5 - 6 June 1997
Jointly Sponsored by the
Electric Power Research Institute
and the
International Institute of Theoretical and Applied Physics


The Project to Intercompare Regional Climate Simulations (PIRCS) held its second modelers workshop 5 - 6 June 1997 at Iowa State University, Ames, Iowa, USA. Twenty-five scientists representing sixteen modeling groups attended. The overall goal of PIRCS is to advance the status of regional climate simulation using atmospheric mesoscale models. In accordance with this goal, active participants convened several months after the release of the boundary conditions for the first PIRCS simulation experiment (Takle, 1995) to discuss several topics:

An underlying theme of these discussions was the challenge presented to the mesoscale climate modeling community by the Working Group on Numerical Experimentation (WGNE) to evaluate thoroughly the feasibility of using mesoscale models for climate simulation.

PIRCS Experiment 1 was established during the first PIRCS workshop in November 1994 (Takle, 1995). Participants at that workshop determined that the initial experiment should focus on the central U.S. drought of 1988 (Exp. 1a) and floods of 1993 (Exp. 1b), two periods offering strong signals of climate variability for the models to reproduce. These choices were motivated also by the substantial observational record available for evaluating simulations and the interest of the GEWEX Continental-Scale International Project (GCIP) in these episodes. A prominent mesoscale feature of this region is a nocturnal, low-level jet that plays a central role in the region's hydrologic cycle. Participants in the November 1994 workshop and follow-on discussions developed a standard output archive for participating models for diagnosing this feature and its interaction with regional energy and water cycles.

Workshop II was supported by the International Institute of Theoretical and Applied Physics (IITAP) at Iowa State and the Electric Power Research Institute (EPRI). Early in the workshop, James Vary, Acting Director of IITAP, reviewed IITAP's support of PIRCS in the context part of IITAP's goal as a UNESCO-sponsored institution to promote forefront research by scientists in developing countries. He also surveyed participants later in the workshop for their collaboration with developing country scientists, stating that IITAP may be able to sponsor such interaction. Chuck Hakkarinen, of the EPRI Environment Group, noted that EPRI has supported substantially efforts to understand climate change on the regional scale, partly to aid the Intergovernmental Panel on Climate Change (IPCC) in its periodic review of the science of climate change and its impacts on human society. Comments by Vary and Hakkarinen provided a broad context for the ensuing discussions.


The initial and boundary conditions for Experiment 1, particularly soil moisture, generated substantial discussion. The relatively short lengths of Exps. 1a and 1b (60 days) prevent models from spinning up their own soil moisture field, so their simulations may be sensitive to the initial condition, which is poorly observed. (Informal discussion at the workshop suggested that 90 days or more of simulation is necessary to spin-up soil moisture.) The experiment's initial soil moisture and atmospheric boundary conditions come from the reanalysis (Kalnay et al., 1997) produced by the U.S. National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR). John Roads showed that the NCEP/NCAR reanalysis soil moisture is damped toward a specified climatology and so may not capture fully the climatological extremes of Exp. 1. Anji Seth relayed a suggestion from Filippo Giorgi that PIRCS provide multiple sets of initial soil moisture for a suite of simulations that would reveal sensitivity to this specification. No definitive conclusion was reached at the workshop, but the PIRCS organizers will continue to discuss this suggestion by electronic mail with participants and possibly prepare alternative initial soil-moisture conditions. William Gutowski noted that one of the intents of PIRCS is to provide a common framework for sensitivity studies, such as the one suggested here, so that such simulation would be encouraged even if not formally part of Exp. 1. Finally, John McGregor pointed out that deep-soil temperature also needs to be included in the initial conditions.

The original PIRCS Exp. 1 boundary conditions specified monthly mean sea-surface temperature (SST). Michael Botzet showed how regional simulations could be sensitive to temporal evolution of SST, suggesting that SST should be updated from observations more frequently than monthly. Song-You Hong stated that the NCEP/NCAR reanalysis updates SST to daily intervals by interpolating weekly observational values. Participants generally agreed that while the simulation domain for Exp. 1 does not contain substantial ocean, PIRCS should nonetheless specify SST more frequently than monthly, in part to maintain consistency with the NCEP/NCAR atmospheric reanalysis output used for boundary conditions.

