(Apologies for cross-posting, but please forward to colleagues/redistribute) ** *PITHIA-NRF Trans-National Access (TNA) Open Call* PITHIA-NRF <https://pithia-nrf.eu>(Plasmasphere Ionosphere Thermosphere Integrated Research Environment and Access services: a Network of Research Facilities) invites applications for access to a variety of the *best **European**research facilities* (nodes) for studies and modelling of physical processes acting in the Earth’s upper atmosphere, with support from experts within the field. There are twelve nodes within PITHIA-NRF all dedicated to investigating the plasmasphere, ionosphere and/or thermosphere. The access can be *physical access* (one-week visit with travel and accommodation included) or *remote access* (one-month remote access with weekly support). The available services or resources are limited, and a competitive process is required following a defined procedure and criteria for the selection of users. *Project opportunities:* Project opportunities and description of the nodes are available at the information page <https://pithia-nrf.eu/pithia-nrf-users/tna/tna-calls/fourth-tna-call>. We encourage any potential applicants to discuss with the relevant node about the project before submitting their proposals. The TNA Support Centre <mailto:tna@pithia-nrf.eu> at PITHIA-NRF can help establishing contact points with the nodes. *When?* This spring 2023 call is running from *15 January 2023* until *15 June**2023*. It is an *O**pen Call* and applications will be handled as they arrive to streamline the timelines of the projects. *Who?* Access is provided for science projects to users from Academia, Small and Medium Enterprises, Industry, and Public Organisations. *How?* The application should be filled in and submitted using the online form <https://pithia-nrf.eu/forms/tna-application-form-4>. After submission, eligibility and feasibility checks will be performed followed by the scientific evaluation. Follow the instructions at https://pithia-nrf.eu/tna/tna-calls/second-tna-call. *Contact:* TNA Support Centre: tna(a)pithia-nrf.eu /EU Horizon 2020 Research and Innovation Programme Grant Agreement No 101007599/ -- Dr. Ingemar Häggström Leader of WP7: PITHIA-NRF Trans-national access