South American Cold Surges: Types, Composites, and Case Studies

Lupo, Anthony R.; Nocera, Joseph J.; Bosart, Lance F.; Hoffman, Eric; Knight, David J.

doi:10.1175/1520-0493(2001)129<1021:sacstc>2.0.co;2

Cited by 49 publications

(63 citation statements)

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“…This is a typical pattern for intense polar outbreak events (e.g. Marengo et al, 1997;Garreaud, 1999;Vera and Vigliarolo, 2000;Lupo et al, 2001 and references cited therein), and indicates a marked baroclinic structure compared with Figure 1(a). From the comparison between Figure 1(a) and (b) it is also interesting to notice that the maximum sea-level pressure anomalies over Paraguay were located below negative geopotential anomalies, suggesting the presence of a shallow layer of cold air.…”

Section: Resultsmentioning

confidence: 56%

Dynamical conditions and synoptic tracks associated with different types of cold surge over tropical South America

Pezza

Ambrizzi

2005

Int. J. Climatol.

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A 1973-2000 synoptic climatology (every 12 h) is presented of the surface cyclone and anticyclone tracks associated with cold surges in tropical South America, complemented by the corresponding atmospheric circulation for the period of 1950-2000. The aim of this study is to provide a new insight into the synoptic paths and the dynamics associated with distinct cold-wave categorization in the tropics. Extreme minimum temperatures and frost occurrence from the University of São Paulo (USP) meteorological station in São Paulo city (Brazil) are used to select cold events with different intensities: extreme (T < 0°C plus frost), strong (0 ≤ T ≤ 2.5°C plus frost), strong without frost (0 ≤ T ≤ 2.5°C without frost) and moderate (T > 2.5°C plus frost).Atmospheric variables at low and upper levels derived from the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis are calculated from day −10 to day 0 with regard to the coldest day in São Paulo. In addition, an automatic tracking scheme is applied to diagnosing and tracking the cyclones and anticyclones at the surface associated with cold surges.Through a superposition technique, climatological 'clouds' showing all tracks on the same map are produced, adding some new insights into the synoptic patterns of propagation and improving the Southern Hemisphere climatology. For all composites the mean cold front crosses the equator, and the extratropical cyclones also play an important role in favouring frost occurrence in São Paulo. The lagged composites indicate that most of the cold events may be tracked up to 9 days before their occurrence, with a persistent upper level signal in the eastern Pacific.

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Section: Resultsmentioning

confidence: 56%

Dynamical conditions and synoptic tracks associated with different types of cold surge over tropical South America

Pezza

Ambrizzi

2005

Int. J. Climatol.

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“…The systems impinging the southern portion of the continent are embedded in the South Pacific storm track, the axis of which is located between 408 and 508S throughout the year (Trenberth 1991;Hoskins and Hodges 2005). Much attention has been devoted to the channeling effects of surface anticyclones along the east (downstream) side of the Andes that lead to rapid incursions of cold air that may reach as far north as the Amazon basin (Garreaud 2000;Lupo et al 2001;Seluchi et al 2006). The disruption of weather systems, particularly cold fronts, along the west (upstream) side of the extratropical Andes has been less studied, in part because of the lack of data over the adjacent Pacific Ocean.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

Barrett

Garreaud

Falvey

2009

Monthly Weather Review

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The effects of the Andes Cordillera, the major mountain range in South America, on precipitation patterns of baroclinic systems approaching from the southeast Pacific remain largely unstudied. This study focuses on a case in late May 2008 when an upper-level trough and surface cold front produced widespread precipitation in central Chile. The primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation.Weather Research and Forecasting (WRF) model simulations indicate that as an upper-level trough approached central Chile, midtropospheric flow below 700 hPa was blocked by the high topography and deflected poleward in the form of a barrier jet. This northerly jet had wind maxima in excess of 15 m s 21 , was centered around 925 hPa, and extended westward 200 km from the mountains. It intersected the cold front, which approached from the south near the coast, thereby increasing convergence along the frontal surface, slowing its equatorward progress, and enhancing rainfall over central Chile. Another separate region of heavy precipitation formed over the upwind slopes of the cordillera. A trajectory analysis confirmed that the barrier jet moved low-level parcels from their origin in the moist southeast Pacific boundary layer to the coast. When model topography was reduced to twenty percent of its original height, the cold front advanced more rapidly to the northeast, generated less precipitation in central Chile between 338 and 368S, and produced minimal orographic precipitation on the upwind Andean slopes. Based on these findings, the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley.

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“…Those studies also show that the anticyclone on the eastern side of the Andes displays the marked meridional elongation and anticyclonic trajectory turning that are the trademark influences of mountains on transient disturbances (Gan and Rao, 1984). The Andes therefore help promote the incursion of midlatitude cold fronts and cold midlatitude air well into the Subtropics and Tropics of South America, a phenomenon that is commonly observed to the east of major north-south oriented mountain ranges (Lupo et al, 2001). Garreaud (2000) used the steep rise in sea-level pressure (SLP) at the leading edge of the anticyclone associated with a cold front to identify the passage of cold surges through South America.…”

Section: Introductionmentioning

confidence: 87%

“…Fortune and Kousky, 1983;Garreaud, 2000;Marengo et al, 1997). Previous studies have attributed the occurrence of 'cold surges' to the impact of the Andes Mountains on eastward propagating synoptic-scale transient disturbances (Garreaud, 2000;Lupo et al, 2001). During a 'cold surge' event, cold air damming enhances the northward flow of cold air along the eastern side of the Andes Mountains.…”

Section: Introductionmentioning

confidence: 99%

“…On the leading edge of a surface anticyclone that is crossing over the Andes from the Eastern Pacific into South America, cold air damming produces a strong southerly barrier jet along the eastern side of the Andes and a strong northward cold air advection into subtropical and tropical South America (e.g. Garreaud, 2000;Lupo et al, 2001). Those studies also show that the anticyclone on the eastern side of the Andes displays the marked meridional elongation and anticyclonic trajectory turning that are the trademark influences of mountains on transient disturbances (Gan and Rao, 1984).…”

Section: Introductionmentioning

confidence: 99%

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The role of cold fronts in the onset of the monsoon season in the South Atlantic convergence zone

Nieto-Ferreira

Rickenbach

Wright

2011

Quart J Royal Meteoro Soc

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The onset of the South American monsoon season culminates with the abrupt establishment of the South American convergence zone (SACZ). The impact of cold fronts on the abrupt establishment of the SACZ is studied using an 11-year composite analysis of the dynamic and thermodynamic structures, intensity and propagation of cold fronts that occur prior to, during, and after monsoon onset in the SACZ. A significant change in the structure and propagation of cold fronts is observed at the time of monsoon onset in the SACZ, with cold fronts suddenly stalling and becoming stationary in southeastern Brazil. It is proposed that this regime change of the structure and propagation of cold fronts causes the abrupt onset of the monsoon in the SACZ. A mechanism for this sudden change in cold

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South American Cold Surges: Types, Composites, and Case Studies

Cited by 49 publications

References 0 publications

Dynamical conditions and synoptic tracks associated with different types of cold surge over tropical South America

Dynamical conditions and synoptic tracks associated with different types of cold surge over tropical South America

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

The role of cold fronts in the onset of the monsoon season in the South Atlantic convergence zone

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