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Rapid urbanization of cities has greatly modified the thermal and dynamic profile in the urban boundary layer. This paper attempts to study the interaction of urban heating and the local topographic‐induced flow circulation for a tropical coastal city, Greater Kuala Lumpur, in Malaysia. The role of sea‐and‐valley‐breeze‐orientated synoptic flow (SBOS) on the interaction is determined by comparing two intermonsoon periods. A state‐of‐the‐art numerical model, Advanced Research Weather Research and Forecasting model, is used to identify the influence of urbanization through modification of urban surfaces. The model reasonably reproduces the vertical sounding data and near‐surface weather parameters. The diurnal urban heating pattern is attributed to three predominant factors: (i) weak under calm and clear‐sky condition (morning heating), (ii) weak under larger atmospheric moisture content (late afternoon convection), and (iii) largest (1.4°C) due to differential cooling rate of urban and rural surface at night. The interaction of urban thermals and upper level SBOS affects the effect of urbanization on local circulation during the day. The urban thermals reduce the weak opposing SBOS (<2 m s−1) and enhance the inflow of moisture‐rich sea breeze passage. This increases the intensity of downwind convective precipitation during late afternoon. On contrary, the strong opposing SBOS (>2 m s−1) suppresses the vertical lifting of urban thermals and decelerates the sea breeze front. It is discovered that the interaction of urban heating and topographic‐induced flow is interdependent while the synoptic flow plays a critical role in modifying both factors, respectively.

This study aims to identify the vertical transport mechanisms that uplifted the forest fire emissions from Sumatra to the upper troposphere during the June 2013 haze crisis. WRF-Chem is used to simulate the formation and transport of biomass-burning haze during the study period of 18 th to 26 th June 2013. The South-Southeast Asian synoptic weather patterns and their effects on the transport of biomass-burning emissions from Sumatra to Peninsular Malaysia were studied computationally to explain the phenomenon. Results show that PM 10 emissions were lifted to 200 hPa height (approximately 12 km) over the Strait of Malacca on 24 th June. The two identified vertical transport mechanisms confirmed a previously conjectured convergence over the Strait of Malacca and orographic lifting over Peninsular Malaysia. These mechanisms were able to uplift the biomass-burning emissions to the upper troposphere and this could have significant long-range transport and global climatic effects.

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