Measuring boundary-layer height under clear and cloudy conditions using three instruments

•Three methods were used to measure boundary layer height (BLH) under different sky conditions.•GPS sounding is the most accurate, but could not capture the diurnal evolution of BLH.•WPR is a promising method, but did not work well for determining the nocturnal BLH of the SBL.•MPL method is accurate but unable to deal with multi-layer structure and sensitivity to moisture.

Boundary-layer height (BLH) under clear, altostratus and low stratus cloud conditions were measured by GPS sounding, wind profiler radar, and micro-pulse lidar during the atmospheric radiation measurement experiment from Sep. to Dec. 2008 in Shouxian, Anhui, China. Results showed that during daytime or nighttime, regardless of cloud conditions, the GPS sounding was the most accurate method for measuring BLH. Unfortunately, because of the long time gap between launchings, sounding data did not capture the diurnal evolution of the BLH. Thus, wind profile radar emerged as a promising instrument for direct and continuous measurement of the mixing height during the daytime, accurately determining BLH using the structure parameter of the electromagnetic refractive index. However, during nighttime, radar was limited by weak signal extraction and did not work well for determining the BLH of the stable boundary layer, often recording the BLH of the residual layer. While micro-pulse lidar recorded the evolution of BLH, it overestimated the BLH of the stable boundary layer. This method also failed to work under cloudy conditions because of the influence of water vapor. Future work needs to develop a method to determine BLH that combines the complimentary features of all three algorithms.

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