Eleven-Year Variation in Polar Ozone and Stratospheric-Ion Chemistry

Solar radiation and malignant melanoma of the skin

Several observations suggest that a majority of cases of malignant melanoma of the skin are linked to sun exposure. Evidence includes higher occurrence of melanoma on anatomic areas heavily exposed during recreation, development of melanoma more frequently in lightly pigmented persons, and correlation of melanoma incidence and mortality with proximity to the equator. The role of the sun exposure in the pathogenesis of melanoma remains unclear, however. Many cases of melanoma may be related to heavy doses of solar radiation received during recreation. Chronic sun exposure is not so clearly linked to the development of melanoma (except in the uncommon lentigo maligna variety). Sunspot cycles have been associated with changes in melanoma incidence; an excess of melanoma cases has been observed every 9 to 12 years after peak sunspot activity. These excess cases may be caused by more intense exposure to solar ultraviolet radiation during sunspot maxima, perhaps related to changes in the stratospheric ozone layer. These epidemiologic and clinical clues suggest that many cases of melanoma are related to sun exposure triggering the appearance of clinically evident melanoma. In this regard, solar radiation behaves as a cocarcinogen or promoter, rather than a dose-dependent carcinogen. These observations also suggest that other factors may be involved in the pathogenesis of melanoma, e.g., nevi, heredity, or exposure to chemical carcinogens.

Ozone and Temperature Trends Associated with the 11-Year Solar Cycle

Evidence is presented which suggests that trends in the ozone concentration and stratospheric temperature, reported between the early 1960's and 1976, are to a large extent due to solar ultraviolet flux variability associated with the 11-year solar cycle. Radiative-convective-photochemical simulations of ozone and temperature variations have been made with a solar ultraviolet flux variability model. Results for temperatures and ozone concentrations, when compared with published data, show good agreement.

Solar cycles and malignant melanoma

There has been a sixfold increase in the incidence of malignant melanoma in the State of Connecticut during the past forty years. Superimposed on a steady incidence rise are cycles of markedly increased incidence rates which follow periods of maximum sunspot activity. We propose that the effect of sunspot cycles on human melanoma occurrence is mediated by modulation of stratospheric ozone and thus indirectly affects UV flux at the earth's surface. This hypothesis would predict a time lag in melanoma incidence cycles, relative to sunspot activity, with increasing distance from polar caps. This appears to be the case. The increase in melanoma incidence related to a given reduction in ozone depletion in this hypothesis, is in great excess of existing models relating anthropogenic ozone depletion and skin cancer.

Increased incidence of malignant melanoma after peaks of sunspot activity

The age-adjusted incidence-rate for malignant melanoma in the State of Connecticut has risen from 1.1 per 100 000 individuals in 1935 to 6.2 per 100 000 individuals in 1975. Superimposed on a steady rise in incidence are 3-5 year periods in which the rate of increase in incidence rises. These periods have a cycle of 8-11 years and follow times of maximum sunspot activity.

Energetic Radiation Belt Electron Precipitation: A Natural Depletion Mechanism for Stratospheric Ozone

During geomagnetically disturbed periods the precipitational loss of energetic electrons from the outer radiation belt of the earth can readily provide the major ionization source for the mesosphere and upper stratosphere. One particularly intense manifestation of this interaction between the radiation belts and the lower atmosphere is the relativistic electron precipitation (REP) event which occurs at subauroral latitudes during magnetospheric substorm activity. At relativistic energies the precipitating electrons produce copious fluxes of energetic bremsstrahlung x-rays, the major portion of which penetrate deep into the stratosphere before undergoing excitation and ionization collisions with the neutral atmosphere. If such REP events occur more than a few percent of the time, they can, on an annual basis, provide a local source of upper stratospheric nitric oxide molecules (via the dissociation of molecular nitrogen) comparable to that from either galactic cosmic rays or energetic solar proton events. Since nitric oxide plays a major role in the removal of stratospheric ozone, it appears that the influence of REP events must also be considered in future photochemical modeling of the terrestrial ozone layer.