Reflexes sobre a ZCAS e fontes de calor Pedro L. Silva Dias - - PowerPoint PPT Presentation

Reflexões sobre a ZCAS e fontes de calor

Pedro L. Silva Dias

Instituto de Astronomia, Geofísica e Ciências Atmosféricas/USP Laboratório Nacional de Computação Científica/ MCTI CPTEC - – Workshop ZCAS - Cachoeira Paulista – 20 a 22 de julho de 2015

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Natural hazards associated with the South Atlantic Convergence Zone during the South American Monsoon

ZCAS e fontes tropicais de calor:

• Qual é o impacto das fontes de calor diabáticas

na circulação?

• Qual é o controle exercido pela circulação no

disparo de fontes tropicais de calor?

.

• Subtropical Convergence Zones (STCZ) - KODAMA (1992)
• Quasi

Quasi-stationary stationary systems; systems;

• high

high pressure pressure to to the the east east; ;

• Associated

Associated to to subtropical subtropical jets jets;

• Associted

Associted to to upper upper level level troughs troughs:

• Moisture

Moisture convergence convergence at at lower lower levels levels;

• Well

Well defined defined air air masses masses (moisture moisture mainly mainly). ).

Precipitation Climatology

Marengo et al. 2010

SACZ

SACZ

SACZ

SACZ

January - low and upper level circulation - peak of the Monsoon Season

SACZ

Air Mass Tropical N. Atlantic Air Mass Higher latitudes S. Hemisphere Air Mass Tropical S. Atlantic

The South Atlantic Convergence Zone – SACZ -

Complexities of the SAMS: significant variability at different time scales

The Last Millenium in South America

LIA MCA

600 800 1000 1200 1400 1600 1800 2000

• 7.5
• 7.0
• 6.5
• 6.0
• 5.5
• 5.0
• 4.5
• 4.0

Wet Wet Dry



Years A.D

• 7.6
• 7.8
• 8.0
• 8.2
• 8.4



600 800 1000 1200 1400 1600 1800 2000

• 0.5
• 1.0
• 1.5
• 2.0
• 2.5
• 3.0
• 3.5
• 4.0



China NE Brasil SE Brasil

Dry Wet Cruz et al. 2011

Interesting point:

• Mud data in the Plata outflow => Picomyo and

Bermejo River - NW Argentina/Bolivia – summer rain

• Biased towards western part of the Plata
• Need marker for the eastern
• Different regimes E/W Plata Basin

Work in collaboration with IRD, INPE, USP, UFF,LNCC…

2010

Circulation patterns: LISAM and ZCAS (continental and oceanic modes)

Large Scale Index for South America Monsoon (LISAM) (Silva and Carvalho 2007)

SAMS is characterized by seasonal changes in:  Circulation anomalies Precipitation Moisture  Temperature LISAM index was designed to characterize the ONSET, DEMISE, DURATION, AMPLITUDE, BREAKS AND ACTIVE PHASES of SAMS based in all variables above.

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Structure of the variability modes (EOF’s) of the precipitation and temperature - Carvalho et al. 2010

Mode 1 - LISAM Mode 2 - SACZ continental monsoon Mostly oceanic

Rain Temp

Moisture and meridional wind Mode 1 - LISAM Mode 2 - SACZ Moisture

Wind

Time series of the monsoon (LISAM) and South Atlantic Convergence (ZCAS) modes.

Amplitude Duration

• 3
• 2
• 1

1 2 3

1 13 25 37 49 61

• 3
• 2
• 1

1 2 3

Northern Amazonia Rainfall Index (NAR) Southern Amazonia Rainfall Index (SAR)

A B Marengo 2004

Intraseasonal variabilty

Precipitation anomaly

Intraseasonal variations in SAMS

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Active phases of the Monsoon (Westerly regime):

• Intensification of convection
• ver Central Brazil and in the

SACZ region: westerly wind anomalies dominate

• shallow cloud tops and

stratiform precipitation dominate

• Less convection over Northern

Amazon and Southern Brazil, Paraguay and Argentina

• Low level jet east of the Andes

weakens

Intraseasonal variations in SAMS

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Break phases of the Monsoon (easterly Regime):

• Less convective systems over

Central Brazil

• Easterly wind anomalies

dominate over Tropical South America

• Deep convective clouds form

especially over Northern Amazon

• Low level jet intensifies east of

the Andes and transports moisture towards Southern Brazil, Argentina and Uruguay

Herdies et al. 2002

(shaded) Mean moisture flux and divergence in active and non active phases of the SACZ – 20-60 days.

Diurnal variability

From Santos 1986

Diurnal Variability

• 1. What is the role of the heat source in the regional tropospheric circulation:

local response, interaction with baroclinic basic state-> barotropic response.

• 2. What is the influence of the Andes ?
• 3. What are the remote impacts of the source?
• 4. What controls the slow evolution of the heat source?

Questions on the role of the Amazon/Central Brazil heat source during summer:

Bolivian High No major changes in the low level circulation

Question : Is latent heating associated to convective activity over the Amazon/Central Brazil able to generate an upper anticyclonic circulation similar to the Bolivian High?

