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11.
K. Goubanova V. Echevin B. Dewitte F. Codron K. Takahashi P. Terray M. Vrac 《Climate Dynamics》2011,36(7-8):1365-1378
The key aspect of the ocean circulation off Peru?CChile is the wind-driven upwelling of deep, cold, nutrient-rich waters that promote a rich marine ecosystem. It has been suggested that global warming may be associated with an intensification of upwelling-favorable winds. However, the lack of high-resolution long-term observations has been a limitation for a quantitative analysis of this process. In this study, we use a statistical downscaling method to assess the regional impact of climate change on the sea-surface wind over the Peru?CChile upwelling region as simulated by the global coupled general circulation model IPSL-CM4. Taking advantage of the high-resolution QuikSCAT wind product and of the NCEP reanalysis data, a statistical model based on multiple linear regressions is built for the daily mean meridional and zonal wind at 10?m for the period 2000?C2008. The large-scale 10?m wind components and sea level pressure are used as regional circulation predictors. The skill of the downscaling method is assessed by comparing with the surface wind derived from the ERS satellite measurements, with in situ wind observations collected by ICOADS and through cross-validation. It is then applied to the outputs of the IPSL-CM4 model over stabilized periods of the pre-industrial, 2?×?CO2 and 4?×?CO2 IPCC climate scenarios. The results indicate that surface along-shore winds off central Chile (off central Peru) experience a significant intensification (weakening) during Austral winter (summer) in warmer climates. This is associated with a general decrease in intra-seasonal variability. 相似文献
12.
ENSO nonlinearity in a warming climate 总被引：1，自引：1，他引：0
J. Boucharel B. Dewitte Y. du Penhoat B. Garel S.-W. Yeh J.-S. Kug 《Climate Dynamics》2011,37(9-10):2045-2065
The El Niño Southern Oscillation (ENSO) is known as the strongest natural inter-annual climate signal, having widespread consequences on the global weather, climate, ecology and even on societies. Understanding ENSO variations in a changing climate is therefore of primordial interest to both the climate community and policy makers. In this study, we focus on the change in ENSO nonlinearity due to climate change. We first analysed high statistical moments of observed Sea Surface Temperatures (SST) timeseries of the tropical Pacific based on the measurement of the tails of their Probability Density Function (PDF). This allows defining relevant metrics for the change in nonlinearity observed over the last century. Based on these metrics, a zonal “see-saw” (oscillation) in nonlinearity patterns is highlighted that is associated with the change in El Niño characteristics observed in recent years. Taking advantage of the IPCC database and the different projection scenarios, it is showed that changes in El Niño statistics (or “flavour”) from a present-day climate to a warmer climate are associated with a significant change in nonlinearity patterns. In particular, in the twentieth century climate, the “conventional” eastern Pacific El Niño relates more to changes in nonlinearity than to changes in mean state whereas the central Pacific El Niño (or Modoki El Niño) is more sensitive to changes in mean state than to changes in nonlinearity. An opposite behaviour is found in a warmer climate, namely the decreasing nonlinearity in the eastern Pacific tends to make El Niño less frequent but more sensitive to mean state, whereas the increasing nonlinearity in the west tends to trigger Central Pacific El Niño more frequently. This suggests that the change in ENSO statistics due to climate change might result from changes in the zonal contrast of nonlinearity characteristics across the tropical Pacific. 相似文献
13.
The Sun's total irradiance at the mean Sun-Earth distance decreased from mid-1979 to mid-1987 during the descending part of solar cycle 21. After the minimum had been reached it increased with the onset of cycle 22 and came to a maximum at mid-1991 during the highest solar activity of cycle 22. From the modelized shape of the time signal of the solar constant based on the Space Absolute Radiometric Reference (SARR), temporal, amplitude and behaviour characteristics are derived. It is suggested that the variation observed over a period of more than 14 years is the response of the outer solar layers, the photosphere in particular, to some excitation originating somewhere near the bottom of the solar convection zone also responsible for the solar spots and the correlated photospheric features. Wavelet analysis and periodiograms are shown for the solar constant and the sunspot index. Their non-stationarity is well illustrated as well as strong recurrent periods. 相似文献
14.
Steven Dewitte Dominique Crommelynck Sabri Mekaoui Alexandre Joukoff 《Solar physics》2004,224(1-2):209-216
A possible long-term trend of the total solar irradiance could be a natural cause for climate variations on Earth. Measurement
of the total solar irradiance with space radiometers started in 1978. We present a new total solar irradiance composite, with
an uncertainty of ± 0.35 W m−2. From the minimum in 1995 to the maximum in 2002 the total solar irradiance increased by 1.6 W m−2. In between the minima of 1987 and 1995 the total solar irradiance increased by 0.15 W m−2. 相似文献
15.
