rediscovering the orinoco low-level jet · and colfuturo – colciencias fellowships. the author is...
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REDISCOVERING THE ORINOCO LOW-LEVEL JET Giovanni Jiménez-Sánchez and Paul Markowski The Pennsylvania State University – Department of Meteorology and Atmospheric Science ([email protected])
The Orinoco low-level jet (OLLJ) in northern South America simulated by WRF-ARW using dynamical downscaling. The higher spatial resolution better depicts the topography and improves the characterization of the low-level jet, which was identified as a single stream tube over Colombia and Venezuela with the greatest wind speeds (~15 m s-1) occurring in January.
m
Longitude
50ºW55ºW60ºW65ºW70ºW75ºW80ºW85ºW
5ºS
0º
5ºN
10ºN
15ºN
20ºN
Colombia
Venezuela
Latitude Orinoco River
Eastern Cordillera
Mérida CordilleraCoastal Cordillera
Guiana Highlands
Macarena Mountain
Range
Vertical cross-sections and horizontal wind speed vertical profiles for the entrance, mid-corridor, and exit regions. The core of the OLLJ has different heights and intensities depending on the location.
Horizontal characterization of the diurnal evolution. The OLLJ exhibits the greatest wind intensity in the morning (~15 m s-1) and the least intensity in the afternoon (~9–10 m s-1).
1. Objective 2. Why? 3. How?To characterize the OLLJ structure, evolution, and mechanisms of formation using finer horizontal, vertical, and temporal resolution than possible in previous studies.
Because the low-level wind shear created by the OLLJ jet poses a risk for more than one million airline passengers per year. The OLLJ dynamics cannot be explained via the well-known Holton or Blackadar mechanisms.
The investigation relies on a 5-month-long simulation (November 2013-March 2014) performed with the Weather Research and Forecasting model, with initial and boundary conditions provided by the Global Forecast System analysis.
WRF dynamical downscaling
• Hourly outputs • 9-km grid spacing • 51 vertical levels • Nov. 2013–Mar. 2014
Topographic map of northern South America showing the WRF domain (colors), the Orinoco River basin limits (red), and locations of the main airports along the OLLJ corridor. Boundary conditions from 0.5º x0.5º GFS Analysis were updated every 6 hours and the model was reinitialized every four days with a preceding spin-up of 12 hours.
• Formation mechanisms. • Model sensitivity to:
- Non-local PBL. - Topography height reduction. - 3-km grid spacing. - No shortwave/longwave radiation. - No latent heat.
Future work
This research is supported by the Colombian Air Force and Colfuturo – Colciencias fellowships. The author is an active member of the Colombian Air Force.
OLLJ diurnal wind speed behavior is related to low-level static stability behavior. Maxima wind speeds occur in the morning when low-level static stability is maximized, whereas minima wind speeds occur in the afternoon when the boundary layer is approximately neutrally stratified.
|V|-Vertical profile 64ºW 07LT
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0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
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Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 |V|-Vertical profile 5ºN 07LT
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0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
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Leve
l (Km
)
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4.5 |V|-Vertical profile 1.5ºN 07LT
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0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
Gro
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Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5
Θ - Vertical profile 64ºW 07LT
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0 295 300 305 310 315 320
Potential Temperature (K)
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 Θ - Vertical profile 5ºN 07LT
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0
Hei
ght A
bove
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l (Km
)
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0.5
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4.5 Θ - Vertical profile 1.5ºN 07LT
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Hei
ght A
bove
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Leve
l (Km
)
1.5
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Potential Temperature (K)Potential Temperature (K)295 300 305 310 315 320295 300 305 310 315 320
EXIT MID-CORRIDOR ENTRANCEMID-CORRIDOR ENTRANCEEXIT
|V|-Vertical profile 64ºW 15LT
1
2
3
4
0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 |V|-Vertical profile 5ºN 15LT
1
2
3
4
0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 |V|-Vertical profile 1.5ºN 15LT
1
2
3
4
0 0 2 4 6 8 10 12 14
wind speed (m s-1)
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5
Θ - Vertical profile 64ºW 15LT
1
2
3
4
0 295 300 305 310 315 320
Potential Temperature (K)
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 Θ - Vertical profile 5ºN 15LT
1
2
3
4
0
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5 Θ - Vertical profile 1.5ºN 15LT
1
2
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4
0
Hei
ght A
bove
Gro
und
Leve
l (Km
)
1.5
0.5
2.5
3.5
4.5
Potential Temperature (K)Potential Temperature (K)295 300 305 310 315 320295 300 305 310 315 320
Intraseasonal Variability
Fourier series analysis
Wind speed and potential temperature exhibit strong diurnal and semi-diurnal signal, which implies a modulation of the wind speed via radiative heating.
MID-CORRIDOR ENTRANCEEXIT