Validation of NCUM Model Forecasts Against FAAM Aircraft Observations Over Monsoon Trough Region: A Diagnostic Case Study

This study assesses the characteristics of atmospheric boundary layer (ABL) between Facility for Airborne Atmospheric Measurements (FAAM) aircraft observations and NCMRWF Unified Model (NCUM) forecasts on 07 July 2016. On this day the flight was operated over monsoon trough region. Two model forecasts data are utilized (global-17 km; regional-4 km) at a lead time of day-1 to day-3. The chosen variables are boundary layer height ( Z i ) in km, wind speed (WS) in m s −1 , vertical velocity ( w ) in m s −1 , water vapor mixing ratio ( r ) in g kg −1 , and temperature ( T ) in o C. Special emphasis is given to the evolution of the ABL and peak of low-level jet (LLJ). Results suggest that both the models have noticed warm biases for T , wet biases for r , and negative biases for w . On the other hand, WS found to have negative (positive) biases during the straight level (profile) runs. Point-by-point correlations suggest that T, and r are in good agreement ( R > = 0.94), and moderate agreement (ranges from 0.66 to 0.77) for WS, whereas the vertical velocities are poorly predicted ( R < 0.2). Strikingly, the correlations (biases) are dropped (increased) with lead time in two models. Small improvements in the statistics ( R , bias) are noticed when the model resolution changes from 17 to 4 km. Both models can identify the observed evolution of the ABL; however, Z i values are slightly lower in models compared to observations. Interestingly, the Z i values are slightly dropped (100–200 m) from day-1 to day-3 forecast in two models. The peak of LLJ follows clear time variation, and its height is decreased with forecast lead time. Wind speeds below (above) the ABL height increases (decreases) with lead time, respectively. By considering all flight points across the flight track, the mean Z i is 100–500 m higher in the global model compared to the regional model. The noticed differences between two model ABL heights are discussed in the light of soil moisture conditions, fluxes, temperature advection, and static stability. Overall, a good correspondence is seen between FAAM observations and model forecasts, whereas the regional forecasts have better agreements in predicting ABL characteristics (10–20%).