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Abstract
In this work we use values of effective radius of cloud drop size distribution and modal radius of liquid water content generated with a parcel model with detailed treatment of liquid phase microphysical process to evaluate the warm rain formation suppression over the Amazon due to the presence of aerosols generated by forest burning. Four cases based on observations are simulated: a clean marine environment as the one observed close to Fortaleza; a clean environment as the ones observed over the apparently unpolluted Amazon forest; a environment observed during the intense burning season in the polluted part of the Amazon; and the same polluted environment observed during the transition season from dry to wet. It is shown that the model reproduces quantitatively some of the observed features of clouds in different environments. The model indicated that in very polluted environment the warm rain formation process can be completely suppressed. Nevertheless, in certain situations the formation of warm rain can still be achieved and significant amount of rainwater can be formed.
Highlights
It is well known that warm rain initiation is a complex, non-linear process (Beard and Ochs, 1992)
The different sites investigated encompass four different types of environments: 1) environments found at Northeast Brazil Coast, which receives aerosols mainly from Atlantic Ocean, due to the predominantly easterly flow. Due to their main source of cloud nuclei this environment was called “Blue Ocean”; 2) environments found at Westerly Amazon, over which the forest remains mostly untouched; 3) environments found over Rondônia, during the month of October, after significant rain events; and 4) environments observed over Mato Grosso and Rondônia states, where a large number of fires is responsible for a significant aerosol loading every year, usually until September
This work presented results form a parcel model with detailed treatment of the liquid phase microphysical process, focusing on changes in the precipitation initiation over the Amazon due to the presence of aerosols generated by forest burning
Summary
It is well known that warm rain initiation is a complex, non-linear process (Beard and Ochs, 1992). When some of them reach a certain autoconversion threshold, close to the cloud top, the first precipitation embryos are formed Those embryos start to fall through the cloud layer, forming the precipitation through collection of smallest droplets. ∫ ∫ reffe = r3f (r)dr r2f (r)dr , where f(r) is the drop size distribution function) threshold for the drop spectrum, after which the warm rain process takes place. We present a parameterization to the liquid water content (LWC) as a function of the effective radius to account for the depth a cloud needs to attain to produce the first precipitation embryo. This parameterization can be straightforward applied to the cloud depth as a function of the effective radius, since the LWC is approximately a linear function of height
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