CIMMS DDRF - Boundary Layer Height

My Role

• Led the design, organization, and 4-week deployment of two mobile boundary layer profiling platforms across three sites.
• Role included oversight, management, data collection/management, and development of new BL height detection algorithms.

PBLTops: Evaluating Polarimetric Retrievals of Boundary Layer Height Using State-of-the-Art Boundary Layer Profiling

Owing to the sparse distribution of atmospheric profilers, numerous studies have sought to use radar detection of Bragg scattering to observe the evolution of planetary boundary layer (BL) height. While radar reflectivity can denote the presence of Bragg scattering (Heinselman et al. 2009; Elmore et al. 2012; Melnikov et al. 2013), biota can mask this signature. Using specialized scanning strategies, Melnikov et al. (2011) showed that dual-polarization radar can help combat this issue, owing to the large difference in intrinsic differential reflectivity (ZDR) between Bragg scattering and biota. This approach was extended to the operational WSR-88D network by Banghoff et al. (2018; hereafter B18) using quasi-vertical profiles obtained from azimuthal averaging (Ryzhkov et al. 2016) and offers the promise of national, real-time estimates of BL height. However, the B18 method was only validated using twice-daily radiosonde observations, thus obscuring its efficacy for retrieving BL height estimates during periods of evolution and complex structure (e.g., morning/evening transitions, residual layers, etc.).

Our work had four primary objectives: (1) validate the polarimetric B18 method using specialized independent measurements from both CLAMPS; (2) extend validation times to include important BL evolution periods beyond synoptic sampling times and identify failure periods and regimes; (3) contextualize and interpret signatures observed in B18 using novel near-continuous data (e.g., overnight signatures); and (4) quantify the skill of the B18 method.

BL height and its evolution can be tracked by the synergistic integration of instruments onboard both CLAMPS platforms. The combination of high-resolution thermodynamic and kinematic profilers can document BL structures such as inversions and mixing layers and their evolution on the order of minutes (Wagner et al. 2019). We conducted a 4-week observation period, split into two 2-week blocks. During block 1, each CLAMPS deployed near KTLX at a radar-adjacent site (0-5 km) and a radar-distant site (10-20 km), respectively. During block 2, the radar-distant CLAMPS repositioned to a radar-adjacent site at another operational radar (KSHV). Our observational approach provides us one continuous 4-week time series within 5 km of KTLX, enabling the analysis required for objectives 1 and 2. Objectives 3 and 4 used all data collected at all sites. Additionally, by moving the second CLAMPS platform between the two blocks, we extended our efforts to include evaluation of impacts due to distance from radar and the local climatology or land-use characteristics, which may modify expected BL evolution.

Quantification of BL height is critical to many research and operational efforts. The proposed research has the potential to advance and improve a method by which real-time nationwide observations of BL height can be collected, and a national climatology of BL height could be built. Both real-time observations and climatological data on a national scale offer research and operational applications relevant to CIMMS research themes. This work directly includes weather radar research and development through the evaluation and potential improvement of an operationally relevant retrieval algorithm, which can expand the capability of the existing operational network at a relatively low cost. Continuously available BL height observations could also support storm-scale and mesoscale modeling research and development by providing an unprecedented dataset for model validation and development efforts. Finally, provision of improved BL height information can aid both human and numerical forecast improvements research and development, especially since BL height is an important indicator of mixing layers and convection potential in severe weather environments. Beyond CIMMS-specific research foci, improved characterization of BL height can also be important for air quality forecasting, renewable resource characterization, wildfire prediction, and more. In total, the research proposed here is capable of far-reaching impacts. Our ability to complete this research in a short time frame with relatively low costs is unique to the state-of-the-art facilities and relevant expertise available at CIMMS.