Towards Obtaining Global PBL Height Retrievals from Multi-instrument, Ground-based, Observations

The need for estimates of PBL height that are high in temporal frequency and global in scope has been made clear in the 2017 Decadal Survey and many recent studies. Recent work has also shown quite clearly that PBL heights can be reliably retrieved from a widely varying set of instruments that are ubiquitous and autonomous. These include, among others, networks of ceilometers, lidars and radar wind profilers. Because none of these instruments alone can provide the spatial density necessary for a global PBL observing system, there is a need for combined multi-instrument surface observations. Consolidating all these estimates requires two important elements. The first is establishing common retrieval algorithms and methodologies with high fidelity in order to obtain PBL heights on a global scale. The second is the ability to reconcile differences among PBL heights retrieved from different instruments, which can be done using data from sites with collocated instruments. We present here results from work on both of these elements.

First, we present hourly PBL heights based on archived wind profiler data from a series of networks located around the globe. An algorithm to estimate PBL heights was developed and successfully applied to a large number of stations located in the U. S. Central Plains region using observations obtained over a 20-year period. The new global dataset of PBL height estimates, called GRWP-PBLH: Global Radar Wind Profiler Planetary Boundary Layer Height, uses the same algorithm and it is available from https://grwp-pblh.hunter.cuny.edu/. This work extends the U. S. analysis by using data from extensive operational networks located in Australia, Europe and Japan during a 10-year period (2009 - 2020).

Second, we discuss case studies from an intercomparison of PBL height retrievals from a ceilometer, a lidar and a radar wind profiler collocated at the Howard University Beltsville Campus in Maryland for the months of July 2011, during DISCOVER-AQ, and February 2020, when a prescribed fire took place in northeastern Virginia. We use ancillary data to allow for a detailed analysis of the different retrievals and to assess their potential for more accurately capturing the height of the PBL under varying meteorological conditions.

The results of our case studies allow for a discussion of the limitations and errors associated with the retrievals from each instrument and will aid in providing recommendations for exploiting the synergy among them.The global scope of the GRWP-PBLH dataset, along with similar datasets from networks of ceilometers and lidars (e.g. Unified Ceilometer Network and Micro Pulse Lidar Network), allows for a wide geographical analysis of connections to seasonality, to latitude, proximity to oceans and synoptic variability.