The International H20 Project (IHOP_2002) was a large field experiment held in the southern High Plains for the purpose of obtaining an improved characterization of the time-varying three-dimensional water vapor field and to determine its importance in the understanding and prediction of convective processes. IHOP incorporated an extensive array of ground-based and airborne systems for making detailed measurement of the water vapor field, as well as a host of high-resolution numerical models that ingested some of these observations to produce real-time forecast guidance. These systems were well-suited for delivering what is probably the most intensive set of observations ever collected of the evolving structure and dynamics of bores and solitons.

Two particularly well-documented bore events occurred on 4 June 2002. Bore A occurred in association with an outflow boundary, whereas bore B (which occurred ~4h later) was generated along a southward-advancing cold front. Multiple deep convective cells ahead of the front appeared to have been initiated by the second bore. In both cases, S-Pol radar data show a “fine line” in the reflectivity fields, and that parallel lines with a spacing of ~10 km developed to its rear. This behavior is characteristic of solitary waves within a soliton, but is in contrast to that exhibited by Kelvin-Helmholtz shear waves, which typically progress rearwards relative to the leading fine line. An ingenious method to retrieve surface-layer refractivity changes from the S-Pol data revealed a narrow band of pronounced warming and/or drying along the leading fine line for bore A that disappeared once solitary waves began to develop within the bore system. In contrast, interferometric observations from a collocated AERI system showed that cooling and moistening occurred above the surface layer with the passage of both bores; detailed flight-level data from a Wyoming King Air aircraft showed similar behavior for bore B. A reverse sequence of events occurred with bore B, in that the refractivity signature became apparent only as the soliton devolved into a single line suggestive of an undular bore. These observations from both bore events suggest the hypothesis that surface layer mixing processes diminish once solitary waves develop within a bore. An impressive set of measurements from an FM-CW radar, Raman lidar, HARLIE and GLOW lidar systems, the MAPR radar system for measuring vertical motions, and a surface mesonet array showed that the solitary waves were amplitude ordered with well-defined vertical circulations and multiple-layered structures or filaments. Tentative hypotheses resulting from the synthesis of the observations are presently being developed for testing with high-resolution three-dimensional and idealized models initialized with the IHOP data.