Observational and dynamic downscaling analysis of a heavy rainfall event in Beijing, China during the 2008 Olympic Games

Abstract

A local precipitation event with several dispersedly distributed heavy rainfall centers exceeding 50 mm occurred in Beijing, China on 14 August 2008 during the Beijing Olympic Games. The heavy rainfall event was produced by a few scattered convective storms. Detailed observational analysis with data from automatic weather stations (AWSs) as well as the meteorological radar in Beijing and a dynamic downscaling analysis with a diagnostic model, California Meteorological Model (CALMET), showed that convergence zones caused by small-scale topography and colliding outflow boundaries were key influencing factors in the initiation and development of the convective storms. Convergence helped to induce upward vertical motion as well as concentrate moisture to reduce the convective inhibition (CIN). Horizontal wind speed may modulate the effectiveness of convergence. Downscaled wind fields by CALMET not only retain the overall features of the original fields, but also present more detailed structures, especially near complex terrain, which is much helpful in analyzing and predicting the development of the storms.

An observational study of the effects of aerosols on diurnal variation of heavy rainfall and associated clouds over Beijing–Tianjin–Hebei

“…The direct effect, by absorbing and scattering solar radiation, leads to heating in the atmosphere (e.g., Jacobson, 2001;Lau et al, 2006) and cooling on the surface (Lelieveld and Heintzenberg, 1992;Guo et al, 2013;Yang et al, 2018), causing changes in atmospheric vertical static stability and subsequently modulation of rainfall (e.g., Rosenfeld et al, 2008). On the other hand, water-soluble aerosols serving as cloud condensation nuclei (CCN) affect the warm-rain and cold-rain processes by influencing the cloud droplet size distributions, cloud top heights and other cloud properties (Jiang et al, 2002;Givati and Rosenfeld, 2004;Chen et al, 2011;Lim and Hong, 2012;Tao et al, 2012). For Beijing-Tianjin-Hebei (BTH) the significant increase in pollution in recent decades has raised issues concerning aerosolradiation-cloud-precipitation interactions.…”