# Presentation: 266481

## Jonathan Pleim
NOAA/ARL
USEPA/ORD
RTP, NC

- NOAA/ARL
- USEPA/ORD
- RTP, NC

***A New Combined Local and Non-Local Boundary Layer Model: ACM2***

## Outline

- Model development
- 1-D testing and evalution
- Large Eddy Simulation (LES)
- GABLS Experiment (CASES99)
- WRF testing and evaluation
- Surface stats
- PBL Heights
- Vertical Profiles
- Preliminary CMAQ testing

## Purpose

- Develop a simple PBL model that:
- Produces realistic fluxes and profiles in PBL
- Accurate PBL height simulations
- Equally applicable to both meteorology and chemistry models
- Appropriate for all stability conditions without discontinuities
- Computationally efficient

## Background

- Local flux-gradient proportionality (i.e. Eddy diffusion) is not appropriate for Convective Boundary Layers
- Upward heat flux penetrates to ~80% of *h* while potential temperature gradients are very small through most of the PBL
- Eddies in CBL are larger that vertical grid spacing (local closure is not appropriate)
- Two common alternative approaches:

- Stull 1984, Blackadar 1976,
- Pleim and Chang 1992

- 1. Gradient adjustment term:

- Deardorff 1966,Troen and Mahrt 1986,
- Holstlag and Boville 1993, Noh et al. 2003

- 2. Transilent or non-local closure:

## Asymmetric Convective Model (ACM)

- Modification of the Blackadar convective scheme
- Simple Transilient model with very sparse, efficient semi-implicit matrix solver
- Rapid upward transport by convectively buoyant plumes
- Gradual downward transport by compensatory subsidence
- Part of the PX-LSM in MM5

## ACM

- ACM2

## ACM2

- Added eddy diffusion to ACM
- Allows local mixing at all levels
- More realistic profiles in lower layers
- Gradual transition from stable to unstable
- Full column integration (PBL and FT together)

## ACM Model equations

- Where *C**i* is mass mixing ratio at center of Layer *i*
*K**i+1/2* is eddy diffusivity at top of layer *i* [m2s-1]
*Mu *is upward convective mixing rate [s-1]
*Md**i** *is downward mixing rate from layer *i* to layer *i-1* [s-1]

*h* is top of PBL

## Non-local Mixing rates

- Convective mixing rate derived by conservation of buoyancy flux:

- Buoyancy** **flux at top of first layer defined by eddy diffusion:

- Thus, Convective mixing rate is a function of *K**z* but not
- a function of potential temperature gradient:

- Where:

## ACM2 Model equations

- Mixing rate, defined by *K**z*, is partitioned into local and
- non-local components

## Partitioning of local and non-local components

- The Question is: How to define *f**conv*?
- Clearly it should increase with increasing instability,
- but what is its upper limit for free convection?
- and what should be its stability function?
- First a sensitivity study for convective conditions

## 1-D experiments –

- Variations in partitioning of local and non-local transport

## Normalized heat flux and potential temperature profiles

***Normalized heat flux and potential temperature profiles***

- LES (Stevens 2000)

- ACM2

## Non-local partitioning

- These tests suggest that the upper limit of *f**conv* should be about 50%
- An expression for *f**conv* can be derived from gradient adjustment models (e.g. Holstlag and Boville 1993) at top of surface layer:

## Non-local fraction (fconv) as function of stability

## LES experiment low heat flux (Q* = 0.05 K m s-1), weak cap

## LES experiment low heat flux (Q* = 0.05 K m s-1), strong cap

## LES experiment high heat flux (Q* = 0.24 K m s-1), strong cap

- Comparison of ACM2, ACM1, and EDDYNL (Holtslag and Boville 1993) compared to the 05WC LES experiment.

**Notes:**
Move to Supplementary Slides?

## Profiles of sensible heat flux.  Local, non-local, and total sensible heat flux compared to LES

***Profiles of sensible heat flux.  Local, non-local, and total sensible heat flux compared to LES***

## The second GABLS model intercomparison 

- Multi-day Intercomparison of 23 PBL models for CASES99 field study
- Given initial profiles
*T**g* time series
- Constant geostrophic wind
- Large scale subsidence
- 2.5% of potential evaporation
- P, zo

## GABLS T-2m Intercomparison

## GABLS Experiment – Simulation of CASES99October 22-24, 1999

## GABLS Profile intercomparison

## CASES99 profiles

## Near surface Temperature profile from CASES99 main tower

***Near surface Temperature profile from CASES99 main tower***

## WRF 

- ARW
- NOAH LSM
- 12 km resolution
- FDDA
- PBL comparisons
- ACM2
- MYJ
- YSU
- August 2006

## Slide 29

## Slide 30

## Slide 31

## Slide 32

## Slide 33

## Slide 34

## PBL Heights from TexAQS II

- PBL heights derived from 10 radar wind profilers in Texas area by Jim Wilczak and Laura Bianco NOAA/ESRL
- Observations and models averaged by hour of the day for August 1-31, 2006

## Average PBL ht for

- Aug 2006

## Average PBL ht for

- Aug 2006

## Ozonesonde 2006

## Beltsville - Aug 28, 18Z

## Houston – 8/31, 18Z

## Houston windspeed and O3

## Narragansett – Aug 2, 17Z

## Narragansett Ozone, CO

## Huntsville – Aug 28, 18Z

## Huntsville – Aug 29, 18Z

## Huntsville – Ozone, CO

## Valparaiso – Aug 31, 19Z

## Egbert – Aug 29, 19Z

## Egbert WS and O3

## CMAQ

- Configuration:
- Domain: 199 x 205 x 34 @ 12 km res
- V4.5 CB4 AE3
- ACM2 vs Eddy
- Preliminary evaluation
- Ground level statistics (AMET)
- Ozonesondes from ICARTT 2004

## O3 Vertical Profiles for urban and

**O****3 ****Vertical Profiles for urban and**
** ****rural grid cells**

## CO

**CO**

## NOx

**NO****x**

## Conclusions

- ACM2 is a combination of local and non-local closure techniques
- Similar capabilities to eddy diffusion w/ counter-gradient adjustment but more readily applicable to any quantity (e.g chemistry)
- ACM2 produces more realistic superadiabatic surface layer than ACM1
- LES and 1-D tests show accurate simulation of vertical profiles and PBL heights
- MM5 and WRF tests show good ground level performance and accurate PBL heights

## More Conclusions

- CMAQ model comparisons show shallower and more well mixed profiles with ACM2 than with eddy diffusion
- Ozonesonde comparisons generally showed ** and *q**v* profiles similar to YSU but deeper PBL structure than MYJ
*ACM2 is uniquely suited for both meteorology and chemistry modeling*

## Acknowledgements

- Rob Gilliam (NOAAASMD)
- Tanya Otte (NOAA/ASMD)
- Lara Reynolds (CSC)
- Jim Wilczak (NOAA/ESRL)
- Laura Bianco (NOAA/ESRL)
- Keith Ayotte (Australia)