Further discussion of boundary conditions focused on specified surface properties. There was substantial disagreement over whether or not standards should be enforced for these and other specified features such as surface roughness and albedo. One group felt that adherence to such standards would reduce uncertainty over the causes of inter-model differences. Another felt that model surface specifications are determined in part for compatibility among all model parameterizations present and that the greater value of PIRCS simulations lies in comparing model performance with observations. Participants agreed, however, that PIRCS organizers should give maps of standard vegetation distributions and topography on the PIRCS Web site, both as references and to establish map contouring and coloring standards.


Another area of substantial discussion was the standard output archive that PIRCS organizers will collect from the modelers and maintain. The workshop gave the modelers an opportunity to review this archive after some had run initial simulations. Special attention focused on output for comparison with observations and output for inter-model diagnosis of mesoscale behavior.

Participants recommended that the standard archive continue to emphasize diurnal cycles of energy and moisture fluxes at the surface. However, several consensus modifications emerged:

Modeling groups are encouraged to submit a supplemental data set:

All participants agreed that having a variety of observations available would be of great benefit to individual as well as collective efforts to understand model behavior. Comparison with observations will also be necessary for addressing the WGNE challenge described above. These observations will be collected by PIRCS. Summary plots of observations will be displayed on the PIRCS Web site (http://www.pircs.iastate.edu) to allow modelers an initial check of their output with observations and also to establish map contouring and coloring standards for comparative study. Observations will emphasize diurnal variations, especially those like precipitation that are closely linked to mesoscale behavior such as the nocturnal, low-level jet. Some specific observational fields include hourly precipitation from first-order stations, four-times daily NCEP and ECMWF analyses, daily maximum/minimum temperatures, and satellite observations of radiative fluxes.

Several models performed Exp. 1a before the workshop and participants informally compared their preliminary output, with several noteworthy features emerging. Models generally showed agreement with the observed time-average, large-scale circulation, though there were differences in details that were rather large at some points. Low-level jet output showed a diurnal variation with maximum strength at night. The degree of agreement in simulated precipitation between models and with observations varied greatly. Additional simulations and further diagnosis are clearly needed.


Concluding discussions focused on the time table for Exp. 1a. Workshop participants agreed to the goal of completing the updated Exp. 1a and producing its output archive by the end of 1997. This archive will be the basis for one or two initial scientific papers. The end-of-1997 goal does not preclude later participation by other models. Participants also agreed that PIRCS should explore hosting a PIRCS participants review session in San Francisco that coincides with the December 1997 American Geophysical Union meeting.

Final discussions considered potential follow-on PIRCS experiments. Jens Hesselbjerg Christensen advocated a suite of simulations with relevant observations and model output that any person with a new model might run to assess model performance. Potential sites discussed included South-east Asia, southern Africa and South America. In this light, Clemente Tanajura presented some results from mesoscale simulation of the South American low-level jet.


Ray Arritt
Department of Agronomy
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-9870
fax (515) 294-3163
email: rwarritt@iastate.edu
Sebastien Biner
Département des sciences de la terre
Université du Québec à Montréal
C.P. 8888, Succursale "Centre-Ville" Montréal (Québec) H3C 3P8
tel. (514) 987-3000 #6813
fax (514) 987-7749
email: biner@phy.uqam.ca

Michael Botzet
Max Planck Institute for Meteorology
Bundesstrasse 55
D-20146 Hamburg
tel. +49-40-41173-374
fax +49-40-41173-298
email: botzet@dkrz.de

Daniel Caya
Département des sciences de la terre
Université du Québec à Montréal
C.P. 8888, Succursale "Centre-Ville"
Montréal (Québec) H3C 3P8
tel. (514) 987-3000 #3126
fax (514) 987-7749
email: caya@phy.uqam.ca

Jens Hesselbjerg Christensen
Danish Meteorological Institute
Lyngbyvej 100
DK-2100 Copenhagen
tel. +45-39157428
fax +45-39157460
email: jhc@dmi.min.dk

Dave Flory
Department of Geol. & Atmos. Sciences
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-4758
fax (515) 294-3163
email: flory@iastate.edu

