Numerical investigation of the multi-scale processes inducing convection initiation

for the 12 June 2002 IHOP case study

Preliminary study: testing the sensitivity of the model to simulate this CI case.

Sophie Bastin, Tammy Weckwerth, Fei Chen, Kevin Manning

NCAR

Acknowledgements: M. Weisman, S. Trier, M. Pagowsky, D. Posselt, D. Birkenheuer, and others (mesouser, …)

Motivations Better understanding of the influence of the processes at different

scales on the location and timing of convection

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50 km

101 100o 99 98

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37o

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Why did CI occur here?

Numerical simulations Control simulation

MM5 model version 3.71 domain, 4-km horizontal resolution44 vertical levels, about 20 half-sigma levels within the boundary layer Initialization at 12Z on June 12 (cold start), from NCEP Eta analyses (40 km resolution) Objective analysis and observations nudging (it’s not a forecast)Eta PBL parameterization, no cumulus scheme, Reisner2 microphysics scheme, Noah LSM

Sensitivity tests:Domain(s) sizeInitialization: time, 3D fields (NCEP ETA, RUC, LAPS, ECMWF), soil moisture and temperature fields (HRLDAS)Parameterizations: PBL processes, microphysics scheme, cumulus scheme

Control simulation (1)

Surface wind at 21 UTC (= initial time + 9h)

OK mesonet data

simulation

Control simulation (2)

Surface temperature at 21 UTC

OK mesonet data simulation

Control simulation (3)

Relative humidity at 21 UTC

OK mesonet data simulation

CONTROL simulation (4)

19 UTC

20 UTC

21 UTC

22 UTC

Column-integrated cloud water

Sensitivity study (1)

YES NO

3D initial conditions X (underway)

HRLDAS (surface conditions)

light

Domains X

Initial time X

PBL parameterization

X

Microphysics scheme

X

Convective scheme (with or without)

X

Sensitivity study (2)

CONTROL 2 domains Cold start at 00 UTC

dryline Good Good ~ good

Outflow boundary

Too weak Good (too strong?)

No

mesolow Good Too weak Larger scale circulation

Surface moisture values

Good Good around the dryline

~ good

Surface temperature

values

Good (except gradient at the outflow boun.)

same as CONTROL

~ good

CI along the dryline

Good but no CI at triple point

Too late Too early

Sensitivity to domainsSurf

ace

mix

ing r

ati

o

and w

ind a

t 2

1 U

TC

Colu

mn-i

nte

gra

ted

cloud w

ate

r at

21

U

TC

Control simulation 2 domains

Sensitivity study (2)

CONTROL 2 domains Cold start at 00 UTC

dryline Good Good ~ good

Outflow boundary

Too weak Good (too strong?)

No

mesolow Good Too weak Larger scale circulation

Surface moisture values

Good Good around the dryline

~ good

Surface temperature

values

Good (too hot western of dryline)

same as CONTROL

~ good

CI along the dryline

Good but no CI at triple point

Too late Too early

Sensitivity to initial time

Control simulation Initialization at 00 UTC

Reflectivity, potential temperature and surface wind at 16 UTC

Conclusion and future prospects

Main results:Current parameterizations do not guarantee high degree of accuracy in reproducing an outflow boundary.The number of factors involved in good simulations makes the success of high resolution simulations of thunderstorms a matter of …luck.

Future worksSensitivity to 3D fields initializationSimulation of gravity waves (GV) and horizontal convective rolls (HCR)

• sensitivity to the horizontal resolution (trying 2km)• WRF model

Analysis of the pre-storm environment in the different simulations to understand the physical processes affecting convection initiation (absence of GV and HCR = reasons of failure?)

Sensitivity study (2)

CONTROL 2 domains

Init. at 00Z MRF param.

dryline Good Good ~ good Good

Outflow boundary

Too weak Good (too strong?)

No Too weak

mesolow Good Too weak Larger scale circulation

Good

Surface moisture values

Good Good around the

dryline

~ good Too weak

Surface temperatur

e values

Good (too hot western of

dryline)

same as CONTROL

~ good Good

CI along the dryline

Good but no CI at triple

point

Too late Too early Good

Sensitivity to PBL parameterizationMRF PBL deeper, surface humidity weaker, moisture gradient at the dryline weaker

ETA Humidity more concentrated in the PBL and moisture gradient stronger, propitious to the development of convectionCI slightly delayed with the MRF parameterization

Control simulation

MRF param.