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
Natural hazards associated with the South Atlantic Convergence Zone during the South American Monsoon 2
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). ).
Marengo et al. 2010 Precipitation Climatology
SACZ
SACZ
SACZ
SACZ
January - low and upper level circulation - peak of the Monsoon Season
The South Atlantic Convergence Zone – SACZ - Air Mass Tropical N. Atlantic Air Mass Tropical S. Atlantic Air Mass Higher SACZ latitudes S. Hemisphere
Complexities of the SAMS: significant variability at different time scales
The Last Millenium in South America MCA LIA -4.0 Wet -3.5 Dry -3.0 18 O FN1 Nordeste -2.5 -2.0 Wet -1.5 NE Brasil -1.0 -0.5 Wet 600 800 1000 1200 1400 1600 1800 2000 -8.4 -8.2 18 O China -8.0 -7.8 China -7.6 -4.0 Dry -4.5 -5.0 18 O Southern Brazil -5.5 -6.0 -6.5 SE Brasil -7.0 -7.5 600 800 1000 1200 1400 1600 1800 2000 Years A.D Cruz et al. 2011
Work in collaboration with IRD, INPE, USP, UFF,LNCC… 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
Circulation patterns: LISAM and ZCAS (continental and oceanic modes) 2010
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. 19
Mode 1 - LISAM Mode 2 - SACZ Rain Temp continental monsoon Mostly oceanic Structure of the variability modes ( EOF’s ) of the precipitation and temperature - Carvalho et al. 2010
Mode 1 - LISAM Mode 2 - SACZ Moisture Wind Moisture and meridional wind
Time series of the monsoon (LISAM) and South Atlantic Convergence (ZCAS) modes.
Amplitude Duration
3 Northern Amazonia Rainfall Index (NAR) A 2 1 0 1 13 25 37 49 61 -1 -2 -3 3 Southern Amazonia Rainfall Index (SAR) B 2 1 0 -1 -2 -3 Marengo 2004
Intraseasonal variabilty Precipitation anomaly
Intraseasonal variations in SAMS Active phases of the Monsoon (Westerly regime): Intensification of convection over 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 26
Intraseasonal variations in SAMS 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 27
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
Questions on the role of the Amazon/Central Brazil heat source during summer: 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?
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? JAS- nov. 1983 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
All modes 16hr 32hr 48hr 64hr Kelvin Mixed Rossby- Gravity Rossby From Silva Dias et al. 1983- JAS
Question: Does the baroclinic response to tropical forcing generates extratropical barotropic perturbations? Forced linear solutions: basic state with shear – Hough Mode interaction coefficients JAS - Volume 43 Issue 18 (September 1986)
Linear response with U=0: Strictly baroclinic, Linear response with vertical shear U(z): tropically confined extratropical barotropic response 870hPa 227hPa
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
Initial basic state at rest No Andes With Andes 850 hPa From Figueroa et al. 1995 - JAS
No Andes With Andes 250Hpa From Figueroa et al. 1995 - JAS
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
Impact heat source in a simple baroclinic instability problem ¶ x * ¶ x * ¶ x T ¶ t + U * ¶ x + U T ¶ x + b . v * = 0 2 ¶ x T ¶ x T ¶ x * T = f ¶ t + U * ¶ x + U T ¶ x + b . v P w 2 ¶ j T ¶ j T - 2 - 2 + 2 * + s 2 w 2 = - g w U * U T . f . v ¶ T ¶ T 2 P P P Impact of heat source: decrease static stability!!! � E-folding time for unstable perturbation Lower limit for the æ ö 2. 1 + q 2 scale of unstable ç ÷ è ø k 2 wave: t e = 1 æ ö k 2 . q 4 ÷- q 4 k 4 - 1 ç 2 4. U T k 4 . c R è ø Lower limit of vertical shear for unstable waves:
U T decreases t e decreases � � • Along SACZ, possible to have small perturbations, • baroclinicaly unstable at low f, L c • 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)? ’ ( , ,t)= G H ( , ,t, ’, ’,t’) . H’( ', ’,t’) cos d ’ d ’ dt' Grimm and Silva Dias (1995) - JAS Barotropic Vorticity Model linearized about zonally assymetric realistic basic state - stationary solution
Influence Functions of the Shallow Water Model • Linear effects compensated by the forcing and non-linear terms • Inverse operator of the linear term • IF satisfies the condition:
JANUARY July JULY Influence Function for a target point in SE Brazil - Grimm and Silva Dias (1995)
Aplications of IFs ENSO impact in Brazil during spring/summer FI January remote influences versus local forcing ? ( Grimm 2003, Grimm et al. 2006) FI November
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