Abstract
The lowest layer of the atmosphere in which all human activity occurs is called the Planetary Boundary Layer (PBL). All physical interactions with the surface, such as heat and moisture transport, pollution dispersion and transport happen in this relatively shallow layer. The ability to understand and model the complex interactions that occur in the PBL is very important to air quality, weather prediction and climate modeling. A fundamental and physically important property of the PBL is its thickness or height. This work presents two methods to obtain global PBL height using satellite lidar data from the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) and the Cloud-Aerosol Transport System (CATS). The first method is a straightforward backscatter threshold technique and the second is a machine learning approach known as a Convolutional Neural Network. The PBL height retrievals from the two methods are compared with each other and with PBL height from the NASA GEOS MERRA-2 reanalysis. The lidar-retrieved PBL heights have a high degree of spatial correlation with the model heights but are generally higher over ocean (∼400 m) and over northern hemisphere high latitude regions (∼1,000 m). Over mid-latitude and tropical land areas, the satellite estimated PBL heights agree well with model mid-day estimates. This work demonstrates the feasibility of using satellite lidar backscatter measurements to obtain global PBL height estimates, as well as determining seasonal and regional variability of PBL height.
Highlights
The Planetary Boundary Layer (PBL) is the lowest region of the atmosphere in contact with the surface that controls the complex interactions between the surface and the free troposphere
In this work we have demonstrated the ability to retrieve PBL height from ICESat-2 and CATS backscatter lidar data on a global scale
The 2019 Planetary Boundary Layer (PBL) height retrievals were compared with those from the MERRA-2 reanalysis and displayed a high degree of spatial correlation with the model heights but were about 400 m higher on average over ocean and over a km higher in northern hemisphere high latitude regions
Summary
The Planetary Boundary Layer (PBL) is the lowest region of the atmosphere in contact with the surface that controls the complex interactions between the surface (land and ocean) and the free troposphere. Ranging in depth from just a few hundred meters to near 6 km, moisture, heat and pollutants at the surface are transferred into the atmosphere within the PBL and are transported to other regions of the atmosphere mainly by turbulence and convective motions. The height of the PBL (PBLH) is an essential aspect of Earth’s coupled system that must be represented properly in weather, climate, and air quality prediction. PBLH varies as a function of regional land and ocean characteristics, seasonal atmospheric patterns, and diurnal solar heating. This variability is a critical indicator of regional surfaceatmosphere energy, mass, and momentum exchanges that strongly influence convection, precipitation, air pollution, and extreme events
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