Analysis of Intraseasonal Variability and Predictability of Regional-Scale Atmospheric Processes at Midlatitudes of the Northern Hemisphere

The issues related to the intraseasonal variability and predictability of regional scale atmospheric processes in the Northern Hemisphere are considered. To identify the latter, circulation indices characterizing large-scale modes of atmospheric variability are used. An assessment is made of the regional intraseasonal variability of the atmospheric processes in the summer and winter seasons of 1991-2020. A study of practical predictability of regional atmospheric processes is carried out using the global semi-Lagrangian model developed at the Institute of Numerical Mathematics, Russian Academy of Sciences, jointly with the Hydrometeorological Center of Russia, as well as reanalyses of the European Center for Medium-Range Weather Forecasts on weekly and monthly time scales. It is concluded that, beyond the first prognostic week, the quality of deterministic (ensemble average) forecasts drops sharply. In winter, the Pacific-North American Oscillation region is an exception, where a signal is traced not only over the first, but also over the second forecast week. The application of probabilistic forecasts makes it possible to increase the time interval of predictability compared to the deterministic approach from one week to a month. The largest errors are revealed in the forecasts of circulation regimes in the Northwest Atlantic and in the North Pacific, in the regions of the most significant intraseasonal variability. The results are planned to be used in the operational practice of intraseasonal forecasting of the North Eurasian Climate Center (NEACC).

Automated summary

This study investigates the intraseasonal variability and predictability of regional atmospheric processes in the Northern Hemisphere. The assessment reveals that deterministic forecasts deteriorate rapidly beyond the first week, except for the Pacific-North American Oscillation region. However, probabilistic forecasts can extend the predictability time interval to one month. The study also identifies significant errors in the forecasts of circulation regimes in the Northwest Atlantic and North Pacific regions.