Reference : UMR8539-ISARIC-081
Workplace : PALAISEAU
Date of publication : Monday, August 1, 2022
Scientific Responsible name : CREVOISIER Cyril
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Biomass burnings are one of the main components of the climate system, particularly the carbon cycle. Fires emit many trace gases, primarily carbon dioxide (CO2), carbon monoxide (CO) and methane (CH4). Strong relationships between climate variability, biomass fires and the growth rate of these trace gases have been demonstrated. However, the precise impact of biomass fires on the climate remains poorly understood. This is particularly the case for tropical fires: very few in situ observations are available in the tropical zone, whereas this region alone is responsible for more than 75% of annual fire emissions!
In climate models, the calculation of emissions from biomass burnings involves the extent of the area burned, the quantity of fuel available and the combustion efficiency, all integrated at the spatio-temporal scale considered. However, the estimate of burned areas, generally made from space observations (for example from MODIS or ATSR), is the most uncertain parameter and strongly limits the construction of an emissions inventory. A second major problem limiting the estimation of emissions comes from the uncertainty associated with the vertical transport of emissions during pyro-convection events, but also from the difficulty that the models have in reproducing the evolution of trace gases during transport in fire plumes.
Hyperspectral satellite observations made by the infrared sounder IASI (Infrared Atmospheric Sounding Interferometer) provide a satisfactory answer to these various problems. They allow global and continuous observation, and offer the possibility of simultaneously monitoring the atmospheric evolution of the three main trace gases emitted by fires, CO2, CO, and CH4. However, these trace gases present sources on the surface that are both similar (notably biomass fires) and distinct. Consequently, the simultaneous consideration of the correlations existing between these different gases can provide important information on their sources and their sinks, as well as on the effect of transport phenomena on their distributions. Nearly fifteen years of IASI observation, carried out day and night, are now available.
The objective of this thesis is to study the diurnal variation of greenhouse gas emissions by biomass fires in the tropical region and to link their evolution to that of various climatic and ecological variables (soil humidity, vegetation). This work will be based on greenhouse gas observations made twice a day by IASI high spectral resolution infrared sounder, for which the challenge will be to extract the diurnal signature of biomass fire emissions from observations made day and night. They will also call on the observations of other instruments operating in the visible (MODIS, for vegetation and the detection of "hot spots" indicators of fires) and microwaves (GRACE, for soil humidity), in the to correlate variations in emissions with various climate signatures.
LMD studies climate, air quality, and changes in planetary atmospheres, through a combination of theoretical approaches, instrumental innovations, collection of observations, analysis of data, in particular satellite data, conceptual developments, and numerical modeling. The successful candidate will join the ABC(t) team of LMD, which is involved in instrumental research and development, and specializes in the analysis of space missions, both passive (IASI, IASI-NG, AIRS, IIR, Flex, MicroCarb) and active (Merlin). Over the years, the team has developed a full processing chain for satellite data that comprises: (i) the management and development of the spectroscopic database GEISA; (ii) the management and development of forward radiative transfer models); (iii) the development of inverse radiative transfer codes for retrieving Essential Climate Variables (ECVs): clouds, aerosols, surface properties, and greenhouse gases (CO2, CH4, CO and N2O); (iv) validation activities, which are essential for providing robust long-term time series of ECVs.
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