TR5.1 A Review and Meta-analysis of Current Understanding and Prospects for Development Based on the ARISE Technologies

This Technical Report reviews current and future needs for weather and climate forecasting, in the context of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project.

Concentrating on the middle atmosphere, the measurements commonly assimilated into NWP models are reviewed, alongside those used for `research', rather than in an operational mode. This review highlights a dearth of measurements in the upper stratosphere and lower mesosphere, with only temperature lidars providing sporadic measurements between 40 and 70km. Below 40km, satellite-based Infra-red and Microwave instruments, and GPS Radio Occultation, provide temperature observations with global coverage but coarse vertical resolution. Wind observations remain sparse, with radiosondes and radar wind profilers offering `point' coverage up to approximately 25km.

Many forecast centres around the world now run standard models extending above the stratopause, with significant stratospheric resolution. The need for improved measurement of the stratosphere, for model initialisation, is highlighted by interviews conducted with staff at NWP organisations: Biases in satellite temperature data can increase significantly above 35km, and noisy GPS measurements at similar altitudes can not be used for their calibration.

Gravity waves are a particular problem for stratosphere resolving models: Coarse temporal and spatial modal resolution mean that gravity waves can rarely be resolved directly; at present, parametrisation of gravity waves assumes global invariance.

This report concludes by discussing the ways that the ARISE network has the potential to improve the initialisation of the middle atmosphere in NWP models. Two particular roles for the ARISE network, that emerged from discussions, are to constrain biases in existing satellite observations, and provide additional high-resolution measurements to test and improve model parametrisation schemes (particularly for gravity waves). Other ARISE work packages will explore that potential in more detail.