This article presents a field-based method to assess site- and rainfall-specific runoff coefficients to be expected for a given period of the year. The method is applied to recognize soil uses/covers leading to reduced runoff water supply of gullies in Kinshasa. The computation of the runoff coefficient needs an infiltration envelope, established on site during a period of interest, and a local pluviogram decomposed in pluviophases. Rainfall simulation is carried out in 35 representative urban sites located in gully runon areas to establish a site-specific infiltration envelope. The runoff coefficient of the 35 sites is calculated for 25 geomorphologically active rains recorded between 1975 and 2012. The results show that several site-specific characteristics control runoff coefficient. The first factor is the over-compaction of the soil. Earthen roads show a runoff coefficient of 96.0 %. The second factor is the presence of a lichen seal. Bare loose soil only colonized by a lichen seal shows a runoff coefficient of 40.7 %. For the other sites, the runoff coefficient is inversely proportional to the percentage of vegetation soil cover, a normally compacted bare soil having a runoff coefficient of up to 30 %, parcels with high grass or cultures providing complete coverage showing no runoff at all. However, mowed lawns develop an impervious root mat close to the surface and, therefore, do not follow this rule: They quickly produce runoff similar to the bare and compacted surfaces. Finally, the factor slope gradient is involved. The differences due to vegetation cover disappear gradually with decreasing slope. Below a slope gradient of 0.08 m m−1, the runoff coefficient is null on a bare surface. Currently, the critical rainfall for gullying in the high town of Kinshasa is 24.9 mm with a mean intensity of 21.8 mm h−1. Roads generate by far most runoff and, therefore, are considered as the primary reason for gullying. The other soil uses lead most of the time to much smaller runoff coefficients, but their relative contribution to the supply of gullies grows with rainfall increase in height and intensity. The results provide material for gully management and adaptation strategies and open perspectives for the development of an early warning system in the region of Kinshasa. The method shows potential for being applied in other urbanized environments.
相似文献16.
Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers 总被引：2，自引：1，他引：1
Sophie Bertrand Boris Dewitte Jorge Tam Erich Díaz Arnaud Bertrand 《Progress in Oceanography》2008,79(2-4):278
Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management. 相似文献
17.
The response of El Niño and Southern Oscillation (ENSO)-like variability to global warming varies comparatively between the two different climate system models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) Coupled General Circulation Models (CGCMs). Here, we examine the role of the simulated upper ocean temperature structure in the different sensitivities of the simulated ENSO variability in the models based on the different level of CO2 concentrations. In the MRI model, the sea surface temperature (SST) undergoes a rather drastic modification, namely a tendency toward a permanent El Niño-like state. This is associated with an enhanced stratification which results in greater ENSO amplitude for the MRI model. On the other hand, the ENSO simulated by GFDL model is hardly modified although the mean temperature in the near surface layer increases. In order to understand the associated mechanisms we carry out a vertical mode decomposition of the mean equatorial stratification and a simplified heat balance analysis using an intermediate tropical Pacific model tuned from the CGCM outputs. It is found that in the MRI model the increased stratification is associated with an enhancement of the zonal advective feedback and the non-linear advection. In the GFDL model, on the other hand, the thermocline variability and associated anomalous vertical advection are reduced in the eastern equatorial Pacific under global warming, which erodes the thermocline feedback and explains why the ENSO amplitude is reduced in a warmer climate in this model. It is suggested that change in stratification associated with global warming impacts the equatorial wave dynamics in a way that enhances the second baroclinic mode over the gravest one, which leads to the change in feedback processes in the CGCMs. Our results illustrate that the upper ocean vertical structure simulated in the CGCMs is a key parameter of the sensitivity of ENSO-like SST variability to global warming. 相似文献
18.
Sensitivity of the Humboldt Current system to global warming: a downscaling experiment of the IPSL-CM4 model 总被引：1，自引：1，他引：0
Vincent Echevin Katerina Goubanova Ali Belmadani Boris Dewitte 《Climate Dynamics》2012,38(3-4):761-774
The impact of climate warming on the seasonal variability of the Humboldt Current system ocean dynamics is investigated. The IPSL-CM4 large scale ocean circulation resulting from two contrasted climate scenarios, the so-called Preindustrial and quadrupling CO2, are downscaled using an eddy-resolving regional ocean circulation model. The intense surface heating by the atmosphere in the quadrupling CO2 scenario leads to a strong increase of the surface density stratification, a thinner coastal jet, an enhanced Peru–Chile undercurrent, and an intensification of nearshore turbulence. Upwelling rates respond quasi-linearly to the change in wind stress associated with anthropogenic forcing, and show a moderate decrease in summer off Peru and a strong increase off Chile. Results from sensitivity experiments show that a 50% wind stress increase does not compensate for the surface warming resulting from heat flux forcing and that the associated mesoscale turbulence increase is a robust feature. 相似文献
19.
A. BenMoussa S. Gissot U. Schühle G. Del Zanna F. Auchère S. Mekaoui A. R. Jones D. Walton C. J. Eyles G. Thuillier D. Seaton I. E. Dammasch G. Cessateur M. Meftah V. Andretta D. Berghmans D. Bewsher D. Bolsée L. Bradley D. S. Brown P. C. Chamberlin S. Dewitte L. V. Didkovsky M. Dominique F. G. Eparvier T. Foujols D. Gillotay B. Giordanengo J. P. Halain R. A. Hock A. Irbah C. Jeppesen D. L. Judge M. Kretzschmar D. R. McMullin B. Nicula W. Schmutz G. Ucker S. Wieman D. Woodraska T. N. Woods 《Solar physics》2013,288(1):389-434
We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions. 相似文献
20.