| dc.description.abstract | The Maritime Continent (MC) is the largest archipelago located between the Indian
and western Pacific Oceans. The MC is surrounded by warm seas surface temperatures
that leads to deep convection, which is also modulated by the land and its topography.
The latent heat release due to condensation in the MC plays a significant role in
modulating the global atmospheric circulation. The MC precipitation is also influenced by
large-scale atmospheric variability such as the Madden-Julian Oscillation (MJO) which in
turn is modulated by the MJO. In the recent past, the MC has gotten more attention due to
a number of field campaigns yet the understanding of precipitation variation during MJO
propagation and how they are modulated by the topography and land-sea contrast remains
a major challenge to the atmospheric community. In this dissertation, I make an effort to
understand the role of topography and land-sea contrast on the precipitation during the
propagation of an MJO event using realistic and idealized regional model simulations. I
conduct four simulations: (i) lower-resolution (12 km) simulations using cumulus
parameterization in the presence (LR) and (ii) absence (LR-Flat) of topography, and (iii)
higher-resolution (4 km) simulations without cumulus parameterization in the presence
(HR) and (iv) absence (HR-Flat) of topography. The results indicate that the important
physical processes for MJO-associated convection may be spatial different in different
parts of the MC. For second part, I explore the role of topography by removing topography in both
low and high resolution simulations. The control simulation (CTL), using observed
topography, captures the timing, magnitude, and location of the diurnal cycle of
precipitation over individual islands. The arrival of peak precipitation in FLAT is delayed
by 1 hour compared with CTL. The largest difference in the precipitation diurnal cycle
between the CTL and FLAT was found over areas with high topography (>1000 m). To
understand the evolution of diurnal precipitation, a moisture diurnal budget analysis was
conducted that indicates that the difference between the CTL and FLAT is primarily
induced by both horizontal and vertical moisture advection. I also explore the relationship
between topographic height and precipitation in detail as well as the relative contribution
of different processes below and above the planetary boundary layer.
Finally, I explore the specific contribution of individual islands to the precipitation
over the surrounding islands during MJO propagation. I designed four experiments
including a control (CTL), removal of Sumatra (E1L), removal of Borneo (E2L), and
removal of New Guinea (E3L). I found a pattern that during background easterlies prior
to MJO arrival, a systematic decrease in precipitation was found in the surrounding
islands to the west side of the removed island. But, on the eastern side of the removed
island, no systematic change in precipitation was found. | en_US |
