PHYSICAL CLIMATOLOGY

Author: OLALLA NIETO MUÑIZ RAQUEL.
Year: 2004.
University: VIGO [www.uvigo.es].
Place of defense: FACULTAD DE CIENCIAS DE OURENSE.
Place of preparation: FACULTAD DE CIENCIAS DE OURENSE.

Summary: SUMMARY: This paper is the first climatology multidecadal (41 years) for the Northern Hemisphere systems isolated depressions in high levels of the troposphere (DANAs). The DANAs were identified using data re-analysis NCAR-NCEP and through an objective method which is based on the imposition of restrictive consecutive and four of the physical characteristics of the conceptual model of DANA (minimum geopotential, circulation closed and isolated flow generally minimal thick equivalent and minimum of PFT in the upper troposphere). This method of imposing restrictive conditions minimizes the possibility of considering as DANAs different systems. The database that is obtained is a good tool to carry out a thorough analysis in terms climatological the DANAs analysis of the spatial and temporal distribution, durations and trajectories more habituales-, as well as to study the effects on those regions which affect DANAs (being in this work the Iberian Peninsula). The results in this study reveal new and interesting properties of DANAs and allow us to validate other already known and can extend to a longer period of time. The results obtained from analysis of the spatial distribution of DANAs for the entire northern hemisphere indicate the existence of three areas preferential its occurrence: Southern Europe and the east coast of the Atlantic Ocean, the Northeast Pacific Ocean and northern China and the regions of Siberia spread to the northwest coast of the Pacific. Of the three regions of Europe is the area of greatest frequency of DANAs. This shows that the DANAs occur preferably in the vicinity of the main vaguadas flow circumpolar long scale. Another outcome shows that DANAs form to a greater extent during the summer months approximately 50% of the DANAs identified occur during the months of July, August and September, with the winter season less frequent. During the summer DANAs occurring in higher latitudes than in the rest of the year in the three areas of greatest occurrence. A more thorough analysis of the three areas of greatest occurrence shows a bimodal distribution in the region of Europe-and differentiate two areas most frequently: the eastern region of the Atlantic Ocean and the southern part of the continent, including the Mediterranean region, a displacement of systems toward the ocean during the summer in the American region and an expansion into the continent in the Asian region during the summer. As for the length of DANAs it can be concluded that most have a life time between 2 and 3 days and very few lasted beyond the 5 days. Subject to limitations, we can say that DANAs have durations greater when they occur at higher latitudes. Generally speaking, most of the DANAs moving any day of their life cycle, with less than 20% those that remain stationary. In most cases the most obvious move is a shift to the north or west, especially when it discusses the transitions from the second day of occurrence toward the third and down to the fourth. The Iberian peninsula is within the area more frequently on the occurrence of DANAs. That is why in this paper also discusses the impact on our region causing these synoptic systems. The analysis of rainfall and cloudiness associated with DANAs on the Iberian Peninsula, the Balearic Islands and Melilla shows: That not all DANAs involve intense precipitation convective type, as is commonly associated with systems historically d 8 enominad 8a7 you as "cold drops," or 'cold pools' in English, as evidenced by examining the precipitation of individual DANA. That precipitation on the Mediterranean area is mainly due to precipitation of DANAs found itself on the region (over 60%), and that the amount they are due, in this case, convective phenomena produced at the center of DANAs . That most of the precipitation associated with DANAs comes from the coat baroclino, as seen when analyzing individual cases of DANAs, especially in cases of DANAs located in the mid-west peninsula. That there were many cases in which precipitation detected on the peninsula should not be the system itself DANA (12.5% of the systems), but the impact caused by the existence of these systems in the general circulation of oestes. This is the case of DANAs occurring in the southern half mainland, resulting in precipitation in the northern third caused by the entry of fronts associated with the general flow that exceeds the DANAs longer isolated in the south. That there are a large number of systems that do not cause any precipitation (approximately 30%), localizándose mostly in the southern half Peninsular, and especially during the autumn. That there is a very significant percentage (30%) of DANAs causing widespread rainfall throughout analyzed -son the DANAs located on the western half Peninsular (approximately 90%) responsible for this type of precipitación-.