getting the convective boundary layer right: how it impacts forecasts of deep convection
DESCRIPTION
Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection. Jack Kain ASP Summer Colloquium July 2006. Getting the Convective Boundary Layer Right in models : How it impacts Human Forecasts of Deep Convection. Jack Kain ASP Summer Colloquium July 2006. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/1.jpg)
Getting the Convective Boundary Layer Right: How it impacts
Forecasts of Deep Convection
Jack Kain
ASP Summer Colloquium
July 2006
![Page 2: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/2.jpg)
Getting the Convective Boundary Layer Right in models: How it impacts Human Forecasts of
Deep Convection
Jack Kain
ASP Summer Colloquium
July 2006
![Page 3: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/3.jpg)
My Background…
I am a numerical modeler by training, but I have spent the last several years working at the interface of research and daily operations – with forecasters from the NCEP/Storm Prediction Center (SPC) and researchers from the NOAA/National Severe Storms Laboratory (NSSL)
![Page 4: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/4.jpg)
Why the Boundary layer?
CAPE
CIN
![Page 5: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/5.jpg)
Why the Boundary layer?
CIN
CAPE
![Page 6: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/6.jpg)
Small changes in Boundary Layer Temperature and Moisture can have a Big Impact on CAPE and CIN…Also, the Temperature Profile just above the
top of the BL strongly affects CIN
But do forecasters actually care about small-scale details in forecast-sounding structure?
Yes! Consider a sampling of DAY 2 OUTLOOKs, a product that SPC forecasters use to provide guidance to local forecast offices…
![Page 7: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/7.jpg)
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1111 AM CST SAT APR 01 2006
VALID 021200Z - 031200Z
...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF IA...MO AND MUCH OF IL...
…FORECAST SOUNDINGS INDICATE A POTENT COMBINATION OF INSTABILITY AND VERTICAL SHEAR ACROSS MODERATE RISK AREA...WHICH SHOULD SUPPORT INTENSE SUPERCELL DEVELOPMENT WITH THE POTENTIAL FOR A FEW STRONG TORNADOES IN ADDITION TO VERY LARGE...DESTRUCTIVE HAIL AND DAMAGING WINDS. WITH TIME...STORMS MAY EVOLVE INTO BOWING LINE SEGMENTS OR A MESOSCALE LEWP STRUCTURE WITH CORRIDORS OF DAMAGING WINDS POSSIBLE EWD ACROSS THE OH VALLEY SUNDAY NIGHT…
…FORECAST SOUNDINGS INDICATE A POTENT COMBINATON OF INSTABILITY AND VERTICAL SHEAR ACROSS MODERATE RISK
![Page 8: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/8.jpg)
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1239 PM CDT MON APR 03 2006 VALID 041200Z - 051200Z ...NO SVR TSTM AREAS FORECAST... ...EARLY MORNING -- TX/SERN NM... …MRGL/CONDITIONAL HAIL PROBABILITIES EXIST OVER THIS REGION FOR FIRST FEW HOURS OF PERIOD...AMIDST EXTENSION OF LATE DAY-1 WAA/MOISTURE RETURN REGIME. ELEVATED BUOYANCY IS FCST TO BE SMALL – GENERALLY AOB 500 J/KG MOST AREAS.
HOWEVER...ANY SUSTAINED CONVECTION WILL HAVE POTENTIAL FOR HAIL GIVEN STRONG VEERING AND SPEED SHEAR WITH HEIGHT THROUGH CONVECTIVE COLUMN...WHICH SHOULD BE ROOTED IN 800-850 MB LAYER BASED ON FCST SOUNDINGS. ACTIVITY SHOULD DIMINISH DURING LATE MORNING AS LLJ WEAKENS…
CONVECTION
ELEVATED BUOYANCY
SHOULD BE ROOTED IN800-850 MB LAYER BASED ON FCST SOUNDINGS.
![Page 9: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/9.jpg)
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1237 PM CDT TUE APR 04 2006 VALID 051200Z - 061200Z ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NRN PLAINS...
...NRN/CENTRAL PLAINS... …WIDELY SCATTERED TSTMS SHOULD DEVELOP FROM MID/LATE AFTERNOON INTO EARLY EVENING ACROSS NRN HIGH PLAINS...FROM SRN MT POTENTIALLY AS FAR E AS INVOF BLACK HILLS. ACTIVITY INITIALLY SHOULD BE HIGH-BASED...SUPPORTED BY MRGL BOUNDARY LAYER MOISTURE...STEEPENING MIDLEVEL LAPSE RATES ASSOCIATED WITH APCHG TROUGH...STRENGTHENING DEEP-LAYER SHEAR...AND DIABATIC SFC HEATING. DEEPLY MIXED SUBCLOUD LAYERS IN FCST SOUNDINGS SUGGEST POTENTIAL FOR BOTH DAMAGING DOWNDRAFTS AND LARGE HAIL TO REACH SFC. DOWNDRAFTS AND LARGE HAIL TO REACH SFC…SOUNDINGS SUGGEST POTENTIAL FOR BOTH DAMAGING
DEEPLY MIXED SUBCLOUD LAYERS IN FCST
![Page 10: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/10.jpg)
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1235 PM CDT THU APR 06 2006
VALID 071200Z - 081200Z
...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA...
…INITIATE FRIDAY AFTERNOON...SUPERCELLS WILL BE LIKELY DUE TO THE STRONG VERTICAL SHEAR ASSOCIATED WITH THE MID-LEVEL JET. NAMKF FORECAST SOUNDINGS FOR TUPELO MS...FLORENCE ALABAMA AND HUNTSVILLE ALABAMA FRIDAY AFTERNOON SEEM REASONABLE WITH MODERATE TO STRONG INSTABILITY (MLCAPE VALUES 2500-3000 J/KG)...0-6 KM SHEAR VALUES AT/ABV 60 KT AND IMPRESSIVE LOW-LEVEL SHEAR PROFILES (0-3 KM SRH AT/ABV 350 M2/S2). IN THIS ENVIRONMENT...STORMS SHOULD REMAIN DISCRETE FOR THE LATE AFTERNOON AND EARLY EVENING HOURS. IN ADDITION...LCL HEIGHTS ARE FORECAST TO REMAIN LOW WHICH COMBINED…
WITH MODERATE TO STRONG INSTABILITYSEEM REASONABLE
NAMKF FORECAST SOUNDINGS
![Page 11: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/11.jpg)
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1235 PM CDT THU APR 06 2006
VALID 071200Z - 081200Z
...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA...
…FAVORABLE FOR TORNADOES. LONG-TRACK STRONG OR EVEN VIOLENT TORNADOES WILL BE POSSIBLE ESPECIALLY WITH SUPERCELLS THAT TRACK ALONG ANY PRE-EXISTING BOUNDARIES OR CONVERGENCE ZONES. THE INSTABILITY...SHEAR AND STEEP MID-LEVEL LAPSE RATES NEAR 8.0 C/KM SHOWN ON THE FORECAST SOUNDINGS WILL ALSO BE FAVORABLE FOR LARGE HAIL AND WIND DAMAGE WITH THE SUPERCELLS. VERY LARGE HAIL WILL ALSO BE POSSIBLE WITH THE STRONGER SUPERCELLS…
MID-LEVEL LAPSE RATES NEAR 8.0 C/KM SHOWN ON THE FORECAST SOUNDINGS WILL ALSO BE FAVORABLE FOR LARGE HAIL AND WIND
SHEAR AND STEEP
![Page 12: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/12.jpg)
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1235 PM CDT THU APR 06 2006
VALID 071200Z - 081200Z
...THERE IS A HIGH RISK OF SVR TSTMS ACROSS NE MS...NRN AL...SCNTRL TN AND FAR NW GA...
…INSTABILITY IN THE AFTERNOON HOURS. THE NAM AND GFS INITIATE POST-FRONTAL CONVECTION EARLY IN THE AFTERNOON NORTH OF A FRONTAL BOUNDARY EXTENDING WSWD TO ENEWD ACROSS THE OH VALLEY. FORECAST SOUNDINGS FOR THIS AREA FRIDAY AFTERNOON SHOW SUFFICIENT INSTABILITY/SHEAR PROFILES AND STEEP LAPSE RATES THAT SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. FURTHER SOUTH ACROSS KY...SFC DEWPOINTS IN THE UPPER 50S TO NEAR 60 F SHOULD ALLOW MODERATE INSTABILITY TO DEVELOP. ALTHOUGH CONVECTIVE INITIATION MAY...
SHOW SUFFICIENT INSTABILITY/SHEAR PROFILES AND STEEP LAPSE
FORECAST SOUNDINGS FOR THIS AREA FRIDAY AFTERNOON
RATES THAT SHOULD BE FAVORABLE FOR SUPERCELLS
![Page 13: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/13.jpg)
What components of a modeling system most strongly
affect (pre-convective) CAPE/CIN and BL structures?
