The Thule High Arctic Atmospheric Observatory (THAAO, 76.5°N, 68.8°W; http://www.thuleatmos-it.it/) is an international infrastructure located on South Mountain, near Thule Air Base, managed by the National Science Foundation. The Observatory is equipped with many instruments devoted to studying the long-term evolution of atmospheric and surface key parameters affecting Arctic climate. The Italian instrumentation installed at the THAAO is managed by the National Institute for Geophysics and Volcanology (INGV) and the National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), with the collaboration of the University of Rome “Sapienza” (URome) and the University of Florence. The Observatory hosts also activities run by US institutes such as the NCAR and the AFRL. The Italian research activities at Thule started in 1990 with a collaboration between the URome and the Danish Meteorological Institute (DMI), which ran the THAAO until 2017. In the period 2001-2013, INGV, ENEA and URome collaborated with the Stony Brook University, operating a millimeter-wave spectrometer (GBMS) at Thule. This research work, aimed also at contributing to the NASA EOS Aura satellite validation, was initially funded by NASA with PI Prof. Robert de Zafra. Science activities at the THAAO focus on monitoring atmospheric and surface physical and chemical parameters by means of in situ sampling and remote sensing measurements. Specifically, the most recent funded research projects aimed at quantifying the impact of clouds, aerosol, and precipitation to the surface radiation budget. More than 15 instruments are operative at the Observatory. They are devoted to measuring the surface radiative budget in the Solar and Infrared wavelengths, the surface albedo, the chemical composition of the atmosphere, precipitation intensity and characteristics, vertical profiles of temperature, pressure, and humidity, as well as to detecting cloud and aerosol occurrence, layering, and physical, chemical and optical properties. Two instruments (the Italian LiDAR and the NCAR FTIR) are among the ground-based instruments enrolled in the International Network for the Detection of Atmospheric Composition Change (NDACC, https://www.ndaccdemo.org/). In 2021, the Italian team installed a cryo-seismic network composed of 4 seismic stations and 1 tide gauge along the Wolstenholme fjord, located few miles North of Pituffik Space Base. The long-term dataset acquired with this network is transmitted to the THAAO for storage and is used to study glacier dynamics and to evaluate the land ice mass loss of the 3 glaciers marine-terminating in the fjord. In 2026, INGV will start monitoring CO2 concentration and its isotopic composition in order to identify greenhouse gas sources as part of research projects funded by the Italian Arctic Program and by the INGV. Some of the datasets collected at the THAAO are publicly available and can be accessed via the THAAO website where the datasets DOI are also indicated.

In contribution to the Network for the Detection of Atmospheric Composition Change (NDAAC https://www.ndaccdemo.org/) and in order to study the long-term evolution of Arctic atmospheric and surface climate parameters, collaborators from INGV, ENEA, and University of Rome will operate several ground-based instruments and launch radiosondes from the Thule High Arctic Atmospheric Observatory (THAAO) at Pituffik Space Base (Pituffik SB) during the decade 2025-2034. During the same period, the indicated team will also operate the cryo-seismic network installed in 2021 along the Wolstenholme Fjord in order to monitor the glacier dynamics and mass loss. In 2026, new instrumentation dedicated to long-term monitoring of CO2 concentration and its isotopic composition will also be installed at the THAAO to identify potential sources of greenhouse gases. Funding will be provided by the Italian Arctic Program, as well as by INGV and ENEA. In 2025 - 2034, researchers will make approximately two trips of 10-12 days each per year. During each trip, researchers will travel to Building 1971 on South Mountain via truck where the THAAO is located and will use a tetra radio for communication with HILLTOP in case of an emergency. This work is on a continuing basis with instruments running and may include periodic participant travel to Pituffik SB. In March/April 2025, three researchers will travel to Pituffik SB via Embassy flights to run calibrations and maintenance on the equipment at the THAAO and perform maintenance on the GIS observing network along the Wolstenholme Fjord as well as support instrumentation at THAAO. In October 2025, two researchers will return to Pituffik SB to support instrumentation at THAAO.

Battelle ARO will provide clearance support for Pituffik SB access, lodging at Building 345, communications equipment, snowmachine access, and NSF vehicle and fuel. Battelle ARO manages user day cost in THAAO by allocation of space, telecommunications, and utilities, and coordinates access with the USSF and Inussuk on-base contractors. NSF will recoup costs associated with this support directly from INGV. All other costs associated with the project will be paid by the PI through the grant.