scholarly journals Variabilité saisonnière et intra-saisonnière de la pluviométrie en milieu forestier dans le Sud-ouest centrafricain

2021 ◽  
Vol 384 ◽  
pp. 367-373
Author(s):  
Jean-Marie Djebata ◽  
Cyriaque R. Nguimalet ◽  
Pierre Camberlin
Keyword(s):  
Station Data ◽  
Contrôle De Qualité ◽  
Base De Données ◽  
Climate Hazards

Abstract. Ce travail présente la variabilité intra-saisonnière de la pluviométrie dans le Sud-ouest centrafricain. Les données pluviométriques journalières utilisées couvrent la période 1981–2017. Elles ont été extraites aux points de grilles les plus proches des quatre stations représentatives de la zone d'étude (Bangui, Berberati, Boukoko et Nola) sur la base de données CHIRPS (Climate Hazards Group InfraRed Precipitation with Station data). Un contrôle de qualité de ces données a été effectué à partir d'une inter-comparaison entre les produits d'estimations et les données in-situ sur différentes sous-périodes : 1998–2011 à Nola, 1998–2012 à Berberati, 1998–2014 à Bangui et 2002–2017 à Boukoko. Le coefficient de corrélation entre les données CHIRPS et les observations au pas annuel est faible à Bangui (r=0,46), moyen à Nola (r=0,57) et Berberati (r=0,60), et bon à Boukoko (r=0,73). Les dates de début de la saison de pluies varient entre le 13 février et le 2 avril et celles de fin entre le 31 octobre et le 4 décembre. Des épisodes secs et humides sont mis en évidence dans le Sud-ouest centrafricain. A Bangui et Berberati, la période du 15 au 22 mai 1999 a été sèche soit 23 jours sans pluie. A Boukoko et Nola, la période du 26 juin au 24 juillet de la même année était caractérisée par des épisodes secs. Ces résultats établissent que la répartition intra-saisonnière des pluies n'est pas uniforme dans le Sud-ouest centrafricain.

On properties of seawater defined by temperature, salinity, and pressure

2021 ◽  
Vol 79 (3) ◽  
pp. 121-147
Author(s):  
George Veronis
Keyword(s):  
Vertical Direction ◽  
Great Depth ◽  
Local Potential ◽  
Potential Density ◽  
Marine Research ◽  
Station Data ◽  
Starting Point ◽  
The World ◽  
Gravitational Stability

Hydrographic station data, consisting principally of temperature and salinity determinations, have been used by physical oceanographers to develop a climatological picture of the distribution of these quantities in the oceans of the world. Density as determined by Knudsen's formula, taken together with hydrostatic and geostrophic dynamics, also provides a crude picture of oceanic flow. However, the data probably contain substantially more information than has been derived from them in the past.The quantity that is orthogonal to potential-density curves in the S plane is suggested as a useful variable to complement the information contained in potential density. The derivation of this quantity, denoted by τ in this paper, is straightforward. A polynomial expression for τ that is suitable for computer calculations of τ from hydrographic station data is given. Shown are examples of hydrographic station data from the Atlantic plotted on the τσ diagram. The information contained in the τσ diagram shows many of the features exhibited in the TS plane. Vertical sections of τ appear to provide information about mixing in different parts of the Atlantic. The distribution of τ for abyssal waters at selected stations in the oceans of the world resembles the distribution of abyssal density as plotted by Lynn and Reid (1968). From the data presented, it appears that τ may serve as a good tracer for abyssal water movements.Since τ is defined to be orthogonal to σ, the expectation is that τ is a dynamically passive variable. However, since σ does not correlate with abyssal densities, it appears to lose dynamical significance at great depth, and τ assumes dynamical significance because of its orthogonality to σ. This unexpected feature leads to an exploration of the dynamical significance of σ. A natural starting point is the question of stability of abyssal water.A distinction is made between stability as determined by in situ determinations and as determined by the potential-density (σ) distribution. Simple examples are presented to show that analysis based on σ alone can lead to incorrect conclusions about gravitational stability of the water in the abyssal ocean. The reason is that seawater is a multicomponent thermodynamic system, and the thermodynamic coefficients are functions of pressure, salinity, and temperature. This functional dependence leads to adjustments in density as a water particle moves adiabatically in the vertical direction so that a layer of water that appears to be unstable near the surface may be stable (as determined by in situ determination) at great depth. A local potential density, which is simply the vertical integral of the in situ stability, is derived. This quantity gives a precise picture of gravitational stability in the vertical direction. Some distributions of local potential density are shown.Originally published May 15, 1972, in the Journal of Marine Research 30(2), 227???255.

