Updates and Evaluation of the PX-LSM in MM5
Jonathan E. Plcim*
Atmospheric Sciences Modeling Division, NOAA,
Research Triangle Park, NC 27711
pleim@hpcc.epa.gov
Ph:919-541 -1336, fax:919-541 -1379
Aijun Xiu
Environmental Programs, MCNC-North Carolina Supercomputing Center,
Research Triangle Park, North Carolina 27709
1.	INTRODUCTION
Starting with Version 3.4 there is a new land surface
model known as the Pleim-Xiu LSM available in the
MM5 system. Pleim and Xiu (1995) described the
initial development and testing of this land surface and
PBL model for use in mesoscale models. Last year's
workshop proceedings provided a basic description of
the model and some evaluation (Pleim and Xiu, 2000).
A recent journal article (Xiu and Pleim 2001) presents a
more detailed description of the LSM and its
implementation in MM5 and further evaluation. This
paper outlines some bug fixes, updates, guidance for
use, and more evaluation.
2.	MODEL DESCRIPTION
/
The PX land surface model's key elements
include soil moisture based on the Interactions between
Soil, Biosphere, and Atmosphere (ISBA) model
(Noilhan and Planton 1989), surface fluxes including
parameterization of vegetation, and a non-local closure
PBL mode! developed by Pleim and Chang (1992). The
surface model includes a two-layer soil model with a 1-
cm surface layer and a 1-m root zone layer. Evaporation
has three pathways: direct soil surface evaporation,
vegetative evapotranspiration, and evaporation from wet
canopies. Ground surface (1 cm) temperature is
computed from the surface energy balance using a force-
restore algorithm for heat exchange within the soil,
Stomatal conductance is parameterized according to root
zone soil moisture, air temperature and air humidity,
photosynthetically active radiation (PAR), and several
vegetation parameters such as leaf area index (LAI) and
minimum stomatal resistance. Although originally
based on the ISBA model, the stomatal and canopy
parameterizations are almost entirely new. New features
include updated stomatal functions with respect to
environmental parameters, and inclusion of a data
assimilation scheme similar to the technique described
by Bouttier et al. (1993). A simple parameterization for
describing seasonal growth of vegetation, including leaf-
out of deciduous trees, has also been developed and
tested. Refer to Xiu and Pleim (2001) for the details of
the model.
3.	BUG FIXES
In the initial release of MM5v3.4 there was a
bug in the PX LSM such that any radiation scheme
other than the surface-only option would not work
correctly. This bug was fixed and the current code
available from the NCAR ftp site (mesouser) is correct.
A naming conflict between the PX LSM and
the RRTM radiation scheme caused another problem.
There was a subroutine named surface.F in
/physics/pbl_sfc/pxpbl and also a common block named
surface in /physics/radiation/rrtm/rrtm. F. The result
was that the model would crash whenever both PX and
RRTM were selected. We fixed this by renaming
surface.F to surfpx.F. This fix is not yet in the
mesouser code but will be for the next release. In the
mean time, to run PX and RRTM together this change
must be made.
4.	UPDATES
In addition to these bug fixes several updates
have been made to the PX code which will be available
in future releases. None of these modifications are
necessary for use of the PX option. All of these
updates are related to surface layer and PBL
parameterizations and should be considered incremental
R&D improvements.
PBL Height
The method for determination of the PBL
height has been updated from the method described by
" on assignment to the National Exposure Research Laboratory, US Environmental Protection Agency

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Holtslag et al, (1990) to the slightly different method
suggested by Holtslag et al. (1995).
U. Estimation
We have done two things to the IJ. calculation.
We removed the minimum of 0.1 m/s and we removed
the eonvective velocity from the wind speed used in the
calculation of U. (see the MM5 model description: Grell
et al. 1994). Figure 1 shows the effects of these
changes. The curve labeled MM5 is the original
version of MM5v3.4 run at 2 km grid resolution over
central Tennessee and southern Kentucky. The curve
labeled modified is a similar model run with the U.
modifications. Note that the most pronounced effect of
the eonvective velocity is the much higher [/.values in
during the daytime. These U. values are quite unrealistic
for these low wind speed conditions (see fig.2).
stable regimes defined by Hogstrom as z/L greater than
and less than 1, respectively. The details of these
updates will be published in a technical note. An
important effect of these changes is to greatly increase
nocturnal heat flux compared to the original Blackadar
formulations.
Eddy diffusivity
The current release of pxpbl includes the
asymmetric eonvective model (ACM) which is a
modification of the Blackadar (1978) non-local scheme
for eonvective conditions. For non-convective
conditions the eddy diffusivity is estimated according to
Blackadar (1979) as in hirpbl. Since v3.4 we have
updated the length scale such that it increases with
heigth above ground with an asymptotic limit of 80 m.
We also changed the Richardson number function to be
U, obs
U. MM5
U modified
CC 0,3
Jul/4	Jul/5
Figure 1. Observed arid modeled U. at Keysburg, KY
Jul/6
Flux-profile relationships
Hie technique for estimating the _ functions
from bulk Richardson number has been updated to
conform more closely to the Hogstrom (1988)
functions. The method in the current v3.4 release is
essentially the same as in hirpbl (Blackadar 1979) using
the 4 stability regimes. We have eliminated regime 3,
which simply set the _ functions to zero, and have
changed regimes 1 and 2 to reflect the stable and very
similar to the form suggested by Liu and Carroll
(1996). The net effect of these changes is to greatly
decrease eddy diffusivity under stable conditions.
Figure 2 shows the aggregate effect of these
changes on wind speed at a site in southern Kentucky as
simulated by MM5 at 2 km grid resolution. After all
these updates the layer 1 wind speed (-19 m AGL)
generally increases, especially at night. However, when
adjusted to 2.5 m height using surface layer similarity

