14 research outputs found
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Toward an improved representation of middle atmospheric dynamics thanks to the ARISE project
This paper reviews recent progress toward understanding the dynamics of the middle atmosphere in the framework of the Atmospheric Dynamics Research InfraStructure in Europe (ARISE) initiative. The middle atmosphere, integrating the stratosphere and mesosphere, is a crucial region which influences tropospheric weather and climate. Enhancing the understanding of middle atmosphere dynamics requires improved measurement of the propagation and breaking of planetary and gravity waves originating in the lowest levels of the atmosphere. Inter-comparison studies have shown large discrepancies between observations and models, especially during unresolved disturbances such as sudden stratospheric warmings for which model accuracy is poorer due to a lack of observational constraints. Correctly predicting the variability of the middle atmosphere can lead to improvements in tropospheric weather forecasts on timescales of weeks to season. The ARISE project integrates different station networks providing observations from ground to the lower thermosphere, including the infrasound system developed for the Comprehensive Nuclear-Test-Ban Treaty verification, the Lidar Network for the Detection of Atmospheric Composition Change, complementary meteor radars, wind radiometers, ionospheric sounders and satellites. This paper presents several examples which show how multi-instrument observations can provide a better description of the vertical dynamics structure of the middle atmosphere, especially during large disturbances such as gravity waves activity and stratospheric warming events. The paper then demonstrates the interest of ARISE data in data assimilation for weather forecasting and re-analyzes the determination of dynamics evolution with climate change and the monitoring of atmospheric extreme events which have an atmospheric signature, such as thunderstorms or volcanic eruptions
Connections of climate change and variability to large and extreme forest fires in southeast Australia
The 2019/20 Black Summer bushfire disaster in southeast Australia was unprecedented: the extensive area of forest burnt, the radiative power of the fires, and the extraordinary number of fires that developed into extreme pyroconvective events were all unmatched in the historical record. Australia’s hottest and driest year on record, 2019, was characterised by exceptionally dry fuel loads that primed the landscape to burn when exposed to dangerous fire weather and ignition. The combination of climate variability and long-term climate trends generated the climate extremes experienced in 2019, and the compounding effects of two or more modes of climate variability in their fire-promoting phases (as occurred in 2019) has historically increased the chances of large forest fires occurring in southeast Australia. Palaeoclimate evidence also demonstrates that fire-promoting phases of tropical Pacific and Indian ocean variability are now unusually frequent compared with natural variability in preindustrial times. Indicators of forest fire danger in southeast Australia have already emerged outside of the range of historical experience, suggesting that projections made more than a decade ago that increases in climate-driven fire risk would be detectable by 2020, have indeed eventuated. The multiple climate change contributors to fire risk in southeast Australia, as well as the observed non-linear escalation of fire extent and intensity, raise the likelihood that fire events may continue to rapidly intensify in the future. Improving local and national adaptation measures while also pursuing ambitious global climate change mitigation efforts would provide the best strategy for limiting further increases in fire risk in southeast Australia
Death rates in HIV-positive antiretroviral-naive patients with CD4 count greater than 350 cells per microL in Europe and North America: a pooled cohort observational study
Whether people living with HIV who have not received antiretroviral therapy (ART) and have high CD4 cell counts have higher mortality than the general population is unknown. We aimed to examine this by analysis of pooled data from industrialised countries
Variable impact on mortality of AIDS-defining events diagnosed during combination antiretroviral therapy: not all AIDS-defining conditions are created equal.
Abstract
Background—The extent to which mortality differs following individual acquired
immunodeficiency syndrome (AIDS)–defining events (ADEs) has not been assessed among
patients initiating combination antiretroviral therapy.
Methods—We analyzed data from 31,620 patients with no prior ADEs who started combination
antiretroviral therapy. Cox proportional hazards models were used to estimate mortality hazard
ratios for each ADE that occurred in >50 patients, after stratification by cohort and adjustment for
sex, HIV transmission group, number of anti-retroviral drugs initiated, regimen, age, date of
starting combination antiretroviral therapy, and CD4+ cell count and HIV RNA load at initiation
of combination antiretroviral therapy. ADEs that occurred in <50 patients were grouped together
to form a “rare ADEs” category.
Results—During a median follow-up period of 43 months (interquartile range, 19–70 months),
2880 ADEs were diagnosed in 2262 patients; 1146 patients died. The most common ADEs were
esophageal candidiasis (in 360 patients), Pneumocystis jiroveci pneumonia (320 patients), and
Kaposi sarcoma (308 patients). The greatest mortality hazard ratio was associated with non-
Hodgkin’s lymphoma (hazard ratio, 17.59; 95% confidence interval, 13.84–22.35) and progressive
multifocal leukoencephalopathy (hazard ratio, 10.0; 95% confidence interval, 6.70–14.92). Three
groups of ADEs were identified on the basis of the ranked hazard ratios with bootstrapped
confidence intervals: severe (non-Hodgkin’s lymphoma and progressive multifocal
leukoencephalopathy [hazard ratio, 7.26; 95% confidence interval, 5.55–9.48]), moderate
(cryptococcosis, cerebral toxoplasmosis, AIDS dementia complex, disseminated Mycobacterium
avium complex, and rare ADEs [hazard ratio, 2.35; 95% confidence interval, 1.76–3.13]), and
mild (all other ADEs [hazard ratio, 1.47; 95% confidence interval, 1.08–2.00]).
Conclusions—In the combination antiretroviral therapy era, mortality rates subsequent to an
ADE depend on the specific diagnosis. The proposed classification of ADEs may be useful in
clinical end point trials, prognostic studies, and patient management