Sector-Based Analysis of Atmospheric Rivers from Dropsondes

Atmospheric rivers are a key part of the Californian climate and over the past few years, atmospheric river reconnaissance has been conducted with the aim of improving forecasts as well as understanding the physical processes present. In this study we begin by describing a method for defining sectors within an atmospheric river (AR): post-AR, AR cold side, AR core (frontal), AR warm side, and pre-AR. Using a large collection of dropsonde data we examine the different atmospheric characteristics observed within each sector. These dropsondes have been deployed over the past 5 years and total over 1000, and with their high vertical resolution, offer a unique insight into small-scale processes.

Using modern reanalyses, we can determine the position of these dropsondes in relation to the AR core based on integrated vapor transport (IVT). We observe distinct differences in vertical profiles in parameters including thermal advection and CAPE, highlighting the different processes occurring in each sector. We also explore the sea surface temperature under the AR and calculate the temperature difference between this surface and the lowest level observed by the dropsondes (<10m). The heat flux potential varies significantly between the sectors, with the AR core exhibiting the characteristics required for a stable internal boundary layer. This method of classifying sectors of the AR will be useful for future studies, including a detailed analysis of ocean-atmosphere interactions that can affect low-level stability.