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theory, the model results compare very favorably with moisture initialization is less important than for other
the 2.5 m observations.	LSMs. We have shown that when using the soil
6
t Obs (2.5 m)
	MM5 (layer 1)
	Modified (layer 1}
—M—Modified (2,5 m)
5
4
TJ 3
a.
1
0 J—
Jul/4
Jul/5
Jul/6
Figure2. Observed and modeled windspeed at Keysburg, KY.
5. USER GUIDANCE
For detailed instructions on how to run the PX
LSM the reader is referred to the NCAR MM5 website
under the heading "What's New in Version 3 since its
Release In this paper we offer additional guidance on
soil moisture initialization, chaining together long
series of runs, soil moisture data assimilation, and
vegetation growth options.
The two LSM options now available in the
MM5 system as well as future additional LSMs have
many similarities but also many important differences.
The choice of model depends on the application since
each model was developed for different purposes. The
PX LSM was developed for mesoscale meteorology
modeling used to drive atmospheric chemistry models
for air quality research and policy. Therefore, the PX
LSM was designed to be run primarily in retrospective
mode for extended periods (weeks to months). Key
parameters for air quality applications include PBL
height, air temperature, boundary layer winds, and
surface fluxes.
Given our emphasis on long-term retrospective
modeling, the indirect soil moisture data assimilation
scheme and the vegetation growth algorithms are
important features of the PX LSM. Consequently, soil
moisture nudging scheme with very different soil
moisture initializations the simulations converge in
about 3-6 days (see Figure 3). Because the soil
moisture assimilation scheme uses the surface analyses
of temperature and humidity, the analysis FDDA
options must be activated.
0 3 ....... 	^		t-j
'	in-Low init
g	¦ ——.Hign init
I o.28.:
I 0.26.: \
"o	¦		
E
=5 0.24.1
m
J 0.22.1
u
£ ;
Jun/16 Jun/17 Jun/18 Jun/19
Figure 3. Deep (lm) soil moisture modeled at
Dickson, TN with 2 different initializations
Typically we run 4-5 days then start the next
run with a 2-12 hour overlap for spin-up. Soil
moisture can be initialized in three different ways: 1. a
-Low init
-Hign init
S.	
Jun/16 Jun/17 Jun/18 Jun/11

