scholarly journals Interannual and Intraseasonal Variations of the Onset and Demise of the Pre-Wet Season and the Wet Season in the Northern Northeast Brazil

2018 ◽  
Vol 33 (3) ◽  
pp. 472-484 ◽  
Author(s):  
Francisco das Chagas Vasconcelos Junior ◽  
Charles Jones ◽  
Adilson Wagner Gandu
Keyword(s):  
Late Onset ◽  
Southern Oscillation ◽  
Wave Train ◽  
South Atlantic Convergence Zone ◽  
Southeastern Brazil ◽  
Precipitation Pattern ◽  
Northeast Brazil ◽  
Tropical Atlantic ◽  
Wet Season ◽  
Sst Anomalies

Abstract The Northern Northeast Brazil (NNB) has two rainy periods, namely Pre-Wet Season (PWS) and Wet Season (WES), which are usually treated as one system. The precipitation pattern on NNB is influenced by sea surface temperature (SST) anomalies in the Atlantic and Pacific Ocean on interannual timescales particularly by the Interhemispheric Gradient of SST anomalies (IGS) and El Niño Southern Oscillation (ENSO). On intraseasonal time scales, the MJO is especially important. This study investigates the variability of the PWS/WES. The PWS is largely associated with the development of the South America Monsoon System and South Atlantic Convergence Zone (SAMS/SACZ); the onset is depicted by incursion of the SAMS/SACZ northward. Anomalous atmospheric cyclonic circulation over the southeastern Brazil along with easterlies over the northern Tropical Atlantic marks the early onset of the PWS, while easterlies over the southern Tropical Atlantic are related to late onset episodes. The demise of the PWS is significantly associated with propagation of the MJO, specifically during phases 4-5 of the MJO lifecycle. A Rossby wave train in 200-hPa geopotential height with positive anomalies over central-southern Brazil is depicted during transition between PWS and WES.

Atmospheric Teleconnections of Tropical Atlantic Variability: Interhemispheric, Tropical–Extratropical, and Cross-Basin Interactions

2007 ◽  
Vol 20 (5) ◽  
pp. 856-870 ◽  
Author(s):  
Lixin Wu ◽  
Feng He ◽  
Zhengyu Liu ◽  
Chun Li
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Wave Train ◽  
Seasonal Migration ◽  
Atmospheric Response ◽  
Tropical Atlantic ◽  
The North ◽  
Atmospheric Teleconnections ◽  
Ocean Atmosphere ◽  
The North Atlantic

Abstract In this paper, the atmospheric teleconnections of the tropical Atlantic SST variability are investigated in a series of coupled ocean–atmosphere modeling experiments. It is found that the tropical Atlantic climate not only displays an apparent interhemispheric link, but also significantly influences the North Atlantic Oscillation (NAO) and the El Niño–Southern Oscillation (ENSO). In spring, the tropical Atlantic SST exhibits an interhemispheric seesaw controlled by the wind–evaporation–SST (WES) feedback that subsequently decays through the mediation of the seasonal migration of the ITCZ. Over the North Atlantic, the tropical Atlantic SST can force a significant coupled NAO–dipole SST response in spring that changes to a coupled wave train–horseshoe SST response in the following summer and fall, and a recurrence of the NAO in the next winter. The seasonal changes of the atmospheric response as well as the recurrence of the next winter’s NAO are driven predominantly by the tropical Atlantic SST itself, while the resulting extratropical SST can enhance the atmospheric response, but it is not a necessary bridge of the winter-to-winter NAO persistency. Over the Pacific, the model demonstrates that the north tropical Atlantic (NTA) SST can also organize an interhemispheric SST seesaw in spring in the eastern equatorial Pacific that subsequently evolves into an ENSO-like pattern in the tropical Pacific through mediation of the ITCZ and equatorial coupled ocean–atmosphere feedback.

scholarly journals An Asymmetry in the IOD and ENSO Teleconnection Pathway and Its Impact on Australian Climate

2012 ◽  
Vol 25 (18) ◽  
pp. 6318-6329 ◽  
Author(s):  
Wenju Cai ◽  
Peter van Rensch ◽  
Tim Cowan ◽  
Harry H. Hendon
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Austral Spring ◽  
Southeast Australia ◽  
Unit Change ◽  
The Impact ◽  
Sst Anomalies

