TY - JOUR
T1 - Quantifying stratospheric biases and identifying their potential sources in subseasonal forecast systems
AU - Lawrence, Zachary D.
AU - Abalos, Marta
AU - Ayarzagüena, Blanca
AU - Barriopedro, David
AU - Butler, Amy H.
AU - Calvo, Natalia
AU - de la Cámara, Alvaro
AU - Charlton-Perez, Andrew
AU - Domeisen, Daniela I.V.
AU - Dunn-Sigouin, Etienne
AU - García-Serrano, Javier
AU - Garfinkel, Chaim I.
AU - Hindley, Neil P.
AU - Jia, Liwei
AU - Jucker, Martin
AU - Karpechko, Alexey Y.
AU - Kim, Hera
AU - Lang, Andrea L.
AU - Lee, Simon H.
AU - Lin, Pu
AU - Osman, Marisol
AU - Palmeiro, Froila M.
AU - Perlwitz, Judith
AU - Polichtchouk, Inna
AU - Richter, Jadwiga H.
AU - Schwartz, Chen
AU - Son, Seok Woo
AU - Statnaia, Irina
AU - Taguchi, Masakazu
AU - Tyrrell, Nicholas L.
AU - Wright, Corwin J.
AU - Wu, Rachel W.Y.
N1 - Publisher Copyright:
© Author(s) 2022.
PY - 2022/8/19
Y1 - 2022/8/19
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85137841180&partnerID=8YFLogxK
U2 - 10.5194/wcd-3-977-2022
DO - 10.5194/wcd-3-977-2022
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AN - SCOPUS:85137841180
SN - 2698-4016
VL - 3
SP - 977
EP - 1001
JO - Weather and Climate Dynamics
JF - Weather and Climate Dynamics
IS - 3
ER -