Apport de la mesure lidar dans l'étude des aérosols et nuages stratosphériques polaires et de leurs perturbations climatiques
Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".