E. Sáez de Cámara

Daily precipitation in Northern Iberia: Understanding the recent changes after the circulation variability in the North Atlantic sector

Trends in the characteristics of daily precipitation over Northern Iberia (NIB) are analyzed after 14 daily records covering the last 40 years plus seven century-length time series. Results reveal an evolution to drier conditions with subregional variations: in western and central subregions, the decrease in both the occurrence and the intensity of wet days results in a statistically significant decline of total precipitation. Contrary to other regions in the Iberian Peninsula, the lack of correlation between the North Atlantic Oscillation (NAO) index and the observed rainfall anomalies within NIB suggests that the dominance of a positive NAO mode from the late 1970s to 2002 cannot explain the trends. The land-sea and mountain distribution creates sharp rainfall transitions depending on the pathways of the moisture-laden winds. Consequently, NIB and other mountainous regions in the margins of the European continental water divide are sensitive to small changes in the NAO pressure centers and can exhibit both positive and negative rainfall anomalies for each NAO mode. A novel methodology for identifying changes in the NAO modes, consistent with the observed pressure/precipitation anomalies at both continental and regional scales, is presented. After the disaggregation of each dominant NAO wet season into two categories, the main rainfall changes in the NIB region can be explained in the context of the NAO variability during the last decades. The reported (sub)regional rainfall differences stress the need of caution when using NAO reconstructions, based in site specific rainfall anomalies, for the interpretation of the past climate precipitation variability in areas of complex terrain.

The Impact of Sub-hourly Meteorology on the Estimation of Odour Concentrations from an Industrial Source in Complex Terrain

Atmospheric pollutant impacts may be evaluated through the use of dispersion models, usually based on averaging times of 1 h. However, some scenarios may require shorter time lapses, as it is the case of odour impact evaluations. Version 6 of the CALPUFF modeling system, which allows the use of sub-hourly temporal resolution, coupled with the mesoscale prognostic model RAMS has been used to simulate the impacts of the odour emissions from a paper mill in a highly urbanized area located several kilometers downwind at the seaside in a mountainous region. A selection of consecutive days under anticyclonic conditions have been simulated using a maximum resolution of 10 min. Thirteen odour sources have been considered, including point, volume and area sources. The preliminary results show that 10 min maximum concentrations can duplicate those of the hourly simulations over wide areas of the study region. Our sub-hourly results show a better agreement with data from field olfactometry.

The Use of a Mesoscale Modeling System Together with Surface and Upper Observational Data to Estimate Hourly Benzene Impacts in a Mountainous Coastal Area

An application of the CALPUFF modeling system in the near-field in an area of very-complex topography is presented. Different configurations for both the meteorological and the dispersion simulations were tested. The RAMS high-resolution (1 km) output as well as the data from a network of surface stations and the high-resolution data from a wind profiler radar (WPR) located in the area were available for assimilation and validation purposes. The 250 m resolution three-dimensional CALMET meteorological fields, after being validated against surface and upper air data, were fed into CALPUFF to simulate the potential impacts of the emissions of a coke factory over a nearby urban area. Benzene was used as a tracer of the emitted pollutants. The results of the dispersion simulations were compared against the available hourly benzene records. Our results showed that, no matter the selected synoptic forcing for RAMS (NCEP/ECMWF), the assimilation of meteorological data into CALMET is necessary for a correct representation of the wind flows in the area, and as a consequence, for a correct representation of the actual benzene impacts.