Abstract
Abstract. We use the global circulation model ECHAM6 extended by the aerosol module HAM2 to simulate global patterns in wildfire emission heights. Prescribed plume heights in ECHAM6 are replaced by an implementation of a simple, semi-empirical plume height parametrization. In a first step, the global performance of the plume height parametrization is evaluated for plumes reported in the Multiangle Imaging Spectroradiometer (MISR) Plume Height Project (MPHP) data set. Our results show that the parametrization simulates a largely reasonable global distribution of plume heights. While the modeled global mean plume height (1411 ± 646 m) is in good agreement with the observed mean (1382 ± 702 m), the upper and lower tails of the plume height distribution tend to be slightly underrepresented. Furthermore, we compare plume heights simulated by the simple parametrization to a more complex, analytical plume model. Major differences in global plume height distributions are found for the lowest 1.5 km, but reasonable agreement is observed for higher plumes. In a second step, fire radiative power (FRP) as reported in the global fire assimilation system (GFAS) is used to simulate plume heights for observed fires globally for the period 2005–2011. The global fraction of simulated daytime plumes injecting emissions into the free troposphere (FT) ranges from 3.7 ± 0.7 to 5.2 ± 1.0 %. This range is comparable to results from observational studies, but it is much lower than results for prescribed plume heights in the ECHAM6-HAM2 standard setup. Nevertheless, occasionally deep emission injections exceeding 5–7 km in height are simulated for intense fires and favorable meteorological conditions. The application of a prescribed diurnal cycle in FRP turns out to be of minor importance. For a hypothetical doubling in FRP, moderate changes in plume heights of 100–400 m are simulated. These small changes indicate that a potential future increase in fire intensity will only slightly impact the emission heights on a global scale.
Highlights
Vegetation fires, either anthropogenic or ignited naturally by lightning, affect the climate through complex interactions between the biosphere and the atmosphere
No nudging against observations is applied for these simulations, because we aim to investigate the basic skills of the ECHAM6-HAM2 model to capture the spectrum of plume heights, not to reproduce individual plume observations
In this study prescribed plume heights in ECHAM6-HAM2.2 have been replaced by the implementation of different versions of a simple, semi-empirical plume height parametrization after Sofiev et al (2012)
Summary
Vegetation fires, either anthropogenic or ignited naturally by lightning, affect the climate through complex interactions between the biosphere and the atmosphere. Aerosols and trace gases emitted into the atmosphere are key parameters of the overall fire climate impact (Bowman et al, 2009; Ward et al, 2012; Keywood et al, 2013). Aerosol particles emitted from fires are known to impact a wide range of atmospheric processes including radiative transfer, atmospheric chemistry and cloud micro-physical processes (Twomey, 1977; Crutzen and Andreae, 1990; Heald et al, 2014). A crucial parameter that has been identified to influence the lifetime of aerosols and potentially their climate impact is the fire emission height, i.e., the altitude above the surface at which fire smoke plumes release emissions into the atmosphere.
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