Antarctic ice sheet paleo-constraint database

We present a database of observational constraints on past Antarctic Ice Sheet changes during the last glacial cycle intended to consolidate the observations that represent our understanding of past Antarctic changes, for state-space estimation, and paleo-model calibrations. The database is a major expansion of the initial work of Briggs and Tarasov (2013). It includes new data types and multi-tier data quality assessment. The updated constraint database “AntICE2” consists of observations of past grounded and floating ice sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. In addition to paleo-observations, the present-day ice sheet geometry and surface ice velocities are incorporated to constrain the present-day ice sheet configuration. The method by which the data is curated using explicitly defined criteria is detailed. Moreover, the observational uncertainties are specified. The methodology by which the constraint database can be applied to evaluate a given ice sheet reconstruction is discussed. The implementation of the “AntICE2” database for Antarctic Ice Sheet model calibrations will improve Antarctic Ice Sheet predictions during past warm and cold periods and yield more robust paleo model spin ups for forecasting future ice sheet changes

Exploiting the ANN Potential in Estimating Snow Depth and Snow Water Equivalent From the Airborne SnowSAR Data at X- and Ku-Bands

Within the framework of European Space Agency (ESA) activities, several campaigns were carried out in the last decade with the purpose of exploiting the capabilities of multifrequency synthetic aperture radar (SAR) data to retrieve snow information. This article presents the results obtained from the ESA SnowSAR airborne campaigns, carried out between 2011 and 2013 on boreal forest, tundra and alpine environments, selected as representative of different snow regimes. The aim of this study was to assess the capability of X- and Ku-bands SAR in retrieving the snow parameters, namely snow depth (SD) and snow water equivalent (SWE). The retrieval was based on machine learning (ML) techniques and, in particular, of artificial neural networks (ANNs). ANNs have been selected among other ML approaches since they are capable to offer a good compromise between retrieval accuracy and computational cost. Two approaches were evaluated, the first based on the experimental data (data driven) and the second based on data simulated by the dense medium radiative transfer (DMRT). The data driven algorithm was trained on half of the SnowSAR dataset and validated on the remaining half. The validation resulted in a correlation coefficient R ≃ 0.77 between estimated and target SD, a root-mean-square error (RMSE) ≃ 13 cm, and bias = 0.03 cm. ANN algorithms specific for each test site were also implemented, obtaining more accurate results, and the robustness of the data driven approach was evaluated over time and space. The algorithm trained with DMRT simulations and tested on the experimental dataset was able to estimate the target parameter (SWE in this case) with R = 0.74, RMSE = 34.8 mm, and bias = 1.8 mm. The model driven approach had the twofold advantage of reducing the amount of in situ data required for training the algorithm and of extending the algorithm exportability to other test sites

CAROLS: A New Airborne L-Band Radiometer for Ocean Surface and Land Observations

The “Cooperative Airborne Radiometer for Ocean and Land Studies” (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer—STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity

Influence océanique du golfe de Guinée sur la mousson en Afrique de l'Ouest

The West African monsoon is a complex interaction between the ocean, the land-surface and the atmosphere. Many studies showed a link between the seasonal cooling of the ocean in the Gulf of Guinea (equatorial upwelling) and the monsoon. The aim of this thesis is to explore the air-sea interaction mechanisms, which act on the coastal precipitation of the monsoon during boreal spring. The study is based on in situ and satellite measurements as well as reanalysis datasets. The 2006 monsoon season is analysed thanks to the vast set of observations collected by the AMMA (African Monsoon Multidisciplinary Analyses) project during this year. This study has led to a description of the marine atmospheric boundary layer in the eastern equatorial Atlantic. Results show that the sea surface temperature (SST) front on the northern boundary of the equatorial upwelling is a key zone for air-sea interactions in this region. Thus, a SST cooling south of the equator is generated by a southeasterly wind burst and intensifies the SST front. Consequently, the surface wind tends to weak above cold SST and to strengthen above warm SST. Then, the effect of southeasterly wind bursts in the Gulf of Guinea on the coastal precipitation is studied with satellite measurements and reanalysis datasets on the 2000-2009 period. Results show that a succession of SST coolings is generated by a succession of southeasterly wind bursts in the eastern equatorial Atlantic. These coolings act on the surface wind and the atmospheric circulation between the front and the Guinean coast and favour convection along the coast. This confirms the key role of the SST front and highlights its influence on the coastal precipitation. Finally, these intraseasonal events seem to play an important role in the seasonal evolution of the precipitation before the onset of the West African monsoon.La mousson africaine est un phénomène complexe issu du couplage entre le continent, l'océan et l'atmosphère. De nombreuses études ont montré un lien entre le refroidissement saisonnier de l'océan dans le golfe de Guinée (upwelling équatorial) et la mousson. Cette thèse vise à explorer les mécanismes d'interactions océan-atmosphère agissant sur les précipitations côtières de la mousson africaine au printemps boreal. Ce travail s'appuie à la fois sur des mesures in situ et satellites, et sur des données de réanalyses. La saison de mousson de 2006 a été analysée grâce au grand nombre de données rassemblées cette année-là par le programme AMMA (Analyse Multidisciplinaire de la Mousson Africaine). Cette étude a permis de décrire la couche limite atmosphérique marine dans l'Est de l'Atlantique équatorial. Il en résulte que le front de température de surface de l'océan (SST) établi au nord de l'upwelling équatorial est une zone clé des interactions océan-atmosphère dans cette région. Ainsi, il a été observé qu'un refroidissement de quelques jours de la SST au sud de l'équateur est engendré par un coup de vent des alizés de sud-est et a pour effet d'intensifier le front de SST. Le vent de surface a alors tendance à ralentir au-dessus des SST froides et accélérer au-dessus des SST chaudes. L'effet des coups de vent dans le golfe de Guinée sur les précipitations côtières a ensuite été étudié à partir de mesures satellites et de réanalyses sur la période 2000-2009. Il apparaît qu'une succession de coup de vent entraîne une succession de refroidissement dans la zone d'upwelling équatorial. Ces refroidissements intensifient le front de SST qui agit sur le vent de surface et la circulation atmosphérique avec pour effet de favoriser la convection à la côte. Ces résultats confirment donc le rôle essentiel du front de SST et confortent l'hypothèse de son influence sur les précipitations côtières. Enfin, ces événements intrasaisonniers semblent influencer l'évolution saisonnière des précipitations durant la période qui précède le déclenchement de la mousson africaine

