Konza Prairie Storm Climate

We have a tendency to think of climate change as that which is about to bash us. We worry, fret and spend money on our estimates of the future. Those of us who like to watch climate change find no shortage in the century long record of the state of our atmosphere. At the request of the Konza LTER group, I recently took a look at the history of climate over their fair site and had the pleasure to report back that their climate had not been constant. One area in which we found important century long variations in Konza climate was in the passage of storms through their area. The storms in question were those that we normally see attached to fronts. The tend to move eastward and northward. Many of these storms first appear on our weather maps along the eastern slopes of the Rockies and the high prairies of the Prairie Peninsula of North America. At the University of Virginia we have been counting these storms and torturing the resulting data set for many years. Our records begin in 1885 and we update the data every so often or when money is available. We tabulate the daily occurrence storms in 2.5 by 5.0 degree latitude by longitude grid cells and sum the tabulation for each month. We do all the continental US and most of southern Canada as well. It is a lot of data. The Konza Prairie is within cross-hairs of our sights.

Storms on the prairies arise from disturbances, vortices, that come ashore on the west coast and travel across the mountains. These systems reform as cyclones along fronts. The main sites of reformation of these storms are the Gulf Coast of Texas, West Texas, central Colorado, southern Wyoming, and Calgary. Hayden (1981), in a study of North American storminess, found that the mean annual number of cyclones over the Prairie Peninsula was greatest around 1915 and reached a minimum in frequency around 1965. This pattern is evident counts of storms in most areas of the Prairie Peninsula. The annual frequency of cyclones over the eastern Kansas shows this long period climate change very well. The change is nearly sinusoidal with a maximum number storm (>25 per year) around 1906 and a minimum near zero around 1965.

We used storm count records for 38 2.5 degree lat by 5.0 degree lon grid cells extending from the 100th meridian for the period that begins in 1885. The resulting data matrix had the dimensions of 38 grid cells x 1272 months. An S-mode principal components analysis of this data set was run. This analysis follows the procedures of Hayden (1981,1982). Six storm tracks were defined by the principal components of storm frequency but we will only look at the one that crosses Konza's back door. This storm track arises out of west Texas and is aligned northeastward crossing Oklahoma, Missouri, Illinois, Indiana, Ohio and on to New England. This track follows the southern margin of the Prairie Peninsula eastward toward New England. The PCA component for the track explained 24.9% of the total variance in the data set.

Analysis of the factor scores for each month of the record reveal the climatic history of the utilization of this track by storms. The average monthly and average annual component scores for component 1 with negative factor scores in winter (November through April) indicates that storms along this track are more frequent than average in winter and less frequent than average in summer. The time series of annual factor scores indicates a century long modulation in the frequency of storms along this storm track with a maximum frequency around 1915 and a minimum around 1970. The amplitude of the long-term change is approximately the same as the amplitude found on a seasonal basis and must be considered a major climate change.

The central axis of the southern margin of the Prairie Peninsula storm track lies just to the south and east of the Konza Prairie. If you were to cut across the contours in the illustration and plot these values it would form a normal distribution (a curve with a bell shape). Sometimes the track is parallel and to the north and sometimes parallel and to the south. As the north west quarter of a storm usually has the strongest winds and the most significant weather we can look on this storm track as providing significant weather events all along the southern margin of the North American Prairie Peninsula, including the Konza Prairie.

Since this is a track of storms that is most frequent in winter, we can look on it as important in the providing the rainfall resources to accomplish groundwater recharge and provide a positive water balance for the prairies. We could then infer that the water resources for the Konza Prairie are part of the historical climate change of the region. We should not that we do not know the cause for this climate variation. However, given the very substantial magnitude of this long-period change it will be hard to detect projected changes against this great change.

Hayden, B.P. (1981). Secular Variation in Atlantic Coast Extratropical Cyclones. Monthly Weather Review, 109(1):159-167.

Hayden, B.P., and Smith, W. (1982). Season-to-Season Cyclone Frequency Prediction. Monthly Weather Review, 110(4):239-253.

Illustration above is from Flammarion, C. 1873. The Atmosphere. Harper & Brothers, Pub. New York, NY. The illustration is not of the Konza Prairie but the Konza Prairie Offices can be seen in the distance.