Moist dynamics of tropical convection zones in monsoons...
Transcript of Moist dynamics of tropical convection zones in monsoons...
Moist dynamics of tropical convection zones inMoist dynamics of tropical convection zones in monsoons, monsoons, teleconnectionsteleconnections and global warming and global warming
• Leveraging a theoretical framework from convective quasi-equilibrium, moist static energy budget, + ….
• Monsoon aspect: what limits seasonal movement of deepconvection zones over continents?
• Tropical regional precipitation anomalies associated withchanges in deep convection zones: including droughtregions in both El Niño & global warming cases.Mechanisms? Similarities?
J. David Neelin*J. David Neelin*
*Dept. of Atmospheric Sciences & Inst. of Geophysics and Planetary Physics, U.C.L.A.
Collaborators: Collaborators: ChiaChia Chou**, Chou**, Hui Hui Su*, Katrina Hales*, Chris Holloway*Su*, Katrina Hales*, Chris Holloway*
**Inst. of Earth Sciences, Academia Sinica, Taiwan
Temperature Temperature TT and Moisture and Moisture qq equations equations
Quasi-equilibrium schemesQuasi-equilibrium schemes
Posit that bulk effects of convection tend to establish statisticalequilibrium among buoyancy-related fieldsApproach here depends on convection tending to constrainvertical structure of temperature field.For now: Smoothly posed convective adjustment
Convective heating: (Betts 1986; Betts & Miller 1986)Qc = (Tc - T)/τc
τc time scale of convective adjustmentTc convective profile; may interact with hbhb atm boundary layer (ABL) moist static energyTc typically moist adiabat or closely relatedCan be expanded about a reference state, Tr
c
Tc = Trc (p) + A(p) T1
c + higher order
A(p) vertical dependence of the moist adiabat perturbation T1
c incl. ABL adjustment by downdrafts to satisfy energy constraint Tends to reduce CAPE (convective available potential energy)
Manabe et al 1965; Arakawa & Schubert 1974; Moorthi & Suarez 1992; Randall & Pan 1993; …
Vertical structure of temperature variationsVertical structure of temperature variations
• Regressions of Temp. on 850-200 hPa Ave. Temp. (squares)• Same for reversible moist adiabats over similar range (grey)
Courtesy, C. Holloway
Daily, COARE Domain Monthly, tropical avg.
Rawinsonde (4 mon) NCEP (2 yr) NCEP (24 yr)
See also, e.g., Xu and Emanuel 1989; Fu et al 1994; Brown and Bretherton 1997; Sobel et al 2004
[Ciesielski et al (2003) data]
QE analyticQE analyticAnalytical solution under quasi-equilibriumAnalytical solution under quasi-equilibriumconvective constraintsconvective constraints
If T constrained to be close to QE temp Tc
baroclinic pressure gradients have strongly constrainedvertical structure
Primitive equations, momentum + hydrostatic:
( ) cc
r
cTpATTT1
+!!
( ) ! "+"#=$++%op
p
omt pTdvfvD &' lnk
( ) o
c
p
p
TpdpAo
!" #+#$% & 1ln
Analytic solution in deep convective regions (cont.)Analytic solution in deep convective regions (cont.)
Vertical structure of baroclinic pressure gradients⇒ structure of baroclinic wind V1. With barotropiccomponent ⇒ v = vo(x,y,p,t) + V1(p)v1(x,y,t)
Continuity eqn. ⇒ ω = Ω1(p) ∇·v1
The moist static energy eqn. becomes
(∂t + D)(T + q) + M∇·v1 = Fnet
where M is the gross moist stability M = 〈Ω∂ph〉
NB: Have not yet used convective closure on moisture.
