Foehn-like Wind in the Mountains of Southeastern Brazil as Seen by the Eta Model Simulation

The present study gives evidence of the occurrence of foehn-like wind on the eastern slopes of the mountains at Southeastern Brazil. A particular case was detected based on observational evidence on 4 July 2015 near the city of Cruzeiro, state of Sao Paulo, on the Serra da Mantiqueira mountains. Results obtained from numerical simulations are consistent with the foehn wind occurrence deducted from the analysis of regional patterns and time series of selected meteorological parameters.

Keywords:
foehn wind; mountain weather; South America; Serra da Mantiqueira

Authorship

Pablo Luis Antico Autor de correspondência: Pablo Luis Antico, pantico@aggo-conicet.gob.ar.

Argentinean-German Geodetic Observatory, Consejo Nacional de Investigaciones Científicas y Técnicas, Berazategui, Buenos Aires, Argentina.Consejo Nacional de Investigaciones Científicas y TécnicasArgentinaBerazategui, Buenos Aires, ArgentinaArgentinean-German Geodetic Observatory, Consejo Nacional de Investigaciones Científicas y Técnicas, Berazategui, Buenos Aires, Argentina.

https://orcid.org/0000-0002-3491-0331

Sin Chan Chou

Instituto Nacional de Pesquisas Espaciais, Cahoeira Paulista, SP, Brasil.Instituto Nacional de Pesquisas EspaciaisBrasilCahoeira Paulista, SP, BrasilInstituto Nacional de Pesquisas Espaciais, Cahoeira Paulista, SP, Brasil.

https://orcid.org/0000-0002-8973-1808

Marcelo Enrique Seluchi

Centro Nacional de Monitoramento e Alertas de Desastres Naturais, São José dos Campos, SP, Brasil.Centro Nacional de Monitoramento e Alertas de Desastres NaturaisBrasilSão José dos Campos, SP, BrasilCentro Nacional de Monitoramento e Alertas de Desastres Naturais, São José dos Campos, SP, Brasil.

Gustavo Sueiro

Autor de correspondência: Pablo Luis Antico, pantico@aggo-conicet.gob.ar.

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Figures

Figures (11)

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Figure 1
Map showing the mountains at Southeastern Brazil. Terrain elevation as seen by the model in meters above sea level. Among the main cities in the area, the Serra da Mantiqueira mountains are depicted north of Cruzeiro city.

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Figure 2
Foehn wall over Serra da Mantiqueira as seen from the city of Cruzeiro heading to NE. The sharp edges of clouds suggest forced lifting of air upstream of the mountain. Descending motion of air prevents cloud formation downstream. Date & time: 4 July 2015 at 09:17 local time (12:17 UTC)

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Figure 3
Satellite imagery from GOES-13 channel 4 (IR) corresponding to 4 July 2015 at 13:30 UTC. Main features are highlighted in color, as in the case of stationary clouds pattern. See text for more details.

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Figure 4
Sea level pressure (contours in hPa) and surface wind (in m s^–1) as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation) and terrain elevation (colors bar in meters above sea level). The outer box encompasses the area covered in next figures. The inner box encompasses the area of the Eta-1 domain used later. The black dot within the inner box shows the location of Cruzeiro city.

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Figure 5
Several parameters at the 850-hPa isobaric level as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation). (a) Wind vector in m s^–1, (b) omega in hPa s^–1, (c) temperature in °C, and (d) relative humidity in fraction. Surface pressure less than 850-hPa are masked. The dashed line is a transect used for vertical cross-sections.

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Figure 6
Vertical cross sections of potential temperature (a) and temperature (b) (in K) as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation). The location of the vertical cross sections are indicated with a transect on the maps of Fig. 5. Dark shadows at the bottom represent terrain elevation.

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Figure 7
As in Fig. 6 but for the wind component parallel (a) and perpendicular (b) (in m s^–1) to the transect. Positive values are northwesterly wind in panel a, and southwesterly wind in panel b.

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Figure 8
As in Fig. 6 but for the relative humidity (in fraction).

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Figure 9
Surface wind (in m s^–1) as simulated by the Eta-1 valid for 4 July 2015 at 13 UTC (1-h simulation) and terrain elevation as seen by the model (colors bar in meters above sea level). The black dot indicates the location of Cruzeiro City.

