Tue 2/16/2016• Finish turbulence and PBL closure:

• Wrap-up on some WRF PBL options• Paper presentations (Hans, Pat, Dylan, Masih, Xia, James)• Begin convective parameterization (if time)

Reminders/announcements:- Next: Convective parameterization assignment coming up- Midterm Thu 3/3- Project hypothesis assignment, due (presented) Tue 3/15

- Added a short “progress report”, due on 2/25, to allow feedback

Micrometeorology and Turbulence Parameterization

NAM 31-h forecast from Sunday (PBL + LSM critical)Valid at RDU airport, 2 pm Monday (yesterday)

NAM 32-h forecast from Sunday (valid 3 pm Mon)

NAM 36-h forecast from Sunday (valid 7pm Mon)

NAM 38-h forecast from Sunday (Valid 9pm Mon)

NAM 40-h forecast from Sunday (Valid 11 pm Mon)

NAM 42-h forecast from Sunday (Valid 1 am today)

NAM 45-h forecast from Sunday (Valid 4am today)This is the time when RDU Temp shot up to 13.3C

NAM 48-h forecast from Sunday (Valid 7am today)MYJ PBL (Obs: 12.2C, 54F)

GFS 48-h forecast from Sunday (Valid 7am today)Non-local PBL for neutral or unstable conditions (like MRF)

Quick SCM comparison of available WRF PBL schemes for hot August day in NC: TEMF, Brenier-Gretheron, MYNN3 “outliers”

For turbulence parameterization, there are issues with scale separation when model resolution is high (terra incognita – Wyngaard 2004)

Begin to resolve some large eddies at high resolution; capture more non-local type behavior (large eddy mixing)

Honnert et al. 2011, JAS: Ratio of grid length to TOTAL PBL height reveals point where parameterized ~ resolved turbulence

This value differs depending on turbulent moment

Shin and Hong (2015) introduce a “scale aware” PBL scheme which offers promise for high-resolution modeling; only recently available (WRF 3.7)

Re-Cap from Thursday

We also discussed papers, including - Baklanov et al. 2011, BAMS (Keith) – summary of state of PBL - Braun and Tao 2000 (Laura) – compared PBL schemes in MM5 for TC- Hong et al. 2006 (Lindsay) – Introduces YSU PBL scheme

Also beware: Vertical entrainment can be represented by:- Separate shallow cumulus scheme (e.g., Bretherton)- PBL scheme (e.g., YSU, TEMF)- Cumulus parameterization (e.g., BMJ)- Diffusion (okay to have always on)

WRF model could do more to warn users about “overlap”, or lack of representation of shallow mixing

Re-Cap from Thursday

NASA Satellite image from Sunday: Cloud-topped, convective PBL in evidence, ocean-effect snow

Should these convective clouds be represented by

the model PBL scheme, or

convective scheme?

Entrainment: Lateral and vertical

http://www.cmmap.org/learn/clouds/howForm3.html

Horizontal entrainment in sides of convective clouds: Represented in convective

parameterization schemes; it can also be accounted for by

diffusion

Vertical entrainment at PBL top:Represented in some convective

parameterization schemes, is also represented by some PBL schemes,

and also by shallow cumulus schemes

Shallow Cumulus and SCM

RTHSHTENRTHBLTEN

Bretherton Shallow Convection (option 2 in shcu_physics) with MYJ

No tendency in hot summer day sounding, strong tendency in Feb

18 sounding

WRF did stop me from running YSU + Shallow Cu

Outline1.) Review of turbulence and properties

- Characteristics, worksheet

- Definitions, TKE, introduction to closure problem

- Tendencies, and flux divergence

2.) Closure strategies- Bulk aerodynamic

- K-theory (mixing length)

- Local and non-local closures

- WRF schemes

- Scale issues, diffusion

Conclude with presentation/discussion of journal papers describing schemes

WRF PBL Options (partially from Dudhia)bl_pbl Scheme Sfc layer Characteristics Design Cloud mixing

1 YSU 1 Explicit entrainment, first order Local + non-local Qc, Qi

2 MYJ 2 TKE scheme Local, 1.5 order Qc, Qi

4 QNSE 4 TKE, a spectral scheme (quasi-normal scale elimination)

Local, 1.5 order Qc, Qi

5 MYNN2 1,2,5 Improves MY length scale, adds buoyancy effects

Local, 1.5 order Qc

6 MYNN3 1,2,5 Higher order version of MYNN2 Local, 2nd order Qc

7 ACM2 1,7 Combines non-local, eddy diff., asymmetric mixing

Local + non-local Qc, Qi

8 BouLac 1,2 TKE similar to MYJ, Tested for orographic turbulence

Local, 1.5 order Qc

9 UW 9 TKE scheme, for CAM, explicit entrainment

Local, 1.5 order Qc, Qi (?)

