1998: Validation of the GISS General Circulation Model SI97 Version

Researchers: Rosa Andujar, Sam Borenstein, Alexandra Estrella, James Hansen, Umit Kenis, John Knox, Ron Miller, Lionel Pandolfo, Sonjae Wallace, and Josh Wilder.

Predictions about Earth's climate are of great interest to many people around the world. A high degree of confidence in climate predictions can potentially influence decisions about the place people choose to live and the use and supply of resources, such as energy and food. We are naturally interested in Earth's climate because we know that it has undergone many changes that have affected its habitability at different times in the planet's history. Today, our study is motivated by questions dealing with whether human activities that increase the amounts of atmospheric gases are warming the Earth and significantly altering our climate. The climate modeling research team is working to improve a computer model that simulates the Earth's atmosphere with the goal of understanding better physical processes such as storms and atmospheric circulation and relationships with such climate events as El Niño and Droughts. This research team is also working on an investigation that aims to understand the influence of aerosols on earth's climate, a forcing that may be causing a cooling effect that masks the actual extent of warming occurring. By improving our knowledge of these climate processes and variables, researchers at ICP hope to make important improvements to the General Circulation Model (GCM) and improve the confidence we have in GCM predictions about future climate.

Project Goal for 1998-99

Following up on the research done over the last academic year, and based upon meetings with J. Hansen, R. Miller, and J. Knox, we propose to continue to validate the improved version of the GISS GCM, which attempts to simulate the behavior of the earth's atmosphere, and in particular to study the realism of its response to forcings such as prescribed Sea Surface Temperature (SST), prescribed Greenhouse gases, and imposed aerosols. The current version of the model differs from previous versions primarily from the increase in the number of vertical layers, which has been increased from 9 to 12, with particular attention to the stratosphere. In addition a number of improvements in the basic underlying physics of the planetary boundary layer and of cloud formation have been implemented. One of the questions is does this eliminate the excessive Canadian surface warmth in DJF, and are the long wave anomalies in the stratosphere changed? Another question is whether the overall correlation between model and observations over the time period 1950 to the present is improved.

Science Questions

1. How realistically does the climatological average of the GCM represent the behavior of the real world in terms of the geographical and seasonal distribution of key diagnostic variables such as temperatures at various vertical levels and precipitation?
2. To what extent do the forcings imposed upon the transient runs over the time period 1950-97 correlate with observational data over the same time period?
3. Under what circumstances does the signal associated with a forcing stand out above the intrinsically chaotic behavior of the climate?

Hypotheses

1. The predictability of the model is better at low latitudes than at high latitudes.
2. During strong forcings conditions such as El Niño, there are some geographical regions which display higher than normal predictability.

Research Tasks

Summer Forecast: A seasonal forecast for summer 1998 using the SST values as of June 1, 1998, has been submitted to the Experimental Long-Lead Forecast Bulletin. We plan to validate this forecast as the June, July and August observational data become available.

Model Development

Transient Experiments: In order to discover whether the improved vertical resolution of the 12 layer model, as well as some of the new boundary layer and cloud physics have improved the performance of the model, we plan to study the results of the transient SI97 experiments, both to see how the results for the period 1979-95 differ from those obtained with SI95 model, and to begin to look at results for the period 1951-97. Many of the plots are from the Forcings & Chaos Paper, JGR, Vol. 102, NO. D22, pp25,679-25,720, Nov. 27, 1997.

1. Temperature Change: Here we will study the evolution of surface temperature, Ts, upper tropospheric temperature (MSU2) and stratospheric temperature (MSU4) with time.
2. Predictability: Study correlations of runs among themselves, correlation between model and observation over the entire time period as well as for selected years where the El Niño signal is particularly strong in either direction.
3. Diurnal Cycle: Compare the Diurnal cycle evolution in the model with observations. Answer the question as to : whether the model captures the changes in the observational record.

Climatological Experiments: In addition to the transient studies, we plan to assign introductory tasks for the new members of the modeling group. These tasks will look at climatological results. In our particular subgroup, we will have the new students compare global maps of temperature at 3 levels in the current GCM and compare these with the real world. The three levels are the surface, MSU2 and MSU4. We would like both DJF and JJA. From this we hope to learn whether, in general, SI97 is more realistic than the earlier models - e.g., is the excessive Canadian surface warmth in DJF improved and how about the long wave anomalies in the stratosphere?

Curriculum Development - Climate Index Projects:

1. Along the lines proposed by John Knox, have early workshops, in which students define their own climate or comfort index, and use current data to measure it.
2. See if there is a measurable Urban Heating effect reflected in the climate index that is on the Web. Have the students download station temperature data for nearby stations, and paste this data into Excel, and study the relationship among the time series of various stations.