Abstract
Abstract. A plume rise algorithm for wildfires was included in WRF-Chem, and applied to look at the impact of intense wildfires during the 2004 Alaska wildfire season on weather simulations using model resolutions of 10 km and 2 km. Biomass burning emissions were estimated using a biomass burning emissions model. In addition, a 1-D, time-dependent cloud model was used online in WRF-Chem to estimate injection heights as well as the vertical distribution of the emission rates. It was shown that with the inclusion of the intense wildfires of the 2004 fire season in the model simulations, the interaction of the aerosols with the atmospheric radiation led to significant modifications of vertical profiles of temperature and moisture in cloud-free areas. On the other hand, when clouds were present, the high concentrations of fine aerosol (PM2.5) and the resulting large numbers of Cloud Condensation Nuclei (CCN) had a strong impact on clouds and cloud microphysics, with decreased precipitation coverage and precipitation amounts during the first 12 h of the integration. During the afternoon, storms were of convective nature and appeared significantly stronger, probably as a result of both the interaction of aerosols with radiation (through an increase in CAPE) as well as the interaction with cloud microphysics.
Highlights
It is well known that Alaska wildfires have a strong impact on air pollution from the local up to the hemispheric scale
The model correctly simulated the smoke in the western part of the domain, which must have originated from the Alaska fires, since no boundary conditions were available for the large domain (D1)
The model complexity in our study is already significantly increased compared to models commonly used in operational environments, yet we feel it still requires a more complete representation of the processes involved
Summary
It is well known that Alaska wildfires have a strong impact on air pollution from the local up to the hemispheric scale. Wildfires occur throughout the US, the largest and greatest number of fires occur in Alaska, the southeastern United States, and the West. Wildfires burn vast areas almost every summer, and are a significant agent of change in the boreal forest ecosystem. Flammable material like dry tundra and leaves and needles at the floor of the boreal forests are well preserved during cold and dry seasons. As a result, both lightning- and humancaused wildfires together burn an average of 400 000 hectares annually. Even small Alaska fires may contribute significantly to air pollution
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