The Importance and Current Limitations of Planetary Boundary Layer (PBL) Retrieval from Space

There is an established need for improved PBL remote sounding over land for hydrology, land-atmosphere (L-A), PBL, cloud/convection, pollution/chemistry studies and associated model evaluation and development. Most notably, the connection of surface hydrology (through soil moisture) to clouds and precipitation relies on proper quantification of water’s transport through the coupled system, which is modulated strongly by PBL structure, growth, and feedback processes such as entrainment. In-situ (ground-based or radiosonde) measurements will be spatially limited to small field campaigns for the foreseeable future, so satellite data is a must in order to understand these processes globally. The scales of these applications require diurnal resolution (e.g. 3-hourly or finer) at <100m vertical and 1-10km spatial resolutions in order to assess processes driving land-PBL coupling and water and energy cycles at their native scales. Today’s satellite sensors do not reach close to any of those targets in terms of accuracy or resolution. Unfortunately, there is very little attention or planning (short or long-term) in place for improving lower tropospheric sounding over land. GOES-R has the required diurnal coverage, but very little improvement over previous GOES sensors in terms of resolving the PBL (structure or evolution). AIRS/IASI are the most promising in terms of spectral resolution but have not been tailored for PBL retrieval and rather are focused on mid-upper level levels. Lidar (e.g. CALIPSO) does will with vertical resolution, but is strongly limited in return time and spatial resolution (‘curtains’) and does not provide state information. Thus, each of these sensors has some advantages, but even more limitations that make them impractical for PBL and L-A studies. As a result of this lack of PBL-focused missions, PBL and L-A interactions have been identified as ‘gaps’ in current programmatic focal areas. It is therefore timely to assess how these technologies can be leveraged, combined, or evolved in order to form a dedicated mission or sub-mission to routinely monitor the PBL on diurnal timescales. In addition, improved PBL monitoring from space needs to be addressed in the next Decadal Survey. In this poster, the importance of PBL information (structure, evolution) for L-A coupling diagnostics and model development will be summarized. The current array of PBL retrieval methods and products from space will then be assessed in terms of meeting the needs of these models, diagnostics, and scales, with a look forward as to how this can and must be improved through future mission and sensor design.