CR2025_57 Simulating monsoon systems at the kilometre scale

Lead Supervisor: Andy Turner, Department of Meteorology, University of Reading and National Centre for Atmospheric Science

Email: a.g.turner@reading.ac.uk

Co-supervisors: Richard W. Jones, Met Office

Monsoon systems supply the majority of water to over two-thirds of the world’s population.   However, large biases in the position and intensity of monsoon rainbands have persisted over generations of weather and climate models (Bock et al., 2020).  “Seamless” model approaches have shown monsoon biases to develop rapidly in weather forecasting models over only a few days, suggesting that the “parameterizations” or statistical representations of sub-grid-scale processes such as tropical convection are to blame (Martin et al., 2010).

The development of regional and near-global models operating at the scales at which tropical convection can be resolved offers the opportunity to better model processes relating to the diurnal (daily) cycle of convective rainfall, the coupling of this convection with the winds and the interaction between the monsoon and the complex orography and coastlines of monsoon regions (Birch et al., 2014; Willetts et al., 2017).  These models include the state-of-the-art kilometre-scale or “k-scale” model infrastructure being developed at the Met Office.

In particular, the timing of the diurnal cycle is known to improve in convective-scale models, and the development of temperature and pressure gradients across coastlines and mountains, which generate land-sea breezes and mountain-valley circulations, respectively, are likely to be better represented.  In addition, subtle variations in the land surface, such as gradients in soil moisture which are resolved at these scales may lead to more realistic representation of convective initiation – the process which makes rainstorms commence.

This project will investigate errors in local-scale monsoon circulations, their scale interactions with modes of climate variability, and how these errors and scale interactions change when modelled at the kilometre scale.  Ultimately, the project will consider whether improvements in the local-scale circulations rectify onto the mean state, leading to improvements in the lower tropospheric circulation and monsoon rainfall biases.

We anticipate that in the first year of the project, the student will analyse a set of Met Office models that have been produced at a variety of different resolutions.  Processes will be examined in detail to understand how increasing resolution towards the kilometre scale may change the behaviour of diurnal cycles of circulation.  Particular focus will be given to the circulations over mountains and across coastlines in monsoon regions.  This work will determine whether there is a fundamental improvement to monsoon behaviour when represented at the kilometre scale.

In the second year, we anticipate the student will diagnose how well-known aspects of tropical climate variability, such as the Madden-Julian Oscillation, alter monsoon circulations and whether the nature of these interactions changes at higher resolution.  Since such interactions are useful for helping predict monsoon rains, this research will prove useful in understanding what processes need to be modelled to help improve monsoon forecasts.

As the student moves towards their final year, they will be expected to design and perform model experiments of their own for monsoon regions of interest (perhaps India or Southeast Asia), to test the sensitivity to changes in the representation of mountains.  For example, at the kilometre-scale, what would be the effect of removing mountains on the west coasts of India, Myanmar, or Sumatra?  The aim of such experiments would be to identify which processes are most crucial for simulation of local-scale behaviour in monsoons and their feedbacks onto the bigger picture.

As part of a Met Office CASE award, the student will have the opportunity to spend time at the Met Office and learn how to run regional configurations of their modelling systems during their studies.

Training opportunities:

As part of a CASE award, the student will run and analyse kilometre-scale regional and global experiments and attend placements at the Met Office to interact with members of the “k-scale” team, thus engaging with a leading employer of PhD graduates.  The student will develop strong coding skills for processing and visualising large datasets, supported by bespoke computational training.  In addition, the student may attend the NCAS Introduction to Atmospheric Science course and Climate Modelling Summer School.  The student will have the typical opportunities associated with a Crocus PhD such as developing presentation skills and networking at international conferences. 

Student profile:

The project would be suitable for students with a degree in physics, maths, meteorology or closely related physical science.  No prior programming skills are required although the student will be expected to develop these and will be working with large, high-resolution model datasets, so an interest in programming is desirable. 

Co-Sponsorship details:

This project will receive a CASE award from the Met Office.

References:

• Birch, C. E., J. H. Marsham, D. J. Parker, and C. M. Taylor (2014). The scale dependence and structure of convergence fields preceding the initiation of deep convection, Geophysical Research Letters, 41, 4769–4776, doi:10.1002/2014GL060493.
• Bock, L., A. Lauer, M. Schlund, M. Barreiro, N. Bellouin, C. Jones, et al. (2020).  Quantifying progress across different CMIP phases with the ESMValTool. Journal of Geophysical Research: Atmospheres, 125, https://doi.org/10.1029/2019JD032321.
• Martin, G. M., S. F. Milton, C. A. Senior, M. E. Brooks, S. Ineson, T. Reichler, and J. Kim (2010).  Analysis and Reduction of Systematic Errors through a Seamless Approach to Modeling Weather and Climate. Journal of Climate, 23, 5933–5957, https://doi.org/10.1175/2010JCLI3541.1.
• Willetts, P. D., J. H. Marsham, C. E. Birch, D. J. Parker, S. Webster and J. Petch (2017).  Moist convection and its upscale effects in simulations of the Indian monsoon with explicit and parametrized convection. Quarterly Journal of the Royal Meteorological Society, 143: 1073-1085, https://doi.org/10.1002/qj.2991.