome A, Antarctica; and Summit Camp, Greenland). Atmospheric properties including precipitable water vapor (PWV), sky brightness temperature fluctuations, ice and liquid water paths are derived and compared. Dome A emerges to be the best among those evaluated, with PWV and fluctuations smaller than the second-best site, South Pole, by more than a factor of 2. It is found that the higher site in Ali (6,100 m) is on par with Cerro Chajnantor (5,612 m) in terms of transmission and stability. The lower site in Ali (5,250 m) planned for first stage of observations at 90/150GHz provides conditions comparable to those on the Chajnantor Plateau. These analyses confirm Ali to be an excellent mm-wave site on the Northern Hemisphere that will complement well-established sites on the Southern Hemisphere. It is also found in this analysis that the observing conditions at Summit Camp are comparable to Cerro Chajnantor. Although it is more affected by the presence of liquid water clouds.

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Section: Atacama Desertsupporting

confidence: 82%

Assessments of Ali, Dome A, and Summit Camp for mm-wave Observations Using MERRA-2 Reanalysis

Kuo

2017

ApJ

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“…These are different in their technical characteristics and measurement techniques, location, altitude, and deployment time coverage. A summary of these instruments including specific location, altitude, and nomenclature is presented in Table 1; more details about these instruments are shown in Table 1 (Cortés et al 2016) and in citations therein. The following are noteworthy comments about these measuring devices: Water vapor radiometers (WVR): The APEX and Universidad de Concepción (UdeC) WVRs provide measurements of the atmospheric brightness temperature of the 183 GHz water line and over a number of defined bandpasses to spectrally characterize the emission.…”

Section: Instruments and Software Toolsmentioning

confidence: 99%

“…In Holdaway et al (2004), the relationship between global warming and PWV for the area was studied in a period of six years with inconclusive results. An atmospheric measurement campaign was performed on Cerro Toco, , a site located within the Chajnantor area, by Turner et al (2010) in 2009 and their data were used in Cortés et al (2016) to assess the vertical distribution of PWV in the area. The atmospheric transparency was studied in depth, spanning long periods of time by Radford et al (2000); Giovanelli et al (2001); Radford et al (2011Radford et al ( , 2016.…”

Section: Introductionmentioning

confidence: 99%

“…We demonstrate that the tippers do not need another instrument as a reference for absolute PWV calibration, as their PWV converted results are only a few percent off the data from the considered measurement standards. This is relevant because the tipping instruments can now be treated as independent integrated PWV measurement devices if they are coupled with an appropriate atmospheric model for the site under study, as discussed in Cortés et al (2016). Ultimately, we hope that existing and future observatories will find this information useful in the planning of their logistical activities at the site, therefore maximizing their scientific return.…”

Section: Introductionmentioning

confidence: 99%

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Twenty years of precipitable water vapor measurements in the Chajnantor area

Cortés

Cortes

Reeves

et al. 2020

A&A

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Context. Interest in the use of the Chajnantor area for millimeter and submillimeter astronomy is increasing because of its excellent atmospheric conditions. Knowing the general site annual variability in precipitable water vapor (PWV) can contribute to the planning of new observatories in the area. Aims. We seek to create a 20-year atmospheric database (1997−2017) for the Chajnantor area in northern Chile using a single common physical unit, PWV. We plan to extract weather relations between the Chajnantor Plateau and the summit of Cerro Chajnantor to evaluate potential sensitivity improvements for telescopes fielded in the higher site. We aim to validate the use of submillimeter tippers to be used at other sites and use the PWV database to detect a potential signature for local climate change over 20 years. Methods. We revised our method to convert from submillimeter tipper opacity to PWV. We now include the ground temperature as an input parameter to the conversion scheme and, therefore, achieve a higher conversion accuracy. Reults. We found a decrease in the measured PWV at the summit of Cerro Chajnantor with respect to the plateau of 28%. In addition, we found a PWV difference of 1.9% with only 27 m of altitude difference between two sites in the Chajnantor Plateau: the Atacama Pathfinder Experiment and the Cosmic Background Imager near the Atacama Large Millimeter Array center. This difference is possibly due to local topographic conditions that favor the discrepancy in PWV. The scale height for the plateau was extracted from the measurements of the plateau and the Cerro Chajnantor summit, giving a value of 1537 m. Considering the results obtained in this work from the long-term study, we do not see evidence of PWV trends in the 20-year period of the analysis that would suggest climate change in such a timescale.

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“…Astronomical observations in the millimeter and sub-millimeter wavelength range require that atmospheric effects affecting absorption at these wavelengths are kept to a minimum (Chamberlin & Grossman 2012, Radford & Peterson 2016, Cortés et al 2016. The main factor contributing to the atmospheric opacity is water vapor, which very efficiently absorbs light in the THz range , Kuhn et al 2002 due to a continuum absorption spectrum formed by collisionally broadened absorption lines of water vapor in this frequency range (Clough et al 1989, Pickett et al 1998, Turner et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

Molano¹,

Suárez²,

Restrepo

et al. 2017

PASP

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Abstract. We set out to evaluate the potential of the Colombian Andes for millimeter-wave astronomical observations. Previous studies for astronomical site testing in this region have suggested that nighttime humidity and cloud cover conditions make most sites unsuitable for professional visible-light observations. Millimeter observations can be done during the day, but require that the precipitable water vapor column above a site stays below ∼10 mm. Due to a lack of direct radiometric or radiosonde measurements, we present a method for correlating climate data from weather stations to sites with a low precipitable water vapor column. We use unsupervised learning techniques to low-dimensionally embed climate data (precipitation, rain days, relative humidity, and sunshine duration) in order to group together stations with similar long-term climate behavior. The data were taken over a period of 30 years by 2046 weather stations across the Colombian territory. We find 6 regions with unusually dry, clear-sky conditions, ranging in elevations from 2200 to arXiv:1705.06121v4 [astro-ph.IM] 15 Sep 2017Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing 2 3800 masl. We evaluate the suitability of each region using a quality index derived from a Bayesian probabilistic analysis of the station type and elevation distributions. Two of these regions show a high probability of having an exceptionally low precipitable water vapor column. We compared our results with global precipitable water vapor maps and find a plausible geographical correlation with regions with low water vapor columns (∼ 10 mm) at an accuracy of ∼ 20 km. Our methods can be applied to similar datasets taken in other countries as a first step toward astronomical site evaluation.

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Analysis of the distribution of precipitable water vapor in the Chajnantor area

Cited by 10 publications

References 12 publications

Assessments of Ali, Dome A, and Summit Camp for mm-wave Observations Using MERRA-2 Reanalysis

Assessments of Ali, Dome A, and Summit Camp for mm-wave Observations Using MERRA-2 Reanalysis

Twenty years of precipitable water vapor measurements in the Chajnantor area

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

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