10 TEMF 10 Explicit shallow cumulus, considers total turb. energy

Local + non-local Qc, Qi

11 Shin-Hong 1 + others?

Scale-aware non-local PBL scheme for “gray zone” runs

Local + Non-local Qc, Qi

12 GBM 9 With entrainment, for coarse vert. resolution (GCM)

Local, 1.5 order Qc, Qi

99 MRF 1 Older version, YSU updates Local + non-local QC, QI

The Sensitivity of the Numerical Simulation of the Southwest Monsoon Boundary Layer to the Choice of 

PBL Turbulence Parameterization in MM5

Authors: David R. Bright & Steven L. MullenJournal: Weather and Forecasting, 2002

How well can the PSU‐NCAR fifth‐generation Mesoscale Model (MM5) predict the evolution of the PBL during the Arizona monsoon season, using a 4 

different PBL schemes?

Schemes

1. Blackadar PBL Parameterization‐ First‐Order, Nonlocal Scheme

2. Burk‐Thompson PBL Parameterization ‐ Second‐Order, Local Scheme

3. ETA PBL Parameterization‐ 1 ½ order, Local Scheme 

4. MRF PBL Parameterization‐ First‐Order, Nonlocal Scheme

Results

Implications and Future Work

The Rise and Fall of Monin‐Obukhov Theory

Keith McNaughtonAsiaFlux Newsletter

Presented by: Pat Hawbecker

Summary

• M‐O issues with scaling parameters– All M‐O variables (u*, z, gq/T) termed “local,” BUT… is z (height) local?

– Problem: in free convection, u* doesn’t exist so no length scale can be made  “self‐patterning”

• Recommend only integral properties (such as z) should be considered

• Deardorff issues in boundary conditions– Scaling variables all sufficiently “local” (zi, w*)– PBL eddy energy f(buoyancy, entrained KE)

Problem and Solution

• Problem – observations typically widely scattered when using these relationships– Scientific community just accepts this to be the way it is

• Solution – new parameter set (uε, z, ε0, zi)– Scaling applies separately to different eddies– Eddies can have mixed length, energy, and velocity scales

– This is now a non‐local theory, so point measurements are not enough

Significance

• M‐O theory is the foundation for PBL models– Inherent issues , but overall good performance– Easily checked / applied to observations

• New scaling variables supposedly improve on shortcomings of M‐O theory (no results shown)– More complete observational datasets needed to verify these scaling relationships

• Question to ask: why was this published in the AsiaFlux newsletter? Is this peer‐reviewed?

Keith McNaughton: New Surface-Layer Formulation

A Hierarchy of Turbulence Closure Models for 

Planetary Boundary LayersMellor and Yamada, 1974

MEA 716Dylan WhiteFeb. 16, 2016

Introduction•At the time, several turbulent field models, but methods were unclear

•Goal: present a hierarchy of closure models and examine adequacy of each level

Level 4

Level 3

Level 2

Level 1

Methods•Begin with full Reynolds stress terms 

•Neglect higher order advection & diffusion

•Neglect lower order advection & diffusion

•Neglect all first order terms

•Apply PBL assumptions to each level

Level 4

Level 3

Level 2

Level 1

Results and Conclusions• Level 2 is adequate, but 3 has advantages

•All levels extinguish turbulence at Ri = 0.21

•One of the 1st papers to present such a hierarchy

• Levels 2 and 3 are still used today (e.g., MYNN schemes)

Level 4

Level 3

Level 2

Level 1

The Step‐Mountain Eta Coordinate Model:Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes. Janjic (1994), Monthly Weather Review

Motivations • Heavy Spurious precipitation over warm water• Widely spread light precipitation over oceans• Producing negative entropy changes (shallow convective scheme)

Diagnosis • Deep and shallow convection schemes• Sea‐air interface processes• Mellor‐Yamada (MY) schemes

• Improving the Betts‐Miller (BM) scheme over the oceans• Tuning the deep convective scheme relaxation time by “cloud efficiency” 

and modifying relaxation time• Defining a range of equilibrium reference states instead of one• Modified shallow cloud top to produce nonnegative entropy

• Designing a new flexible viscous sublayer• A viscous sublayer with only molecular diffusion• A layer above it with only vertical turbulent diffusion

• Retuning the MY level 2 and 2.5• Modified MY so that the excessive TKE is dissipated during PBL spin up• Calculation of master length scale is modified• Possible overestimation of level 2 surface fluxes over water are avoided

Tests1. Unsuccessful 48 hour heavy spurious 

precipitation forecast2. Successful 36 hour forecast of tropical storm

Old BM, no viscous layerRevised BM, no viscous layerOld BM, with viscous layerRevised BM, with viscous layer

Control runs

Heavy spurious precipitation case

Old BM, no viscous layer New MYJ scheme

Janjic (1994)

Results

• Excessive precipitation over warm water is not completely eliminated and might be associated to inconsistency between eta model and assimilation system producing strong initial stability

• Relatively thick surface layer is a potential weakness

• Improved mean sea level pressure • More realistic precipitation accumulation• Improved tropical storm track, particularly at the later stages 

Future work

J O N A T H A N E . P L E I MJ O U R N A L O F A P P L I E D M E T E O R O L O G Y A N D

C L I M A T O L O G Y2 0 0 6

A Combined Local and Nonlocal Closure Model for the Atmospheric Boundary Layer.

