Modelling Study of Atmospheric Boundary Layer Characteristics in Industrial City by the Example of Chelyabinsk

An applicability of Weather Research and Forecasting Model (WRF) with single-layer surface parameterization scheme to quantifying urban planetary boundary layer (PBL) structure and evolution is evaluated by comparing model-derived results versus conventional thermal profiler, surface and satellite data obtained in Chelyabinsk metropolitan area during typical winter anticyclon. Influence of detailed description of anthropogenic surface processes and landscape inhomogeneities onto urban heat island patterns is discussed also.

WRF relatively well describes the observed vertical PBL structure with temperature inversion in stable surface layer below 150 m, and isothermal well-mixed layer above 300 m, but significantly (more than 4 grad C) underestimates subsidence inversion cape intensity. Experiments reveal that an absolute difference between modeling and observed temperatures monotically decrease with time, and, after 18 hours model runs continuing within ±1 grad C interval at all levels of PBL. Some inertia in evolution of modeled PBL is observed during sunrise/sunset when rapid temperature change at low levels (less than 150 м) occur.

As was expected for cold weather temperatures below -15 grad C and light winds, model fields are perturbed by presence of pronounced urban heat island (UHI) with two surface temperature anomaly up +2÷4 grad C separated by cold river valley. Simulated 3D wind flows suggest that highest temperature maxima in industrial park corresponds to surface divergence region and is produced by descending vertical air motion in contrast to valley convergence induced by horizontal “tunnel effects”. The interaction of UHI and complex terrain induced flows resulting unusually strong low level jet. It is assumed that such jet development produces wind shift. Overall circulations structure can be considered in term of UHI stationary frontal boundary – one of new object to future mesoscale studies.