scholarly journals Suivi hydrologique par altimétrie spatiale dans le bassin du Congo

2021 ◽  
Vol 384 ◽  
pp. 37-41
Author(s):  
Christophe Brachet ◽  
Alice Andral ◽  
Georges Gulemvuga Guzanga ◽  
Blaise Léandre Tondo ◽  
Pierre-Olivier Malaterre ◽  
...  
Keyword(s):  
Base De Données

Abstract. Le satellite SWOT sera lancé fin 2022 par le Centre National d'Etudes Spatiales (CNES) français et la National Aeronautics and Space Administration (NASA) américaine. L'altimétrie spatiale permet de compléter les données hydrométriques in situ à travers l'établissement de «stations virtuelles», au croisement de la trace au sol du satellite avec un cours d'eau. SWOT améliorera encore la couverture des zones observées ainsi que la précision grâce à une technologie innovante. Un projet d'appui à la Commission Internationale du bassin Congo-Oubangui-Sangha (CICOS) développé depuis 2016 sur financement de l'Agence Française de Développement (AFD) et facilité par l'Office International de l'Eau (OiEau) permet de promouvoir l'hydrologie spatiale à travers un groupe d'institutions françaises, en appui à la CICOS. Diverses activités ont été développées dont la fourniture d'une base de données spatiales par l'Institut de Recherche pour le Développement (IRD), ainsi que la comparaison avec des données in situ. Une méthodologie innovante a été proposée par l'Institut national de recherche pour l'agriculture, l'alimentation et l'environnement (INRAE) pour passer des altitudes aux débits aux stations virtuelles. Des applications spécifiques ont par ailleurs été développées par la Compagnie Nationale du Rhône (CNR) pour l'hydroélectricité et la navigation fluviale.

Constitution d’une base de données centralisée pour le contrôle de qualité interne en radiothérapie

2009 ◽  
Vol 13 (6-7) ◽  
pp. 645
Author(s):  
P. Fau ◽  
C. Rodrigues ◽  
R. Ruchaud ◽  
J. Bravetti
Keyword(s):  
Contrôle De Qualité ◽  
Base De Données

scholarly journals Potencial uso das informações de chuvas obtidas por sensoriamento remoto na análise não paramétrica de eventos extremos na bacia do rio Madeira

Revista DAE ◽  
2021 ◽  
Vol 69 (231) ◽  
pp. 110-123
Author(s):  
Vinicius Alexandre Sikora de Souza ◽  
Daniel Medeiros Moreira ◽  
Otto Corrêa Rotunno Filho ◽  
Anderson Paulo Rudke ◽  
Claudia Daza Andrade ◽  
...  
Keyword(s):  
Climate Hazards ◽  
Rio Madeira