^ ^
Neelin 1997; Yu et al 1998; Neelin and Zeng 2000
Moist convection interacting with large-scale dynamicsMoist convection interacting with large-scale dynamics
•• Convective Quasi- Convective Quasi- Equilibrium: Equilibrium: Fast convective motions reduce Convective Available Potential Energy (CAPE) Constrains temperature through deep column Baroclinic pressure gradients
•• Gross moist stability Gross moist stability at large scales at large scales
Refs: Arakawa & Schubert 1974;Emanuel et al 1994; Neelin & Yu 1994;Brown & Bretherton 1997; Neelin & Zeng2000
GalerkinGalerkin expansion expansion
Have approx. analytic solution for convective regions:Extend to full nonlinearity, non-convective regions,…Use analytic solutions for leading basis functions inGalerkin expansion in vertical
•Horizontal gradients of T matter; specify reference stateTr(p) to improve accuracy.•Simplest case: 1 basis function in T, q
Extra basis function for external mode ⇒ 2 in v
,),,()()(1
!=
++=K
k
Rkkr TtyxTpapTT
Neelin and Zeng (2000)
Quasi-equilibrium Tropical circulation model:Quasi-equilibrium Tropical circulation model:
• Primitive equations projected onto vertical basis functions fromconvective quasi-equilibrium analytical solutions
• for Betts-Miller (1986) convective scheme, accurate verticalstructure in deep convective regions for low vertical resolution
• GCM-like parameters but easier to analyzeRadiation/cloud parameterization:Radiation/cloud parameterization:• Longwave and shortwave schemes simplified from GCM
schemes (Harshvardhan et al. 1987, Fu and Liou 1993)• deep convective cloud, CsCc fraction param. on precipSimple land model:Simple land model:• 1 soil moisture layer; evapotranspiration with stomatal/root
resistance dep. on surface type (e.g., forest, desert, grassland)• low heat capacity; Darnell et al 1992 albedo
• http://www.atmos.ucla.edu/~csi/QTCM
• Seasonal movement of deep convection zones over continentsdeep convection zones over continents• Dynamical mechanisms mediating land-ocean contrast?• Given the large insolation extending poleward over continents, why
do deep convection zones not extend farther poleward?• Do mechanisms affecting convection zones differ from continent to
continent?• QTCM coupled to a mixed-layer ocean and simple land model• Focus on dynamical aspects, less on surface type• No-topography case emphasizes ocean-land contrast
Dynamics of summer monsoon convective zonesDynamics of summer monsoon convective zones
Wind-based vs. Wind-based vs. precipprecip. regime-based monsoon definitions. regime-based monsoon definitions
Freq. of surface wind direction; Khromov (1957); from Ramage (1971)
Pronounced summer precip maximum; sfc low; upper level high andoutflow, … (e.g., Tang and Reiter 1984; Barlow et al 1998; Higgins et al 1998;Zhou and Lau 1998; Yu and Wallace 2000; …)
i.e., characteristics of seasonal arrival of deep convection zone
Seasonal precipitation minus Annual AverageSeasonal precipitation minus Annual Average
DJF ave. – Annual ave.
JJA ave. – Annual ave.
mm/day
Latitude-height cross section at 90E from Bay of BengalLatitude-height cross section at 90E from Bay of Bengalacross Tibetan Plateau across Tibetan Plateau (shaded regions are rising motion)(shaded regions are rising motion)
From Yanai et al. (1992)
precFnet Observed climatology JanuaryObserved climatology January
Net Flux into theatmosphere
Precipitation
precFnet Observed climatology JulyObserved climatology July
Net Flux into theatmosphere
Precipitation
Precipitation Net flux into atmosphere
Low-level wind Upper-level wind
QTCM climatology JulyQTCM climatology July(coupled to a mixed-layer ocean)(coupled to a mixed-layer ocean)
QTCM1V2.2
Precipitation Net flux into atmosphere
Low-level wind Upper-level wind
4panel Observed climatology JulyObserved climatology July
Ventilation and the Ventilation and the ““interactiveinteractiveRodwell-HoskinsRodwell-Hoskins”” mechanism mechanism
Chou, Neelin and Su 2001
The The ““ventilation mechanismventilation mechanism””
• import of low moist static energy air from oceanwhere heat storage opposes summer warming
• oceanic air: cooler and moisture is lower thanconvection threshold over warm continent
• import to continents by wind (including upperlevel jets) via advection terms in temperature andmoisture equations
Chou, Neelin and Su 2001
The The ““interactiveinteractive Rodwell Rodwell-Hoskins mechanism-Hoskins mechanism””
• Rodwell and Hoskins (1996): imposed convectiveheating in Asia gives Rossby wave descent pattern towest, enhancing deserts.
