scholarly journals Climatology of Heavy Orographic Rainfall Induced by Tropical Cyclones over Madagascar: From Synoptic to Mesoscale Perspectives

2016 ◽  
Vol 5 (2) ◽  
pp. 132 ◽  
Author(s):  
Tatiana A. Arivelo ◽  
Yuh-Lang Lin
Keyword(s):  
Tropical Cyclones ◽  
Southern Oscillation Index ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Eastern Coast ◽  
Quasi Biennial Oscillation ◽  
Trade Winds ◽  
Southwest Indian Ocean ◽  
The North ◽  
Orographic Rainfall

Variability of and generation mechanisms for Madagascar rainfall are studied by conducting climatological, synoptic and mesoscale analyses. It is found the rainfall variability is highly sensitive to seasons with high variability in summer (Nov-Apr). The rainfall in summer is controlled by the Intertropical Convergence Zone (ITCZ) and orographic rainfall associated with tropical cyclones (TCs), while the rainfall in winter (May-Oct) is controlled by trade winds and local orographic rainfall along the eastern coast. Synoptic analysis reveals that major climate variations in summer are associated with ITCZ position, which is closely related to TC genesis locations and quasi-biennial oscillation (QBO). Linkages between El-Niño Southern Oscillation Index (ENSO) and Southern Oscillation Index (SOI) are identified as the cause of inconsistent dry or wet summers. Mesoscale analysis depicts the importance of the orographic effects on prevailing wind, which are controlled by the orography in both seasons. In winter, the prevailing trade winds over the Southwest Indian Ocean are from the east and are split to the north and south when it impinges on Malagasy Mountains. On the other hand, in summer the prevailing easterlies are weaker leading to the production of lee vortices, in addition to the flow splitting upstream of the mountain. Thus, the flow is classified into two regimes: (a) flow-over regime with no lee vortices under high Froude number (Fr=1.2-1.8) flow, and (b) flow-around regime with lee vortices under low Fr (=0.88-1.16) flow. A case study of TC Domoina (1984) indicates that the long-lasting heavy rainfall was induced by the strong orographic blocking of Madagascar. The shorter-term (e.g., 2 days) heavy orographic precipitation is characterized by large VH ∙Ñh which is composed by two common ingredients, namely a strong low-level wind normal to the mountain (VH) and a steep mountain slope (∇h).

scholarly journals On the Relationship between Winter Sea Ice and Summer Atmospheric Circulation over Eurasia

2013 ◽  
Vol 26 (15) ◽  
pp. 5523-5536 ◽  
Author(s):  
Bingyi Wu ◽  
Renhe Zhang ◽  
Rosanne D'Arrigo ◽  
Jingzhi Su
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Eastern Coast ◽  
Northern Eurasia ◽  
Sea Ice Concentration ◽  
The North ◽  
Circulation Anomalies ◽  
Atmospheric Circulation Anomalies

Abstract Using NCEP–NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) data, this paper investigates the association between winter sea ice concentration (SIC) in Baffin Bay southward to the eastern coast of Newfoundland, and the ensuing summer atmospheric circulation over the mid- to high latitudes of Eurasia. It is found that winter SIC anomalies are significantly correlated with the ensuing summer 500-hPa height anomalies that dynamically correspond to the Eurasian pattern of 850-hPa wind variability and significantly influence summer rainfall variability over northern Eurasia. Spring atmospheric circulation anomalies south of Newfoundland, associated with persistent winter–spring SIC and a horseshoe-like pattern of sea surface temperature (SST) anomalies in the North Atlantic, act as a bridge linking winter SIC and the ensuing summer atmospheric circulation anomalies over northern Eurasia. Indeed, this study only reveals the association based on observations and simple simulation experiments with SIC forcing. The more precise mechanism for this linkage needs to be addressed in future work using numerical simulations with SIC and SST as the external forcings. The results herein have the following implication: Winter SIC west of Greenland is a possible precursor for summer atmospheric circulation and rainfall anomalies over northern Eurasia.

scholarly journals Stratospheric Influences on the MJO-Induced Rossby Wave Train: Effects on Intraseasonal Climate

2020 ◽  
Vol 33 (1) ◽  
pp. 365-389 ◽  
Author(s):  
Lon L. Hood ◽  
Malori A. Redman ◽  
Wes L. Johnson ◽  
Thomas J. Galarneau
Keyword(s):  
Solar Cycle ◽  
Rossby Wave ◽  
Southern Oscillation ◽  
Wave Train ◽  
Winter Season ◽  
Surface Air Temperature ◽  
Quasi Biennial Oscillation ◽  
Sea Level Pressure ◽  
The North ◽  
Rossby Wave Train

