A Case Study of Low‐Level Jets in Yerevan Simulated by the WRF Model

Capabilities of high-resolution (3 km) Weather Research and Forecasting (WRF) simulations to reproduce topographically induced mountain-valley winds and low-level jets (LLJs) in Yerevan have been evaluated using high-frequency observational and modeled data. High sensitivities of simulations of near-surface winds and LLJ characteristics observed on 4 July 2015 to both boundary layer and initial and lateral boundary conditions setup have been demonstrated. Among the nine tested planetary boundary layer (PBL) parameterization schemes the MYJ, QNSE, and TEMF PBL schemes showed greater skill in simulation of near-surface valley winds over Yerevan, while the other PBL schemes tend to significantly underestimate the strength of valley winds, with the BouLac PBL scheme being the worst performer. Most of PBL schemes simulate well-defined LLJs in Yerevan associated with evening valley winds. The simulated jet cores are mostly located between 150 and 250 m above ground with magnitudes varying from 12 to 21 m s(-1). However, the intensity of the observed nocturnal LLJ in Yerevan (located at 110 m above ground) is strongly underestimated by most of the WRF runs while the Shin and Hong and YSU PBL schemes simulate nocturnal LLJs higher than the observed LLJ. The WRF runs initiated with newly released European Centre for Medium-Range Weather Forecasts ERA-5 data set showed improved simulation of near-surface winds and nighttime potential temperatures in Yerevan relative to those forced by the Global Forecast System fields.