O trabalho se propõe a avaliar o emprego de dados satelitais do tipo Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) para a geração de curvas de intensidade-duração-frequência (IDF) na bacia do rio Madeira. Curvas IDF foram geradas simultaneamente para dados observados em 37 pluviômetros distribuídos na bacia e para os píxeis do CHIRPS que abrangem geograficamente essas estações observacionais in situ. Inicialmente, os dados foram analisados mediante o ajuste da distribuição de Gumbel para períodos de retorno que se estendem de 2 a 100 anos e duração da chuva de 5 minutos a 24 horas. Na validação das equações IDF, utilizou-se o coeficiente de determinação da regressão (r²) e avaliaram-se os resíduos produzidos. Observa-se que as equações obtidas pelo estudo apresentam uma vasta aplicabilidade em obras de engenharia e, em especial, em atividades que requeiram suporte hidrológico devido à diversidade de durações e de tempos de recorrência utilizados. Além disso, a análise de erros e a estimava dos coeficientes de determinação das funções IDF, que estiveram próximos de 0,70, ressaltam o uso das mesmas na representação dos eventos extremos. A comparação das bases de dados observacionais e de satélite permitiu estabelecer a confiabilidade do uso de dados do satélite CHIRPS na construção de relações IDF para situações em que não se dispõe de informações pluviométricas locais, embora as discrepâncias entre as bases tendam a aumentar e a ser diretamente proporcionais ao período de retorno. Palavras-chave: Eventos extremos de chuva. Precipitação máxima. Curva IDF Sensoriamento remoto.

scholarly journals Análisis de la precipitación y la evaporación en el Orinoco colombiano según los modelos climáticos regionales del experimento CORDEX-CORE

TecnoLógicas ◽  
2021 ◽  
Vol 24 (52) ◽  
pp. e2144
Author(s):  
Carolina Florian-Vergara ◽  
Hernán D. Salas ◽  
Alejandro Builes-Jaramillo
Keyword(s):  
Precipitation Climatology ◽  
Station Data ◽  
Global Precipitation Climatology Center ◽  
Global Land ◽  
Climate Hazards ◽  
Global Precipitation

Con el fin de representar la precipitación y evaporación total mensual en una cuenca hidrográfica del Orinoco colombiano, este trabajo evaluó la capacidad de los modelos climáticos regionales incluidos en el Experimento regional coordinado de reducción de escala (CORDEX-CORE). Para ello, complementariamente, se incluyeron datos de precipitación y evaporación total de fuentes como Climate Hazards Center InfraRed Precipitation with Station data (CHIRPS), el reanálisis atmosférico (ERA5), Global Precipitation Climatology Center (GPCC) y Global Land Evaporation Amsterdam Model (GLEAM). Las comparaciones entre los ensambles de los modelos y las observaciones se hicieron utilizando métodos gráficos y métodos cuantitativos, entre ellos: diagramas de cajas, porcentajes de sesgo, eficiencia de Nash-Sutcliffe, entre otros. Los resultados evidencian que los valores promedio de precipitación están adecuadamente representados, en términos de su temporalidad y magnitud, por el ensamble del modelo RegCM, mientras que los valores promedio de evaporación total están mejor representados por el ensamble del modelo REMO en términos de la temporalidad, más no en su magnitud. Por otra parte, las estimaciones de caudal de largo plazo evidencian que los valores de evaporación total proporcionados por los modelos permiten una adecuada estimación del caudal promedio de largo plazo, pero no la adecuada estimación del ciclo anual de caudales. Este trabajo es pionero en la evaluación de los datos de precipitación y evaporación total mensual suministrados por CORDEX-CORE en el Orinoco colombiano, sienta precedentes para la incorporación de datos de modelos regionales para fines hidrológicos en zonas poco instrumentadas del país, y es el primer paso hacia la evaluación de escenarios regionalizados de cambio climático.  

scholarly journals Spring snow albedo feedback over northern Eurasia: Comparing in situ measurements with reanalysis products

2018 ◽  
Vol 12 (6) ◽  
pp. 1887-1898 ◽  
Author(s):  
Martin Wegmann ◽  
Emanuel Dutra ◽  
Hans-Werner Jacobi ◽  
Olga Zolina
Keyword(s):  
State Of The Art ◽  
Northern Eurasia ◽  
Albedo Feedback ◽  
Snow Albedo ◽  
Station Data ◽  
In Situ Observations ◽  
Improved Performance ◽  
Set Up ◽  
Modern Era