AbstractThe tropical Madden–Julian oscillation (MJO) excites a northward propagating Rossby wave train that largely determines the extratropical surface weather consequences of the MJO. Previous work has demonstrated a significant influence of the tropospheric El Niño–Southern Oscillation (ENSO) on the characteristics of this wave train. Here, composite analyses of ERA-Interim sea level pressure (SLP) and surface air temperature (SAT) data during the extended northern winter season are performed to investigate the additional role of stratospheric forcings [the quasi-biennial oscillation (QBO) and the 11-yr solar cycle] in modifying the wave train and its consequences. MJO phase composites of 20–100-day filtered data for the two QBO phases show that, similar to the cool phase of ENSO, the easterly phase of the QBO (QBOE) produces a stronger wave train and associated modulation of SLP and SAT anomalies. In particular, during MJO phases 5–7, positive SLP and negative SAT anomalies in the North Atlantic/Eurasian sector are enhanced during QBOE relative to the westerly phase of the QBO (QBOW). The opposite occurs during the earliest MJO phases. SAT anomalies over eastern North America are also more strongly modulated during QBOE. Although less certain because of the short data record, there is some evidence that the minimum phase of the solar cycle (SMIN) produces a similar increased modulation of SLP and SAT anomalies. The strongest modulations of SLP and SAT anomalies are produced when two or more of the forcings are superposed (e.g., QBOE/cool ENSO, SMIN/QBOE, etc.).

scholarly journals The GloSea4 Ensemble Prediction System for Seasonal Forecasting

2011 ◽  
Vol 139 (6) ◽  
pp. 1891-1910 ◽  
Author(s):  
Alberto Arribas ◽  
M. Glover ◽  
A. Maidens ◽  
K. Peterson ◽  
M. Gordon ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Regional Climate ◽  
Model Development ◽  
Seasonal Forecasting ◽  
Ensemble Prediction ◽  
Quasi Biennial Oscillation ◽  
Ensemble Prediction System ◽  
The North ◽  
Enso Teleconnections ◽  
The North Atlantic Oscillation

Abstract Seasonal forecasting systems, and related systems for decadal prediction, are crucial in the development of adaptation strategies to climate change. However, despite important achievements in this area in the last 10 years, significant levels of skill are only generally found over regions strongly connected with the El Niño–Southern Oscillation. With the aim of improving the skill of regional climate predictions in tropical and extratropical regions from intraseasonal to interannual time scales, a new Met Office global seasonal forecasting system (GloSea4) has been developed. This new system has been designed to be flexible and easy to upgrade so it can be fully integrated within the Met Office model development infrastructure. Overall, the analysis here shows an improvement of GloSea4 when compared to its predecessor. However, there are exceptions, such as the increased model biases that contribute to degrade the skill of Niño-3.4 SST forecasts starting in November. Global ENSO teleconnections and Madden–Julian oscillation anomalies are well represented in GloSea4. Remote forcings of the North Atlantic Oscillation by ENSO and the quasi-biennial oscillation are captured albeit the anomalies are weaker than those found in observations. Hindcast length issues and their implications for seasonal forecasting are also discussed.

Are the socioeconomic impacts associated with tropical cyclones in Mexico exacerbated by local vulnerability and ENSO conditions?

2021 ◽  
Author(s):  
Alejandro Jaramillo ◽  
Christian Dominguez
Keyword(s):  
Tropical Cyclones ◽  
Natural Hazards ◽  
Social Vulnerability ◽  
Southern Oscillation ◽  
Climate Risk ◽  
Eastern Coast ◽  
Economic Losses ◽  
Social Vulnerability Index ◽  
Socioeconomic Impacts ◽  
Northwestern Mexico

<p>Tropical Cyclones (TCs) are among the most dangerous natural hazards because they can cause severe economic losses and high mortality. Climate risk is defined as a metric that depends on social vulnerability and the occurrence of natural hazards. A social vulnerability index was constructed for this study using two metrics: the degree of local marginalization and the local social gap. The accumulated rainfall and duration of extreme precipitation associated with TC passages are examined as a natural hazard during the period 1981–2017. TC days are depicted as days when TC‐related rainfall exceeded the 95th percentile of daily precipitation from May to November, defined as summer precipitation. In this way, changes in climate risk under El Niño‐Southern Oscillation (ENSO) conditions are explored to determine regions where both social vulnerability and TC days are high. These changes are useful to find out when disasters have more chances to occur. In the present study, climate risk was found to increase more than 80% from average in southwestern Mexico during strong El Niño years. Under neutral conditions, climate risk values rise to more than 40% than average over northwestern Mexico. Under strong La Niña conditions, climate risk increases by more than 80% from average over the eastern coast of Mexico. Our approach is validated through a comparison between anomalies in climate risk and disaster costs (socioeconomic impacts). Both local vulnerability and ENSO conditions exacerbate socioeconomic impacts associated with TCs, and an analysis of linear trends in TC rainfall and TC days reveals that most of the coastal regions in Mexico have a significant rising trend in both variables. Thus, Mexico should be prepared to face more TC extreme rainfall events. Suggestions for how Mexico can meet the objectives of international risk agendas are discussed.</p>

scholarly journals Some Factors That Influence Seasonal Precipitation in Argentinean Chaco

