Quantifying stratospheric biases and identifying their potential sources in subseasonal forecast systems

The stratosphere can be a source of predictability for surface weather on timescales of several weeks to months. However, the potential predictive skill gained from stratospheric variability can be limited by biases in the representation of stratospheric processes and the coupling of the stratosphere with surface climate in forecast systems. This study provides a first systematic identification of model biases in the stratosphere across a wide range of subseasonal forecast systems. It is found that many of the forecast systems considered exhibit warm global-mean temperature biases from the lower to middle stratosphere, too strong/cold wintertime polar vortices, and too cold extratropical upper-troposphere/lower-stratosphere regions. Furthermore, tropical stratospheric anomalies associated with the Quasi-Biennial Oscillation tend to decay toward each system’s climatology with lead time. In the Northern Hemisphere (NH), most systems do not capture the seasonal cycle of extreme-vortex-event probabilities, with an underestimation of sudden stratospheric warming events and an overestimation of strong vortex events in January. In the Southern Hemisphere (SH), springtime interannual variability in the polar vortex is generally underestimated, but the timing of the final breakdown of the polar vortex often happens too early in many of the prediction systems. These stratospheric biases tend to be considerably worse in systems with lower model lid heights. In both hemispheres, most systems with low-top atmospheric models also consistently underestimate the upward wave driving that affects the strength of the stratospheric polar vortex. We expect that the biases identified here will help guide model development for subseasonal-to-seasonal forecast systems and further our understanding of the role of the stratosphere in predictive skill in the troposphere.

Fil: Lawrence, Zachary D.. State University of Colorado at Boulder; Estados Unidos. National Oceanic And Atmospheric Administration; Estados Unidos

Fil: Abalos, Marta. Universidad Complutense de Madrid; España

Fil: Ayarzagüena, Blanca. Universidad Complutense de Madrid; España

Fil: Barriopedro, David. Universidad Complutense de Madrid; España

Fil: Butler, Amy H.. National Oceanic And Atmospheric Administration; Estados Unidos

Fil: Calvo, Natalia. Universidad Complutense de Madrid; España

Fil: de la Cámara, Alvaro. Universidad Complutense de Madrid; España

Fil: Charlton-Perez, Andrew. University of Reading; Reino Unido

Fil: Domeisen, Daniela I.V.. Universite de Lausanne; Suiza. Eidgenossische Technische Hochschule zurich (eth Zurich);

Fil: Dunn Sigouin, Etienne. Norwegian Research Centre and Bjerknes Centre for Climate Research; Noruega

Fil: García Serrano, Javier. Universidad de Barcelona; España

Fil: Garfinkel, Chaim I.. The Hebrew University of Jerusalem; Israel

Fil: Hindley, Neil P.. University of Bath; Reino Unido

Fil: Jia, Liwei. University Corporation For Atmospheric Research; Estados Unidos. National Oceanic And Atmospheric Administration; Estados Unidos

Fil: Jucker, Martin. Arc Centre Of Excellence For Climate Extremes; Australia. University of New South Wales; Australia

Fil: Karpechko, Alexey Y.. Finnish Meteorological Institute; Islandia

Fil: Kim, Hera. Seoul National University; Corea del Sur

Fil: Lang, Andrea L.. State University of New York; Estados Unidos

Fil: Lee, Simon H.. Columbia University; Estados Unidos

Fil: Lin, Pu. National Oceanic And Atmospheric Administration; Estados Unidos. University of Princeton; Estados Unidos

Fil: Osman, Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Karlsruhe Institute of Technology; Alemania

Fil: Palmeiro, Froila M.. Universidad de Barcelona; España

Fil: Perlwitz, Judith. National Oceanic And Atmospheric Administration; Estados Unidos

Fil: Polichtchouk, Inna. European Centre For Medium-range Weather Forecasts; Reino Unido

Fil: Richter, Jadwiga H.. National Center for Atmospheric Research; Estados Unidos

Fil: Schwartz, Chen. The Hebrew University of Jerusalem; Israel

Fil: Son, Seok Woo. Seoul National University; Corea del Sur

Fil: Statnaia, Irina. Finnish Meteorological Institute; Finlandia

Fil: Taguchi, Masakazu. Aichi University Of Education; Japón

Fil: Tyrrell, Nicholas L.. Finnish Meteorological Institute; Finlandia

Fil: Wright, Corwin J.. University of Bath; Reino Unido

Fil: Wu, Rachel W.-Y.. Eidgenossische Technische Hochschule zurich (eth Zurich);