Characterization of the atmospheric component of the winter hydrological cycle in the Galicia/North Portugal Euro-region: a Lagrangian approach

Abstract

The Lagrangian 3-dimensional FLEXPART model was used to investigate the main sources of moisture for the Galician/northern Portugal (GALNP) region, as well as their inter-annual variability during winter. FLEXPART identifies humidity contributions to the moisture budget over a region through the computation of changes in the specific humidity along backward trajectories of up to 10 d. Two analyses were done for the period between 1990/1991 and 1998/1999: the first consider- ing all winter days and the second only precipitation days over GALNP. Two dominant source regions of moisture were detected: the extended Bay of Biscay (BB) and the Tropical and Subtropical North Atlantic corridor (TSNA). The BB presented a large 1 d maximum and a very significant contribution in the period from 1 to 4 d backward. The TSNA only showed a net uptake of moisture for GALNP from 2 d backward, and its contribution reached a maximum on the 5th day backward. The results suggest that the inter-annual variations in winter precipitation over GALNP could be directly associ- ated with the variability observed in the contribution of moisture from the TSNA. A large part of the contribution of moisture from the BB occurs during anticyclonic conditions over the GALNP region, which relate to stable atmospheric conditions and the inhibition of precipitation. On the other hand, around 75% of the total TSNA winter contribution occurred during precipitation days. Once dynamic conditions are favourable for generating precipitation, it appears that there is some contribution from the BB to precipitation days in the GALNP region.