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Marcela Hebe González ◽  
María Laura Cariaga ◽  
María de los Milagros Skansi
Keyword(s):  
Southern Oscillation ◽  
Rainfall Variability ◽  
Southern Annular Mode ◽  
Spring Precipitation ◽  
Study Region ◽  
Central Brazil ◽  
The North ◽  
Interannual Rainfall Variability ◽  
Oceanic Forcing ◽  
Main Activity

The Chaco plain region in Argentina is located in the north of the country and east of Los Andes where the main activity is the agriculture. As such activity is highly affected by interannual rainfall variability, the influence of some of the principal atmospheric and oceanic forcing is investigated in this paper. Results show that the factors which affect precipitation highly depend on the season and the subregion. The position of the South Atlantic Height and the sea surface temperature in the coast of southern Brazil and Buenos Aires seem to be the factors that affect rainfall, all over the year. The El Niño-Southern Oscillation phenomenon affects summer and spring rainfall and the Southern Annular Mode involves spring precipitation but both only in the east of the study region. Furthermore, enhanced convection in Central Brazil, mainly influences autumn and spring rainfall.

scholarly journals The Role of Tropical Cyclones on the Total Precipitation in Cuba during the Hurricane Season from 1980 to 2016

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1156
Author(s):  
José C. Fernández–Alvarez ◽  
Rogert Sorí ◽  
Albenis Pérez–Alarcón ◽  
Raquel Nieto ◽  
Luis Gimeno
Keyword(s):  
Tropical Cyclones ◽  
Southern Oscillation ◽  
Warm Pool ◽  
Total Precipitation ◽  
Data Set ◽  
The North ◽  
Atlantic Warm Pool ◽  
Significant Difference ◽  
Great Heterogeneity ◽  
Del Rio

This study quantifies the amount of rainfall supplied by tropical cyclones (TCs) to Cuba. It uses the long–term global gridded Multi–Source Weighted–Ensemble Precipitation (MSWEP) v2 data set, with a resolution of 0.1° in latitude and longitude, and a temporal resolution of 3 h during the hurricane seasons from 1980–2016. During this study period, 146 TCs were identified within a 500–km radius of Cuba. The contribution of TCs to the total precipitation over Cuba during the cyclonic season was ~11%. The maximum contribution occurs in October and November, representing 18% and 28% of the total precipitation, respectively. The interannual precipitation contribution shows a positive correlation (~0.74) with the number of TCs, but without a significant trend for the period. A climatological spatial analysis of the rainfall associated with TCs revealed great heterogeneity, although the major contribution was observed along the southern coast of the eastern and central provinces of Cuba, and in the western province of Pinar del Río. No significant difference was observed between the number of TCs that affected Cuba and their rainfall contribution under the positive and negative phases of the El Niño Southern Oscillation. However, the negative phase of the NAO led to an increase in the genesis of TCs that later affected Cuba, which led to a greater contribution to precipitation compared to that obtained from TCs during the positive phase of this oscillation. Our results also confirm that anomalous warmth of the tropical Atlantic Ocean, revealed through the Atlantic Meridional Mode, and enlargement of the Atlantic Warm Pool, enhances the genesis in the North Atlantic Basin of the TCs that affect Cuba, which was associated with an increase of the rainfall contribution to the total precipitation compared to that calculated for TCs formed during the opposite phases.

scholarly journals Comments on “Reexamination of Tropical Cyclone Wind–Pressure Relationship”

2008 ◽  
Vol 23 (4) ◽  
pp. 758-761 ◽  
Author(s):  
Shyamnath Veerasamy
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
North Atlantic ◽  
Wind Pressure ◽  
Maximum Wind Speed ◽  
Central Pressure ◽  
Southwest Indian Ocean ◽  
Maximum Wind ◽  
The North ◽  
The North Atlantic

Abstract In their study on the wind–pressure relationship (WPR) that exists in tropical cyclones, Knaff and Zehr presented results of the use of the Dvorak Atlantic WPR for estimating central pressure and maximum wind speed of tropical cyclones. These show some fairly large departures of estimated central pressure and maximum surface winds from observed values. Based on a study carried out in the southwest Indian Ocean (SWIO), it is believed that improvements in the use of the Dvorak WPR can be achieved by using the size of a closed isobar (it is the 1004-hPa closed isobar in the SWIO) to determine whether to use the North Atlantic (NA), the western North Pacific (WNP), or a mean of the NA and WNP Dvorak WPR for estimating central pressure and maximum wind speed in tropical cyclones.

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