1 Challenges in Mesoscale Meteorology Suzanne Gray With thanks to Jeffrey Chagnon, Helen Dacre, Humphrey Lean, Ian Renfrew, Nigel Roberts, David Schultz September 2010

2  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 Outline

3 What is mesoscale meteorology? Definition by space- and time-scales Markowski and Richardson: Mesoscale meteorology in midlatitudes

4 What is mesoscale meteorology?  Mesoscale phenomena are strongly influenced by communication with the synoptic- and convective-scales A broader perspective Mesoscale bridge information

5  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 Outline

6 Over-riding themes  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. Multi-(time and space)-scale prediction

7 Over-riding themes  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)? Predicability and ensembles

8 Over-riding themes  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? Diagnostics ? Wokingham supercell storm (Browning and Ludlam, 1962)

9  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 Outline

10 Convective organisation and banding The large-scale as a constraint Water vapour and sferics (Roberts, 2000) CAPE>300 Jkg -1 (thick contour) and CIN>10 Jkg -1 (shaded) (Done et al., 2007)

© Crown copyright Met Office Storm-permitting Ensembles Nigel Roberts xxx 55mm 96mm

12 Convective organisation and banding 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? Challenges

13 Convective organisation and banding Banding Convective snowbands – observed reflectivity (Schumacher et al., 2010) Stacked slantwise circulations in an ana cold front – doppler radar (Browning et al, 2001)

14 Convective organisation and banding 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. Challenges

15 Convective organisation and banding Weak CAPE/strong shear regime Mean CAPE for August (Romero et al., 2007) High resolution (x=1km) MetUM simulation and structure of one PV dipole (Chagnon and Gray, 2009)

16 Convective organisation and banding Determination of the local dynamical consequences of horizontally tilted PV dipoles.  How do the circulations associated with the dipoles 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? Challenges z

17  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 Outline

18 Mesoscale structures in extratropical cyclones Types of structures I Browning 2005

19 Mesoscale structures in extratropical cyclones Types of structures II tropopause Cloud head top Slantwise ascent Upright convection Layers of max vertical wind shear Inertia-gravity waves High level convection

20 Mesoscale structures in extratropical cyclones Conceptual picture: Clark et al., (2005), Browning (2004) 0518 UTC Sting Jets

21 Mesoscale structures in extratropical cyclones 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? Challenges

22  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 Outline

23 Mesoscale weather phenomena Impact of climate change Polar low density distribution (Zahn and von Storch,2010)

24 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)

25 Mesoscale weather phenomena 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 large- scale 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. Challenges

26  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 Outline

27 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. Stuff that didn’t fit anywhere else

28 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) Conclusions

29 Challenges that are potentially Addressable within NCAS (-weather) Fundable Hence I’m concentrating on ‘big challenges’ that 1.Can only be properly addressed by a group of researchers with different types of expertise 2.Are primarily associated with the Atlantic-European region. Links exist with all other challenges discussed today (except possibly urban?). Scope

30 What is mesoscale meteorology? Orlanski (1975)  Meso-(2-20 km): thunderstorm convection, complex terrain flows, inertia gravity waves, clear air turbulence, urban effects.  Meso- ( km): sea breezes, lake effect snow storms, mountain effects, sting jets.  Meso- ( km):fronts, squall lines, mesoscale convective systems (MCS), tropical cyclones, polar lows. More phenomena

31 Mesoscale structures in extratropical cyclones Sting Jets Windstorm Anna Moist PV along trajectories Pressure (hPa) PVU

32 Mesoscale structures in extratropical cyclones DIAMET: PV fields showing diabatic influences on the upper-level trough (Chagnon, pers comm) Objectively identified fronts (Hewson and Titley, 2010).