• when convection is interactive: associated flow feedsback on heating, creating characteristicconvection/dry region pattern» we emphasize feedback
(convection ⇔ baroclinic Rossby wave dynamics),hence:
» “interactive Rodwell-Hoskins” (IRH) mechanism
Chou, Neelin and Su 2001
ControlSaturated soil moisture over
South American region
No ventilation: v•∇q, v•∇T set tozero over South American region
No ventilation and no β-effect:f = constant in South American
region (9S-56S - 70W-20W)
South American region case (observed albedo) JanSouth American region case (observed albedo) JanPrecipitationPrecipitation
Chou and Neelin 2001
Refinement of experimental designRefinement of experimental design
• Irrotational (purely divergent) wind component vχ• Non-divergent wind component vψ “No ventilation” = suppress vψ •∇T, vψ •∇q Retains conservation property:
Domain
(vχ •∇q + q ∇ • v)dA = 0since ∇ • vψ= 0
∫
1. Consistent treatment of vχ :
Asian region case Asian region case –– July July (1) V2.3b
Control Saturated soil moisture
No ventilation: v•∇q, v•∇T set to zero No β-effect: f = constant
PrecipitationPrecipitationAsian region case Asian region case –– July July (1) V2.3b
Chou and Neelin 2003QTCM v2.3
Saturated soil moisture
North American region case North American region case 1 V2.3b
Control
No ventilation: v•∇q, v•∇T set to zero No β-effect: f = constant in region
July PrecipitationJuly Precipitation
Chou and Neelin 2003
North American region case North American region case 3 V2.3b
No T ventilation No q ventilation
July PrecipitationJuly Precipitation
Chou and Neelin 2003
Control No ventilation: v•∇q, v•∇T set to zero
Saturated soil moisture
No ventilation: v•∇q, v•∇T set to zero No ventilation and no β-effect:
African region case (observed African region case (observed albedoalbedo) July ) July V2.3b
ControlPrecipitationPrecipitation
Chou and Neelin 2003(red contour: albedo = 0.3)
Saturated soil moisture
No ventilation: v•∇q, v•∇T set to zero No ventilation and no β-effect:
African region constant African region constant albedoalbedo case ( case (0.26 over Africa0.26 over Africa) July ) July V2.3b
ControlPrecipitationPrecipitation
Chou and Neelin 2003
Mechanisms affecting convective zones (S. American case)Mechanisms affecting convective zones (S. American case)
Ocean heat transportout of the tropics
Ventilation and theinteractive
Rodwell-Hoskins mechanism
African northern summer monsoon climatologyAfrican northern summer monsoon climatology
• Albedo is leadingeffect on polewardextent of convection
• Dynamicalmechanisms: affect margin ofconvective zone take over if albedogradient is flattened
African monsoon & mid-Holocene (6kaBP) green SaharaAfrican monsoon & mid-Holocene (6kaBP) green Sahara
• Paleo Model Intercomp Proj (PMIP): orbital parameterchange => small monsoon boundary shift (Joussaume et al1999) rel to pollen data (Jolly et al 1998; Prentice & Webb 1998)
• LMD and ECHAM GCMs with same interactive veg modelyield different results (DeNoblet et al 2000)
• QTCM expts with grass-like albedo over Sahara (Su et al, inprep) & interactive vegetation (Hales et al, in prep)
• Ventilation opposes rise of moisture; may not increaseenough to reach increase in trop temp.
• Reduced ventilation expts: e.g. reduce advection affecting qanomalies rel. to control; or reduce ventilation in control and6kaBP cases
African mid-Holocene 6kabp monsoonAfrican mid-Holocene 6kabp monsoonSchematic of QTCM - Schematic of QTCM - SVeg exptsSVeg expts..
• Tropical regional precipitation anomaliesassociated with changes in deep convection zones:including drought regions in both El Niño &global warming cases. Mechanisms? Similarities?
