From June, 1973 to May, 1979, the University of Alaska maintained a small radar system to monitor near shore ice motion and conditions at the Naval Arctic Research Laboratory near Point Barrow, Alaska. The purpose was to support research projects which required that information. In this report, the data acquired are compiled to describe the annual cycle of the ice year in the area. A short open water season can be defined as extending from late-July to late-September. This is followed by freezeup, which is characterized by a decreasing frequency of occurrence of drifting pack ice in the area between October and January. The winter season extends from January through May and is marked by generally stable or slow-drifting pack ice, or by the absence of pack ice offshore from the edge of the fast ice. The onset of breakup in June is characterized by the increasing occurrence of drifting pack ice again. Comparison of the ice cycle with climatologic data indicates no strong correlations with variables other than (possibly) air temperature. As expected, ice activity is greatest during freezeup and breakup, with rapid changes in the directions and velocity of ice motion. Similar movement patterns occur in winter, but the ice velocities are slower. Data of the type generated by the radar system would be useful for any area in which development of offshore installations is planned. Clearly, a knowledge of the range of possible ice motion patterns and events can provide the basis for improving the design of such installations.

The riometer records of 27.6 Mc/s cosmic noise from the Alaskan IGY stations are used to study the phenomenon of aurorally associated absorption. The emphasis of the work is on the comparison of the auroral absorption recorded at different latitudes, and the primary result is the definition of an auroral absorption zone. This zone is compared to the analogous visual auroral zone, and the geomagnetic latitude of maximum intensity of the absorption zone is found to be near College (64.65°) whereas the latitude of the peak of the visual zone is near Ft. Yukon (66.69°). The auroral absorption zone is more pronounced during magnetically disturbed periods, but daily and seasonal variations are generally the most effective secondary factors determining its character. Absorption is found to exhibit a daytime maximum at all stations, and a winter maximum in auroral absorption is observed at College. Possible interpretations of the discrepancy between the absorption and visual zones are suggested in terms of the relation of these zones to the primary auroral particles.

The Geophysical Institute has established and now operates a large aperture seismic telemeter network in Alaska. At present four stations are operated and two more will be added shortly. The system is described in its technical details, including the remote site equipment and the method of recording at the Geophysical Institute. Without the use of methods for improving signal-to-noise ratio (such as velocity and/or frequency filtering) the sensitivity of the seismic stations for detecting distant earthquakes is similar to that of the U.S.C.&G.S. College Observatory. This sensitivity allows recording of earthquakes down to magnitude 4 (U.S.C.&G.S. magnitude) in the 80° distant range. Epicenter maps for three 1-month periods for interior and coastal Alaska are presented.

The spatial and temporal variations in cosmic radio noise absorption were investigated at College, Alaska, during 1962-1963 by means of riometers using one narrow beam antenna and two relatively broad beam antennas which were pointed at different direction along the magnetic meridian. The narrow beam antenna had a 12° beamwidth and was periodically swung in the magnetic meridian from 12° north of zenith to 12° south of zenith. Each of the broad beam antennas had a 26° beamwidth and was directed to 40° from zenith, one to the south and the other to the north. In order to explore the relation of the spatial variations in absorption with the differences in auroral luminosity existing in different directions at a given time, two λ 5577A photometers were operated in the two switching directions of the narrow bean antenna i.e. 12°N and 12°S. The information about the auroral coverage of the various antenna beams was obtained from all-sky photographs. A simultaneous study of radio-wave absorption in relation to luminous aurora resulted in the conclusion that the nighttime radio-wave absorption observed at College, Alaska falls into the following two main categories. The absorption belonging to Category I is observed at any time between 2000-0200 hrs., correlates well with the intensity fluctuations of λ 5577A, and is limited to luminous regions of the sky only. Included in the above category is the absorption associated with the quiet as well as bright and active phases of the display. The absorption belonging to Category II is observed only in the post-midnight hours, does not correlate with the intensity fluctuations of λ 5577A and, most probably, is not limited to luminous regions of sky only. With the absorption making a transition from Category I to Category II, a 10-100 fold increase takes place in the ration of absorption to λ 5577A intensity. In order to explore the contribution of bremsstrahlung X-rays to the observed absorption of both categories, the X-ray intensity is calculated on top of the D-region assuming reasonable flux values of the primary electrons. Using the results of the generalized magnetoionic theory, it is shown that the contribution of X-rays to the observed absorption is at the most 2¹/₂% and therefore may be safely neglected. The close association between radio-wave absorption and luminous aurora during absorption events of Category I suggests that the primary particles responsible for the absorption are approximately in the energy range 10-20 kev. It is shown that the absorption associated with the quiet phase of the auroral display is easily explained by a flux of 107-108 electrons cm⁻² sec⁻¹ in the above energy range. It is also shown that the transition from the quiet phase to the bright and active phase is the result of a momentary 10-100 fold increase in the flux of low energy electrons. The lack of correlation between absorption and λ 5577A intensity fluctuations and the pronounced increase in the ratio of absorption to λ 5577A intensity observed during absorption events of Category II are indicative of a hardening of the primary particle energy spectrum, possibly due to the injection of a large number of electrons in the energy range 30-100 kev. It is estimated that a flux of 106-107 electron cm⁻² sec⁻¹ in the above energy range can adequately account for the observed absorption. In the light of the above observations, the apparent discrepancy between the results of two rocket flights at Fort Churchill, one by McIlwain and the other by McDiarmid et al, is easily resolved. This work was supported by National Science Foundation, Grants 14133 and 947.

