Quantifying evaporation of precipitation below the cloud base using a vertically pointing radar
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Evaporation is the transformative process by which liquid water becomes water vapor. This is a very complex process that many times gets parameterized or even omitted in model forecasting. Previous work has been undertaken to quantify evaporation in an effort to overcome the lack of accountability for evaporation in forecasting. This is especially important for rainfall accumulation forecasting. This study aims to use a micro rain radar and radiosonde data from weather balloon flights to obtain observed data that can be used to calculate evaporation rates. Discussed here will be the variables that make evaporation so complex and how these variables can be better quantified attempting to calculate evaporation rates. Case studies are presented here with an example case study taken from the 29th of July 2018 in which balloon flights were performed ahead of an approaching frontal system. This was done in order to analyze the erosion of low-level dry layers as the system approaches. In doing so, the evolution of raindrop sizes can be studied between the cloud base and the surface. Also analyzed is how the evolution changes over time as the dry layer gets eroded by moisture advection ahead of the approaching storm system. A drop size to drop size viewpoint is discussed along with a look at total liquid water content which is a crucial variable in the quantification of evaporation. Finally, we used the lens of individual drop sizes and total liquid water content to analyze the effects of initial DSD height, averaged relative humidity, and vertical velocity on the evaporation process.
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