Introduction to the special issue on GOCE Earth science applications and models

With the launch of the Gravity field and Ocean Circulation Explorer (GOCE) in 2009 the study of Earth's gravity field received another boost. After the time-dependent and long-wavelength information fromthe Gravity Recovery and Climate Experiment (GRACE) mission a new sensor with high accuracy andspatial resolution was available for determination of the Earth's gravity field and geoid. Equipped with a 6-component gradiometer and flying at an altitude of 260 km and less, GOCE provides the most detailed measurements of Earth's gravity from space to date. Additionally, GOCE provides gravity gradients, i.e., the three-dimensional second derivatives of the gravitational potential. This special issue provides a reviewof the results presented at the 'GOCE solid Earth workshop' at the University of Twente, The Netherlands (2012). The goal of this 2-day workshop was to provide training on the usage of GOCE data as well asto present the latest scientific results. The main workshop components were: to show the latest resultson GOCE data in relation to solid Earth, provide new users with tips and tricks on which models and software to use, discuss quality and reliability of gravity data and models, and how to integrate GOCE data with own (local) gravity data. The workshop specifically focussed on where GOCE data has made a unique contribution and provides insights that would not have been possible without GOCE.