Quintic vertical interpolation improves forecasts of the stratosphere

Polichtchouk, Inna ; Diamantakis, Michail ; Váňa, Filip

Année de publication
2020
Résumé
<p align="justify"> ECMWF has over the years repeatedly increased the horizontal resolution of its forecasts to today's grid spacing of 9 km in high-resolution forecasts (HRES) and 18 km in ensemble forecasts (ENS). The resolution increases have greatly improved forecast quality in most parts of the atmosphere but have led to unphysical cooling in the lower to mid-stratosphere. This unphysical model behaviour arises from numerical errors accumulating due to insufficient vertical resolution in the stratosphere. In ECMWF's Integrated Forecasting System (IFS), fifth-order (quintic) vertical interpolation offers a cost-effective alternative to increasing the vertical resolution. Tests have shown that it leads to more physical model behaviour, reduced sensitivity to horizontal resolution, and better forecast skill in the lower to mid-stratosphere. It will therefore be implemented in the next upgrade of the forecasting system to IFS Cycle 47r1 planned for later this year.</p>

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