Characterizing the Vertical Stratification of the Earth’s Planetary Boundary Layer with GNSS Radio Occultation
Presenter:
Chi Ao
JPL
JPL, UCLA
Talk
The planetary boundary layer (PBL) is the lowest 1-2 km of the atmosphere that interacts directly with the surface. As such, it mediates the exchanges of mass, momentum, and energy between the surface and the free troposphere. It plays a significant role in a number of important Earth science areas including extreme weather, air quality, and climate feedback. The 2017–2027 National Academy of Sciences Decadal Survey for Earth Science and Application identified the PBL as a key “target observable”. Recognizing the complexity of the PBL and the challenges in sensing this region from space, the Decadal Survey recommends further study of the PBL and candidate instrument technologies under the “Incubation Program”.
GNSS radio occultation (RO) from COSMIC and other missions has demonstrated strong potential in sensing the PBL from space. In particular, multiple studies have shown that GNSS-RO profiles can be used to infer PBL heights over the globe. The algorithms used to estimate the PBL heights are based on the strong vertical change in variables such as specific humidity, temperature, refractivity, or bending angles in the transition from the PBL to the free troposphere. These methods are especially effective over the subtropics where the transitions can be very sharp.
In this study, we investigate the vertical structure of the PBL retrieved from GNSS-RO. We define a decoupling parameter that characterizes the change in specific humidity within the PBL. The decoupling parameter obtained from GNSS-RO is validated with radiosonde soundings from the MAGIC campaign over the Northeast Pacific Ocean. We then present climatologies of the decoupling parameter over different ocean basins and compare the GNSS-RO results with those obtained from ECMWF analysis and climate models. Limitations of the GNSS-RO observations in sensing the PBL vertical structure will be discussed, and our recent work carried out to overcome some of these limitations will be briefly described. Finally, we will provide some thoughts on the future of GNSS-RO in addressing the Decadal Survey.
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