EXPLORING CLOUD-PLANETARY BOUNDARY LAYER COUPLING OVER LAND: VARIABILITY, CLIMATOLOGY, AND IMPACT ON AEROSOL-CLOUD INTERACTIONS

Abstract

Planetary boundary layer (PBL) processes regulate land-atmosphere interactions and control the mixing and exchange of energy, water, carbon, and other atmospheric constituents between the earth surface and the atmosphere. They critically influence atmospheric phenomena such as cloud formation, convection initiation, and air quality. Over land, surface fluxes drive convective clouds, creating a coupled cloud-surface system that governs cloud development. However, the coupling state of continental clouds remains underexplored, particularly given the complex and unique land-atmosphere interactions shaped by heterogeneous soil moisture, topography, and land cover, which contrast with those in marine environments. This study addresses this gap by investigating PBL processes, cloud-surface coupling over five continental Atmospheric Radiation Measurement (ARM) observatories. To this end, a key component of this work involves developing a robust PBL Height (PBLH) dataset capable of capturing diurnal variability across these sites. Using the Different ThermoDynamic Stabilities (DTDS) algorithm, I derived PBLH estimates from ground-based Micropulse Lidars and the spaceborne CATS lidar aboard the International Space Station. Validation against radiosonde-based PBLH measurements revealed strong correlations, with R ranging from 0.6 for satellite retrievals to 0.77–0.93 for ground-based measurements. This PBLH dataset, along with cloud base height, enabled the classification of clouds into coupled and decoupled regimes. Our analysis revealed consistent coupling thresholds and percentages across diverse climatic and geographical regions, with 66% of clouds classified as coupled and 34% as decoupled. This commonality could reflect shared atmospheric mechanisms across continental regions. Building on this foundation, we investigated the role of cloud-surface coupling in aerosol cloud interactions (ACI) for convective clouds. The state of the coupling relationship is found to play an important role dictating the strength of ACI. It is only under cloud-surface coupled conditions that a robust positive relationship exists between cloud thickness and aerosol loading—with weaker or no relationship under decoupled conditions. Convective available potential energy (CAPE) also plays an important role in the development of convective clouds; its impact is successfully differentiated from that of aerosol. The most pronounced joint impacts are found for coupled clouds with high CAPE and low cloud bases below 1km. Decoupled clouds show no such systematic changes. These results suggest that an invigorating effect is possible; however, further research is needed to determine whether these findings hold across other regions.