scholarly journals An Analysis of West African Dynamics Using a Linearized GCM*

2008 ◽  
Vol 65 (4) ◽  
pp. 1182-1203 ◽  
Author(s):  
S. E. Nicholson ◽  
A. I. Barcilon ◽  
M. Challa
Keyword(s):  
Interannual Variability ◽  
Spherical Model ◽  
Planetary Scale ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Key Factor ◽  
Wave Development ◽  
Basic States ◽  
Vertical Development ◽  
The Waves

Abstract This study utilizes a linear, primitive equation spherical model to study the development and propagation of easterly wave disturbances over West Africa. Perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time. The perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the Sahel and two dry years. The model simulations show consistent contrasts in wave activity between the wet and dry years. The waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere. The waves tend to extend throughout the troposphere to the level of the tropical easterly jet (TEJ) in the wet years, but not in the dry years. The upper-tropospheric shear, which is stronger in wet years, appears to be a key factor in wave development. This shear is dependent on the intensity of the TEJ, suggesting that the TEJ is an important factor in interannual variability in the Sahel. When the overall shear is weak, vertical development is suppressed. Another contrast is that in the dry years the growth rates show a single maximum around 3000–4000 km, but in the wet years there is a second, around 6000–7000 km. This suggests that both synoptic-scale and planetary-scale waves are active in the rainy season of some wet years. Imposing considerations of potential vorticity, the generation of planetary-scale waves implies a strong link between the surface and the TEJ in wet years. Such a link is absent in the dry years. This is likely a major factor in the interannual variability of rainfall in the Sahel.

scholarly journals Wave Activity on the Tropical Easterly Jet

2007 ◽  
Vol 64 (7) ◽  
pp. 2756-2763 ◽  
Author(s):  
S. E. Nicholson ◽  
A. I. Barcilon ◽  
M. Challa ◽  
J. Baum
Keyword(s):  
West Africa ◽  
Asian Monsoon ◽  
Model Simulation ◽  
Reanalysis Data ◽  
West African ◽  
Planetary Scale ◽  
African Easterly Jet ◽  
Wave Disturbances ◽  
Tropical Easterly Jet ◽  
Wave Development

Abstract This article examines the question of the existence of waves on the tropical easterly jet (TEJ) over West Africa. The TEJ is a well-known feature of the Asian monsoon and waves on the jet have been implicated in various weather phenomena. Its role in West African meteorology has received little attention. A model simulation of wet and dry years over West Africa predicted wave development on the TEJ. NCEP reanalysis data confirmed the existence of these waves, using case studies in the dry year 1983 and the wet year 1950. Both the simulated and observed waves are of planetary scale, with a period of 5–6 days. Potential vorticity (PV) theory suggests that they develop via interactions between the surface and the TEJ. Overall, the results suggest that interactions between the TEJ and African easterly jet play an important role in the development of wave disturbances over West Africa.

scholarly journals Interacting vorticity waves as an instability mechanism for magnetohydrodynamic shear instabilities

2015 ◽  
Vol 767 ◽  
pp. 199-225 ◽  
Author(s):  
E. Heifetz ◽  
J. Mak ◽  
J. Nycander ◽  
O. M. Umurhan
Keyword(s):  
Magnetic Field ◽  
Phase Locking ◽  
Unstable Flow ◽  
Background Magnetic Field ◽  
Non Local ◽  
Action At A Distance ◽  
Shear Instabilities ◽  
Basic States ◽  
The Waves ◽  
Stable Flow

AbstractThe interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MHD) setting, to provide a mechanistic description for stabilising and destabilising shear instabilities by the presence of a background magnetic field. The interpretation relies on local vorticity anomalies inducing a non-local velocity field, resulting in action at a distance. It is shown here that the waves supported by the system are able to propagate vorticity via the Lorentz force, and waves may interact. The existence of instability then rests upon whether the choice of basic state allows for phase locking and constructive interference of the vorticity waves via mutual interaction. To substantiate this claim, we solve the instability problem of two representative basic states, one where a background magnetic field stabilises an unstable flow and the other where the field destabilises a stable flow, and perform relevant analyses to show how this mechanism operates in MHD.