Influence océanique du golfe de Guinée sur la mousson en Afrique de l'Ouest

The West African monsoon is a complex interaction between the ocean, the land-surface and the atmosphere. Many studies showed a link between the seasonal cooling of the ocean in the Gulf of Guinea (equatorial upwelling) and the monsoon. The aim of this thesis is to explore the air-sea interaction mechanisms, which act on the coastal precipitation of the monsoon during boreal spring. The study is based on in situ and satellite measurements as well as reanalysis datasets. The 2006 monsoon season is analysed thanks to the vast set of observations collected by the AMMA (African Monsoon Multidisciplinary Analyses) project during this year. This study has led to a description of the marine atmospheric boundary layer in the eastern equatorial Atlantic. Results show that the sea surface temperature (SST) front on the northern boundary of the equatorial upwelling is a key zone for air-sea interactions in this region. Thus, a SST cooling south of the equator is generated by a southeasterly wind burst and intensifies the SST front. Consequently, the surface wind tends to weak above cold SST and to strengthen above warm SST. Then, the effect of southeasterly wind bursts in the Gulf of Guinea on the coastal precipitation is studied with satellite measurements and reanalysis datasets on the 2000-2009 period. Results show that a succession of SST coolings is generated by a succession of southeasterly wind bursts in the eastern equatorial Atlantic. These coolings act on the surface wind and the atmospheric circulation between the front and the Guinean coast and favour convection along the coast. This confirms the key role of the SST front and highlights its influence on the coastal precipitation. Finally, these intraseasonal events seem to play an important role in the seasonal evolution of the precipitation before the onset of the West African monsoon.La mousson africaine est un phénomène complexe issu du couplage entre le continent, l'océan et l'atmosphère. De nombreuses études ont montré un lien entre le refroidissement saisonnier de l'océan dans le golfe de Guinée (upwelling équatorial) et la mousson. Cette thèse vise à explorer les mécanismes d'interactions océan-atmosphère agissant sur les précipitations côtières de la mousson africaine au printemps boreal. Ce travail s'appuie à la fois sur des mesures in situ et satellites, et sur des données de réanalyses. La saison de mousson de 2006 a été analysée grâce au grand nombre de données rassemblées cette année-là par le programme AMMA (Analyse Multidisciplinaire de la Mousson Africaine). Cette étude a permis de décrire la couche limite atmosphérique marine dans l'Est de l'Atlantique équatorial. Il en résulte que le front de température de surface de l'océan (SST) établi au nord de l'upwelling équatorial est une zone clé des interactions océan-atmosphère dans cette région. Ainsi, il a été observé qu'un refroidissement de quelques jours de la SST au sud de l'équateur est engendré par un coup de vent des alizés de sud-est et a pour effet d'intensifier le front de SST. Le vent de surface a alors tendance à ralentir au-dessus des SST froides et accélérer au-dessus des SST chaudes. L'effet des coups de vent dans le golfe de Guinée sur les précipitations côtières a ensuite été étudié à partir de mesures satellites et de réanalyses sur la période 2000-2009. Il apparaît qu'une succession de coup de vent entraîne une succession de refroidissement dans la zone d'upwelling équatorial. Ces refroidissements intensifient le front de SST qui agit sur le vent de surface et la circulation atmosphérique avec pour effet de favoriser la convection à la côte. Ces résultats confirment donc le rôle essentiel du front de SST et confortent l'hypothèse de son influence sur les précipitations côtières. Enfin, ces événements intrasaisonniers semblent influencer l'évolution saisonnière des précipitations durant la période qui précède le déclenchement de la mousson africaine

Role of air-sea interactions on the coastal rainfall in the Gulf of Guinea during boreal spring

International audienceThe role of air-sea interactions in the boreal spring precipitation of the West African monsoon is explored through the wind variability in the Gulf of Guinea. Satellite measurements and reanalyses data are used to describe the atmosphere and the sea surface in the Gulf of Guinea from 2000 to 2009. Previous results showed a statistical link between the strengthening of southerlies between the Equator and the Guinean coast, and precipitation along the coast. In this study, linear regressions are first performed in May-June (2000-2009) to investigate the mechanisms at stake : an equatorial SST cooling strengthens the wind north of the equator, via the SST front located along 1°N. This wind acceleration intensifies the low atmospheric local circulation, which components are surface southerlies, coastal convergence, low atmosphere southward return flow, and subsidence over the Gulf of Guinea. When this circulation is stronger than normal, it brings more humidity toward the coast, which triggers deeper atmospheric convection and increases the coastal rainfall . In addition, an abrupt change in the surface wind pattern is observed between April and July. Composites are used to analyse temporal and spatial variations of the SST, surface wind speed and humidity, in surface as well as in altitude. A clear transition is observed during the spring season, when the wind strengthens between the equator and 5°N, which generally occurs at the end of May. Eventually, this study emphasizes very clearly the importance of the intraseasonal variability in the seasonal evolution and setting of the guinean coastal rainfall

Role of air-sea interactions on the coastal rainfall in the Gulf of Guinea during boreal spring

