Search results for "oscillation"
showing 10 items of 1257 documents
Discussion of "Hydraulic Model of Transition of Transient to Steady Flows in the Vadose Zone" by Yaguo Zhang, Tonglu Li, Wei Shen, and Yu Wang
2020
The authors wrote an interesting article dealing with a simple hydraulic model to illustrate the transition mechanism of transient to steady flows in the vadose zone. The soil behavior is described by a set of nine vertically aligned cylinders, each opened at the top and with a small outlet at the bottom. The water level dynamic of each cylinder, associated with an intermittent constant rainfall applied to the top cylinder, C0, was analyzed and numerical simulations were performed. The only objective of this discussion is to show that results similar to those proposed by the authors could be obtained by using the recently introduced Richards equation analytical solution, under gravity-drive…
North-Atlantic Oscillation and regional-scale sea-surge variability in Gulf of Lions during the 20th century
2010
Article soumis; International audience; Sea-surge variations recorded at three tide-gauge stations (Grau-de-la-Dent, Sète, and Port-Vendres) around the Gulf of Lions (Northwest Mediterranean Sea) are mostly locally forced by onshore winds blowing from 90° to 180° related to an atmospheric depression usually centered between the Bay of Biscay and the British Island, which is more prevalent during the negative phase of the North-Atlantic Oscillation (NAO). During the second half of the 20th century, the long-term increase of sea-surge height at Grau-de-la-Dent finds no counterpart in the positive deviation of the NAO. The relationship between the monthly frequency of sea surges > 20 cm at Gra…
Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO
2010
The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: unt…
Global atmospheric response to specific linear combinations of the main SST modes. Part I: numerical experiments and preliminary results
1996
Abstract. This article investigates through numerical experiments the controversial question of the impact of El Niño-Southern Oscillation (ENSO) phenomena on climate according to large-scale and regional-scale interhemispheric thermal contrast. Eight experiments (two considering only inversed Atlantic thermal anomalies and six combining ENSO warm phase with large-scale interhemispheric contrast and Atlantic anomaly patterns) were performed with the Météo-France atmospheric general circulation model. The definition of boundary conditions from observed composites and principal components is presented and preliminary results concerning the month of August, especially over West Africa and the …
Physics at a future Neutrino Factory and super-beam facility
2009
The conclusions of the Physics Working Group of the international scoping study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Superbeams, Laboratori Nazionali di Frascati, Rome, June 21-26, 2005) and NuFact06 (Ivine, California, 24{30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second generation super-beam experiments, …
Nonlinear electrostatic oscillations in a cold magnetized electron-positron plasma
2017
We study the spatio-temporal evolution of the nonlinear electrostatic oscillations in a cold magnetized electron-positron (e-p) plasma using both analytics and simulations. Using a perturbative method we demonstrate that the nonlinear solutions change significantly when a pure electrostatic mode is excited at the linear level instead of a mixed upper-hybrid and zero-frequency mode that is considered in a recent study. The pure electrostatic oscillations undergo phase mixing nonlinearly. However, the presence of the magnetic field significantly delays the phase-mixing compared to that observed in the corresponding unmagnetized plasma. Using 1D PIC simulations we then analyze the damping of t…
Variabilité intra-saisonnière et multi-décennale de la téléconnexion entre les pressions de surface (100°W–50°E ; 30°–70°N) et les ENSO/LNSO (1873–19…
2000
Abstract The relationships between an index of the NINO3.4 region and the wintertime sea level pressure (hereafter SLP) anomalies on the extratropical North Atlantic and the bordering areas (100°W–50°E; 30°–70°N) are studied for 1873–1996. This study emphasizes the need of a careful pooling of months and the multi-decadal variability of the ENSO/LNSO influence on the extratropical North Atlantic. We calculate the mean monthly climate anomalies for the 20 warmest and the 20 coldest NINO3.4 (170°–120°W; 5°N–5°S) years from October to March. The composite of SLP anomalies for the 20 warmest NINO3.4 years shows an anomalous trough centered near 30°W in November–December, and positive (respectiv…
Global equatorial variability of 850 and 200 hPa zonal winds from rawinsondes between 1963 and 1989
1995
The longitude-height-time variability of 3-month averaged zonal wind anomalies at 850 and 200 hPa over the equatorial area (5{degrees}N-5{degrees}S) is analyzed using a three-dimensional dataset constructed from rawinsonde data (1963-1989). The first mode, closely related to the Southern Oscillation Index, suggests a strong vertical coupling associated with a horizontal out-of-phase pattern between the central/western Pacific and the remainder of the equatorial belt. The vertical coupling appears to be phase-locked to the annual cycle with strongest intensities found over South America and near the maritime continent early in the calendar year and over the Pacific basin and Africa during th…
Sahel droughts and Enso dynamics
1996
Correlations between summer Sahel rainfall and Southern Oscillation Index has increased during the last thirty years. At high frequency time scale (periods lower than 8 years), an intertropical Atlantic zonal divergent circulation anomaly is forced by the difference of sea surface temperature (SST) anomalies between the eastern equatorial parts of Pacific and Atlantic. This zonal connection worked well during most of the E1 Nino/Southern Oscillation (ENSO) events occurring after 1970; positive/negative SST anomalies in the eastern Pacific/Atlantic led to rainfall deficits over the whole West Africa. At low frequency time scale (periods greater than 8 years), positive SST anomalies in the In…
Rainfall variability in subequatorial America and Africa and relationships with the main sea-surface temperature modes (1951–1990)
1995
The rainfall variability of subequatorial South America and Africa is poorly documented owing to the scarcity of data. We present a new land-only data set of monthly precipitation from 1951 to 1990, focusing on subequatorial South America and Africa, which improves the knowledge of rainfall variability and allows comparisons with GCM outputs. The results of multivariate analyses are compared with those performed on the best actual global rainfall data set developed by Mike Hulme. The main modes of bimonthly rainfall variability are not located in the major rain-forest basins of Za'ke and Amazonia, but rather on the tropical margins, such as Venezuela or Sudan, and near-coastal equatorial ar…