1995: Storm Tracks: Observations and Simulations

Research by students from George Washington High School, Queensborough CC, Brooklyn Polytechnic, and Medgar Evers College
GISS scientist: Mark Chandler

Summary of Previous Work

During the first summer and academic year of the ICP program, this project team has worked to define and describe the pathways traveled by the mid-latitude storm systems of the northern hemisphere. These pathways, the so-called "storm tracks", define regions affected by the major cyclones that move from west to east across the heavily populated mid latitudes. The storms in these systems are responsible for much of the weather we experience in the mid latitudes, particularly in the wintertime. They are a critical component of the Earth's atmosphere that control, and which are controlled by, the Earth's climate.

The Storm Tracks team first evaluated our ability to track individual extratropical cyclones (low pressure cells) using a computer analysis technique and sea level pressure data from the National Meteorological Center. Based on comparisons with daily weather maps we fine-tuned the analysis technique and processed all of the sea level pressure data for the years 1957 through 1988, mapping the pathways of all storms that occurred during that period. In addition, we calculated seasonal storm track statistics for 1957-1988 including: storm frequency, storm intensity and most severe storm. Finally, we categorized the data based on the presence, absence and intensity of El Niños and analyzed the storm frequency for the various scenarios. All information was placed in an electronic image atlas and has been made available over the Internet via the world wide web - The Storm Track Atlas. By better defining the real-world storm tracks we have now provided a database that can be used to validate the accuracy of the storm tracks simulated by the GISS GCM and, ultimately, to predict the impact of climate change on the Earth's storm systems.

Summer 1995 Objectives

Were the 1988 midwest drought and 1993 midwest flood related to climate "forcings", i.e. was the likelihood (probability) of the drought/flood altered by climate boundary conditions?

Methods: Using the 25 GCM simulations conducted by Hansen et al. we will calculate the position, frequency, and intensity of storms over the United States and evaluate the impact of altered sea surface temperatures on the results. We will also compare the statistics from these experiments to the analysis of real-world storm tracks. This will require that we complete the processing of the NMC sea level pressure data through the year 1993.

Are the storm tracks, as calculated by the computer SLP tracking program, related to the properties of storms that have critical climatic impacts such as, precipitation and high winds?

Methods: We will use the daily precipitation records from 200 weather recording stations in the United States to correlate precipitation events with the positions of storms and storm tracks. Individual storms will be analyzed first, followed by statistical comparisons between the time-averaged characteristics of storm tracks and precipitation. When this task is complete (probably not until the end of the summer institute) we will do the same for winds.

Are there other, perhaps more accurate, meteorological and computational methods that can be used to track storm systems from observations and in the GCM?

Methods: Vorticity is an atmospheric property which can be calculated from horizontal wind data and it seems likely to provide a better diagnostic for tracking storm systems than our current technique. Consequently, we will begin to develop a computer program which calculates vorticity and which can track the pathways of high-vorticity cells. Wind data is available from the NMC analyses, as was sea level pressure, so we can validate the technique using observations. When complete we will use this new technique on GCM-generated wind diagnostics to evaluate model accuracy.