A Regression Model for Annual Streamflow in the Upper Mississippi River Basin Based on Solar Irradiance
By Charles A. Perry
Annual streamflow in the upper Mississippi River Basin demonstrates an apparent connection to annual solar-irradiance variations. The relation is associated with the amount of solar energy available for absorption by the tropical Pacific Ocean and the subsequent effects this stored energy has on mid-latitude atmospheric circulation and precipitation occurrence. The suggested physical mechanism for this relation includes varying solar-energy input that creates ocean-temperature anomalies in the tropical ocean. The temperature anomalies are transported northward by ocean currents to locations where ocean and atmospheric processes can modify jet-stream patterns. These patterns affect jet-stream location and characteristics downwind over North America, which affect the occurrence of precipitation and, ultimately, the amount of streamflow in the upper Mississippi River Basin. The relation provides an opportunity to estimate the annual streamflow of the upper Mississippi River. A multivariate model using solar-irradiance variations and the previous year's basin precipitation explains nearly one-half of the annual streamflow variability. When data for only La Nina years are considered, the model explains more than two-thirds of the variability since 1950.
In the past solar/climate connections have been considered tenuous at best, with apparent significant correlations or complete correlation breakdowns. Solar/climate correlations that pass significance tests lack physical explanations. At the decadal and interdecadal scales, there is growing evidence that long-term changes in the Sun's radiation output do have an effect on global air temperature and on global sea-surface temperatures, even though the observed change in solar irradiance during the average 11-year solar cycle is small and amounts to only 0.15% variation. However, mean irradiance can differ by 0.25% from month to month and by as much as 0.50% day to day.
Solar irradiance has been measured in space by sensors on several spacecraft...
A mechanism proposed for the coupling of global total solar irradiance with short-term regional hydroclimatology was suggested by Perry (1994) and entails four major linkages.
The four major components of the physical connection between solar irradiance and hydroclimatology of the upper Mississippi River Basin. A period of increased total solar irradiance heats the Pacific Warm Pool (the western tropical Pacific Ocean) to an anomalously warm temperature forming a warm ocean water (WOW) anomaly. Two years later the WOW has been transported northward by the ocean currents and is east of Japan. The atmosphere responds to the warmer ocean surface by moving the jet stream farther north forming a high-pressure ridge. This ridge causes the atmosphere to have anticyclonic curvature that results in dynamically sinking air, which inhibits development of precipitation and causes dry conditions to prevail beneath the ridge. Downwind, east of the ridge, the perturbed jet stream must turn back to the left, and a trough is induced. To the east of the trough's axis, the atmosphere is dynamically lifted and precipitation occurrence is enhanced. Five years after its formation, the WOW is in the eastern North Pacific Ocean along with its accompanying upper level ridge. A trailing cool ocean water (COW) anomaly, formed during a period of decreased irradiance 2 to 3 years after the strong increase, has moved northward and has pulled the jet stream southward forming a trough. These two areas of ocean-temperature anomalies together result in a vigorous jet-stream pattern that places a strong persistent trough over western North America. This could have been the case in 1993 when a strong persistent trough over the Rocky Mountains helped to create very persistent rains over the upper Mississippi River Basin and historic flooding. This persistent trough may have originated from a very strong increase in solar irradiance that occurred in 1988-89, which then was followed by a sharp irradiance decrease in 1990.
The fundamental conclusion of this paper is that short-term changes in total solar irradiance from the Sun may have an effect on the short-term regional climate of North America through global oceanic and atmospheric processes. Annual solar-irradiance variations may create warm and cool ocean water anomalies in the tropical Pacific Ocean, which can affect streamflow in the Mississippi 5 years later through induced position of ridges and troughs in the jet stream.
The relation between solar irradiance and streamflow in the upper Mississippi River Basin allows the development of a model to predict annual mean streamflow. A stepwise multivariate regression analysis using the previous year's average basin precipitation and changes in weighted solar irradiance lagged 5 years produces a model that explains nearly one-half of the variability in annual streamflow. When data for only La Niņa years (cold phase) are considered, the model explains more than two-thirds of the variability since 1950.