IAG Commission 3, ‘Earth Rotation and Geodynamics’

A model of the root-mean-square variability of the vertical displacement of the solid Earth’s surface caused by atmospheric pressure loading. The largest variability is on land areas at middle to high latitudes; the smallest variability is on areas covered by the oceans (Image courtesy: Tonie van Dam, University of Luxembourg).

The IAG is organised into Commissions, Services, the Global Geodetic Observing System (GGOS) and the Inter-Commission Committee on Theory (ICCT). Details can be found in the Geodesists’ Handbook [1]. The four Commissions, their goals and their activities are being highlighted in a series of articles in GIM International.

The ‘Terms of Reference’ for Commission 3 acknowledge that the solid Earth moves and deforms in response to forces acting on it, whether they derive from outside or inside our planet. This includes the entire range of phenomena associated with Earth rotation and Earth orientation such as polar motion, length of day, precession and nutation, the observation and understanding of which are critical to the transformation between terrestrial and celestial reference frames. It also includes tidal processes such as solid Earth and ocean loading tides, and crust and mantle deformation associated with tectonic motions and glacial isostatic adjustment. Commission 3 interacts with the IAG’s GGOS and the other Commissions and Services of the IAG as well as with other organisations such as the International Astronomical Union (IAU) in order to accomplish its objectives.

Commission 3 has the objectives of promoting co-operation and collaboration on the theory, modelling and observation of Earth rotation and geodynamics, of serving the geophysical community by facilitating interactions with organisations that provide the data needed to study Earth rotation and geodynamics, and of ensuring the development of research in Earth rotation and geodynamics by organising meetings, symposia and sessions at conferences and general assemblies, by creating working groups on specific topics, and by encouraging the exchange of ideas and data and the comparison of methods and results with the goal of improving accuracy, content, methods, theories and understanding of Earth rotation and geodynamics.

Commission 3 is grouped into a number of sub-commissions as below (with the chairpersons listed in brackets):

• SC3.1 Earth Tides and Geodynamics (Spiros Pagiatakis, Canada)

• SC3.2 Crustal Deformation (Markku Poutanen, Finland): SC3.2a Global Crustal Deformation (Jeff Freymueller, USA), SC3.2b Regional Crustal Deformation (Manabu Hashimoto, Japan)

• SC3.3 Earth Rotation and Geophysical Fluids (Maik Thomas, Germany)

• SC3.4 Cryospheric Deformation (Matt King, United Kingdom)

• SC3.5 Tectonics and Earthquake Geodesy (Haluk Ozener, Turkey)

The Commission 3 Steering Committee comprises president Richard Gross (USA), vice president Aleksander Brzezinski (Poland), the chairs of the five sub-commissions and two sub-sub-commissions, the chair of Joint Study Group 3.1: Séverine Rosat (France), representatives of the Services: Brian Luzum (USA) and Srinivas Bettadpur (USA), and a member-at-large: Ben Chao (China – Taipei).

The main tasks of Commission 3 in the future will include:

• Assisting the sub-commissions with accomplishing their objectives, including improving models of the rotational and deformational response of the solid Earth to forces acting on it, such as tidal forces, earthquakes and other tectonic phenomena, and changes in the load acting on the Earth’s surface caused by changes in the distribution of mass in the atmosphere, oceans and continental ice and water

• Establishing a Joint Working Group with Commission 19 of the IAU with the objective of improving the theory of the Earth’s rotation

• Organising commission-wide and more topical symposia such as the recent Earth Tides Symposium that was held in Warsaw, Poland, in April 2013

• Developing a dedicated website for all Commission 3 activities.

Commission 3 will co-ordinate a number of sessions at the upcoming IAG Scientific Assembly to be held in Potsdam, Germany, 1-6 September 2013, to celebrate the 150th anniversary of the IAG [2].

[1] http://www.iag-aig.org/index.php?tpl=text&id_c=39&id_t=566

[2] http://www.iag2013.org/IAG_2013/Welcome.html