Project Plans: 1994
The projects for the GISS Summer Institute on Climate and Planets involve science issues at the cutting edge of current research. The four projects are all interrelated, providing opportunities for interactions and mutual learning activities among all of the Summer Institute participants.
The Pinatubo project will examine possible causes of observed global climate changes during the past several years, and possibly make predictions for the next few years. The approach will be to take advantage of the natural climate experiment which Nature provided with the eruption of the Philippine volcano Pinatubo in 1991. This volcano injected an enormous quantity, about 15 megatons, of sulfur dioxide gas into the stratosphere, which was soon converted into a fine mist of tiny sulfuric acid droplets. That mist takes years to settle out of the atmosphere, about 5 percent of it still being in the stratosphere today. At its maximum the mist scattered back to space about two percent of the sunlight reaching the Earth, providing a mechanism which, other things being equal, should have cooled the Earth during the past three years.
Is it possible that the Pinatubo mist was responsible for the unusually cool summer of 1992 in North America and Asia, the almost equally cool summer of 1993 with record floods in the Midwest, the harsh winter in the Northeast this year? These questions can be examined with the help of a global climate model, a computer program which simulates the world's climate, by adding the sulfuric acid mist into the model's stratosphere and noting how it modifies the simulated climate. But there are many factors which complicate this procedure. First, the climate models have many deficiencies, which may affect conclusions of experiments in which a climate "forcing" such as the sulfuric acid mist is inserted. Second, the climate system involves a substantial amount of "chaos", or climate variability which occurs without any forcing. Third, there have been other forcings in the past few years, such as ozone depletion.
The Pinatubo research teams will be divided into groups, each responsible for one of the key climate parameters: temperature, precipitation, or winds. They will first examine how will the new GISS climate model can simulate the average value of their climate parameter for the past decade, including the seasonal variation of the parameter, because the seasonal change of sunlight providing a very large climate "forcing". Next they will examine the natural year to year variability of their parameter in the real world and in the climate model when there is no volcanic or other forcing, to obtain a measure of climate chaos. Then they will examine model results when the Pinatubo sulfuric acid mist is included, and compare the results with observations. If the model does a reasonably good job of simulating the climate anomalies of the past few years, it will be interesting to let the model run a few more years to make predictions for the remainder of the 1990s.
The Storm Tracks project team will examine observations and simulations of storms, which are one of the most important factors shaping climate in middle latitudes, where we and much of the world's population live. The nature of extreme climate events, such as the frequency and severity of storms, is generally of much more importance to people than are the mean values of climate parameters.
Good examples of the importance of Storm Tracks occurred during the past 12 months. In the summer of 1993 a storm track seemed stuck over the Midwest U.S., guided by a "jet stream" of upper atmospheric winds, bringing repeated rains and record floods. Then in the past winter an unusual positioning of storm tracks brought storm after storm to the Northeast U.S., with cold, snow and sleet.
The Storm Track project team will learn about storm tracks and how to use a recently developed computer program to define and plot storm tracks from meteorological measurements. A principal objective will be to prepare and analyze an atlas or climatology of storm tracks.
This atlas can then be used to examine how storm tracks vary from year to year, and whether there are systematic relationships between storm tracks and global climate phenomena such as El Niños and volcanic eruptions. Also the storm track group will compare the observed climatology of storm tracks with the nature of storm tracks in the GISS global climate model.
The Storm Track project obviously must interact with and work together with the Pinatubo project. Some of the most interesting climate events after the Pinatubo eruption involved changes of storm tracks, and analysis of the possible relation of these extreme climate events to Pinatubo requires a thorough understanding of storm tracks in nature as well as the ability of the model to simulate storms.
The Cloud project, more precisely called the "Cloud Structure Over Storm Lifecycles" project, is closely related to both the Pinatubo and Storm Tracks projects. In a general sense the Cloud project is concerned with the fundamental issue of how clouds change as climate changes.
It is generally agreed that clouds are the greatest source of uncertainty when we attempt to understand how climate will change as a result of a climate "forcing" such as the addition to the atmosphere of the Pinatubo aerosols or greenhouse gases. Clouds are obviously very important in influencing climate parameters such as temperature, and we could calculate reasonably well the effect of a specified cloud change, but we do not know how clouds will change in response to a climate forcing.
The Clouds project will help to attack the fundamental uncertainties about the role of clouds in climate change by analyzing how midlatitude clouds change over the lifecycle of large storms. Midlatitude storms, associated with cold and warm fronts in weather reports, are the primary producers of clouds in the middle latitudes where we live.
The Clouds project will study how the nature of clouds change as a storm evolves from the developing stage, to the mature phase, and finally to the dissipating stage of its lifecycle. The cloud and storm lifecycles will be studied in satellite observations, conventional meteorological data, and in the simulations of the GTSS global climate model.
This study should provide information on different cloud-making processes that occur during the life of the storm, and the nature of the clouds produced by each process. This will allow a testing of the climate model used in the Pinatubo and Storm Track projects, and hopefully it will point the way to improvements of climate models in the future.
The Jupiter project, an investigation of stratospheric aerosols in the Jovian atmosphere, is of much scientific interest in its own right, and it also has strong relations to the terrestrial projects. Just as on Earth, fine particles in the upper atmosphere of Jupiter scatter and absorb solar radiation, thus influencing the temperature of the atmosphere.
However, Jovian aerosol properties are very poorly known, so there is the potential for scientific discovery in analysis of appropriate observations of Jupiter. The purpose of the Jupiter project will be to analyze observations taken by the Hubble Space Telescope and by the Voyager flyby spacecraft to try to determine cloud and aerosol properties on Jupiter.
The approach will involve examining the spectra, that is the variation with wavelength, of sunlight reflected by Jupiter and heat radiation emitted by Jupiter. These spectra tend to be influenced by the properties of the atmospheric clouds and by any aerosols located above the clouds. Locations of special interest, such as the Great Red Spot and the polar regions, will be examined and compared. Interpretation of the observed spectra will require numerical simulations of the spectra of radiation with appropriate computer programs.
1994 Projects
