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Meteorología del Pacifico Sur Oriental
René D. GarreaudDepartamento de Geofísica – Universidad de Chile
www.dgf.uchile.cl/rene
SENAMHI – Perú
Curso de Climatología Sinóptica en la Costa Oeste de América del Sur16-20 Abril 2007; Lima - Perú
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Presentación No. 2: Meteorología del Pacifico Sur Oriental
En esta exposición se describen los rasgos climáticos mas relevantes en la región sur-oriental del Océano Pacifico, con especial énfasis en la zona tropical-subtropical y franja costera. Tópicos incluidos en esta exposición incluyen el origen y mantención del anticiclón del Pacifico, los vientos costeros y la surgencia oceánica.
• El campo de presión y vientos de gran escala• El campo de nubosidad• Mantención del anticiclón subtropical del Pacifico• El campo de viento de meso-escala y surgencia oceánica• Ciclo diario lejos y fuera de la costa
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SubtropicalHigh Coastal
jet
SCu deck
SAMITCZ
Andes Mts.
Key atmospheric features over the SEP
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1
2
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Jan
Apr
Jul
Oct
Annual cycle of SST
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Jan
Apr
Jul
Oct
Annual cycle of SLP
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The extensive and persistent deck of SCu over the SSEP plays an important role in the regional and global climate by substancially reducing the ammount of solar radiation that reaches the sea
surface
LTM bi-monthly albedo
60-80%temp. freq.
Albedo ( nubosidad)
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Cloud field has significant spatial variability
SCuSc
Cu
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Cloud pattern related to MBL depth
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Cloud pattern related to MBL depth
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Full: Continental monsoon + Hadley cell + MountainsTopo: Hadley cell + Mountains
(674 hPa) (887 hPa)
Full
Topo
“The similarities between upper and lower panels imply an important role for the interaction between the zonal mean flow and the topography in sustaining the subtropical anticyclones. The differences emphasize the importance of the zonally asymmetric heating”. (Rodwell and Hoskins 2001)
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(Rodwell and Hoskins 2001)
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v
Ideal monsoon heating@ 25°S-90°E
+ Continental drag
+ Newtonian cooling
+ Ideal. mountain
(Rodwell and Hoskins 2001)
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(674 hPa) (887 hPa)
Mt.+SAM
Mt.+SAM+SPac
(Rodwell and Hoskins 2001)
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Y. Wang et al. 2004
Cooling effect of the SCu deck over the SEP further enhance the subsidence and hence the southerly flow
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Formation and maintenanceof the SCu deck
(moist air confined to the MBL)
Enhanced equatorward flowv fw/ z
Enhanced LS subsidence tokeep T/ t 0
Net cooling at the top of the SCu(Radiative effect
– condensational heating)
Large Scale Circulation set the stage:
Subsidence (adiab. Warming)+ Equatorward flow (low SST)
= Temperature Inversion
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From K. Takahashi (2006)
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SCu: Low level, shallow cloud layer at the top of the MBL
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Net Cloud Radiative Forcing
R = LW + SH, where = clear - average
For SCu clouds:LW ~ 0 as Tc ~ SSTSH < 0 (albedo effect)R < 0 : Cooling effect SEP SCu: -50 W/m2
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Annual cycle of SCu an inter-regional differences largely explained by low level stability: 700- sfc (Klein and Hartmann 1993)
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LTM annual mean SLP and surface wind speed
(NCEP-NCAR Reanalysis)
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Bi-monthly means of the surface wind speed (near the coast, the flow is largely along-shore). An "atmospheric" jet is a closed maxima of wind speed (i.e., you need closed contours of ws). Thus, there are only two jets along the coast: one off central Chile (30°-35°S) and a small one off Sechura (5°S aprox).
Nevertheless, there is a conspicuous maximum of wind speed off Pisco (15°S). The wind speed there has a very marked seasonality (from 3 m/s in JF up to +7 m/s in JA). When the maximum is present during austral winter, its along-shore scale is rather short (i.e., a very windy region of about 300 km bounded by "calm" regions to the north and south of it). Of course, its narrowness and seasonality make this maximum particularly susceptible to "climate change" either in the past or future.
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Surgencia: Afloramiento de aguas profundas (frías, ricas en O2 y nutrientes) por efecto del viento
Surgenciacostera
Surgenciaecuatorial
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V
U
w
V
U
w
Simulated (MM5) structure of the coastal jet
V > 18 m/sGarreaud and Muñoz 2005
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21v
H
C
y
p d
vf
x
p
vuHd
Cfv
x
p
y
uv
x
uu
t
u
1
vvH
Cfu
y
p
y
vv
x
vu
t
v d
1
Steady-stateDynamics
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•V > 8 m/s off central Chile almost alwayd associated with a southerly jet (dark shaded)
•Jet events typically a week long (3-15 days)
•More frequent, stronger and longer in summer.
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SQ3. Coastal Jet under Clear Skies…Why?(+300 W/m2 reaching the surface)
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Renault et al. 2006
SQ4. Impacts of Jet Events on SST
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Renault et al. 2006
Impacts of Jet Events on SST
Wind, SST and SST anomalies
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A distinctive feature of this Sc deck is its particularly pronounced diurnal cycle in cloud amount (Minnis and Harrison 1984; Rozendaal et al.
1995) and LWP (Bretherton et al. 2003; Wood et al. 2002), that is highly relevant to the quantification of the true impact of Sc on climate
(Bergman and Salby 1997).
Bretherton et al. 1995
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- q - q
Mean diurnal cycle at Antofagasta (Rutllant et al. 2003)
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MM5 results
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• Significant diurnal cycle in up to 5 km ASL• Subsidence interrupted by period of upward motion• Cooling largely produced by vertical advection
W C W C W C
MM5 results
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Diurnal cycle of vertical velocity at 800 hPa MM5 results
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Coastal Diurnal Cycle
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