scholarly journals Climatology of easterly wave disturbances over the tropical South Atlantic

2019 ◽  
Vol 53 (3-4) ◽  
pp. 1393-1411 ◽  
Author(s):  
Helber B. Gomes ◽  
Tércio Ambrizzi ◽  
Bruce F. Pontes da Silva ◽  
Kevin Hodges ◽  
Pedro L. Silva Dias ◽  
...  
Keyword(s):  
South Atlantic ◽  
Wave Disturbances ◽  
Easterly Wave

scholarly journals Michio Yanai and Tropical Waves

2016 ◽  
Vol 56 ◽  
pp. 3.1-3.21 ◽  
Author(s):  
Yukari N. Takayabu ◽  
George N. Kiladis ◽  
Victor Magaña
Keyword(s):  
Fundamental Problem ◽  
Tropical Meteorology ◽  
Current Understanding ◽  
Tropical Atmosphere ◽  
Design Phase ◽  
Wave Disturbances ◽  
Cloud Clusters ◽  
Tropical Waves ◽  
Tropical Wave ◽  
The Waves

Abstract Insights by Professor Michio Yanai on tropical waves, which have been vital ingredients for progress in tropical meteorology over the last half-century, are recollected. This study revisits various aspects of research on tropical waves over the last five decades to examine, in Yanai’s words, “the nature of ‘A-scale’ tropical wave disturbances and the interaction of the waves and the ‘B-scale’ phenomena (cloud clusters),” the fundamental problem posed by Yanai at the design phase of the GARP Atlantic Tropical Experiment (GATE) in 1971. The various contributions of Michio Yanai to the current understanding of the dynamics of the tropical atmosphere are briefly reviewed to show how his work has led to several current theories in this field.

scholarly journals ФОРМОУТВОРЕННЯ ПРОСТОРОВИХ ОБОЛОНОК ЗА ДОПОМОГОЮ ВИБУХОВОГО ШТАМПУВАННЯ

2020 ◽  
pp. 146-152
Author(s):  
Володимир Васильович Третяк
Keyword(s):  
Mining Industry ◽  
Spherical Model ◽  
Middle Part ◽  
Mean Deviation ◽  
Regional Effect ◽  
Technical Parameters ◽  
Double Curvature ◽  
The Matrix ◽  
The Waves ◽  
Mathematical Design

A target of work is verification of the adequacy of the theoretical model of correction by the dynamic fold and verification of capacity of principle technological charts of the explosive stamping of flat purveyances.  Of researches, exposure is a task of technological dependences, the receipt of which is possible only by the experimental path. The article presented results of experimental verification of the technological process of formation of form for the spatial shells on the typical models. Of the conducted work verification was a target of the rightness of theoretical positions, results of mathematical design and conclusions, and also approbation of methods of computations of technical parameters and charts of punching. The experiments are conducted on the flat models of edging, spherical and parabolic edging of large flexibility, and also curvilinear baskets models, models, and model standards. In the article, a process is explored of slanting collision, remaining tensions, deformations, and form of edging after deformation. Influencing of size, forms, and distances of charge on deviation from the matrix. The approbation was conducted on the party of the spherical model edging.  Purveyances are approved on the model fragment.Formulated conclusions and prospects of development and introduction of technology in thermonuclear researches, building, mining industry, rocket, and air production. Experimentally it is set, that the reduction of distance below recommended results in exceeding of deformation of punching of the middle part (curvature more than matrix) and reduction of deformation of punching of the periphery (curvature is a less than matrix). Most rejections are details noticeable in the angular areas. This it is possible to explain by the regional effect from the waves of unloading, and by some asymmetry of installation of charge. The greater part of the surface has a rejection of about 1 mm, which is exceeded by exactness on 8 degrees on the base of 1200 mm. Application of technological admittances by the size of about 50 mm with subsequent their deleting, allows to decrease the mean deviation twice (0,5 mm), and promote exactness of the prepared edging. The experimental working off of technology of correction of declivous petals of double curvature showed a rightness of outputs of the theoretical part.

scholarly journals THE MODEL STUDY OF THE WIND STRESS IMPACT TO THE INTERANNUAL VARIABILITY OF THE ANTARCTIC CIRCUMPOLAR CURRENT SOUTH OF AUSTRALIA

