The Low-Level Jet off the West Coast of Subtropical South America: Structure and Variability

2005 ◽  
Vol 133 (8) ◽  
pp. 2246-2261 ◽  
Author(s):  
RenéD. Garreaud ◽  
Ricardo C. Muñoz
Keyword(s):  
Wind Speed ◽  
South America ◽  
West Coast ◽  
Inversion Layer ◽  
Surface Winds ◽  
The West ◽  
Subtropical Anticyclone ◽  
Central Chile ◽  
Low Level ◽  
Southeast Pacific

Abstract The subtropical anticyclone over the southeast Pacific drives low-level southerly flow along the west coast of South America. In turn, the alongshore flow induces coastal upwelling that supports a wealth of fishery resources. Within this region, satellite data, marine reports, and coastal observations indicate the existence of a southerly coastal jet (i.e., a maximum of wind speed) off central Chile (26°–36°S). The mean features and variability of this southerly jet is documented in this work using 4 yr of satellite-derived sea surface winds, complemented by satellite-derived cloud amount fields and atmospheric reanalysis. Furthermore, analysis of in situ data and model results of a well-defined jet event during October 2000 allows a preliminary description of the jet’s three-dimensional structure and a comparison with the northerly jet off the coast of California. Southerly jet events off central Chile occur year-round, but they are more frequent during spring–summer (over 60% of the time). The jet is characterized by an elongated maximum of surface wind speed (∼10 m s−1) with its axis at about 150 km off the coast and a cross-shore scale of about 500 km. The two Quick Scatterometer (QuikSCAT) fields per day (a.m. and p.m. passes) allow a rough estimate of the amplitude of the diurnal cycle of the surface winds, which appears to be remarkably small in the region of the jet. The jet events are associated with the passage of a midlatitude ridge over the southeast Pacific strengthening the subtropical anticyclone. Upstream and over the jet region the coastal deck of stratocumulus clouds tends to dissipate in contrast to an increase in cloudiness downstream of the jet. In the case study the jet core resides at the top of the marine boundary layer (MBL)/inversion layer. Weak offshore flow prevails above the jet axis, and even weaker onshore flow prevails in the MBL. Consistent with its subtropical location the jet is embedded in a region of large-scale subsidence; nevertheless a mesoscale area of mean upward motion is simulated just downstream of the jet core.

scholarly journals Recent Changes in the Low-Level Jet along the Subtropical West Coast of South America

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 465
Author(s):  
Catalina Aguirre ◽  
Valentina Flores-Aqueveque ◽  
Pablo Vilches ◽  
Alicia Vásquez ◽  
José A. Rutllant ◽  
...  
Keyword(s):  
South America ◽  
West Coast ◽  
Southern Boundary ◽  
Central Chile ◽  
Low Level ◽  
Long Term Trends ◽  
Low Level Jet ◽  
Wind Events ◽  
Ocean Environment ◽  
June July

Surface winds along the subtropical west coast of South America are characterized by the quasi-weekly occurrences of low-level jet events. These short lived but intense wind events impact the coastal ocean environment. Hence, identifying long-term trends in the coastal low-level jet (CLLJ) is essential for understanding changes in marine ecosystems. Here we use ERA5 reanalysis (1979–2019) and an objective algorithm to track anticyclones to investigate recent changes in CLLJ events off central Chile (25–43 °S). Results present evidence that the number of days with intense wind (≥10 ms−1), and the number and duration of CLLJ events have significantly changed off central Chile in recent decades. There is an increase in the number of CLLJ events in the whole study area during winter (June-July-August; JJA), while during summer (December–January–February; DJF) a decrease is observed at lower latitudes (29–34 °S), and an increase is found at the southern boundary of the Humboldt system. We suggest that changes in the central pressures and frequency of extratropical, migratory anticyclones that reach the coast of South America, which force CLLJs, have played an important role in the recent CLLJ changes observed in this region.

scholarly journals Warm Winter Storms in Central Chile

2013 ◽  
Vol 14 (5) ◽  
pp. 1515-1534 ◽  
Author(s):  
R. Garreaud
Keyword(s):  
South America ◽  
West Coast ◽  
Moisture Flux ◽  
Central Pacific ◽  
The West ◽  
Winter Storms ◽  
Central Chile ◽  
Warm Winter ◽  
Freezing Level ◽  
The Andes

Abstract Central Chile is a densely populated region along the west coast of subtropical South America (30°–36°S), limited to the east by the Andes. Precipitation is concentrated in austral winter, mostly associated with the passage of cold fronts. The freezing level over central Chile is typically between 1500 and 2500 m when precipitation is present. In about a third of the cases, however, precipitation occurs accompanied by warm temperatures and freezing levels above 3000 m, leading to a sizeable increment in the pluvial area of Andean basins and setting the stage for hydrometeorological hazards. Here, warm winter storms in central Chile are studied, including a statistical description of their occurrence and an estimate of their hydrological impacts. Remote-sensed data and high-resolution reanalysis are used to explore the synoptic-scale environment of a typical case, generalized later by a compositing analysis. The structure of warm storms is also contrasted with that of the more recurrent cold cases. Precipitation during warm events occurs in the warm sector of a slow-moving cold front because of the intense moisture flux against the mountains in connection with a land-falling atmospheric river. This is in turn driven by a strong zonal jet aloft and reduced mechanical blocking upstream of the Andes. On a broader scale, a key element is the presence of a slowly moving anticyclone over the south Pacific, fostering advection of cold air into midlatitudes. The intense and persistent zonal jet stretches a moist-air corridor from the central Pacific to the west coast of South America.

