Desert–Oasis Convergence Line and Deep Convection Experiment (DECODE)

Abstract The heterogeneous land surface spanning the Yellow River irrigated oasis and the adjacent Kubuqi and Ulan Buh Desert (Hetao area) in Inner Mongolia, China, has been noted to frequently generate planetary boundary layer convergence line (BLCL), providing an important source of low-level lifting for convection initiation (CI). As the first field experiment to collect comprehensive observations of vegetation-contrast-resulting thermal circulations that consistently generate BLCLs and lead to CI, the Desert–Oasis Convergence Line and Deep Convection Experiment (DECODE) was conducted from 5 July to 9 August 2022 in the Hetao area. Two oasis and four desert observation sites were set up in the region that exhibits the highest frequency of BLCL and CI occurrences, equipped with a suite of advanced instruments probing land–atmosphere interactions, planetary boundary layer processes, and evolution of BLCLs and their associated CI, including Doppler lidars, microwave radiometers, soil temperature and moisture sensors, eddy covariance systems, portable radiosondes, C-band polarimetric Doppler radar, aircraft, and Geostationary High-speed Imager onboard FY-4B satellite. DECODE captured 29 BLCLs (16 with CI), 66 gust fronts, 12 horizontal convective rolls, and one tornado. The observations unveiled full thermal circulations spanning the desert–oasis boundary characterized by a horizontal width of ∼25 km, a convergence height of ∼1 km above ground level (AGL), and divergence from 2 to ∼3.5 km AGL, with vertical wind speeds of up to 2 m s −1 . Future publications stemming from DECODE will delve into a spectrum of scientific inquiries, including but not limited to land surface and boundary layer processes, BLCL dynamics, CI mechanisms, convective organization, predictability, and model evaluation. Significance Statement The purpose of Desert–Oasis Convergence Line and Deep Convection Experiment (DECODE) is to collect intensive observations around desert–oasis divide to better understand the physical processes of boundary layer convergence lines (BLCLs), their associated thermal circulations, convection initiation (CI), and organization over heterogeneous land surfaces. This is important because deep convection initiation poses a major challenge for weather forecasting over heterogeneous land surfaces due to limited understanding of land–atmosphere interactions. In addition, the targeting divide between a desert and an irrigated oasis facilitates a unique situation where human activities can change the weather. This campaign captured 29 BLCLs (16 with CI), which provided a rich dataset for studies not only on convection dynamics and microphysics but also on land–atmosphere interactions, boundary layer processes, and even interdisciplinary studies such as wind farm impact and convective dust storms.

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