Mechanisms for regional precipitation anomalies inMechanisms for regional precipitation anomalies inteleconnectionsteleconnections and and
global warmingglobal warming
www.atmos.ucla.edu/~csi
Observed anomalies during July-Nov 1997Observed anomalies during July-Nov 1997
Precipitation(mm/day)
TroposphericTemperature
Neelin et al 2003; Neelin and Su 2004 subm
QTCM anomalies forced by Pacific positive SSTQTCM anomalies forced by Pacific positive SSTanomalies July-Nov 1997anomalies July-Nov 1997
TroposphericTemperature
Precipitation(mm/day)
QTCM POSPAC-FluxesQTCM POSPAC-Fluxes
Surface temperature
Net surface flux
Net flux intoatmospheric column
QTCM July-Nov 1997: Anomaly budget contributionsQTCM July-Nov 1997: Anomaly budget contributions11
Moistureconvergence
Mq∇·v(by divergent flow)
Moist staticenergy
divergence*
M ∇·v
* Gross moist stability M=Ms–Mq is an effective stability that includes partial cancellation of adiabatic cooling by diabatic heating
QTCM July-Nov 1997: Anomaly budget contributionsQTCM July-Nov 1997: Anomaly budget contributions22
Radiative coolinganom. (top of
atmosphere) dueto temp. anom.
Mean windadvection of
moisture anomalyv·∇q'
ENSO ENSO teleconnectionsteleconnections to regional to regional precipprecip. anomalies. anomalies
Su & Neelin, 2002
ENSO ENSO teleconnectionsteleconnections to regional to regional precipprecip. anomalies. anomalies
• a small zoo of mechanisms with moist convective and cloudradiative feedbacks
Zeng & Neelin 1999; Giannini et al 2001; Su et al 2001; Bretherton & Sobel 2002;Chiang and Sobel 2002; Chiang et al 2002; Su and Neelin 2002; Neelin et al 2003;Neelin and Su 2004 subm…
The The ““upped-anteupped-ante”” mechanism mechanism22
Margin ofconvective zonewith v inward
from dry region
Neelin, Chou & Su, 2003
QTCM experiments suppressing upped-ante mechanismQTCM experiments suppressing upped-ante mechanism
Control
(v · ∇q)'
T' contribution toCAPE
Anomaly ( )' termsuppressed in region:
Precipitation Anomalies
Other mechanismsOther mechanisms
• MMoist SStatic EEnergy transport by divergent flow ≈ M ∇·v• GGross MMoist SStability MM = MMss- MMqq, (Mq inc. with moisture)
Perturbation MSEMSE budget + ocean mixed layer / landocean mixed layer / landM ∇·v' = –M' ∇·v – (v·∇q)' – cc∂∂ttTT '' + F net' + (v·∇T)' …
Yields precip anoms as T' ⇒ q' ⇒ ∇q' , M' ; v' , q' ⇒ E' etc.
P' ≈ –(v·∇q)' + ∇·v(–M' ) – cc∂∂ttTT '' + …
tops
GMSGMS multiplier effect
MqM [ ]
Upped-ante
SST disequilibrium
Anomalous GMS Rad cooling, (v·∇T)' ocean transp, …
ss
Mixed layer ocean in Atlantic: 1Mixed layer ocean in Atlantic: 1stst year year vsvs equilibrium equilibrium
•Long termequilibrium withEl Nino SST anomartificiallysustained
•Positive 1997 ElNino Jul.-Nov.SST anom inPacific: tropicalAtlantic 50m MLSST is adjusting
Precipitationanomalies
(anomalies relative to climatology of ML Atlantic, clim. SST elsewhere)
Global Warming case: GCM Global Warming case: GCM PrecipPrecip. . AnomAnom..
DJF precip. anom.Three GCM
Greenhouse gasscenarios for
2070-2090rel. to 1961-1990 clim
QTCM doubled COQTCM doubled CO22 experiments experimentsQfluxQflux mixed-layer ocean mixed-layer ocean
Dec - FebPrecip change
Dec - FebQTCM Precip
climatology
Neelin et al 2003; Chou & Neelin 2004
Mq' ∇·v
Anomalous moistureconvergence due to
moisture anom. q'
QTCM doubled COQTCM doubled CO22 experiments experimentsMoisture budget contributionsMoisture budget contributions 11
(v·∇q)'
Anomalous moistureadvection
QTCM doubled COQTCM doubled CO22 experiments experimentsMoisture budget contributionsMoisture budget contributions 22
Mq ∇·v'
Anomalous moistureconvergence due to
anomalous divergence(GMS multiplier effect
feedback )
The The ““upped-anteupped-ante”” mechanism mechanism11
Margin ofconvective zonewith v inward
from dry region
Neelin, Chou & Su, 2003
QTCM 2xCOQTCM 2xCO22 ExptExpt. suppressing change in moisture. suppressing change in moistureadvectionadvection
Experiment2xCO2 Precip. change
(mm/day)
Control2xCO2 Precip. change
(testing the upped-ante mechanism)
Response to imposed T change in CAPEResponse to imposed T change in CAPE
• T' =1.5 C added to temperature only inside convection scheme• Mimicks 2xCO2 moisture and regional precip response• DJF Precip (W/m2), surface temp, moisture (K), tropospheric mean temp
Anomalous Gross Moist Stability (MAnomalous Gross Moist Stability (M'') mechanism) mechanism
•• MMoist SStatic EEnergy transport by divergent flow ≈ M ∇·v• M = Ms- Mq
• M ∇·v' + M' ∇·v = F'net - (v·∇q)' + …
• P' ≈ ∇·v(-M')
• Mechanism increases convergence & precip. in strongconvergence zones: “rich-get-richer”
may partially compensate if cloud top risesincreases with increasing moisture, tends to reduce M
reducedincreases to compensate
MMq
QTCM 2xCOQTCM 2xCO22 ExptExpt. suppressing change in gross moist. suppressing change in gross moiststability, Mstability, M
Experiment2xCO2 Precip. change
(mm/day)
Control2xCO2 Precip. change
(testing the M' mechanism)
Summary: Regional Summary: Regional precipprecip. . TeleconnTeleconn./global warming./global warming• tropical regional precipitation anomalies in ENSO teleconnection
case ⇒ a handful of contributing mechanisms• 2XCO2 case, mixed-layer ocean case ⇒ set of mechanisms with
some cross-over to ENSO case• the "upped-ante mechanism": substantial negative precip. anomaly regions in both cases drought occurs at margins of convection zones with climatologicalwind inflow from dry zone into convection zone
• the "anomalous gross moist stability (M') mechanism": contributes positive precipitation changes in strong precipitationregions in global warming case (but theory for M' very poor)
• Surface heat fluxes & SST′ important only when SST is indisequilibrium (∂t SST or ocean transport anom.)
Regional Regional precipprecip. . anomanom. relation to monsoon case. relation to monsoon case
• role of QE mediation: moisture rel to T of free troposphere vsimported q
• Fnet: favorable but not sufficient in monsoon; small in land anoms ocean heat storage & transport ⇒ ocean land contrast in monsoon,contrib. some Atl. negative precip. anoms. in ENSO case
• vψ •∇(q, T) terms: strong impact on precip/precip anomalies dueto role in moist static energy budget partial cancellation of adiab. cooling & diab. heating ⇒ small MMq/M large ⇒ GMS multiplier effect oppose precip in parts of trop convg zones & limit poleward extent role in upped-ante mechanism; involves QE to not QE transition
Last SlideLast Slide
• Title page
• ENSO teleconnections section
• Global warming case
• End show
Neelin 1997
Model Summary Model Summary –– QTCM equations QTCM equations
∂tv1 + DV1(v0,v1) + fk x v1 = -κ∇T1 - stress
∂tv0= … (barotropic component)
a1(∂t + DT1)T1 + MS1∇·v1 = 〈Qc〉 + Rad + H
b1(∂t + Dq1)q1 + Mq1∇·v1 = 〈Qq〉 + E
Moisture sink and convective heating
−〈Qq〉 = 〈Qc〉 = εc(q1 – T1)
^
^
Zeng, Neelin and Chou 2000 QTCM1 V2.0 clrad1
ENSO Composite (DJF)ENSO Composite (DJF)
QTCM climatology JanuaryQTCM climatology January(coupled to a mixed-layer ocean)(coupled to a mixed-layer ocean)
Precipitation Net flux into atmosphere
Low-level wind Upper-level wind
QTCM1V2.2
4panel Observed climatology JanuaryObserved climatology January
Precipitation Net flux into atmosphere
Low-level wind Upper-level wind
QTCM experiments suppressing various mechanismsQTCM experiments suppressing various mechanisms
T' radiative effects
(v · ∇T)'
(surface stress)'
Precipitation AnomaliesAnomaly ( )' term
suppressed in region: