Possibility of Terahertz Observations at the ALMA site

TL;DR

This study assesses the feasibility of terahertz observations at the ALMA site by analyzing opacity data, revealing seasonal and annual variations that impact observational rates, especially under very low opacity conditions.

Contribution

It provides the first detailed analysis of THz observational feasibility at ALMA, linking atmospheric conditions with seasonal and climate phenomena.

Findings

12.4% annual observational rate under THz opacity < 3.0

Higher rates in winter and La Niña years

Only 1.9% rate under THz opacity < 2.0

Abstract

Observational rates under terahertz (THz) opacities less than 3.0 and 2.0 at the Atacama Large Millimeter/submillimeter Array (ALMA) site have been calculated using the 225 GHz tipping radiometer monitoring data and the opacity correlation between 225 GHz and THz opacities. The observational rate with THz opacity condition less than 3.0 is 12.4% in a year, and in winter (November - April) it is about twice higher than in summer (May - October). This observational rate shows a large sinusoidal annual variation, and it seems to have relation with the El Ni\~no and La Ni\~na phenomena; the La Ni\~na years tend to have high observational rates, but the El Ni\~no years show low rates. On the other hand, the observational rate with the THz opacity condition less than 2.0 is only 1.9%, and no obvious annual and seasonal variations are observed. This indicates that THz observations under low opacity condition of less than 2.0 at the ALMA site are very difficult to be performed.