Thèse Vers une Amélioration des Projections Climatiques pour les Sociétés d'Asie du Sud-Est Représenter et Comprendre le Rôle du Compartiment Océanique H/F - Doctorat.Gouv.Fr
- Toulouse - 31
- CDD
- Doctorat.Gouv.Fr
Les missions du poste
Établissement : Université de Toulouse École doctorale : SDU2E - Sciences de l'Univers, de l'Environnement et de l'Espace Laboratoire de recherche : LEGOS - Laboratoire d'Etudes en Géophysique et Océanographie Spatiale Direction de la thèse : Marine HERRMANN ORCID 0000000161257238 Début de la thèse : 2027-09-01 Date limite de candidature : 2026-11-23T23:59:59 L'Asie du Sud-Est (SEA), constituée d'une mosaïque de bassins et îles, plateaux continentaux et zones abyssales, régions montagneuses et larges deltas, a une configuration géographique unique entre les Océans Pacifique et Indien. Les populations de SEA sont en première ligne face aux aléas climatiques et changements globaux, des cyclones à l'effet d'ENSO jusqu'au changement climatique. Siège d'une activité de convection atmosphérique intense et lieu de passage et de transformation des eaux de surface de la circulation océanique entre les Océans Pacifique et Indien, la SEA joue un rôle essentiel dans le climat global. C'est donc une région clé pour la compréhension du fonctionnement du système climatique et de ses effets sur les sociétés, des échelles locales à globales.
Pour construire des stratégies de mitigation et d'adaptation aux impacts climatiques, il est essentiel pour les décideurs de disposer de données robustes sur la variabilité et l'évolution du système régional climatique de SEA. Les projections climatiques constituent pour cela un élément clef, or la SEA est l'une des régions les plus difficiles à représenter dans les modèles de climat. Pour mieux comprendre le fonctionnement de ce système régional et sa réponse aux facteurs de variabilité à différentes échelles, et mieux prévoir son évolution à long terme, la communauté scientifique, en particulier le groupe CORDEX-SEA d'étude régionale du climat, plaide pour et travaille à la mise en place d'outils de modélisation adaptés. L'un des verrous majeurs au réalisme des projections climatiques dans la région réside aujourd'hui dans le fait que l'océan n'est pas représenté dans les modèles utilisés, malgré son rôle clef dans le fonctionnement de ce système climatique. Le CORDEX-CLIVAR ROCP Joint Working Group du WCRP a été récemment fondé pour coordonner cet effort nécessaire de régionalisation des projections océaniques, en miroir au travail mené par le programme CORDEX pour l'atmosphère. S'inscrivant dans cet effort collectif, le LEGOS et l'USTH, au sein du laboratoire mixte international LOTUS et de CORDEX-SEA, se sont engagés dans le développement d'un modèle régional couplé océan-atmosphère. Ils disposent aujourd'hui d'un outil réaliste et robuste pour étudier et prévoir la dynamique de l'océan et de l'atmosphère et leurs interactions dans le système régional climatique de SEA.
L'objectif de cette thèse sera de comprendre le rôle du compartiment océanique dans la variabilité à différentes échelles du système climatique de SEA, en examinant les différences induites par la prise en compte de la dynamique océanique sur la représentation de la variabilité et des projections climatiques de ce système. L'outil principal sera le modèle régional couplé SYMPHONIE-RegCM développé par le LEGOS et l'USTH sur la zone. La capacité du modèle à représenter la variabilité à différentes échelles de la dynamique océanique et atmosphérique de la région sur une période longue sera d'abord évaluée par comparaison aux observations. La contribution du compartiment océaniques aux principaux modes de variabilité sera examinée à partir d'un ensemble de simulations de sensibilité aux différents processus étudiés. La seconde partie sera consacrée à l'étude de la réponse du système climatique océan-atmosphère de SEA au changement climatique, à partir d'un ensemble de simulations effectuées sur les périodes historiques et futures. L'outil et les connaissances construites seront transmis aux décideurs dans le cadre des actions de menées par CORDEX-SEA pour le dialogue science-société.
