Comparison of frost depth penetration based on an updated Air-Freezing Index and on USCRN soil temperatures

Previous estimates of soil frost depth have been based on indices using air temperature. With recent deployments of new soil instrumentation across the U.S. Climate Reference Network, more accurate estimates of frost depth are now possible. At sites that have soil properties that can sustain full installation protocol, probes were installed at 5cm, 10cm, 20cm, 50cm, and 100cm soil depths. Soil temperature measurements at each of these depths allow for direct observations of frozen soil. This research compares USCRN soil temperature observations with recently completed derived soil frost depths from the air-freezing index generated from the newly completed 1981-2010 climate normals. Our research will compare Air-Freezing Index's current estimation of the depth of frost penetration with USCRN soil temperature observations, and use these results to improve the methodology of estimating frost depth penetration using daily mean air temperatures. Primary focus will be on improving the existing formula that uses air temperature to estimate the depth of frost penetration. This will be completed by looking at the correlation between USCRN soil temperature observations against their respective estimated AFI values. These enhancements will provide the construction industry with more accurate data and maps to guide the building of shallow foundations in the contiguous United States.