Abstract Recent research has shown that the climatic impact from El Niño–Southern Oscillation (ENSO) on middle latitudes west of the western Pacific (e.g., southeast Australia) during austral spring (September–November) is conducted via the tropical Indian Ocean (TIO). However, it is not clear whether this impact pathway is symmetric about the positive and negative phases of ENSO and the Indian Ocean dipole (IOD). It is shown that a strong asymmetry does exist. For ENSO, only the impact from El Niño is conducted through the TIO pathway; the impact from La Niña is delivered through the Pacific–South America pattern. For the IOD, a greater convection anomaly and wave train response occurs during positive IOD (pIOD) events than during negative IOD (nIOD) events. This “impact asymmetry” is consistent with the positive skewness of the IOD, principally due to a negative skewness of sea surface temperature (SST) anomalies in the east IOD (IODE) pole. In the IODE region, convection anomalies are more sensitive to a per unit change of cold SST anomalies than to the same unit change of warm SST anomalies. This study shows that the IOD skewness occurs despite the greater damping, rather than due to a breakdown of this damping as suggested by previous studies. This IOD impact asymmetry provides an explanation for much of the reduction in spring rainfall over southeast Australia during the 2000s. Key to this rainfall reduction is the increased occurrences of pIOD events, more so than the lack of nIOD events.

scholarly journals Maximizing ENSO as a source of western US hydroclimate predictability

2019 ◽  
Vol 54 (1-2) ◽  
pp. 351-372 ◽  
Author(s):  
Christina M. Patricola ◽  
John P. O’Brien ◽  
Mark D. Risser ◽  
Alan M. Rhoades ◽  
Travis A. O’Brien ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Global Climate Model ◽  
Western Us ◽  
El Niño Events ◽  
Fixed Region ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Until recently, the El Niño–Southern Oscillation (ENSO) was considered a reliable source of winter precipitation predictability in the western US, with a historically strong link between extreme El Niño events and extremely wet seasons. However, the 2015–2016 El Niño challenged our understanding of the ENSO-precipitation relationship. California precipitation was near-average during the 2015–2016 El Niño, which was characterized by warm sea surface temperature (SST) anomalies of similar magnitude compared to the extreme 1997–1998 and 1982–1983 El Niño events. We demonstrate that this precipitation response can be explained by El Niño’s spatial pattern, rather than internal atmospheric variability. In addition, observations and large-ensembles of regional and global climate model simulations indicate that extremes in seasonal and daily precipitation during strong El Niño events are better explained using the ENSO Longitude Index (ELI), which captures the diversity of ENSO’s spatial patterns in a single metric, compared to the traditional Niño3.4 index, which measures SST anomalies in a fixed region and therefore fails to capture ENSO diversity. The physically-based ELI better explains western US precipitation variability because it tracks the zonal shifts in tropical Pacific deep convection that drive teleconnections through the response in the extratropical wave-train, integrated vapor transport, and atmospheric rivers. This research provides evidence that ELI improves the value of ENSO as a predictor of California’s seasonal hydroclimate extremes compared to traditional ENSO indices, especially during strong El Niño events.

scholarly journals On the influences of the El Niño, La niña and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998

2000 ◽  
Vol 30 (2) ◽  
pp. 305-318 ◽  
Author(s):  
Everaldo B de SOUZA ◽  
Mary T KAYANO ◽  
Julio TOTA ◽  
Luciano PEZZI ◽  
Gilberto FISCH ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Austral Summer ◽  
La Niña ◽  
Tropical Atlantic ◽  
La Nina ◽  
Precipitation Anomalies ◽  
Dipole Pattern ◽  
Sst Anomalies

The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Niño or La Niña) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Niño or La Niña) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Niño and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.

scholarly journals Analysis of the Atlantic Meridional Mode Using Linear Inverse Modeling: Seasonality and Regional Influences

2012 ◽  
Vol 25 (4) ◽  
pp. 1194-1212 ◽  
Author(s):  
Daniel J. Vimont
Keyword(s):  
High Latitude ◽  
Inverse Modeling ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Boreal Spring ◽  
Meridional Mode ◽  
Atlantic Meridional Mode ◽  
Sst Anomalies

Abstract Predictability and variability of the tropical Atlantic Meridional Mode (AMM) is investigated using linear inverse modeling (LIM). Analysis of the LIM using an “energy” norm identifies two optimal structures that experience some transient growth, one related to El Niño–Southern Oscillation (ENSO) and the other to the Atlantic multidecadal oscillation (AMO)/AMM patterns. Analysis of the LIM using an AMM-norm identifies an “AMM optimal” with similar structure to the second energy optima (OPT2). Both the AMM-optimal and OPT2 exhibit two bands of SST anomalies in the mid- to high-latitude Atlantic. The AMM-optimal also contains some elements of the first energy optimal (ENSO), indicating that the LIM captures the well-known relationship between ENSO and the AMM. Seasonal correlations of LIM predictions with the observed AMM show enhanced AMM predictability during boreal spring and for long-lead (around 11–15 months) forecasts initialized around September. Regional LIMs were constructed to determine the influence of tropical Pacific and mid- to high-latitude Atlantic SST on the AMM. Analysis of the regional LIMs indicates that the tropical Pacific is responsible for the AMM predictability during boreal spring. Mid- to high-latitude SST anomalies contribute to boreal summer and fall AMM predictability, and are responsible for the enhanced predictability from September initial conditions. Analysis of the empirical normal modes of the full LIM confirms these physical relationships. Results indicate a potentially important role for mid- to high-latitude Atlantic SST anomalies in generating AMM (and tropical Atlantic SST) variations, though it is not clear whether those anomalies provide any societally useful predictive skill.

