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Toll V.,University of Tartu | Toll V.,Estonian Environment Agency formerly EMHI | Mannik A.,University of Tartu | Mannik A.,Estonian Environment Agency formerly EMHI | And 3 more authors.
Atmospheric Research | Year: 2014

On August 8, 2010, a derecho swept over Northern Europe, causing widespread wind damage and more than 2 million Euros in economic loss in Estonia during its most destructive stage. This paper presents a modelling study of the derecho-producing storm utilising the Hirlam Aladin Research for Mesoscale Operational Numerical Weather Prediction in Europe (HARMONIE) model. The model setup is chosen to mimic near-future, nearly kilometre-scale, operational environments in European national weather services. The model simulations are compared to remote sensing and in situ observations. The HARMONIE model is capable of reproducing the wind gust severity and precipitation intensity. Moreover, 2.5-km grid spacing is shown to be sufficient for producing a reliable signal of the severe convective storm. Storm dynamics are well simulated, including the rear inflow jet. Although the model performance is promising, a strong dependence on the initial data, a weak trailing stratiform precipitation region and an incorrect timing of the storm are identified. © 2014 Elsevier B.V.


Toll V.,University of Tartu | Toll V.,Estonian Environment Agency formerly EMHI | Reis K.,University of Tartu | Ots R.,University of Tartu | And 6 more authors.
Atmospheric Environment | Year: 2015

Persistent high pressure conditions over the European part of Russia during summer 2010 were responsible for an extended period of hot and dry weather, creating favourable conditions for severe wildfires. The chemical transport model SILAM is used to simulate the dispersion of smoke aerosol for this case. Aerosol fields from SILAM are compared to the Monitoring Atmospheric Composition and Climate (MACC) reanalysis. Moreover, the model output is compared to in situ and remote sensing measurements, paying particular attention to the most intense fire period of August 7 to 9, when the plume reached the Baltic countries and Finland. The maximum observed aerosol optical depth was more than 4 at 550nm during this time. The aerosol distributions from the SILAM run and the MACC reanalysis are subsequently used in meteorological simulations using the Hirlam Aladin Research for Mesoscale Operational Numerical Weather Prediction in Euromed (HARMONIE) model. The modelling results show a significant reduction of the daily average shortwave radiation fluxes at the surface (up to 125W/m2) and daily average near-surface temperature (up to 4°C) through the aerosol direct radiative effect. The simulated near-surface temperature and vertical temperature profile agree better with the observations, when the aerosol direct radiative effect is considered in the meteorological simulation. The boundary layer is more stably stratified, creating poorer dispersion conditions for the smoke. © 2015 Elsevier Ltd.


Toll V.,University of Tartu | Toll V.,Estonian Environment Agency formerly EMHI | Mannik A.,University of Tartu | Mannik A.,Estonian Environment Agency formerly EMHI
Atmospheric Research | Year: 2015

On August 8, 2010, a severe derecho type thunderstorm in the Baltic Sea region coincided with smoke from wildfires in Russia. Remarkable smoke aerosol concentrations, with a maximum aerosol optical depth of more than 2 at 550nm, were observed near the thunderstorm. The impact of the wildfire smoke on the thunderstorm through direct radiative effects was investigated using the Hirlam Aladin Research for Mesoscale Operational Numerical Weather Prediction in Euromed (HARMONIE) model. HARMONIE was successfully able to resolve the dynamics of the thunderstorm, and simulations that considered the influence of the smoke-related aerosols were compared to simulation without aerosols. As simulated by the HARMONIE model, the smoke reduced the shortwave radiation flux at the surface by as much as 300W/m2 and decreased the near-surface temperature by as much as 3°C in the vicinity of the thunderstorm and respectively 100W/m2 and 1°C in the thunderstorm region. Atmospheric instability decreased through the direct radiative effect of aerosols, and several dynamic features of the simulated thunderstorm appeared slightly weaker. © 2014 Elsevier B.V.

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