scholarly journals Dynamics of the Low-Level Jet off the West Coast of Subtropical South America

2005 ◽  
Vol 133 (12) ◽  
pp. 3661-3677 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
RenéD. Garreaud
Keyword(s):  
Boundary Layer ◽  
South America ◽  
Pressure Gradient ◽  
West Coast ◽  
Marine Boundary Layer ◽  
Force Balance ◽  
North Central ◽  
Central Chile ◽  
Low Level ◽  
Coastal Jet

Abstract The subtropical west coast of South America is under the influence of the southeast Pacific anticyclone year-round, which induces persistent southerly winds along the coast of north-central Chile. These winds often take the form of a low-level coastal jet, in many aspects similar to the coastal jet existing off the California coast. Extensive diagnostics of mesoscale model results for a case in October 2000 are used here to describe the mean momentum budget supporting the coastal jet. The jet appears to occur when midlatitude synoptic conditions induce a northerly directed pressure gradient force along the coast of north-central Chile. The very steep coastal terrain precludes the development of a significant easterly low-level wind that would geostrophically balance the pressure gradient. Instead, the meridional flow accelerates until turbulent friction in the marine boundary layer balances the meridional pressure gradient. The resulting force balance is semigeostrophic, with geostrophy valid only in the zonal (cross shore) direction. At higher levels, the topographic inhibition of the easterlies relaxes, and a small easterly flow ensues, which turns out to be very important in the temperature and stability budgets of the layer capping the marine boundary layer.

scholarly journals HARVARD'S METEOROLOGICAL WORK ON THE WEST COAST OF SOUTH AMERICA

Science ◽  
1898 ◽  
Vol 7 (160) ◽  
pp. 95-98
Author(s):  
R. DeC. WARD
Keyword(s):  
South America ◽  
West Coast ◽  
The West

Tidal Investigations on the West Coast of South America

1943 ◽  
Vol 33 (2) ◽  
pp. 299
Author(s):  
H. A. Marmer
Keyword(s):  
South America ◽  
West Coast ◽  
The West

scholarly journals Analysis of Possible Triggering Mechanisms of Severe Thunderstorms in the Tropical Central Andes of Peru, Mantaro Valley

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 301 ◽  
Author(s):  
J.L. J.L. ◽  
A.S. A.S. ◽  
S. S. ◽  
D. D. ◽  
E. E. ◽  
...  
Keyword(s):  
Central Andes ◽  
The South ◽  
The West ◽  
Subtropical Anticyclone ◽  
Low Level ◽  
The Andes ◽  
Severe Thunderstorms ◽  
Westerly Winds ◽  
Moisture Fluxes ◽  
Triggering Mechanisms

The aim of the present study is to analyze the triggering mechanisms of three thunderstorms (TSs) associated with severe rainfall, hail and lightening in the tropical central Andes of Peru, specifically above the Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m a.s.l.) located in the Mantaro valley during the spring-summer season (2015–2016). For this purpose, we used a set of in-situ pluviometric observations, satellite remote sensing data, the Compact Meteorological Ka-Band Cloud Radar (MIRA-35C), the Boundary Layer Tropospheric Radar and downscaling model simulations with the Weather Research and Forecasting (WRF) Model (resolutions: 18 km, 6 km and 2 km), and the Advance Regional Prediction System (ARPS) (resolution: 0.5 km) models in order to analyze the dynamic of the atmosphere in the synoptic, meso and local scales processes that control the occurrence of the three TS events. The results show that at synoptic scale, the TSs are characterized by the southern displacement of the South-east Pacific Subtropical Anticyclone up to latitudes higher than 35 ∘ S, by the weakening and south-eastern displacement of the Bolivian high–North east low system and by the intrusion of westerly winds along the west side of the central Andes at upper and medium levels of the atmosphere. At meso-scale, apparently, two important moisture fluxes from opposite directions are filtered through the passes along the Andes: one from the north-west and the other from the south-east directions converge and trigger the deep convection into the Mantaro valley. These moisture fluxes are generated by the intrusion of the sea-breeze from the Pacific ocean along the west of the Andes coupling with upper and middle westerly winds and by the thermally induced moisture fluxes coming from the South American low level jet at the east side of the Andes. At the local scale, there is a low-level conditional instability in the previous hours as well as during the occurrence of the TSs above the Huancayo observatory. In addition, the simulation results indicated the possibility of generation of inertial gravity waves in the Amazon basin, associated with geostrophic adjustment which transports energy and moisture into the central Andes plateau and consequently intensifies the thunderstorms above the Mantaro valley.

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