Evaluation of retrieval methods for planetary boundary layer height based on radiosonde data

Abstract

Abstract. Radiosonde (RS) is widely used to detect the vertical\nstructures of the planetary boundary layer (PBL), and numerous methods have\nbeen proposed for retrieving PBL height (PBLH) from RS data. However, an\nalgorithm that is suitable under all atmospheric conditions does not exist.\nThis study evaluates the performance of four common PBLH algorithms under\ndifferent thermodynamic stability conditions based on RS data collected from\nnine sites in January–December 2019. The four RS algorithms are the\npotential temperature gradient method (GMθ), relative humidity\n(RH) gradient method (GMRH), parcel method (PM) and Richardson number\nmethod (RM). Atmospheric conditions are divided into convective boundary\nlayer (CBL), neutral boundary layer (NBL) and stable boundary layer (SBL) on\nthe basis of the potential temperature profile. Results indicate that SBL is\ndominant at nighttime, whilst CBL dominates at daytime. Under all and SBL\nclassifications, PBLH retrieved by RM is typically higher than those\nretrieved using the other methods. On the contrary, the PBLH result retrieved by\nPM is the lowest. Under CBL and NBL classifications, PBLH retrieved by PM is\nthe highest. PBLH retrieved by GMθ and GMRH is relatively\nlow under all classifications. Moreover, the uncertainty analysis shows that\nthe consistency of PBLH retrieved by different algorithms is more than\n80\u2009% under CBL and NBL classifications. By contrast, the consistency of\nPBLH is less than 60\u2009% under SBL classification. The average profiles and\nstandard deviations of wind speed and potential temperature under consistent\nand inconsistent conditions are also investigated. The results indicate that\nconsistent cases are typically accompanied by evident atmospheric\nstratification, such as a large gradient in the potential temperature\nprofile or a low-level jet in the wind speed profile. These results indicate\nthat the reliability of the PBLH results retrieved from RS data is affected\nby the structure of the boundary layer. Overall, GMθ and RM are\nappropriate for CBL condition. GMθ and PM are recommended for NBL\ncondition. GMθ and GMRH are robust for SBL condition. This\ncomprehensive comparison provides a reference for selecting the appropriate\nalgorithm when retrieving PBLH from RS data.\n