El Niño

Résumé

El Niño est un phénomène climatique particulier qui se caractérise par des températures anormalement élevées de l'eau dans la partie est de l'océan Pacifique sud, représentant une extension vers le sud du courant côtier saisonnier chaud éponyme au large du Pérou et de l'Équateur mettant fin à la saison de pêche. Les années El Niño ont pour habitude des températures caniculaire mondiale. Il a été relié à un cycle de variation de la pression atmosphérique globale entre les zones est et ouest du Pacifique, nommé « oscillation australe », et les deux phénomènes sont réunis sous le titre de ENSO (El Niño-Southern Oscillation). El Niño est une conséquence régionale d'une perturbation dans la circulation atmosphérique générale entre les pôles et l'équateur. Son apparition déplace les zones de précipitations vers l'est dans l’océan Pacifique et empêche la remontée d'eau froide le long de la côte de l’Amérique du Sud, ce qui coupe la source de nutriments pour la faune de ces e

Source officielle

https://fr.wikipedia.org/wiki/El_Ni%C3%B1o

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Concepts associés (32)

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Séances de cours associées (13)

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The response of stomatal conductance to seasonal drought in tropical forests

Charlotte Grossiord

Stomata regulate CO2 uptake for photosynthesis and water loss through transpiration. The approaches used to represent stomatal conductance (g s) in models vary. In particular, current understanding of drivers of the variation in a key parameter in those models, the slope parameter (i.e. a measure of intrinsic plant water‐use‐efficiency), is still limited, particularly in the tropics. Here we collected diurnal measurements of leaf gas exchange and leaf water potential (Ψleaf), and a suite of plant traits from the upper canopy of 15 tropical trees in two contrasting Panamanian forests throughout the dry season of the 2016 El Niño. The plant traits included wood density, leaf‐mass‐per‐area (LMA), leaf carboxylation capacity (V c,max), leaf water content, the degree of isohydry, and predawn Ψleaf. We first investigated how the choice of four commonly used leaf‐level g s models with and without the inclusion of Ψleaf as an additional predictor variable influence the ability to predict g s, and then explored the abiotic (i.e. month, site‐month interaction) and biotic (i.e. tree‐species‐specific characteristics) drivers of slope parameter variation. Our results show that the inclusion of Ψleaf did not improve model performance and that the models that represent the response of g s to vapor pressure deficit performed better than corresponding models that respond to relative humidity. Within each g s model, we found large variation in the slope parameter, and this variation was attributable to the biotic driver, rather than abiotic drivers. We further investigated potential relationships between the slope parameter and the six available plant traits mentioned above, and found that only one trait, LMA, had a significant correlation with the slope parameter (R 2 = 0.66, n = 15), highlighting a potential path towards improved model parameterization. This study advances understanding of g s dynamics over seasonal drought, and identifies a practical, trait‐based approach to improve modeling of carbon and water exchange in tropical forests.

2020

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Multi-Channel Amplifier-Discriminator for Highly Time-Resolved Detection

Matthieu Despeisse, François Eric Powolny

A low-power multi-channel amplifier-discriminator was developed for application in highly time-resolved detection systems. The proposed circuit architecture, so-called Nino, is based on a time-over-threshold approach and shows a high potential for time-resolved readout of solid-state photo-detectors and of detectors based on vacuum technologies. The Irpics circuit was designed in a 250 nm CMOS technology, implementing 32 channels of a Nino version optimized to achieve high-time resolution on the output low-voltage differential signals (LVDS) while keeping a low power consumption of 10 mW per channel. Electrical characterizations of the circuit demonstrate a very low intrinsic time jitter on the output pulse leading edge, measured below 10 ps rms for each channel for high input signal charges ( > 100 fC) and below 25 ps rms for low input signal charges (20-100 fC). The read-out architecture moreover permits to retrieve the input signal charge from the timing measurements, while a calibration procedure was developed to correct for time walk variations of the output pulses. The Irpics circuit therefore shows a high potential of application in multi-channel detection systems requiring a high time resolution, as needed for Time Of Flight systems (TOF), Positron Emission Tomography (PET) or time-resolved spectroscopy.

2011

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Global measurements of atmospheric methane (CH4) concentrations continue to show large interannual variability whose origin is only partly understood. Here we quantify the influence of the El Nino-Southern Oscillation (ENSO) on wetland CH4 emissions, which are thought to be the dominant contributor to interannual variability of the CH4 sources. We use a simple wetland CH4 model that captures variability in wetland extent and soil carbon to model the spatial and temporal dynamics of wetland CH4 emissions from 1950-2005 and compare these results to an ENSO index. We are able to explain a large fraction of the global and tropical variability in wetland CH4 emissions through correlation with the ENSO index. We find that repeated El Nino events throughout the 1980s and 1990s were a contributing factor towards reducing CH4 emissions and stabilizing atmospheric CH4 concentrations. An increase in emissions from the boreal region would likely strengthen the feedback between ENSO and interannual variability in global wetland CH4 emissions. Our analysis emphasizes that climate variability has a significant impact on wetland CH4 emissions, which should be taken into account when considering future trends in CH4 sources. Citation: Hodson, E. L., B. Poulter, N. E. Zimmermann, C. Prigent, and J. O. Kaplan (2011), The El Nino-Southern Oscillation and wetland methane interannual variability, Geophys. Res. Lett., 38, L08810, doi:10.1029/2011GL046861.

American Geophysical Union2011

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The response of stomatal conductance to seasonal drought in tropical forests

Charlotte Grossiord

2020