5:15 PM - 7:15 PM
[AAS06-P07] Future Changes in the Frequency of Sudden Stratospheric Warmings: Variability Depending on Sea Surface Temperature Conditions
Keywords:Sudden Stratospheric Warming / Stratospheric Sudden Warming, Global Warming, El Niño-Southern Oscillation
The characteristics of sudden stratospheric warmings (SSWs), which play a crucial role in shaping the winter climate, are influenced by various external factors. One of the significant uncertainties in future climate projections is whether the frequency of SSWs will increase or decrease in a warming climate. Even in intercomparison projects using the latest climate models, no clear consensus has been reached on this issue. The interpretation of multi-model comparison results is challenging, and it is necessary to conduct analyses under more controlled conditions to identify the factors contributing to this uncertainty.
In this study, we analyzed the frequency of SSWs using large-ensemble simulations produced by a single model (MRI-AGCM3.2). The dataset used for the analysis is from the "database for policy decision making for future climate change" (d4PDF), which includes global climate simulations with multiple future sea surface temperature (SST) change patterns. This experimental design allows us to examine the impact of SST change diversity on the future variability of SSW frequency.
Our analysis revealed that SSW frequency generally decreases in future climates within this database. In the +4 K warming experiment, the frequency of SSWs was 0.67 times that of the non-warming experiment, with historical simulations lying between these two scenarios. Further analysis of future changes in SSW frequency across different SST patterns showed substantial variations, with differences that exceeded those observed among different experimental conditions.
Furthermore, we investigated how variations in SST change patterns influence the differences in SSW frequency. Our results indicate that these differences are primarily amplified through modulations of tropospheric circulation variability over the North Pacific during El Niño. Indeed, significant differences were observed in the blocking frequency over the North Pacific, and in particular, the frequency of wavenumber-1 SSWs was found to be a key factor characterizing the variability among SST patterns. In addition, not only tropical SST changes but also midlatitude SST structures, such as oceanic fronts, contributed significantly to these variations.
These findings emphasize that the representation of midlatitude oceanic frontal structures in climate models can have a significant impact on the future projections of SSW frequency, highlighting the importance of accurately modeling ocean-atmosphere interactions in midlatitude regions.
In this study, we analyzed the frequency of SSWs using large-ensemble simulations produced by a single model (MRI-AGCM3.2). The dataset used for the analysis is from the "database for policy decision making for future climate change" (d4PDF), which includes global climate simulations with multiple future sea surface temperature (SST) change patterns. This experimental design allows us to examine the impact of SST change diversity on the future variability of SSW frequency.
Our analysis revealed that SSW frequency generally decreases in future climates within this database. In the +4 K warming experiment, the frequency of SSWs was 0.67 times that of the non-warming experiment, with historical simulations lying between these two scenarios. Further analysis of future changes in SSW frequency across different SST patterns showed substantial variations, with differences that exceeded those observed among different experimental conditions.
Furthermore, we investigated how variations in SST change patterns influence the differences in SSW frequency. Our results indicate that these differences are primarily amplified through modulations of tropospheric circulation variability over the North Pacific during El Niño. Indeed, significant differences were observed in the blocking frequency over the North Pacific, and in particular, the frequency of wavenumber-1 SSWs was found to be a key factor characterizing the variability among SST patterns. In addition, not only tropical SST changes but also midlatitude SST structures, such as oceanic fronts, contributed significantly to these variations.
These findings emphasize that the representation of midlatitude oceanic frontal structures in climate models can have a significant impact on the future projections of SSW frequency, highlighting the importance of accurately modeling ocean-atmosphere interactions in midlatitude regions.