frendeitrues

Séminaires

2019 03 vovsq10ansLe Latmos, poursuit son cycle de conférences organisées à l'occasion de son anniversaire.

Il vous propose ce deuxième acte revenant sur la recherche menée sur Mars avec l'instrument SAM embarqué sur le rover Curiosity.

Vous pouvez réserver votre place (et un sandwich !) en suivant les modalités indiquées sur l'affiche ou vous présenter librement.

 

00 10ansbaseline

Tristan L'Ecuyer, professeur à l'Université du Wisconsin à Madison (USA) et expert en observation de la pluie et des nuages pour l'étude du système climatique, viendra au LATMOS / Guyancourt  le

    vendredi 21 septembre à 11h, salle 2202
et donnera un séminaire intitulé

A Quest to Fill a Startling Gap in Observing Arctic Climate

 

Far-infrared radiation (that occurring at wavelengths longer than 15 microns) makes up 60% of the thermal emission from the Arctic and nearly half of Earth's emission, globally.           Remarkably, however, while far-infrared spectra have been collected from every planet in the solar system, Earth's far-infrared emission spectrum has never been systematically documented. These measurements could offer powerful new insights into the key processes at work in the rapidly changing Arctic. This presentation will describe a new satellite mission concept aimed at addressing this critical observational gap. The Polar Radiant Energy in the Far-InfaRed Experiment (PREFIRE) utilizes two CubeSats in asynchronous orbits to systematically document the spectral variation of thermal emission across the mid- and far-infrared (5 – 45 microns) throughout the Arctic. We anticipate that the resulting measurements will reveal changes in the full spectrum of Arctic radiant energy associated with processes that operate on scales ranging from sub-daily to seasonal. By distinguishing the unique spectral fingerprints of changes in temperature, water vapor, clouds, and surface melt processes, PREFIRE will help untangle the complex time-varying errors in model physics responsible for the large spread in simulations of the Arctic energy budget.

2018 09 seminaireLecuyer

Vendredi 9 mars 2018 à 11h

LATMOS site UPMC
Salle de réunion 411, tour 45-46, 4ème étage

Ozone under (Laser) Light : new insights into an old molecule

Christof Janssen

LERMA, Paris

Ozone is a key molecule in atmospheric chemistry. The measurement of this reactive molecule poses a challenge for the scientific community. We will present new precision measurements of the ozone cross sections at 325 nm that resuscitate an old debate about the consistency of currently recommended UV data with IR intensities. Implications of the accuracy of ozone measurements in the Huggins bands are discussed.

We will also report on new measurements of the isotope fractionation in the vis light decomposition of ozone.

Le jeudi 7 juin 2018 à 11h

LATMOS site Guyancourt
Amphithéâtre Gérard Mégie, Observatoire Versailles St Quentin

Probabilistic Quantitative Precipitation Estimates with Ground- and Space-based Remote Sensing

Pierre-Emmanuel Kirstetter

National Severe Storm Laboratory, University of Oklahoma (USA)

Progress in precipitation estimation is critical to advance weather and water budget studies and prediction of natural hazards caused by extreme rainfall events from local to global scale. An interdisciplinary challenge in remote sensing, meteorology and hydrology is the impact, representation, and use of uncertainty. Understanding of hydrometeorological processes and applications require more than just one deterministic "best estimate" to adequately cope with the intermittent, highly skewed distribution that characterizes precipitation. Yet the uncertainty structure of quantitative precipitation estimation (QPE) from ground-based radar networks like NEXRAD and satellite-based active and passive sensors of the Global Precipitation Measurement (GPM) mission is largely unknown at fine spatiotemporal scales near the sensor measurement scale (e.g. 1-km/5-min for ground-based radars, 5-km/instantaneous for space-based radars). We propose to advance the use of uncertainty as an integral part of QPE for ground-based and space-borne sensors. Probability distributions of precipitation rates are computed instead of deterministic values using models quantifying the relation between the sensor measurement and the corresponding "true" precipitation. This approach preserves the fine space/time sampling properties of the sensor and integrates sources of error in QPE. It provides a framework to diagnose uncertainty when instruments sample raining scenes or processes challenging the assumptions of the QPE algorithms. Precipitation probability maps compare favorably to deterministic QPE and improve precipitation estimation. Probabilistic QPE is shown to mitigate systematic biases from deterministic retrievals, quantify uncertainty, and advance the monitoring of precipitation extremes. It provides the basis radar and satellite precipitation ensembles needed for multisensor merging of precipitation, early warning and mitigation of hydrometeorological hazards, and hydrological modeling. Perspectives for improved understanding and parameterizations of precipitation processes, estimation of precipitation at multiple scales, hydrological prediction and risk monitoring will be presented.

Mardi 28 novembre 2017 à 11h

LATMOS site UPMC
Salle de réunion 411, tour 45-46, 4ème étage

Evidence for continued ozone layer reduction

William Ball

ETH Zürich and PMOD, Davos

Stratospheric ozone protects life from harmful ultraviolet radiation. The Montreal Protocol, enacted to prevent ozone depletion from human activity, halted declines in column-integrated ozone in the 1990s; the upper stratosphere is recovering, but lower stratospheric trends are unknown. I will present clear evidence that lower stratospheric ozone continues to decline, preventing total ozone recovery. This result contradicts expectations and, with no clear understanding of why this trend has emerged, implies that the problem of ozone depletion is not yet fully solved. The decline may impact future estimates of ozone layer recovery, the stratospheric response to climate change, radiative climate forcing, ozone exchange between the stratosphere and troposphere, and surface levels of ultraviolet radiation.