This study describes the three-dimensional structure and migration process of a westward-migrating precipitation system with a diurnal cycle observed on 10 November 2006 in west Sumatera as based on dual-Doppler radar analysis, rawinsonde data, and surface data. The location of convective cell generation over land in the daytime and the timing of an evening change in the migration direction of precipitation systems from landward to seaward were influenced by local circulation: in the morning, an isolated convective cell generated near the west coast propagated inland (toward the mountains) via the successive generation of new convective cells over the sea breeze. In the afternoon, convective cells in a precipitation system were generated over the western slopes of the mountains surrounding Lake Maninjau by thermally induced local circulation and the slope effect. In the evening, precipitation systems located over the mountains started to propagate toward the sea (westward) in response to a change in local circulation from landward to seaward winds. Subsequently, precipitation systems were newly generated over the sea near the west coast of Sumatera Island, merging with the systems that originated over land. These two sets of systems formed a larger system (long axis > 100 km) than that over land (long axis of several tens of kilometers). The expanded precipitation system had a convective region with a long axis oriented parallel to the west coast of Sumatera Island and a short axis (∼7 km) oriented perpendicular to the west coast at the leading edge of the system. The echo top height of the system was located at approximately 13 km and an anvil moved faster than the convective region above 6 km in height. The convergence was formed by an easterly wind component in the system and a southerly wind component over the sea around the leading edge of the system at the lowest layer. The expanded system migrated farther offshore at a speed of about 5 m s −1 via the self-replication of convective cells over the convergence at the leading edge of the system and via advection by ambient wind in the lower troposphere. The convergence regions at the leading edge of the system were continuously strengthened by downward transportation of horizontal momentum below 4 km, meaning that the system could be maintained for a long time and migrate offshore for a long distance.
In this study, the processes responsible for an intense wind event that occurred in west Sumatera on November 19, 2006, during the first campaign of the Hydrometeorological ARay for Isv-Monsoon AUtomonitoring (HAR-IMAU) were investigated.Strong winds of 17 m s À1 and a sudden temperature drop of 5 K were observed at an X-band Doppler radar site associated with the passage of a convective system, and some houses were severely damaged. The convective system developed under an environment of strong low-level easterly vertical shear associated with the easterly region of an equatorial Rossby wave. The northern part of the convective system possessed qualitatively similar structures to midlatitude bow echoes, including the convex shape of the convective line, a descending rear-inflow jet positioned at its apex, and mesoscale vortices on both sides of the rear-inflow jet. The low-level wind behind the convective system formed a channel of strong easterly wind as it passed through an area of relatively low topography in the mountain range. The enhanced easterly wind was thought to contribute to the formation of the bow echo-like structure in the northern part of the convective system. This easterly rear-inflow jet was further accelerated in the convective system and descended near the leading edge, forming divergent strong winds at the surface.The sounding data that were taken after the passage of the convective system indicated that dry air appeared in the lower troposphere associated with an enhancement of the southerly component of the wind. An analysis of objective reanalysis data suggests that the southerly was probably associated with westward-propagating mixed Rossby-gravity waves with a period of approximately 5 days. It is suggested that the dry air intruded into the convective system across the back edge of the precipitation area and caused enhanced evaporative cooling, which resulted in the e¤ective downward transport of the enhanced easterly momentum.
The cold pool outflow has been previously shown to be generated by decaying Mesoscale Convective Complexes (MCCs) in the Maritime Continent. The cold pool also has a main role in the development processes of oceanic convective systems inducing heavy rainfall. This study investigated a cold pool event (January 1-2, 2021) related to a heavy rainfall system over the coastal region of Lampung, Southern Sumatra, within a high-resolution model simulation using a regional numerical weather prediction of the Weather Research and Forecasting (WRF) with convection permitting of 1 km spatial resolution, which was validated by satellite and radar data observations. It is important to note that the intensity, duration, timing, and structure of heavy rainfall simulated were in good agreement with satellite-observed rainfall. The results also showed that a cold pool (CP) plays an important role in inducing Mesoscale Convective Complex (MCC) and was responsible for the development of an offshore propagation of land-based convective systems due to the late afternoon rainfall over inland. This study also suggests that the propagation speed of the CP 8.8 m·s−1 occurring over the seaside of the coastal region, the so-called CP-coastal, is a plausible mechanism for the speed of the offshore-propagating convection, which is dependent on both the background prevailing wind and outflow. These conditions help to maintain the near-surface low temperatures and inhibit cold pool dissipation, which has implications for the development of consecutive convection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.