5:15 PM - 6:45 PM
[MIS01-P05] The effects of the low frequency ocean-atmosphere variability on the extreme weather events in the Northern Hemisphere extratropics
Keywords:climate modes, extreme weather events, temperature, precipitation
Beyond the general trend of global temperature and the associated changes in the precipitation regime, the internal dynamics of the climate system can exert a significant influence on the occurrence of extreme weather events. Meanwhile, the low-frequency (interannual to decadal) climate modes influence the climate conditions over large areas via teleconnection mechanisms. Therefore, the frequency of air temperature and precipitation extremes may be significantly influenced by low-frequency climate modes. This study aims to identify the main climate modes that influence the probability of weather extremes in the extratropical latitudes of the Northern Hemisphere. Such anomalies can have a significant impact on greenhouse gas fluxes in different plant communities.
The large-scale climate modes (El Niño-Southern Oscillation (SOI), Pacific Decadal Oscillation (PDO), Interdecadal Pacific Oscillation (IPO), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Indian Ocean Dipole (IOD)) as well as regional climate indices (SCAND, Siberian Anticyclone Index (SHI), and East Atlantic-West Russia Index (EA-WR)) were considered in our study.
For each climate mode, the phases of positive and negative values during 1991-2021 were identified. Furthermore, the frequency of extreme (above 95% quantile or below 5% quantile) values of daily mean temperature or daily precipitation was calculated for each phase. Temperature and precipitation were obtained from ERA5 reanalysis data for the region bounded by 180°E - 180°W and 40°-85°N. The difference in the frequency of extremes between the positive and negative phases of the climate modes was estimated.
The positive phase of the Arctic Oscillation and the North Atlantic Oscillation is associated with a significant increase (up to 50% and more) of extremely hot conditions, while the negative phase coincides with a higher frequency of extremely cold conditions in the extratropics of the Northern Hemisphere. For the AO, this effect occurs in both Europe and Asia, while for the NAO it is most pronounced in Northern and Central Europe. The positive phase of the AO and NAO also contributes to an increased frequency of extremely dry conditions in Southern Europe and wetter conditions in the Great American Lakes region.
The positive phase of the PDO and IPO is associated with more frequent extreme low temperatures and rare hot conditions in Europe, Eastern North America, and the Far East. The influence of the Pacific climate indices on extreme precipitation is less pronounced and more mosaic. The positive phase of the IOD index contributes to an increase in extremely warm days and a decrease in extremely cold days in Europe (especially in the south), eastern North America, and northeastern Russia. The SOI effect is close to the IOD effect, but rather weak.
The SCAND and EA-WR indices have the strongest effect on the European area. Thus, the positive phase of the EA-WR index is associated with an increase (decrease) in the frequency of hot (cold) days and the opposite effect in Northern Europe and the European part of Russia, as well as a decrease in the frequency of intense precipitation over most of Europe. The opposite trend is observed for the SCAND index.
The strongest effect of the Siberian Anticyclone Index is observed in Mongolia. Positive phases of the SHI are accompanied by frequent extremely low temperatures, which coincide with periods of anticyclone intensification in winter.
Our results indicate a significant influence of climate modes on the frequency of extreme weather conditions. The strongest effect was found for AO, NAO, IPO over large areas of the Northern Hemisphere and for regional indices EA-WR and SCAND over European territory.
Funding for this research was provided by the Russian Science Foundation, grant number 22-17-00073.
The large-scale climate modes (El Niño-Southern Oscillation (SOI), Pacific Decadal Oscillation (PDO), Interdecadal Pacific Oscillation (IPO), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Indian Ocean Dipole (IOD)) as well as regional climate indices (SCAND, Siberian Anticyclone Index (SHI), and East Atlantic-West Russia Index (EA-WR)) were considered in our study.
For each climate mode, the phases of positive and negative values during 1991-2021 were identified. Furthermore, the frequency of extreme (above 95% quantile or below 5% quantile) values of daily mean temperature or daily precipitation was calculated for each phase. Temperature and precipitation were obtained from ERA5 reanalysis data for the region bounded by 180°E - 180°W and 40°-85°N. The difference in the frequency of extremes between the positive and negative phases of the climate modes was estimated.
The positive phase of the Arctic Oscillation and the North Atlantic Oscillation is associated with a significant increase (up to 50% and more) of extremely hot conditions, while the negative phase coincides with a higher frequency of extremely cold conditions in the extratropics of the Northern Hemisphere. For the AO, this effect occurs in both Europe and Asia, while for the NAO it is most pronounced in Northern and Central Europe. The positive phase of the AO and NAO also contributes to an increased frequency of extremely dry conditions in Southern Europe and wetter conditions in the Great American Lakes region.
The positive phase of the PDO and IPO is associated with more frequent extreme low temperatures and rare hot conditions in Europe, Eastern North America, and the Far East. The influence of the Pacific climate indices on extreme precipitation is less pronounced and more mosaic. The positive phase of the IOD index contributes to an increase in extremely warm days and a decrease in extremely cold days in Europe (especially in the south), eastern North America, and northeastern Russia. The SOI effect is close to the IOD effect, but rather weak.
The SCAND and EA-WR indices have the strongest effect on the European area. Thus, the positive phase of the EA-WR index is associated with an increase (decrease) in the frequency of hot (cold) days and the opposite effect in Northern Europe and the European part of Russia, as well as a decrease in the frequency of intense precipitation over most of Europe. The opposite trend is observed for the SCAND index.
The strongest effect of the Siberian Anticyclone Index is observed in Mongolia. Positive phases of the SHI are accompanied by frequent extremely low temperatures, which coincide with periods of anticyclone intensification in winter.
Our results indicate a significant influence of climate modes on the frequency of extreme weather conditions. The strongest effect was found for AO, NAO, IPO over large areas of the Northern Hemisphere and for regional indices EA-WR and SCAND over European territory.
Funding for this research was provided by the Russian Science Foundation, grant number 22-17-00073.