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Mid-latitudinal cyclones are a key factor for understanding regional anomalies in primary meteorological parameters such as temperature or precipitation. Extreme cyclones can produce notable impacts on human society and economy, for example, by causing enormous economic losses through wind damage. Based on 41 annually initialised (1961-2001) hindcast ensembles, this study evaluates the ability of a single-model decadal forecast system (MPI-ESM-LR) to provide skilful probabilistic three-category forecasts (enhanced, normal or decreased) of winter (ONDJFM) extra-tropical cyclone frequency over the Northern Hemisphere with lead times from 1 yr up to a decade. It is shown that these predictions exhibit some significant skill, mainly for lead times of 2-5 yr, especially over the North Atlantic and Pacific. Skill for intense cyclones is generally higher than for all detected systems. A comparison of decadal hindcasts from two different initialisation techniques indicates that initialising from reanalysis fields yields slightly better results for the first forecast winter (month 10-15), while initialisation based on an assimilation experiment provides better skill for lead times between 2 and 5 yr. The reasons and mechanisms behind this predictive skill are subject to future work. Preliminary analyses suggest a strong relationship of the model's skill over the North Atlantic with the ability to predict upper ocean temperatures modulating lower troposphere baroclinicity for the respective area and time scales. [ABSTRACT FROM AUTHOR]

Comparison of simulated and reconstructed past climate variability within the last millennium provides an opportunity to aid the understanding and interpretation of palaeoclimate proxy data and to test hypotheses regarding external forcings, feedback mechanisms and internal climate variability under conditions close to those of the present day. Most such comparisons have been made at the Northern Hemispheric scale, of which a selection of recent results is briefly discussed here. Uncertainties in climate and forcing reconstructions, along with the simplified representations of the true climate system represented by climate models, limit our possibility to draw certain conclusions regarding the nature of forced and unforced climate variability. Additionally, hemispheric-scale temperature variations have been comparatively small, wherefore the last millennium is apparently not a particularly useful period for estimating climate sensitivity. Nevertheless, several investigators have concluded that Northern Hemispheric-scale decadal-mean temperatures in the last millennium show a significant influence from natural external forcing, where volcanic forcing is significantly detectable while solar forcing is less robustly detected. The amplitude of centennial-scale variations in solar forcing has been a subject for much debate, but current understanding of solar physics implies that these variations have been small - similar in magnitude to those within recent sunspot cycles - and thus they have not been a main driver of climate in the last millennium. This interpretation is supported by various comparisons between forced climate model simulations and temperature proxy data. Anthropogenic greenhouse gas and aerosol forcing has been detected by the end of Northern Hemispheric temperature reconstructions. [ABSTRACT FROM AUTHOR]

The satellite ozone data comprising The New Zealand National Institute of Water and Atmospheric Research (NIWA) total ozone database version 2.7, total ozone by the Ozone Monitoring Instrument (OMI) spectrophotometer on the Aura platform, and the ozone mixing ratios by SBUV/2 measurements on The National Oceanic and Atmospheric Administration (NOAA) platforms are analysed for ozone variability over the sunlit part of the Northern Hemisphere polar region. An extended area, with unusually low ozone values, is observed in a two-month period beginning in mid February 2011. The total area with extremely depleted total ozone reached the maximum at the end of March 2011, equal to ~11 × 106 km². The area is even larger in the lower/mid stratosphere. A multiple regression model is proposed to attribute the polar total ozone variability to various chemical and dynamical ozone forcings. The model reproduces the ozone loss in early 2011 and the overall picture of the ozone long-term changes. The extreme ozone decline in 2011 could be attributed to the long-lasting period with low stratospheric temperature (B195K), weaker than the normal Brewer-Dobson circulation, and the Arctic Oscillation in a strong positive phase. A deficit of total ozone in the following summer months (June-July-August), after the total ozone decline in March, was predicted and supported by later OMI observations. [ABSTRACT FROM AUTHOR]

The mean temperature for the Northern Hemisphere had a warming trend from 1890 to 1950 and a cooling trend since 1950. The eastern and central United States had colder temperatures in 1961–1970 than in 1931–1960. The temperature changes were associated with an adjustment of hemispheric circulation from more frequent zonal flow between 1900 to 1950 to more frequent meridional flow since 1950. Regional variations in magnitude and direction of the change were largely related to position in relation to the upper air westerly wave pattern. Time series of individual circulation indices tend to resemble the step function model of climatic change. [ABSTRACT FROM AUTHOR]

Describes weather conditions and patterns over the Northern Hemisphere during 1985. Alternations of temperature and precipitation resulting from the rapid changes in the upper level wind currents; Winter conditions from 1984 to 1985; Destruction of acres of woodlands from wildfires during the spring season; Temperature patterns; Observation of seasonal circulation and accompanying temperature and precipitation anomalies.