Long-Period Global Variations of Incoming Solar Radiation

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A watt is measurement of power, or the amount of energy that something generates or uses over time. How much power is 1, watts? An incandescent light bulb uses anywhere from 40 to watts. A microwave uses about watts. Only half the Earth is ever lit by the Sun at one time, which halves the total solar irradiance. Energy from sunlight is not spread evenly over Earth. One hemisphere is always dark, receiving no solar radiation at all. On the daylight side, only the point directly under the Sun receives full-intensity solar radiation.

In addition, the total solar irradiance is the maximum power the Sun can deliver to a surface that is perpendicular to the path of incoming light. Because the Earth is a sphere, only areas near the equator at midday come close to being perpendicular to the path of incoming light.

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Everywhere else, the light comes in at an angle. The progressive decrease in the angle of solar illumination with increasing latitude reduces the average solar irradiance by an additional one-half. This graph illustrates the relationship between latitude, time, and solar energy during the equinoxes.

On the equinoxes, the Sun rises at a. The strength of sunlight increases from sunrise until noon, when the Sun is directly overhead along the equator casting no shadow.

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After noon, the strength of sunlight decreases until the Sun sets at p. The tropics from 0 to Water vapor is less dense than dry air, resulting in lower atmospheric pressure over warm water than over cool water. Low pressure allows convergence of air near the surface, followed by lifting and adiabatic cooling of the air until condensation and formation of clouds, and ultimately the release of the latent heat into the upper levels of the atmosphere. The release of the latent heat increases the buoyancy of the air and further lifting occurs.

The greater the supply of energy available at the ocean surface, the greater the probability of cloud formation, precipitation, and the injection of energy into the upper atmosphere. Energy patterns in the upper atmosphere are responsible for the persistent upper air flow patterns that interact on a global scale. The strength, curvature, and location of the upper level winds, which are critical factors in precipitation formation, are largely dependent upon temperature patterns generated by the oceans and continents.

Upper air flow patterns can generate new surface or low level pressure systems. For example, an upper level low may be formed initially by a surface low that extends upward into the atmosphere. In the middle latitudes, the predominant westerlies would advect that upper level low downstream to the east away from its initial surface-energy supply. As the upper level low moves eastward, it could induce low level cyclogenesis. Energy released from the induced low could be added to the upper level low, maintaining or even strengthening it.

In the absence of available energy in the atmosphere near the surface, the upper-level low would not be reinforced, expending its energy and dissipating. The hypothesis that the combination of absorption of solar energy by water in the western Pacific Ocean, the transport of that energy by the currents of the Pacific Ocean Gyre, and the modification of the atmosphere by warmer or cooler pools of water affecting precipitation distributions in North America is tested in this paper.

For increased precipitation in the western parts of the United States, the following scenario is suggested:. The irradiance of the Sun generally increases each month for a year.

Water slowly moving westward along the southwestern part of the Pacific Gyre absorbs this increasing energy and stores it at depth, increasing the temperature slightly in a large volume of water. Nearing the Asian landmass this slightly warmer than normal volume of water turns northward.

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Then, irradiance of the Sun begins a year of decrease, and the water now in the southwestern part of the Pacific Gyre receives less energy. The result is that the leading pool of water has more stored energy than the trailing pool. As both pools travel around the gyre, the stored energy at depth begins to be expelled at the surface by evaporation. The leading pool with its greater energy content could spawn rain showers or thunderstorms that would inject moisture into the mid-levels of the atmosphere.

The trailing pool, relinquishing less energy to the atmosphere, would be shadowed by a fairer weather pattern. Once the leading pool enters the North Pacific Drift, at least 1 to 2 years have passed since it turned northward. Here, the energy within the warm pool supports extratropical storms that are driven eastward by the prevailing westerlies.

Still far from North America, these storms would expend their precipitation over the open ocean but, nonetheless would affect global atmospheric flow patterns. One or 2 additional years pass, and the leading pool of water, cooler now but still warmer than the pool following it, continues to supply energy to the atmosphere. North America is much closer now, and the storms make landfall bringing precipitation to the northwestern part of the United States.

