January 12, 1999
Dallas, Texas


Attending: Michael MacCracken (National Assessment Coordination Office, US Global Change Research Program), Daniel Caya (Université du Québec à Montréal), Sebastien Biner (Université du Québec à Montréal), Pete Robertson (NASA Marshall), Jan Paegle (Univ. of Utah), John Roads (Scripps Institute of Oceanography), Uri Stein (Univ. of Maryland), Michael Fox-Rabinovitz (Univ. of Maryland), Jack Katzfey (CSIRO), Chuck Hakkarinen (EPRI), Roger Pielke Sr. (Colorado State Univ.), Tom Wigley (NCAR), Rick Lawford (NOAA), Zaitao Pan (ISU), Chris Anderson (ISU), Song-You Hong (NCEP), Jinwon Kim (Lawrence Berkeley National Laboratory), Bill Gutowski (ISU), Gene Takle (ISU), and Ray Arritt (ISU)


The meeting was preceded by a buffet dinner courtesy of EPRI. Gutowski thanked attendees for their participation and Hakkarinen for making arrangements. Attendees introduced themselves and the agenda was briefly viewed.


The group reviewed various past and upcoming meetings relevant to PIRCS:


Hakkarinen provided background on recently completed runs of the NCAR CSM on a NEC SX-4 in Japan. Wigley then gave an extended description of these runs, which were completed in December 1998. The CSM was run at horizontal resolution T42. The period 1870 to about 2000 was run at NCAR and then the period 1980-2100 was run in Japan for two scenarios: business-as-usual, and CO2 stabilization around 550 ppm. The runs included direct sulfate forcing only, which corresponds to radiative forcing of about –0.6 W m-2. It is planned that a future run will include solar variability. The ocean was initialized to representative SSTs for the late 19th century. The SO2 emissions are very different from IS92a and most previous scenarios in that emissions reduce by about 60 percent by 2075.

Two 20-year data records were saved at 6-hourly intervals for driving regional models. It will be at least another month before the runs have been sufficiently evaluated to release. Pielke noted possible consequences of the fact that the CSM runs don’t include land use changes.

Overview of PIRCS 1b (1993 flood)

The group discussed diagnostics for PIRCS 1b. The ISU group has constructed a 0.5 degree precipitation analysis from NCDC data and compared this to predicted precipitation for 1993 for several models. All models reproduced the precipitation maximum over the north-central US and did not have the spurious precipitation maximum in the southeastern US that appears in the NCEP/NCAR reanalysis. (Hong mentioned that this was corrected in Reanalysis-2 with the new convection and PBL schemes adopted in 1995.) Magnitudes of predicted precipitation maxima corresponded reasonably well to observations. A presentation in the GCIP meeting earlier that evening noted that 12-24 hour precipitation forecasted in the ECMWF reanalysis gives error of 10-20%, to which absolute errors of PIRCS models compare favorably.

The question of "value added" by mesoscale simulations was raised. It was suggested that we look at the intense rainfall events in comparison with time history of rainfall over the Upper Mississippi River area to see if models again are able to capture individual events. The stationary front over the central US was important for the flood and may represent value added for mesoscale models. We also should check if the nocturnal precipitation max shows up in 1993. Roads suggested that since the LLJ was stronger in 1993 the nocturnal maximum may be better captured. Lawford asked what is the added value for the surface data and can we understand the process. Hong suggested we look at individual heavy precipitation events, e.g. 7 July 1993. Roads recommended comparison to daily gridded precipitation.


Reviewers of the JGR paper on the Experiment 1a results say there needs to be more analysis. Analysis of the 1988 case is hindered somewhat by the lack of profiler observations. We need to explain common problems and collective biases among the models. There is a European model comparison report that provides an example of ways to do analysis. A specific addition to the analysis is cumulative precipitation maps compared to the 0.5 degree precipitation analysis produced by the ISU group. Presently the comparison focuses too much on the large scale flow. Gutowski suggested diagnosis of mesoscale circulation for the precipitation episode on Day 160 in 1988, which apparently was an organized mesoscale system. Another diagnostic is predicted precipitation in the southwest US monsoon for 1988. While all models show an indication of monsoon onset, some give unrealistically large precipitation.

There was discussion regarding a follow-up paper on Experiment 1b. It was suggested that we look at the intense rainfall events in comparison with time history of rainfall over the Upper Mississippi River area to see if models again are able to capture individual events. Kim mentioned that the models can produce most events in western U.S. where precipitation is anchored to the terrain. There was discussion as to whether models can be expected to reproduce specific events. Katzfey suggested we look at whether mesoscale processes generally can be produced, not necessarily specific events. We have profiler data available for 1993 for evaluating the predicted wind field, especially the low-level jet.

Results from a stretched grid model

Michael Fox-Rabinovitz showed results for several simulations of the 1988 case. These included both a uniform resolution GCM and a stretched grid model driven with observed SSTs. Output was also shown for data assimilation with data withdrawn over target area as an "imitation" of the nested grid approach. This method shows very good results. There was general agreement that PIRCS should include variable-resolution models.

Future activities

Roads mentioned that Rick Lawford is asking for observations for a climatology of the Mississippi River basin. PIRCS may be able to contribute evaporation simulations or energy budget information.

The group briefly discussed some sensitivity experiments. Results were shown from grid extension experiments for the 1993 flood, done at ISU by Zaitao Pan. Extending the domain to the south or east produced a similar or slightly improved precipitation field compared with the standard PIRCS domain while extending the domain to the west produced worse results. Arritt mentioned that extending the domain westward pushes the inflow boundary into a data-poor region (the Pacific Ocean). Hong showed simulations comparable to Seth and Giorgi (1988, J. Climate) which gave different results for soil moisture sensitivity. Notably, Hong found there always was positive feedback from soil moisture to precipitation amount.

Possible follow-up experiments were briefly discussed. Among the ideas presented were a multi-year simulation using the present domain; repeating the runs for 1988 and 1993 at higher resolution; and intercomparison for the Amazon region for comparison with forthcoming LBA results. It was agreed that PIRCS should develop closer affiliation with AMIP.

The next meeting of PIRCS modelers is not likely before Fall AGU. Hakkarinen encouraged planning for a next meeting. A paper describing 1993 results should be prepared by Fall AGU, preferably sooner. Continuing to publish results is important for modelers to justify participation in PIRCS.

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