Lower atmospheric profiling for climate studies pertaining to aerosols, radiation and turbulence using Unmanned Aerial System in India: Initial results

Abstract

The lower atmosphere close to the Earth's surface, though crucial for various process studies and models, still remained a gap area for a long. The Indian Institute of Tropical Meteorology (IITM) pioneered in collecting aerosol and cloud data using manned aircraft. However, to fill the data gap in the lower atmosphere, IITM envisaged Unmanned Aerial System (UAS) as an innovative aerial platform and the program ‘Lower Atmospheric Research using Unmanned Aerial System Facility (LARUS)’ is instigated to demonstrate the efficacy of a fixed-wing medium size UAS for probing the lower atmosphere for climate studies. The UAS is equipped with lightweight advanced science payload and an isokinetic aerosol inlet, for targeted in-situ measurements of aerosol, chemistry, radiation, turbulence and meteorological parameters (temperature (T) and Relative Humidity (RH)). The vertical profiles on different flight days depicted high vertical diurnal variability of the measured parameters. Comparison of T & RH profiles of INSAT-3DR Sounder and UAS depicted huge data gap in satellite profiles in the lower altitudes. The new approach in our study is obtaining high frequency simultaneous in-situ measurements within the footprint of 5 km with high vertical resolution to study local atmospheric processes.

The data emphasises elevated absorbing aerosol layers (AAL) or haze layers with maximum absorption up to 500 m above the ground due to local anthropogenic activities. The sample filter papers revealed the type, source and morphology of the observed aerosols. The incoming and reflected (outgoing) shortwave radiation indicated distinct features with an albedo of 0.178 above the haze layer (at 500 m) and 0.017 at the surface and solar absorption of 70 W/m² in the layer 0–500 m. The presence of haze also influenced the turbulence parameters (u, v, w) and Turbulent Kinetic Energy (TKE) at those altitudes. This study demonstrates instrumented UAS for lower atmospheric research, the first of its kind in India, highlighting various results essential for climate studies.