La thèse sera réalisée entre le LEGOS, avec un soutien fort du Code Communautaire SIROCCO responsable du développement du modèle océanique SYMPHONIE et l'USTH où est développé le modèle atmosphérique RegCM, avec des échanges étroits avec la communauté CORDEX-SEA. La thèse bénéficiera des liens que ces deux laboratoires entretiennent avec le CNRM, Mercator Océan International et la Scripps Institution (USA). South-East Asia (or SEA), including the maritime continent, has a unique geographical configuration at the interface between the Pacific and Indian Oceans, comprising a mosaic of basins, straits and thousands of islands, alternating between continental shelves and deep-sea areas, mountainous regions and broad deltas. One tenth of the world's population lives in these tropical coastal countries, which are subject to a wide range of natural and human-induced hazards on various scales, linked in particular to multiple modes of atmospheric and oceanic variability (from intraseasonal (MJO) to seasonal (monsoon) and interannual (ENSO) to multidecennal (PDO)), to extreme events (typhoons, droughts) and global changes.
SEA also plays a vital role in the global climate. From an atmospheric perspective, this region, where ocean temperatures are high, is the site of some of the most powerful deep convection on the planet, associated with the ascending branch of the Pacific Walker circulation, making it the rainiest region in the world and releasing considerable energy that strengthens global atmospheric circulation (Jin & Hoskins 1995). This frequent and intense convective activity is primarily controlled by the diurnal cycle (Chen & Houze 1997), which is itself strongly influenced by sea-to-land and land-to-sea breezes induced by the numerous islands (Wei et al. 2020). SEA is also a well-known barrier to the propagation of the MJO (Zhang & Ling 2017), and an area of very high cyclonic activity (Tran et al. 2022). From an oceanographic perspective, it is the passageway for global ocean circulation between the Pacific and Indian Oceans (SCSTF and ITF, Gordon 2005, Qu et al. 2006), during which water masses undergo profound transformation under the influence of multiple modes of variability and processes: atmospheric forcing and air-sea interactions (Xue et al. 2020), tidal-induced mixing (Ffield & Gordon 1996, KochLarrouy et al. 2007), exchanges across the straits (Sprintall et al. 2019, Trinh et al. 2024), freshwater river plumes (Nguyen Duy et al. 2021, 2023), upwellings (Da et al. 2019, To-Duy et al. 2022, Herrmann et al. 2023, 2024), jets (Li et al. 2014) and eddy dynamics (Chu et al. 2020, Ni et al. 2021). In order to develop mitigation and adaptation strategies to climate impacts, it is essential for decision-makers to have access to robust data on the variability and evolution of the SEA regional climate system. The SEA is therefore a key region for understanding how the climate system functions, at both local and global scales.
