Atmospheric Boundary Layer Dynamics over Agartala, a North-Eastern Indian Location: Insights from Ground-based Lidar Observations and Reanalysis Datasets

The atmospheric boundary layer (ABL) is the lowest part of the atmosphere, shaped directly by the Earth's surface beneath it. It governs how heat, moisture, momentum, and pollutants are exchanged between the surface and the free atmosphere. How this layer behaves matters enormously: it influences local weather, cloud formation, how pollutants spread, and broader regional climate. Yet over many parts of India, direct observations of ABL structure remain sparse.

This study looks at how the ABL behaves over Agartala (23.83°N, 91.28°E), a fast-growing city in Northeast India, using measurements from a newly installed ground-based Lidar at Tripura University alongside ERA5 reanalysis data. The observations reveal a strongly diurnal variability: during the monsoon and post-monsoon transition, the boundary layer grows to around 2 km through the day before collapsing to below 500 m at night. A recurring feature is the presence of low-level cloud layers in the morning that effectively cap the rising boundary layer, pointing to a close coupling between ABL development and cloud processes that is not always appreciated in model frameworks.

Comparing these observations against ERA5 exposes meaningful biases; the reanalysis tends to overestimate daytime boundary layer height by roughly 1 km while underestimating nighttime depths by about 300 m. Given Agartala's position within the Indo-Burma region, where monsoon circulation exerts a dominant influence on atmospheric structure, these discrepancies have real consequences for how well models represent the local environment. The findings offer a grounded picture of boundary layer evolution in this understudied region, with practical relevance for weather forecasting, air-quality monitoring, and regional climate research across Northeast India.