Application of satellite scatterometer to the study of Earth angular momentum balance.

摘要

The dynamics of the Earth system has been studied for many years; however, it is still not fully understood on a fundamental level because of its underlying complexity. The interactions among the atmosphere, ocean and solid Earth, which occur through energy and momentum exchanges and mass transport, are often essential. However, the actual mechanisms by which the angular momentum is transferred from the atmosphere to the solid Earth still remain unclear. The atmosphere exchanges angular momentum with the solid Earth through the two major torques: wind stress torque and mountain torque. The ocean exchanges angular momentum with the solid Earth through pressure and friction torque acting on the ocean floor. Since a large portion of the atmospheric angular momentum is exchanged with the ocean through the wind stress torque acting on the sea surface, precise observations of sea surface wind, the major driven force causing the oceanic circulation, can provide an opportunity for fully understanding these mechanisms. A quantitative understanding of the relations between the wind forcing and the reaction of the ocean is also desirable.; In this research, the European Remote Sensing Satellite 1 (ERS-1) scatterometer measurements were reprocessed using the European Space Agency (ESA)'s CMOD4 model function and a line-wise ambiguity removal algorithm with sea-ice detection scheme to obtain the unique wind vector from the scatterometer's multi-solutions. The reprocessed wind stress fields were compared with both ESA's wind products and the National Center for Environmental Prediction (NCEP) analytical fields. The results indicated that the wind stress fields generated by the new algorithm are reasonably better.; This more accurate and consistent ERS-1 scatterometer global high resolution surface wind data was then used to study the Earth system angular momentum balance, including forcing a parallel free-surface ocean general circulation model to investigate the changes of the oceanic angular momentum and its contribution to the Earth angular momentum balance. The calculated global torque agrees very well with changes in the atmospheric angular momentum. The oceanic angular momentum itself only accounts for a relatively small portion in the Earth angular momentum balance. Torques that include the ERS-1 scatterometer wind forcing over the ocean produce a better balance with the rate of change of global atmospheric angular momentum compared to those from the NCEP model system alone.