Robert G. Roosen

Worldwide Variations in Atmospheric Transmission: Baseline Results from Smithsonian Observations

Abstract Analysis is made of atmospheric transmission measurements taken during the first half of the twentieth century at thirteen widely separated sites by the Astrophysical Observatory of the Smithsonian Institution. Long and short period variations in the atmospheric transmission have been examined for the individual sites. Significant variations from one day to the next are not unusual. Seasonal variations are found for all sites, with characteristic summer maxima. The variations appear to be due almost entirely to variations in the aerosol component above the observing sites. The observed phases of these variations, the derived characteristic size distributions of the particles which cause them, and the correlations between atmospheric moisture and transmission lead to the conclusion that differences in the nature and sources of aerosols above arid and vegetated regions are detectable. Including the results of more recent studies, our best estimate is that, except for sporadic perturbations due to v...

The gegenschein and interplanetary dust outside the Earth's orbit

Abstract The gegenschein has been observed in a four-year program including photographic observations and high-resolution photoelectric scans. The results of these observations are interpreted with the help of model calculations which theoretically consider (1) the apparent phase function of the particles producing the gegenschein; ( (2) the distribution of these particles with respect to distance from the Earth and the Sun; and (3) the effect of the Earths shadow on the illumination of these particles. All previous explanations for the gegenschein found in the literature are considered; the only one found tenable is that the gegenschein is caused by light reflected from particles of dust in heliocentric orbits. Further, models for the zodiacal light that assume that the spatial distribution of particles follows an inverse power law R − P (where R is heliocentric distance and P ⩾ 0) cannot satisfactorily explain the gegenschein. There must be an increase in the spatial density of reflecting cross section (and hence presumably of reflecting material) outside the Earths orbit. The asteroid belt is suggested as the source of the material.

Tail structure farr from the head of Comet Kohoutek. I

Abstract Two tail structures 0.1AU from the head of Comet Kohoutek were photographed during January 1974. One was a wavy structure resembling a helix while the other was an irregular Swan-like cloud. Both features were propagating down the tail at approximately 250km/sec, and the observed speed is probably the phase speed. We discuss the physical origin of these structures and interpret the helix as a kink instability resulting from currents flowing along the tail axis.

Interplanetary gas. XX - Does the radial solar wind speed increase with latitude

The astrometric technique used to derive solar wind speeds from ionic comet-tail orientations has been used to test the suggestion that the radial solar wind speed is higher near the solar poles than near the equator. We find no evidence for the suggested latitude variation.

Stratospheric ozone as viewed from the Chappuis band

Stratospheric total ozone values have been obtained for the period 1912–50 from analysis of Smithsonian data. Naturally caused variations of 25% or more are common over time scales ranging from months to decades. We suggest that the ozone layer acts as a shutter on the incoming solar energy, providing one of the long sought trigger mechanisms betwen solar activity and climatic change. The present state of knowledge of ozone climatology is not sufficient to support popular speculations about mans effects on the ozone layer.

Atmospheric transmission and climate: results from smithsonian measurements

Abstract A combination of published and archival observations from the Smithsonian Institutions Astrophysical Observatory (APO) is presented and analyzed. This paper concentrates on the data from the two primary sites—Mount Montezuma, Chile, and Table Mountain, California, from 1923 to 1957. Baseline values and their variations are presented for solar aureole brightness, precipitable water vapor, pyrheliometry, corrected pyrheliometry, and spectrobolometry. In addition to clouds and water vapor, possible causes for the observed variations in atmospheric transmission are volcanic eruptions, nuclear weapons testing, and aerosols from plants. Physical theories may not be sufficient to explain climate change, and considerations of biological processes may be required.

VARIATIONS IN ATMOSPHERIC WATER VAPOR: BASELINE RESULTS FROM SMITHSONIAN OBSERVATIONS

Analysis is made of midmorning measurements of absolute humidity at ground level, and spectroscopic determinations of total atmospheric precipitable water vapor above the field stations of the Astrophysical Observatory of the Smithsonian Institution (APO). The APO data used in this study cover the period 191252 and nine mountain sites (altitudes 1500 m-2711 m) in North and South America and Africa. Reported values for over 3000 days are used. Large seasonal variations are apparent, with the maximum amounts of precipitable water vapor occurring very close to midsummer at all sites. Substantial longer-term variations are also present. The observed mean amounts of precipitable water vapor for various APO sites show reasonable agreement with Kuipers generalized predictions. Study of the relation between precipitable water vapor and surface humidity shows a strong positive correlation, but the variance is so large that surface humidity is not a reliable indicator of precipitable water vapor for any particular day. Key words: atmospheric water vapor-atmospheric extinction

Earth tides, volcanos and climatic change

A STATISTICALLY significant correlation has been found between the derivatives of the envelopes of peak tidal stresses at high northern latitudes and the mean temperature of the Northern Hemisphere as reflected in oxygen isotope ratios in the Greenland ice cap. We suggest that variations in tidal stresses on the Earth caused by the Sun and Moon cause changes in the amount of stratospheric dust produced by volcanic activity; this in turn changes the thickness of the stratospheric dust veil and hence the atmospheric radiation balance. We find that, for a simple model, periodic variations in tidal stress account for 13% of the variance in the ice-core temperature record.

Interplanetary gas. XIX - Observational evidence for a meridional solar-wind flow diverging from the plane of the solar equator.

The astrometric technique used by Brandt, Roesen, and Harrington is reapplied to the analysis of ionic comet-tail orientations but allowing for the possibility of a meridional flow converging or diverging from the plane of the solar equator. Our best solution indicates significant meridional flow away from the solar equator amounting to 2.6 plus or minus 1.2 km s-1 at 1 a.u. for solar latitudes of plus or minus 45 deg the associated best values for the radial and azimuthal speeds are 402 plus or minus 12 and 7.0 plus or minus 1.8 km s-1, respectively. Finally, the meridional now found here is in agreement with the theoretical estimate by Suess and Nerney.

Baseline ozone results from 1923 to 1955

Abstract Baseline total atmospheric ozone values have been derived, using the Chappuis band, from historical data for 11 Smithsonian sites, including both Northern and Southern Hemispheres. The main baselines consist of 1194 and 970 days respectively for Mt. Montezuma, Chile and Table Mountain, California, covering a period of time from about 1923 to 1955. These are the two baselines reported on here. An earlier reported decrease in the ozone beginning in 1940 (Angione et al.) is erroneous and resulted from the use of the wavelengths published in the Smithsonian Annals, one of which was incorrect. A modern filter wheel radiometer was used to further develop and evaluate the Chappuis-band method. Two intercomparisons at Mauna Loa Observatory show the Chappuis-band measurements to be systematically lower than simultaneous Dobson values by about 14 percent. Because this difference could result from errors in the ozone absorption coefficients, it is important to firmly establish the correct values of these co...