## 1 Introduction  
The structure of the lower troposphere is affected by many factors such as radiation, synoptic weather, and turbulent eddies. Solar radiation heats the surface and causes convection, which mixes air at different levels. Synoptic weather induces temperature or moisture advections, and dramatically changes the air temperature and water vapor mixing ratio in the lower troposphere. The turbulent eddies produced by surface forcing (e.g., surface heating and drag by topography) generate complicated wind patterns and mix the air. The changes in the lower troposphere directly affect humans near the surface; thus, many researchers have tried to reveal their nature through observation [1; 2; 3; 4] and numerical simulation [5; 6; 7; 8]. Observations of the lower troposphere using various instruments, such as radiosonde, radar, and lidar, have shown that the development of the convective boundary layer (CBL), one of the important processes in the lower troposphere, is variable and intricate in space and time. [PERSON] and [PERSON] (2018) observed the daytime lower troposphere and found that convective structures such as thermal plumes and convective eddies are produced by solar heating and play an important role in the development of the CBL. They also found that in the daytime lower troposphere, the upward transport of warm and polluted air near the surface is mainly governed by a spatially inhomogeneous process driven by convective structures. In addition to convective structures, the growth in the CBL is complex and affected by synoptic weather, land-use characteristics, local advection, land-sea contrast, and topography. For example, [PERSON] et al. (2018) found that cold-air advection induced by sea breeze decreased air temperature and impeded the growth of the CBL. [PERSON] et al. (2018) observed that the development of the CBL in the lower troposphere was not always continuous and the CBL height could sharply increase when the residual layer became a part of the CBL. However, the time intervals of the abovementioned direct in situ observations were insufficient (i.e., typically larger than a 3 h interval) to capture such an abrupt change in the development of the CBL. Numerical models have also been widely used to investigate the boundary layer structures in the lower troposphere. Because the length-scale of turbulence in the boundary layer is generally small, numerical models with a horizontal grid resolution larger than \(\sim\)1 km use a planetary boundary layer (PBL) scheme, which parameterizes small-scale turbulence in the boundary layer based on observation, theory, and high-resolution simulation ([PERSON] et al., 2017; [PERSON] et al., 2018; [PERSON] et al., 2019). PBL schemes can successfully reproduce the general characteristics of boundary layer (e.g., air temperature, wind speed, and wind direction in boundary layer) ([PERSON] et al., 2017; [PERSON] et al., 2019; [PERSON] et al., 2019). However, detailed or abrupt changes in the CBL structures, such as convective structures, may not be reproduced by numerical simulations with PBL parameterization schemes. The aforementioned studies commonly emphasize that the important CBL processes in the lower troposphere cannot easily be captured by operational in situ observations because of insufficient time interval nor reproduced by numerical models even incorporating typical PBL parameterization schemes, which motivates this study. In this study, we performed radiosonde observations with a 1 h interval on 17 and 18 January 2017 to intensively investigate abrupt changes in the CBL and lower troposphere in Seoul, South Korea. Additionally, we evaluated the performance of PBL schemes in simulating temporal changes in the structure of the lower troposphere through comparisons with the radiosonde observations. In Section 2, we analyze the synoptic weather conditions on 17 and 18 January 2017. In Section 3, we describe the radiosonde observation and simulation design. In Section 4, we present and discuss the radiosonde observation and simulation results.