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Vignon E.,French National Center for Scientific Research | van de Wiel B.J.H.,Technical University of Delft | van Hooijdonk I.G.S.,TU Eindhoven | Genthon C.,French National Center for Scientific Research | And 6 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2017

Investigation of meteorological measurements along a 45 m tower at Dome C on the high East Antarctic Plateau revealed two distinct stable boundary layer (SBL) regimes at this location. The first regime is characterized by strong winds and continuous turbulence. It results in full vertical coupling of temperature, wind magnitude and wind direction in the SBL. The second regime is characterized by weak winds, associated with weak turbulent activity and very strong temperature inversions reaching up to 25 K in the lowest 10 m. Vertical temperature profiles are generally exponentially shaped (convex) in the first regime and 'convex-concave-convex' in the second. The transition between the two regimes is particularly abrupt when looking at the near-surface temperature inversion and it can be identified by a 10 m wind-speed threshold. With winds under this threshold, the turbulent heat supply toward the surface becomes significantly lower than the net surface radiative cooling. The threshold value (including its range of uncertainty) appears to agree with recent theoretical predictions from the so-called 'minimum wind speed for sustainable turbulence' (MWST) theory. For the quasi-steady, clear-sky winter cases, the relation between the near-surface inversion amplitude and the wind speed takes a characteristic 'S' shape. Closer analysis suggests that this relation corresponds to a 'critical transition' between a steady turbulent and a steady 'radiative' regime, with a dynamically unstable branch in the transition zone. These fascinating characteristics of the Antarctic boundary layer challenge present and future numerical models to represent this region in a physically correct manner. © 2017 Royal Meteorological Society.


Kangah Y.,CNRM GAME Toulouse France | Ricaud P.,CNRM GAME Toulouse France | Attie J.-L.,CNRS Laboratory for Aerology | Saitoh N.,Chiba University | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2017

The aim of this paper is to study the transport of nitrous oxide (N2O) from the Asian surface to the eastern Mediterranean Basin (MB). We used measurements from the spectrometer Thermal and Near infrared Sensor for carbon Observation Fourier transform spectrometer on board the Greenhouse gases Observing SATellite (GOSAT) over the period of 2010-2013. We also used the outputs from the chemical transport model LMDz-OR-INCA over the same period. By comparing GOSAT upper tropospheric retrievals to aircraft measurements from the High-performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations, we calculated a GOSAT High-performance Instrumented Airborne Platform for Environmental Research standard deviation (SD error) of ~2.0 ppbv for a single pixel and a mean bias of approximately -1.3 ppbv (approximately -0.4%). This SD error is reduced to ~0.1 ppbv when we average the pixels regionally and monthly over the MB. The use of nitrogen fertilizer coupled with high soil humidity during the summer Asian monsoon produces high N2O emissions, which are transported from Asian surfaces to the eastern MB. This summertime enrichment over the eastern MB produces a maximum in the difference between the eastern and the western MB upper tropospheric N2O (east-west difference) in July in both the measurements and the model. N2O over the eastern MB can therefore be considered as a footprint of Asian summertime emissions. However, the peak-to-peak amplitude of the east-west difference observed by GOSAT (~1.4 ± 0.3 ppbv) is larger than that calculated by LMDz-OR-INCA (~0.8 ppbv). This is due to an underestimation of N2O emissions in the model and to a relatively coarse spatial resolution of the model that tends to underestimate the N2O accumulation into the Asian monsoon anticyclone. © 2017. The Authors.


Vignon E.,French National Center for Scientific Research | Hourdin F.,CNRS Dynamic Meteorology Laboratory | Genthon C.,French National Center for Scientific Research | Gallee H.,French National Center for Scientific Research | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2017

The parametrization of the atmospheric boundary layer (ABL) is critical over the Antarctic Plateau for climate modelling since it affects the climatological temperature inversion and the negatively buoyant near-surface flow over the ice-sheet. This study challenges state-of-the-art parametrizations used in general circulation models to represent the clear-sky summertime diurnal cycle of the ABL at Dome C, Antarctic Plateau. The Laboratoire de Météorologie Dynamique-Zoom model is run in a 1-D configuration on the fourth Global Energy and Water Cycle Exchanges Project Atmospheric Boundary Layers Study case. Simulations are analyzed and compared to observations, giving insights into the sensitivity of one model that participates to the intercomparison exercise. Snow albedo and thermal inertia are calibrated leading to better surface temperatures. Using the so-called "thermal plume model" improves the momentum mixing in the diurnal ABL. In stable conditions, four turbulence schemes are tested. Best simulations are those in which the turbulence cuts off above 35 m in the middle of the night, highlighting the contribution of the longwave radiation in the ABL heat budget. However, the nocturnal surface layer is not stable enough to distinguish between surface fluxes computed with different stability functions. The absence of subsidence in the forcings and an underestimation of downward longwave radiation are identified to be likely responsible for a cold bias in the nocturnal ABL. Apart from model-specific improvements, the paper clarifies on which are the critical aspects to improve in general circulation models to correctly represent the summertime ABL over the Antarctic Plateau. © 2017. American Geophysical Union. All Rights Reserved.


Douville H.,CNRM GAME Toulouse France | Colin J.,CNRM GAME Toulouse France | Krug E.,CNRM GAME Toulouse France | Cattiaux J.,CNRM GAME Toulouse France | Thao S.,CNRM GAME Toulouse France
Geophysical Research Letters | Year: 2016

Projected changes in daily temperatures are highly model dependent, particularly in the summer midlatitudes where the spread in the response of heat waves represents a major obstacle for the design of adaptation strategies. Understanding the main reasons for such uncertainties is obviously a research priority. Here we use a set of global atmospheric simulations to assess the contribution of the soil moisture feedback to changes in the full distribution of daily maximum summer temperatures projected in the late 21st century. Results show that this feedback (i) accounts for up to one third of the mean increase in daily maximum temperatures, (ii) dominates changes in the shape of the distribution, and (iii) explains about half of the increase in the severity of heat waves over densely populated areas of the northern midlatitudes. A dedicated intercomparison project is therefore needed to assess and constrain land surface feedbacks in the new generation Earth System Models. ©2015. American Geophysical Union.

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