Variability of Rossby Wave Breaking and its Impacts on the Large-scale Circulation and Extreme Weathers: Implications for S2S Prediction and Predictability

“Rossby wave breaking (RWB) is characterized by large-scale, irreversible overturning of potential vorticity (PV) on isentropic surfaces. The eddy-mean interaction involved in RWB is an important process for the maintenance and variability of the midlatitude jet, and mixing associated with RWB plays an important role in moisture and momentum transport between the tropics and extratropics. In particular, extratropical PV intrusion modulates the moisture distribution in the subtropical dry zone, which affects the infrared energy loss and is an important factor in the global energy budget.

RWB is also closely related to extreme weathers, such as blocking and atmospheric rivers. Our recent study revealed a strong relationship between RWB and Atlantic tropical cyclones (TC). Anomalously frequent RWB enhances the equatorward intrusion of cold, dry extratropical air and leads to a significant reduction in precipitable water over the tropical/subtropical Atlantic and an increase in vertical wind shear, both hindering TC formation and intensification. The correlation of Atlantic hurricane counts with a basinwide RWB frequency index is comparable to the correlation with the Atlantic Main Development Region SST, and stronger than the correlation with the ENSO.

In this project, we propose to i) examine the variability and impacts of RWB on the subseasonal to seasonal (S2S) time scales using reanalysis and observational data; ii) assess the representation of RWB in global prediction systems and investigate model deficiencies using the WWRP/THORPEX/WCRP S2S prediction project database; and iii) investigate the implications of the findings for the S2S prediction and predictability, especially for the prediction and predictability of Atlantic tropical cyclones.

Studies on S2S prediction have primarily focused on tropical forcing and processes (such as the MJO and tropical SST) in the past. This project complements those efforts through its unique perspective in emphasizing the extratropical impacts on tropical circulation and extreme weathers and stressing the link between midlatitude transient eddies and the S2S prediction and predictability. The ultimate goal of the project is to improve the prediction skill of global models on the S2S time scales, and it is well aligned with the focus of the NOAA MAPP Competition 2 to “improve the understanding of predictability” and “advance the prediction of phenomena occurring on S2S time scales”. It is also highly relevant to the NOAA’s long-term climate goal to improve the scientific understanding of the changing climate system and its impacts. This project team consists of scientists from research institutes and operational centers. Their combined expertise in atmospheric dynamics, global modeling, and operational forecasting together forms the particular strength of this project, and will also facilitate transition from research to operations and help to bridge the gap between numerical weather forecasting and short-term climate prediction.”