Part II: Application and Evaluation in aMesoscale Meteorological Model

GOAL:Overall performance of three-dimensional modeling systems

(MM5) with ACM2 used as PBL parameterization?

Application of ACM2 in MM5

Modified scheme for diagnosis of PBL height Lower-upper decomposition matrix solver for

semi- implicit integration Upgraded eddy diffusivity scheme

¡� Boundary layer scaling¡� Local wind shear and stability-based formulation

Model setting¡� 12km resolution¡� Pleim-Xiu LSM, RRTM for longwave radiation, KF2 cumulus,

Reisner2 microphysics¡� Four-dimensional data assimilation used for nudging

Results

2-m temperature¡� Nighttime warm bias, especially during cooler, stable nights¡� Very little bias in daytime

10-m wind speed¡� Slight positive bias at night, consistent with warm bias¡� Negative bias in the daytime, associated with dominance of airport

measurement sites which tend to be in large open areasPBL height

¡� Overestimate PBL height during morning hours¡� Close agreement with obs during the evening height decline

Vertical profile of potential temperature and relative humidity¡� Trustable results during clear-sky, low-wind condition

Statistical comparisons¡� 2-m temperature and humidity, 10-m wind speed and direction¡� Show similar results to previous MM5 evaluation studies with ACM

Future work

Performance of ACM2 in the WRF model without integrating with LSMs

Research into improved stable boundary layer modeling

Evaluation of the ACM2 in an air quality model,like Community Multiscale Air Quality model (see Ifthe premature collapse of the PBL would bealleviated)

Angevine, Jiang, and Mauritsen, 2010: Performance of an Eddy Diffusivity-Mass

Flux Scheme for Shallow Cumulus Boundary Layers

James RussellMEA716

TEMF SchemeVertical Mixing

Eddy Diffusivity Mass Flux

Calculated from TE = TKE+TPE

Advantage:Buoyancy destruction term

vanishes in stable BL

Buoyancy Destruction: Critical Ri limit beyond which turbulence cannot exist i.e. no turbulence in stable BL

• Combines shallow cumulus and PBL scheme.

• Explicit representation of shallow cu.

Method:

• Comparison to LES’s run and compared to field experiment in Texas (LES=control/truth)

• Emphasis on daytime convection (not stable BL)

• SCM simulations

u=updraft

TEMF vs LES: Cloud base biasComparing apples and oranges:• Multiple clouds in LES vs

single cloud in TEMF• Different ways of

calculating base between LES and TEMF

TEMF grows BL more quickly since TEMF responds instantly. More entrainment in TEMF Leads to a warmer and drier sub-cloud

layer. Higher cloud base in TEMF than in LES

Mixing Particulates• TEMF moister in lower-

mid cloud layer• Drier subcloud layer in

TEMF

• Too much mass flux across cloud base in TEMF

• Existing PBL schemes: no subgrid scale processes lead to a much drier cloud and moister lower profile

Other points / Future Work• TEMF scheme intended to be used in mesoscale models

over a range of grid spacings.

• Determining cloud fraction and cloud liquid will require a sub-grid condensation scheme.

• Further work needed to find the best way to couple TEMF to other parts of the model system, e.g. radiation schemes, shallow cumulus schemes, and moist convection schemes.

• Final point: Should have compared to other PBL schemes to ascertain benefits.

The TEMF Scheme

Authors view shallow cumulus as “part of the boundary layer”, and therefore…

“…preferred solution is an integrated boundary layer and shallow cumulus scheme rather than separate schemes”

TEMF is a merger of two other schemes:‐ Unstable case: Eddy Diffusivity‐Mass Flux (EDMF, 

Angevine 2005); mixing by 2 methods‐ Stable case:  Follows Mauritsen et al. (2007)

Eddy diffusivity computed from total turbulent energy (TE) + length scale.  TE = TKE + TPE; TE conserved in more circumstances

The TEMF Scheme

“Purely local schemes based on TKE maintain (unrealistic) unstable stratification throughout the PBL…”

Results:‐ TEMF grows BL more rapidly than LES, more 

entrainment; argue that LES may be weaker than obs

‐ Surface fluxes communicated through BL instantly in TEMF, whereas LES requires time to propagate upward

‐ TEMF tends to dry subcloud layer and moisten cloud layer relative to LES:  Too much moisture into cloud?

‐ Perhaps TEMF “entrains too much”?  (p. 2908)

Conclusions

Hybrid non‐local and local configuration, explicit account of vertical cumulus entrainment

Eddy diffusivity a function of total turbulent energy; authors argue for superiority of method (Angevine 2005)

TEMF designed for cloud‐topped boundary layers, perhaps best in neutral or unstable conditions

Seems best not to run with shallow mixing, or with a CP scheme that includes strong shallow mixing (more soon)

PBL Wrap-Up• How reliable are the PBL options available in WRF?

• Do you feel comfortable in choosing one WRF PBL/surface layer package over another for a given application?

• What are some situations to avoid? What are some “best practices” in selecting a PBL scheme?

• How can one gain a sense of how a PBL scheme is “behaving” in a given situation?