The surface energy balance in the Indian monsoon
Prof Douglas Parker (SEE), Dr Jennifer Fletcher (SEE, NCAS), Dr Christopher Taylor (Centre for Ecology and Hydrology)Project partner(s): Dr Christopher Taylor (Centre for Ecology and Hydrology)Contact email: firstname.lastname@example.org
This project will focus on the interaction between atmospheric circulations, rainfall, and land surface processes in the Indian monsoon. The student will analyse high quality in situ data covering several years from three locations in India. From this the student will develop an understanding of the surface energy balance for the Indian monsoon season, the effect of rainfall on the land surface, and how land surface processes feed back on the atmospheric circulation and rainfall. This can be used to improve the next generation of weather and climate models, improving prediction of monsoon rainfall.
The Indian summer monsoon is a dramatic seasonal change in atmospheric circulation and precipitation, bringing the majority of the year’s rainfall to the subcontinent between June and September. The monsoon presents a challenge for both conceptual understanding and prediction. Processes affecting the monsoon range in scale from individual cloud elements to continental scale circulations. Unsurprisingly, this range of scales makes the Indian monsoon difficult to predict, with many climate models, including the Met Office Unified Model, having a severe and persistent dry bias in the region. One of the problems in understanding and predicting the monsoon is moisture sources: e.g., what is the relative importance of remote transport of water vapour into the region by the continental-scale monsoon circulation compared to the recycling of water from the land surface as the monsoon progresses? Relatedly, what role do pre-monsoon showers, which moisten the dry land surface, play in the progression of the monsoon into northwestern India in June and July?
Because of these gaps in understanding and predicting the Indian monsoon, a joint Indian-UK programme called INCOMPASS has brought about new state of the art observations of atmospheric and land processes in the monsoon. These include the installation of permanent flux towers: ground-based measurement sites which measure the transfer of heat, moisture, and radiation between the land surface and the atmosphere, in addition to standard meteorological measurements and precipitation. The flux towers were installed in early 2016 at three sites capturing a range of rainfall regimes within the monsoon: two in the rainy Western Ghats mountains and one in Kanpur in northern India. Preliminary analysis has already shown that the seasonal evolution of surface fluxes – the transfer of heat and moisture between the land surface and atmosphere – is quite different between the sites as a result of their different surface types. Other results have suggested that early in the monsoon season the surface energy balance is very sensitive to precipitation, with rainfall leading to a substantial increase in evaporation and hence recycling of water vapour back into the atmosphere. This recycling is likely important for the development of the monsoon early in the season, but weather and climate models struggle to capture this process.
Key questions for PhD project
- After rainfall events, how long does it take soil moisture to dry down and surface evaporation to reduce back to what it was before the rain? How does that change between locations, over the course of the season, and according to the nature of the rainfall event?
- How does the diurnal cycle of rainfall and surface fluxes change over the course of the season at the three sites? Does the diurnal amplitude go down as the monsoon progresses? How does the diurnal cycle respond to active and break phases of the monsoon?
Related undergraduate subjects:
- Applied mathematics
- Atmospheric science
- Computer science
- Environmental science
- Natural sciences
- Physical science