Abstract. This study uses daily observations and modern reanalyses in order to evaluate reanalysis products over northern Eurasia regarding the spring snow albedo feedback (SAF) during the period from 2000 to 2013. We used the state-of-the-art reanalyses from ERA-Interim/Land and the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) as well as an experimental set-up of ERA-Interim/Land with prescribed short grass as land cover to enhance the comparability with the station data while underlining the caveats of comparing in situ observations with gridded data. Snow depth statistics derived from daily station data are well reproduced in all three reanalyses. However day-to-day albedo variability is notably higher at the stations than for any reanalysis product. The ERA-Interim grass set-up shows improved performance when representing albedo variability and generates comparable estimates for the snow albedo in spring. We find that modern reanalyses show a physically consistent representation of SAF, with realistic spatial patterns and area-averaged sensitivity estimates. However, station-based SAF values are significantly higher than in the reanalyses, which is mostly driven by the stronger contrast between snow and snow-free albedo. Switching to grass-only vegetation in ERA-Interim/Land increases the SAF values up to the level of station-based estimates. We found no significant trend in the examined 14-year time series of SAF, but interannual changes of about 0.5 % K−1 in both station-based and reanalysis estimates were derived. This interannual variability is primarily dominated by the variability in the snowmelt sensitivity, which is correctly captured in reanalysis products. Although modern reanalyses perform well for snow variables, efforts should be made to improve the representation of dynamic albedo changes.

scholarly journals Soil Moisture Retrievals by Combining Passive Microwave and Optical Data

2020 ◽  
Vol 12 (19) ◽  
pp. 3173
Author(s):  
Cheng Tong ◽  
Hongquan Wang ◽  
Ramata Magagi ◽  
Kalifa Goïta ◽  
Luyao Zhu ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Local Time ◽  
Temporal Dynamics ◽  
Ordinary Least Squares ◽  
Optical Data ◽  
Support Vector ◽  
Learning Approaches ◽  
Station Data ◽  
Level 2

This paper aims to retrieve the temporal dynamics of soil moisture from 2015 to 2019 over an agricultural site in Southeast Australia using the Soil Moisture Active Passive (SMAP) brightness temperature. To meet this objective, two machine learning approaches, Random Forest (RF), Support Vector Machine (SVM), as well as a statistical Ordinary Least Squares (OLS) model were established, with the auxiliary data including the 16-day composite MODIS NDVI (MOD13Q1) and Surface Temperature (ST). The entire data were divided into two parts corresponding to ascending (6:00 p.m. local time) and descending (6:00 a.m. local time) orbits of SMAP overpasses. Thus, the three models were trained using the descending data acquired during the five years (2015 to 2019), and validated using the ascending product of the same period. Consequently, three different temporal variations of the soil moisture were obtained based on the three models. To evaluate their accuracies, the retrieved soil moisture was compared against the SMAP level-2 soil moisture product, as well as to in-situ ground station data. The comparative results show that the soil moisture obtained using the OLS, RF and SVM algorithms are highly correlated to the SMAP level-2 product, with high coefficients of determination (R2OLS = 0.981, R2SVM = 0.943, R2RF = 0.983) and low RMSE (RMSEOLS = 0.016 cm3/cm3, RMSESVM = 0.047 cm3/cm3, RMSERF = 0.016 cm3/cm3). Meanwhile, the estimated soil moistures agree with in-situ station data across different years (R2OLS = 0.376~0.85, R2SVM = 0.376~0.814, R2RF = 0.39~0.854; RMSEOLS = 0.049~0.105 cm3/cm3, RMSESVM = 0.073~0.1 cm3/cm3, RMSERF = 0.047~0.102 cm3/cm3), but an overestimation issue is observed for high vegetation conditions. The RF algorithm outperformed the SVM and OLS, in terms of the agreement with the ground measurements. This study suggests an alternative soil moisture retrieval scheme, in complementary to the SMAP baseline algorithm, for a fast soil moisture retrieval.

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