National Aeronautics and Space Administration

In response to the NASA ROSES 2021 Decadal Survey Incubation (DSI) program, the proposal entitled “Exploring Strategies and Developing PBL Data Assimilation Including PBL Height from Multiple Observing Systems in the Global GEOS System” was submitted and selected. Several GMAO members are involved in this proposal, including PI Yanqiu Zhu, Co-I Nathan Arnold, and Collaborators Erica McGrath-Spangler, Arlindo Da Silva, Andrea Molod, Amal El Akkraoui, and Ricardo Todling.

The 2018 National Academies of Sciences, Engineering, and Medicine (NASEM) Earth Science Decadal Survey designated the Planetary Boundary Layer (PBL) as a key Earth science targeted observable. There is an urgent need for global modeling and data assimilation (DA) development in order to utilize Program of Record (POR) observations, assess their impacts, and identify gaps to be filled by future PBL missions. However, current global data assimilation centers severely under-utilize observations of the boundary layer and estimates of PBL height (PBLH), in particular, are completely unused. This leaves analyses and forecasts of the PBL poorly constrained and hinders assessment of future mission architectures. In part, this under-utilization is due to observation limitations. For example, Global Navigation Satellite System Radio Occultation (GNSS-RO) data are currently either not used or down-weighted by being given very large observation errors in the lower troposphere due to uncertainties in refractivity and bending angle in moist air.

Traditional DA methodologies also tend to focus on amplitude error, whereas error in the PBL is often positional, such as a misplaced inversion height. As a consequence, current DA algorithms tend to distort inversion structures. A further issue is that model parameterizations can rapidly compensate for analysis tendencies, effectively reducing retention of observation information. In this proposal, we present novel approaches to address all these issues.

The overall objective is to develop PBL DA capabilities in NASA Global Earth Observing System (GEOS) to support the assessment and use of future PBL observations. In this study, the team will assimilate PBLH from multiple observing systems to improve the PBL thermodynamic structure, identify data gaps in the existing POR, and build the platform for future routine global monitoring of PBLH data. They will explore an innovative approach to use GNSS-RO data in the lower troposphere, investigate the interactions and combined impacts from surface-sensitive radiances, PBLH data, and GNSS-RO data in the GEOS system. They will also develop methods to improve retention of information from PBL observations by adjusting model turbulence length scales.

The 2021 DSI program is funded by NASA's Earth Science Technology Office.