Bill Gutowski
Department of Geol. & Atmos. Sciences
Iowa State University
3021 Agronomy
Ames, IA 50011-1010
tel. (515) 294-5632
fax (515) 294-3163
email: gutowski@iastate.edu

Chuck Hakkarinen
Electric Power Research Inst.
3412 Hillview Avenue
Palo Alto, CA 94304-1395
tel. (415) 855-2592
fax (415) 855-1069
email: chakk@eprinet.epri.com

Song-You Hong
5200 Auth Road, Room 207
Camp Springs, MD 20746
tel. (301) 763-8000, ext. 7014
fax (301) 763-8545
email: songyou.hong@noaa.gov

Yimin Ji
4322 Rowalt Drive #102
College Park, MD 20740
tel. (301) 902-1273
fax (301) 595-9793
email: ji@cola.iges.org

Jinwon Kim
Lawrence Livermore Nat. Lab
L-256, PO Box 808
Livermore, CA 94551
tel. (510) 422-1848
fax (510) 422-6388
email: kim1@LLNL.gov

Bill Lapenta
Global Hydrology and Climate Center
NASA Marshall Space Flight Center
977 Explorer Blvd.
Huntsville, AL 35806
tel. (205) 922-5834
fax (205) 922-5723
email: bill.lapenta@msfc.nasa.gov

Glen Liston
Department of Atmospheric Science
Colorado State University
Fort Collins, Colorado 80523-1371
tel. (970) 491-7473
fax (970) 491-8449
email: liston@iceberg.atmos.colostate.edu

John McGregor
CSIRO, Div. of Atmospheric Research
PB1 Aspendale
Victoria 3195
fax +61-3-9239-4444
email: jlm@dar.csiro.au

Zekai Otles
Department of Geol. & Atmos. Sciences
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-0264
fax (515) 294-3163
email: zekai@iastate.edu

Jan Paegle
819 Browning Building
Meteorology Department
University of Utah
Salt Lake City, UT 84112
tel. (801) 581-7180
fax (801) 585-3681
email: jpaegle@atmos.met.utah.edu

Zaitao Pan
Department of Geol. & Atmos. Sciences
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-0264
fax (515) 294-3163
email: panz@iastate.edu

Renato Ramos Da Silva
Department of Geol. & Atmos. Sciences
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-2551
fax (515) 294-3163
email: renato@iastate.edu

John Roads
Scripps Institution of Oceanography
UCSD 0224
8605 La Jolla Shores Dr., NH 441
La Jolla, CA 92093-0224
tel. (619) 534-2099
fax (619) 534-8561
email: jroads@ucsd.edu

Moti Segal
Department of Agronomy
Iowa State University
3027 Agronomy
Ames, IA 50011-1010
tel. (515) 294-2804
fax (515) 294-3163
email: segal@iastate.edu

Anji Seth
Institute for Atmospheric Physics
PAS Bldg 81
University of Arizona
Tucson, AZ 85721
tel. (520) 621-6840
fax (520) 621-6833
msg. (520) 621-8836
email: seth@halo.atmo.arizona.edu

Andrew Staniforth
Recherche en prévision numérique
Environnement Canada
5e étage
2121 route Transcanadienne
Dorval, P.Q. H9P 1J3
tel. (514) 421-4748
fax (514) 421-2106
email: Andrew.Staniforth@ec.gc.ca

Gene Takle
Department of Geol. & Atmos. Sciences
Iowa State University
3013 Agronomy
Ames, IA 50011-1010
tel. (515) 294-9871
fax (515) 294-3163
email: gstakle@iastate.edu

Clemente A. S. Tanajura
Rodovia Presidente Dutra km 40
Cachoeira Paulista SP 12630-000
tel. +55-12-560-8479
fax +55-12-561-2835
email: cast@cptec.inpe.br

Rafael Terra
UCLA, Department of Atmospheric Sciences
Box 951565
Los Angeles, CA 90095-1565
tel. (310) 825-7407
fax (310) 206-5219
email: rterra@atmos.ucla.edu

Dennis Todey
Department of Agronomy
Iowa State University
3010 Agronomy
Ames, IA 50011-1010
tel. (515) 294-4758
fax (515) 294-3163
email: dptodey@iastate.edu

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