The Statistical Analysis Of The Winter Mid-latitude Cyclone In The Northern Hemisphere

Mid-latitude cyclone, especially the oceanic mid-latitude cyclone, plays an very important role in the moisture transfer and the latent heat transfer. Thus, mid-latitude cyclone is highly important for climatic system. So that making research on the statistics of the winter mid-latitude cyclone is good for improving the accuracy in medium-range and long-range weather forecast.First, the cyclone-tracking algorithm of previous author has been revised. In this paper, European Centre for Medium-Range Weather Forecast(ECMWF)ERA-40 re-analysis data is used to make out the statistical analysis for the winter (December-January-February)mid-latitude cyclone in the whole Northern Hemisphere. Storm track, cyclone density, cyclogenesis density, mature cyclone density and cyclolysis has been done separately. Results show that there are two maintain regions of cyclones activity: the North Pacific basin and the North Atlantic basin. The two regions correspond two storm tracks respectively. In the North Pacific, cyclogenesis maximum regions are in the Western Pacific, and then cyclones travel through the central of the North Pacific and reach maximum intensity in this area. At last, they travel northeastward to the Gulf of Alaska and end their life cycle in this area. In the North Atlantic basin, cyclogensis maximum regions is the east coast of North American and the Iceland. Most of these cyclones are move northeastward to the Iceland.These cyclones reach their maximum intensity and end their lives both in Iceland region. Only a few cyclones could move into the North Europe.Then, PDO indices has been used in this study. Composite analysis of North Pacific is done for 13 positive PDO year, which is defined as the PDO index above 0.5, and 14 negative PDO year, which is defined as the PDO index below -0.5. Results show that the maximum regions of cyclone activities are restricted between the longitude between 0°to 170°W in the positive PDO year, while in the negative PDO year, its regions are restricted westward of the date line .And the Eady growth rate index at 500hPa, which has been calculated later, reveal that there are more favorable conditions for cyclone growth in the west of date line in the negative PDO year.At last, composite analysis is also done in the North Atlantic for the NAO indices, in which the positive NAO indices is defined as the values above 1 and the negative NAO indices is defined as the values below -1. The results show distinctly that storm track in positive year is much stronger than in negative year. And the cyclone density map show that few cyclones could move east of 20°W in the negative year, while there are almost 1/3 cyclones end their lives in the Norwegian Sea(between 10°W to 10°E).