• Parameterizations of:
– Boundary Layer/Turbulence* – Shallow moist convection* (do we need this with
~1-4 km grid spacing?)– Surface processes– Atmospheric radiation
• Advection
![Page 14: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/14.jpg)
Consider two very different shallow Convective Parameterizations (both used in
the NCEP SREF)
• Kain-Fritsch scheme: a “mass-flux” convective adjustment scheme
• Betts-Miller-Janjic (BMJ) scheme: a “static profile” convective adjustment scheme
![Page 15: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/15.jpg)
KF scheme: Checking for the possibility of deep (precipitating) convection…can a
parcel reach its LFC and form a deep cloud?
![Page 16: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/16.jpg)
KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?
![Page 17: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/17.jpg)
KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?
![Page 18: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/18.jpg)
KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?
![Page 19: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/19.jpg)
KF scheme: Can a parcel reach its LFC and form a deep (precipitating) cloud?
![Page 20: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/20.jpg)
KF scheme: determining shallow-convection adjustment profiles
Updraft path
Entrainment Layer
Detrainment Layer
Updraft mass-flux
profile
Cloud-base mass flux: At what rate is mass is processed by moist shallow convection? Currently scaled as a function of TKE in the BL
![Page 21: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/21.jpg)
KF shallow convection parameterization…requires many assumptions
• We think we have a good handle on:
•Cloud-base thermodynamic properties
•Cloud base, cloud top
•Adjustment time scale
• We have less confidence in assumptions related to:
•Cloud-base mass flux – how much of the BL mass participates in moist convection?
•Vertical profiles of entrainment, detrainment and vertical mass flux, which determine profiles of heating and drying.
![Page 22: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/22.jpg)
…It’s cloud illusions that I recallI really don’t know clouds at all…
- Joni Mitchell
![Page 23: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/23.jpg)
KF scheme adjustment profiles
![Page 24: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/24.jpg)
The Betts-Miller-Janjic (BMJ) parameterization: based on the philosophy
of Alan Betts (Alan knows clouds):
• The fundamental characteristics of updrafts and downdrafts depend on internal cloud dynamics and microphysics, which cannot be represented adequately by simple sub-models used in mass-flux parameterizations
• Observations and theoretical considerations tell us that convecting atmospheres never stray too far from definable profiles.
• Convective sources of heat and moisture can be defined in terms of these profiles.
![Page 25: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/25.jpg)
Like the KF scheme, the BMJ scheme first checks for the possibility of deep
(precipitating) convection
• As with all convective parameterizations, CAPE is a necessary condition for activation of deep convection, but the BMJ scheme reverts to shallow (non-precipitating) convection if
– The cloud (unstable) layer is too dry
– The cloud layer is too shallow
![Page 26: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/26.jpg)
Conceptual basis for BMJ shallow-convection parameterization
- from Betts (1986 – QJRMS)
![Page 27: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/27.jpg)
BMJ Scheme: determining shallow-convection adjustment profiles
1) Find the LCL of cloud base and cloud top air
2) Draw a linear “mixing line” between these two layers
3) Anchor Tadj to the sounding at cloud base, draw it parallel to mixing line
4) Slide Tadj so that net heating is zero
5) Draw qv,adj so that net moistening is zero.
![Page 28: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/28.jpg)
Consider the impact of parameterized BMJ shallow convection in a “normal” diurnal cycle…
Model Initial Condition
Raob
BMX 12 Z 11 May 2000
![Page 29: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/29.jpg)
BMJ adjustment process (Eta model forecast)…
Initial time 1 h forecast
![Page 30: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/30.jpg)
BMJ adjustment process (Eta model forecast)…
3 h forecast 9 h forecast
![Page 31: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/31.jpg)
Compare Eta model forecast with raob at 00Z: 12 h forecast
Model forecast
Raob
BMX 00Z 12 May 2000
![Page 32: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/32.jpg)
How about same 12h forecast using KF shallow How about same 12h forecast using KF shallow convection instead of BMJ (EtaKF)?convection instead of BMJ (EtaKF)?
12 h EtaKF forecast
Raob
BMX 00Z 12 May 2000
![Page 33: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/33.jpg)
24 h Eta/EtaKF soundings vs. DFW raob
00Z RAOB
Opnl Eta
00Z RAOB
Etakf
![Page 34: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/34.jpg)
Shallow convection mean moisture tendencies 21h fcst
Opnl Eta EtaKF
![Page 35: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/35.jpg)
Performance characteristics like this that are common knowledge to model developers are often a mystery (but
potentially very useful) to forecasters…
![Page 36: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/36.jpg)
Interactions with forecasters convinced us that Interactions with forecasters convinced us that knowledge of these behavior characteristics could knowledge of these behavior characteristics could
help forecasters interpret model forecast help forecasters interpret model forecast soundings, motivating us to….soundings, motivating us to….
