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The frontal structures of extratropical cyclones developing in the northwestern Pacific storm track are relatively poorly understood compared with those in Europe and the Atlantic Ocean, for which representative conceptual models have been developed. In this paper, the structures of cyclones and their associated fronts in the northwestern Pacific (NP), as well as in the Okhotsk Sea and Sea of Japan (OJ), are examined at their developing and mature stages using Japanese 55-year Reanalysis dataset. Furthermore, the frontal structures in the NP are compared with those in the northwestern Atlantic (NA). At the time of maximum deepening rate, cyclones in the NP are accompanied by strong warm and cold fronts, whereas cyclones in the OJ are more frequently accompanied by cold fronts than by warm fronts and tend to have stronger cold fronts than warm fronts. The weaker warm fronts than cold fronts to the east and northeast of cyclones in the OJ is likely due to the cyclones developing to the north and away from the region where the horizontal gradient of environmental potential temperature is strong. A comparison between mature cyclones in the NP and NA shows that the warm fronts in the NA tend to extend northeastward, whereas those in the NP extend more southeastward. These differences in warm fronts between NP and NA are suggested to be due to the difference in the horizontal structures of the warm currents between NP and NA. [ABSTRACT FROM AUTHOR]

This paper investigates the transient characteristics in 41 velocity records of 19 thunderstorm events from around the world—9 from Europe, 9 from the United States, and 1 from Australia. The transient features of thunderstorm winds were examined by introducing an objective method for the detection of changepoints in the time series. The methodology divides velocity records into segments characterized by different statistical properties. The segmentation is based on the following properties of the isolated segments: mean (M) and the standard deviation (SD). This study demonstrated that the maximum velocity during the thunderstorm peak in the events from Europe is typically 2–4 times larger than the mean wind speed before the thunderstorm. The duration of the thunderstorm velocity peak was 2–5 min in approximately 60% of the analyzed records using the M statistic and 5–10 min when analyzed using the SD statistic. Therefore, the velocity fluctuations caused by thunderstorm winds last longer than the abrupt changes in the mean wind field. Similarly, the rampup time was longer when the records were analyzed using the SD statistic. The segmentation methodology was tested for different duration of velocity records and using data with different sampling frequencies. The performances of the introduced method were compared against the results of two other segmentation procedures proposed in the literature. One of the practical applications of this method is the physical separation between the thunderstorm and nonthunderstorm components of a wind event. [ABSTRACT FROM AUTHOR]

The Madden–Julian oscillation (MJO), a prominent feature of the tropical atmospheric circulation at sub seasonal time scales, is known to modulate atmospheric variability in the Euro-Atlantic region. However, current sub seasonal prediction systems fail to accurately reproduce the physical processes involved in these teleconnection mechanisms. This paper explores the observed impact of strong MJO events on surface wind speed over Europe. It is found that some MJO phases are accompanied by strong wind anomalies in Europe. After showing that this teleconnective mechanism is not present in the predictions of the ECMWF monthly forecasting system, a methodology to reconstruct forecasts of daily mean wind speed in the continent weeks ahead is proposed. This method combines MJO forecasts from the S2S project database and the observed teleconnection impacts in the historical records. Although it is found that strong MJO events cannot be skillfully predicted more than 10 days ahead with current prediction systems, a theoretical experiment shows that this method can effectively transform a dynamical MJO forecast into a probabilistic wind speed prediction in Europe. [ABSTRACT FROM AUTHOR]

This paper presents an approach to postprocess ensemble forecasts for the discrete and bounded weather variable of total cloud cover. Two methods for discrete statistical postprocessing of ensemble predictions are tested: the first approach is based on multinomial logistic regression and the second involves a proportional odds logistic regression model. Applying them to total cloud cover raw ensemble forecasts from the European Centre for Medium-Range Weather Forecasts improves forecast skill significantly. Based on stationwise postprocessing of raw ensemble total cloud cover forecasts for a global set of 3330 stations over the period from 2007 to early 2014, the more parsimonious proportional odds logistic regression model proved to slightly outperform the multinomial logistic regression model. [ABSTRACT FROM AUTHOR]