A new perspective of the climatological features of upper-level cut-off lows in the Southern Hemisphere

This study presents a detailed view of the seasonal variability of upper-level cut-off lows (COLs) in the Southern Hemisphere. The COLs are identified and tracked using data from a 36-year period of the European Centre for Medium Range Weather Forecast reanalysis (ERA-Interim). The objective identification of the COLs uses a new approach, which is based on 300 hPa relative vorticity minima, and three restrictive criteria of the presence of a cold-core, stratospheric potential vorticity intrusion, and cut-off cyclonic circulation. The highest COL activity is in agreement with previous studies, located near three main continental areas (Australia, South America, and Africa), with maximum frequencies usually observed in the austral autumn. The COL mean intensity values show a marked seasonal and spatial variation, with maximum (minimum) values during the austral winter (summer), a unique feature that has not been observed previously in studies based on the geopotential. The link between intensity and lysis is examined, and finds that weaker systems are more susceptible to lysis in the vicinity of the Andes Cordillera, associated with the topographic Rossby wave. Lysis and genesis regions are close to each other, confirming that COLs are quasi-stationary systems. Also, COLs tend to move eastward and are faster over the higher latitudes. The mean growth/decay rates coincide with the major genesis and lysis density regions, such as the significant decay values across the Andes all year. As a consequence of using vorticity for the tracking method a longer lifetime of COLs is detected than in other studies, but this does not affect the total frequency of occurrence. Comparisons with other studies suggest that the differences in seasonality are due to uncertainties in the reanalyses and the methods used to identify COLs

Leucobryum glaucum

Bryophyte

Marsupella emarginata

Bryophyte

Report on the Herring Acoustic Surveys in the North Sea, Skagerrak and Kattegat during Summer 1989

Four herring acoustic surveys coordinated by ICES were carried out by Scottish, Norwegian, Swedish and Danish research vessels during the period 28 June to 9 August 1989. The reports on the individual surveys, giving a short description of the survey, and a presentation of the results, are collected in this paper. The combined estimated spawning stock biomasses of herring were 1.6 million tonnes autumn spawners and 255 000 tonnes of spring spawners. The combined results are discussed in the paper

A review of extratropical cyclones: observations and conceptual models over the past 100 years

This article reviews synoptic extratropical cyclone research starting from the skilfully constructed conceptual diagrams of the Bergen school in the 1920s. Careful analysis of multiple surface observations allowed Norwegian scientists to deduce the existence of cold and warm fronts and to characterise a complete cyclone lifecycle. Since then, new observing systems and advances in computational capabilities have enabled scientific research which has greatly expanded and enriched our knowledge of extratropical cyclone structure and evolution