However, SEA's dynamic nature and complex configuration make it one of the most difficult regions to model using numerical weather prediction systems and climate models, from both an atmospheric and an oceanic perspective. Systematic biases in precipitation, winds and the characteristics of water bodies, as well as in their various modes of variability, are therefore observed in the majority of climate models (Yamanaka et al. 2018, Wang et al. 2019, Herrmann et al. 2020, 2021, Trinh et al. 2024, Garinet et al. 2024). These biases stem in particular from the configuration of the models used (resolution, failure to account for tides and feedbacks between the oceanic and atmospheric compartments, choice of parameterisations, etc.), which does not allow for the complexity of the region's topography and its dynamic, atmospheric and oceanic processes to be represented. To gain a better understanding of how this regional climate system functions and how it responds to variability factors at different scales, and to better predict its long-term evolution, the scientific community is calling for the development of appropriate regional modelling tools (see the review articles by Xue et al. 2020 and Yoneyama et Zhang 2020). CORDEX-SEA has thus been working for over 15 years to implement and operate high-resolution regional atmospheric models in the SEA (Tangang et al. 2021). However, interactions with the ocean compartment have not been taken into account to date. A few studies using coupled ocean-atmosphere regional models have been carried out (e.g. Li et al. 2020, Wu et al. 2018, Nguyen-Thanh et al. 2025). However, their relatively short study periods (extreme events spanning a few years) and/or the configuration choices made (resolution, tidal representation, etc.) do not allow for the characteristics and circulation of water masses to be accurately represented over significantly long climatic time scales. The CORDEX-CLIVAR ROCP Joint Working Group was recently established to encourage and coordinate this necessary effort to regionalise ocean projections, mirroring the work carried out under the CORDEX programme for the atmosphere. As part of this collective effort and within the framework of the international CORDEX-SEA and ROCP groups, LEGOS and USTH, through the LMI LOTUS consortium which they have jointly led since 2018, have thus committed to developing a coupled ocean-atmosphere model for the SEA region. Supported also by the SEASTERS project (funded by CNES), a programme of numerical development and optimisation focusing in particular on tidal mixing and ocean-atmosphere coupling was carried out as part of the recent PhD theses by Q. Desmet and A. Garinet (defended in 2024). We now therefore have a robust coupled model that realistically represents the dynamics of the ocean and atmosphere and their interactions within the SEA regional climate system.
This thesis topic is situated within the scientific and methodological context outlined below: drawing on the numerical tools we have developed in recent years, combined with the satellite data we have compiled and evaluated in the region as part of previous theses and associated projects, the overall scientific objective of the thesis will be to explore issues relating to the role and influence of interactions between the atmospheric and oceanic compartments on the climate of South-East Asia.
More specifically, the aim will be to study the role of the oceanic compartment in the variability at different scales of the South-East Asian climate system, by examining the differences introduced by the three-dimensional, high-resolution and high-frequency modelling of ocean dynamics on the representation of variability and climate projections for this system.
The model's ability to represent the characteristics and variability at different scales of the region's oceanic and atmospheric dynamics over a long period for which observational datasets are available will first be assessed, and the role of tidal mixing and the diurnal cycle in particular will be examined. This will enable us to identify the model's strengths and limitations, and potentially address its shortcomings. The second part of the thesis will be devoted to studying the response of the ocean-atmosphere climate system to climate change, based on a set of simulations carried out for historical and future periods within the CMIP7 framework.
1) Tool : the SYMPHONIE-RegCM regional coupled model
The SYMPHONIE three-dimensional ocean model (Marsaleix et al. 2008, 2019) is a French community model developed at LEGOS by SIROCCO (a community code accredited by INSU) which incorporates several features particularly relevant to the study of the seas of South-East Asia: VQS coordinates, exposed shoals, explicit representation of tides, etc. It has thus been used in 10 PhD theses (supervised or co-supervised at LEGOS) to study a wide range of processes in the region, from the very fine scale (estuaries, plumes, Piton et al. 2021, Nguyen-Duy et al. 2021, 2023) to the coastal scale (To Duy et al. 2022, Herrmann et al. 2023, 2024, Tran et al. 2025) and the regional scale, including straits (Trinh et al. 2024). In particular, a 5 km resolution scheme was implemented and optimised over the CORDEX-SEA domain (shown in Fig. 1, Garinet et al. 2024). During A. Garinet's PhD thesis (defended in 2024), significant numerical developments were carried out on the advection scheme, making it possible to considerably reduce the excessive numerical mixing associated with the presence of strong internal tides in the region-a recurring problem in ocean models (Garinet et al. 2024).
