The diurnal variation of the planetary boundary layer height (PBLH) over the contiguous United States (CONUS) is examined using Aircraft Meteorological Data Reports (AMDAR) at 54 major airports and the ERA5 reanalysis product. The bulk Richardson number method is used to derive the PBLH at hourly scales from the AMDAR profiles. It is found that the estimated PBLH is sensitive to the value of the critical bulk Richardson number and to the consideration of the surface friction effect, especially under stable and near-neutral conditions. Parameters constrained by field campaign observations are finally selected to estimate the PBLH. The results reveal that the diurnal climatology of PBLH exhibits seasonal and spatial variations, with greater diurnal variations in spring and summer and in the western regions. It is demonstrated that the traditional twice-daily radiosonde data may roughly capture the diurnal amplitude of PBLH in the western but not the eastern CONUS. Compared to the AMDAR data, the ERA5 reanalysis product overestimates the daytime PBLH throughout the CONUS by 18-41% and shows an earlier peak time by 1-2 hr in the western regions and a later peak time by 1 hr in the eastern regions.

High‐quality measurements of planetary boundary layer (PBL) profiles are important for advancing our understanding of land‐atmosphere coupling and PBL processes and improving the predictive capability of numerical models. Now with more than 10 years of observations from Aircraft Meteorological Data Reports (AMDAR), a decade‐long (from 2007 to 2016) data record of hourly PBL profiles is developed over 54 U.S. airports. Comparisons between the derived hourly profiles and nearby radiosonde data, which are typically only available twice a day (at 00 and 12 UTC), show good agreement between the two data sets. The root‐mean‐square errors (RMSEs) between the AMDAR and radiosonde data are found to be dependent on the distance between the two data sets, especially at lower levels. The RMSEs of temperature generally decrease as the altitude increases, while the RMSEs of specific humidity and wind are positively correlated with the measurement magnitude. At perfect collocations (i.e., the separation distance is zero), the seasonal RMSEs at measurement levels with pressure larger than 850 hPa are 1.16–1.52 K, 0.64–1.25 g/kg, and 2.00–2.26 m/s for temperature, humidity, and wind components, respectively. Compared to the RMSEs, the mean biases of AMDAR profiles are much smaller and are less dependent on the separation distance. The RMSEs show little dependence on flight phases (ascent or descent) in the lower troposphere. Overall, our results indicate that the aircraft measurements are accurate enough to be an alternative to the radiosonde data and are better suited for investigating the diurnal variation of PBL due to their higher temporal resolution.

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