Apport de la mesure lidar dans l'étude des aérosols et nuages stratosphériques polaires et de leurs perturbations climatiques
Notice bibliographique
Résumé
As the understanding of the interactions between stratospheric ozone chemistry and climate change progresses, the consequences of both temperature change and perturbations in stratospheric aerosol loading are becoming a topic of major scientific interest.It is well established that volcanism is the main source of stratospheric aerosols and that major volcanic episodes are associated with negative ozone anomalies. However, the high latitude effect of an overload of sulphate aerosols, precursors of polar stratospheric clouds (PSC), remains poorly understood.In addition, stratospheric injections of carbonaceous aerosols have been observed during major fires in recent years. In Canada in 2017 and Australia in 2020, aerosol masses comparable to those emitted by moderate volcanism were reported. This is of great scientific interest, as carbon does not naturally occur in the stratosphere and the effects of its significant intake are yet to be studied. Also, climate change is expected to favour the occurrence of major fires, adding the question of long-term trends in aerosol loading to the need to finely characterise the effect of such a disturbance.PSCs, formed on aerosols, are the precursors of seasonal ozone destruction and are at the heart of these issues. Lidar is a suitable instrument for studying these condensed phases. Using the lidar at the French Antarctic station Dumont d'Urville (DDU) and relevant space instruments, this thesis investigates trends and processes related to PSCs and stratospheric aerosol perturbations.Measurements acquired at DDU use different classifications of PSCs to illustrate fine processes that are only accessible through the geometry of a ground-based instrument. The parameterisation of the PSCs is based on a concise and representative classification, and the coastal location of the station is an advantage due to the high variability of the particle observations it allows. A trend in the number of PSC days per year at DDU from 2007 to 2020 is established by combining lidar and temperature measurements. This trend, of -4.4 PSC days per year per decade, reflects an opposite trend in stratospheric temperatures over this period. The latter, recently confirmed by other studies, raises questions about long-term trends in the context of climate change.The Australian fires in 2020 injected an unprecedented mass of aerosols into the stratosphere, some of which was transported to the high southern latitudes. The DDU lidar was able to probe these aerosols from January to October 2020. This allowed a rich characterisation of the plumes over time. Their presence within the vortex was confirmed and raises the delicate question of the interactions between carbonaceous aerosols and PSC. The high ozone depletion reported at DDU in October 2020 can only be compared to the year 2015, marked by an aerosol overload due to the Calbuco eruption. We also highlight the technological challenge around aerosol speciation on fine signatures.In order to adapt to recent scientific questions, a field campaign allowed the evolution of the lidar installed at DDU towards a multispectral infrared / visible / ultraviolet laser source. This configuration offers new possibilities, including access to granulometry that can directly resolve aerosol and cloud speciation. The historical eruption in Tonga in January 2022 injected a large amount of aerosols, partly detected at DDU from February to September 2022. This thesis therefore includes work on this event using field instrumentation as a technical and especially scientific perspective for the study of aerosols and clouds at high latitudes.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,002 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».