The RegCM regional atmospheric model (Giorgi et al. 2012) is widely used by the CORDEX community, particularly CORDEX-SEA (Tangang et al. 2020, 2021). A 25 km resolution configuration is notably used over the CORDEX-SEA domain to study processes at different timescales, ranging from typhoons and extreme precipitation to climate change (Ngo-Duc et al. 2016, Herrmann et al. 2020, 2021). RegCM can also be used for long-term integrations at higher resolutions (3 km), in a non-hydrostatic configuration and on sub-domains of interest in connection with high-resolution activities (e.g. Lipzig et al. 2022). The benefits of high resolution in climate mode have thus been demonstrated for the diurnal cycle of convection.
The coupling between RegCM (at 25 km resolution, following the configuration used by the CORDEX-SEA group) and the SYMPHONIE ocean model (at 5 km) was implemented over the SEA domain using the OASIS3-MCT coupler (Craig et al. 2017) as part of Q. Desmet's PhD thesis. A substantial effort was made to evaluate and optimise this coupled configuration in order to improve the representation of heat, water and momentum fluxes at the air-sea interface (Desmet et al. 2024, Desmet et al. in prep).
1) Workplan
- Evaluation of the simulations and analysis of variability over the current period
A series of long-term simulations (hindcasts, with a 5-year spin-up followed by 20 years of simulations) will first be carried out for the period 2000-2025 using reanalysis outputs (ERA5 for the atmosphere, Hersbach et al. 2020; GLORYS for the ocean, Lellouche et al. 2021; GLOFAS for rivers, Prudhomme et al. 2024). This period is well suited to the study of interannual variability, notably featuring several ENSO events (El Niño, 2009-10, 2015-15, 2023-24; La Niña, 2007-08, 2010-11, 2020-22, 2024-26), which plays a major role in the region (Nguyen-Thanh et al. 2023, Da et al. 2019, Sprintall et al. 2019). This will enable us to assess the model's ability to realistically represent the dynamics and oceanic and atmospheric characteristics of the climate system, to examine the influence of air-sea interactions on this representation, and then to study their role in the variability of this system and the associated mechanisms. To this end, a high-resolution control simulation (5 km for the ocean, 25 to 10 km for the atmosphere) incorporating key small-scale processes in the region (tides, air-sea interactions, diurnal cycle, and continental freshwater fluxes), as well as sensitivity simulations regarding the inclusion of tides, the frequency of coupling, and atmospheric resolution, will be carried out.
- Regional climate system's response to climate change
In the second part of the thesis, a series of long-term simulations (5 years of spin-up + 20 years) will be carried out for historical and future periods, following the example of work conducted in other semi-enclosed seas (e.g. the Mediterranean, Herrmann et al. 2014, Parras-Berrocal et al. 2024). For the sake of feasibility, we will use the outputs from a single coupled global climate model (GCM) in this thesis to provide the initial and boundary conditions. The ensemble simulations carried out for the CMIP7 exercise are expected to be available by March 2027, and we plan to use the projections provided by CNRM-CERFACS (see Voldoire et al. 2019 for CMIP5), initially examining one or even two climate change scenarios.
This will enable us, firstly, by focusing on the historical period, to examine the added value of the regional model compared with the global model. Secondly, by comparing future and historical periods, we will examine the system's response to climate change, and the difference in climate projections resulting from the use of the regional model versus the global model. Here too, sensitivity analyses incorporating the various processes identified as key determinants in the first part of the thesis will be carried out to examine their influence on the response to climate change.
To assess variability at different scales (diurnal cycle, intra-seasonal variability including extreme events, seasonal and interannual variability, and climate change) and the realism of its representation, and to identify the contribution of the processes under study, systematic statistical analyses will be applied in both components (analysis of the observed period and climate projections) to the key variables and process indicators of the climate system: temperature, salinity and sea surface height; temperature and salinity profiles for the ocean; and precipitation, radiative fluxes and wind for the atmosphere. Water and heat exchanges across the straits (SCSTF and ITF) will also be examined. These variables will be compared with estimates provided by satellite observation datasets (evaluated and compiled for the variables mentioned above in the SEASTERS project database) and in situ (derived in particular from Argo profilers and measurements at the straits from the INSTANT and MITF, programmes, 2004-18, Gordon et al. 2010, 2019) will enable the simulations to be evaluated. Cross-comparison of sensitivity simulations will allow the influence of the processes taken into account to be quantified, and the associated mechanisms to be identified through analysis of the simulations.
