EOMF-16. Analysis of Updraft Characteristics from a Micro-pulsed Doppler Lidar During FIREX-AQ
Climate change has ushered in an age of extremes that has led to increased costs at all levels of government, displacements in population (e.g., population dispersal), and the loss of life. Extreme events such as natural disasters caused by wildfires represents one such extreme with an overwhelming contribution in California as well as a significant fraction to the remaining states that make up the western half of CONUS. It was estimated in 2018 that California spent $148 billion in costs from wildfires, or 1.5% of its gross domestic product (GDP) - the fifth largest economy in the world as of the same year. In order to limit these costs will require a plan that can be enacted ahead of time that elicits a quick response toward wildfire containment. One way to improve our response time is through improving near real-time models to guide policymakers and first responders on coordinating containment field strategies and evacuation routes. This can be done by participating in multi-agency efforts that plan targeted observation strategies centered over active wildfire areas. The Fire Influence on Regional-to Global Experiments - Air Quality (FIREX_AQ) campaign in July-August, 2019 represents one such example with participation from the Cooperative Institute for Research in Environmental Sciences (CIRES) aimed at improving our understanding about how wildfires behave under different environmental conditions, and what the local and non-local impacts are on human health as it relates to air quality. A component of this effort was sampling the fine structure of updrafts and downdrafts embedded in plumes extended over wildfire sources at a relatively slow cruising speed (60-m/s) and at a high vertical (62-m) and temporal resolution (10-Hz). Available scanning modes to probe wildfires included a motion compensated stare at nadir and a 15 degree off-nadir conically scanning velocity azimuth display (VAD) configuration. While the VAD setting allowed for the determination of the inflow/outflow characteristics near wildfires, the nadir pointing configuration detailed the updrafts/downdrafts embedded in the plume. The latter setting was used to develop a technique for isolating updrafts over wildfires to examine the geometry, lateral mixing, and vertical and horizontal variability centered over energetic updraft cores. Measurements of fire temperature was used to zoom in on probable sources while instances of positive motion above the sources were used to isolate updrafts. Given that wildfire behavior is rooted in the planetary boundary layer (PBL), and many questions remain as to how wildfires interact with the environment, then a closer examination of the fine structure details is in order. The research presented classifies updrafts based upon characteristic behavior and suspected interactions that updrafts have with the environment. This is done first by analyzing cases where downward motion is evident at the flanks of isolated updrafts. Examples are shown to highlight the profile structure of counter-rotating vortices that can develop during updraft ascent and recirculate with the updraft that generates them. A second component of this work examines instances where horizontal meandering is evident, either through shifting in the vertical velocity maximum or in the updraft plume itself, which is then used to determine the phase of change of the horizontal meandering with height if, and only if, the horizontal meandering can be modeled approximately by a sinusoid. Using derived phase information, a fire whirl diagnostic is developed following key assumptions and conditions outlined in the presentation. Although results are preliminary, the work that will be presented shows promise at targeting otherwise elusive dynamics that alter the updraft structure over relatively short time-scales - an important component of how transport is modified locally. These results are also timely given the planned effort that will be underway in August - namely, the California Fire Dynamics Experiment (CalFiDE).