CAREER: Quantifying the Effects of Liquid Water Content on the Spectral Albedo of Snow

About This Grant

The highly reflective nature of snow means that it plays a critical role in the climate system; snow reflects solar energy and regulates global temperatures. Snow processes are especially relevant in the Arctic system, where temperatures are rising more rapidly than the global average, partially because of feedback processes that take place as snow melts. As air temperatures increase, snow begins to melt, which lowers the snow’s reflectivity and increases the amount of sunlight it absorbs. The absorbed light leads to further temperature increase, and this warming process can have far-reaching implications for our climate. Although snow is one of nature’s most reflective materials, the exact reflectivity can be quite variable. Several factors darken snow, such as larger snow grain sizes and impurities in the snow like dust, soot and algae. One factor that is not well understood is how the liquid water content in snow reduces reflectivity. This presents significant uncertainty in determining how changing snowpacks will impact the climate system, particularly in the Arctic, as wet snow becomes more prevalent due to more frequent rain on snow events and larger extent and duration of surface melt on ice sheets and glaciers. This project will enhance our understanding of wet snow reflectivity through field measurements in Minnesota and Colorado, lab experiments, and modeling. Our results will probe fundamental physical relationships and therefore, broadly apply to cold regions. As part of this work, undergraduate students will be engaged in the research projects. They will collect and analyze data in an Engineering Thermodynamics class and will design and build instrumentation for this work and to support other faculty projects in a new Engineering Fellows Program. The investigator will also share teaching materials about snow reflectivity and climate online and at a workshop for faculty at minority serving institutions. The naturally high albedo (or reflectivity) of snow provides a strong control on earth’s surface temperatures. Because of this critical role, accurately reproducing snow albedo is essential for effective climate modeling. Even in the Arctic, the already prevalent periods of wet snow are increasing because of more frequent rain on snow events and increased extent and duration of glacial surface melt; however, nearly all existing snow albedo models employ albedo schemes designed for dry snow. These models play a key role during snow melt because of the amplifying effects of the snow albedo feedback process, where melting snow leads to lower albedo, higher temperatures, and further snow melt. Therefore, explicitly incorporating the effects of liquid water content on snow albedo is a critical next step in improving model accuracy. The proposed work aims to quantify the effect of liquid water content on snow albedo, combining several approaches. 1) The investigator will conduct field-based measurements of albedo, liquid water content, grain size and snow impurities in Minnesota and at Niwot Ridge in Colorado to determine the effects of individual physical properties on the overall snow albedo. Wet snow conditions at these locations represent those that are increasingly common in the Arctic. 2) Through a new course-based undergraduate research experience (CURE) implemented in the Engineering Thermodynamics class, students will conduct laboratory measurements of the reflectance of artificial snow with controlled grain size and liquid water content. 3) The investigator will complement this work with two different modeling approaches to calculate wet snow albedo to investigate an array of snow conditions and inform potential changes to physically based snow albedo models. Studying these phenomena in different landscapes, in the laboratory, and in simulations will allow us to extrapolate our understanding of wet snow albedo to cold regions more broadly, particularly in the rapidly changing Arctic. This project will support the development of students through multiple avenues by providing opportunities to engage in research and build their scientific identities. The investigator will develop an Engineering Fellows Program in which students work with faculty over the course of the year on a design project, in addition to enrolling in a professional development seminar course. The investigator will also partner with the Ice Drilling Program Education team to serve as a visiting scientist in the School of Ice workshop and create an online Virtual Field Lab on snow albedo. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.