2019 ◽  
Vol 47 (2) ◽  
pp. 172-182 ◽  
Author(s):  
K.V. Lebedev
Keyword(s):  
Interannual Variability ◽  
Wind Stress ◽  
Numerical Experiments ◽  
Antarctic Circumpolar Current ◽  
Wind Forcing ◽  
Global Ocean ◽  
The Real ◽  
Key Factor ◽  
Circumpolar Current ◽  
The Antarctic

The interannual variability of the Antarctic Circumpolar Current (ACC) in the region south of Australia is studied on the base of numerical simulations performed with the use of the Argo-based model for Investigation of the Global Ocean (AMIGO). The model consists of a block for variational interpolation to a regular grid of Argo floats data and a block for model hydrodynamic adjustment of variationally interpolated fields. The mean ACC transport for the period of 2005–2014 through the Australia-Antarctica section was estimated at 178±6 Sv (1 Sv = 106m3/с-1). Additional numerical experiments were carried out in order to study the contribution of the wind forcing to the interannual variability of the ACC transport: the real thermohaline fields corresponding to the particular time period were replaced by climatic ones (1) and by replacing the real wind forcing data with the climatic ones (2). Analysis of the numerical experiments results has shown that the variable wind stress forcing is the key factor determining the interannual variability of the ACC transport through the Australia-Antarctica section.

scholarly journals On the new modes of planetary-scale electromagnetic waves in the ionosphere

2004 ◽  
Vol 22 (4) ◽  
pp. 1203-1211 ◽  
Author(s):  
G. D. Aburjania ◽  
K. Z. Chargazia ◽  
G. V. Jandieri ◽  
A. G. Khantadze ◽  
O. A. Kharshiladze
Keyword(s):  
Electromagnetic Waves ◽  
Large Scale ◽  
Low Frequency ◽  
Planetary Scale ◽  
Phase Velocities ◽  
F Region ◽  
E Region ◽  
General Dispersion ◽  
Fast Waves ◽  
The Waves

Abstract. Using an analogy method the frequencies of new modes of the electromagnetic planetary-scale waves (with a wavelength of 103 km or more), having a weather forming nature, are found at different ionospheric altitudes. This method gives the possibility to determine spectra of ionospheric electromagnetic perturbations directly from the dynamic equations without solving the general dispersion equation. It is shown that the permanently acting factor-latitude variation of the geomagnetic field generates fast and slow weakly damping planetary electromagnetic waves in both the E- and F-layers of the ionosphere. The waves propagate eastward and westward along the parallels. The fast waves have phase velocities (1–5)km s–1 and frequencies (10–1–10–4), and the slow waves propagate with velocities of the local winds with frequencies (10–4–10–6)s–1 and are generated in the E-region of the ionosphere. Fast waves having phase velocities (10-1500)km s–1 and frequencies (1–10–3)s–1 are generated in the F-region of the ionosphere. The waves generate the geomagnetic pulsations of the order of one hundred nanoTesla by magnitude. The properties and parameters of the theoretically studied electromagnetic waves agree with those of large-scale ultra-low frequency perturbations observed experimentally in the ionosphere. Key words. Ionosphere (ionospheric disturbances; waves propagation; ionosphere atmosphere interactions)

scholarly journals Cluster Analysis Applied to Spatiotemporal Variability of Monthly Precipitation over Paraíba State Using Tropical Rainfall Measuring Mission (TRMM) Data

2019 ◽  
Vol 11 (6) ◽  
pp. 637 ◽  
Author(s):  
Celso Santos ◽  
Reginaldo Brasil Neto ◽  
Richarde da Silva ◽  
Samir Costa
Keyword(s):  
Cluster Analysis ◽  
Tropical Rainfall Measuring Mission ◽  
Spatiotemporal Variability ◽  
Monthly Precipitation ◽  
Trade Winds ◽  
Tropical Rainfall ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Precipitation Variation ◽  
Climate Systems

