Mean Structure and Variability Ren D. Gareaud Geophysics - - PowerPoint PPT Presentation

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Mean Structure and Variability Ren D. Gareaud Geophysics - - PowerPoint PPT Presentation

Nov 25, 2022 352 likes •793 views

Coastal winds over EBUS Mean Structure and Variability Ren D. Gareaud Geophysics Department, Universidad de Chile Center for Climate and Resilience Research Thanks to Jos Rutllant 1,2 , Ricardo Muoz 1 , David Rahn Outline Subtropical

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Coastal winds over EBUS Mean Structure and Variability

René D. Gareaud Geophysics Department, Universidad de Chile Center for Climate and Resilience Research

Thanks to José Rutllant1,2, Ricardo Muñoz1, David Rahn

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Outline

  • Subtropical anticyclones: Hadley + Mnts + Monsoons
  • Coastal jets (large-scale and local-scale mean structure)
  • Extra bonus….when upwelling is gone….
  • Coastal winds variability
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EBUS: Subtropical anticyclones, equatorward flow and cold SST

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General circulation in an aqua-planet

Perpetual Equinox

0° 45° NE trades SE trades ITCZ: Intertropical Convergence Zone

Surface wind (arrows) Precipitation (green shadow) But we want subtropical highs!

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SLIDE 5

0° 60°

General circulation in an aqua-planet

Perpetual Equinox

Jet stream (westerly flow) aloft (10-12 km): long term mean. Boundary between subtropical and extratropical air masses ITCZ Midlatitude precipitation maximum and westerly belt

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Zonal wind just upstream of the Andes (over the SE Pacific). Note that in winter the subtropical Jet (30ºS) impinges against the high Andes (not so much in summer).

Atmospheric flow – mountain interaction

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SLIDE 7

West East North

H = constant

South

5 km 12 km

Atmospheric flow – mountain interaction

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H = constant

Atmospheric flow – mountain interaction

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Austral winter: Mountain only run (no latent heating) is quite good in simulating the SEP anticyclone

w(700 hPa) Stream function at 900 hPa Full (heat+mnt)

  • Mnt. only

Anticyclone split Strong subsidence Rodwell and Hoskins 2001

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SLIDE 10

July 850 hPa winds CTRL NSAO CTRL NSAO

Atmospheric flow – mountain interaction

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Atmospheric flow – mountain interaction

Low cloud feedback Evaporative cooling

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Atmospheric flow – mountain interaction

Control noAndes

900 hPa wind & Temp Clouds: Control - noAndes

Warm air into MBL No Andes No clouds!

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Atmospheric flow – mountain interaction

No Andes No clouds!

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No Andes No clouds! Warm ocean…

SST and Sfc Wind: Control - No Andes Clouds & LTS Control - No Andes

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Zonal wind just upstream of the Andes (over the SE Pacific). Note that in winter the subtropical Jet (30ºS) impinges against the high Andes (not so much in summer).

Monsoonal (continental heating) influence

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w(700 hPa) Stream function at 900 hPa Full (heat+mnt)

  • Mnt. only

Subsidence in right place but only ¼ of the full value

Austral summer: Mountain only run not good in simulating the SEP anticyclone. Continental heating is essential.

Anticyclone split much weaker

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Efecto monsonal (Rodwell and Hoskins 2001)

  • Calentamiento diabático en zona de precipitación
  • Expansión del calentamiento por ondas de Kelvin/Rossby
  • Advección fría al Oeste del continente
  • Incremento de la subsidencia sobre Pacifico SE

Precipitation 200 hPa wind 500 hPa temperature 200 hPa wind Horizontal cold advection

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Efecto monsonal (Rodwell and Hoskins 2001)

200 hPa Hor Temp Adv SLP

Sobre el SEP el calentamiento diabático es levemente negativo por lo que advección horizontal fría es compensada por subsidencia (calentamiento adiabático). Notar qué lo contrario ocurre en el SACZ. Sobre la Amazonia el balance es entre ascenso y calentamiento diabatico.