JJA DJF Transform method based on Matsuno’s eigenfunctions - Rossby, Inertio-gravity, mixed Rossby-gravity and Kelvin waves: allows for energy decomposition in fast and slow modes JAS- nov. 1983

Rossby Kelvin Mixed Rossby- Gravity All modes 16hr 32hr 48hr 64hr From Silva Dias et al. 1983- JAS

JAS - Volume 43 Issue 18 (September 1986) Forced linear solutions: basic state with shear – Hough Mode interaction coefficients

Question: Does the baroclinic response to tropical forcing generates extratropical barotropic perturbations?

Linear response with U=0: Strictly baroclinic, tropically confined 870hPa 227hPa Linear response with vertical shear U(z): extratropical barotropic response

Numerical experiment with linearized version of the primitive equations linearized about a basic state U = U (y,p) in geostrophic balance with the T field.

Typical mean zonal wind profile for January

Heat source centered at the Equator

Question: What is the effect of the Andes in the latent heat forced circulation over tropical S. America during summer?

Figueroa et al. 1995 - JAS PE model in eta-coordinate forced by diurnally varying heat source

No Andes With Andes Initial basic state at rest

From Figueroa et al. 1995 - JAS 850 hPa

No Andes

With Andes

From Figueroa et al. 1995 - JAS 250Hpa

Partial Conclusions:

• Linear response to localized tropical heat source triggers

circulation response with a pronounced trough to the E/SE - elongated form;

• Vertical shear enhances the NW/SW elongated response
• Andes: help organizing low level response
• Slow dispersion due to Rossby wave contribution and

Mixed Rossby-Gravity wave -> long time response after a tropical convective burst;

• However, stationary of the SACZ in some cases exceeds

the expectation based on internal mode dispersion time. What could be the reason?

Role of heat source in changing time scale of atmospheric response

2013 – JAS

• ¶x*

¶t +U* ¶x* ¶x +UT ¶xT ¶x +b.v

* = 02

¶xT ¶t +U* ¶xT ¶x +UT ¶x* ¶x +b.v

T = f

Pw2

Impact heat source in a simple baroclinic instability problem

te = 1 k

• 2. 1+ q2

k2 æ è ç ö ø ÷ 4.UT

• 2. q4

k4 -1 æ è ç ö ø ÷- q4 k4 .cR

2

E-folding time for unstable perturbation Impact of heat source: decrease static stability!!!

• 2

P ¶jT ¶T

• 2

P U* ¶jT ¶T + 2 P

• UT. f.v

* +s 2w2 = -g w 2

Lower limit for the scale of unstable wave: Lower limit of vertical shear for unstable waves:

• Lc

UT decreases te decreases

• Along SACZ, possible to have small perturbations,
• baroclinicaly unstable at low f,
• due to decreased static stability (role of

convective heating)

• Fast growth
• Lower propagation speed due to static stability

Observations studies indicate connection between ZCPS and ZCAS. How about modeling evidences?

Question: What is the remote impact of a localized heat source in the

Amazon? Or, can we associate anomalous climatic conditions in remote areas to changes in the precipitation regime in the tropics (e.g, in the Amazon/Central Brazil)?

Grimm and Silva Dias (1995) - JAS Barotropic Vorticity Model linearized about zonally assymetric realistic basic state - stationary solution

’(,,t)=    GH(,,t,’,’,t’).H’(',’,t’) cos d’ d’ dt'

• Linear effects

compensated by the forcing and non-linear terms

• Inverse operator of

the linear term

• IF satisfies the

condition:

Influence Functions of the Shallow Water Model

JANUARY July Influence Function for a target point in SE Brazil - Grimm and Silva Dias (1995) JULY

Aplications of IFs

• ENSO impact in Brazil during spring/summer

FI January FI November

( Grimm 2003, Grimm et al. 2006)

remote influences versus local forcing ?

Conclusion – chicken and egg

• Localized heat sources in the tropical sector of S.America lead to

upper tropospheric circulation with Bolivian High and trough to the east

• Slow dispersion –> stationarity
• Heat source effect: reduces static stability
• even slower dispersion;
• Baroclinic instabilty possible at lower latitudes with smaller

scale, lower e-folding time and small vertical shear - typical conditions along SACZ

• Eddies along SACZ
• Upper trough associated with ZCAS has strong coupling to ZCPS

(i.e, remote influence)

• Needs major changes in the Pacific Ocean circulation in order to

break SACZ

Land cover Vegetation type and state Soil Type and Soil Moisture Large scale Dynamics and thermodynamics Aerosol type and concentration (radiative forcing) Topography Non linear Wave interactions Global Teleconnections Vertical Profile of Convective Heating Effect on Extended Range Forecasts Aerosol type and concentration (effect on microphysics) Diurnal Cycle of Convection

Obrigado

pldsdias@lncc.br

Conclusion

From Enver, Silva Dias and Raupp (2013 – in preparation)