If the pool of warmer than normal ocean water is large enough, a part of it may be drawn into the eddy of the Gulf of Alaska Gyre, supplying energy to the Aleutian low-pressure system for an extended length of time.

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If the pool is smaller, it may exhaust its surplus stored energy and lose its ability to significantly alter the atmosphere. Also, some of the warm pool may be drawn into the California Current and continue to affect atmospheric conditions farther south and east. The trailing pool of cooler than normal water would have a negative effect on the formation of storms.

As this pool moves across the Northern Pacific, fewer storms would be associated with it, and less precipitation would be the result. A large pool of cooler than normal water could be incorporated into the Gulf of Alaska Gyre, and surface low-pressure formation would be suppressed for an extended period of time, bringing multi-year droughts to North America.

The entire Pacific Gyre could be considered as a slowly rotating oblate disk, with its elements moving at various velocities, gaining or losing energy as a function of solar irradiance, latitude, season, sky conditions, water transparency, and surface conditions. The elements of anomalously warm or cool pools of ocean water within this disk could affect surface and upper atmospheric temperature, moisture, and wind patterns including the position and strength of the jet stream Maxwell, several years after their initial formation.

Data needed to test the hypothesis that solar variations affect regional climate include the independent variable, solar irradiance fluctuations, and the dependent climatic variable precipitation.

Long-Period Global Variations Of Incoming Solar Radiation

Annual regional precipitation was chosen as the unit of measure for several reasons. Annual values eliminate the seasonal precipitation variations and provide a better time scale for global influences. Utilization of regional data reduces the variability of point precipitation data. The use of regional data also provides the opportunity to detect regional variations of climate that may have been forced by a single global factor, ie. Presently , these measurements account for more than 14 years of nearly continuous data.

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However, 14 years is a short time for comparison with climatic data. Fortunately, Lean and Foukal developed an empirical model for total solar irradiance that is based on changes in excess radiation from bright magnetic faculae and on changes in reduced radiation from dark sunspots. Using this model, estimates of bright magnetic faculae were made back to using daily Estimates of irradiance were later extended back to by Foukal and Lean using monthly means of the sunspot number in place of the This later model relied on the correlation between the monthly sunspot number and monthly Because the Irradiance values generated by this later model are shown in figure 4a.

This paper is based on the hypothesis that increases or decreases in solar irradiance have an effect on climate. Therefore, monthly differences Figure 4b and the annual average of monthly differences of solar irradiance were determined Figure 4c. Monthly precipitation data for the United States were arranged into regions according to the State divisions of climatological data National Oceanic and Atmospheric Administration, These regions included all the states except Alaska and Hawaii. Each annual regional precipitation average is an arithmetic mean of the precipitation for the stations within that region from January through December.

The number of stations within any one division varies from less than 5 to more than Correlation coefficients were calculated between the annual average of the monthly differences of the modeled solar-irradiance values hereafter referred to as the annual average irradiance difference and the annual average precipitation values for each of the regions for the period The differences between monthly solar irradiance values were summed for the interval between January and December and divided by 12 to obtain the annual average irradiance differences.

Eight series of annual average irradiance differences, with time lags from 0 to 7 years, were correlated with precipitation data. For example, in a 2-year lag correlation, precipitation was correlated to the annual average irradiance difference that occurred 2 years previous.

Correlation coefficients for each lag time were mapped for the 48 contiguous States. Correlation coefficients for each of the regions for all lag times are shown in Figures 5ab , 5cd , 5ef , 5gh. Correlation coefficients are plotted at the centroid of each region; correlation coefficients between 0. Correlation coefficients R for the eight lag times and the regions ranged between To be significant at the 1 per cent level, R must be less than At this time lag, droughts coincided with periods of lower irradiance averages decreased energy availability , and greater than average precipitation coincided with periods of higher irradiance averages increased energy availability.