This paper considers the feasibility of numerical simulation of large-scale atmospheric transport of allergenic pollen. It is shown that at least small grains, such as birch pollen, can stay in the air for a few days, which leads to a characteristic scale for their transport of approximately 10(3) km. The analytical consideration confirmed the applicability of existing dispersion models to the pollen transport task and provided some reference parameterizations of the key processes, including dry and wet deposition. The results were applied to the Finnish Emergency Dispersion Modelling System (SILAM), which was then used to analyze pollen transport to Finland during spring time in 2002-2004. Solutions of the inverse problems (source apportionment) showed that the main source areas, from which the birch flowering can affect Finnish territory, are the Baltic States, Russia, Germany, Poland, and Sweden-depending on the particular meteorological situation. Actual forecasting of pollen dispersion required a birch forest map of Europe and a unified European model for birch flowering, both of which were nonexistent before this study. A map was compiled from the national forest inventories of Western Europe and satellite images of broadleaf forests. The flowering model was based on the mean climatological dates for the onset of birch forests rather than conditions of any specific year. Utilization of probability forecasting somewhat alleviated the problem, but the development of a European-wide flowering model remains the main obstacle for real-time forecasting of large-scale pollen distribution.

A birch pollen emission model is described and its main features are discussed. The development of the model is based on a double-threshold temperature sum model that describes the propagation of the flowering season and naturally links to the thermal time models to predict the onset and duration of flowering. For the flowering season, the emission model considers ambient humidity and precipitation rate, both of which suppress the pollen release, as well as wind speed and turbulence intensity, which promote it. These dependencies are qualitatively evaluated using the aerobiological observations. Reflecting the probabilistic character of the flowering of an individual tree in a population, the model introduces relaxation functions at the start and end of the season. The physical basis of the suggested birch pollen emission model is compared with another comprehensive emission module reported in literature. The emission model has been implemented in the SILAM dispersion modelling system, the results of which are evaluated in a companion paper.

No abstract

The paper presents an assessment of birch pollen seasons in Finland and Russia. The re-analysis covered the period from 1994 to 2005 and was focused on suspected long-range transport events that were recorded both in Moscow and at several Finnish sites. In order to trace the origin of airborne pollen before the onset of local pollination, we used both aerobiological and phenological observations combined with forward and adjoint (inverse) dispersion model simulations. It is shown that, although the Moscow region is surrounded by extensive birch forests, it still receives substantial amounts of foreign pollen before local pollination. In the Moscow region, the sources of long-range-transported pollen are in the south and south-west, sometimes even in the east. In Finland, there are frequently cases, before the local flowering season, in which Finnish territory receives Russian pollen; however in the opposite direction, from Finland to the Moscow region, no transport episodes were unequivocally registered. Analysis of the end of the seasons was more problematic, due to contributions to pollen observations from local sources; this results in difficulties in the reliable identification of the long-range transport episodes. Apart from its short-term effects on the pollen seasons, long-range transport can have substantial impacts on the exchange of genetic material within Europe. A quick atmospheric pathway for gene transport can be important for adaptation of plants to a changing climate.

No abstract

In an experimental set‐up in and around Helsinki, Finland (60°N, 25°E), we have detected pest insect immigration using weather radars and insect traps in the field. This study was part of a project to develop a system to give warning of a possible arrival of long‐range migrant insect pests. Bird‐cherry aphid, Rhopalosiphum padi, and diamondback moth, Plutella xylostella, were found on the ground following migrations in warm airstreams at the end of May 2007. This migration episode was successfully forecast by the meteorologists in the project team. For the summer 2008, we developed a pest insect immigration alarm system based on SILAM, a Finnish Meteorological Institute atmospheric dispersion model. The first important pest insect immigration occurred in late June, bringing bird‐cherry aphids. Our alarm system correctly produced a warning of this immigration. We studied the migration path in the observed events in 2007 and 2008 with the help of the atmospheric dispersion model. Weather radars frequently showed rain echo over the area, but there was also a lot of echoes originating from the migrating insects. Using the polarimetric weather radar in Helsinki, we could differentiate insects from other sources of echoes. Insects were common in layers below 1 km, and were observed up to height of about 2.5 km. Using Doppler weather radars we were able to observe the speed and direction of the migration. The experiment showed that an atmospheric dispersion model is an effective tool for predicting the movement of airborne migrants. The alarm system would work still better, if the sources of the immigrants were known in more detail. In addition, the very simple modelling of airborne migration should be refined. Weather radars, and especially polarimetric systems, are able to detect insect migrations and reveal details of the phenomenon not obtainable by other means.

This study analyses the spatial and temporal distribution of regional and long-range transported birch (Betula L.) pollen in Lithuania and the neighbouring countries. The potential long-range transport cases of birch pollen in Lithuania were analysed for the whole period of available observations, 2004-2007. The birch pollen was recorded at three measurement stations in Lithuania by using Hirst-type volumetric spore traps. The phenological observations in Lithuania were also used for the detection of potential long-range transport-induced episodes. Two variants of the regional and continental scale atmospheric dispersion model SILAM (Lagrangian and Eulerian) in an adjoint mode (used for inverse dispersion modelling and data assimilation), and the trajectory model HYSPLIT were employed to evaluate the source origins of the observed pollen. During four seasons in 2004-2007, we found in total 24 cases, during which remarkable pollen concentrations were recorded before the local flowering season. According to modelling, most of these were originated from the sources outside Lithuania: Latvia, southern Sweden, Denmark, Belarus, Ukraine and Moldova, possibly, also coastal regions of Germany and Poland. Two episodes were attributed to local early-flowering birch trees. The spatial and temporal patterns of the long-range transport of early pollen to Lithuania were found out to be highly variable; the predicted source regions for the cases considered were similar only for some dates in 2004 and 2006. During the analysed period, we found both cases, in which the predictions of the SILAM model variants and those of the HYSPLIT model were similar, and cases, in which there were substantial differences. In general, for complicated atmospheric circulation patterns the model predictions can be drastically different, with a tendency of trajectory model to fail reproducing the key episode features.

Abstract. This paper presents the first ensemble modelling experiment in relation to birch pollen in Europe. The sevenmodel European ensemble of MACC-ENS, tested in trial simulations over the flowering season of 2010, was run through the flowering season of 2013. The simulations have been compared with observations in 11 countries, all members of the European Aeroallergen Network, for both individual models and the ensemble mean and median. It is shown that the models successfully reproduced the timing of the very late season of 2013, generally within a couple of days from the observed start of the season. The end of the season was generally predicted later than observed, by 5 days or more, which is a known feature of the source term used in the study. Absolute pollen concentrations during the seaPublished by Copernicus Publications on behalf of the European Geosciences Union. M. Sofiev et al.: MACC regional multi-model ensemble simulations of birch pollen dispersionson were somewhat underestimated in the southern part of the birch habitat. In the northern part of Europe, a recordlow pollen season was strongly overestimated by all models. The median of the multi-model ensemble demonstrated robust performance, successfully eliminating the impact of outliers, which was particularly useful since for most models this was the first experience of pollen forecasting.