- Document characteristic biases during 2001 Document characteristic biases during 2001 Spring ProgramSpring Program
- Provide formal SPC/WFO training on - Provide formal SPC/WFO training on model forecast sounding interpretationmodel forecast sounding interpretation
- Introduce diagnostic versions of BMJ and - Introduce diagnostic versions of BMJ and KF schemes into the SPC’s NSHARP KF schemes into the SPC’s NSHARP sounding analysis programsounding analysis program
- Publish guidance for forecasters (Baldwin Publish guidance for forecasters (Baldwin et al. 2002, et al. 2002, Wea. ForecastingWea. Forecasting))
![Page 37: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/37.jpg)
48 h Eta CAPE forecast
48 h EtaKF CAPE forecast
Consider a real forecasting Consider a real forecasting dilemma from several years dilemma from several years ago…ago…
Wind barbs: 0-6 km shear vector
![Page 38: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/38.jpg)
48 h Eta model forecast for SHV:48 h Eta model forecast for SHV:
BMJ T, Td reference profiles
![Page 39: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/39.jpg)
48 h EtaKF model forecast for SHV…48 h EtaKF model forecast for SHV…
![Page 40: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/40.jpg)
SPC forecasters identified the
characteristic bias of the Eta model, boldly suggested the 48 h forecast sounding
was “in error”
SPC day 2 convective outlook valid 28 Mar 2002
![Page 41: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/41.jpg)
48 h later: SHV observed sounding…48 h later: SHV observed sounding…
![Page 42: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/42.jpg)
Preliminary Summary: PBL structures, CAPE, CIN values, etc. are all quite sensitive to
parameterization of shallow moist convection…
• How about the sensitivities to PBL/turbulence parameterizations? Compare CBL soundings from dx~4km forecasts from
– WRF-ARW using the YSU (Yonsei University) PBL
– WRF-NMM using the MYJ (Mellor-Yamada-Janjic) PBL
…without parameterization of moist convection
![Page 43: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/43.jpg)
Possible Approaches for Parameterization of the Convective Boundary Layer
- From Stull (1988)
MYJ PBL Param
YSU PBL Param
![Page 44: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/44.jpg)
Sounding comparison: 24h forecast valid 00Z 24 May at DDC
ARW withYSU PBL
NMM withMYJ PBL
Good forecast…
PBL too shallow, cold, & moist…clouds just broke up!
Model Raob
Model Raob
![Page 45: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/45.jpg)
Sounding comparison: 24h forecast valid 00Z 18 May at DDC
NCAR
EMC
Too dry in PBL, too moist above; Where is the PBL top?
Good forecast…
Model Raob
Model Raob
ARW withYSU PBL
NMM withMYJ PBL
![Page 46: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/46.jpg)
Sounding comparison: 24h forecast valid 00Z 28 April at OUN
NCAR
EMC
Good in PBL, but CIN layer is washed out
PBL too shallow and moist, but CIN layer looks good
Model
Raob
Model
Raob
ARW withYSU PBL
NMM withMYJ PBL
![Page 47: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/47.jpg)
Quantifying errors in model-forecast soundings…simple comparison of T, qv values
at a given pressure level is inadequate!
Is the forecast sounding any good?
What aspects of the sounding are predicted well?
![Page 48: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/48.jpg)
How does one quantify these errors?
That one was way off!
![Page 49: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/49.jpg)
How does one quantify these errors?
![Page 50: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/50.jpg)
How does one quantify these errors?
That one was BS! (Bad Sounding)
![Page 51: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/51.jpg)
A simple approach to quantifying important structure errors in convective-BL soundings…
Use criteria based on static stability to define top of CBL
- Compute depth of CBL (top of ~constant layer)
- Compute mean in CBL
- Compute mean qv in CBL
How about the CIN layer?
![Page 52: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/52.jpg)
Sounding verification: How well is the CIN layer defined?
100 mb
- Compare this area in forecasts and observations
![Page 53: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/53.jpg)
Sounding verification: How well is the moisture profile at the top of the BL defined?
100 mb
- Compare this area in forecasts and observations
![Page 54: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/54.jpg)
Qualitative assessment of systematic biases in Convective Boundary Layers
![Page 55: Getting the Convective Boundary Layer Right: How it impacts Forecasts of Deep Convection](https://reader036.vdocuments.us/reader036/viewer/2022081520/56815a25550346895dc7692e/html5/thumbnails/55.jpg)
Summary
• Getting the boundary layer right is critically important for predicting moist convection.
• Currently available parameterizations of the BL and of shallow convection are deficient in many (hard to define) ways.
• We are counting on the next generation of meteorologists (that’s you!) to solve these problems