Tue 2/16/2016. Wrap-up on some WRF PBL options Paper presentations (Hans, Pat, Dylan, Masih, Xia, James) Begin convective parameterization (if time)

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1 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

2 Micrometeorology and Turbulence Parameterization

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

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

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

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

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

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

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

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

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

12 Re-Cap from Thursday 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 nonlocal 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)

13 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 (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

14 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?

15 Entrainment: Lateral and vertical 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

16 Shallow Cumulus and SCM Bretherton Shallow Convection (option 2 in shcu_physics) with MYJ RTHBLTEN No tendency in hot summer day sounding, strong tendency in Feb 18 sounding WRF did stop me from running YSU + Shallow Cu RTHSHTEN

17 Outline 1.) 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

18 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 (quasinormal scale elimination) 5 MYNN2 1,2,5 Improves MY length scale, adds buoyancy effects Local, 1.5 order Local, 1.5 order Qc, Qi Qc 6 MYNN3 1,2,5 Higher order version of MYNN2 Local, 2 nd order Qc 7 ACM2 1,7 Combines non-local, eddy diff., asymmetric mixing 8 BouLac 1,2 TKE similar to MYJ, Tested for orographic turbulence 9 UW 9 TKE scheme, for CAM, explicit entrainment 10 TEMF 10 Explicit shallow cumulus, considers total turb. energy 11 Shin-Hong 1 + others? Scale-aware non-local PBL scheme for gray zone runs Local + non-local Local, 1.5 order Qc, Qi Qc Local, 1.5 order Qc, Qi (?) Local + non-local Local + Non-local Qc, Qi Qc, Qi 12 GBM 9 With entrainment, for coarse Local, 1.5 order Qc, Qi vert. resolution (GCM) 99 MRF 1 Older version, YSU updates Local + non-local QC, QI

19 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. Mullen Journal: 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?

20 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

21 Results

22 Implications and Future Work

23 The Rise and Fall of Monin Obukhov Theory Keith McNaughton AsiaFlux Newsletter Presented by: Pat Hawbecker

24 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 (z i, w * ) PBL eddy energy f(buoyancy, entrained KE)

25 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 (u ε, z, ε 0, z i ) 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

26 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?

27 Keith McNaughton: New Surface-Layer Formulation

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29 A Hierarchy of Turbulence Closure Models for Planetary Boundary Layers Mellor and Yamada, 1974 MEA 716 Dylan White Feb. 16, 2016

30 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

31 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

32 Results and Conclusions Level 2 is adequate, but 3 has advantages All levels extinguish turbulence at Ri =0.21 One of the 1 st 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

33 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

34 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 Tests 1. Unsuccessful 48 hour heavy spurious precipitation forecast 2. Successful 36 hour forecast of tropical storm Control runs Old BM, no viscous layer Revised BM, no viscous layer Old BM, with viscous layer Revised BM, with viscous layer

35 Heavy spurious precipitation case Janjic (1994) Old BM, no viscous layer New MYJ scheme

36 Results Improved mean sea level pressure More realistic precipitation accumulation Improved tropical storm track, particularly at the later stages Future work 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

37 A Combined Local and Nonlocal Closure Model for the Atmospheric Boundary Layer. Part II: Application and Evaluation in a Mesoscale Meteorological Model JONATHAN E. PLEIM JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2006 GOAL: Overall performance of three-dimensional modeling systems (MM5) with ACM2 used as PBL parameterization?

38 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

39 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 areas PBL 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

40 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 If the premature collapse of the PBL would be alleviated)

41 Angevine, Jiang, and Mauritsen, 2010: Performance of an Eddy Diffusivity-Mass Flux Scheme for Shallow Cumulus Boundary Layers James Russell MEA716

42 TEMF Scheme Combines shallow cumulus and PBL scheme. Vertical Mixing Explicit representation of shallow cu. Eddy Diffusivity Mass Flux 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 Calculated from TE = TKE+TPE Advantage: Buoyancy destruction term vanishes in stable BL u=updraft Buoyancy Destruction: Critical Ri limit beyond which turbulence cannot exist i.e. no turbulence in stable BL

43 TEMF vs LES: Cloud base bias 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 Comparing apples and oranges: Multiple clouds in LES vs single cloud in TEMF Different ways of calculating base between LES and TEMF

44 Mixing Particulates TEMF moister in lowermid 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

45 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 subgrid 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.

46 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

47 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)

48 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)

49 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?