characteristics maritime region: study origin …...characteristics of equatorial / tropical region...
TRANSCRIPT
Characteristics of Rainfall in the Continent‐Maritime Region: Study of the Origin of
Intense Rainfall & Drought
Didi Satiadi
National Institute of Aeronautics and Space
Global Earth Observation System of Systems (GEOSS) Asia‐Pacific SymposiumBali – Indonesia , March 10‐12, 2010
Characteristics of Equatorial / Tropical Region(Esp. the Continent‐Maritime)
• Maximum insolation: abundant heat & moisture.• Convergence zone coupled with convection driving global circulation.
• Small corriolis effect. Hydrostropic equilibrium (gravity vs buoyancy) dominated by wave (stable) & convection (unstable).
• Surplus energy, non‐adiabatic, non‐equilibrium, non‐linear dynamics.
• Intense convection, the world’s largest factory of cloud and rainfall.
• Additional complexities in the Continent‐Maritime: topography, hot‐spot, sea breeze.
Characteristics of Equatorial / Tropical Region
Maximum insolation Surplus energy Intense convection & cloud
Convergence coupled with convectiondriving global circulation
Maximum rainfall
Monsoon /Inter‐Tropical
Convergenze Zone (ITCZ)
El‐Nino Southern Oscillation (ENSO)
Indian Ocean Dipole Mode
(IODM)
Madden Jullian Oscillation (MJO)
Tropical Cyclone (TC) / Extra‐Tropics
forcings
Large Scale Interference
Constructive/Destructive interference of these could generate a large scale potential for intense rainfall / draught in the Continent‐Maritime Region
IODM
ENSO
MJO
Asian Monsoon TC
ITCZ
Australian Monsoon
Boundary Layer & Convective Inhibition
Convergence, front, vortex and other persistent system
Hotspots & Land‐Sea Breeze
Orographic lifting & Local Circulation
Local Scale Effects
The total resulting effect at any spatio‐temporal point will be a combination between large‐scale effects and local scale effects
Diurnal Evolution of Boundary Layer Structure
Local effects such as diurnal evolution of boundary layer structure is important in determining convective inhibition and initiation in the location
Intense convection due to inhibition
Ref. EOM-Train
White region. No inversion. Low CINH. CAPE directly converted into convection. Shalow cumulus.
Dark region. Inversion. High CINH. CAPE accumulatedand eventually released. Deep Convection.
Local effect such as convective inhibition (CINH) alows for the accumulation of instability (CAPE) leading to eruption of intense convection
SOC behaviour in rainfall• Self‐organized criticality (SOC) describes dynamical systems with a critical point as an
attractor. Their macroscopic behavior displays the spatial and/or temporal scale‐invariance characteristic of the critical point of a phase transition. SOC is typically observed in slowly‐driven non‐equilibrium systems with extended degrees of freedom and a high level of non‐linearity.
• It is known that rainfall shows an SOC behaviour similar to that of an earthquake or avalanche, so that rainfall is sometime called as “an earthquake in the sky”.
System Atmosphere Crust of Earth Granular Pile Energy Source Sun Convection Adding Grains
Energy Storage Vapor Tension Potential
Threshold Saturation Friction Friction
Relaxation Rain Event Earthquake Avalanches
Ref. http://www.cmth.ph.ic.ac.uk
Rainfall Earthquake
SOC Signature in CAPEKototabang Station
Time Series of CAPE during the first radiosonde campaign in April-May 2004 (A) and the second radiosonde campaign in Nov-Dec 2005 (B).
Frequency distribution of CAPE values on log-log scale axes (C).
A
B
SOC Signature
Atmospheric instability (CAPE) values tend to follow a simple power law, which is a signature of an SOC system. This means that atmospheric instability was accumulated in the atmosphere up to a critical value before converted into convective motion.
C
SOC Signature
SOC signature in rainfallKototabang Station
Time series of rain event size (mm) from ORG at Kototabang during 2002‐2006
Frequency distribution of rain event size on a log‐log scale axes.
Rain event at Kototabang Station tend to follow a simple power law, which is a signature of an SOC system.
SOC Signature in DroughtKototabang Station
Time Series of Rainfall
Time Series of Drought
Frequency Distribution of Rainfall
frequency Distribution of Drought
EAR WWND+ 2001‐2006 AVE
ORG RAIN 2002‐2006 AVE
BLR WWND‐ 1998‐2003 AVE
SDR WWND+ 2003‐2004 AVE
RDS‐CAPE 04/2004 & 11/2005 AVE
Long‐term average diurnal cycleKototabang Station
EARUpdrafthr. 2‐20km
BLRDowndrafthr. 0.7‐5km
SODARUpdrafthr. 0 – 700m
ORGRain rateSurface
RadiosondeCAPEColumn
2 x diurnal local time 00:00 – 24:00
Inter‐correlation among updraft, rainfall, & +DCAPE
Tropopause
Melting Layer
StableLayer
Average diurnal cycles of convective parametersKototabang Station
CAPE
CINH
LCL
LFC
LNB
LNB‐LCL LFC‐LCL
CAP
CLOUD BASE
CLOUD TOP
FREE CONVECTION
CLOUD DEPTH
INSTABILITY
INHIBITION
CAP STRENGTH
DIFFERENCE‐
Avalanche of updraft and rainfall correspond to small convective inhibition (CINH), which in turn correspond to the merging between LCL and LFC.
Convective triggering mechanism(based on observation)
LCL is going up (eg. due to boundary layer uprising), LFC is going down (eg. due to large scale destabilization). When LCL & LFC are merged, CINH become small enough, then convection, cloud formation and rainfall established.
Convective trigger function algorithm
+DCAPE
+DCINH
START
ADJUSTMENT
STOP
NO
NO
YES
YES
Handshaking
Large scale criteria
Local scale criteria
For convection to occur, two criteria must be satisfied: (1) DCAPE must be positive and (2) CINH must be small.
The first criteria is determined by large scale destabilization in the free atmosfer, and hence called “large scale criteria”.
The second criteria is determined by boundary layer evolution, and hence called “local scale criteria”.
Convective inhibition will allow for accumulation of large scale destabilization resulting in intense convection and rainfall.
LNB
LFC
LCL
CAPE
CINH
Local Scale Inhibition
Large Scale Destabilization
Large scale determine intensity
Local scale determine distribution
Role of large‐scale & local‐scale
Xie et. al. (2004) produced improved simulation results using a new triggering function based on large scale contribution of rate of change of CAPE.
Impact of a revised convective trigger mechanism
Ref: Journal of Geophysical Research, Vol. 109, D14102, 2004
Monthly average rainfall Jan‐Oct 2009Simulation (top) vs Observation (bottom)
CSIRO‐9 GCM Mark 25.2°x3.4°
TRMM 3A120.5°x0.5°
The continent‐maritime has not been well represented in the coarse GCM
Monthly average rainfall Jan‐Oct 2009LAM (top) vs TRMM (bottom)
TRMM 3A120.5°x0.5°
DARLAM nesting in GCMRes. 100 km
Simulated rainfall is generally under‐estimate compared to that of observation.
Monthly average rainfall Jan‐Oct 2009DARLAM Simulation
DCAPE > 0 J/kg
DCAPE > 70 J/kg
Increasing DCAPE treshold to 70 J/kg (from Zhang & McFarlane) produce spatial discontinuities in rainfall like those observed by TRMM
3 years of TRMM PR data (1998‐2000)
(Mori et al. 2004)
Diurnal Cycle of Convection over
Maritime Continent
Diurnal forcing by land and sea breezes continuously
triggers convection
Illustration of the Little Monsoon Effect in the Continent‐Maritime
Sea‐Breeze in the afternoon
Land‐Breeze in the evening
Land‐Sea contrast gives a double impact: increasing rainfall both over the land and over the ocean
The impact will be proportional to the length of the land‐sea interface.
Conclusions
• Intense rainfall & drought are inherent characteristic of the continent‐maritime region. According to SOC study, 80% of rainfall is delivered in only 20% of event. Therefore adaptation is required.
• Interaction between large‐scale and local‐scale effects in generating extreme event (rainfall & drought) play an important role and need to be further investigated through observation and modeling.
• High resolution observation and dynamical modeling is required to represent the continent‐maritime region, in order to better simulate land/sea‐breezes, which depend on the length of the land‐sea interface.
• There may be a need for a better representation of convection in numerical model allowing for accumulation of energy leading to intense release of the energy.
Thank You!