In Paraíba state, precipitation is strongly affected by several climate systems, such as trade winds, the intertropical convergence zone (ITCZ), easterly wave disturbances (EWDs), and the South Atlantic subtropical high. Accordingly, the objective of this study was to analyze the spatiotemporal variability in precipitation to identify homogeneous trends of that variable and the effects of climate systems in Paraíba state by cluster analysis. The precipitation data used in this study derive from the Tropical Rainfall Measuring Mission (TRMM) satellite for the period from January 1998 to December 2015, and hierarchical clustering was used to classify the sites into different groups with similar trends. The findings show an uneven spatiotemporal precipitation distribution in all mesoregions of the state and considerable monthly precipitation variation in space. The estimated precipitation depth was highest in coastal regions and in high-altitude areas due to orographic precipitation. In general, the precipitation over Paraíba is characterized by strong gradients in the coastal zone towards the continent (Agreste, Borborema, and Sertão mesoregions) and from north to south due to the physiography of the region and the effects of climate systems with different time scales. Finally, the proposed clustering method using TRMM data was effective in characterizing climatic systems.

scholarly journals Easterly Wave Disturbances over Northeast Brazil: An Observational Analysis

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Helber Barros Gomes ◽  
Tércio Ambrizzi ◽  
Dirceu Luís Herdies ◽  
Kevin Hodges ◽  
Bruce Francisco Pontes da Silva
Keyword(s):  
Propagation Speed ◽  
Relative Vorticity ◽  
Northeast Brazil ◽  
Automatic Tracking ◽  
Observational Analysis ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Circulation Patterns ◽  
The Mean ◽  
Low Levels

This paper aims to identify the circulation associated with Easterly Wave Disturbances (EWDs) that propagate toward the Eastern Northeast Brazil (ENEB) and their impact on the rainfall over ENEB during 2006 and 2007 rainy seasons (April–July). The EWDs identification and trajectory are analyzed using an automatic tracking technique (TracKH). The EWDs circulation patterns and their main features were obtained using the composite technique. To evaluate the TracKH efficiency, a validation was done by comparing the EWDs number tracked against observed cases obtained from an observational analysis. The mean characteristics of EWDs are 5.5-day period, propagation speed of ~9.5 m·s−1, and a 4500 km wavelength. A synoptic analysis shows that between days −2 d and 0 d, the low level winds presented cyclonic relative vorticity and convergence anomalies both in 2006 and 2007. The EWDs signals are strongest at low levels. The EWDs propagation is associated with relative humidity and precipitation positive anomalies and OLR and omega negative anomalies. The EWDs tracks are seen over all ENEB and their lysis occurs between the ENEB and marginally inside the continent. The tracking captured 71% of EWDs in all periods, indicating that an objective analysis is a promising method for EWDs detection.

scholarly journals An analytical study of easterly waves over southern peninsular India during the northeast monsoon 2010

MAUSAM ◽  
2021 ◽  
Vol 65 (4) ◽  
pp. 591-602
Author(s):  
B. GEETHA ◽  
S. BALACHANDRAN
Keyword(s):  
Monsoon Season ◽  
Wave Radiation ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Upper Troposphere ◽  
Easterly Waves ◽  
Easterly Wave ◽  
Time Period ◽  
Meridional Winds ◽  
The Waves

Easterly wave characteristics over southern peninsular India during the northeast monsoon season of 2010 are examined by means of synergetic analysis involving synoptic, statistical and numerical methods. NCEP        6-hourly reanalysis datasets of zonal and meridional winds, vertical velocity, temperature and net long wave radiation at 2.5° × 2.5° grid resolution for the period 20th October to 31st  December, 2010 form the main database for the analysis.  During this period, 3 easterly waves could be identified to have passed over this region and the time period of these waves are determined to be 4.2 days (4.5 days) by statistical methods (synoptic methods). The speed of movement, wavelength and amplitude of the waves are determined to be 7.28 ms-1, 2800 km and 6.7 ms-1 respectively. While rising motion is observed at most of the tropospheric levels over and behind the trough, subsidence occurs ahead of the trough. Divergence is noted over and behind the trough at upper troposphere while convergence occurs in the lower to mid-troposphere. Concomitantly warming is noted ahead of the trough while colder anomalies are noted in the lower levels over and behind the trough. 

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