************************************************************************ IERS Message No. 530 March 05, 2025 ************************************************************************ CCTF-IERS workshop on negative leap second - March 13, 2025 Aim: Understanding the probability of a negative leap second, to support the decision on Continuous UTC at the next CGPM 2026. Dear Colleagues, The General Conference on Weights and Measures (CGPM) decided in 2022 to extend the tolerance between UTC and UT1 to avoid the frequent discontinuities given by the leap seconds. The resolution is available here: https://www.bipm.org/en/cgpm-2022/resolution-4 The CGPM has to decide which will be the new tolerance and when it should be implemented "in, or before, 2035". One of the main issues to anticipate the date with respect to 2035 is the risk of a negative leap second which has never been applied and raise a considerable risk of malfunctioning in several applications. This decision will be discussed at the Consultative Committee for Time and Frequency (CCTF) in September 2025 in view of final adoption by the member states during the CGPM in October 2026. Studying the rotation of the Earth needs several expertise such as: the interaction between core and mantle, the effect of melting ice, the secular slowing down, ... To bring together insights from various scientific disciplines, the CCTF, in collaboration with the IERS, is organizing a dedicated workshop. The goal is to assess the probability of a negative leap second within the next decade. In this workshop Earth rotation experts give a short presentation, from different points of view, on the variation of the Earth rotation and LOD, and its prediction that could lead to the need of a negative leap second. Workshop Details: Date: Thursday, March 13, 2025 Time: 14:00 - 16:00 UTC Format: Online (Zoom Webinar) Agenda: Each presentation will be 10-15 minutes long: 1. Stamatakos (USNO): IERS Observations of UT1 and LOD 2. McCarthy (IAU): An Astronomer's Overview 3. Mitrovica (Harvard University): Historical Geophysical Effects on Earth Rotation 4. Agnew (UCSD): The Future of UT1 - A Geophysical Perspective 5. Surendra Adhikari: Climate-Driven LOD Changes in the 20th and 21st Centuries 5. Dehant V., Chicot G., Laariara D., Gillet N., Mandea M., Cazenave A. (ORB, Belgium): Core Contributions to LOD 7. Giulio Tagliaferro (BIPM): Stochastic Modeling and Prediction To participate, please register via the following link: [https://bipm-org.zoom.us/webinar/register/ WN_eK8oWapXR3CMGi3vg_f04g#/registration] (Please note that due to message formatting constraints, the link may appear split into two lines. When accessing it, ensure you copy and paste the entire URL into your browser.) Best regards, Noel Dimarcq, President of the CCTF Patrizia Tavella, executive secretary Robert Heinkelmann, IERS Analysis Coordinator ************************************************************************ IERS Messages are edited and distributed by the IERS Central Bureau. If not stated otherwise, the IERS is only the distributor of the message and is not responsible for its content. To submit texts for distribution, please write to . To subscribe or unsubscribe, please create an IERS account or modify it: https://www.iers.org/Login/Login/EN/login_node.html or write to . Archives: http://www.iers.org/IERS/Messages ************************************************************************