Examining Planetary Boundary Layer Height Climatology, Trends, and Variability over India using High-Resolution Indian Reanalysis

Abstract

Abstract This work investigates the spatio-temporal variability of planetary boundary layer height (PBLH) characteristics by leveraging multi-decadal (1980–2019) data from India’s first high-resolution regional atmospheric reanalysis–IMDAA, in conjunction with ERA5 and MERRA-2. The spatial variability in the seasonal and annual climatological mean PBLH obtained from IMDAA agree well with ERA5 and MERRA-2, albeit with some inconsistencies. The IMDAA and ERA5 PBLH exhibits a high correlation (> 0.6) over entire India, and is also exhibits a significant positive (negative) correlation with MERRA-2 over northwest and central (southern and eastern) Indian regions. However, IMDAA tends to overestimate ERA5 PBLH ( ~ < 500 m) and underestimate MERRA-2 PBLH ( ~ > 500 m) during all seasons. Despite these discrepancies, IMDAA successfully captures the diurnal changes in PBLH similar to ERA5 and MERRA-2. Furthermore, the evaluation of IMDAA PBLH with other meteorological factors suggests that PBLH correlates negatively with relative humidity (RH), indicating a decrease in PBLH as RH increases. On the other hand, PBLH shows positive correlations with surface temperature and surface zonal winds. Surface sensible and latent heat flux exhibit positive and negative correlations with PBLH, respectively, over Indian sub-regions throughout all seasons. Moreover, IMDAA realistically represents the declining trend of PBLH (-1.1 to -76.2 m decade− 1) compared to ERA5 in India during all seasons. The results from IMDAA, in concurrence with other reanalyses, demonstrate that the decreasing trend in PBLH over India is associated with rising surface temperatures and weakening surface zonal winds. This trend is attributed to increasing latent heat flux and decreasing sensible heat flux. The changes in surface fluxes over India are attributed to the intensification of Indian monsoon rainfall in the last three decades. Moreover, El Niño appears to be an important control on PBLH variability over India during different seasons, which is realistically represented by IMDAA as in ERA5 and MERRA-2.