Pour construire des stratégies de mitigation et d'adaptation aux impacts climatiques, il est essentiel pour les décideurs de disposer de données robustes sur la variabilité et l'évolution du système régional climatique de SEA. Les projections climatiques constituent pour cela un élément clef, or la SEA est l'une des régions les plus difficiles à représenter dans les modèles de climat. Pour mieux comprendre le fonctionnement de ce système régional et sa réponse aux facteurs de variabilité à différentes échelles, et mieux prévoir son évolution à long terme, la communauté scientifique, en particulier le groupe CORDEX-SEA d'étude régionale du climat, plaide pour et travaille à la mise en place d'outils de modélisation adaptés. L'un des verrous majeurs au réalisme des projections climatiques dans la région réside aujourd'hui dans le fait que l'océan n'est pas représenté dans les modèles utilisés, malgré son rôle clef dans le fonctionnement de ce système climatique. Le CORDEX-CLIVAR ROCP Joint Working Group du WCRP a été récemment fondé pour coordonner cet effort nécessaire de régionalisation des projections océaniques, en miroir au travail mené par le programme CORDEX pour l'atmosphère. S'inscrivant dans cet effort collectif, le LEGOS et l'USTH, au sein du laboratoire mixte international LOTUS et de CORDEX-SEA, se sont engagés dans le développement d'un modèle régional couplé océan-atmosphère. Ils disposent aujourd'hui d'un outil réaliste et robuste pour étudier et prévoir la dynamique de l'océan et de l'atmosphère et leurs interactions dans le système régional climatique de SEA.
L'objectif de cette thèse sera de comprendre le rôle du compartiment océanique dans la variabilité à différentes échelles du système climatique de SEA, en examinant les différences induites par la prise en compte de la dynamique océanique sur la représentation de la variabilité et des projections climatiques de ce système. L'outil principal sera le modèle régional couplé SYMPHONIE-RegCM développé par le LEGOS et l'USTH sur la zone. La capacité du modèle à représenter la variabilité à différentes échelles de la dynamique océanique et atmosphérique de la région sur une période longue sera d'abord évaluée par comparaison aux observations. La contribution du compartiment océaniques aux principaux modes de variabilité sera examinée à partir d'un ensemble de simulations de sensibilité aux différents processus étudiés. La seconde partie sera consacrée à l'étude de la réponse du système climatique océan-atmosphère de SEA au changement climatique, à partir d'un ensemble de simulations effectuées sur les périodes historiques et futures. L'outil et les connaissances construites seront transmis aux décideurs dans le cadre des actions de menées par CORDEX-SEA pour le dialogue science-société.
La thèse sera réalisée entre le LEGOS, avec un soutien fort du Code Communautaire SIROCCO responsable du développement du modèle océanique SYMPHONIE et l'USTH où est développé le modèle atmosphérique RegCM, avec des échanges étroits avec la communauté CORDEX-SEA. La thèse bénéficiera des liens que ces deux laboratoires entretiennent avec le CNRM, Mercator Océan International et la Scripps Institution (USA). South-East Asia (or SEA), including the maritime continent, has a unique geographical configuration at the interface between the Pacific and Indian Oceans, comprising a mosaic of basins, straits and thousands of islands, alternating between continental shelves and deep-sea areas, mountainous regions and broad deltas. One tenth of the world's population lives in these tropical coastal countries, which are subject to a wide range of natural and human-induced hazards on various scales, linked in particular to multiple modes of atmospheric and oceanic variability (from intraseasonal (MJO) to seasonal (monsoon) and interannual (ENSO) to multidecennal (PDO)), to extreme events (typhoons, droughts) and global changes.
