Transcript ppt Presentation

Challenges in Mesoscale
Meteorology
Suzanne Gray
With thanks to Jeffrey Chagnon, Helen Dacre,
Humphrey Lean, Ian Renfrew, Nigel Roberts,
David Schultz
September 2010
www.met.reading.ac.uk/~sws98slg1
Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
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What is mesoscale meteorology?
Definition by space- and time-scales
Markowski and
Richardson:
Mesoscale
meteorology in
midlatitudes
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What is mesoscale meteorology?
A broader perspective
 Mesoscale phenomena are strongly influenced by
communication with the synoptic- and convective-scales
Mesoscale bridge
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Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
5
Over-riding themes
Multi-(time and space)-scale prediction
 From case studies to climatologies to future predictions:
 Case studies are usually of interesting or extreme
cases, what is typical?
 How do mesoscale weather features impact climate?
 How will mesoscale weather features change in the
future?
 From convective to synoptic scales:
 What are the benefits of convection-permitting
simulations for predicting mesoscale features?
 What is the upscale impact? Configurations that are
both convection-permitting and large-scale
accommodating are now practicable.
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Over-riding themes
Predicability and ensembles
 Predictability and ensembles: ensembles
are being run operationally at resolutions
capable of resolving mesoscale features.
 What is the spread-skill relationship for
mesoscale features?
 What is the impact of stochastic
parameterization schemes on the
prediction of mesoscale features – in
ensembles/deterministic forecasts
(upscale transfer of information)?
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Over-riding themes
Diagnostics
 What diagnostics/metrics should be used to evaluate
`convection-permitting and large-scale accommodating’
experiments? Diabatically generated PV, moist
exergetics, entropy production?
 Can we design a system of diagnostics to objectively
analyse mesoscale flows in weather systems?
?
Wokingham supercell storm
(Browning and Ludlam, 1962)
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Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
The large-scale as a constraint
Banding
The weak CAPE/strong shear regime
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
9
Convective organisation and banding
The large-scale as a constraint
CAPE>300 Jkg-1 (thick
contour) and CIN>10
Jkg-1 (shaded) (Done
et al., 2007)
Water vapour and sferics
(Roberts, 2000)
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Storm-permitting Ensembles
x
55mm
© Crown copyright
x
55mm
Met Office
x
96mm
Nigel Roberts
Convective organisation and banding
Challenges
• Determination of the scales and environments that have
predictability
 What leads to that predictability? Errors grow faster at
smaller scales.
 When is the finescale detail is controlled by the
envelope of mesoscale weather (e.g., more likely in
quasi-equilibrum situations?)?
 Analogous to the seasonal/decadal predictability
problem.
• Determination of the scales (and mechanisms) by which
the convective scale feeds back to the synoptic scale
 Over what scales do we need to predict convection
correctly to lead to the correct feedbacks
(momentum/heat) at the larger-scales?
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Convective organisation and banding
Banding
Stacked slantwise
circulations in an ana cold
front – doppler radar
(Browning et al, 2001)
Convective
snowbands –
observed
reflectivity
(Schumacher et
al. , 2010)
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Convective organisation and banding
Challenges
• Characterization of the complex interactions between
frontogenetically forced circulations, complex terrain,
inertial/convective/symmetric instabilities and
convectively generated gust fronts.
• Prediction of mesoscale banding: can models predict the
occurrence and structure of banding in certain
circumstances (e.g. when tied to larger-scale features
such as fronts – link to DIAMET)?
• Determination of the importance of banding for
quantitative precipitation forecasting (flooding)
• Diagnosis of instabilities – identification of instabilities
can be sensitive to methods of diagnosis.
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Convective organisation and banding
Weak CAPE/strong shear regime
Mean CAPE for August
(Romero et al., 2007)
High resolution (Dx=1km) MetUM
simulation and structure of one PV
dipole (Chagnon and Gray, 2009)
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Convective organisation and banding
Challenges
• Determination of the local dynamical consequences of
horizontally tilted PV dipoles.
 How do the circulations
associated with the dipoles
z
interact?
• Determination of the larger-scale dynamical
consequences of horizontally tilted PV dipoles.
 Is there a momentum flux on the larger-scale?
 Is the storm-integrated PV structure correctly
represented by convection-parameterizing simulations?
 Can mesoscale convective systems be properly
represented in convection-parameterizing simulations?
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Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
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Mesoscale structures in extratropical cyclones
Types of structures I
Browning 2005
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Mesoscale structures in extratropical cyclones
Types of structures II
Inertia-gravity waves
Cloud head top
tropopause
High level
convection
Layers of max
vertical wind
shear
Slantwise ascent
Upright convection
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Mesoscale structures in extratropical cyclones
0518 UTC
Sting Jets
Conceptual picture: Clark et al., (2005), Browning (2004)
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Mesoscale structures in extratropical cyclones
Challenges
• Determination of the predictability of such features in
high resolution operational NWP models.
 Can we predict them? Does it matter?
 What is their relationship with `extreme weather’:
clear air turbulence, quantitative precipitation
forecasting (flooding), localised strong surface wind
gusts
• Determination of their impact on the synoptic scales, e.g.
the modification of upper-level trough structure from
diabatically (or frictionally?) generated PV and impact on
downstream development.
• Determination of their climatological importance and
sensitivity to climate change, e.g. how will the frequency
of sting jet storms change in the future?
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Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
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Mesoscale weather phenomena
Impact of climate change
Polar low
density
distribution
(Zahn and von
Storch ,2010)
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Mesoscale weather phenomena
Oceanic pathways to impact
Turbulent heat fluxes in ERA-40 without
and with a parameterized westerly tip jet
(Sproson et al. ,2010)
Observed cloud vortices and % of
these vortices detectable in ERA-40
(Condron et al., 2008)
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Mesoscale weather phenomena
Challenges
• Improving weather forecasts of e.g. polar lows,
medicanes, tropical cyclones and the extratropical
transition of tropical cyclones
 Many recent observations/modelling studies of
mesoscale arctic features (IPY-THORPEX) and tropical
cyclones and their extratropical transitions (T-PARC)
Case study based.
 What benefit do convection-permitting (but largescale accommodating) simulations provide?
• Determining the climate impact of unresolved mesoscale
weather features such as polar lows.
• Predicting the impacts of climate change on frequency,
tracks and intensity.
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Outline
 What is mesoscale meteorology?
 Over-riding themes
 Specific research areas
 Convective organisation and banding
 Mesoscale structures in extratropical cyclones
 Mesoscale weather systems
 Stuff that didn’t fit anywhere else.
 Conclusions
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Stuff that didn’t fit anywhere else
• Coupling at high resolution: current Met Office work on
coupling the high resolution atmospheric model to ocean
and hydrological models (e.g. freshwater discharges from
rivers affect SSTs in shelf seas which could impact the
atmosphere, lake models...).
• Dynamics of sea breezes: effects of complex coastlines,
near shore islands, synoptic wind directions etc. on sea
breeze structure, interaction with cumulus convection.
• Organisation of convection by orography.
• Effects of cloud-radiation interaction – known to affect
MCSs, contributing to their diurnal cycle.
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Conclusions
I’ve emphasized
 Upscale impacts and downscale controls on predictability.
 The progression from case studies to climatologies and
the change in climatologies with climate.
 New diagnostic methods for examining mesoscale
phenomena.
 New forecast methods: ensembles, downscaling.
“Understanding the connection between the cloud-scale
and the synoptic-scale is a prerequisite to understanding
the relationship between weather and climate” (Jeffrey
Chagnon)
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