The Engineer and the Law

Radford, J. D.

doi:10.1007/978-1-349-17506-2_6

Cited by 4 publications

(5 citation statements)

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“…We note here that there are many studies that compare the opacity conditions at the summit of Maunakea, which is also a well-established submm site, with those at the ALMA and South Pole sites; opacity quartiles of Maunakea are ~50% higher than those of the ALMA site (Matsushita et al 1999;Radford & Chamberlin 2000;Radford 2011;Radford & Peterson 2016).…”

Section: Cumulative Distribution and Histogrammentioning

confidence: 75%

“…We then compared the opacity quartiles using our 3.5 year period statistics with those at the ALMA and the South Pole sites, which are well-established sites for submm observations. The 225 GHz opacity data for the ALMA site have been obtained from Radford & Chamberlin (2000) and Radford (2011), whose measurements have been made between 1995 April and 2006 April (∼11 years), and that for the South Pole site from Chamberlin & Bally (1994, 1995 measured between 1992 January and December (one year). Since both the ALMA and the South Pole sites are located in the southern hemisphere, we define winter as between the beginning of May through the end of October, and summer as November through April.…”

Section: Cumulative Distribution and Histogrammentioning

confidence: 99%

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3.5 Year Monitoring of 225 GHz Opacity at the Summit of Greenland

Matsushita¹,

Asada²,

Martin-Cocher³

et al. 2016

PASP

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We present the 3.5-yr monitoring results of 225 GHz opacity at the summit of the Greenland ice sheet (Greenland Summit Camp) at an altitude of 3200 m using a tipping radiometer. We chose this site as our submillimeter telescope (Greenland Telescope; GLT) site, because conditions are expected to have low submillimeter opacity and because its location offers favorable baselines to existing submillimeter telescopes for global-scale Very Long Baseline Interferometry (VLBI). The site shows a clear seasonal variation with the average opacity lower by a factor of two during winter. The 25%, 50%, and 75% quartiles of the 225 GHz opacity during the winter months of November through April are 0.046, 0.060, and 0.080, respectively. For the winter quartiles of 25% and 50%, the Greenland site is about 10%− 30% worse than the Atacama Large Millimeter/submillimeter Array (ALMA) or the South Pole sites. Estimated atmospheric transmission spectra in winter season are similar to the ALMA site at lower frequencies (< 450 GHz), which are transparent enough to perform astronomical observations almost all of the winter time with opacities < 0.5, but 10%−25% higher opacities at higher frequencies (> 450 GHz) than those at the ALMA site. This is due to the lower altitude of the Greenland site and the resulting higher line wing opacity from pressure-broadened saturated water lines in addition to higher dry air continuum absorption at higher frequencies. Nevertheless, half of the winter time at the Greenland Summit Camp can be used for astronomical observations at frequencies between 450 GHz and 1000 GHz with opacities < 1.2, and 10% of the time show > 10% transmittance in the THz (1035 GHz, 1350 GHz, and 1500 GHz) windows. Summer season is good for observations at frequencies lower than 380 GHz. One major advantage of the Greenland Summit Camp site in winter is that there is no diurnal variation due to the polar night condition, and therefore the durations of low-opacity conditions are significantly longer than at the ALMA site. Opacities lower than 0.05 or 0.04 can continue for more than 100 hours. Such long stable opacity conditions do not occur as often even at the South Pole; it happens only for the opacity lower than 0.05. Since the opacity variation is directly related to the sky temperature (background) variation, the Greenland Summit Camp is suitable for astronomical observations that need unusually stable sky background.

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Section: Cumulative Distribution and Histogrammentioning

confidence: 75%

Section: Cumulative Distribution and Histogrammentioning

confidence: 99%

3.5 Year Monitoring of 225 GHz Opacity at the Summit of Greenland

Matsushita¹,

Asada²,

Martin-Cocher³

et al. 2016

PASP

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“…This paper describes the instrument design and construction, the deployments, and the measurements; discusses the site characteristics; and compares the results with data from other instruments and with model predictions. Previous accounts of these measurements presented preliminary findings (Radford 2002(Radford , 2011Peterson et al 2003;Radford et al 2008).…”

Section: Introductionmentioning

confidence: 87%

Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

Radford

Peterson

2016

PASP

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For a systematic assessment of submillimeter observing conditions at different sites, we constructed tipping radiometers to measure the broad band atmospheric transparency in the window around 350 µm wavelength. The tippers were deployed on Maunakea, Hawaii, at the South Pole, and in the vicinity of Cerro Chajnantor in northern Chile. Identical instruments permit direct comparison of these sites. Observing conditions at the South Pole and in the Chajnantor area are better than on Maunakea. Simultaneous measurements with two tippers demonstrate conditions at the summit of Cerro Chajnantor are significantly better than on the Chajnantor plateau.

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“…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. In addition, PWV ratios between the plateau and Cerro Chajnantor were presented in Bustos et al (2014) for a time span of five days and expanded over longer periods in Cortés et al (2016), including estimates for atmospheric scale heights.…”

Section: Introductionmentioning

confidence: 99%

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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The Engineer and the Law

Cited by 4 publications

References 0 publications

3.5 Year Monitoring of 225 GHz Opacity at the Summit of Greenland

3.5 Year Monitoring of 225 GHz Opacity at the Summit of Greenland

Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

Twenty years of precipitable water vapor measurements in the Chajnantor area

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