SEA also plays a vital role in the global climate. From an atmospheric perspective, this region, where ocean temperatures are high, is the site of some of the most powerful deep convection on the planet, associated with the ascending branch of the Pacific Walker circulation, making it the rainiest region in the world and releasing considerable energy that strengthens global atmospheric circulation (Jin & Hoskins 1995). This frequent and intense convective activity is primarily controlled by the diurnal cycle (Chen & Houze 1997), which is itself strongly influenced by sea-to-land and land-to-sea breezes induced by the numerous islands (Wei et al. 2020). SEA is also a well-known barrier to the propagation of the MJO (Zhang & Ling 2017), and an area of very high cyclonic activity (Tran et al. 2022). From an oceanographic perspective, it is the passageway for global ocean circulation between the Pacific and Indian Oceans (SCSTF and ITF, Gordon 2005, Qu et al. 2006), during which water masses undergo profound transformation under the influence of multiple modes of variability and processes: atmospheric forcing and air-sea interactions (Xue et al. 2020), tidal-induced mixing (Ffield & Gordon 1996, KochLarrouy et al. 2007), exchanges across the straits (Sprintall et al. 2019, Trinh et al. 2024), freshwater river plumes (Nguyen Duy et al. 2021, 2023), upwellings (Da et al. 2019, To-Duy et al. 2022, Herrmann et al. 2023, 2024), jets (Li et al. 2014) and eddy dynamics (Chu et al. 2020, Ni et al. 2021). In order to develop mitigation and adaptation strategies to climate impacts, it is essential for decision-makers to have access to robust data on the variability and evolution of the SEA regional climate system. The SEA is therefore a key region for understanding how the climate system functions, at both local and global scales.
However, SEA's dynamic nature and complex configuration make it one of the most difficult regions to model using numerical weather prediction systems and climate models, from both an atmospheric and an oceanic perspective. Systematic biases in precipitation, winds and the characteristics of water bodies, as well as in their various modes of variability, are therefore observed in the majority of climate models (Yamanaka et al. 2018, Wang et al. 2019, Herrmann et al. 2020, 2021, Trinh et al. 2024, Garinet et al. 2024). These biases stem in particular from the configuration of the models used (resolution, failure to account for tides and feedbacks between the oceanic and atmospheric compartments, choice of parameterisations, etc.), which does not allow for the complexity of the region's topography and its dynamic, atmospheric and oceanic processes to be represented. To gain a better understanding of how this regional climate system functions and how it responds to variability factors at different scales, and to better predict its long-term evolution, the scientific community is calling for the development of appropriate regional modelling tools (see the review articles by Xue et al. 2020 and Yoneyama et Zhang 2020). CORDEX-SEA has thus been working for over 15 years to implement and operate high-resolution regional atmospheric models in the SEA (Tangang et al. 2021). However, interactions with the ocean compartment have not been taken into account to date. A few studies using coupled ocean-atmosphere regional models have been carried out (e.g. Li et al. 2020, Wu et al. 2018, Nguyen-Thanh et al. 2025). However, their relatively short study periods (extreme events spanning a few years) and/or the configuration choices made (resolution, tidal representation, etc.) do not allow for the characteristics and circulation of water masses to be accurately represented over significantly long climatic time scales. The CORDEX-CLIVAR ROCP Joint Working Group was recently established to encourage and coordinate this necessary effort to regionalise ocean projections, mirroring the work carried out under the CORDEX programme for the atmosphere. As part of this collective effort and within the framework of the international CORDEX-SEA and ROCP groups, LEGOS and USTH, through the LMI LOTUS consortium which they have jointly led since 2018, have thus committed to developing a coupled ocean-atmosphere model for the SEA region. Supported also by the SEASTERS project (funded by CNES), a programme of numerical development and optimisation focusing in particular on tidal mixing and ocean-atmosphere coupling was carried out as part of the recent PhD theses by Q. Desmet and A. Garinet (defended in 2024). We now therefore have a robust coupled model that realistically represents the dynamics of the ocean and atmosphere and their interactions within the SEA regional climate system.
