Solar Effect on North American Hydroclimatology Through Sea-Surface Temperatures and Atmospheric Vorticity

Significant correlations exist between total solar irradiance (SI) and measured hydroclimatologic characteristics in North America. These characteristics include annual regional precipitation, annual glacier-mass change, mean annual lake lvels, and annual river flow. A physical mechanism is proposed to account for these correlations that begins with the absorption of varying amounts of solar energy into the tropical Pacific Ocean Warm Pool, creating ocean-temperature anomalies. The ocean-temperature anomalies then are transported over time by ocean currents to the North Pacific where the warmer or colder than normal water initiates the development of ridges or troughs in the upper atmosphere. Upper atmospheric ridges or troughs in the North Pacific have a distinct effect on the formation of lower atmospheric low-pressure or high-pressure systems over North America. Low-pressure systems produce precipitation, and their intensity and frequency determine the regional hydrologic response.

In this study evidence for the mechanism for the solar/climate correlation is examined step by step. A 50-year sequence of Lean's annual SI is first correlated with sea-surface temperatures (SSTs) just northeast of the Philippine Islands in the area 130 to 140 degrees E. and 20 to 30 degrees N. (Area 1). Next, the SSTs in Area 1 are correlated with SSTs in the eastern North Pacific Ocean at 150 degrees W. and 50 degrees N. (Area 2). Then the SSTs in Area 2 are correlated with the vorticity of the upper atmosphere, which provides a measure of upper atmospheric ridging or troughing above Area 2. Subsequently, the upper atmospheric vorticity over Area 2 is correlated with the lower atmospheric vorticity over central North America near 92 degrees W. and 41 degrees N. (Area 3). Finally, the lower atmospheric vorticity in Area 3 is correlated with a standardized flow index for six major rivers in Iowa, which is significantly correlated with the original annual SI variations now lagged 4 to 5 years.

Variations in the correlations among the individual steps indicate that the solar/climate mechanism is complex and has a time element (lag) that is not constant. The Pacific Decadal Oscillation (PDO) phase seems to have some effect on the lag time between various steps of the mechanism with the cool, eastern Pacific phase creating shorter lag times. When the average SST of the North Pacific Ocean (20 to 55 degrees N. to 130 degrees E. to 110 degrees W.) is considered, there appears to be a direct relation between SI and average SST.

Perry, C.A., 2002, Solar effect on North American hydroclimatology through Pacific sea-surface temperatures and atmospheric vorticity [abs.], in Abstracts, 19th Annual PACLIM Workshop, March 2002, Pacific Grove, California: p. 30.