A new hydromagnetic model for the sudden commencement (SC) of a magnetic storm is presented. The model is based on a new morphology of the SC field that was derived from an analysis of the characteristics of vector diagrams for the first few minutes of the SC field variation. The vector diagrams representing the locus of the end point of the total horizontal disturbance vector of the SC field were constructed from rapid-run magnetograms from stations all over the world for SC’s that occurred during a four year period beginning with the I.G.Y. The most characteristic feature of the SC field is the polarization of the field that is due to a combination of circularly and linearly polarized components. The variation of the SC field over the earth is described in terms of the variations with local time and latitude of the direction of polarization (i.e. clockwise or counterclockwise) and initial phase of the circularly polarized component and the ration of the amplitudes of the two components. The two polarized components of the SC field are identified as circularly polarized transverse and linearly polarized longitudinal hydromagnetic waves. The longitudinal wave is the immediate consequence of the impact of a solar plasma cloud on the magnetosphere; whereas the transverse wave is produced by a coupling with the longitudinal shock wave in the magnetosphere. The triply refracting nature of the plasma in the magnetosphere results in the production of three hydromagnetic modes by the SC disturbance; namely, ordinary and extraordinary transverse waves with opposite directions of circular polarization which propagate to high latitudes in the morning and evening hemispheres respectively, and longitudinal waves which propagate to the earth in low latitudes.

This final report summarizes an investigation of radiowave scattering in the auroral ionosphere, based on observations of radio-star and satellite signals. The observations were carried out near solar minimum and are compared with radio-star observations performed near the previous solar maximum. Results show that 223 MHz scintillations of the radio-star Cassiopeia A declined from the start of the current observations in 1962 through the winter of 1964-65. Subsequently, scintillations on 223 MHz have continuously increased. Observations at 137 MHz, begun in 1965, also have shown continuously increasing scintillation. Both radio-star and satellite scintillations have shown a nighttime maximum and a daytime minimum in their diurnal variations, showing little change from the diurnal pattern found near solar maximum. Satellite scintillation at 136 MHz has shown the statistical center of the scattering zone to be north of Fairbanks, Alaska (geomagnetic latitude, 65°N), during 1965-66. A close relation of severe satellite scatter events and radio-star visibility fades, on the one hand, to visible auroral luminosity, on the other, has been found. In addition, strong refraction of satellite signals has been found to occur near auroral arcs, with angular deviations up to at least 7° being observed at 137 MHz. Quantitative predictions are made regarding the severity of scatter effects to be expected during the next solar maximum on VHF and UHF satellite communications links in the auroral zones.

The equation for radiation transport in vertical inhomogeneous absorbing, scattering, and emitting atmospheres is derived from first principles. It is cast in a form amenable to solution, and solved using the discrete ordinate method. Based on the discrete ordinate solution a new computationally efficient and stable two-stream algorithm which accounts for spherical geometry is developed. The absorption and scattering properties of atmospheric molecules and particulate matter is discussed. The absorption cross sections of the principal absorbers in the atmosphere, H₂O, CO₂ and O₃, vary erratically and rapidly with wavelength. To account for this variation, the correlated-𝘬 distribution method is employed to simplify the integration over wavelength necessary for calculation of warming/cooling rates. The radiation model, utilizing appropriate absorption and scattering cross sections, is compared with ultraviolet radiation measurements. The comparison suggests that further experiments are required. Ultraviolet (UV) and photosynthetically active radiation (PAR) is computed for high and low latitudes for clear and cloudy skies under different ozone concentrations. An ozone depletion increases UV-B radiation detrimental to life. Water clouds diminish UV-B, UV-A and PAR for low surface albedos and increase them for high albedos. The relative amount of harmful UV-B increases on overcast days. The daily radiation doses exhibit small monthly variations at low latitudes but vary by a factor of 3 at high latitudes. Photodissociation and warming/cooling rates are calculated for clear skies, aerosol loaded atmospheres, and atmospheres with cirrus and water clouds. After major volcanic explosions aerosols change O₃ and NO₂ photodissociation rates by 20%. Both aged aerosols and cirrus clouds have little effect on photodissociation rates. Water clouds increase (~ 100%) photodissociation rates that are sensitive to visible radiation above the cloud. Solar warming rates vary by 50% in the stratosphere due to changing surface albedo. Water clouds have a similar effect. The net effect of cirrus clouds is to warm the troposphere and the stratosphere. Only extreme volcanic aerosol loadings affect the terrestrial warming rate, causing warming below the aerosol layer and cooling above it. Aerosols give increased solar warming above the aerosol layer and cooling below it.