Supercell storms: In-class demo and Experiment 3 ATM 419/563 Spring 2017 Fovell

Goals Start idealized WRF 3D run to simulate a splitting supercell thunderstorm (in-class demo) Review supercell storm structure and behavior (while model runs) Analyze demo simulation Investigate sensitivity to microphysics Employ GrADS ensemble dimension, and compute ensemble mean and standard deviation Submit WRF jobs to the Snow batch system

In-class portion

Setup Create a folder called SUPERCELL in your lab space Copy /network/rit/lab/atm419lab/SUPERCELL/SETUP.tar there and unpack Files included: make_all_links.csh, namelist.input, input_sounding, read_wrfinput.py, submit_wrf, control_file.z Pre-configured for a 2-h run in a 168km by 168km domain at 2km horizontal resolution Initial sounding derived from Weisman and Klemp (1982) “quarter-circle” wind profile favors storm splitting and right-mover Purdue Lin microphysics (mp_physics = 2) Time step 12 seconds History output every 10 min Computes some AFWA diagnostic fields (&afwa section) read_wrfinput.py WK sounding was slightly modified from original

Boundary layer mixing ratio is 14 g/kg in input_sounding Weisman and Klemp (1982)

Hodograph (see input_sounding) 2 km AGL 7 km AGL surface

Using the Snow batch system Look at the file submit_wrf: #!/bin/bash # Job name: #SBATCH --job-name=ATM419 #SBATCH -n 6 #SBATCH -N 1 #SBATCH --mem-per-cpu=7G #SBATCH -p snow #SBATCH -o sbatch.out #SBATCH -e sbatch.err.out […] echo "running WRF" srun -N 1 -n 6 -o wrf.srun.out ./wrf.exe Change to your name Requests 6 cpus on 1 node Where run time errors might be reported This runs the model. The –N and –n values must match those provided at the top

Initialize model Allocate resources csh make_all_links.csh srun ideal.exe This MPI version does not write to screen anymore To see if the job worked: type trsl, which stands for “tail –f rsl.out.0000”. Type CTRL-C to break free. What is the lowest scalar model level height? python read_wrfinput.py wrfinput_d01 Submit your batch job: $ sbatch –p snow submit_wrf Check on your job $ squeue –u yournetid Lowest scalar height: 285 m. Not uncommon for cloud model simulations. Not even trying to capture PBL properly.

As the model runs… The model writes output to four kinds of files (in addition to wrfout…) rsl.out.XXXX (numbered 0000 to 1-n, n =number of nodes requested) rsl.error.XXXX (numered as above) sbatch.out (timing info when job completed) sbatch.err.out (hopefully it is empty!) As the model runs, you can “watch” it with $ trsl [This is an alias for tail -f rsl.out.0000] [type ‘CTRL-c’ to quit/escape from this] Look for SUCCESS COMPLETE WRF as usual

Supercell structure and behavior

Supercells Characterized by rotating updrafts (vertical velocity and vertical vorticity co-located) Mesocyclone and “hook echo” Develop in environments with large vertical wind shear Evolve from ordinary cells by “splitting” into “left-movers” and “right-movers” Clockwise directional vertical wind shear favors right-movers

Split L mover weaker R mover turns right R mover hook Purple = hail 24apr2006_split_dfx_n0r01.GIF Split L mover weaker R mover turns right R mover hook Purple = hail

Splitting storms Wilhelmson and Klemp (1981)

Shear-induced horizontal vorticity

Dynamics of storm splitting • Lifting of vortex tubes by updraft creates counter-rotating vortices (vertical vorticity) • Low perturbation pressure develops that establishes new updrafts on flanks of original storm • New cells are rotational: CCW or CW • Old cell dies, giving appearance of split • Actually, precipitation does NOT cause the updraft split

Original updraft

Counter-rotating vortices

New storms form on flanks

Old cell decays

reflectivity > 65+ dBZ (hail or airborne debris) hook echo

radial velocity

Supercell conceptual model

Storm-scale fronts T = tornado location

mesocyclone meso = Gk., middle

Updraft velocities can easily exceed 100 mph

RFD = rear flank downdraft FFD = forward flank downdraft

warm, moist air lifted into updraft

Supercell storm structure Plan view at surface UD = updraft FFD = forward flank downdraft RFD = rear flank downdraft Gust front Hook echo Dot ~ tornado location Lemon and Doswell (1979)

{Do Supercell in-class demo here}

Experiment 3

EXP03 overview Make 5 different simulations with 5 different microphysics schemes Do not select schemes 1, 3, 4, 5, 11, 12 or 14, as they do not produce radar reflectivity fields and/or have graupel as a species Do not select scheme 2, as we did that in class Do not choose bin schemes 30 or 32 Use the default time step of 12 sec srun ideal.exe as usual. Check tail of rsl.out.0000 file. WRF simulations have to be submitted to the Snow batch queue, using the submit_wrf script Given our setup, you can only run one job at a time Unpack the 5 simulations using control_file.z, using a naming convention like mpXX, where XX = mp_physics Note that some schemes create QHAIL but control_file.z will ignore this field. The ensemble members need identical CTL files

EXP03 tasks You have created a small WRF microphysics ensemble Write a GrADS CTL file for the ensemble Use the SQUALL demo’s mp_ensemble.ctl for guidance Run GrADS and open your ensemble CTL file Write a GrADS script to compute the mean and standard deviation of w_up_max at the final time (2 hours) Std deviation shaded and mean field contoured and superimposed. Use squall_ensemble.gs for guidance. Make a plot, and label axes Send to me: A list of which microphysics schemes you selected A PNG plot (or screenshot) of your w_up_max field Your GrADS script Your ensemble CTL file One additional plot, properly labeled, of anything you want. (Make sure I know what I am looking at.)