Ozone-Circulation Interaction in the Stratosphere
Ozone is a key constituent of the stratosphere that modulates the thermal structure of the atmosphere and prevents harmful ultraviolet radiation from the surface. It is well known that during the Arctic circulation extremes, e.g., Stratospheric Sudden Warming, anomalous high ozone concentration occurred in the polar cap region due to enhanced dynamical ozone transport from the lower latitudes. Our study indicated that significant decreases in ozone were also observed in the tropics, highlighting the global influences of Arctic circulation extremes. We also developed a simplified chemistry-dynamical model (SCDM V1.0), which couples a linear ozone scheme and a shortwave radiative parameterization into a widely used idealized model. The new model is economical and has the advantage of isolating the ozone effect on circulation. Our ongoing work is to use the model for an in-depth study of the role of interactive ozone in the variability of the coupled stratosphere-troposphere system.

The Northeast Pacific SST Variability
The Northeast Pacific (NEP) had two record-breaking marine heatwave events (MHWs) in the winters of 2013–2015 and summer of 2019, which had a detrimental impact on the fisheries, marine ecosystems, and climate in North America. Here, we investigated the cause of sea surface temperature (SST) variability in NEP during late spring–summer of 1981–2020. The regression circulation anomalies to the principal component of leading EOF mode suggested that the warm NEP SST were characterized by a cyclonic circulation anomaly in the midlatitude North Pacific and a warming SST center in the Gulf of Alaska. We noted that this cyclonic circulation anomaly, attributable to a barotropic atmospheric wave originating from the tropical central Pacific (CP) in the preceding spring, reduced the surface heat flux loss from the ocean to the atmosphere in the NEP and led to the warm SST anomalies in summer. This finding was confirmed by not only empirical diagnosis but also long-term numerical simulations forced by the observed SST perturbations in the tropical CP. Our results highlight the role of the tropical CP SST in driving the summertime North Pacific SST variability through the atmospheric bridge in recent decades.