Water Resources of North Dakota

Relations Between Upper-Air Flow Patterns, Climate, and Hydrologic Variability in the Red River of the North Basin, United States and Canada

By Gregg J. Wiche and John L. Knox

Abstract: Proceedings of the North Dakota Academy of Science 89th Annuanl Meeting, April 1993

In 1990, the North Dakota District of the U.S. Geological Survey and the Hydroclimatological Section, Canadian Climate Centre, Atmospheric Environment Service, began a cooperative study to investigate the relations between large-scale atmospheric circulation anomalies in the lower troposphere and hydrologic variability in the Red River of the North basin. Large-scale anomalies in windspeed and direction, mean temperature, and pressure heights in the lower troposphere are related to hydrologic variability of the Red River of the North basin. Anomalous winds at both the 100- and 50-kilopascal (kPa) pressure surface heights and the mean temperature for the thickness of the air column from the 50- to the 100-kPa height are related to monthly precipitation within the basin for wet and dry study years. In addition, teleconnection indices at the 50-kPa height are related to high and low streamflow years. The purpose of this presentation is to describe the relations.

The Red River of the North basin is located at the eastern margin of the northern Great Plains. The Red River of the North drains about 290,000 square kilometers in parts of Minnesota, South Dakota, and North Dakota in the United States and parts of Manitoba and Saskatchewan in Canada. Upper-air flow data are available for 1946-89. A 200-year flood history is available from documents of fur traders, explorers, and missionaries, as well as from gaging station records. Several major floods occurred during the 1800's that were larger than major floods that occurred since 1946. Although the upper-air flow data can be used to describe relations between precipitation and streamflow, the relations may not represent the most extreme climatic conditions that have occurred during the last 200 years.

The Pacific-North American (PNA) teleconnection index has the largest amplitude and the most consistent change in sign relative to bimonthly precipitation for the wet and dry study years. The sign of the PNA index is negative for most bimonthly periods for the wet study years and positive for most bimonthly periods for the dry study years. The location, amplitude, and sign of the 100- and 50-kPa pressure surface height anomalies, based on bimonthly precipitation, are most strongly related to the large-scale atmospheric circulation that supports the precipitation regime.

A strong relation exists between the direction of the anomalous wind at both the 100- and 50-kPa pressure surface heights and bimonthly precipitation (wet or dry study years). For wet study years in the Red River of the North subbasins east of the river at the 100-kPa height, the anomalous wind direction is east-southeast and the anomalous windspeed is 0.5 meter per second (m/s). At the 50-kPa height, the anomalous wind direction is south and the anomalous windspeed is 2.4 m/s. For dry study years, the sign of the anomaly is reversed, indicating a prevailing anticylonic flow over the Red River of the North basin. An anomalous west-northwesterly windspeed of 0.6 m/s occurs at the 100-kPa height, and an anomalous northerly windspeed of 1.0 m/s occurs at the 50-kPa height.

The thickness of the air column from the 100- to the 50-kPa pressure surface height was used to compute the mean temperature of the air column. Temperatures for October-November, December-January, and February-March wet study years are about 1oC less than the mean (1946-89) for the Red River of the North basin, and temperatures for the dry study years are about 0.8oC greater than the mean. However, the temperature anomaly is not uniform.

The PNA teleconnection index was computed on the basis of the mean October-May 50-kPa height data for low-flow and high-flow years for the Red River of the North basin. Even for this 8-month mean, the PNA index for low-flow years is positive. For the low-flow years, an elongated north-south oriented central cell whose axis intersects latitude 50o north at about longitude 120o west exists. A negative PNA index occurs during high-flow years, and the central cell of the teleconnection is located at about latitude 50o north longitude 130o west along the west coast of North America.

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