Multidecadal Modulations of ENSO influence on cyclogenesis in the Tropical Atlantic

2020 ◽  
Author(s):  
Adama Badiane ◽  
Belén Rodríguez-Fonseca ◽  
Teresa Losada ◽  
Abdou Lahat Dieng ◽  
Saidou Moustapha Sall
Keyword(s):  
Southern Oscillation ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Tropical Atlantic ◽  
Enso Events ◽  
Tropical North Atlantic ◽  
Development Region ◽  
Decadal Variations ◽  
The Impact ◽  
Sst Anomalies

<p align="justify"><span>The impact of ENSO (El Niño Southern Oscillation) events on the cyclogenesis of the eastern tropical North Atlantic is highlighted, focusing on decadal variations of the interannual relationship at the Senegalese coast, which is the main cyclone development region (MDR). SST anomalies in the Equatorial Pacific associated with ENSO events affect vertical wind shear over the eastern Atlantic, by inducing strong subsidence of dry air over the eastern Atlantic which tends to inhibit deep convection and thus be unfavorable to cyclonic activity. Based on 20yr- correlations between the number of cyclones that are born in the MDR and ENSO index, we have selected two different periods of study (period1: 1950-1969; and period2: 1996-2015).The results show that period2 presents the highest scores of negative correlations between ENSO and tropical Atlantic cyclogenesis. Although there is an intensification of ENSO events during period2 compared to period1, we have found that decadal changes in climatology have a more significant effect on the MDR than the interannual changes. Additionally, the changes in the interannual signal appear to be related to the concomitant action of interannual SST anomalies over the whole tropical basins.</span></p>

scholarly journals Study on the possibility of predicting the onset and rainfall of wet season in Yogyakarta Special Province, Indonesia

2020 ◽  
Vol 35 (2) ◽  
pp. 55
Author(s):  
Dewi Galuh Condro Kirono ◽  
Budi Salmon
Keyword(s):  
Extreme Event ◽  
Late Onset ◽  
Southern Oscillation ◽  
Flood Hazard ◽  
Onset Time ◽  
Daily Rainfall ◽  
Rainfall Anomaly ◽  
Air Pressure ◽  
Wet Season ◽  
June July

Indonesian region frequently experiences a prolonged drought and/or flood hazard One of the key factors that often triggers these Awards is the occurrence of seasonal rainfall anomaly. To minimize the possible impact of such extreme event, it is necessary to develop a model that can be applied to predict the wet season onset and wet season rainfall. This paper is a preliminary effort on this mailer. As a pilot study, Yogyakarta Special Province (DIY) has been selected for this purpose. In particular; the analysis is emphasized on the Adisucipto airport station, Yogyakarta, as it is one of the first-class climatological station in DIY which has a very good and long data required for such intention. Detail objectives of this study are to address the following three questions: (1) is it possible to predict wet season onset in Adisucipto airport station using local and regional atmospheric indicators? (2) if it is possible and the model(s) have been developed, can the model(s) be applied for predicting the onset of wet season in other parts of DIY and its surround? (3) does an early or late onset of wet season provide any indication to subsequent rainfall during the wet season? To achieve these objectives, the study requires several types of data including daily rainfall data, monthly air pressure data, Southern Oscillation Index (SO!) and Sea Surface Temperature data. Most of the data cover the period of 1976 to 2001. Methods that have been applied to meet the goals are statistical descriptive and simple liner regression analysis. The results suggest that: (I) wet season onset time in Yogyakarta can be predicted using both local and regional atmospheric factors. namely August and September SOI, and air pressure index at Adisucipto airport station in June. July and August; (2) models that have been developed for Adisucipto airport station are modest enough to be applied for predicting the onset of wet season at other location; (3) the onset of wet season cannot be used as an indicator to estimate rainfall in wet season itself.

scholarly journals Multidecadal Changes in the Relationship between ENSO and Wet-Season Precipitation in the Arabian Peninsula

