(Apologies for cross-posting, but please forward to colleagues/redistribute) ** *PITHIA-NRF Trans-National Access (TNA) Open Call* *PITHIA-NRF* (Plasmasphere Ionosphere Thermosphere Integrated Research Environment and Access services: a Network of Research Facilities) launches its *sixth call* to provide effective and convenient access to the best European research facilities for observations of the upper atmosphere, including the *plasmasphere*, *ionosphere* and *thermosphere*. The access is organised through the Trans-National Access (TNA) programme, and provides an opportunity for researcher and other users to execute and carry out their own projects at one of the twelve PITHIA-NRF research facilities. You can get information on the */PITHIA-NRF Nodes/* here <https://pithia-nrf.eu/pithia-nrf-users/tna/nodes> and view details on PITHIA-NRF assets by accessing the */PITHIA-NRF Knowledge Book/* here <http://194.177.195.242/pithia_entities/ui>. *What?* The PITHIA-NRF nodes provide access to key experimental and data processing facilities for studies and modelling of physical processes acting in the Earth’s plasmasphere, ionosphere and thermosphere. The facilities connected to the nodes are geographically distributed over Europe, as well as internationally, and their expertise and dedication span over a wide range of topics within the research area. Users can request either *physical access* (one-week visit at the node with support at site) or *remote access* (one month access from distance with weekly support). Users with granted projects will learn how to work with the facilities during the full access cycle, from setting up a campaign, to collection, analysis and finally exploitation of data. *When?* The call is an *Open Call* - applications are handled as they arrive with typical evaluation times of 2 to 3 weeks. The call closes on *31 May 2024*. *Who?* Access can be requested by scientific users from academia, Small and Medium Enterprises, large companies and public organizations. *How?* The application is made by using the online form <https://pithia-nrf.eu/forms/tna-application-form-6>. Follow the instructions at the PITHIA-NRF webpage for the Sixth TNA Call <https://pithia-nrf.eu/pithia-nrf-users/tna/tna-calls/sixth-tna-call>. We strongly 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. *Contact:* TNA Support Centre: tna(a)pithia-nrf.eu -- Dr. Anders Tjulin Staff Scientist, EISCAT Bengt Hultqvists väg 1 981 92 Kiruna, Sweden Phone: +46 (0)706 608972 e-mail:anders.tjulin@eiscat.se