Journal of Atmospheric & Ocean Science

This article was downloaded by:[Universidad de Vigo] [Universidad de Vigo] On: 9 March 2007 Access Details: [subscription number 758062590] Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Atmospheric & Ocean Science Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713719147 Influences of atmospheric variability on freshwater input in Galician Rías in winter To link to this article: DOI: 10.1080/17417530601127472 URL: http://dx.doi.org/10.1080/17417530601127472 Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. © Taylor and Francis 2007 Journal of Atmospheric and Ocean Science Vol. 10, No. 4, December 2005, 377–387 Influences of atmospheric variability on freshwater input in Galician Rıás in winter M. N. LORENZO*y and J. J. TABOADAz yGrupo de Fı´sica de la Atmo´sfera y del Oceáno, Facultad de Ciencias, Universidad de Vigo, 32004 Ourense, Spain zGrupo de Fı´sica Nolineal, MeteoGalicia, University of Santiago de Compostela, Spain The influence of the preferred modes of variation of the atmosphere in the North Hemisphere on the precipitation variability was evaluated in Galicia (NW Iberian Peninsula). The special location of Galicia requires consideration of the influence of several indices that characterize the atmosphere in order to explain the variability of precipitation and consequently the flow regime of its rivers. We calculate the correlation between the precipitation data obtained from 47 rain-gauge stations covering Galicia from 1977 to 1998 and the five principal teleconnection patterns on the Atlantic area of North Hemisphere (NAO, EA, EA/WR, SCA, and POL). The results obtained show significant correlations between winter precipitation and these patterns, and clear spatial distribution Downloaded By: [Universidad de Vigo] At: 08:32 9 March 2007 of their influence within Galicia. This result could be related directly to the freshwater discharge in the different Galician Rıás each winter, which would improve the hydrodynamical description of these estuaries. Keywords: Atmospheric variability; Precipitation; Teleconnection patterns; Galicia (NW Spain) 1. Introduction Estuarine circulation has been the subject of many studies in the last decades because of its main impacts: economical, societal, and environmental (Jones and Millward 2002, and references therein). As a boundary area between the open sea and main- land, estuaries have oceanic and terrestrial influences. To explain its circulation, it is necessary to take into account tidal movements, wind driven currents, and stratification. A main source of stratification comes from the freshwater input of the rivers. This input depends directly upon precipitation. Moreover, freshwater discharge is necessary for an understanding of the physicochemical characteristics of waters along the Iberian continental margin. Their influence can be very important for an understanding of transport in the rainy season. Thus, the presence of strong river plumes in winter was relevant at the time of Prestige oil spill in November–December 2002 (Ruiz-Villareal et al. 2006). Moreover, river plumes induce gradients and fronts in seawater that can be related to the well-known *Corresponding author. Email: [email protected] Journal of Atmospheric and Ocean Science ISSN 1741–7538 print/ISSN 1741–7546 online # 2005 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/17417530601127472 378 M. N. Lorenzo and J. J. Taboada enhanced productivity of the Atlantic coast associated with the northern part of the Eastern North Atlantic coastal upwelling system (Bode et al. 2002). Galicia is a region characterized by a complex terrain and a great number of short rivers that rise in the mountains in the middle part of Galicia and flow into the Rıás, or directly into the ocean. Rivers that flow into the Cantabrian Sea are the shorter ones, due to the location of an east–west range called ‘‘O Xistral’’ near the coast. The most important river of Galicia is the Min˜ o river, whose length is 307 km and in its final part serves as a natural border between Spain and Portugal. Nevertheless, the northwestern part of the Iberian Peninsula is affected by cold fronts associated with low-pressure systems traveling from the north Atlantic, producing between 1000 and 2000 mm of annual precipitation. This quantity of precipitation provokes an increase of river flow, mainly in winter, and freshwater input into the Rıás and directly into the ocean. Several studies point out that the variability of the precipitation has a strong relationship with the main atmospheric circulation modes and therefore, they will have also influence on the river flow regime. Although the atmosphere can be considered at certain scales as a chaotic system, as a reflection of its internal dynamics some large-scale patterns arise, characterized by the teleconnection indices. In the Atlantic area of the North Hemisphere, NAO (North Atlantic Oscillation) is the dominant pattern of atmospheric circulation variability. Other teleconnection patterns appearing in this area in winter Downloaded By: [Universidad de Vigo] At: 08:32 9 March 2007 (Barnston and Livezey 1987) are: EA (East Atlantic), EA/WR (East Atlantic/ Western Russia), SCA (Scandinavian Pattern), and POL (Polar/Eurasia Pattern). In this article, the goal is to correlate winter precipitation in Galicia (NW Spain) with those indices. One of the most prominent teleconnection patterns in all seasons is the NAO (Barnston and Livezey 1987). NAO combines parts of the East- and West-Atlantic patterns originally identified by Wallace and Gutzler (1981) for the winter season. It consists of a north–south dipole of anomalies, with one center located over Iceland and the other of opposite sign spanning the central latitudes of the North Atlantic between 35N and 40N. The positive phase of the NAO reflects below-normal heights and pressure across the high latitudes of the North Atlantic and above-normal heights and pressure over the central North Atlantic, the eastern United States and western Europe. The negative phase reflects an opposite pattern of height and pressure anomalies over these regions. Both phases of the NAO are associated with basin-wide changes in the intensity and location of the North Atlantic jet stream and storm track, and in large-scale modulations of the normal patterns of zonal and meridional heat and moisture transport (Hurrel 1995). These in turn result in changes in temperature and precipitation patterns often extending from eastern North America to western and central Europe. The SCA consists of a primary circulation center over Scandinavia, with weaker centers of opposite sign over western Europe and eastern Russia/western Mongolia. The SCA has been previously referred to as the Eurasia-1 pattern by Barnston and Livezey (1987). The positive phase of this pattern is associated with positive height anomalies, sometimes reflecting major blocking anticyclones, over Scandinavia and western Russia, while the negative phase of the pattern is associated with negative height anomalies in these regions. The EA pattern is the second prominent mode of low-frequency variability over the North Atlantic, and appears as a leading mode in all months. The EA pattern is structurally similar to the NAO, and consists of a north–south dipole of anomaly Atmospheric variability on freshwater input 379 centers spanning the North Atlantic from east to west. The anomaly centers of the EA pattern are displaced southeastward to the approximate nodal lines of the NAO pattern. For this reason, the EA pattern is often interpreted as a southward-shifted NAO pattern. However, the lower-latitude center contains a strong subtropical link in association with modulations in the subtropical ridge intensity and location. This subtropical link makes the EA pattern distinct from its NAO counterpart. This EA pattern is similar to that shown in the Barnston and Livezey (1987) study, but is distinctly different from the EA pattern originally defined by Wallace and Gutzler (1981). The EA/WR pattern is one of three prominent teleconnection patterns that affects Eurasia throughout year. This pattern has been referred to as the Eurasia-2 pattern by Barnston and Livezey (1987). The EA/WR pattern consists of four main anomaly centers. The positive phase is associated with positive height anomalies located over Europe and northern China, and negative height anomalies located over the central North Atlantic and north of the Caspian Sea. Finally, the POL pattern appears in all seasons. The positive phase of this pattern consists of negative

Load more