2015 ◽  
Vol 28 (12) ◽  
pp. 4743-4752 ◽  
Author(s):  
In-Sik Kang ◽  
Irfan Ur Rashid ◽  
Fred Kucharski ◽  
Mansour Almazroui ◽  
Abdulrahman K. Alkhalaf
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Arabian Peninsula ◽  
El Nino ◽  
Southern Oscillation ◽  
Wet Season ◽  
The Pacific ◽  
The Indian Ocean ◽  
The Relationship ◽  
Sst Anomalies

Abstract Multidecadal variations in the relationship between El Niño–Southern Oscillation (ENSO) and the Arabian Peninsula rainfall are investigated using observed data for the last 60 years and various atmospheric general circulation model (AGCM) experiments. The wet season in the Arabian Peninsula from November to April was considered. The 6-month averaged Arabian rainfall was negatively correlated with ENSO for an earlier 30-yr period from 1950 to 1979 and positively correlated to ENSO for a more recent period from 1981 to 2010. The multidecadal variations can be attributed to the variations in Indian Ocean SST anomalies accompanied by ENSO. In the early 30-yr period, ENSO accompanied relatively large SST anomalies in the Indian Ocean, whereas in the recent 30-yr period it accompanied relatively small SST anomalies in the Indian Ocean. The atmospheric anomalies in the Arabian region during ENSO are combined responses to the Pacific and Indian Ocean SST anomalies, which offset each other during ENSO. The recent El Niño events accompanied negative 200-hPa geopotential height (GH) anomalies over the Arabian region, mainly forced by the Pacific SST anomalies, resulting in an increase of precipitation over the region. In contrast, in the early 30-yr period, Indian Ocean SST anomalies played a dominant role in the atmospheric responses over the Arabian region during ENSO, and the negative GH anomalies and more precipitation over the Arabian region were mainly forced by the negative SST anomalies over the Indian Ocean, which appeared during La Niña. These observed findings are confirmed by various AGCM experiments.

scholarly journals Biomass Burning and Water Balance Dynamics in the Lake Chad Basin in Africa

Earth ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 340-356
Author(s):  
Forrest W. Black ◽  
Jejung Lee ◽  
Charles M. Ichoku ◽  
Luke Ellison ◽  
Charles K. Gatebe ◽  
...  
Keyword(s):  
Water Balance ◽  
Biomass Burning ◽  
Water Cycle ◽  
Potential Evapotranspiration ◽  
Southern Oscillation ◽  
Wet Season ◽  
Lake Chad ◽  
Chad Basin ◽  
Lake Chad Basin ◽  
Logone Catchment

The present study investigated the effect of biomass burning on the water cycle using a case study of the Chari–Logone Catchment of the Lake Chad Basin (LCB). The Chari–Logone catchment was selected because it supplies over 90% of the water input to the lake, which is the largest basin in central Africa. Two water balance simulations, one considering burning and one without, were compared from the years 2003 to 2011. For a more comprehensive assessment of the effects of burning, albedo change, which has been shown to have a significant impact on a number of environmental factors, was used as a model input for calculating potential evapotranspiration (ET). Analysis of the burning scenario showed that burning grassland, which comprises almost 75% of the total Chari–Logone land cover, causes increased ET and runoff during the dry season (November–March). Recent studies have demonstrated that there is an increasing trend in the LCB of converting shrubland, grassland, and wetlands to cropland. This change from grassland to cropland has the potential to decrease the amount of water available to water bodies during the winter. All vegetative classes in a burning scenario showed a decrease in ET during the wet season. Although a decrease in annual precipitation in global circulation processes such as the El Niño Southern Oscillation would cause droughts and induce wildfires in the Sahel, the present study shows that a decrease in ET by the human-induced burning would cause a severe decrease in precipitation as well.

scholarly journals Spurious North Tropical Atlantic precursors to El Niño

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Wenjun Zhang ◽  
Feng Jiang ◽  
Malte F. Stuecker ◽  
Fei-Fei Jin ◽  
Axel Timmermann
Keyword(s):  
El Niño ◽  
Cross Correlation ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Tropical Atlantic ◽  
The North ◽  
Sst Variability ◽  
Primary Driver ◽  
North Tropical Atlantic

AbstractThe El Niño-Southern Oscillation (ENSO), the primary driver of year-to-year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead-lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies did not properly account for ENSO’s autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time-varying ENSO frequency, and greenhouse warming, we demonstrate that the cross-correlation characteristics between NTA SST and ENSO, are consistent with a one-way Pacific to Atlantic forcing, even though the interpretation of lead-lag relationships may suggest otherwise.

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