1994: Tracking Storms: Observations and Simulations

Storms are responsible for mixing heat and moisture between the low and high latitudes. They transport tropical air (warm and moist) poleward, while polar air (cold and dry) is transported toward the equator. In the mid-latitude regions storms do not occur uniformly, rather they are concentrated in preferential regions of the respective hemispheres referred to as storm tracks. The Jet Stream, a region of high speed winds at some 30,000 feet, moves or steers weather systems along, including storms.

The weather of a region averaged over longer time scales is known its the climate of that region. Because precipitation and temperature are dependent on the storm track, the proximity of a given region to the predominant storm track is essential in determining the climate. Also, if the storm track shifts in its location, this will have a significant impact on the regions climate. The summer of 1993 and the winter of 1994 are good examples of how the weather and climate are impacted by storm tracks. In the summer of 1993 the Jet Stream was anomalously south and strong over the center of the country, causing historic flooding. In the winter of 1994 two components of the Jet Stream combined over the Northeast, bringing continuous cold, snow and sleet.

If storms are one of the most important factors in shaping the climate of the mid-latitudes, then a greater understanding of the climate in the mid-latitudes could be gained by knowing the storm tracks and their shifts across the globe. This understanding can help predict future storm tracks and ultimately, improve predictions of the Earth's future climate.

Knowing the climatology of the Northern Hemisphere storm tracks is essential for any complete study of the region's climate. Despite its importance, limited research exists in studying storm tracks. There are many reasons contributing to this problem. Questions and debate surround the exact importance of storm tracks to the overall climate. Also, there are problems in defining storms. Only recently, have computer models acquired the sophistication to simulate or predict future storm tracks to the extent they can be compared with observations.

Our GISS Summer Institute research team will compile a decadal and yearly climatology of storm tracks in the Northern Hemisphere. Monthly and seasonal analysis will also be included. Storms are most universally defined as local minimums in the sea-level pressure field. GISS has obtained a complete data set of semi-daily, Northern Hemisphere, sea-level pressure field for the past 50 years.

We plan to compare the storm climatologies to other climate parameters, i.e. temperature and precipitation, to determine the significance of storm tracks to the overall climate. After storm tracks are developed from observations, similar storm track climatologies will be compiled for the GISS general circulation model for comparison. Such a comparison will help us access the model's ability to simulate current climate and predict future climate.

Research Tasks and Scientific Questions

Understand the importance of storms and storm tracks.

Learn to contour various parameters found on synoptic surface maps, e.g. temperature, pressure and winds.

Learn to contour fronts and storms on synoptic surface maps and compare to surface maps contoured by National Weather Service.

Learn to use the storm track program and examine storm definitions other than the one used in the program for the purpose of comparative analysis.

Plot individual storm tracks using the default settings of the storm track program and compare with storm path as shown on daily surface maps to validate storm tracking program for plotting primary and secondary storms. Vary default settings to analyze changes in the storm track.

• How do storm tracks in daily weather maps compare to plots from the storm track program in terms of frequency, intensity, severity and track?

Prepare and analyze storm track clinaatologies for production of an Atlas. Prepare monthly and seasonal plots for decadal and yearly periods.

• How do storm tracks vary over different seasonal scales?
• How do other parameters/patterns associated with storm tracks vary?
• Do monthly storm tracks shift within a season?
• Are there changes in the storm tracks during El Niño years or the Pinatubo period?

Compare and analyze observed storm tracks with those generated by the GISS general circulation model.

• What are the differences and similarities in terms of frequency, intensity, track, severity?
• How well does the model simulate current storm tracks?

Key Concepts

• Cyclone
• Central sea-level pressure Isobar
• Storm track
• Jet Stream
• Primary-secondary cycogenisis Climate parameters
• Surface map analysis
• Climate impacts
• General circulation model
• El Niño Climatology
• Climate anomaly