International audienceThe role of air-sea interactions in the boreal spring precipitation of the West African monsoon is explored through the wind variability in the Gulf of Guinea. Satellite measurements and reanalyses data are used to describe the atmosphere and the sea surface in the Gulf of Guinea from 2000 to 2009. Previous results showed a statistical link between the strengthening of southerlies between the Equator and the Guinean coast, and precipitation along the coast. In this study, linear regressions are first performed in May-June (2000-2009) to investigate the mechanisms at stake : an equatorial SST cooling strengthens the wind north of the equator, via the SST front located along 1°N. This wind acceleration intensifies the low atmospheric local circulation, which components are surface southerlies, coastal convergence, low atmosphere southward return flow, and subsidence over the Gulf of Guinea. When this circulation is stronger than normal, it brings more humidity toward the coast, which triggers deeper atmospheric convection and increases the coastal rainfall . In addition, an abrupt change in the surface wind pattern is observed between April and July. Composites are used to analyse temporal and spatial variations of the SST, surface wind speed and humidity, in surface as well as in altitude. A clear transition is observed during the spring season, when the wind strengthens between the equator and 5°N, which generally occurs at the end of May. Eventually, this study emphasizes very clearly the importance of the intraseasonal variability in the seasonal evolution and setting of the guinean coastal rainfall

Influence océanique du golfe de Guinée sur la mousson en Afrique de l'Ouest

La mousson africaine démarre chaque année à la fin du printemps boréal, lorsqu un fort contraste thermique se développe entre le Sahara surchauffé et le golfe de Guinée qui se refroidit en surface. De nombreuses études montrent le rôle majeur des températures de surface de l'océan dans le système de mousson. Cette thèse vise à explorer les mécanismes d'interactions océan-atmosphère agissant sur les précipitations côtières de la mousson africaine au printemps. L'étude s'appuie à la fois sur des mesures in situ et satellites, et sur des données de modèle. La saison de mousson de l'année 2006 a été analysée grâce au grand nombre de données rassemblées cette année-là par le programme AMMA (Analyse Multidisciplinaire de la Mousson Africaine). Il a ainsi été mis en évidence que le refroidissement de la surface de l'océan crée un front océanique à l'équateur qui engendre une accélération du vent au nord de l'équateur semblant favoriser l'activité convective le long de la côte africaine. L'étape suivante a été d'étendre l'étude à une période de dix ans (2000-2009) à l'aide des mesures satellites et des données de réanalyses. Les phénomènes observés pour la saison de mousson 2006 ont été retrouvés et les analyses réalisées ont mis en avant un mécanisme liant les coups de vents dans l'Est de l'Atlantique équatorial aux précipitations côtières. Ainsi, un coup de vent entraîne un refroidissement de la surface de l'océan à l'équateur. En retour, ce refroidissement allié à l'accélération du vent au nord de l'équateur, agit sur la circulation atmosphérique de basse couche dans le golfe de Guinée. L'activité convective est alors favorisée et les précipitations augmentent à la côte.The West African monsoon starts each year at the end of boreal spring, when a strong thermal contrast develops between the warmer Sahara region and the cooler Gulf of Guinea. Many studies show that sea surface temperatures play a key role in the monsoon system. The aim of this thesis is to explore the air-sea interactions occurring in this region, and the mechanisms through which they may impact the coastal rainfall of the monsoon during spring. The study is based on in situ and satellite measurements as well as model data. The 2006 monsoon season is analysed thanks to the vast set of observations collected by the AMMA (African Monsoon Multidisciplinary Analyses) project during this year. Results show that a cooling of the sea surface creates an oceanic front at the equator. This strengthens the wind north of the equator and seems to favour the convective activity along the African coast. The next step is to extend this study to a ten-year period (2000-2009) with satellite measurements and reanalyses data. Results are consistent with the process observed in the 2006 case study, and the statistical analyses show a link between the wind burst in the East Equatorial Atlantic and the coastal rainfall. In this context, a wind burst generates a cooling of the sea surface at the equator. This cooling combined with the wind strengthening north of the equator, in turn, impacts the low-level atmospheric circulation in the Gulf of Guinea. This enhances convective activity and increases precipitation along the coast.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF