Jan 18, 2018
Cascade Scale interactions and organized convection in the
tropical atmosphere Project Manager: Steve Woolnough Outline
Motivation Cascade Project
Examples of scale interactions in organized tropical convection
Scientific and Technical Challenges Cascade Project The Science of
Cascade Project Structure Organization of tropical convection
Tropical convection is organized across a wide range of scales
associated with Individual cloud systems Squall lines and mesoscale
convective complexes African Easterly Waves, Tropical Cyclones,
Equatorial Waves Madden-Julian Oscillation, Monsoon circulations
Interactions between space and time scales of tropical
convection
Diurnal Cycle Seasonal Cycle Monsoons Modulates activity Upscale
organisation? MJO MJO Suppressed Phase? Mesoscale systems 10-100s
km Hours 100s km Days 1000s km Weeks Extended Predictability
(THORPEX) El Nino & Climate Change (WCRP) Monsoon Onset?
Trigger Synoptic waves Mean Climate over the Maritime
Continent
Precipitation over the Maritime Continent plays a dominant role in
driving the circulation over the Indo-Pacific Warm Pool Modelled
precipitation shows dry bias around the islands of the Maritime
Continent Large wet biases in Western Indian Ocean and West Pacific
Wet biases over the islands of the Maritime Continent CMAP HadGAM1
Difference From Jane Strachan (Walker Institute) Diurnal Cycle in
the Maritime Continent
1100LT 1700LT 2300LT 0500LT Observations from TRMM Strong diurnal
cycle inprecipitation Little or no precipitation over landduring
morning Precipitation develops over landin late afternoon and into
the lateevening Precipitation moves out overocean during early
hours of themorning Convection in the MaritimeContinent is
stronglyinfluenced by diurnal cycleand land-sea breezes From Jane
Strachan (Walker Institute) Diurnal Cycle of Precipitation in
HadGAM1
Maximum precipitation overland during morning Precipitation dies
out overland in late afternoon Little or no precipitation overseas
around MaritimeContinent Do weaknesses in therepresentation of key
physicalphenomena in the modelimpact the mean climate of theregion?
1230LT 1830LT 0030LT 0630LT From Jane Strachan (Walker Institute)
Organization of convection by equatorial waves
Observations (e.g. Wheeler and Kiladis 1999, Yang et al ) show
convection is organized by large-scale equatorial waves from
Wheeler and Kiladis (J. Atmos. Sci, 1999) Equatorial Waves in
HadGAM
Observed HadGAM1 By what processes are the convection and dynamics
coupled? How does the model represent these processes? Lin et al.
(J. Clim, 2006) (CGCMs)
MJO in Climate Models Lin et al. (J. Clim, 2006) (CGCMs) MJO
variance approaches observed value in only 2 of 14 models Ratio of
eastward to westward variance is too small, consistent with lack of
coherent eastward propagation Variance in 13 of 14 models not
associated with pronounced spectral peak. Multiscale Organization
in the MJO
Eastward propagating envelope of convection Short lived, westward
propagating systems within envelope With individual mesoscale cloud
systems embedded within them from Chen et al. (J. Atmos. Sci, 1996)
from Rickenbach & Rutledge (J. Atmos. Sci, 1998) Multiscale
Organization in the MJO
What role do the different scales of organization play in the
transports of heat, moisture and momentum by the convection? How
are these processes represented within conventional parametrization
schemes? Organized Convection in AEWs
Complex organization on synoptic and meso-scales Strong temporal
development linked to diurnal cycle Triggering of convection by
orography and convergence along cold pools 15Z 18Z Scientific &
Technical Challenges
How does convection organise itself across a range of time and
space scales? How are energy and momentum transferred? Why do
preferred structures emerge? How can these be represented in global
models? But we cannot answer these questions using observations -
so we must use models as pseudo field experiments. This requires
large domains and very high resolution so that the energy spectrum
is not compromised. Needs very significant computational resource,
only just becoming available. Cascade Project Natural Environmental
Research Council (NERC) Funded Consortium Project Walker Institute,
University of Reading National Centre for Atmospheric Science
University of Leeds University of East Anglia Met Office 3 year
project which started on 1st October 2007 Proposal Develop
modelling framework for large domain (100 longitude by 30latitude),
high resolution (1-2 km) simulations. Perform numerical case
studies of organised convection over West Africa and the
Indo-Pacific Warm Pool. Evaluate these simulations using advanced
satellite and in situ observations of cloud structures. Analyse the
simulations in terms of scale-dependent energy and momentum
budgets. Use idealised case studies to explore the links between
convection and equatorial wave modes. Bring this new understanding
into the development of new representations of tropical convection
for global weather and climate models. Project Structure WP1:
Development of Modelling Tools and Infrastructure WP2: Scale
interactions in African Weather Systems WP3: Organized Convection
over the Indian Ocean and West Pacific Warm Pool WP4: Model
Evaluation against Observations WP5: Synthesis of Results
Development of Modelling Tools and Infrastructure
Model Development (Met Office) Met Office Unified Model Build on
existing work in the Met Office to develop 1km resolution LAM for
use as forecasting tool and CRM research tool Includes options for
3D turbulence scheme 5 phase microphysics scheme Test small domain
case studies Modelling Infrastructure (Lois Steenman Clark, NCAS
CMS) Optimatization Scalability Performance of I/O Management of TB
of data Evidence of modelling capability:
Simulations of the diurnal cycle and land-sea breezes over the Tiwi
Islands in the Timor Sea Evidence of modelling capability:
Realistic physical-dynamical coupling in 1 km version of the
Unified Model Evidence of model skill:
Simulations of the diurnal cycle and land-sea breezes over the Tiwi
Islands in the Timor Sea Evidence of model skill: Good agreement
with radar observations Scale Interactions in African Weather
Systems
Diurnal Cycle of Convection (Tony Slingo, Walker Institute) What
mechanisms control the organization of convection by the diurnal
cycle over varying land surface conditions and forcing regimes
typical of North Africa? MCSs and AEWs (Doug Parker, U of Leeds)
What is the role of MCSs, particular those forced by the diurnal
cycle, in the dynamics of the regional and synoptic waves and
vortices over Africa? Organized Convection in the Indo-Pacific Warm
Pool
Scale Interactions in the MJO (Steve Woolnough, Walker Institute)
How do the vertical heating profiles and momentum transports
associated with convection influence the evolution of the MJO? The
diurnal cycle and the climate of the Maritime Continent (Adrian
Matthews, UEA) What role do the diurnal cycle and land-sea breezes
play in determining the mean climate of the Maritime Continent?
Organized Convection in the Warm Pool
Idealized Simulations of organized convection and equatorial waves
(Brian Hoskins, Mike Blackburn, Walker Institute) How is convection
organized by equatorial waves and how does it modify the structures
predicted by the dry theory? Case Study Methodology
Use the high resolution simulations as pseudo-observations to
investigate the energy and momentum budgets associated with
organized convection the interactions between the various scales of
organization Compare with low resolution simulations to identify
weaknesses and missing processes in convection parametrization
schemes Model Evaluation against Advanced Observations
(Robin Hogan, Walker Institute) Use geostationary Satellites to
evaluate temporal development of organized cloud clusters Use
CloudSat, CALIPSO, and surface ARM sites to evaluate vertical
structure of clouds Synthesis of Results (Met Office)
Review the results from a parametrization perspective including
role of organized convection Environmental influences on
organization Temporal evolution of convection Test new
parametrization ideas in low resolution simulations of case studies
Project Timeline Model Development, Porting and Optimization
Oct 07 Apr 08 09 10 11 Model Development, Porting and Optimization
African Case Studies Case Identification and Model Configuration
Diurnal Cycle AEW Warm Pool Case Studies MJO Maritime Continent
Equatorial Waves Model Evaluation against Observations Synthesis of
Results