## 3 Results of Studying Atmospheric Propagation of subTHz Radiation  
Among the surveyed sites, which are noticeably inferior in terms of absorption to the best-known locations for subTHz instruments (Atacama, Tibet, or Pamir) practically everywhere, there are good prospects for working in the first (a wavelength of 3 mm) and second (2 mm) subTHz atmosphere transparency windows. Seasonal variations make it possible to effectively use the instruments installed at these sites and the waves of the third transparency window (\(\lambda\sim\) 1.3 mm) in winter. Several sites have good prospects even in the summer season; for example, Mount Muus-Khaya in Yakutia is about 2000 m above sea level and located near the Nothern \"cold pole\" of the Earth. Virtually nowhere among the studied places do the conditions for the effective use of instruments in the studied areas with submillimeter waves (an atmospheric transparency window of 0.8 mm) last long enough to be of any practical use. Therefore, some conclusions regarding the practical use of the sites under study are negative. In particular, in the vast territory of northeastern Eurasia chosen for experiments,in contrast to the western hemisphere (Andes, Antarctica, Greenland, etc.) or the more southern places of the eastern hemisphere (Tibet, Pamir, etc. ), no place has yet been confirmed to present a good opportunity for sub-mm tools. Even the seasonal options for working in the 1.3 mm transparency window offered by these sites are minimal. When comparing the main results of the measurements supplemented by the latest data about the studied sites with those previously studied [28], we can see that the most promising site, Muus-Khaya Mountain, is not an excellent choice due to the place being remote and having no infrastructure to be found. Our on-land journey to the site included a 4-day horse ride on the route's final leg, and the return journey was by air onboard a helicopter. The site has no infrastructure or power supply; the only \"facility\" found there was an old weather station that closed in the 1970s. An attempt to find a northern option for placing an instrument analogous to the SPO installed near the south cold pole of the Earth in Antarctica was unsuccessful. There are no places above sea level, and the altitudes of about 1500 m in Svalbard are under the influence of the Gulf Stream, which carries a noticeable quantity of moisture even in winter (we carried out a year-round cycle of observations there). Thus, there is no dry air comparable to that of Antarctica. The conclusions we made after many years of observations on the Suffa Plateau (the site proposed for installation of a 70 m antenna) are not entirely encouraging, not even for the 0.8 mm transparency window. This extreme window of atmospheric transparency, the only one available for this site, shows up for only about a dozen days a year when conditions are favorable for signal propagation. Such fact makes both radio astronomy observations and space communication possible only in the near-zenith directions. As the path gets more inclined to the horizon, atmospheric absorption increases sharply. As for radar applications, the beam has to cross the atmosphere twice, so the problem of locating low-lying objects becomes insoluble. There are quite promising sites in Siberia (Badary and Mondy) [35], confirmed by satellite data [3]. However, they are rather far from the best record-breaking radio astronomy sites like ALMA and, at the very least, require further research to find the most prosperous locations, which will probably involve some mountain climbing. The Caucas seems to be the most attractive in terms of infrastructure, engineering, and staffing, as well as due to the Earth's surface coverage by subTHz instruments [39]. The instrument coverage of the Earth's surface plays an essential role in all three main types of subTHz applications: astronomy, communication, and radar.