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Subtropical Hig igh

SC SCu deck

SAM IT ITCZ

Key atmospheric features over the SEP

Coastal je jet Coastal Fog

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Zonal flow – Andes interaction Monsonal connection (austral summer only) Equatorward flow ↑ Low Trop. Stability Drying of MBL ↑ subsidence ↑ coastal upwelling ↑ Evaporative cooling ↑ Stratus clouds ↓Solar rad. at sfc ↑ MBL cooling ↓ SST (near shore and offshore) Oceanic transport

Svedrup balance

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Coastal Low Level Jets

NCEP-NCAR Reanalysis, 1000 hPa meridional (NS) winds, annual long term mean

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A A

Surface wind speed & coastal jets

Jet costero (máxima magnitud) a lo largo de la costa Variabilidad sinóptica y estacional dictada por (SLP) / y

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V

U  w

V

U  w

Along shore

V > 18 m/s

Simulated (MM5) structure of the coastal jet Cross shore

Garreaud & Muñoz 2006

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v u H d C fv x p y u v x u u t u  − +   =   +   +    1 v v H C fu y p y v v x v u t v

d

 − +   − =   +   +    1

2

1 v H C y p

d

=   − 

Garreaud & Muñoz 2006

Coastal jet dynamics

Along-shore pressure gradient  friction

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Goals of Fondecyt 1090492 (Garreaud, Muñoz, Rutllant)

Understand the alongshore structure of the MBL and its diurnal cycle

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Coastal jets intensify downstream of major capes. Upwelling maximum Cloud free

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QSCAT also reveals some meso-scale details and insights on the diurnal cycle

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Max Upwelling Min SST Expansion Fan?

SQ1-Climatological near-coastal wind maxima around 30°S:

Structure? Wind-SST feedback or expansion fan Effect?

  • Aircraft zonal coastal jet missions
  • Radiosonde from R/V
  • Modeling: control(?) + sens. runs

SST Front Coastal Jet Core: vp/y

74°W 72°W 70°W 30°S 28°S 32°S

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New Conceptual Model for Coastal Jet (30ºS)

Rahn & Garreaud 2012

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Synoptic variability during CUpEx: Local T(Ocean) & wind

R1 R2

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PGF

Synoptic variability during CUpEx

v v H C y p

d

 =   −

2

1 

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Synoptic variability during CUpEx: SSMI SST

High wind SST field [C] Low - High wind SST field [C]

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U,V elsewhere (vectors) WS elsewhere (contour) Cloud elsewhere (colors)

U,V elsewhere (vectors) V elsewhere (contour) SST elsewhere (colors) Jet events associated with: Stronger anticyclone / Reduced Sc near the coast / Increased Sc off the coast / Sea surface cooling at and downstream the jet 1-Point correlation map. V(33S/73W) regresed upon

Synoptic variability of Coastal winds

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Composite upwelling events in near Concepción (37ºS, Chile)

Relaxation begins Upwelling begins

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Composite upwelling events in near Concepción (37ºS, Chile)

Relaxation begins Upwelling begins

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(a) 200 hPa height and OLR anomalies (15-30 January 2017) (b) Rainfall deciles January 2017

Coastal El Niño 2017

3 weeks with very weak westerlies impinging the Andes Garreaud 2017

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NW Peru storms, 03 March 2017 GPM radar 17 dBZ isosurface

Source: Harold Pierce, NASA GSFC

>200 fallecidos, 3.1 Bill US$

Coastal El Niño 2017

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The March 2015 Atacama Storm. Three days of intense rainfall triggered landslides and widespread flooding. More than 80 causalities and major damage to public and private infrastructure. Most acute impact during the event but many problems (e.g. public health) in subsequent months.

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Niño 1-2 SST SST anomaly 23 March 2015

COL Track

Plausible suspect: marked, sudden SST warming off South America (EN 2015) Destabilize the atmosphere and provide extra moisture

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Numerical experiment using RegCM (forced by ERA)

In a sensitivity run the SST was keep equal to the field at March 10 (prior to the warming) thus causing a sfc BC cooler than the control run

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RegCM simulated precipitation

CTR Sens Sens-CTR Sens/CTR %

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CTR PW (contours) and SENS-CTR PW (colors)