Transport of Ship Emissions in the Strait of Malacca Using a High-Resolution WRF Simulation and Low-Resolution GDAS Data Coupled with Hysplit

The goal of this research is to describe and quantify the role of deep convection within the Strait of Malacca (hereafter referred to as the "Strait" a part of the Maritime Continent in Southeast Asia) on the long-range transport of ship emissions. It utilizes a combination of the Weather Research and Forecasting (WRF) Model with a 2 km horizontal grid spacing and the HYbrid Single Particle Lagrangian Integrated Trajectories model (HYSPLIT 4). Results from the high-resolution WRF simulations are compared to the coarse-resolution (1° horizontal grid spacing) Global Data Assimilation System (GDAS) data provided by the Air Resources Laboratory. World Wide Lightning Network (WWLLN) observations reveal that the Strait region has a pronounced diurnal cycle of lightning with a nighttime (1900–0700 LT) maximum that is 2–3 times greater in the Strait itself than the daytime (0700–1900 LT) maximum on the surrounding landmasses. WWLLN observations also reveal that the Strait region has a seasonal cycle that is influenced by the Intertropical Convergence Zone and is out of phase with the Asian monsoon. April is the month with the most lightning, followed by October. Conversely, February is the month with the least amount of lightning. Therefore, these three months are the focus of this study. The Emissions Database for Global Atmospheric Research v4.2 is used to find an average emissions rate from ships within the Strait. A mass is assigned to each HYSPLIT particle in order to display a three-dimensional representation of CO concentrations. HYSPLIT results using WRF as the meteorological input reveal that more CO is transported to the upper troposphere/lower stratosphere (UTLS) during April than any other month. October is also efficient at transporting CO to the UTLS, but in smaller concentrations than April. CO transport during February is primarily in the lower to middle troposphere. The effect of model resolution is shown by comparing WRF-derived trajectories to GDAS-derived trajectories. The coarse-resolution GDAS-derived trajectories remain close to their point of release after 120 h. The high-resolution WRF-derived trajectories exhibit more horizontal and vertical transport than GDAS. Result of vertical mass flux calculations show that April has the greatest influence on the UTLS which is consistent with WWLLN lightning observations and a climatology of GDAS convective available potential energy within the Strait. April has the greatest hydrostatic instability of the three months studied, and therefore has the most lightning and deepest transport; October is second in this regard; and February is third.