Improvement in the Accuracy of Back Trajectories Using WRF to Identify Pollen Sources in Southern Iberian Peninsula

Airborne pollen transport at micro-, meso-gamma and meso-beta scales must be studied by atmospheric models, having special relevance in complex terrain. In these cases, the accuracy of these models is mainly determined by the spatial resolution of the underlying meteorological dataset. This work examines how meteorological datasets determine the results obtained from atmospheric transport models used to describe pollen transport in the atmosphere. We investigate the effect of the spatial resolution when computing backward trajectories with the HYSPLIT model. We have used meteorological datasets from the WRF model with 27, 9 and 3 km resolutions and from the GDAS files with 1 ° resolution. This work allows characterizing atmospheric transport of Olea pollen in a region with complex flows. The results show that the complex terrain affects the trajectories and this effect varies with the different meteorological datasets. Overall, the change from GDAS to WRF-ARW inputs improves the analyses with the HYSPLIT model, thereby increasing the understanding the pollen episode. The results indicate that a spatial resolution of at least 9 km is needed to simulate atmospheric flows that are considerable affected by the relief of the landscape. The results suggest that the appropriate meteorological files should be considered when atmospheric models are used to characterize the atmospheric transport of pollen on micro-, meso-gamma and meso-beta scales. Furthermore, at these scales, the results are believed to be generally applicable for related areas such as the description of atmospheric transport of radionuclides or in the definition of nuclear-radioactivity emergency preparedness

The potential impact of upper stratospheric measurements on sub-seasonal forecasts in the extra-tropics

This chapter examines the potential improvements in tropospheric weather forecasts that might arise from an enhanced representation of the upper stratospheric state. First, the chapter reviews current operational practice regarding observation of the atmosphere and the relative paucity of observations in the altitude range 40–70 km. Then, we describe some idealised model calculations to quantify the potential gain in skill available from improved monitoring in this region. The idealised model experiments use a relaxation technique with the Hadley Centre General Environment Model, to assess the potential gain in skill from observations both of the whole stratosphere and the upper stratosphere. At weather forecasting timescales (up to forecast day 30), better knowledge of the stratosphere, close to the onset of a sudden stratospheric warming, improves forecasts of the tropospheric northern annular mode. Whole-stratosphere information significantly improved average surface temperature anomalies over northern North America, whilst upper stratosphere information improved anomalies over Central Siberia. These results suggest any new observational technique which can contribute to monitoring of the 40–70 km region would likely benefit tropospheric forecast skill during wintertime

Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation

The recent European mega-heatwaves of 2003 and 2010 broke temperature records across Europe(1-5). Although events of this magnitude were unprecedented from a historical perspective, they are expected to become common by the end of the century(6,7). However, our understanding of extreme heatwave events is limited and their representation in climate models remains imperfect(8). Here we investigate the physical processes underlying recent mega-heatwaves using satellite and balloon measurements of land and atmospheric conditions from the summers of 2003 in France and 2010 in Russia, in combination with a soil-water-atmosphere model. We find that, in both events, persistent atmospheric pressure patterns induced land-atmosphere feedbacks that led to extreme temperatures. During daytime, heat was supplied by large-scale horizontal advection, warming of an increasingly desiccated land surface and enhanced entrainment of warm air into the atmospheric boundary layer. Overnight, the heat generated during the day was preserved in an anomalous kilometres-deep atmospheric layer located several hundred metres above the surface, available to re-enter the atmospheric boundary layer during the next diurnal cycle. This resulted in a progressive accumulation of heat over several days, which enhanced soil desiccation and led to further escalation in air temperatures. Our findings suggest that the extreme temperatures in mega-heatwaves can be explained by the combined multi-day memory of the land surface and the atmospheric boundary layer