Meteorología del Pacifico Sur Oriental SENAMHI – Perú Curso de Climatología Sinóptica en la Costa Oeste de América del Sur 16-20 Abril 2007; Lima - Perú Meteorología del Pacifico Sur Oriental René D. Garreaud Departamento de Geofísica – Universidad de Chile www.dgf.uchile.cl/rene

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

Key atmospheric features over the SEP Subtropical High Coastal jet SCu deck SAM ITCZ Andes Mts.

1 2

Annual cycle of SST Jan Apr Jul Oct

Annual cycle of SLP Jan Apr Jul Oct

LTM bi-monthly albedo Albedo ( nubosidad) 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 60-80% temp. freq. LTM bi-monthly albedo Albedo ( nubosidad)

Cloud field has significant spatial variability Cu SCu Sc

Cloud pattern related to MBL depth

Cloud pattern related to MBL depth

(674 hPa) (887 hPa) Full Topo Full: Continental monsoon + Hadley cell + Mountains Topo: Hadley cell + Mountains “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)

(Rodwell and Hoskins 2001)

 v Ideal monsoon heating @ 25°S-90°E + Continental drag + Newtonian cooling + Ideal. mountain (Rodwell and Hoskins 2001)

(674 hPa) (887 hPa) Mt.+SAM Mt.+SAM +SPac (Rodwell and Hoskins 2001)

Y. Wang et al. 2004 Cooling effect of the SCu deck over the SEP further enhance the subsidence and hence the southerly flow

Subsidence (adiab. Warming) + Equatorward flow (low SST) Large Scale Circulation set the stage: Subsidence (adiab. Warming) + Equatorward flow (low SST) = Temperature Inversion Enhanced equatorward flow v  fw/ z Enhanced LS subsidence to keep T/ t  0 Formation and maintenance of the SCu deck (moist air confined to the MBL) Net cooling at the top of the SCu (Radiative effect – condensational heating)

From K. Takahashi (2006)

SCu: Low level, shallow cloud layer at the top of the MBL

Net Cloud Radiative Forcing R = LW + SH, where  = clear -  average For SCu clouds: LW ~ 0 as Tc ~ SST SH < 0 (albedo effect) R < 0 : Cooling effect SEP SCu: -50 W/m2

Annual cycle of SCu an inter-regional differences largely explained by low level stability: 700- sfc (Klein and Hartmann 1993)

LTM annual mean SLP and surface wind speed (NCEP-NCAR Reanalysis)

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.

Surgencia: Afloramiento de aguas profundas (frías, ricas en O2 y nutrientes) por efecto del viento costera Surgencia ecuatorial

Simulated (MM5) structure of the coastal jet V U  w V > 18 m/s Garreaud and Muñoz 2005

Steady-state Dynamics

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.

SQ3. Coastal Jet under Clear Skies…Why? (+300 W/m2 reaching the surface)

SQ4. Impacts of Jet Events on SST Renault et al. 2006

Impacts of Jet Events on SST Wind, SST and SST anomalies Renault et al. 2006

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

Mean diurnal cycle at Antofagasta (Rutllant et al. 2003) - q - q

MM5 results

MM5 results W C W C W C Significant diurnal cycle in  up to 5 km ASL Subsidence interrupted by period of upward motion Cooling largely produced by vertical advection

Diurnal cycle of vertical velocity at 800 hPa MM5 results

Coastal Diurnal Cycle