This thesis topic is situated within the scientific and methodological context outlined below: drawing on the numerical tools we have developed in recent years, combined with the satellite data we have compiled and evaluated in the region as part of previous theses and associated projects, the overall scientific objective of the thesis will be to explore issues relating to the role and influence of interactions between the atmospheric and oceanic compartments on the climate of South-East Asia.
More specifically, the aim will be to study the role of the oceanic compartment in the variability at different scales of the South-East Asian climate system, by examining the differences introduced by the three-dimensional, high-resolution and high-frequency modelling of ocean dynamics on the representation of variability and climate projections for this system.
The model's ability to represent the characteristics and variability at different scales of the region's oceanic and atmospheric dynamics over a long period for which observational datasets are available will first be assessed, and the role of tidal mixing and the diurnal cycle in particular will be examined. This will enable us to identify the model's strengths and limitations, and potentially address its shortcomings. The second part of the thesis will be devoted to studying the response of the ocean-atmosphere climate system to climate change, based on a set of simulations carried out for historical and future periods within the CMIP7 framework.
1) Tool : the SYMPHONIE-RegCM regional coupled model
The SYMPHONIE three-dimensional ocean model (Marsaleix et al. 2008, 2019) is a French community model developed at LEGOS by SIROCCO (a community code accredited by INSU) which incorporates several features particularly relevant to the study of the seas of South-East Asia: VQS coordinates, exposed shoals, explicit representation of tides, etc. It has thus been used in 10 PhD theses (supervised or co-supervised at LEGOS) to study a wide range of processes in the region, from the very fine scale (estuaries, plumes, Piton et al. 2021, Nguyen-Duy et al. 2021, 2023) to the coastal scale (To Duy et al. 2022, Herrmann et al. 2023, 2024, Tran et al. 2025) and the regional scale, including straits (Trinh et al. 2024). In particular, a 5 km resolution scheme was implemented and optimised over the CORDEX-SEA domain (shown in Fig. 1, Garinet et al. 2024). During A. Garinet's PhD thesis (defended in 2024), significant numerical developments were carried out on the advection scheme, making it possible to considerably reduce the excessive numerical mixing associated with the presence of strong internal tides in the region-a recurring problem in ocean models (Garinet et al. 2024).
The RegCM regional atmospheric model (Giorgi et al. 2012) is widely used by the CORDEX community, particularly CORDEX-SEA (Tangang et al. 2020, 2021). A 25 km resolution configuration is notably used over the CORDEX-SEA domain to study processes at different timescales, ranging from typhoons and extreme precipitation to climate change (Ngo-Duc et al. 2016, Herrmann et al. 2020, 2021). RegCM can also be used for long-term integrations at higher resolutions (3 km), in a non-hydrostatic configuration and on sub-domains of interest in connection with high-resolution activities (e.g. Lipzig et al. 2022). The benefits of high resolution in climate mode have thus been demonstrated for the diurnal cycle of convection.
The coupling between RegCM (at 25 km resolution, following the configuration used by the CORDEX-SEA group) and the SYMPHONIE ocean model (at 5 km) was implemented over the SEA domain using the OASIS3-MCT coupler (Craig et al. 2017) as part of Q. Desmet's PhD thesis. A substantial effort was made to evaluate and optimise this coupled configuration in order to improve the representation of heat, water and momentum fluxes at the air-sea interface (Desmet et al. 2024, Desmet et al. in prep).
