Severe weather over Southeast Asia: fieldwork and modelling

The Maritime Continent in Southeast Asia is a key region in the global weather and climate system. Its complex island geography and position among the warmest oceans on Earth lead to a multi-scale concoction of severe atmospheric convective and dynamical weather systems. The atmospheric response to this heating affects weather and climate across the Earth.

The diurnal cycle is the fundamental building block of organised convection over the Maritime Continent. Conceptual models suggest that convection is initiated inland of the coastlines during the late afternoon due to upslope mountain winds and sea breeze convergence. During the night, a combination of downslope mountain winds, the land breeze and gravity waves causes the convection to propagate offshore and become more organised, producing a distinct diurnal cycle that is common to many of the islands. These conceptual models have not been tested using detailed observations, and the interplay between the processes is not well understood.

There are major knowledge gaps in our understanding of the processes within this multi-scale system due to difficulties modelling the tropical atmosphere and ocean over such complex geography, and a dearth of suitable observations against which to evaluate models. This lack of understanding is a significant limitation to regional weather forecasting, medium-range forecasting of the mid-latitudes and climate projections.

There is a unique opportunity for the student to participate in and use the data from a major international field campaign on Java, Indonesia and Christmas Island between November 2019 and February 2020. The 5 year NERC-funded research programme “TerraMaris: The Maritime Continent – Driver of the Global Climate System" will make the field observations as a major contribution to the international initiative "Years of the Maritime Continent". There will be two ground-based supersites on Java and Christmas Island (NCAS X-band Radar, 3 hourly radiosondes, flux towers, radiometer, lidar etc) and oceanography measurements in the ocean between the two sites. The BAe146 FAAM research aircraft will be based in Jakarta on Java and will make measurements between there and Christmas Island. TerraMaris is a collaborative project between UK Universities, the Met Office and the Indonesian Weather Service (BMKG).

This PhD project provides a unique and attractive opportunity for a student to take part in a major international field campaign, develop understanding of convective processes and use the observations to evaluate and improve the suite of Met Office models. Specifically, the project will address the following science questions:

• What is the role of upslope mountain flows and sea-breeze convergence in initiating convection over the Maritime Continent islands?
• What is the relative role of land breezes, storm outflows, and gravity waves in controlling the offshore propagation of convective systems?
• How does the atmospheric boundary layer develop over land through the diurnal cycle? How does this interact with the maritime atmospheric boundary layer?
• How does propagating convection that originates over land interact with convection originating from the open ocean?
• How do low-frequency modulations of the background state (e.g. variability in wind, large-scale vertical motion, environmental stability and humidity, and cloud through the Madden-Julian Oscillation) impact the diurnal cycle of Maritime Continent convection?
• How well do numerical weather models of varying complexity represent important processes relating to the triggering, organization and propagation of convection?