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Figure 10
Wind vector (in m s^–1) at the 850-hPa isobaric level as simulated by the Eta-1 valid for 4 July 2015 at 13 UTC (1-h simulation). Surface pressure less than 850 hPa are masked. The black dot indicates the location of Cruzeiro City, and the white dots denoted with A and B are selected sites upwind and downwind the mountains (see text for more explanation).

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Figure 11
Time evolution of meteorological parameters at two points in Fig. 10 as simulated by the Eta-1 from 04 July 2015 at 13 UTC to 05 July 2015 at 13 UTC. Column (a) corresponds to point A in Fig. 10); column (b) to point B in the same figure. Temperature and dew point in the upper panel (in °C), relative humidity in the middle panel (%), and wind velocity and direction (black and white dots, respectively) expressed in knots (scale on the left) and compass degrees (scale on the right).

Figure 1 Map showing the mountains at Southeastern Brazil. Terrain elevation as seen by the model in meters above sea level. Among the main cities in the area, the Serra da Mantiqueira mountains are depicted north of Cruzeiro city.

Figure 2 Foehn wall over Serra da Mantiqueira as seen from the city of Cruzeiro heading to NE. The sharp edges of clouds suggest forced lifting of air upstream of the mountain. Descending motion of air prevents cloud formation downstream. Date & time: 4 July 2015 at 09:17 local time (12:17 UTC)

Figure 3 Satellite imagery from GOES-13 channel 4 (IR) corresponding to 4 July 2015 at 13:30 UTC. Main features are highlighted in color, as in the case of stationary clouds pattern. See text for more details.

Figure 4 Sea level pressure (contours in hPa) and surface wind (in m s^–1) as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation) and terrain elevation (colors bar in meters above sea level). The outer box encompasses the area covered in next figures. The inner box encompasses the area of the Eta-1 domain used later. The black dot within the inner box shows the location of Cruzeiro city.

Figure 5 Several parameters at the 850-hPa isobaric level as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation). (a) Wind vector in m s^–1, (b) omega in hPa s^–1, (c) temperature in °C, and (d) relative humidity in fraction. Surface pressure less than 850-hPa are masked. The dashed line is a transect used for vertical cross-sections.

Figure 6 Vertical cross sections of potential temperature (a) and temperature (b) (in K) as simulated by the Eta-5 valid for 4 July 2015 at 12 UTC (24-h simulation). The location of the vertical cross sections are indicated with a transect on the maps of Fig. 5. Dark shadows at the bottom represent terrain elevation.

Figure 7 As in Fig. 6 but for the wind component parallel (a) and perpendicular (b) (in m s^–1) to the transect. Positive values are northwesterly wind in panel a, and southwesterly wind in panel b.

Figure 8 As in Fig. 6 but for the relative humidity (in fraction).

Figure 9 Surface wind (in m s^–1) as simulated by the Eta-1 valid for 4 July 2015 at 13 UTC (1-h simulation) and terrain elevation as seen by the model (colors bar in meters above sea level). The black dot indicates the location of Cruzeiro City.

Figure 10 Wind vector (in m s^–1) at the 850-hPa isobaric level as simulated by the Eta-1 valid for 4 July 2015 at 13 UTC (1-h simulation). Surface pressure less than 850 hPa are masked. The black dot indicates the location of Cruzeiro City, and the white dots denoted with A and B are selected sites upwind and downwind the mountains (see text for more explanation).

Figure 11 Time evolution of meteorological parameters at two points in Fig. 10 as simulated by the Eta-1 from 04 July 2015 at 13 UTC to 05 July 2015 at 13 UTC. Column (a) corresponds to point A in Fig. 10); column (b) to point B in the same figure. Temperature and dew point in the upper panel (in °C), relative humidity in the middle panel (%), and wind velocity and direction (black and white dots, respectively) expressed in knots (scale on the left) and compass degrees (scale on the right).

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Foehn-like Wind in the Mountains of Southeastern Brazil as Seen by the Eta Model Simulation

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[1] Autor de correspondência: Pablo Luis Antico, pantico@aggo-conicet.gob.ar.