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 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 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 Intense Precipitation and Area of Risk: A Case Study of Mass Movement in the City of Natal, Brazil

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3346
Author(s):  
Marcos Samuel Matias Ribeiro ◽  
Maria Helena Constantino Spyrides ◽  
Lara de Melo Barbosa Andrade ◽  
Kellen Carla Lima ◽  
Venerando Eustáquio Amaro ◽  
...  
Keyword(s):  
Mass Movement ◽  
Moisture Flux ◽  
Atmospheric Conditions ◽  
Environmental Aspects ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Intense Precipitation ◽  
Synoptic Conditions ◽  
The City

This study aims to analyze the atmospheric conditions associated with an event of intense precipitation caused by Easterly Wave Disturbances (EWDs), as well as the environmental conditions related to the mass gravitational movement that occurred between 14th June and 15th June of 2014, in the district of Mãe Luiza, Natal/RN/Brazil. The synoptic conditions, the vertical integrated moisture flux and the energetic behavior in the EWD’s performance phases were analyzed. In addition to these factors, local environmental aspects were assessed, classifying the vulnerability to disaster events in the affected area. Over the days of the operation of the atmospheric system, the daily accumulation of precipitation was greater than 100 mm, with precipitation accumulated in 3 h in the order of 60 mm for the stages of maturation of the disturbance. The main synoptic conditions associated with EWDs were exhibited by the intense anomalies of wind speed and high humidity flux on the east coast of the Northeast, which intensified the influx of moisture into the continent over the period of the operation of the system. Conditions of high to very high vulnerability were identified in the area where the event took place and also in other expressive parts of the district.

scholarly journals Beach-foredune ridges as proxies for climate-induced wave direction changes in South Atlantic during Late Holocene

2020 ◽  
Author(s):  
Ana Paula Da Silva ◽  
Antonio Henrique da Fontoura Klein ◽  
Antonio Fernando Harter Fetter Filho ◽  
Christopher Hein ◽  
Fernando Mendez ◽  
...  
Keyword(s):  
Sea Level ◽  
Late Holocene ◽  
Wave Climate ◽  
South Atlantic ◽  
Wave Direction ◽  
Sea Level Pressure ◽  
Mean Sea Level ◽  
Easterly Wave ◽  
Wave Energy Flux

<p>Variability in global wave climate has been observed to occur in response to climate changes influencing the wave-generating zones. This highlights the need for an improved understanding of long-term wave-climate cycles, considering the multi-decadal variability of the atmospheric patterns and large-scale climate drivers. In this study, a novel use of the morphology of former shorelines preserved in beach-foredune ridges was applied to reconstruct changes in predominant wave directions in the Subtropical South Atlantic during the Late Holocene. A 3km wide semi-continuous sequence of beach-foredune ridges preserved within the Pinheira Strandplain (Santa Catarina State, Brazil) was mapped in order to extract the orientation of the former shorelines and derive a 3000-year record of inferred mean wave direction. The mean wave direction series was compared to ~1000 years of decadal means of mid-latitude mean sea-level pressure gradients (∆MSLP) and zonal westerly wind velocities estimated from the CESM1-CAM5 “Last Millennium Ensemble (LME)”, and to 2000 years of air-surface temperature anomalies for Southern Hemisphere. Results showed that multi-centennial cycles of oscillation in predominant wave direction occurred in accordance with stronger (weaker) South Atlantic mid-latitude mean sea-level pressure and zonal westerlies winds, favouring wave generation zones in higher (lower) latitudes and consequent southerly (easterly) wave climate dominance. It was identified the Southern Annular Mode as the main climate driver responsible for these changes, responding for 43% of the variance in the Subtropical South Atlantic atmospheric patterns in the last 1000 years. Long-term variations in interhemispheric air-surface temperature offsets, coincident with oscillations in wave direction, may have influenced wave-generation patterns similarly to the seasonal behaviour observed over recent decades. Periods of relatively warmer Southern Hemisphere (SH) as compared with Northern Hemisphere (NH) (e.g., during 400–800 CE and the Little Ice Age) favours the predominance of easterly wave energy flux along the eastern South American coast, whereas periods with equivalent NH-SH temperature anomalies (e.g., Medieval Warm Period) or with colder relative SH (last ~150 years) support an increase in the influence of the southerly wave energy flux over the South Atlantic. These results provide a novel geomorphic proxy for paleoenvironmental reconstructions and present new insights into the role of multi-decadal to multi-centennial climate variability on controlling coastal ocean wave climate.</p>

scholarly journals Case Studies of Easterly Wave Disturbances over Northeast Brazil Using the Eta Model

2011 ◽  
Vol 26 (2) ◽  
pp. 225-235 ◽  
Author(s):  
Roger Rodrigues Torres ◽  
Nelson Jesus Ferreira
Keyword(s):  
Case Studies ◽  
East Coast ◽  
Northeast Brazil ◽  
Wind Fields ◽  
Model Sensitivity ◽  
Convective Parameterization ◽  
Wave Disturbances ◽  
Easterly Wave ◽  
Eta Model ◽  
Cumulus Parameterizations

Abstract This research aims to analyze two easterly wave disturbance events that reached the east coast of Northeast Brazil (NEB) on 15 May 2005 and 20 June 2006. The performance of the regional Eta Model was evaluated through four sets of experiments using different horizontal resolutions (10 and 40 km) and convective parameterization schemes [Betts–Miller–Janjić (BMJ) and Kain–Fritsch (KF)]. Through analysis of 700-hPa wind fields, all experiments, with 40- and 10-km horizontal resolutions and using the BMJ and KF schemes, were shown to well represent a trough propagating westward from about 20°W to NEB, with a 5-day forecast range. When evaluating the model sensitivity to different convective parameterizations, all the experiments showed similar results and underestimated rainfall in most of the domain. The obtained results suggest the need to extend this analysis to a larger number of cases and to test other cumulus parameterizations in order to improve the rainfall forecast in eastern NEB.

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