1) Workplan
- Evaluation of the simulations and analysis of variability over the current period
A series of long-term simulations (hindcasts, with a 5-year spin-up followed by 20 years of simulations) will first be carried out for the period 2000-2025 using reanalysis outputs (ERA5 for the atmosphere, Hersbach et al. 2020; GLORYS for the ocean, Lellouche et al. 2021; GLOFAS for rivers, Prudhomme et al. 2024). This period is well suited to the study of interannual variability, notably featuring several ENSO events (El Niño, 2009-10, 2015-15, 2023-24; La Niña, 2007-08, 2010-11, 2020-22, 2024-26), which plays a major role in the region (Nguyen-Thanh et al. 2023, Da et al. 2019, Sprintall et al. 2019). This will enable us to assess the model's ability to realistically represent the dynamics and oceanic and atmospheric characteristics of the climate system, to examine the influence of air-sea interactions on this representation, and then to study their role in the variability of this system and the associated mechanisms. To this end, a high-resolution control simulation (5 km for the ocean, 25 to 10 km for the atmosphere) incorporating key small-scale processes in the region (tides, air-sea interactions, diurnal cycle, and continental freshwater fluxes), as well as sensitivity simulations regarding the inclusion of tides, the frequency of coupling, and atmospheric resolution, will be carried out.
- Regional climate system's response to climate change
In the second part of the thesis, a series of long-term simulations (5 years of spin-up + 20 years) will be carried out for historical and future periods, following the example of work conducted in other semi-enclosed seas (e.g. the Mediterranean, Herrmann et al. 2014, Parras-Berrocal et al. 2024). For the sake of feasibility, we will use the outputs from a single coupled global climate model (GCM) in this thesis to provide the initial and boundary conditions. The ensemble simulations carried out for the CMIP7 exercise are expected to be available by March 2027, and we plan to use the projections provided by CNRM-CERFACS (see Voldoire et al. 2019 for CMIP5), initially examining one or even two climate change scenarios.
This will enable us, firstly, by focusing on the historical period, to examine the added value of the regional model compared with the global model. Secondly, by comparing future and historical periods, we will examine the system's response to climate change, and the difference in climate projections resulting from the use of the regional model versus the global model. Here too, sensitivity analyses incorporating the various processes identified as key determinants in the first part of the thesis will be carried out to examine their influence on the response to climate change.
To assess variability at different scales (diurnal cycle, intra-seasonal variability including extreme events, seasonal and interannual variability, and climate change) and the realism of its representation, and to identify the contribution of the processes under study, systematic statistical analyses will be applied in both components (analysis of the observed period and climate projections) to the key variables and process indicators of the climate system: temperature, salinity and sea surface height; temperature and salinity profiles for the ocean; and precipitation, radiative fluxes and wind for the atmosphere. Water and heat exchanges across the straits (SCSTF and ITF) will also be examined. These variables will be compared with estimates provided by satellite observation datasets (evaluated and compiled for the variables mentioned above in the SEASTERS project database) and in situ (derived in particular from Argo profilers and measurements at the straits from the INSTANT and MITF, programmes, 2004-18, Gordon et al. 2010, 2019) will enable the simulations to be evaluated. Cross-comparison of sensitivity simulations will allow the influence of the processes taken into account to be quantified, and the associated mechanisms to be identified through analysis of the simulations.
Le profil recherché
Expertise en modélisation numérique et en traitement de données, connaissance des outils de programmation associés (fortran, python)
Bagage académique en sciences de l'océan et de l'atmosphère
Bon niveau d'anglais
Bonnes capacités rédactionnelles
Capacité d'adaptation, goût du travail en équipe et appétence pour le questionnement scientifique
Application link : https://edd-projets.utoulouse.fr/
Bagage académique en sciences de l'océan et de l'atmosphère
Bon niveau d'anglais
Bonnes capacités rédactionnelles
Capacité d'adaptation, goût du travail en équipe et appétence pour le questionnement scientifique
Application link : https://edd-projets.utoulouse.fr/