On precursors of South American cyclogenesis

Mendes, David; Souza, Ênio Pereira de; Trigo, Isabel F.; Miranda, Pedro

doi:10.1111/j.1600-0870.2006.00215.x

Cited by 36 publications

(27 citation statements)

References 18 publications

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“…6b. These features are also very similar to those shown by Garreaud and Wallace (1998) and Mendes et al (2007) related to the peaking at the time of extratropical cyclogeneses over SA during austral season. It creates a confluence region around 25 • S; 58 • W that can contribute with advection of warm air from the north by the SALLJ and cold advection from the south due to the cyclone position near the east coast of Argentina.…”

Section: Interannual Variability Of Sallj Frequencysupporting

confidence: 69%

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Silva¹,

Ambrizzi²,

Marengo

2009

Ann. Geophys.

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Abstract. The differences on the phase and wavelength of the quasi-stationary waves over the South America generated by El Niño (EN) and La Niña (LN) events seem to affect the daily evolution of the South American Low Level Jet east of the Andes (SALLJ). For the austral summer period of 1977-2004 the SALLJ episodes detected according to Bonner criterion 1 show normal to above-normal frequency in EN years, and in LN years the episodes show normal to below-normal frequency.During EN and LN years the SALLJ episodes were associated with positive rainfall anomalies over the La Plata Basin, but more intense during LN years. During EN years the increase in the SALLJ cases were associated to intensification of the Subtropical Jet (SJ) around 30 • S and positive Sea Level Pressure (SLP) anomalies over the western equatorial Atlantic and tropical South America, particularly over central Brazil. This favored the intensification of the northeasterly trade winds over the northern continent and it channeled by the Andes mountain to the La Plata Basin region where negative SLP are found. The SALLJ cases identified during the LN events were weaker and less frequent when compared to those for EN years. In this case the SJ was weaker than in EN years and the negative SLP anomalies over the tropical continent contributed to the inversion of the northeasterly trade winds. Also a southerly flow anomaly was generated by the geostrophic balance due to the anomalous blocking over southeast Pacific and the intense cyclonic transient over the southern tip of South America. As result the warm tropical air brought by the SALLJ encounters the cold extratropical air from the southerly winds over the La Correspondence to: G. A. M. Silva (gyrlene@model.iag.usp.br) Plata basin. This configuration can increase the conditional instability over the La Plata basin and may explain the more intense positive rainfall anomalies in SALLJ cases during LN years than in EN years.

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Section: Interannual Variability Of Sallj Frequencysupporting

confidence: 69%

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Silva¹,

Ambrizzi²,

Marengo

2009

Ann. Geophys.

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“…23,26 We intend to assess trends of cyclonic activity based on the objective methodology developed by one of us to detect and track all mid-and high-latitude Atlantic (and Mediterranean) cyclones. 5,27,28 This approach enables the evaluation of interannual variability and trends of cyclone frequencies for the NAE region and relates these with continental climate trends and changes of ocean wave height.…”

Section: Introductionmentioning

confidence: 99%

The Impact of North Atlantic Wind and Cyclone Trends on European Precipitation and Significant Wave Height in the Atlantic

Trigo

Valente

Trigo

et al. 2008

Annals of the New York Academy of Sciences

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105

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An analysis of the frequency of cyclones and surface wind velocity for the Euro-Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October-March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January-March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50 degrees N up to -3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern.

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“…Intra-seasonal and decadal variability in rainfall and streamflow have also been the subject of many studies (Robertson and Mechoso, 2000;Robertson et al, 2001;Zhou and Lau, 2001;Paegle and Mo, 2002;Carvalho et al, 2004). Most of the moisture that reaches UPRB is from the Amazon region (Drumond et al, 2008;Carvalho et al, 2011), and the rainfall mechanisms are also associated with MCSs along the South American low-level jet (SALLJ; see Velasco and Fritsch, 1987;Marengo et al, 2004;Salio et al, 2007) and transient systems related to extratropical cyclones and cold fronts (Mendes et al, 2007;Silva and Ambrizzi, 2010). El Niño events have also been linked to extreme rainfalls and floods in the UPRB (Camilloni and Barros, 2003;Grimm and Tedeschi, 2009;Muza et al, 2009;Cavalcanti et al, 2015;Antico et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Classification of mechanisms, climatic context, areal scaling, and synchronization of floods: the hydroclimatology of floods in the Upper Paraná River basin, Brazil

2017

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Abstract. Floods are the main natural disaster in Brazil, causing substantial economic damage and loss of life. Studies suggest that some extreme floods result from a causal climate chain. Exceptional rain and floods are determined by large-scale anomalies and persistent patterns in the atmospheric and oceanic circulations, which influence the magnitude, extent, and duration of these extremes. Moreover, floods can result from different generating mechanisms. These factors contradict the assumptions of homogeneity, and often stationarity, in flood frequency analysis. Here we outline a methodological framework based on clustering using self-organizing maps (SOMs) that allows the linkage of large-scale processes to local-scale observations. The methodology is applied to flood data from several sites in the flood-prone Upper Paraná River basin (UPRB) in southern Brazil. The SOM clustering approach is employed to classify the 6-day rainfall field over the UPRB into four categories, which are then used to classify floods into four types based on the spatiotemporal dynamics of the rainfall field prior to the observed flood events. An analysis of the vertically integrated moisture fluxes, vorticity, and high-level atmospheric circulation revealed that these four clusters are related to known tropical and extratropical processes, including the South American low-level jet (SALLJ); extratropical cyclones; and the South Atlantic Convergence Zone (SACZ). Persistent anomalies in the sea surface temperature fields in the Pacific and Atlantic oceans are also found to be associated with these processes. Floods associated with each cluster present different patterns in terms of frequency, magnitude, spatial variability, scaling, and synchronization of events across the sites and subbasins. These insights suggest new directions for flood risk assessment, forecasting, and management.

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On precursors of South American cyclogenesis

Cited by 36 publications

References 18 publications

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

The Impact of North Atlantic Wind and Cyclone Trends on European Precipitation and Significant Wave Height in the Atlantic

Classification of mechanisms, climatic context, areal scaling, and synchronization of floods: the hydroclimatology of floods in the Upper Paraná River basin, Brazil

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