APR CRM simulations of the development of convection – some sensitivities Jon Petch Richard Forbes Met Office Andy Brown ECMWF October 29 th 2003 GCSS/ARM Broomfield

APR Content Motivation  Results from an NWP limited area model Impacts of resolution, domain size and 2D/3D differences  Results from the GCSS shallow cumulus »ARM diurnal cycle case  Results from EUROCS »Weakly forced convection »Stronger forced convection  Preliminary results from LBA case Summary

APR Motivation NWP model now run at 12 and 1 km resolution  Event forecasts (Wimbledon etc…)  Flood prediction Sensitivities in NWP simulations  Resolution has been shown to impact timing of convection  Parametrizations also shown to impact timing of convection Timing/location of convection is key in flood prediction  Too late (too far down stream – wrong catchment area?)  Too soon (on upslope for orographic rain – definitely wrong catchment area)

APR Motivation Bridge the gap between LES/CRM and NWP models  Resolution impacts  2D/3D differences Benchmark simulations from LES and CRM  Parametrization/tuning for 1 and 12km simulations »Microphysics (e.g. impacts of rain advection or graupel) »Sub-grid condensation

APR NWP Model Experiments Impacts of rain advection on 1km NWP simulation

APR km 3D NWP model

APR and 12 km NWP model 2 km 12 km Vertical cross sections of w and ice over Wales Thanks to HumphreyLean (Met Office)

APR Bridging the gap between experiments LES resolution experiments  ARM/GSCC WG1: [10’s to 100’s m] high resolution simulations of the development of shallow cumulus CRM resolution experiments  EUROCS: [100’s to 1000 m] 2D and 3D CRM experiments of the diurnal cycle of deep precipitating convection  LBA: [100’s m] 2D and 3D CRM simulations of the development of convection High resolution NWP  1 to 12 km 3D simulations of weather events over U.K  LBA: 1 km case?

APR LES results The development of shallow cumulus

APR Results from shallow case – high resolution tests TKE Cloud liqud water path

APR Results from shallow case – high resolution tests Cloud fraction Cloud top

APR Results from shallow case – low resolution tests TKE Cloud liqud water path

APR Results from shallow case – low resolution tests Cloud fraction Cloud top

APR Shallow case summary Basic information  Cloud forms around 12 local time  Cloud fractions peak around 20% between 1 and 4pm Resolution study  100 m and less shows convergence  200 m not too bad  Worse than 200 m is poor or forms no cloud  Other models gave similar results at default 100 m (not shown) Domain and 2D/3D differences  2D not tested but had given strange results in BOMEX case  Domain was 6.4km x 6.4 km

APR Some questions (I don’t plan to answer all of them!) Can we begin to bridge the gap between this shallow case and deeper cases? Model related questions:  What is the impact of 250 m to 100m or higher horizontal resolution?  What is the impact of smaller domain?  What is impact of going from 2-D to 3-D

APR More questions Simulation related questions  What is the impact of large scale forcing?  What is impact of interactive radiation?  How important are the initial conditions?  How important are the surface fluxes? Points of interest  At what point does the shallow cumulus deepen?  How long does it stay shallow?  How long does it take to rain after it goes deeper?  How long does it take to reach upper troposphere?  Do interesting things occur at freezing level?

APR Deeper convection EUROCS – diurnal cycle of deeper convection

APR EUROCS simulations LES -> CRM Model  Met Office CRM/LEM (as used in shallow case)  120 vertical levels (15 km domain)  100m or higher vertical resolution  Forced with standard semi-idealised case Simulation  2D »250 m ensemble from 15 runs (250 km domain) »100 m (160 km domain)  3D (100x100 points) »100 m (10 km x 10 km) »250 m (25 km x 25 km)

APR Initial conditions

APR EUROCS surface fluxes cf. ARM Case 3

APR Impact of NSF on basic 2D runs: rain rate New Surface Fluxes

APR Rain rate and w max (NSF)

APR Cloud fraction and total hydrometeor (NSF)

APR Water vapour transport (NSF) 2D 3D

APR In-cloud liquid water (NSF)

APR Cloud fraction (NSF)

APR Double domain size

APR Increased moisture and rectangular domain

APR Increased moisture, bigger domain but lower resolution (1km)

APR Vertical water vapour transport 3D 250m (tot)3D 1km (tot) 3D 250m (res)3D 1km (res) (Res)

APR D (250km) 3D av (60km) 3D plan (60km)

APR D 2D

APR D 2D 9

APR km 5km 1.5km 2D

APR m v 250m cloud sizes

APR Poor representation of the formation of clouds in 1km simulations

APR Summary of EUROCS case CRM runs are very similar to shallow case  timing of initial cloud and peak; cloud fractions; LWP Shallow phase lasts for 2-3 hours but water contents are low 3D produces less deep cloud and rain than 2D at 250m and 100m resolution  no very large domain 3-D runs (50km x 50 km)  some sensitivity to domain size between 25 and 50 km 3D and 2D produce similar amounts of cloud and rain at 1km resolution  even with smaller domains (i.e. ones used at high res.)  much of the transport of water vapour is by sub grid processes right up to the time of significant precipitation

APR LBA LES->CRM->NWP Diurnal cycle again Early days yet! Some problems setting Up NWP model for this case

APR LBA Differences from EUROCS

APR LBA v EUROCS [SH and LH]

APR LBA runs

APR LBA runs

APR D 3D differences

APR LBA – comparison with NWP

APR Rain 5 hours CRM NWP 100 km

APR Final summary A range of simulations and model set ups are being used to improve convective development in high resolution NWP models:  Benchmark simulations »some experiments have resolved all important scales »which microphysical processes dominate? »impacts of sub-grid sensitivity Along the way:  Understand sensitivity to domain size, resolution and 2D/3D differences in LEM/CRM »2D still needed to allow many runs and very detailed microphysics and radiation