The blocking anticyclones: the state of studies and forecasting

Abstract

In connection with analysis of anomalous weather in summer of 2010, the state-of-the-art is reviewed of climatology of the blocking anticyclones, of mechanism for their onset and persistence, as well as possibilities of their forecasting. The main results are quoted on occurrence frequency, intensity, and duration of blockings and on their connection with features of general circulation of the atmosphere in the Northern and Southern hemispheres. As the primary cause of the blocking formation, nonlinear instability of the Rossby waves is considered with intense energy exchange with planetary waves and with synoptic-scale eddies. Mathematical means have been developed to investigate the energy exchange on the real data of objective analysis (reanalysis). This approach can be applied to analyze causes of anomalous duration of the summer blocking. From the point of view of forecasting, blockings do not differ much from other atmospheric pressure systems. Namely, within the framework of medium-range forecasting, the blocking onset, under condition of its absence in the initial fields, can be predicted with a projection of several days; also, the ensemble forecasts are generally more successful than those obtained with any single model. The blocking duration and decay can be predicted successfully within the medium-range forecasting.

Atmospheric blocking events: a review

“…Today's climatological studies have also used some measure for intensity or strength as related to the midlatitude mass or potential vorticity gradients. 27 Additionally, current climatological studies are mainly devoted to refining our understanding of the interannual and interdecadal variability in both hemispheres as well as their tendency for change in the face of a changing climate.…”

Forest trees filter chronic wind‐signals to acclimate to high winds

“…The first is differential heating of the earth's surface producing surface winds known as thermal winds, with a return period of 12 h (Dai & Deser, 1999). A second mechanism involves the forcing of the surface winds by geostrophic winds at a synoptic scale, that is, meteorological systems at the continental scale such as low-pressure areas (Shakina & Ivanova, 2011). This second synoptic-scale mechanism usually results in the strongest variation in surface winds and in the northern Atlantic region its average return period is 4 d. The last peak in the wind spectrum is related to changes in wind conditions over the years.…”

Changes in the Metastability of the Midlatitude Southern Hemisphere Circulation and the Utility of Nonstationary Cluster Analysis and Split-Flow Blocking Indices as Diagnostic Tools

“…Moreover such indices have been used to assess climate GCM performances (Tibaldi 1993) and to develop blocking climatologies (Pook and Gibson 1999). Pook and Gibson (1999) discuss in some detail the respective definitions of SH blocking and the development of the modern blocking index used at the Australian Bureau of Meteorology (BoM) as developed by Wright (1994) [see Shakina and Ivanova (2010) for a more general review of the literature on blocking indices]. This index is defined as 0:5(U 25 1 U 30 2 U 40 2 2U 45 2 U 50 1 U 55 1 U 60 ) .…”