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generic initialization based on the moisture availability
factor by land use, 2, interpolation from the Eta
analyses of soil moisture, and 3. directly from
MMINPUT. The first two options are used for the first
of a series of runs. The third option is used to chain
together runs into a continuous simulation. A utility
program call Interppx is used to extract soil moisture
and temperature for the initial time from a previous
MMOUT file which are then added to MMINPUT.
There are three vegetation growth options that
can be important for extended runs to account for
seasonal changes in vegetation parameters. The first
option uses the monthly VEGFRAC fields provided by
Terrain to scale LAI and vegetation fractions for each
grid cell. The second option estimates LAI of natural
vegetation according to the model's deep soil
temperature and estimates LAI, roughness length, and
vegetation fraction of agricultural vegetation using
simple growth algorithms starting from crop
emergence, which is estimated from gridded planting
data information read in from an additional ASCII file.
Note that this option was created for a specific project
studying pesticides where the focus was on agricultural
areas. The third option is similar to the second except
that the planting dates are estimated from the
VEGFRAC fields thus obviating the need for the
additional planting date input file. The second and third
options were specifically designed for the winter-spring-
summer transition. These schemes are particularly well
suited for simulating year-specific leaf-out and early
season crop growth, but they are not recommended for
the autumn season. Note that the PX LSM aggregates
vegetation parameters by grid cell from fractional land
use and soil data rather then using the dominant land use
category.
6.	FUTURE WORK
Evaluation and development efforts are
continuing. Our current focus is the simulation of the
SOS Nashville 1999 field experiment.
Ideas for future development include comparison of the
current Jarvis-type stomatal conductance model with a
photosynthesis based stomatal model. If the
photosynthesis model proves superior, the current
scheme will be replaced. Another goal is to decouple
the LSM from the PBL model so that other PBL
models could be used with the LSM.
7.	ACKNOWLEDGMENT
Our thanks to Tilden Meyers of NOAA/ARUATDD in
Oak Ridge, TN for providing the measurement data
from the Keysburg, KY site.
8. REFERENCES
Blackadar, A. K., 1978: Modeling pollutant transfer during
daytime convection. Preprints, Fourth Symp. on
Atmospheric Turbulence, Diffusion, and Air Quality,
Reno, NV, Amer. Meteor. Soc., 443-447.
Blackadar, A.K., 1979: High resolution models of the
planetary boundary layer. Advances in Environmental
Science and Engineering, 1, Pfafflin and Ziegler, Eds.,
Gordon and Briech Sci. Publ., New York, 50-85.
Bouttier, F., J. F. Mahfouf, and J. Noilhan, 1993: Sequential
assimilation of soil moisture from atmospheric low-
level parameters. Part I: Sensitivity and calibration
studies. J. Appl. Meteor. 32, 1335-1351.
Grell, G. A., J. Dudhia, and D. R. Stauffer, 1994, A
Description of the Fifth-Generation Penn State/NCAR
Mesoscale Model (MM5). NCAR Technical Note,
NCAR/TN-398+STR, 122 pp.
Hogstrom, U., 1988: Non-dimensional wind and
temperature profiles in the atmospheric surface layer.
Bound.-Layer Meteorol., 42, 55-78.
Holtslag, A. A. M, de Bruijn, E. I. F., and Pan, H.-L.,
1990: A high resolution air mass transformation
model for short-range weather forecasting. Mon. Wea.
Rev., 118, 1561-1575.
Holtslag, A. A. M, E. V. Meijgaard, and W. C. DeRooy,
1995: A comparison of boundary layer diffusion
schemes in unstable conditions over land. Bound. -
Layer Meteorol., 76, 69-95.
Liu, M. and J, I. Carroll, 1996: A high-resolution air
pollution model suitable for dispersion studies in
complex terrain. Mon. Wea. Rev., 124, 2396-2409.
Noilhan, J., and S. Planton, 1989: A simple parameterization
of land surface processes for meteorological models.
Mon. Wea. Rev., 117, 536-549.
Pleim, J. E., and J. S. Chang, 1992: A non-local closure
model for vertical mixing in the convective boundary
layer. Atmos. Environ., 26A, 965-981.
Pleim, J. E„ and A. Xiu, 1995: Development and testing of
a surface flux and planetary boundary layer model for
application in mesoscale models. J. Appl Meteor,,
34, 16-32.
Pleim, J. E, and A. Xiu, 2000: A new land-surface model in
MM5. Preprints of The Tenth PSU/NCAR Mesoscale
Mode! Users* Workshop, June 21-22, 2000, Boulder, CO
Xiu, A., and J. E. Pleim, 2001: Development of a land
surface model part I: Application in a mesoscale
meteorology model. J. Appl. Meteor., 40,192-209.
DISCLAIMER
This paper has been reviewed in accordance with the US
Environmental Protection Agency's peer and
administrative review policies and approved for
presentation and publication.

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NERL-RTP-AMD-01-127 TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-01/082
2.
3
4. TITLE AND SUBTITLE
Updates and Evaluation of the PX-LSM in MM5
5.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Jonathan E. Pleim1 and Aijun XiuJ
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
'Same as Block 12
'Environmental Programs, MCNC, North Carolina
Supercomputing Center, Research Triangle Park, NC 27709
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Research and Development
National Exposure Research Laboratory
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
Proceedings, FY-01
14. SPONSORING AGENCY CODE ,
EPA/600/9
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Starting with Version 3.4 there is a new land surface model known as the Pleim-Xiu
LSH available in the MM5 system. Pleim and Xiu (1995) described the initial
development and testing of this land surface and workshop proceedings provided a
basic description of the model and some evaluation (Pleim and Xiu, 2000). A recent
journal article (Xiu and Pleim, 2001) presents a more detailed description of the
LSM and its implementation in MM5 and further evaluation. This paper outlines some
bug fixes, updates, guidance for use, and more evaluation.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED
TERMS
c.COSATI



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RELEASE TO PUBLIC
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4
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